--- /srv/rebuilderd/tmp/rebuilderdCWGjks/inputs/erlang-doc_27.3.4.1+dfsg-1_all.deb
+++ /srv/rebuilderd/tmp/rebuilderdCWGjks/out/erlang-doc_27.3.4.1+dfsg-1_all.deb
├── file list
│ @@ -1,3 +1,3 @@
│  -rw-r--r--   0        0        0        4 2025-07-08 07:27:28.000000 debian-binary
│ --rw-r--r--   0        0        0    39584 2025-07-08 07:27:28.000000 control.tar.xz
│ --rw-r--r--   0        0        0 16774188 2025-07-08 07:27:28.000000 data.tar.xz
│ +-rw-r--r--   0        0        0    39608 2025-07-08 07:27:28.000000 control.tar.xz
│ +-rw-r--r--   0        0        0 16775296 2025-07-08 07:27:28.000000 data.tar.xz
├── control.tar.xz
│ ├── control.tar
│ │ ├── ./md5sums
│ │ │ ├── ./md5sums
│ │ │ │┄ Files differ
│ │ │ ├── line order
│ │ │ │ @@ -46,15 +46,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/doc/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/doc/dist/search_data-FF8A98E6.js
│ │ │ │ +usr/share/doc/erlang-doc/html/doc/dist/search_data-0744904A.js
│ │ │ │  usr/share/doc/erlang-doc/html/doc/dist/sidebar_items-8A43D419.js
│ │ │ │  usr/share/doc/erlang-doc/html/doc/edoc.html
│ │ │ │  usr/share/doc/erlang-doc/html/doc/efficiency_guide.html
│ │ │ │  usr/share/doc/erlang-doc/html/doc/eldap.html
│ │ │ │  usr/share/doc/erlang-doc/html/doc/embedded.html
│ │ │ │  usr/share/doc/erlang-doc/html/doc/erl_interface.html
│ │ │ │  usr/share/doc/erlang-doc/html/doc/erts.html
│ │ │ │ @@ -129,15 +129,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/doc/system/dist/search_data-D62CB992.js
│ │ │ │ +usr/share/doc/erlang-doc/html/doc/system/dist/search_data-CC135E6A.js
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/dist/sidebar_items-4A143270.js
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/distributed.html
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/distributed_applications.html
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/documentation.html
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/drivers.html
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/eff_guide_functions.html
│ │ │ │  usr/share/doc/erlang-doc/html/doc/system/eff_guide_processes.html
│ │ │ │ @@ -247,15 +247,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/search_data-2EF91EE2.js
│ │ │ │ +usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/search_data-A22E82DE.js
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/sidebar_items-EAF8F760.js
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/driver.html
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/driver_entry.html
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/epmd_cmd.html
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_cmd.html
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_dist_protocol.html
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_driver.html
│ │ │ │ @@ -484,15 +484,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/dist/search_data-B265D67F.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/dist/search_data-B8379476.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/dist/sidebar_items-2E1AB7CA.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/i.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/index.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/int.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/introduction.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/notes.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/debugger-5.5/doc/html/search.html
│ │ │ │ @@ -673,15 +673,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/search_data-D82831C4.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/search_data-1F14090C.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/sidebar_items-8A5CCEF3.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/ei.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/ei_connect.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/ei_global.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/ei_users_guide.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/erl_call_cmd.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/erl_interface.epub
│ │ │ │ @@ -811,15 +811,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/dist/search_data-11662227.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/dist/search_data-F2AB287C.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/dist/sidebar_items-2623356F.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/http_client.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/http_server.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/http_uri.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/httpc.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/httpd.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/inets-9.3.2/doc/html/httpd_custom_api.html
│ │ │ │ @@ -1542,15 +1542,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/dist/search_data-A8FEFDA9.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/dist/search_data-B0E7D2CF.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/dist/sidebar_items-29A63FCF.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/index.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/notes.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/search.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/ssl.epub
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/ssl.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.1/doc/html/ssl_app.html
│ │ │ │ @@ -1684,15 +1684,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/dist/search_data-4186676F.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/dist/search_data-D423CF30.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/dist/sidebar_items-0D795EAC.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/epp_dodger.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/erl_comment_scan.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/erl_prettypr.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/erl_recomment.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/erl_syntax.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/syntax_tools-3.2.2/doc/html/erl_syntax_lib.html
│ │ │ │ @@ -1756,15 +1756,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/search_data-6515C1E6.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/search_data-074D3797.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/sidebar_items-11035E81.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/eprof.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/erlang-el.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/erlang_mode_chapter.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/fprof.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/fprof_chapter.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/index.html
│ │ │ │ @@ -2072,15 +2072,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/search_data-EF647235.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/search_data-2C01025C.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/sidebar_items-7ADBDE09.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/index.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/notes.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/search.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/xmerl.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/xmerl_eventp.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/xmerl_examples.html
├── data.tar.xz
│ ├── data.tar
│ │ ├── file list
│ │ │ @@ -95,15 +95,15 @@
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23236 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23580 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23040 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5624 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5472 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5368 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     1956 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/dist/remixicon-NKANDIL5.woff2
│ │ │ --rw-r--r--   0 root         (0) root         (0)   111810 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/dist/search_data-FF8A98E6.js
│ │ │ +-rw-r--r--   0 root         (0) root         (0)   111810 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/dist/search_data-0744904A.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5083 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/dist/sidebar_items-8A43D419.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)      290 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/edoc.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      288 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/efficiency_guide.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      294 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/eldap.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      280 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/embedded.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      299 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/erl_interface.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      287 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/erts.html
│ │ │ @@ -137,15 +137,15 @@
│ │ │  -rw-r--r--   0 root         (0) root         (0)      292 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/ssh.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      293 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/ssl.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      294 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/stdlib.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      298 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/syntax_tools.html
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/
│ │ │  -rw-r--r--   0 root         (0) root         (0)     2286 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/.build
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5648 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/404.html
│ │ │ --rw-r--r--   0 root         (0) root         (0)   654613 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/Erlang System Documentation.epub
│ │ │ +-rw-r--r--   0 root         (0) root         (0)   654574 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/Erlang System Documentation.epub
│ │ │  -rw-r--r--   0 root         (0) root         (0)    53540 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/applications.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    97489 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/appup_cookbook.html
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/assets/
│ │ │  -rw-r--r--   0 root         (0) root         (0)     7982 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/assets/ballpoint-pen.svg
│ │ │  -rw-r--r--   0 root         (0) root         (0)     2284 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/assets/dist1.gif
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5214 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/assets/dist2.gif
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5007 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/assets/dist3.gif
│ │ │ @@ -181,15 +181,15 @@
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23236 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23580 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23040 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5624 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5472 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5368 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     1956 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/dist/remixicon-NKANDIL5.woff2
│ │ │ --rw-r--r--   0 root         (0) root         (0)  1016759 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/dist/search_data-D62CB992.js
│ │ │ +-rw-r--r--   0 root         (0) root         (0)  1016759 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/dist/search_data-CC135E6A.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)    32130 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/dist/sidebar_items-4A143270.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)    29975 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/distributed.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    20667 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/distributed_applications.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    52922 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/documentation.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    15016 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/drivers.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    26935 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/eff_guide_functions.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    52153 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/doc/system/eff_guide_processes.html
│ │ │ @@ -304,15 +304,15 @@
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23236 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23580 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23040 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5624 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5472 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5368 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     1956 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ --rw-r--r--   0 root         (0) root         (0)  2376764 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/search_data-2EF91EE2.js
│ │ │ +-rw-r--r--   0 root         (0) root         (0)  2376764 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/search_data-A22E82DE.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)    99839 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/dist/sidebar_items-EAF8F760.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)    67715 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/driver.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    34514 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/driver_entry.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    20636 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/epmd_cmd.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)   124663 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_cmd.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    93996 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_dist_protocol.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)   159604 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_driver.html
│ │ │ @@ -351,15 +351,15 @@
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/
│ │ │  -rw-r--r--   0 root         (0) root         (0)     1060 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/.build
│ │ │  -rw-r--r--   0 root         (0) root         (0)     6010 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/404.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)     6692 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/api-reference.html
│ │ │ --rw-r--r--   0 root         (0) root         (0)    96826 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/asn1.epub
│ │ │ +-rw-r--r--   0 root         (0) root         (0)    96813 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/asn1.epub
│ │ │  -rw-r--r--   0 root         (0) root         (0)   140490 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/asn1_getting_started.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)     9328 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/asn1_introduction.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)     7454 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/asn1_overview.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    78800 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/asn1_spec.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    35427 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/asn1ct.html
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/assets/
│ │ │  -rw-r--r--   0 root         (0) root         (0)     1340 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/asn1-5.3.4.1/doc/html/assets/exclusive_Win_But.gif
│ │ │ @@ -397,15 +397,15 @@
│ │ │  -rw-r--r--   0 root         (0) root         (0)    10672 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/api-reference.html
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/assets/
│ │ │  -rw-r--r--   0 root         (0) root         (0)     4963 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/assets/config.gif
│ │ │  -rw-r--r--   0 root         (0) root         (0)    10726 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/assets/html_logs.gif
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5837 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/assets/logo.png
│ │ │  -rw-r--r--   0 root         (0) root         (0)     9561 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/assets/tc_execution.gif
│ │ │  -rw-r--r--   0 root         (0) root         (0)    21795 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/basics_chapter.html
│ │ │ --rw-r--r--   0 root         (0) root         (0)   399348 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/common_test.epub
│ │ │ +-rw-r--r--   0 root         (0) root         (0)   399350 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/common_test.epub
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│ │ │  -rw-r--r--   0 root         (0) root         (0)    59626 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/config_file_chapter.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    25541 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/cover_chapter.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)   182222 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/ct.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    12294 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/ct_cover.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    30006 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/ct_ftp.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    77102 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/common_test-1.27.7/doc/html/ct_hooks.html
│ │ │ @@ -466,15 +466,15 @@
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/compiler-8.6.1/doc/html/assets/
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5837 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/compiler-8.6.1/doc/html/assets/logo.png
│ │ │  -rw-r--r--   0 root         (0) root         (0)    24220 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/compiler-8.6.1/doc/html/beam_ssa.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)   450427 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/compiler-8.6.1/doc/html/cerl.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    28687 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/compiler-8.6.1/doc/html/cerl_clauses.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    28945 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/compiler-8.6.1/doc/html/cerl_trees.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    84316 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/compiler-8.6.1/doc/html/compile.html
│ │ │ --rw-r--r--   0 root         (0) root         (0)   182069 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/compiler-8.6.1/doc/html/compiler.epub
│ │ │ +-rw-r--r--   0 root         (0) root         (0)   182060 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/compiler-8.6.1/doc/html/compiler.epub
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/compiler-8.6.1/doc/html/dist/
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│ │ │  -rw-r--r--   0 root         (0) root         (0)     3043 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tftp-1.2.2/doc/html/dist/sidebar_items-3CBBBF05.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)     9543 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tftp-1.2.2/doc/html/getting_started.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      262 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tftp-1.2.2/doc/html/index.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)     7929 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tftp-1.2.2/doc/html/introduction.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    14762 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tftp-1.2.2/doc/html/notes.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5920 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tftp-1.2.2/doc/html/search.html
│ │ │ --rw-r--r--   0 root         (0) root         (0)    28828 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tftp-1.2.2/doc/html/tftp.epub
│ │ │ +-rw-r--r--   0 root         (0) root         (0)    28824 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tftp-1.2.2/doc/html/tftp.epub
│ │ │  -rw-r--r--   0 root         (0) root         (0)    44611 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tftp-1.2.2/doc/html/tftp.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    11771 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tftp-1.2.2/doc/html/tftp_logger.html
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/
│ │ │  -rw-r--r--   0 root         (0) root         (0)     1139 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/.build
│ │ │  -rw-r--r--   0 root         (0) root         (0)     6010 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/404.html
│ │ │ @@ -1988,29 +1988,29 @@
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23236 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23580 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23040 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5624 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5472 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5368 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     1956 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ --rw-r--r--   0 root         (0) root         (0)   305159 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/search_data-6515C1E6.js
│ │ │ +-rw-r--r--   0 root         (0) root         (0)   305159 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/search_data-074D3797.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)    36457 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/dist/sidebar_items-11035E81.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)    42648 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/eprof.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    28459 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/erlang-el.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    18986 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/erlang_mode_chapter.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)   131865 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/fprof.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    12996 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/fprof_chapter.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      263 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/index.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    67284 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/lcnt.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    53417 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/lcnt_chapter.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    18406 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/make.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)   106911 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/notes.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5926 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/search.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    28575 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/tags.html
│ │ │ --rw-r--r--   0 root         (0) root         (0)   239556 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/tools.epub
│ │ │ +-rw-r--r--   0 root         (0) root         (0)   239546 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/tools.epub
│ │ │  -rw-r--r--   0 root         (0) root         (0)   173561 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/tprof.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)   184227 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/xref.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    39616 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/xref_chapter.html
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/
│ │ │  -rw-r--r--   0 root         (0) root         (0)     1612 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/.build.gz
│ │ │ @@ -2040,15 +2040,15 @@
│ │ │  -rw-r--r--   0 root         (0) root         (0)  1664774 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/dist/search_data-7BF0929D.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)   578643 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/dist/sidebar_items-A20B6997.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)  1720241 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/gl.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    77298 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/glu.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      260 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/index.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    58699 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/notes.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5908 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/search.html
│ │ │ --rw-r--r--   0 root         (0) root         (0)  1607141 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/wx.epub
│ │ │ +-rw-r--r--   0 root         (0) root         (0)  1607142 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/wx.epub
│ │ │  -rw-r--r--   0 root         (0) root         (0)    53893 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/wx.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    19428 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/wxAcceleratorEntry.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    15124 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/wxAcceleratorTable.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    12369 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/wxActivateEvent.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    19119 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/wxArtProvider.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    17623 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/wxAuiDockArt.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    62993 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3/doc/html/wxAuiManager.html
│ │ │ @@ -2314,15 +2314,15 @@
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23236 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23580 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23040 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5624 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5472 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5368 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     1956 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ --rw-r--r--   0 root         (0) root         (0)   133453 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/search_data-EF647235.js
│ │ │ +-rw-r--r--   0 root         (0) root         (0)   133453 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/search_data-2C01025C.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)    14478 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/dist/sidebar_items-7ADBDE09.js
│ │ │  -rw-r--r--   0 root         (0) root         (0)      265 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/index.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    86197 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/notes.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5823 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/search.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    44740 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/xmerl.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    24438 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/xmerl_eventp.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)    40755 2025-07-08 07:27:28.000000 ./usr/share/doc/erlang-doc/html/lib/xmerl-2.1.3.1/doc/html/xmerl_examples.html
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/.build
│ │ │ @@ -30,15 +30,15 @@
│ │ │  dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │  dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │  dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │  dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │  dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │  dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │  dist/remixicon-NKANDIL5.woff2
│ │ │ -dist/search_data-FF8A98E6.js
│ │ │ +dist/search_data-0744904A.js
│ │ │  dist/sidebar_items-8A43D419.js
│ │ │  edoc.html
│ │ │  edoc.html
│ │ │  efficiency_guide.html
│ │ │  efficiency_guide.html
│ │ │  eldap.html
│ │ │  eldap.html
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/search.html
│ │ │ @@ -108,15 +108,15 @@
│ │ │  <div id="search">
│ │ │    <h1>
│ │ │      <span></span>
│ │ │    </h1>
│ │ │  
│ │ │    <div class="loading"><div></div><div></div><div></div><div></div></div>
│ │ │  </div>
│ │ │ -<script src="dist/search_data-FF8A98E6.js"></script>
│ │ │ +<script src="dist/search_data-0744904A.js"></script>
│ │ │      <footer class="footer">
│ │ │        <p>
│ │ │  
│ │ │          <span class="line">
│ │ │            <button class="a-main footer-button display-quick-switch" title="Search HexDocs packages">
│ │ │              Search HexDocs
│ │ │            </button>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/.build
│ │ │ @@ -37,15 +37,15 @@
│ │ │  dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │  dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │  dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │  dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │  dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │  dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │  dist/remixicon-NKANDIL5.woff2
│ │ │ -dist/search_data-D62CB992.js
│ │ │ +dist/search_data-CC135E6A.js
│ │ │  dist/sidebar_items-4A143270.js
│ │ │  distributed.html
│ │ │  distributed_applications.html
│ │ │  documentation.html
│ │ │  drivers.html
│ │ │  eff_guide_functions.html
│ │ │  eff_guide_processes.html
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/Erlang System Documentation.epub
│ │ │ ├── zipinfo {}
│ │ │ │ @@ -1,93 +1,93 @@
│ │ │ │ -Zip file size: 654613 bytes, number of entries: 91
│ │ │ │ -?rw-r--r--  6.1 unx       20 bx stor 25-Jul-08 08:11 mimetype
│ │ │ │ -?rw-r--r--  6.1 unx    17922 bx defN 25-Jul-08 08:11 OEBPS/versions.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx     4673 bx defN 25-Jul-08 08:11 OEBPS/upgrade.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx    53439 bx defN 25-Jul-08 08:11 OEBPS/typespec.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx     2166 bx defN 25-Jul-08 08:11 OEBPS/tutorial.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx      764 bx defN 25-Jul-08 08:11 OEBPS/title.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx    46256 bx defN 25-Jul-08 08:11 OEBPS/tablesdatabases.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx    12466 bx defN 25-Jul-08 08:11 OEBPS/system_principles.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx     7346 bx defN 25-Jul-08 08:11 OEBPS/system_limits.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx    63476 bx defN 25-Jul-08 08:11 OEBPS/sup_princ.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx   253918 bx defN 25-Jul-08 08:11 OEBPS/statem.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx   111264 bx defN 25-Jul-08 08:11 OEBPS/spec_proc.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx   249951 bx defN 25-Jul-08 08:11 OEBPS/seq_prog.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx    70943 bx defN 25-Jul-08 08:11 OEBPS/robustness.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx    20854 bx defN 25-Jul-08 08:11 OEBPS/release_structure.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx    59888 bx defN 25-Jul-08 08:11 OEBPS/release_handling.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx     4596 bx defN 25-Jul-08 08:11 OEBPS/reference_manual.xhtml
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│ │ │ │ -?rw-r--r--  6.1 unx    15206 bx defN 25-Jul-08 08:11 OEBPS/profiling.xhtml
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│ │ │ │ -?rw-r--r--  6.1 unx    14065 bx defN 25-Jul-08 08:11 OEBPS/nif.xhtml
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│ │ │ │ -?rw-r--r--  6.1 unx    24284 bx defN 25-Jul-08 08:11 OEBPS/distributed.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx    14562 bx defN 25-Jul-08 08:11 OEBPS/dist/epub-erlang-ESPT6BQV.css
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│ │ │ │ -?rw-r--r--  6.1 unx    13187 bx defN 25-Jul-08 08:11 OEBPS/content.opf
│ │ │ │ -?rw-r--r--  6.1 unx   129900 bx defN 25-Jul-08 08:11 OEBPS/conc_prog.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx    33231 bx defN 25-Jul-08 08:11 OEBPS/commoncaveats.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx    11935 bx defN 25-Jul-08 08:11 OEBPS/code_loading.xhtml
│ │ │ │ -?rw-r--r--  6.1 unx      803 bx defN 25-Jul-08 08:11 OEBPS/cnode.xhtml
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│ │ │ │ -?rw-r--r--  6.1 unx      252 bx defN 25-Jul-08 08:11 META-INF/container.xml
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│ │ │ │ +?rw-r--r--  6.1 unx     4673 bx defN 25-Aug-22 21:52 OEBPS/upgrade.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx     2166 bx defN 25-Aug-22 21:52 OEBPS/tutorial.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx      764 bx defN 25-Aug-22 21:52 OEBPS/title.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx    12466 bx defN 25-Aug-22 21:52 OEBPS/system_principles.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx     7346 bx defN 25-Aug-22 21:52 OEBPS/system_limits.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx   249951 bx defN 25-Aug-22 21:52 OEBPS/seq_prog.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    70943 bx defN 25-Aug-22 21:52 OEBPS/robustness.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    20854 bx defN 25-Aug-22 21:52 OEBPS/release_structure.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    59888 bx defN 25-Aug-22 21:52 OEBPS/release_handling.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx     4596 bx defN 25-Aug-22 21:52 OEBPS/reference_manual.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    19455 bx defN 25-Aug-22 21:52 OEBPS/ref_man_records.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    48276 bx defN 25-Aug-22 21:52 OEBPS/ref_man_processes.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    14454 bx defN 25-Aug-22 21:52 OEBPS/ref_man_functions.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    49542 bx defN 25-Aug-22 21:52 OEBPS/records_macros.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx     2190 bx defN 25-Aug-22 21:52 OEBPS/readme.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx      785 bx defN 25-Aug-22 21:52 OEBPS/programming_examples.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx    15206 bx defN 25-Aug-22 21:52 OEBPS/profiling.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx     7012 bx defN 25-Aug-22 21:52 OEBPS/misc.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx     5477 bx defN 25-Aug-22 21:52 OEBPS/memory.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx    42996 bx defN 25-Aug-22 21:52 OEBPS/list_comprehensions.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx     2211 bx defN 25-Aug-22 21:52 OEBPS/installation_guide.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    55516 bx defN 25-Aug-22 21:52 OEBPS/install.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    28229 bx defN 25-Aug-22 21:52 OEBPS/install-win32.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    35715 bx defN 25-Aug-22 21:52 OEBPS/install-cross.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    20858 bx defN 25-Aug-22 21:52 OEBPS/included_applications.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx     2353 bx defN 25-Aug-22 21:52 OEBPS/getting_started.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    31341 bx defN 25-Aug-22 21:52 OEBPS/gen_server_concepts.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx   255000 bx defN 25-Aug-22 21:52 OEBPS/expressions.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx     2365 bx defN 25-Aug-22 21:52 OEBPS/example.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    26747 bx defN 25-Aug-22 21:52 OEBPS/events.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    16629 bx defN 25-Aug-22 21:52 OEBPS/errors.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx    42501 bx defN 25-Aug-22 21:52 OEBPS/erl_interface.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    18220 bx defN 25-Aug-22 21:52 OEBPS/embedded.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx    21209 bx defN 25-Aug-22 21:52 OEBPS/eff_guide_functions.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx     9338 bx defN 25-Aug-22 21:52 OEBPS/drivers.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    47180 bx defN 25-Aug-22 21:52 OEBPS/documentation.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    14892 bx defN 25-Aug-22 21:52 OEBPS/distributed_applications.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    24284 bx defN 25-Aug-22 21:52 OEBPS/distributed.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    14562 bx defN 25-Aug-22 21:52 OEBPS/dist/epub-erlang-ESPT6BQV.css
│ │ │ │ +?rw-r--r--  6.1 unx      499 bx defN 25-Aug-22 21:52 OEBPS/dist/epub-LSJCIYTM.js
│ │ │ │ +?rw-r--r--  6.1 unx    36780 bx defN 25-Aug-22 21:52 OEBPS/design_principles.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    15003 bx defN 25-Aug-22 21:52 OEBPS/debugging.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    71771 bx defN 25-Aug-22 21:52 OEBPS/data_types.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx   115067 bx defN 25-Aug-22 21:52 OEBPS/create_target.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    13187 bx defN 25-Aug-22 21:52 OEBPS/content.opf
│ │ │ │ +?rw-r--r--  6.1 unx   129900 bx defN 25-Aug-22 21:52 OEBPS/conc_prog.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    33231 bx defN 25-Aug-22 21:52 OEBPS/commoncaveats.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    11935 bx defN 25-Aug-22 21:52 OEBPS/code_loading.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx     5177 bx defN 25-Aug-22 21:52 OEBPS/character_set.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    40707 bx defN 25-Aug-22 21:52 OEBPS/c_portdriver.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    35510 bx defN 25-Aug-22 21:52 OEBPS/c_port.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx     7606 bx defN 25-Aug-22 21:52 OEBPS/benchmarking.xhtml
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│ │ │ │ +?rw-r--r--  6.1 unx      162 bx defN 25-Aug-22 21:52 META-INF/com.apple.ibooks.display-options.xml
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│ │ │ │ +0002B   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +0002F   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │  00033 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │  00035   Length              000B (11)
│ │ │ │  00037   Version             01 (1)
│ │ │ │  00038   UID Size            04 (4)
│ │ │ │  00039   UID                 00000000 (0)
│ │ │ │  0003D   GID Size            04 (4)
│ │ │ │  0003E   GID                 00000000 (0)
│ │ │ │ @@ -31,30 +31,30 @@
│ │ │ │  
│ │ │ │  00056 LOCAL HEADER #2       04034B50 (67324752)
│ │ │ │  0005A Extract Zip Spec      14 (20) '2.0'
│ │ │ │  0005B Extract OS            00 (0) 'MS-DOS'
│ │ │ │  0005C General Purpose Flag  0000 (0)
│ │ │ │        [Bits 1-2]            0 'Normal Compression'
│ │ │ │  0005E Compression Method    0008 (8) 'Deflated'
│ │ │ │ -00060 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ +00060 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │  00064 CRC                   D1CBDA94 (3519797908)
│ │ │ │  00068 Compressed Size       000015AD (5549)
│ │ │ │  0006C Uncompressed Size     00004602 (17922)
│ │ │ │  00070 Filename Length       0014 (20)
│ │ │ │  00072 Extra Length          001C (28)
│ │ │ │  00074 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │  #
│ │ │ │  # WARNING: Offset 0x74: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │  #          Zero length filename
│ │ │ │  #
│ │ │ │  00088 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │  0008A   Length              0009 (9)
│ │ │ │  0008C   Flags               03 (3) 'Modification Access'
│ │ │ │ -0008D   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -00091   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ +0008D   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +00091   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │  00095 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │  00097   Length              000B (11)
│ │ │ │  00099   Version             01 (1)
│ │ │ │  0009A   UID Size            04 (4)
│ │ │ │  0009B   UID                 00000000 (0)
│ │ │ │  0009F   GID Size            04 (4)
│ │ │ │  000A0   GID                 00000000 (0)
│ │ │ │ @@ -62,30 +62,30 @@
│ │ │ │  
│ │ │ │  01651 LOCAL HEADER #3       04034B50 (67324752)
│ │ │ │  01655 Extract Zip Spec      14 (20) '2.0'
│ │ │ │  01656 Extract OS            00 (0) 'MS-DOS'
│ │ │ │  01657 General Purpose Flag  0000 (0)
│ │ │ │        [Bits 1-2]            0 'Normal Compression'
│ │ │ │  01659 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -0165B Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ +0165B Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │  0165F CRC                   AB09C204 (2869543428)
│ │ │ │  01663 Compressed Size       000006D5 (1749)
│ │ │ │  01667 Uncompressed Size     00001241 (4673)
│ │ │ │  0166B Filename Length       0013 (19)
│ │ │ │  0166D Extra Length          001C (28)
│ │ │ │  0166F Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │  #
│ │ │ │  # WARNING: Offset 0x166F: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │  #          Zero length filename
│ │ │ │  #
│ │ │ │  01682 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │  01684   Length              0009 (9)
│ │ │ │  01686   Flags               03 (3) 'Modification Access'
│ │ │ │ -01687   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -0168B   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ +01687   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +0168B   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │  0168F Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │  01691   Length              000B (11)
│ │ │ │  01693   Version             01 (1)
│ │ │ │  01694   UID Size            04 (4)
│ │ │ │  01695   UID                 00000000 (0)
│ │ │ │  01699   GID Size            04 (4)
│ │ │ │  0169A   GID                 00000000 (0)
│ │ │ │ @@ -93,6187 +93,6187 @@
│ │ │ │  
│ │ │ │  01D73 LOCAL HEADER #4       04034B50 (67324752)
│ │ │ │  01D77 Extract Zip Spec      14 (20) '2.0'
│ │ │ │  01D78 Extract OS            00 (0) 'MS-DOS'
│ │ │ │  01D79 General Purpose Flag  0000 (0)
│ │ │ │        [Bits 1-2]            0 'Normal Compression'
│ │ │ │  01D7B Compression Method    0008 (8) 'Deflated'
│ │ │ │ -01D7D Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -01D81 CRC                   47F54438 (1207256120)
│ │ │ │ -01D85 Compressed Size       00002DA3 (11683)
│ │ │ │ +01D7D Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +01D81 CRC                   3220A0FE (840999166)
│ │ │ │ +01D85 Compressed Size       00002D9E (11678)
│ │ │ │  01D89 Uncompressed Size     0000D0BF (53439)
│ │ │ │  01D8D Filename Length       0014 (20)
│ │ │ │  01D8F Extra Length          001C (28)
│ │ │ │  01D91 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │  #
│ │ │ │  # WARNING: Offset 0x1D91: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │  #          Zero length filename
│ │ │ │  #
│ │ │ │  01DA5 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │  01DA7   Length              0009 (9)
│ │ │ │  01DA9   Flags               03 (3) 'Modification Access'
│ │ │ │ -01DAA   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -01DAE   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ +01DAA   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +01DAE   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │  01DB2 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │  01DB4   Length              000B (11)
│ │ │ │  01DB6   Version             01 (1)
│ │ │ │  01DB7   UID Size            04 (4)
│ │ │ │  01DB8   UID                 00000000 (0)
│ │ │ │  01DBC   GID Size            04 (4)
│ │ │ │  01DBD   GID                 00000000 (0)
│ │ │ │  01DC1 PAYLOAD
│ │ │ │  
│ │ │ │ -04B64 LOCAL HEADER #5       04034B50 (67324752)
│ │ │ │ -04B68 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -04B69 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -04B6A General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -04B6C Compression Method    0008 (8) 'Deflated'
│ │ │ │ -04B6E Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -04B72 CRC                   67C49326 (1740935974)
│ │ │ │ -04B76 Compressed Size       000003F0 (1008)
│ │ │ │ -04B7A Uncompressed Size     00000876 (2166)
│ │ │ │ -04B7E Filename Length       0014 (20)
│ │ │ │ -04B80 Extra Length          001C (28)
│ │ │ │ -04B82 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4B82: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -04B96 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -04B98   Length              0009 (9)
│ │ │ │ -04B9A   Flags               03 (3) 'Modification Access'
│ │ │ │ -04B9B   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -04B9F   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -04BA3 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -04BA5   Length              000B (11)
│ │ │ │ -04BA7   Version             01 (1)
│ │ │ │ -04BA8   UID Size            04 (4)
│ │ │ │ -04BA9   UID                 00000000 (0)
│ │ │ │ -04BAD   GID Size            04 (4)
│ │ │ │ -04BAE   GID                 00000000 (0)
│ │ │ │ -04BB2 PAYLOAD
│ │ │ │ -
│ │ │ │ -04FA2 LOCAL HEADER #6       04034B50 (67324752)
│ │ │ │ -04FA6 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -04FA7 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -04FA8 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -04FAA Compression Method    0008 (8) 'Deflated'
│ │ │ │ -04FAC Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -04FB0 CRC                   EC6C7C96 (3966532758)
│ │ │ │ -04FB4 Compressed Size       000001AE (430)
│ │ │ │ -04FB8 Uncompressed Size     000002FC (764)
│ │ │ │ -04FBC Filename Length       0011 (17)
│ │ │ │ -04FBE Extra Length          001C (28)
│ │ │ │ -04FC0 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4FC0: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -04FD1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -04FD3   Length              0009 (9)
│ │ │ │ -04FD5   Flags               03 (3) 'Modification Access'
│ │ │ │ -04FD6   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -04FDA   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -04FDE Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -04FE0   Length              000B (11)
│ │ │ │ -04FE2   Version             01 (1)
│ │ │ │ -04FE3   UID Size            04 (4)
│ │ │ │ -04FE4   UID                 00000000 (0)
│ │ │ │ -04FE8   GID Size            04 (4)
│ │ │ │ -04FE9   GID                 00000000 (0)
│ │ │ │ -04FED PAYLOAD
│ │ │ │ -
│ │ │ │ -0519B LOCAL HEADER #7       04034B50 (67324752)
│ │ │ │ -0519F Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -051A0 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -051A1 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -051A3 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -051A5 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -051A9 CRC                   39BDC93C (968739132)
│ │ │ │ -051AD Compressed Size       000020C6 (8390)
│ │ │ │ -051B1 Uncompressed Size     0000B4B0 (46256)
│ │ │ │ -051B5 Filename Length       001B (27)
│ │ │ │ -051B7 Extra Length          001C (28)
│ │ │ │ -051B9 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x51B9: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -051D4 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -051D6   Length              0009 (9)
│ │ │ │ -051D8   Flags               03 (3) 'Modification Access'
│ │ │ │ -051D9   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -051DD   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -051E1 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -051E3   Length              000B (11)
│ │ │ │ -051E5   Version             01 (1)
│ │ │ │ -051E6   UID Size            04 (4)
│ │ │ │ -051E7   UID                 00000000 (0)
│ │ │ │ -051EB   GID Size            04 (4)
│ │ │ │ -051EC   GID                 00000000 (0)
│ │ │ │ -051F0 PAYLOAD
│ │ │ │ -
│ │ │ │ -072B6 LOCAL HEADER #8       04034B50 (67324752)
│ │ │ │ -072BA Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -072BB Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -072BC General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -072BE Compression Method    0008 (8) 'Deflated'
│ │ │ │ -072C0 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -072C4 CRC                   23989D4C (597204300)
│ │ │ │ -072C8 Compressed Size       00000E6F (3695)
│ │ │ │ -072CC Uncompressed Size     000030B2 (12466)
│ │ │ │ -072D0 Filename Length       001D (29)
│ │ │ │ -072D2 Extra Length          001C (28)
│ │ │ │ -072D4 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x72D4: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -072F1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -072F3   Length              0009 (9)
│ │ │ │ -072F5   Flags               03 (3) 'Modification Access'
│ │ │ │ -072F6   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -072FA   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -072FE Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -07300   Length              000B (11)
│ │ │ │ -07302   Version             01 (1)
│ │ │ │ -07303   UID Size            04 (4)
│ │ │ │ -07304   UID                 00000000 (0)
│ │ │ │ -07308   GID Size            04 (4)
│ │ │ │ -07309   GID                 00000000 (0)
│ │ │ │ -0730D PAYLOAD
│ │ │ │ -
│ │ │ │ -0817C LOCAL HEADER #9       04034B50 (67324752)
│ │ │ │ -08180 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -08181 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -08182 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -08184 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -08186 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -0818A CRC                   E1B38941 (3786639681)
│ │ │ │ -0818E Compressed Size       00000972 (2418)
│ │ │ │ -08192 Uncompressed Size     00001CB2 (7346)
│ │ │ │ -08196 Filename Length       0019 (25)
│ │ │ │ -08198 Extra Length          001C (28)
│ │ │ │ -0819A Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x819A: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -081B3 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -081B5   Length              0009 (9)
│ │ │ │ -081B7   Flags               03 (3) 'Modification Access'
│ │ │ │ -081B8   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -081BC   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -081C0 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -081C2   Length              000B (11)
│ │ │ │ -081C4   Version             01 (1)
│ │ │ │ -081C5   UID Size            04 (4)
│ │ │ │ -081C6   UID                 00000000 (0)
│ │ │ │ -081CA   GID Size            04 (4)
│ │ │ │ -081CB   GID                 00000000 (0)
│ │ │ │ -081CF PAYLOAD
│ │ │ │ -
│ │ │ │ -08B41 LOCAL HEADER #10      04034B50 (67324752)
│ │ │ │ -08B45 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -08B46 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -08B47 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -08B49 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -08B4B Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -08B4F CRC                   2A71CBBF (712100799)
│ │ │ │ -08B53 Compressed Size       00003880 (14464)
│ │ │ │ -08B57 Uncompressed Size     0000F7F4 (63476)
│ │ │ │ -08B5B Filename Length       0015 (21)
│ │ │ │ -08B5D Extra Length          001C (28)
│ │ │ │ -08B5F Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8B5F: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -08B74 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -08B76   Length              0009 (9)
│ │ │ │ -08B78   Flags               03 (3) 'Modification Access'
│ │ │ │ -08B79   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -08B7D   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -08B81 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -08B83   Length              000B (11)
│ │ │ │ -08B85   Version             01 (1)
│ │ │ │ -08B86   UID Size            04 (4)
│ │ │ │ -08B87   UID                 00000000 (0)
│ │ │ │ -08B8B   GID Size            04 (4)
│ │ │ │ -08B8C   GID                 00000000 (0)
│ │ │ │ -08B90 PAYLOAD
│ │ │ │ -
│ │ │ │ -0C410 LOCAL HEADER #11      04034B50 (67324752)
│ │ │ │ -0C414 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -0C415 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -0C416 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -0C418 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -0C41A Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -0C41E CRC                   F9745AFD (4185152253)
│ │ │ │ -0C422 Compressed Size       0000AADF (43743)
│ │ │ │ -0C426 Uncompressed Size     0003DFDE (253918)
│ │ │ │ -0C42A Filename Length       0012 (18)
│ │ │ │ -0C42C Extra Length          001C (28)
│ │ │ │ -0C42E Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xC42E: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -0C440 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -0C442   Length              0009 (9)
│ │ │ │ -0C444   Flags               03 (3) 'Modification Access'
│ │ │ │ -0C445   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -0C449   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -0C44D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -0C44F   Length              000B (11)
│ │ │ │ -0C451   Version             01 (1)
│ │ │ │ -0C452   UID Size            04 (4)
│ │ │ │ -0C453   UID                 00000000 (0)
│ │ │ │ -0C457   GID Size            04 (4)
│ │ │ │ -0C458   GID                 00000000 (0)
│ │ │ │ -0C45C PAYLOAD
│ │ │ │ -
│ │ │ │ -16F3B LOCAL HEADER #12      04034B50 (67324752)
│ │ │ │ -16F3F Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -16F40 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -16F41 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -16F43 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -16F45 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -16F49 CRC                   C29A5D7D (3264896381)
│ │ │ │ -16F4D Compressed Size       00003B20 (15136)
│ │ │ │ -16F51 Uncompressed Size     0001B2A0 (111264)
│ │ │ │ -16F55 Filename Length       0015 (21)
│ │ │ │ -16F57 Extra Length          001C (28)
│ │ │ │ -16F59 Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x16F59: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -16F6E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -16F70   Length              0009 (9)
│ │ │ │ -16F72   Flags               03 (3) 'Modification Access'
│ │ │ │ -16F73   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -16F77   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -16F7B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -16F7D   Length              000B (11)
│ │ │ │ -16F7F   Version             01 (1)
│ │ │ │ -16F80   UID Size            04 (4)
│ │ │ │ -16F81   UID                 00000000 (0)
│ │ │ │ -16F85   GID Size            04 (4)
│ │ │ │ -16F86   GID                 00000000 (0)
│ │ │ │ -16F8A PAYLOAD
│ │ │ │ -
│ │ │ │ -1AAAA LOCAL HEADER #13      04034B50 (67324752)
│ │ │ │ -1AAAE Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -1AAAF Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -1AAB0 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -1AAB2 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -1AAB4 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -1AAB8 CRC                   5B4833BB (1531458491)
│ │ │ │ -1AABC Compressed Size       00009085 (36997)
│ │ │ │ -1AAC0 Uncompressed Size     0003D05F (249951)
│ │ │ │ -1AAC4 Filename Length       0014 (20)
│ │ │ │ -1AAC6 Extra Length          001C (28)
│ │ │ │ -1AAC8 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x1AAC8: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -1AADC Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -1AADE   Length              0009 (9)
│ │ │ │ -1AAE0   Flags               03 (3) 'Modification Access'
│ │ │ │ -1AAE1   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -1AAE5   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -1AAE9 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -1AAEB   Length              000B (11)
│ │ │ │ -1AAED   Version             01 (1)
│ │ │ │ -1AAEE   UID Size            04 (4)
│ │ │ │ -1AAEF   UID                 00000000 (0)
│ │ │ │ -1AAF3   GID Size            04 (4)
│ │ │ │ -1AAF4   GID                 00000000 (0)
│ │ │ │ -1AAF8 PAYLOAD
│ │ │ │ -
│ │ │ │ -23B7D LOCAL HEADER #14      04034B50 (67324752)
│ │ │ │ -23B81 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -23B82 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -23B83 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -23B85 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -23B87 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -23B8B CRC                   166FC7BA (376424378)
│ │ │ │ -23B8F Compressed Size       00002A67 (10855)
│ │ │ │ -23B93 Uncompressed Size     0001151F (70943)
│ │ │ │ -23B97 Filename Length       0016 (22)
│ │ │ │ -23B99 Extra Length          001C (28)
│ │ │ │ -23B9B Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x23B9B: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -23BB1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -23BB3   Length              0009 (9)
│ │ │ │ -23BB5   Flags               03 (3) 'Modification Access'
│ │ │ │ -23BB6   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -23BBA   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -23BBE Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -23BC0   Length              000B (11)
│ │ │ │ -23BC2   Version             01 (1)
│ │ │ │ -23BC3   UID Size            04 (4)
│ │ │ │ -23BC4   UID                 00000000 (0)
│ │ │ │ -23BC8   GID Size            04 (4)
│ │ │ │ -23BC9   GID                 00000000 (0)
│ │ │ │ -23BCD PAYLOAD
│ │ │ │ -
│ │ │ │ -26634 LOCAL HEADER #15      04034B50 (67324752)
│ │ │ │ -26638 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -26639 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -2663A General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -2663C Compression Method    0008 (8) 'Deflated'
│ │ │ │ -2663E Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -26642 CRC                   7F8EA835 (2140055605)
│ │ │ │ -26646 Compressed Size       000014DA (5338)
│ │ │ │ -2664A Uncompressed Size     00005176 (20854)
│ │ │ │ -2664E Filename Length       001D (29)
│ │ │ │ -26650 Extra Length          001C (28)
│ │ │ │ -26652 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x26652: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -2666F Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -26671   Length              0009 (9)
│ │ │ │ -26673   Flags               03 (3) 'Modification Access'
│ │ │ │ -26674   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -26678   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -2667C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -2667E   Length              000B (11)
│ │ │ │ -26680   Version             01 (1)
│ │ │ │ -26681   UID Size            04 (4)
│ │ │ │ -26682   UID                 00000000 (0)
│ │ │ │ -26686   GID Size            04 (4)
│ │ │ │ -26687   GID                 00000000 (0)
│ │ │ │ -2668B PAYLOAD
│ │ │ │ -
│ │ │ │ -27B65 LOCAL HEADER #16      04034B50 (67324752)
│ │ │ │ -27B69 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -27B6A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -27B6B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -27B6D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -27B6F Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -27B73 CRC                   D4CAE8E4 (3570067684)
│ │ │ │ -27B77 Compressed Size       000037FB (14331)
│ │ │ │ -27B7B Uncompressed Size     0000E9F0 (59888)
│ │ │ │ -27B7F Filename Length       001C (28)
│ │ │ │ -27B81 Extra Length          001C (28)
│ │ │ │ -27B83 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x27B83: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -27B9F Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -27BA1   Length              0009 (9)
│ │ │ │ -27BA3   Flags               03 (3) 'Modification Access'
│ │ │ │ -27BA4   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -27BA8   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -27BAC Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -27BAE   Length              000B (11)
│ │ │ │ -27BB0   Version             01 (1)
│ │ │ │ -27BB1   UID Size            04 (4)
│ │ │ │ -27BB2   UID                 00000000 (0)
│ │ │ │ -27BB6   GID Size            04 (4)
│ │ │ │ -27BB7   GID                 00000000 (0)
│ │ │ │ -27BBB PAYLOAD
│ │ │ │ -
│ │ │ │ -2B3B6 LOCAL HEADER #17      04034B50 (67324752)
│ │ │ │ -2B3BA Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -2B3BB Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -2B3BC General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -2B3BE Compression Method    0008 (8) 'Deflated'
│ │ │ │ -2B3C0 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -2B3C4 CRC                   B106FD76 (2970025334)
│ │ │ │ -2B3C8 Compressed Size       000006A0 (1696)
│ │ │ │ -2B3CC Uncompressed Size     000011F4 (4596)
│ │ │ │ -2B3D0 Filename Length       001C (28)
│ │ │ │ -2B3D2 Extra Length          001C (28)
│ │ │ │ -2B3D4 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x2B3D4: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -2B3F0 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -2B3F2   Length              0009 (9)
│ │ │ │ -2B3F4   Flags               03 (3) 'Modification Access'
│ │ │ │ -2B3F5   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -2B3F9   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -2B3FD Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -2B3FF   Length              000B (11)
│ │ │ │ -2B401   Version             01 (1)
│ │ │ │ -2B402   UID Size            04 (4)
│ │ │ │ -2B403   UID                 00000000 (0)
│ │ │ │ -2B407   GID Size            04 (4)
│ │ │ │ -2B408   GID                 00000000 (0)
│ │ │ │ -2B40C PAYLOAD
│ │ │ │ -
│ │ │ │ -2BAAC LOCAL HEADER #18      04034B50 (67324752)
│ │ │ │ -2BAB0 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -2BAB1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -2BAB2 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -2BAB4 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -2BAB6 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -2BABA CRC                   6290960D (1653642765)
│ │ │ │ -2BABE Compressed Size       00001081 (4225)
│ │ │ │ -2BAC2 Uncompressed Size     00004BFF (19455)
│ │ │ │ -2BAC6 Filename Length       001B (27)
│ │ │ │ -2BAC8 Extra Length          001C (28)
│ │ │ │ -2BACA Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x2BACA: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -2BAE5 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -2BAE7   Length              0009 (9)
│ │ │ │ -2BAE9   Flags               03 (3) 'Modification Access'
│ │ │ │ -2BAEA   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -2BAEE   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -2BAF2 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -2BAF4   Length              000B (11)
│ │ │ │ -2BAF6   Version             01 (1)
│ │ │ │ -2BAF7   UID Size            04 (4)
│ │ │ │ -2BAF8   UID                 00000000 (0)
│ │ │ │ -2BAFC   GID Size            04 (4)
│ │ │ │ -2BAFD   GID                 00000000 (0)
│ │ │ │ -2BB01 PAYLOAD
│ │ │ │ -
│ │ │ │ -2CB82 LOCAL HEADER #19      04034B50 (67324752)
│ │ │ │ -2CB86 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -2CB87 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -2CB88 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -2CB8A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -2CB8C Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -2CB90 CRC                   ED4F3856 (3981391958)
│ │ │ │ -2CB94 Compressed Size       000033AA (13226)
│ │ │ │ -2CB98 Uncompressed Size     0000BC94 (48276)
│ │ │ │ -2CB9C Filename Length       001D (29)
│ │ │ │ -2CB9E Extra Length          001C (28)
│ │ │ │ -2CBA0 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x2CBA0: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -2CBBD Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -2CBBF   Length              0009 (9)
│ │ │ │ -2CBC1   Flags               03 (3) 'Modification Access'
│ │ │ │ -2CBC2   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -2CBC6   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -2CBCA Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -2CBCC   Length              000B (11)
│ │ │ │ -2CBCE   Version             01 (1)
│ │ │ │ -2CBCF   UID Size            04 (4)
│ │ │ │ -2CBD0   UID                 00000000 (0)
│ │ │ │ -2CBD4   GID Size            04 (4)
│ │ │ │ -2CBD5   GID                 00000000 (0)
│ │ │ │ -2CBD9 PAYLOAD
│ │ │ │ -
│ │ │ │ -2FF83 LOCAL HEADER #20      04034B50 (67324752)
│ │ │ │ -2FF87 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -2FF88 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -2FF89 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -2FF8B Compression Method    0008 (8) 'Deflated'
│ │ │ │ -2FF8D Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -2FF91 CRC                   C64C8DB7 (3326905783)
│ │ │ │ -2FF95 Compressed Size       00000D6A (3434)
│ │ │ │ -2FF99 Uncompressed Size     00003876 (14454)
│ │ │ │ -2FF9D Filename Length       001D (29)
│ │ │ │ -2FF9F Extra Length          001C (28)
│ │ │ │ -2FFA1 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x2FFA1: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -2FFBE Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -2FFC0   Length              0009 (9)
│ │ │ │ -2FFC2   Flags               03 (3) 'Modification Access'
│ │ │ │ -2FFC3   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -2FFC7   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -2FFCB Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -2FFCD   Length              000B (11)
│ │ │ │ -2FFCF   Version             01 (1)
│ │ │ │ -2FFD0   UID Size            04 (4)
│ │ │ │ -2FFD1   UID                 00000000 (0)
│ │ │ │ -2FFD5   GID Size            04 (4)
│ │ │ │ -2FFD6   GID                 00000000 (0)
│ │ │ │ -2FFDA PAYLOAD
│ │ │ │ -
│ │ │ │ -30D44 LOCAL HEADER #21      04034B50 (67324752)
│ │ │ │ -30D48 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -30D49 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -30D4A General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -30D4C Compression Method    0008 (8) 'Deflated'
│ │ │ │ -30D4E Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -30D52 CRC                   92045684 (2449757828)
│ │ │ │ -30D56 Compressed Size       00001C69 (7273)
│ │ │ │ -30D5A Uncompressed Size     0000C186 (49542)
│ │ │ │ -30D5E Filename Length       001A (26)
│ │ │ │ -30D60 Extra Length          001C (28)
│ │ │ │ -30D62 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x30D62: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -30D7C Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -30D7E   Length              0009 (9)
│ │ │ │ -30D80   Flags               03 (3) 'Modification Access'
│ │ │ │ -30D81   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -30D85   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -30D89 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -30D8B   Length              000B (11)
│ │ │ │ -30D8D   Version             01 (1)
│ │ │ │ -30D8E   UID Size            04 (4)
│ │ │ │ -30D8F   UID                 00000000 (0)
│ │ │ │ -30D93   GID Size            04 (4)
│ │ │ │ -30D94   GID                 00000000 (0)
│ │ │ │ -30D98 PAYLOAD
│ │ │ │ -
│ │ │ │ -32A01 LOCAL HEADER #22      04034B50 (67324752)
│ │ │ │ -32A05 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -32A06 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -32A07 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -32A09 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -32A0B Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -32A0F CRC                   2632F341 (640873281)
│ │ │ │ -32A13 Compressed Size       000003A3 (931)
│ │ │ │ -32A17 Uncompressed Size     0000088E (2190)
│ │ │ │ -32A1B Filename Length       0012 (18)
│ │ │ │ -32A1D Extra Length          001C (28)
│ │ │ │ -32A1F Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x32A1F: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -32A31 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -32A33   Length              0009 (9)
│ │ │ │ -32A35   Flags               03 (3) 'Modification Access'
│ │ │ │ -32A36   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -32A3A   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -32A3E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -32A40   Length              000B (11)
│ │ │ │ -32A42   Version             01 (1)
│ │ │ │ -32A43   UID Size            04 (4)
│ │ │ │ -32A44   UID                 00000000 (0)
│ │ │ │ -32A48   GID Size            04 (4)
│ │ │ │ -32A49   GID                 00000000 (0)
│ │ │ │ -32A4D PAYLOAD
│ │ │ │ -
│ │ │ │ -32DF0 LOCAL HEADER #23      04034B50 (67324752)
│ │ │ │ -32DF4 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -32DF5 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -32DF6 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -32DF8 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -32DFA Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -32DFE CRC                   24939ACA (613653194)
│ │ │ │ -32E02 Compressed Size       000001D4 (468)
│ │ │ │ -32E06 Uncompressed Size     00000311 (785)
│ │ │ │ -32E0A Filename Length       0020 (32)
│ │ │ │ -32E0C Extra Length          001C (28)
│ │ │ │ -32E0E Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x32E0E: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -32E2E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -32E30   Length              0009 (9)
│ │ │ │ -32E32   Flags               03 (3) 'Modification Access'
│ │ │ │ -32E33   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -32E37   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -32E3B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -32E3D   Length              000B (11)
│ │ │ │ -32E3F   Version             01 (1)
│ │ │ │ -32E40   UID Size            04 (4)
│ │ │ │ -32E41   UID                 00000000 (0)
│ │ │ │ -32E45   GID Size            04 (4)
│ │ │ │ -32E46   GID                 00000000 (0)
│ │ │ │ -32E4A PAYLOAD
│ │ │ │ -
│ │ │ │ -3301E LOCAL HEADER #24      04034B50 (67324752)
│ │ │ │ -33022 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -33023 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -33024 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -33026 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -33028 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -3302C CRC                   BA4C527E (3125564030)
│ │ │ │ -33030 Compressed Size       000017AB (6059)
│ │ │ │ -33034 Uncompressed Size     00009CD3 (40147)
│ │ │ │ -33038 Filename Length       001B (27)
│ │ │ │ -3303A Extra Length          001C (28)
│ │ │ │ -3303C Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3303C: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -33057 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -33059   Length              0009 (9)
│ │ │ │ -3305B   Flags               03 (3) 'Modification Access'
│ │ │ │ -3305C   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -33060   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -33064 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -33066   Length              000B (11)
│ │ │ │ -33068   Version             01 (1)
│ │ │ │ -33069   UID Size            04 (4)
│ │ │ │ -3306A   UID                 00000000 (0)
│ │ │ │ -3306E   GID Size            04 (4)
│ │ │ │ -3306F   GID                 00000000 (0)
│ │ │ │ -33073 PAYLOAD
│ │ │ │ -
│ │ │ │ -3481E LOCAL HEADER #25      04034B50 (67324752)
│ │ │ │ -34822 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -34823 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -34824 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -34826 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -34828 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -3482C CRC                   454623A7 (1162224551)
│ │ │ │ -34830 Compressed Size       00001371 (4977)
│ │ │ │ -34834 Uncompressed Size     00003B66 (15206)
│ │ │ │ -34838 Filename Length       0015 (21)
│ │ │ │ -3483A Extra Length          001C (28)
│ │ │ │ -3483C Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3483C: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -34851 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -34853   Length              0009 (9)
│ │ │ │ -34855   Flags               03 (3) 'Modification Access'
│ │ │ │ -34856   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3485A   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3485E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -34860   Length              000B (11)
│ │ │ │ -34862   Version             01 (1)
│ │ │ │ -34863   UID Size            04 (4)
│ │ │ │ -34864   UID                 00000000 (0)
│ │ │ │ -34868   GID Size            04 (4)
│ │ │ │ -34869   GID                 00000000 (0)
│ │ │ │ -3486D PAYLOAD
│ │ │ │ -
│ │ │ │ -35BDE LOCAL HEADER #26      04034B50 (67324752)
│ │ │ │ -35BE2 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -35BE3 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -35BE4 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -35BE6 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -35BE8 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -35BEC CRC                   081E11CF (136188367)
│ │ │ │ -35BF0 Compressed Size       00000AD1 (2769)
│ │ │ │ -35BF4 Uncompressed Size     00002135 (8501)
│ │ │ │ -35BF8 Filename Length       0011 (17)
│ │ │ │ -35BFA Extra Length          001C (28)
│ │ │ │ -35BFC Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x35BFC: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -35C0D Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -35C0F   Length              0009 (9)
│ │ │ │ -35C11   Flags               03 (3) 'Modification Access'
│ │ │ │ -35C12   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -35C16   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -35C1A Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -35C1C   Length              000B (11)
│ │ │ │ -35C1E   Version             01 (1)
│ │ │ │ -35C1F   UID Size            04 (4)
│ │ │ │ -35C20   UID                 00000000 (0)
│ │ │ │ -35C24   GID Size            04 (4)
│ │ │ │ -35C25   GID                 00000000 (0)
│ │ │ │ -35C29 PAYLOAD
│ │ │ │ -
│ │ │ │ -366FA LOCAL HEADER #27      04034B50 (67324752)
│ │ │ │ -366FE Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -366FF Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -36700 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -36702 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -36704 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -36708 CRC                   3A63D38A (979620746)
│ │ │ │ -3670C Compressed Size       000003FE (1022)
│ │ │ │ -36710 Uncompressed Size     00000E99 (3737)
│ │ │ │ -36714 Filename Length       0014 (20)
│ │ │ │ -36716 Extra Length          001C (28)
│ │ │ │ -36718 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x36718: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3672C Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3672E   Length              0009 (9)
│ │ │ │ -36730   Flags               03 (3) 'Modification Access'
│ │ │ │ -36731   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -36735   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -36739 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3673B   Length              000B (11)
│ │ │ │ -3673D   Version             01 (1)
│ │ │ │ -3673E   UID Size            04 (4)
│ │ │ │ -3673F   UID                 00000000 (0)
│ │ │ │ -36743   GID Size            04 (4)
│ │ │ │ -36744   GID                 00000000 (0)
│ │ │ │ -36748 PAYLOAD
│ │ │ │ -
│ │ │ │ -36B46 LOCAL HEADER #28      04034B50 (67324752)
│ │ │ │ -36B4A Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -36B4B Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -36B4C General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -36B4E Compression Method    0008 (8) 'Deflated'
│ │ │ │ -36B50 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -36B54 CRC                   009A6A7C (10119804)
│ │ │ │ -36B58 Compressed Size       00001261 (4705)
│ │ │ │ -36B5C Uncompressed Size     00003469 (13417)
│ │ │ │ -36B60 Filename Length       0014 (20)
│ │ │ │ -36B62 Extra Length          001C (28)
│ │ │ │ -36B64 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x36B64: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -36B78 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -36B7A   Length              0009 (9)
│ │ │ │ -36B7C   Flags               03 (3) 'Modification Access'
│ │ │ │ -36B7D   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -36B81   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -36B85 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -36B87   Length              000B (11)
│ │ │ │ -36B89   Version             01 (1)
│ │ │ │ -36B8A   UID Size            04 (4)
│ │ │ │ -36B8B   UID                 00000000 (0)
│ │ │ │ -36B8F   GID Size            04 (4)
│ │ │ │ -36B90   GID                 00000000 (0)
│ │ │ │ -36B94 PAYLOAD
│ │ │ │ -
│ │ │ │ -37DF5 LOCAL HEADER #29      04034B50 (67324752)
│ │ │ │ -37DF9 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -37DFA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -37DFB General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -37DFD Compression Method    0008 (8) 'Deflated'
│ │ │ │ -37DFF Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -37E03 CRC                   8C678CDB (2355596507)
│ │ │ │ -37E07 Compressed Size       00000ACF (2767)
│ │ │ │ -37E0B Uncompressed Size     000022FF (8959)
│ │ │ │ -37E0F Filename Length       001B (27)
│ │ │ │ -37E11 Extra Length          001C (28)
│ │ │ │ -37E13 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x37E13: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -37E2E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -37E30   Length              0009 (9)
│ │ │ │ -37E32   Flags               03 (3) 'Modification Access'
│ │ │ │ -37E33   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -37E37   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -37E3B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -37E3D   Length              000B (11)
│ │ │ │ -37E3F   Version             01 (1)
│ │ │ │ -37E40   UID Size            04 (4)
│ │ │ │ -37E41   UID                 00000000 (0)
│ │ │ │ -37E45   GID Size            04 (4)
│ │ │ │ -37E46   GID                 00000000 (0)
│ │ │ │ -37E4A PAYLOAD
│ │ │ │ -
│ │ │ │ -38919 LOCAL HEADER #30      04034B50 (67324752)
│ │ │ │ -3891D Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3891E Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3891F General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -38921 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -38923 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -38927 CRC                   32905960 (848320864)
│ │ │ │ -3892B Compressed Size       00000A8F (2703)
│ │ │ │ -3892F Uncompressed Size     0000237A (9082)
│ │ │ │ -38933 Filename Length       0013 (19)
│ │ │ │ -38935 Extra Length          001C (28)
│ │ │ │ -38937 Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x38937: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3894A Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3894C   Length              0009 (9)
│ │ │ │ -3894E   Flags               03 (3) 'Modification Access'
│ │ │ │ -3894F   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -38953   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -38957 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -38959   Length              000B (11)
│ │ │ │ -3895B   Version             01 (1)
│ │ │ │ -3895C   UID Size            04 (4)
│ │ │ │ -3895D   UID                 00000000 (0)
│ │ │ │ -38961   GID Size            04 (4)
│ │ │ │ -38962   GID                 00000000 (0)
│ │ │ │ -38966 PAYLOAD
│ │ │ │ -
│ │ │ │ -393F5 LOCAL HEADER #31      04034B50 (67324752)
│ │ │ │ -393F9 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -393FA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -393FB General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -393FD Compression Method    0008 (8) 'Deflated'
│ │ │ │ -393FF Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -39403 CRC                   5A75F568 (1517679976)
│ │ │ │ -39407 Compressed Size       00000F49 (3913)
│ │ │ │ -3940B Uncompressed Size     000036F1 (14065)
│ │ │ │ -3940F Filename Length       000F (15)
│ │ │ │ -39411 Extra Length          001C (28)
│ │ │ │ -39413 Filename              'XXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x39413: Filename 'XXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -39422 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -39424   Length              0009 (9)
│ │ │ │ -39426   Flags               03 (3) 'Modification Access'
│ │ │ │ -39427   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3942B   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3942F Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -39431   Length              000B (11)
│ │ │ │ -39433   Version             01 (1)
│ │ │ │ -39434   UID Size            04 (4)
│ │ │ │ -39435   UID                 00000000 (0)
│ │ │ │ -39439   GID Size            04 (4)
│ │ │ │ -3943A   GID                 00000000 (0)
│ │ │ │ -3943E PAYLOAD
│ │ │ │ -
│ │ │ │ -3A387 LOCAL HEADER #32      04034B50 (67324752)
│ │ │ │ -3A38B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3A38C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3A38D General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3A38F Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3A391 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -3A395 CRC                   262FB9B0 (640661936)
│ │ │ │ -3A399 Compressed Size       0000066A (1642)
│ │ │ │ -3A39D Uncompressed Size     000018DF (6367)
│ │ │ │ -3A3A1 Filename Length       000F (15)
│ │ │ │ -3A3A3 Extra Length          001C (28)
│ │ │ │ -3A3A5 Filename              'XXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3A3A5: Filename 'XXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3A3B4 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3A3B6   Length              0009 (9)
│ │ │ │ -3A3B8   Flags               03 (3) 'Modification Access'
│ │ │ │ -3A3B9   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3A3BD   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3A3C1 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3A3C3   Length              000B (11)
│ │ │ │ -3A3C5   Version             01 (1)
│ │ │ │ -3A3C6   UID Size            04 (4)
│ │ │ │ -3A3C7   UID                 00000000 (0)
│ │ │ │ -3A3CB   GID Size            04 (4)
│ │ │ │ -3A3CC   GID                 00000000 (0)
│ │ │ │ -3A3D0 PAYLOAD
│ │ │ │ -
│ │ │ │ -3AA3A LOCAL HEADER #33      04034B50 (67324752)
│ │ │ │ -3AA3E Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3AA3F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3AA40 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3AA42 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3AA44 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -3AA48 CRC                   753BC529 (1966851369)
│ │ │ │ -3AA4C Compressed Size       00001A4B (6731)
│ │ │ │ -3AA50 Uncompressed Size     000064F2 (25842)
│ │ │ │ -3AA54 Filename Length       0013 (19)
│ │ │ │ -3AA56 Extra Length          001C (28)
│ │ │ │ -3AA58 Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3AA58: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3AA6B Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3AA6D   Length              0009 (9)
│ │ │ │ -3AA6F   Flags               03 (3) 'Modification Access'
│ │ │ │ -3AA70   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3AA74   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3AA78 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3AA7A   Length              000B (11)
│ │ │ │ -3AA7C   Version             01 (1)
│ │ │ │ -3AA7D   UID Size            04 (4)
│ │ │ │ -3AA7E   UID                 00000000 (0)
│ │ │ │ -3AA82   GID Size            04 (4)
│ │ │ │ -3AA83   GID                 00000000 (0)
│ │ │ │ -3AA87 PAYLOAD
│ │ │ │ -
│ │ │ │ -3C4D2 LOCAL HEADER #34      04034B50 (67324752)
│ │ │ │ -3C4D6 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3C4D7 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3C4D8 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3C4DA Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3C4DC Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -3C4E0 CRC                   936899C3 (2473105859)
│ │ │ │ -3C4E4 Compressed Size       000009A6 (2470)
│ │ │ │ -3C4E8 Uncompressed Size     00001B64 (7012)
│ │ │ │ -3C4EC Filename Length       0010 (16)
│ │ │ │ -3C4EE Extra Length          001C (28)
│ │ │ │ -3C4F0 Filename              'XXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3C4F0: Filename 'XXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3C500 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3C502   Length              0009 (9)
│ │ │ │ -3C504   Flags               03 (3) 'Modification Access'
│ │ │ │ -3C505   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3C509   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3C50D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3C50F   Length              000B (11)
│ │ │ │ -3C511   Version             01 (1)
│ │ │ │ -3C512   UID Size            04 (4)
│ │ │ │ -3C513   UID                 00000000 (0)
│ │ │ │ -3C517   GID Size            04 (4)
│ │ │ │ -3C518   GID                 00000000 (0)
│ │ │ │ -3C51C PAYLOAD
│ │ │ │ -
│ │ │ │ -3CEC2 LOCAL HEADER #35      04034B50 (67324752)
│ │ │ │ -3CEC6 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3CEC7 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3CEC8 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3CECA Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3CECC Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -3CED0 CRC                   E9E04E21 (3923791393)
│ │ │ │ -3CED4 Compressed Size       000006B7 (1719)
│ │ │ │ -3CED8 Uncompressed Size     00001565 (5477)
│ │ │ │ -3CEDC Filename Length       0012 (18)
│ │ │ │ -3CEDE Extra Length          001C (28)
│ │ │ │ -3CEE0 Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3CEE0: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3CEF2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3CEF4   Length              0009 (9)
│ │ │ │ -3CEF6   Flags               03 (3) 'Modification Access'
│ │ │ │ -3CEF7   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3CEFB   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3CEFF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3CF01   Length              000B (11)
│ │ │ │ -3CF03   Version             01 (1)
│ │ │ │ -3CF04   UID Size            04 (4)
│ │ │ │ -3CF05   UID                 00000000 (0)
│ │ │ │ -3CF09   GID Size            04 (4)
│ │ │ │ -3CF0A   GID                 00000000 (0)
│ │ │ │ -3CF0E PAYLOAD
│ │ │ │ -
│ │ │ │ -3D5C5 LOCAL HEADER #36      04034B50 (67324752)
│ │ │ │ -3D5C9 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3D5CA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3D5CB General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3D5CD Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3D5CF Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -3D5D3 CRC                   97DFF56C (2548036972)
│ │ │ │ -3D5D7 Compressed Size       00002A16 (10774)
│ │ │ │ -3D5DB Uncompressed Size     0000B1C5 (45509)
│ │ │ │ -3D5DF Filename Length       0010 (16)
│ │ │ │ -3D5E1 Extra Length          001C (28)
│ │ │ │ -3D5E3 Filename              'XXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3D5E3: Filename 'XXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3D5F3 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3D5F5   Length              0009 (9)
│ │ │ │ -3D5F7   Flags               03 (3) 'Modification Access'
│ │ │ │ -3D5F8   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3D5FC   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -3D600 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3D602   Length              000B (11)
│ │ │ │ -3D604   Version             01 (1)
│ │ │ │ -3D605   UID Size            04 (4)
│ │ │ │ -3D606   UID                 00000000 (0)
│ │ │ │ -3D60A   GID Size            04 (4)
│ │ │ │ -3D60B   GID                 00000000 (0)
│ │ │ │ -3D60F PAYLOAD
│ │ │ │ -
│ │ │ │ -40025 LOCAL HEADER #37      04034B50 (67324752)
│ │ │ │ -40029 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4002A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4002B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4002D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4002F Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -40033 CRC                   62EDD7EF (1659754479)
│ │ │ │ -40037 Compressed Size       00001E82 (7810)
│ │ │ │ -4003B Uncompressed Size     00009AAA (39594)
│ │ │ │ -4003F Filename Length       0012 (18)
│ │ │ │ -40041 Extra Length          001C (28)
│ │ │ │ -40043 Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x40043: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -40055 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -40057   Length              0009 (9)
│ │ │ │ -40059   Flags               03 (3) 'Modification Access'
│ │ │ │ -4005A   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -4005E   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -40062 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -40064   Length              000B (11)
│ │ │ │ -40066   Version             01 (1)
│ │ │ │ -40067   UID Size            04 (4)
│ │ │ │ -40068   UID                 00000000 (0)
│ │ │ │ -4006C   GID Size            04 (4)
│ │ │ │ -4006D   GID                 00000000 (0)
│ │ │ │ -40071 PAYLOAD
│ │ │ │ -
│ │ │ │ -41EF3 LOCAL HEADER #38      04034B50 (67324752)
│ │ │ │ -41EF7 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -41EF8 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -41EF9 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -41EFB Compression Method    0008 (8) 'Deflated'
│ │ │ │ -41EFD Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -41F01 CRC                   9414FC7D (2484403325)
│ │ │ │ -41F05 Compressed Size       00001477 (5239)
│ │ │ │ -41F09 Uncompressed Size     00007ACF (31439)
│ │ │ │ -41F0D Filename Length       0018 (24)
│ │ │ │ -41F0F Extra Length          001C (28)
│ │ │ │ -41F11 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x41F11: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -41F29 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -41F2B   Length              0009 (9)
│ │ │ │ -41F2D   Flags               03 (3) 'Modification Access'
│ │ │ │ -41F2E   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -41F32   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -41F36 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -41F38   Length              000B (11)
│ │ │ │ -41F3A   Version             01 (1)
│ │ │ │ -41F3B   UID Size            04 (4)
│ │ │ │ -41F3C   UID                 00000000 (0)
│ │ │ │ -41F40   GID Size            04 (4)
│ │ │ │ -41F41   GID                 00000000 (0)
│ │ │ │ -41F45 PAYLOAD
│ │ │ │ -
│ │ │ │ -433BC LOCAL HEADER #39      04034B50 (67324752)
│ │ │ │ -433C0 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -433C1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -433C2 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -433C4 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -433C6 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -433CA CRC                   0C216798 (203515800)
│ │ │ │ -433CE Compressed Size       000018D1 (6353)
│ │ │ │ -433D2 Uncompressed Size     0000A7F4 (42996)
│ │ │ │ -433D6 Filename Length       001F (31)
│ │ │ │ -433D8 Extra Length          001C (28)
│ │ │ │ -433DA Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x433DA: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -433F9 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -433FB   Length              0009 (9)
│ │ │ │ -433FD   Flags               03 (3) 'Modification Access'
│ │ │ │ -433FE   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -43402   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -43406 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -43408   Length              000B (11)
│ │ │ │ -4340A   Version             01 (1)
│ │ │ │ -4340B   UID Size            04 (4)
│ │ │ │ -4340C   UID                 00000000 (0)
│ │ │ │ -43410   GID Size            04 (4)
│ │ │ │ -43411   GID                 00000000 (0)
│ │ │ │ -43415 PAYLOAD
│ │ │ │ -
│ │ │ │ -44CE6 LOCAL HEADER #40      04034B50 (67324752)
│ │ │ │ -44CEA Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -44CEB Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -44CEC General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -44CEE Compression Method    0008 (8) 'Deflated'
│ │ │ │ -44CF0 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -44CF4 CRC                   D64849DE (3595061726)
│ │ │ │ -44CF8 Compressed Size       000003F7 (1015)
│ │ │ │ -44CFC Uncompressed Size     000008A3 (2211)
│ │ │ │ -44D00 Filename Length       001E (30)
│ │ │ │ -44D02 Extra Length          001C (28)
│ │ │ │ -44D04 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x44D04: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -44D22 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -44D24   Length              0009 (9)
│ │ │ │ -44D26   Flags               03 (3) 'Modification Access'
│ │ │ │ -44D27   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -44D2B   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -44D2F Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -44D31   Length              000B (11)
│ │ │ │ -44D33   Version             01 (1)
│ │ │ │ -44D34   UID Size            04 (4)
│ │ │ │ -44D35   UID                 00000000 (0)
│ │ │ │ -44D39   GID Size            04 (4)
│ │ │ │ -44D3A   GID                 00000000 (0)
│ │ │ │ -44D3E PAYLOAD
│ │ │ │ -
│ │ │ │ -45135 LOCAL HEADER #41      04034B50 (67324752)
│ │ │ │ -45139 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4513A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4513B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4513D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4513F Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -45143 CRC                   9488B892 (2491988114)
│ │ │ │ -45147 Compressed Size       00004293 (17043)
│ │ │ │ -4514B Uncompressed Size     0000D8DC (55516)
│ │ │ │ -4514F Filename Length       0013 (19)
│ │ │ │ -45151 Extra Length          001C (28)
│ │ │ │ -45153 Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x45153: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -45166 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -45168   Length              0009 (9)
│ │ │ │ -4516A   Flags               03 (3) 'Modification Access'
│ │ │ │ -4516B   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -4516F   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -45173 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -45175   Length              000B (11)
│ │ │ │ -45177   Version             01 (1)
│ │ │ │ -45178   UID Size            04 (4)
│ │ │ │ -45179   UID                 00000000 (0)
│ │ │ │ -4517D   GID Size            04 (4)
│ │ │ │ -4517E   GID                 00000000 (0)
│ │ │ │ -45182 PAYLOAD
│ │ │ │ -
│ │ │ │ -49415 LOCAL HEADER #42      04034B50 (67324752)
│ │ │ │ -49419 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4941A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4941B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4941D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4941F Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -49423 CRC                   D1484C40 (3511176256)
│ │ │ │ -49427 Compressed Size       000026C5 (9925)
│ │ │ │ -4942B Uncompressed Size     00006E45 (28229)
│ │ │ │ -4942F Filename Length       0019 (25)
│ │ │ │ -49431 Extra Length          001C (28)
│ │ │ │ -49433 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x49433: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -4944C Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -4944E   Length              0009 (9)
│ │ │ │ -49450   Flags               03 (3) 'Modification Access'
│ │ │ │ -49451   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -49455   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -49459 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -4945B   Length              000B (11)
│ │ │ │ -4945D   Version             01 (1)
│ │ │ │ -4945E   UID Size            04 (4)
│ │ │ │ -4945F   UID                 00000000 (0)
│ │ │ │ -49463   GID Size            04 (4)
│ │ │ │ -49464   GID                 00000000 (0)
│ │ │ │ -49468 PAYLOAD
│ │ │ │ -
│ │ │ │ -4BB2D LOCAL HEADER #43      04034B50 (67324752)
│ │ │ │ -4BB31 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4BB32 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4BB33 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4BB35 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4BB37 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -4BB3B CRC                   8F94BE1C (2408889884)
│ │ │ │ -4BB3F Compressed Size       00002739 (10041)
│ │ │ │ -4BB43 Uncompressed Size     00008B83 (35715)
│ │ │ │ -4BB47 Filename Length       0019 (25)
│ │ │ │ -4BB49 Extra Length          001C (28)
│ │ │ │ -4BB4B Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4BB4B: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -4BB64 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -4BB66   Length              0009 (9)
│ │ │ │ -4BB68   Flags               03 (3) 'Modification Access'
│ │ │ │ -4BB69   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -4BB6D   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -4BB71 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -4BB73   Length              000B (11)
│ │ │ │ -4BB75   Version             01 (1)
│ │ │ │ -4BB76   UID Size            04 (4)
│ │ │ │ -4BB77   UID                 00000000 (0)
│ │ │ │ -4BB7B   GID Size            04 (4)
│ │ │ │ -4BB7C   GID                 00000000 (0)
│ │ │ │ -4BB80 PAYLOAD
│ │ │ │ -
│ │ │ │ -4E2B9 LOCAL HEADER #44      04034B50 (67324752)
│ │ │ │ -4E2BD Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4E2BE Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4E2BF General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4E2C1 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4E2C3 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -4E2C7 CRC                   FA6C2ECC (4201393868)
│ │ │ │ -4E2CB Compressed Size       00000CF1 (3313)
│ │ │ │ -4E2CF Uncompressed Size     0000517A (20858)
│ │ │ │ -4E2D3 Filename Length       0021 (33)
│ │ │ │ -4E2D5 Extra Length          001C (28)
│ │ │ │ -4E2D7 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4E2D7: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -4E2F8 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -4E2FA   Length              0009 (9)
│ │ │ │ -4E2FC   Flags               03 (3) 'Modification Access'
│ │ │ │ -4E2FD   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -4E301   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -4E305 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -4E307   Length              000B (11)
│ │ │ │ -4E309   Version             01 (1)
│ │ │ │ -4E30A   UID Size            04 (4)
│ │ │ │ -4E30B   UID                 00000000 (0)
│ │ │ │ -4E30F   GID Size            04 (4)
│ │ │ │ -4E310   GID                 00000000 (0)
│ │ │ │ -4E314 PAYLOAD
│ │ │ │ -
│ │ │ │ -4F005 LOCAL HEADER #45      04034B50 (67324752)
│ │ │ │ -4F009 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4F00A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4F00B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4F00D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4F00F Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -4F013 CRC                   07042E48 (117714504)
│ │ │ │ -4F017 Compressed Size       00000468 (1128)
│ │ │ │ -4F01B Uncompressed Size     00000931 (2353)
│ │ │ │ -4F01F Filename Length       001B (27)
│ │ │ │ -4F021 Extra Length          001C (28)
│ │ │ │ -4F023 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4F023: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -4F03E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -4F040   Length              0009 (9)
│ │ │ │ -4F042   Flags               03 (3) 'Modification Access'
│ │ │ │ -4F043   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -4F047   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -4F04B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -4F04D   Length              000B (11)
│ │ │ │ -4F04F   Version             01 (1)
│ │ │ │ -4F050   UID Size            04 (4)
│ │ │ │ -4F051   UID                 00000000 (0)
│ │ │ │ -4F055   GID Size            04 (4)
│ │ │ │ -4F056   GID                 00000000 (0)
│ │ │ │ -4F05A PAYLOAD
│ │ │ │ -
│ │ │ │ -4F4C2 LOCAL HEADER #46      04034B50 (67324752)
│ │ │ │ -4F4C6 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4F4C7 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4F4C8 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4F4CA Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4F4CC Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -4F4D0 CRC                   5C46A04F (1548132431)
│ │ │ │ -4F4D4 Compressed Size       000016F2 (5874)
│ │ │ │ -4F4D8 Uncompressed Size     00007A6D (31341)
│ │ │ │ -4F4DC Filename Length       001F (31)
│ │ │ │ -4F4DE Extra Length          001C (28)
│ │ │ │ -4F4E0 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4F4E0: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -4F4FF Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -4F501   Length              0009 (9)
│ │ │ │ -4F503   Flags               03 (3) 'Modification Access'
│ │ │ │ -4F504   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -4F508   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -4F50C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -4F50E   Length              000B (11)
│ │ │ │ -4F510   Version             01 (1)
│ │ │ │ -4F511   UID Size            04 (4)
│ │ │ │ -4F512   UID                 00000000 (0)
│ │ │ │ -4F516   GID Size            04 (4)
│ │ │ │ -4F517   GID                 00000000 (0)
│ │ │ │ -4F51B PAYLOAD
│ │ │ │ -
│ │ │ │ -50C0D LOCAL HEADER #47      04034B50 (67324752)
│ │ │ │ -50C11 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -50C12 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -50C13 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -50C15 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -50C17 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -50C1B CRC                   5B663FF6 (1533427702)
│ │ │ │ -50C1F Compressed Size       00004170 (16752)
│ │ │ │ -50C23 Uncompressed Size     0001CF93 (118675)
│ │ │ │ -50C27 Filename Length       0010 (16)
│ │ │ │ -50C29 Extra Length          001C (28)
│ │ │ │ -50C2B Filename              'XXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x50C2B: Filename 'XXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -50C3B Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -50C3D   Length              0009 (9)
│ │ │ │ -50C3F   Flags               03 (3) 'Modification Access'
│ │ │ │ -50C40   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -50C44   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -50C48 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -50C4A   Length              000B (11)
│ │ │ │ -50C4C   Version             01 (1)
│ │ │ │ -50C4D   UID Size            04 (4)
│ │ │ │ -50C4E   UID                 00000000 (0)
│ │ │ │ -50C52   GID Size            04 (4)
│ │ │ │ -50C53   GID                 00000000 (0)
│ │ │ │ -50C57 PAYLOAD
│ │ │ │ -
│ │ │ │ -54DC7 LOCAL HEADER #48      04034B50 (67324752)
│ │ │ │ -54DCB Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -54DCC Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -54DCD General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -54DCF Compression Method    0008 (8) 'Deflated'
│ │ │ │ -54DD1 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -54DD5 CRC                   4474668F (1148479119)
│ │ │ │ -54DD9 Compressed Size       00000A94 (2708)
│ │ │ │ -54DDD Uncompressed Size     00002105 (8453)
│ │ │ │ -54DE1 Filename Length       0014 (20)
│ │ │ │ -54DE3 Extra Length          001C (28)
│ │ │ │ -54DE5 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x54DE5: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -54DF9 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -54DFB   Length              0009 (9)
│ │ │ │ -54DFD   Flags               03 (3) 'Modification Access'
│ │ │ │ -54DFE   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -54E02   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -54E06 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -54E08   Length              000B (11)
│ │ │ │ -54E0A   Version             01 (1)
│ │ │ │ -54E0B   UID Size            04 (4)
│ │ │ │ -54E0C   UID                 00000000 (0)
│ │ │ │ -54E10   GID Size            04 (4)
│ │ │ │ -54E11   GID                 00000000 (0)
│ │ │ │ -54E15 PAYLOAD
│ │ │ │ -
│ │ │ │ -558A9 LOCAL HEADER #49      04034B50 (67324752)
│ │ │ │ -558AD Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -558AE Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -558AF General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -558B1 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -558B3 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -558B7 CRC                   E750F924 (3880843556)
│ │ │ │ -558BB Compressed Size       0000AC97 (44183)
│ │ │ │ -558BF Uncompressed Size     0003E418 (255000)
│ │ │ │ -558C3 Filename Length       0017 (23)
│ │ │ │ -558C5 Extra Length          001C (28)
│ │ │ │ -558C7 Filename              'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x558C7: Filename 'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -558DE Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -558E0   Length              0009 (9)
│ │ │ │ -558E2   Flags               03 (3) 'Modification Access'
│ │ │ │ -558E3   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -558E7   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -558EB Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -558ED   Length              000B (11)
│ │ │ │ -558EF   Version             01 (1)
│ │ │ │ -558F0   UID Size            04 (4)
│ │ │ │ -558F1   UID                 00000000 (0)
│ │ │ │ -558F5   GID Size            04 (4)
│ │ │ │ -558F6   GID                 00000000 (0)
│ │ │ │ -558FA PAYLOAD
│ │ │ │ -
│ │ │ │ -60591 LOCAL HEADER #50      04034B50 (67324752)
│ │ │ │ -60595 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -60596 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -60597 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -60599 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6059B Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -6059F CRC                   1D15B8EB (487962859)
│ │ │ │ -605A3 Compressed Size       00000401 (1025)
│ │ │ │ -605A7 Uncompressed Size     0000093D (2365)
│ │ │ │ -605AB Filename Length       0013 (19)
│ │ │ │ -605AD Extra Length          001C (28)
│ │ │ │ -605AF Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x605AF: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -605C2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -605C4   Length              0009 (9)
│ │ │ │ -605C6   Flags               03 (3) 'Modification Access'
│ │ │ │ -605C7   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -605CB   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -605CF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -605D1   Length              000B (11)
│ │ │ │ -605D3   Version             01 (1)
│ │ │ │ -605D4   UID Size            04 (4)
│ │ │ │ -605D5   UID                 00000000 (0)
│ │ │ │ -605D9   GID Size            04 (4)
│ │ │ │ -605DA   GID                 00000000 (0)
│ │ │ │ -605DE PAYLOAD
│ │ │ │ -
│ │ │ │ -609DF LOCAL HEADER #51      04034B50 (67324752)
│ │ │ │ -609E3 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -609E4 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -609E5 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -609E7 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -609E9 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -609ED CRC                   7A12CC58 (2048052312)
│ │ │ │ -609F1 Compressed Size       000014E4 (5348)
│ │ │ │ -609F5 Uncompressed Size     0000687B (26747)
│ │ │ │ -609F9 Filename Length       0012 (18)
│ │ │ │ -609FB Extra Length          001C (28)
│ │ │ │ -609FD Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x609FD: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -60A0F Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -60A11   Length              0009 (9)
│ │ │ │ -60A13   Flags               03 (3) 'Modification Access'
│ │ │ │ -60A14   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -60A18   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -60A1C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -60A1E   Length              000B (11)
│ │ │ │ -60A20   Version             01 (1)
│ │ │ │ -60A21   UID Size            04 (4)
│ │ │ │ -60A22   UID                 00000000 (0)
│ │ │ │ -60A26   GID Size            04 (4)
│ │ │ │ -60A27   GID                 00000000 (0)
│ │ │ │ -60A2B PAYLOAD
│ │ │ │ -
│ │ │ │ -61F0F LOCAL HEADER #52      04034B50 (67324752)
│ │ │ │ -61F13 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -61F14 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -61F15 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -61F17 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -61F19 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -61F1D CRC                   80F035B2 (2163226034)
│ │ │ │ -61F21 Compressed Size       000011EC (4588)
│ │ │ │ -61F25 Uncompressed Size     000040F5 (16629)
│ │ │ │ -61F29 Filename Length       0012 (18)
│ │ │ │ -61F2B Extra Length          001C (28)
│ │ │ │ -61F2D Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x61F2D: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -61F3F Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -61F41   Length              0009 (9)
│ │ │ │ -61F43   Flags               03 (3) 'Modification Access'
│ │ │ │ -61F44   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -61F48   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -61F4C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -61F4E   Length              000B (11)
│ │ │ │ -61F50   Version             01 (1)
│ │ │ │ -61F51   UID Size            04 (4)
│ │ │ │ -61F52   UID                 00000000 (0)
│ │ │ │ -61F56   GID Size            04 (4)
│ │ │ │ -61F57   GID                 00000000 (0)
│ │ │ │ -61F5B PAYLOAD
│ │ │ │ -
│ │ │ │ -63147 LOCAL HEADER #53      04034B50 (67324752)
│ │ │ │ -6314B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6314C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6314D General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6314F Compression Method    0008 (8) 'Deflated'
│ │ │ │ -63151 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -63155 CRC                   F8DD639B (4175258523)
│ │ │ │ -63159 Compressed Size       000009D9 (2521)
│ │ │ │ -6315D Uncompressed Size     00003529 (13609)
│ │ │ │ -63161 Filename Length       0019 (25)
│ │ │ │ -63163 Extra Length          001C (28)
│ │ │ │ -63165 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x63165: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6317E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -63180   Length              0009 (9)
│ │ │ │ -63182   Flags               03 (3) 'Modification Access'
│ │ │ │ -63183   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -63187   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6318B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6318D   Length              000B (11)
│ │ │ │ -6318F   Version             01 (1)
│ │ │ │ -63190   UID Size            04 (4)
│ │ │ │ -63191   UID                 00000000 (0)
│ │ │ │ -63195   GID Size            04 (4)
│ │ │ │ -63196   GID                 00000000 (0)
│ │ │ │ -6319A PAYLOAD
│ │ │ │ -
│ │ │ │ -63B73 LOCAL HEADER #54      04034B50 (67324752)
│ │ │ │ -63B77 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -63B78 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -63B79 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -63B7B Compression Method    0008 (8) 'Deflated'
│ │ │ │ -63B7D Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -63B81 CRC                   A1689AA9 (2707987113)
│ │ │ │ -63B85 Compressed Size       000018B4 (6324)
│ │ │ │ -63B89 Uncompressed Size     0000A605 (42501)
│ │ │ │ -63B8D Filename Length       0019 (25)
│ │ │ │ -63B8F Extra Length          001C (28)
│ │ │ │ -63B91 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x63B91: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -63BAA Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -63BAC   Length              0009 (9)
│ │ │ │ -63BAE   Flags               03 (3) 'Modification Access'
│ │ │ │ -63BAF   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -63BB3   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -63BB7 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -63BB9   Length              000B (11)
│ │ │ │ -63BBB   Version             01 (1)
│ │ │ │ -63BBC   UID Size            04 (4)
│ │ │ │ -63BBD   UID                 00000000 (0)
│ │ │ │ -63BC1   GID Size            04 (4)
│ │ │ │ -63BC2   GID                 00000000 (0)
│ │ │ │ -63BC6 PAYLOAD
│ │ │ │ -
│ │ │ │ -6547A LOCAL HEADER #55      04034B50 (67324752)
│ │ │ │ -6547E Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6547F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -65480 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -65482 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -65484 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -65488 CRC                   16F6295E (385231198)
│ │ │ │ -6548C Compressed Size       0000177D (6013)
│ │ │ │ -65490 Uncompressed Size     0000472C (18220)
│ │ │ │ -65494 Filename Length       0014 (20)
│ │ │ │ -65496 Extra Length          001C (28)
│ │ │ │ -65498 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x65498: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -654AC Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -654AE   Length              0009 (9)
│ │ │ │ -654B0   Flags               03 (3) 'Modification Access'
│ │ │ │ -654B1   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -654B5   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -654B9 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -654BB   Length              000B (11)
│ │ │ │ -654BD   Version             01 (1)
│ │ │ │ -654BE   UID Size            04 (4)
│ │ │ │ -654BF   UID                 00000000 (0)
│ │ │ │ -654C3   GID Size            04 (4)
│ │ │ │ -654C4   GID                 00000000 (0)
│ │ │ │ -654C8 PAYLOAD
│ │ │ │ -
│ │ │ │ -66C45 LOCAL HEADER #56      04034B50 (67324752)
│ │ │ │ -66C49 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -66C4A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -66C4B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -66C4D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -66C4F Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -66C53 CRC                   E49D33FF (3835507711)
│ │ │ │ -66C57 Compressed Size       0000040A (1034)
│ │ │ │ -66C5B Uncompressed Size     00000825 (2085)
│ │ │ │ -66C5F Filename Length       001C (28)
│ │ │ │ -66C61 Extra Length          001C (28)
│ │ │ │ -66C63 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x66C63: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -66C7F Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -66C81   Length              0009 (9)
│ │ │ │ -66C83   Flags               03 (3) 'Modification Access'
│ │ │ │ -66C84   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -66C88   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -66C8C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -66C8E   Length              000B (11)
│ │ │ │ -66C90   Version             01 (1)
│ │ │ │ -66C91   UID Size            04 (4)
│ │ │ │ -66C92   UID                 00000000 (0)
│ │ │ │ -66C96   GID Size            04 (4)
│ │ │ │ -66C97   GID                 00000000 (0)
│ │ │ │ -66C9B PAYLOAD
│ │ │ │ -
│ │ │ │ -670A5 LOCAL HEADER #57      04034B50 (67324752)
│ │ │ │ -670A9 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -670AA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -670AB General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -670AD Compression Method    0008 (8) 'Deflated'
│ │ │ │ -670AF Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -670B3 CRC                   280BFB81 (671873921)
│ │ │ │ -670B7 Compressed Size       00002483 (9347)
│ │ │ │ -670BB Uncompressed Size     0000B56F (46447)
│ │ │ │ -670BF Filename Length       001F (31)
│ │ │ │ -670C1 Extra Length          001C (28)
│ │ │ │ -670C3 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x670C3: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -670E2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -670E4   Length              0009 (9)
│ │ │ │ -670E6   Flags               03 (3) 'Modification Access'
│ │ │ │ -670E7   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -670EB   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -670EF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -670F1   Length              000B (11)
│ │ │ │ -670F3   Version             01 (1)
│ │ │ │ -670F4   UID Size            04 (4)
│ │ │ │ -670F5   UID                 00000000 (0)
│ │ │ │ -670F9   GID Size            04 (4)
│ │ │ │ -670FA   GID                 00000000 (0)
│ │ │ │ -670FE PAYLOAD
│ │ │ │ -
│ │ │ │ -69581 LOCAL HEADER #58      04034B50 (67324752)
│ │ │ │ -69585 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -69586 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -69587 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -69589 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6958B Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -6958F CRC                   CCAE3E9A (3433971354)
│ │ │ │ -69593 Compressed Size       00000E7F (3711)
│ │ │ │ -69597 Uncompressed Size     000052D9 (21209)
│ │ │ │ -6959B Filename Length       001F (31)
│ │ │ │ -6959D Extra Length          001C (28)
│ │ │ │ -6959F Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6959F: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -695BE Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -695C0   Length              0009 (9)
│ │ │ │ -695C2   Flags               03 (3) 'Modification Access'
│ │ │ │ -695C3   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -695C7   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -695CB Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -695CD   Length              000B (11)
│ │ │ │ -695CF   Version             01 (1)
│ │ │ │ -695D0   UID Size            04 (4)
│ │ │ │ -695D1   UID                 00000000 (0)
│ │ │ │ -695D5   GID Size            04 (4)
│ │ │ │ -695D6   GID                 00000000 (0)
│ │ │ │ -695DA PAYLOAD
│ │ │ │ -
│ │ │ │ -6A459 LOCAL HEADER #59      04034B50 (67324752)
│ │ │ │ -6A45D Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6A45E Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6A45F General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6A461 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6A463 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -6A467 CRC                   26C2BC4D (650296397)
│ │ │ │ -6A46B Compressed Size       00000A44 (2628)
│ │ │ │ -6A46F Uncompressed Size     0000247A (9338)
│ │ │ │ -6A473 Filename Length       0013 (19)
│ │ │ │ -6A475 Extra Length          001C (28)
│ │ │ │ -6A477 Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6A477: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6A48A Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -6A48C   Length              0009 (9)
│ │ │ │ -6A48E   Flags               03 (3) 'Modification Access'
│ │ │ │ -6A48F   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6A493   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6A497 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6A499   Length              000B (11)
│ │ │ │ -6A49B   Version             01 (1)
│ │ │ │ -6A49C   UID Size            04 (4)
│ │ │ │ -6A49D   UID                 00000000 (0)
│ │ │ │ -6A4A1   GID Size            04 (4)
│ │ │ │ -6A4A2   GID                 00000000 (0)
│ │ │ │ -6A4A6 PAYLOAD
│ │ │ │ -
│ │ │ │ -6AEEA LOCAL HEADER #60      04034B50 (67324752)
│ │ │ │ -6AEEE Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6AEEF Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6AEF0 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6AEF2 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6AEF4 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -6AEF8 CRC                   E0E40597 (3773040023)
│ │ │ │ -6AEFC Compressed Size       00002488 (9352)
│ │ │ │ -6AF00 Uncompressed Size     0000B84C (47180)
│ │ │ │ -6AF04 Filename Length       0019 (25)
│ │ │ │ -6AF06 Extra Length          001C (28)
│ │ │ │ -6AF08 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6AF08: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6AF21 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -6AF23   Length              0009 (9)
│ │ │ │ -6AF25   Flags               03 (3) 'Modification Access'
│ │ │ │ -6AF26   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6AF2A   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6AF2E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6AF30   Length              000B (11)
│ │ │ │ -6AF32   Version             01 (1)
│ │ │ │ -6AF33   UID Size            04 (4)
│ │ │ │ -6AF34   UID                 00000000 (0)
│ │ │ │ -6AF38   GID Size            04 (4)
│ │ │ │ -6AF39   GID                 00000000 (0)
│ │ │ │ -6AF3D PAYLOAD
│ │ │ │ -
│ │ │ │ -6D3C5 LOCAL HEADER #61      04034B50 (67324752)
│ │ │ │ -6D3C9 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6D3CA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6D3CB General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6D3CD Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6D3CF Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -6D3D3 CRC                   19609D49 (425762121)
│ │ │ │ -6D3D7 Compressed Size       00000EF8 (3832)
│ │ │ │ -6D3DB Uncompressed Size     00003A2C (14892)
│ │ │ │ -6D3DF Filename Length       0024 (36)
│ │ │ │ -6D3E1 Extra Length          001C (28)
│ │ │ │ -6D3E3 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6D3E3: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6D407 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -6D409   Length              0009 (9)
│ │ │ │ -6D40B   Flags               03 (3) 'Modification Access'
│ │ │ │ -6D40C   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6D410   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6D414 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6D416   Length              000B (11)
│ │ │ │ -6D418   Version             01 (1)
│ │ │ │ -6D419   UID Size            04 (4)
│ │ │ │ -6D41A   UID                 00000000 (0)
│ │ │ │ -6D41E   GID Size            04 (4)
│ │ │ │ -6D41F   GID                 00000000 (0)
│ │ │ │ -6D423 PAYLOAD
│ │ │ │ -
│ │ │ │ -6E31B LOCAL HEADER #62      04034B50 (67324752)
│ │ │ │ -6E31F Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6E320 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6E321 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6E323 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6E325 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -6E329 CRC                   0FBF3481 (264189057)
│ │ │ │ -6E32D Compressed Size       00001AC1 (6849)
│ │ │ │ -6E331 Uncompressed Size     00005EDC (24284)
│ │ │ │ -6E335 Filename Length       0017 (23)
│ │ │ │ -6E337 Extra Length          001C (28)
│ │ │ │ -6E339 Filename              'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6E339: Filename 'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6E350 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -6E352   Length              0009 (9)
│ │ │ │ -6E354   Flags               03 (3) 'Modification Access'
│ │ │ │ -6E355   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6E359   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6E35D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6E35F   Length              000B (11)
│ │ │ │ -6E361   Version             01 (1)
│ │ │ │ -6E362   UID Size            04 (4)
│ │ │ │ -6E363   UID                 00000000 (0)
│ │ │ │ -6E367   GID Size            04 (4)
│ │ │ │ -6E368   GID                 00000000 (0)
│ │ │ │ -6E36C PAYLOAD
│ │ │ │ -
│ │ │ │ -6FE2D LOCAL HEADER #63      04034B50 (67324752)
│ │ │ │ -6FE31 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6FE32 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6FE33 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6FE35 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6FE37 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -6FE3B CRC                   11E32AF1 (300100337)
│ │ │ │ -6FE3F Compressed Size       00000ED3 (3795)
│ │ │ │ -6FE43 Uncompressed Size     000038E2 (14562)
│ │ │ │ -6FE47 Filename Length       0023 (35)
│ │ │ │ -6FE49 Extra Length          001C (28)
│ │ │ │ -6FE4B Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6FE4B: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6FE6E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -6FE70   Length              0009 (9)
│ │ │ │ -6FE72   Flags               03 (3) 'Modification Access'
│ │ │ │ -6FE73   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6FE77   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -6FE7B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6FE7D   Length              000B (11)
│ │ │ │ -6FE7F   Version             01 (1)
│ │ │ │ -6FE80   UID Size            04 (4)
│ │ │ │ -6FE81   UID                 00000000 (0)
│ │ │ │ -6FE85   GID Size            04 (4)
│ │ │ │ -6FE86   GID                 00000000 (0)
│ │ │ │ -6FE8A PAYLOAD
│ │ │ │ -
│ │ │ │ -70D5D LOCAL HEADER #64      04034B50 (67324752)
│ │ │ │ -70D61 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -70D62 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -70D63 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -70D65 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -70D67 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -70D6B CRC                   2DB7929F (767005343)
│ │ │ │ -70D6F Compressed Size       00000113 (275)
│ │ │ │ -70D73 Uncompressed Size     000001F3 (499)
│ │ │ │ -70D77 Filename Length       001B (27)
│ │ │ │ -70D79 Extra Length          001C (28)
│ │ │ │ -70D7B Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x70D7B: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -70D96 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -70D98   Length              0009 (9)
│ │ │ │ -70D9A   Flags               03 (3) 'Modification Access'
│ │ │ │ -70D9B   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -70D9F   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -70DA3 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -70DA5   Length              000B (11)
│ │ │ │ -70DA7   Version             01 (1)
│ │ │ │ -70DA8   UID Size            04 (4)
│ │ │ │ -70DA9   UID                 00000000 (0)
│ │ │ │ -70DAD   GID Size            04 (4)
│ │ │ │ -70DAE   GID                 00000000 (0)
│ │ │ │ -70DB2 PAYLOAD
│ │ │ │ -
│ │ │ │ -70EC5 LOCAL HEADER #65      04034B50 (67324752)
│ │ │ │ -70EC9 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -70ECA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -70ECB General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -70ECD Compression Method    0008 (8) 'Deflated'
│ │ │ │ -70ECF Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -70ED3 CRC                   CE2A6869 (3458885737)
│ │ │ │ -70ED7 Compressed Size       0000188F (6287)
│ │ │ │ -70EDB Uncompressed Size     00008FAC (36780)
│ │ │ │ -70EDF Filename Length       001D (29)
│ │ │ │ -70EE1 Extra Length          001C (28)
│ │ │ │ -70EE3 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x70EE3: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -70F00 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -70F02   Length              0009 (9)
│ │ │ │ -70F04   Flags               03 (3) 'Modification Access'
│ │ │ │ -70F05   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -70F09   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -70F0D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -70F0F   Length              000B (11)
│ │ │ │ -70F11   Version             01 (1)
│ │ │ │ -70F12   UID Size            04 (4)
│ │ │ │ -70F13   UID                 00000000 (0)
│ │ │ │ -70F17   GID Size            04 (4)
│ │ │ │ -70F18   GID                 00000000 (0)
│ │ │ │ -70F1C PAYLOAD
│ │ │ │ -
│ │ │ │ -727AB LOCAL HEADER #66      04034B50 (67324752)
│ │ │ │ -727AF Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -727B0 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -727B1 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -727B3 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -727B5 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -727B9 CRC                   835FA0AD (2204082349)
│ │ │ │ -727BD Compressed Size       0000164C (5708)
│ │ │ │ -727C1 Uncompressed Size     00003A9B (15003)
│ │ │ │ -727C5 Filename Length       0015 (21)
│ │ │ │ -727C7 Extra Length          001C (28)
│ │ │ │ -727C9 Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x727C9: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -727DE Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -727E0   Length              0009 (9)
│ │ │ │ -727E2   Flags               03 (3) 'Modification Access'
│ │ │ │ -727E3   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -727E7   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -727EB Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -727ED   Length              000B (11)
│ │ │ │ -727EF   Version             01 (1)
│ │ │ │ -727F0   UID Size            04 (4)
│ │ │ │ -727F1   UID                 00000000 (0)
│ │ │ │ -727F5   GID Size            04 (4)
│ │ │ │ -727F6   GID                 00000000 (0)
│ │ │ │ -727FA PAYLOAD
│ │ │ │ -
│ │ │ │ -73E46 LOCAL HEADER #67      04034B50 (67324752)
│ │ │ │ -73E4A Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -73E4B Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -73E4C General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -73E4E Compression Method    0008 (8) 'Deflated'
│ │ │ │ -73E50 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -73E54 CRC                   CC48B127 (3427316007)
│ │ │ │ -73E58 Compressed Size       00003B4B (15179)
│ │ │ │ -73E5C Uncompressed Size     0001185B (71771)
│ │ │ │ -73E60 Filename Length       0016 (22)
│ │ │ │ -73E62 Extra Length          001C (28)
│ │ │ │ -73E64 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x73E64: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -73E7A Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -73E7C   Length              0009 (9)
│ │ │ │ -73E7E   Flags               03 (3) 'Modification Access'
│ │ │ │ -73E7F   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -73E83   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -73E87 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -73E89   Length              000B (11)
│ │ │ │ -73E8B   Version             01 (1)
│ │ │ │ -73E8C   UID Size            04 (4)
│ │ │ │ -73E8D   UID                 00000000 (0)
│ │ │ │ -73E91   GID Size            04 (4)
│ │ │ │ -73E92   GID                 00000000 (0)
│ │ │ │ -73E96 PAYLOAD
│ │ │ │ -
│ │ │ │ -779E1 LOCAL HEADER #68      04034B50 (67324752)
│ │ │ │ -779E5 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -779E6 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -779E7 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -779E9 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -779EB Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -779EF CRC                   6B03DA8B (1795414667)
│ │ │ │ -779F3 Compressed Size       00003E86 (16006)
│ │ │ │ -779F7 Uncompressed Size     0001C17B (115067)
│ │ │ │ -779FB Filename Length       0019 (25)
│ │ │ │ -779FD Extra Length          001C (28)
│ │ │ │ -779FF Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x779FF: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -77A18 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -77A1A   Length              0009 (9)
│ │ │ │ -77A1C   Flags               03 (3) 'Modification Access'
│ │ │ │ -77A1D   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -77A21   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -77A25 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -77A27   Length              000B (11)
│ │ │ │ -77A29   Version             01 (1)
│ │ │ │ -77A2A   UID Size            04 (4)
│ │ │ │ -77A2B   UID                 00000000 (0)
│ │ │ │ -77A2F   GID Size            04 (4)
│ │ │ │ -77A30   GID                 00000000 (0)
│ │ │ │ -77A34 PAYLOAD
│ │ │ │ -
│ │ │ │ -7B8BA LOCAL HEADER #69      04034B50 (67324752)
│ │ │ │ -7B8BE Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -7B8BF Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -7B8C0 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -7B8C2 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -7B8C4 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -7B8C8 CRC                   F547F549 (4115133769)
│ │ │ │ -7B8CC Compressed Size       00000833 (2099)
│ │ │ │ -7B8D0 Uncompressed Size     00003383 (13187)
│ │ │ │ -7B8D4 Filename Length       0011 (17)
│ │ │ │ -7B8D6 Extra Length          001C (28)
│ │ │ │ -7B8D8 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x7B8D8: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -7B8E9 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -7B8EB   Length              0009 (9)
│ │ │ │ -7B8ED   Flags               03 (3) 'Modification Access'
│ │ │ │ -7B8EE   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -7B8F2   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -7B8F6 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -7B8F8   Length              000B (11)
│ │ │ │ -7B8FA   Version             01 (1)
│ │ │ │ -7B8FB   UID Size            04 (4)
│ │ │ │ -7B8FC   UID                 00000000 (0)
│ │ │ │ -7B900   GID Size            04 (4)
│ │ │ │ -7B901   GID                 00000000 (0)
│ │ │ │ -7B905 PAYLOAD
│ │ │ │ -
│ │ │ │ -7C138 LOCAL HEADER #70      04034B50 (67324752)
│ │ │ │ -7C13C Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -7C13D Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -7C13E General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -7C140 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -7C142 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -7C146 CRC                   8FB16754 (2410768212)
│ │ │ │ -7C14A Compressed Size       0000518E (20878)
│ │ │ │ -7C14E Uncompressed Size     0001FB6C (129900)
│ │ │ │ -7C152 Filename Length       0015 (21)
│ │ │ │ -7C154 Extra Length          001C (28)
│ │ │ │ -7C156 Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x7C156: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -7C16B Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -7C16D   Length              0009 (9)
│ │ │ │ -7C16F   Flags               03 (3) 'Modification Access'
│ │ │ │ -7C170   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -7C174   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -7C178 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -7C17A   Length              000B (11)
│ │ │ │ -7C17C   Version             01 (1)
│ │ │ │ -7C17D   UID Size            04 (4)
│ │ │ │ -7C17E   UID                 00000000 (0)
│ │ │ │ -7C182   GID Size            04 (4)
│ │ │ │ -7C183   GID                 00000000 (0)
│ │ │ │ -7C187 PAYLOAD
│ │ │ │ -
│ │ │ │ -81315 LOCAL HEADER #71      04034B50 (67324752)
│ │ │ │ -81319 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8131A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8131B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8131D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8131F Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -81323 CRC                   E5A05A87 (3852491399)
│ │ │ │ -81327 Compressed Size       00001B07 (6919)
│ │ │ │ -8132B Uncompressed Size     000081CF (33231)
│ │ │ │ -8132F Filename Length       0019 (25)
│ │ │ │ -81331 Extra Length          001C (28)
│ │ │ │ -81333 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x81333: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -8134C Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -8134E   Length              0009 (9)
│ │ │ │ -81350   Flags               03 (3) 'Modification Access'
│ │ │ │ -81351   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -81355   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -81359 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -8135B   Length              000B (11)
│ │ │ │ -8135D   Version             01 (1)
│ │ │ │ -8135E   UID Size            04 (4)
│ │ │ │ -8135F   UID                 00000000 (0)
│ │ │ │ -81363   GID Size            04 (4)
│ │ │ │ -81364   GID                 00000000 (0)
│ │ │ │ -81368 PAYLOAD
│ │ │ │ -
│ │ │ │ -82E6F LOCAL HEADER #72      04034B50 (67324752)
│ │ │ │ -82E73 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -82E74 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -82E75 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -82E77 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -82E79 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -82E7D CRC                   3F4E6540 (1062102336)
│ │ │ │ -82E81 Compressed Size       00000D96 (3478)
│ │ │ │ -82E85 Uncompressed Size     00002E9F (11935)
│ │ │ │ -82E89 Filename Length       0018 (24)
│ │ │ │ -82E8B Extra Length          001C (28)
│ │ │ │ -82E8D Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x82E8D: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -82EA5 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -82EA7   Length              0009 (9)
│ │ │ │ -82EA9   Flags               03 (3) 'Modification Access'
│ │ │ │ -82EAA   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -82EAE   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -82EB2 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -82EB4   Length              000B (11)
│ │ │ │ -82EB6   Version             01 (1)
│ │ │ │ -82EB7   UID Size            04 (4)
│ │ │ │ -82EB8   UID                 00000000 (0)
│ │ │ │ -82EBC   GID Size            04 (4)
│ │ │ │ -82EBD   GID                 00000000 (0)
│ │ │ │ -82EC1 PAYLOAD
│ │ │ │ -
│ │ │ │ -83C57 LOCAL HEADER #73      04034B50 (67324752)
│ │ │ │ -83C5B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -83C5C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -83C5D General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -83C5F Compression Method    0008 (8) 'Deflated'
│ │ │ │ -83C61 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -83C65 CRC                   B52BB549 (3039540553)
│ │ │ │ -83C69 Compressed Size       000001E0 (480)
│ │ │ │ -83C6D Uncompressed Size     00000323 (803)
│ │ │ │ -83C71 Filename Length       0011 (17)
│ │ │ │ -83C73 Extra Length          001C (28)
│ │ │ │ -83C75 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x83C75: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -83C86 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -83C88   Length              0009 (9)
│ │ │ │ -83C8A   Flags               03 (3) 'Modification Access'
│ │ │ │ -83C8B   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -83C8F   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -83C93 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -83C95   Length              000B (11)
│ │ │ │ -83C97   Version             01 (1)
│ │ │ │ -83C98   UID Size            04 (4)
│ │ │ │ -83C99   UID                 00000000 (0)
│ │ │ │ -83C9D   GID Size            04 (4)
│ │ │ │ -83C9E   GID                 00000000 (0)
│ │ │ │ -83CA2 PAYLOAD
│ │ │ │ -
│ │ │ │ -83E82 LOCAL HEADER #74      04034B50 (67324752)
│ │ │ │ -83E86 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -83E87 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -83E88 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -83E8A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -83E8C Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -83E90 CRC                   2404DB02 (604297986)
│ │ │ │ -83E94 Compressed Size       000006C2 (1730)
│ │ │ │ -83E98 Uncompressed Size     00001439 (5177)
│ │ │ │ -83E9C Filename Length       0019 (25)
│ │ │ │ -83E9E Extra Length          001C (28)
│ │ │ │ -83EA0 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x83EA0: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -83EB9 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -83EBB   Length              0009 (9)
│ │ │ │ -83EBD   Flags               03 (3) 'Modification Access'
│ │ │ │ -83EBE   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -83EC2   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -83EC6 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -83EC8   Length              000B (11)
│ │ │ │ -83ECA   Version             01 (1)
│ │ │ │ -83ECB   UID Size            04 (4)
│ │ │ │ -83ECC   UID                 00000000 (0)
│ │ │ │ -83ED0   GID Size            04 (4)
│ │ │ │ -83ED1   GID                 00000000 (0)
│ │ │ │ -83ED5 PAYLOAD
│ │ │ │ -
│ │ │ │ -84597 LOCAL HEADER #75      04034B50 (67324752)
│ │ │ │ -8459B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8459C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8459D General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8459F Compression Method    0008 (8) 'Deflated'
│ │ │ │ -845A1 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -845A5 CRC                   53B37456 (1404269654)
│ │ │ │ -845A9 Compressed Size       00001B87 (7047)
│ │ │ │ -845AD Uncompressed Size     00009F03 (40707)
│ │ │ │ -845B1 Filename Length       0018 (24)
│ │ │ │ -845B3 Extra Length          001C (28)
│ │ │ │ -845B5 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x845B5: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -845CD Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -845CF   Length              0009 (9)
│ │ │ │ -845D1   Flags               03 (3) 'Modification Access'
│ │ │ │ -845D2   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -845D6   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -845DA Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -845DC   Length              000B (11)
│ │ │ │ -845DE   Version             01 (1)
│ │ │ │ -845DF   UID Size            04 (4)
│ │ │ │ -845E0   UID                 00000000 (0)
│ │ │ │ -845E4   GID Size            04 (4)
│ │ │ │ -845E5   GID                 00000000 (0)
│ │ │ │ -845E9 PAYLOAD
│ │ │ │ -
│ │ │ │ -86170 LOCAL HEADER #76      04034B50 (67324752)
│ │ │ │ -86174 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -86175 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -86176 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -86178 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8617A Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -8617E CRC                   747C5D76 (1954307446)
│ │ │ │ -86182 Compressed Size       000016F7 (5879)
│ │ │ │ -86186 Uncompressed Size     00008AB6 (35510)
│ │ │ │ -8618A Filename Length       0012 (18)
│ │ │ │ -8618C Extra Length          001C (28)
│ │ │ │ -8618E Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8618E: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -861A0 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -861A2   Length              0009 (9)
│ │ │ │ -861A4   Flags               03 (3) 'Modification Access'
│ │ │ │ -861A5   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -861A9   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -861AD Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -861AF   Length              000B (11)
│ │ │ │ -861B1   Version             01 (1)
│ │ │ │ -861B2   UID Size            04 (4)
│ │ │ │ -861B3   UID                 00000000 (0)
│ │ │ │ -861B7   GID Size            04 (4)
│ │ │ │ -861B8   GID                 00000000 (0)
│ │ │ │ -861BC PAYLOAD
│ │ │ │ -
│ │ │ │ -878B3 LOCAL HEADER #77      04034B50 (67324752)
│ │ │ │ -878B7 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -878B8 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -878B9 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -878BB Compression Method    0008 (8) 'Deflated'
│ │ │ │ -878BD Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -878C1 CRC                   E33FD622 (3812611618)
│ │ │ │ -878C5 Compressed Size       00001E14 (7700)
│ │ │ │ -878C9 Uncompressed Size     00008803 (34819)
│ │ │ │ -878CD Filename Length       0016 (22)
│ │ │ │ -878CF Extra Length          001C (28)
│ │ │ │ -878D1 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x878D1: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -878E7 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -878E9   Length              0009 (9)
│ │ │ │ -878EB   Flags               03 (3) 'Modification Access'
│ │ │ │ -878EC   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -878F0   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -878F4 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -878F6   Length              000B (11)
│ │ │ │ -878F8   Version             01 (1)
│ │ │ │ -878F9   UID Size            04 (4)
│ │ │ │ -878FA   UID                 00000000 (0)
│ │ │ │ -878FE   GID Size            04 (4)
│ │ │ │ -878FF   GID                 00000000 (0)
│ │ │ │ -87903 PAYLOAD
│ │ │ │ -
│ │ │ │ -89717 LOCAL HEADER #78      04034B50 (67324752)
│ │ │ │ -8971B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8971C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8971D General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8971F Compression Method    0008 (8) 'Deflated'
│ │ │ │ -89721 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -89725 CRC                   93A5D815 (2477119509)
│ │ │ │ -89729 Compressed Size       000029A7 (10663)
│ │ │ │ -8972D Uncompressed Size     0000D04F (53327)
│ │ │ │ -89731 Filename Length       001A (26)
│ │ │ │ -89733 Extra Length          001C (28)
│ │ │ │ -89735 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x89735: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -8974F Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -89751   Length              0009 (9)
│ │ │ │ -89753   Flags               03 (3) 'Modification Access'
│ │ │ │ -89754   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -89758   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -8975C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -8975E   Length              000B (11)
│ │ │ │ -89760   Version             01 (1)
│ │ │ │ -89761   UID Size            04 (4)
│ │ │ │ -89762   UID                 00000000 (0)
│ │ │ │ -89766   GID Size            04 (4)
│ │ │ │ -89767   GID                 00000000 (0)
│ │ │ │ -8976B PAYLOAD
│ │ │ │ -
│ │ │ │ -8C112 LOCAL HEADER #79      04034B50 (67324752)
│ │ │ │ -8C116 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8C117 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8C118 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8C11A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8C11C Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -8C120 CRC                   D99C18FD (3650885885)
│ │ │ │ -8C124 Compressed Size       000009AC (2476)
│ │ │ │ -8C128 Uncompressed Size     00001DB6 (7606)
│ │ │ │ -8C12C Filename Length       0018 (24)
│ │ │ │ -8C12E Extra Length          001C (28)
│ │ │ │ -8C130 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8C130: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -8C148 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -8C14A   Length              0009 (9)
│ │ │ │ -8C14C   Flags               03 (3) 'Modification Access'
│ │ │ │ -8C14D   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -8C151   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -8C155 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -8C157   Length              000B (11)
│ │ │ │ -8C159   Version             01 (1)
│ │ │ │ -8C15A   UID Size            04 (4)
│ │ │ │ -8C15B   UID                 00000000 (0)
│ │ │ │ -8C15F   GID Size            04 (4)
│ │ │ │ -8C160   GID                 00000000 (0)
│ │ │ │ -8C164 PAYLOAD
│ │ │ │ -
│ │ │ │ -8CB10 LOCAL HEADER #80      04034B50 (67324752)
│ │ │ │ -8CB14 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8CB15 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8CB16 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8CB18 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8CB1A Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -8CB1E CRC                   F5E2129F (4125233823)
│ │ │ │ -8CB22 Compressed Size       000016BC (5820)
│ │ │ │ -8CB26 Uncompressed Size     000016CD (5837)
│ │ │ │ -8CB2A Filename Length       0015 (21)
│ │ │ │ -8CB2C Extra Length          001C (28)
│ │ │ │ -8CB2E Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8CB2E: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -8CB43 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -8CB45   Length              0009 (9)
│ │ │ │ -8CB47   Flags               03 (3) 'Modification Access'
│ │ │ │ -8CB48   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -8CB4C   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -8CB50 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -8CB52   Length              000B (11)
│ │ │ │ -8CB54   Version             01 (1)
│ │ │ │ -8CB55   UID Size            04 (4)
│ │ │ │ -8CB56   UID                 00000000 (0)
│ │ │ │ -8CB5A   GID Size            04 (4)
│ │ │ │ -8CB5B   GID                 00000000 (0)
│ │ │ │ -8CB5F PAYLOAD
│ │ │ │ -
│ │ │ │ -8E21B LOCAL HEADER #81      04034B50 (67324752)
│ │ │ │ -8E21F Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8E220 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8E221 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8E223 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8E225 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -8E229 CRC                   F5E2129F (4125233823)
│ │ │ │ -8E22D Compressed Size       000016BC (5820)
│ │ │ │ -8E231 Uncompressed Size     000016CD (5837)
│ │ │ │ -8E235 Filename Length       001C (28)
│ │ │ │ -8E237 Extra Length          001C (28)
│ │ │ │ -8E239 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8E239: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -8E255 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -8E257   Length              0009 (9)
│ │ │ │ -8E259   Flags               03 (3) 'Modification Access'
│ │ │ │ -8E25A   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -8E25E   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -8E262 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -8E264   Length              000B (11)
│ │ │ │ -8E266   Version             01 (1)
│ │ │ │ -8E267   UID Size            04 (4)
│ │ │ │ -8E268   UID                 00000000 (0)
│ │ │ │ -8E26C   GID Size            04 (4)
│ │ │ │ -8E26D   GID                 00000000 (0)
│ │ │ │ -8E271 PAYLOAD
│ │ │ │ -
│ │ │ │ -8F92D LOCAL HEADER #82      04034B50 (67324752)
│ │ │ │ -8F931 Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -8F932 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8F933 General Purpose Flag  0000 (0)
│ │ │ │ -8F935 Compression Method    0000 (0) 'Stored'
│ │ │ │ -8F937 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -8F93B CRC                   FC95F24B (4237685323)
│ │ │ │ -8F93F Compressed Size       00001B84 (7044)
│ │ │ │ -8F943 Uncompressed Size     00001B84 (7044)
│ │ │ │ -8F947 Filename Length       0016 (22)
│ │ │ │ -8F949 Extra Length          001C (28)
│ │ │ │ -8F94B Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8F94B: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -8F961 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -8F963   Length              0009 (9)
│ │ │ │ -8F965   Flags               03 (3) 'Modification Access'
│ │ │ │ -8F966   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -8F96A   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -8F96E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -8F970   Length              000B (11)
│ │ │ │ -8F972   Version             01 (1)
│ │ │ │ -8F973   UID Size            04 (4)
│ │ │ │ -8F974   UID                 00000000 (0)
│ │ │ │ -8F978   GID Size            04 (4)
│ │ │ │ -8F979   GID                 00000000 (0)
│ │ │ │ -8F97D PAYLOAD
│ │ │ │ -
│ │ │ │ -91501 LOCAL HEADER #83      04034B50 (67324752)
│ │ │ │ -91505 Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -91506 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -91507 General Purpose Flag  0000 (0)
│ │ │ │ -91509 Compression Method    0000 (0) 'Stored'
│ │ │ │ -9150B Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -9150F CRC                   D0D71F86 (3503759238)
│ │ │ │ -91513 Compressed Size       00000B7B (2939)
│ │ │ │ -91517 Uncompressed Size     00000B7B (2939)
│ │ │ │ -9151B Filename Length       0016 (22)
│ │ │ │ -9151D Extra Length          001C (28)
│ │ │ │ -9151F Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9151F: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -91535 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -91537   Length              0009 (9)
│ │ │ │ -91539   Flags               03 (3) 'Modification Access'
│ │ │ │ -9153A   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -9153E   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -91542 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -91544   Length              000B (11)
│ │ │ │ -91546   Version             01 (1)
│ │ │ │ -91547   UID Size            04 (4)
│ │ │ │ -91548   UID                 00000000 (0)
│ │ │ │ -9154C   GID Size            04 (4)
│ │ │ │ -9154D   GID                 00000000 (0)
│ │ │ │ -91551 PAYLOAD
│ │ │ │ -
│ │ │ │ -920CC LOCAL HEADER #84      04034B50 (67324752)
│ │ │ │ -920D0 Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -920D1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -920D2 General Purpose Flag  0000 (0)
│ │ │ │ -920D4 Compression Method    0000 (0) 'Stored'
│ │ │ │ -920D6 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -920DA CRC                   FFF9C4D2 (4294558930)
│ │ │ │ -920DE Compressed Size       0000138F (5007)
│ │ │ │ -920E2 Uncompressed Size     0000138F (5007)
│ │ │ │ -920E6 Filename Length       0016 (22)
│ │ │ │ -920E8 Extra Length          001C (28)
│ │ │ │ -920EA Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x920EA: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -92100 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -92102   Length              0009 (9)
│ │ │ │ -92104   Flags               03 (3) 'Modification Access'
│ │ │ │ -92105   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -92109   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -9210D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -9210F   Length              000B (11)
│ │ │ │ -92111   Version             01 (1)
│ │ │ │ -92112   UID Size            04 (4)
│ │ │ │ -92113   UID                 00000000 (0)
│ │ │ │ -92117   GID Size            04 (4)
│ │ │ │ -92118   GID                 00000000 (0)
│ │ │ │ -9211C PAYLOAD
│ │ │ │ -
│ │ │ │ -934AB LOCAL HEADER #85      04034B50 (67324752)
│ │ │ │ -934AF Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -934B0 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -934B1 General Purpose Flag  0000 (0)
│ │ │ │ -934B3 Compression Method    0000 (0) 'Stored'
│ │ │ │ -934B5 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -934B9 CRC                   A1037E8E (2701360782)
│ │ │ │ -934BD Compressed Size       0000145E (5214)
│ │ │ │ -934C1 Uncompressed Size     0000145E (5214)
│ │ │ │ -934C5 Filename Length       0016 (22)
│ │ │ │ -934C7 Extra Length          001C (28)
│ │ │ │ -934C9 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x934C9: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -934DF Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -934E1   Length              0009 (9)
│ │ │ │ -934E3   Flags               03 (3) 'Modification Access'
│ │ │ │ -934E4   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -934E8   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -934EC Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -934EE   Length              000B (11)
│ │ │ │ -934F0   Version             01 (1)
│ │ │ │ -934F1   UID Size            04 (4)
│ │ │ │ -934F2   UID                 00000000 (0)
│ │ │ │ -934F6   GID Size            04 (4)
│ │ │ │ -934F7   GID                 00000000 (0)
│ │ │ │ -934FB PAYLOAD
│ │ │ │ -
│ │ │ │ -94959 LOCAL HEADER #86      04034B50 (67324752)
│ │ │ │ -9495D Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -9495E Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -9495F General Purpose Flag  0000 (0)
│ │ │ │ -94961 Compression Method    0000 (0) 'Stored'
│ │ │ │ -94963 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -94967 CRC                   5E9E64F1 (1587438833)
│ │ │ │ -9496B Compressed Size       000008EC (2284)
│ │ │ │ -9496F Uncompressed Size     000008EC (2284)
│ │ │ │ -94973 Filename Length       0016 (22)
│ │ │ │ -94975 Extra Length          001C (28)
│ │ │ │ -94977 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x94977: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9498D Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -9498F   Length              0009 (9)
│ │ │ │ -94991   Flags               03 (3) 'Modification Access'
│ │ │ │ -94992   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -94996   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -9499A Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -9499C   Length              000B (11)
│ │ │ │ -9499E   Version             01 (1)
│ │ │ │ -9499F   UID Size            04 (4)
│ │ │ │ -949A0   UID                 00000000 (0)
│ │ │ │ -949A4   GID Size            04 (4)
│ │ │ │ -949A5   GID                 00000000 (0)
│ │ │ │ -949A9 PAYLOAD
│ │ │ │ -
│ │ │ │ -95295 LOCAL HEADER #87      04034B50 (67324752)
│ │ │ │ -95299 Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -9529A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -9529B General Purpose Flag  0000 (0)
│ │ │ │ -9529D Compression Method    0000 (0) 'Stored'
│ │ │ │ -9529F Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -952A3 CRC                   42E340AB (1122189483)
│ │ │ │ -952A7 Compressed Size       00001F2E (7982)
│ │ │ │ -952AB Uncompressed Size     00001F2E (7982)
│ │ │ │ -952AF Filename Length       001E (30)
│ │ │ │ -952B1 Extra Length          001C (28)
│ │ │ │ -952B3 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x952B3: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -952D1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -952D3   Length              0009 (9)
│ │ │ │ -952D5   Flags               03 (3) 'Modification Access'
│ │ │ │ -952D6   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -952DA   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -952DE Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -952E0   Length              000B (11)
│ │ │ │ -952E2   Version             01 (1)
│ │ │ │ -952E3   UID Size            04 (4)
│ │ │ │ -952E4   UID                 00000000 (0)
│ │ │ │ -952E8   GID Size            04 (4)
│ │ │ │ -952E9   GID                 00000000 (0)
│ │ │ │ -952ED PAYLOAD
│ │ │ │ -
│ │ │ │ -9721B LOCAL HEADER #88      04034B50 (67324752)
│ │ │ │ -9721F Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -97220 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -97221 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -97223 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -97225 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -97229 CRC                   FE097844 (4262033476)
│ │ │ │ -9722D Compressed Size       00003D6D (15725)
│ │ │ │ -97231 Uncompressed Size     00016649 (91721)
│ │ │ │ -97235 Filename Length       001A (26)
│ │ │ │ -97237 Extra Length          001C (28)
│ │ │ │ -97239 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x97239: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -97253 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -97255   Length              0009 (9)
│ │ │ │ -97257   Flags               03 (3) 'Modification Access'
│ │ │ │ -97258   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -9725C   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -97260 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -97262   Length              000B (11)
│ │ │ │ -97264   Version             01 (1)
│ │ │ │ -97265   UID Size            04 (4)
│ │ │ │ -97266   UID                 00000000 (0)
│ │ │ │ -9726A   GID Size            04 (4)
│ │ │ │ -9726B   GID                 00000000 (0)
│ │ │ │ -9726F PAYLOAD
│ │ │ │ -
│ │ │ │ -9AFDC LOCAL HEADER #89      04034B50 (67324752)
│ │ │ │ -9AFE0 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -9AFE1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -9AFE2 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -9AFE4 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -9AFE6 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -9AFEA CRC                   E0A63F39 (3768991545)
│ │ │ │ -9AFEE Compressed Size       000029C0 (10688)
│ │ │ │ -9AFF2 Uncompressed Size     0000BA6A (47722)
│ │ │ │ -9AFF6 Filename Length       0018 (24)
│ │ │ │ -9AFF8 Extra Length          001C (28)
│ │ │ │ -9AFFA Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9AFFA: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9B012 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -9B014   Length              0009 (9)
│ │ │ │ -9B016   Flags               03 (3) 'Modification Access'
│ │ │ │ -9B017   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -9B01B   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -9B01F Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -9B021   Length              000B (11)
│ │ │ │ -9B023   Version             01 (1)
│ │ │ │ -9B024   UID Size            04 (4)
│ │ │ │ -9B025   UID                 00000000 (0)
│ │ │ │ -9B029   GID Size            04 (4)
│ │ │ │ -9B02A   GID                 00000000 (0)
│ │ │ │ -9B02E PAYLOAD
│ │ │ │ -
│ │ │ │ -9D9EE LOCAL HEADER #90      04034B50 (67324752)
│ │ │ │ -9D9F2 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -9D9F3 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -9D9F4 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -9D9F6 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -9D9F8 Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -9D9FC CRC                   DCB3B516 (3702764822)
│ │ │ │ -9DA00 Compressed Size       000000AE (174)
│ │ │ │ -9DA04 Uncompressed Size     000000FC (252)
│ │ │ │ -9DA08 Filename Length       0016 (22)
│ │ │ │ -9DA0A Extra Length          001C (28)
│ │ │ │ -9DA0C Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9DA0C: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9DA22 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -9DA24   Length              0009 (9)
│ │ │ │ -9DA26   Flags               03 (3) 'Modification Access'
│ │ │ │ -9DA27   Modification Time   686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -9DA2B   Access Time         686CD29B (1751962267) 'Tue Jul  8 08:11:07 2025'
│ │ │ │ -9DA2F Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -9DA31   Length              000B (11)
│ │ │ │ -9DA33   Version             01 (1)
│ │ │ │ -9DA34   UID Size            04 (4)
│ │ │ │ -9DA35   UID                 00000000 (0)
│ │ │ │ -9DA39   GID Size            04 (4)
│ │ │ │ -9DA3A   GID                 00000000 (0)
│ │ │ │ -9DA3E PAYLOAD               XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
│ │ │ │ +04B5F LOCAL HEADER #5       04034B50 (67324752)
│ │ │ │ +04B63 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +04B64 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +04B65 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +04B67 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +04B69 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +04B6D CRC                   67C49326 (1740935974)
│ │ │ │ +04B71 Compressed Size       000003F0 (1008)
│ │ │ │ +04B75 Uncompressed Size     00000876 (2166)
│ │ │ │ +04B79 Filename Length       0014 (20)
│ │ │ │ +04B7B Extra Length          001C (28)
│ │ │ │ +04B7D Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x4B7D: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +04B91 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +04B93   Length              0009 (9)
│ │ │ │ +04B95   Flags               03 (3) 'Modification Access'
│ │ │ │ +04B96   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +04B9A   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +04B9E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +04BA0   Length              000B (11)
│ │ │ │ +04BA2   Version             01 (1)
│ │ │ │ +04BA3   UID Size            04 (4)
│ │ │ │ +04BA4   UID                 00000000 (0)
│ │ │ │ +04BA8   GID Size            04 (4)
│ │ │ │ +04BA9   GID                 00000000 (0)
│ │ │ │ +04BAD PAYLOAD
│ │ │ │ +
│ │ │ │ +04F9D LOCAL HEADER #6       04034B50 (67324752)
│ │ │ │ +04FA1 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +04FA2 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +04FA3 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +04FA5 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +04FA7 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +04FAB CRC                   EC6C7C96 (3966532758)
│ │ │ │ +04FAF Compressed Size       000001AE (430)
│ │ │ │ +04FB3 Uncompressed Size     000002FC (764)
│ │ │ │ +04FB7 Filename Length       0011 (17)
│ │ │ │ +04FB9 Extra Length          001C (28)
│ │ │ │ +04FBB Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x4FBB: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +04FCC Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +04FCE   Length              0009 (9)
│ │ │ │ +04FD0   Flags               03 (3) 'Modification Access'
│ │ │ │ +04FD1   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +04FD5   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +04FD9 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +04FDB   Length              000B (11)
│ │ │ │ +04FDD   Version             01 (1)
│ │ │ │ +04FDE   UID Size            04 (4)
│ │ │ │ +04FDF   UID                 00000000 (0)
│ │ │ │ +04FE3   GID Size            04 (4)
│ │ │ │ +04FE4   GID                 00000000 (0)
│ │ │ │ +04FE8 PAYLOAD
│ │ │ │ +
│ │ │ │ +05196 LOCAL HEADER #7       04034B50 (67324752)
│ │ │ │ +0519A Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +0519B Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +0519C General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +0519E Compression Method    0008 (8) 'Deflated'
│ │ │ │ +051A0 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +051A4 CRC                   92DDF273 (2464019059)
│ │ │ │ +051A8 Compressed Size       000020C6 (8390)
│ │ │ │ +051AC Uncompressed Size     0000B4B0 (46256)
│ │ │ │ +051B0 Filename Length       001B (27)
│ │ │ │ +051B2 Extra Length          001C (28)
│ │ │ │ +051B4 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x51B4: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +051CF Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +051D1   Length              0009 (9)
│ │ │ │ +051D3   Flags               03 (3) 'Modification Access'
│ │ │ │ +051D4   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +051D8   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +051DC Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +051DE   Length              000B (11)
│ │ │ │ +051E0   Version             01 (1)
│ │ │ │ +051E1   UID Size            04 (4)
│ │ │ │ +051E2   UID                 00000000 (0)
│ │ │ │ +051E6   GID Size            04 (4)
│ │ │ │ +051E7   GID                 00000000 (0)
│ │ │ │ +051EB PAYLOAD
│ │ │ │ +
│ │ │ │ +072B1 LOCAL HEADER #8       04034B50 (67324752)
│ │ │ │ +072B5 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +072B6 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +072B7 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +072B9 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +072BB Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +072BF CRC                   23989D4C (597204300)
│ │ │ │ +072C3 Compressed Size       00000E6F (3695)
│ │ │ │ +072C7 Uncompressed Size     000030B2 (12466)
│ │ │ │ +072CB Filename Length       001D (29)
│ │ │ │ +072CD Extra Length          001C (28)
│ │ │ │ +072CF Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x72CF: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +072EC Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +072EE   Length              0009 (9)
│ │ │ │ +072F0   Flags               03 (3) 'Modification Access'
│ │ │ │ +072F1   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +072F5   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +072F9 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +072FB   Length              000B (11)
│ │ │ │ +072FD   Version             01 (1)
│ │ │ │ +072FE   UID Size            04 (4)
│ │ │ │ +072FF   UID                 00000000 (0)
│ │ │ │ +07303   GID Size            04 (4)
│ │ │ │ +07304   GID                 00000000 (0)
│ │ │ │ +07308 PAYLOAD
│ │ │ │ +
│ │ │ │ +08177 LOCAL HEADER #9       04034B50 (67324752)
│ │ │ │ +0817B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +0817C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +0817D General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +0817F Compression Method    0008 (8) 'Deflated'
│ │ │ │ +08181 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +08185 CRC                   E1B38941 (3786639681)
│ │ │ │ +08189 Compressed Size       00000972 (2418)
│ │ │ │ +0818D Uncompressed Size     00001CB2 (7346)
│ │ │ │ +08191 Filename Length       0019 (25)
│ │ │ │ +08193 Extra Length          001C (28)
│ │ │ │ +08195 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x8195: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +081AE Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +081B0   Length              0009 (9)
│ │ │ │ +081B2   Flags               03 (3) 'Modification Access'
│ │ │ │ +081B3   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +081B7   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +081BB Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +081BD   Length              000B (11)
│ │ │ │ +081BF   Version             01 (1)
│ │ │ │ +081C0   UID Size            04 (4)
│ │ │ │ +081C1   UID                 00000000 (0)
│ │ │ │ +081C5   GID Size            04 (4)
│ │ │ │ +081C6   GID                 00000000 (0)
│ │ │ │ +081CA PAYLOAD
│ │ │ │ +
│ │ │ │ +08B3C LOCAL HEADER #10      04034B50 (67324752)
│ │ │ │ +08B40 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +08B41 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +08B42 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +08B44 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +08B46 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +08B4A CRC                   C18FB0F4 (3247419636)
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│ │ │ │ +08B52 Uncompressed Size     0000F7F4 (63476)
│ │ │ │ +08B56 Filename Length       0015 (21)
│ │ │ │ +08B58 Extra Length          001C (28)
│ │ │ │ +08B5A Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x8B5A: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +08B6F Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +08B78   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +08B7C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +08B8B PAYLOAD
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│ │ │ │ +0C40C Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +0C40D Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +0C40E General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +0C410 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +0C412 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +0C416 CRC                   11DAE00E (299556878)
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│ │ │ │ +0C41E Uncompressed Size     0003DFDE (253918)
│ │ │ │ +0C422 Filename Length       0012 (18)
│ │ │ │ +0C424 Extra Length          001C (28)
│ │ │ │ +0C426 Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0xC426: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +0C438 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +16F3A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +16F3B General Purpose Flag  0000 (0)
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│ │ │ │ +16F3F Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +16F43 CRC                   D386A0EC (3548815596)
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│ │ │ │ +16F53 Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
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│ │ │ │ +#          Zero length filename
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│ │ │ │ +1AAA8 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +1AAA9 General Purpose Flag  0000 (0)
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│ │ │ │ +1AAAD Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +1AAB1 CRC                   83319CE1 (2201066721)
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│ │ │ │ +1AAB9 Uncompressed Size     0003D05F (249951)
│ │ │ │ +1AABD Filename Length       0014 (20)
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│ │ │ │ +1AAC1 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
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│ │ │ │ +#          Zero length filename
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│ │ │ │ +1AADE   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
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│ │ │ │ +1AAF1 PAYLOAD
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│ │ │ │ +23B7F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +23B80 General Purpose Flag  0000 (0)
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│ │ │ │ +23B84 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +23B88 CRC                   D841329D (3628151453)
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│ │ │ │ +23B90 Uncompressed Size     0001151F (70943)
│ │ │ │ +23B94 Filename Length       0016 (22)
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│ │ │ │ +#
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│ │ │ │ +#          Zero length filename
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│ │ │ │ +23BB7   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
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│ │ │ │ +26633 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +26638 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +2663C CRC                   1BBBA233 (465281587)
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│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x2664C: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +26672   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
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│ │ │ │ +27B63 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +27B64 General Purpose Flag  0000 (0)
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│ │ │ │ +27B68 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +2B3B6 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +2B3B7 General Purpose Flag  0000 (0)
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│ │ │ │ +2B3BB Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +2B3BF CRC                   B106FD76 (2970025334)
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│ │ │ │ +2BAAC Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +2BAB1 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +2CB7D Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +2CB7E General Purpose Flag  0000 (0)
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│ │ │ │ +2CB82 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +2CB86 CRC                   7057E246 (1884807750)
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│ │ │ │ +2FF7F Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +2FF84 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +2FF88 CRC                   42DF9C4A (1121950794)
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│ │ │ │ +2FF98 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +#          Zero length filename
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│ │ │ │ +30D3E Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +30D3F General Purpose Flag  0000 (0)
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│ │ │ │ +30D43 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +30D47 CRC                   99B98379 (2579071865)
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│ │ │ │ +# WARNING: Offset 0x30D57: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +3C4CA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +3C4CB General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
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│ │ │ │ +3C4CF Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +3C4D3 CRC                   936899C3 (2473105859)
│ │ │ │ +3C4D7 Compressed Size       000009A6 (2470)
│ │ │ │ +3C4DB Uncompressed Size     00001B64 (7012)
│ │ │ │ +3C4DF Filename Length       0010 (16)
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│ │ │ │ +3C4E3 Filename              'XXXXXXXXXXXXXXXX'
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│ │ │ │ +3C4FC   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
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│ │ │ │ +3CEBA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +3CEBB General Purpose Flag  0000 (0)
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│ │ │ │ +3CEBF Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +3CEC3 CRC                   E9E04E21 (3923791393)
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│ │ │ │ +3D5BD Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +3D5BE General Purpose Flag  0000 (0)
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│ │ │ │ +3D5C2 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +4001C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +4001D General Purpose Flag  0000 (0)
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│ │ │ │ +40021 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +40025 CRC                   694BEBE0 (1766583264)
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│ │ │ │ +41EEF Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +41EF0 General Purpose Flag  0000 (0)
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│ │ │ │ +41EF4 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +433BC Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +433C1 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +44CE8 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +44CE9 General Purpose Flag  0000 (0)
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│ │ │ │ +44CED Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +44CF1 CRC                   D64849DE (3595061726)
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│ │ │ │ +44D01 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +#          Zero length filename
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│ │ │ │ +45137 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +45138 General Purpose Flag  0000 (0)
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│ │ │ │ +4513C Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +45140 CRC                   9488B892 (2491988114)
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│ │ │ │ +4514C Filename Length       0013 (19)
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│ │ │ │ +45150 Filename              'XXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +# WARNING: Offset 0x45150: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +4516C   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
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│ │ │ │ +49417 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +49418 General Purpose Flag  0000 (0)
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│ │ │ │ +4941C Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +49420 CRC                   C29C087D (3265005693)
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│ │ │ │ +4942E Extra Length          001C (28)
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│ │ │ │ +# WARNING: Offset 0x49430: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +49452   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
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│ │ │ │ +4BB2E Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +4BB2F General Purpose Flag  0000 (0)
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│ │ │ │ +4BB33 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +4BB37 CRC                   8F94BE1C (2408889884)
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│ │ │ │ +4BB47 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +# WARNING: Offset 0x4BB47: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +4BB69   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
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│ │ │ │ +4E2BA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +4E2BB General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
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│ │ │ │ +4E2BF Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +4E2C3 CRC                   23598AC4 (593070788)
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│ │ │ │ +4E2D3 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x4E2D3: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +4E2FD   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
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│ │ │ │ +4F005 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +4F006 General Purpose Flag  0000 (0)
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│ │ │ │ +4F00A Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +4F00E CRC                   07042E48 (117714504)
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│ │ │ │ +4F01E Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x4F01E: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +4F039 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +4F042   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
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│ │ │ │ +7C131 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +83C40 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +83E66 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +83E67 General Purpose Flag  0000 (0)
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│ │ │ │ +83E6B Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +8457B Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +84580 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +86156 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +8618A   Access Time         68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
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│ │ │ │ +878A0 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +896FF Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +89704 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +8C0FC General Purpose Flag  0000 (0)
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│ │ │ │ +8C100 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +8CAFC Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
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│ │ │ │ +# WARNING: Offset 0x8CB10: Filename 'XXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9E339: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -9E35C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9E3F1: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
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│ │ │ │ -# WARNING: Offset 0x9E457: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9E4B8: Filename 'XXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -9E57E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -# WARNING: Offset 0x9E5C4: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9E61E: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -9E639 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -9E65D Modification Time     5AE84163 (1525170531) 'Tue Jul  8 08:11:06 2025'
│ │ │ │ -9E661 CRC                   32905960 (848320864)
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9E8DF: Filename 'XXXXXXXXXXXXXXXXXX'
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│ │ │ │ -# WARNING: Offset 0x9E937: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9E995: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9F097: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9F403: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9F684: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9F6E3: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -9F73D Local Header Offset   00086170 (549232)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9F741: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9F753 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -9F75C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -9F77B CRC                   E33FD622 (3812611618)
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│ │ │ │ -9F799 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9F799: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9F7AF Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -9F7B8 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +9FC33 Local Header Offset   0009D9C7 (645575)
│ │ │ │ +9FC37 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x9FC37: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +9FC4D Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +9FC4F   Length              0005 (5)
│ │ │ │ +9FC51   Flags               01 (1) 'Modification'
│ │ │ │ +9FC52   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +9FC56 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +9FC58   Length              000B (11)
│ │ │ │ +9FC5A   Version             01 (1)
│ │ │ │ +9FC5B   UID Size            04 (4)
│ │ │ │ +9FC5C   UID                 00000000 (0)
│ │ │ │ +9FC60   GID Size            04 (4)
│ │ │ │ +9FC61   GID                 00000000 (0)
│ │ │ │ +
│ │ │ │ +9FC65 CENTRAL HEADER #91    02014B50 (33639248)
│ │ │ │ +9FC69 Created Zip Spec      3D (61) '6.1'
│ │ │ │ +9FC6A Created OS            03 (3) 'Unix'
│ │ │ │ +9FC6B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +9FC6C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +9FC6D General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +9FC6F Compression Method    0008 (8) 'Deflated'
│ │ │ │ +9FC71 Modification Time     5B16AE84 (1528213124) 'Fri Aug 22 21:52:08 2025'
│ │ │ │ +9FC75 CRC                   58439733 (1480824627)
│ │ │ │ +9FC79 Compressed Size       00000077 (119)
│ │ │ │ +9FC7D Uncompressed Size     000000A2 (162)
│ │ │ │ +9FC81 Filename Length       002D (45)
│ │ │ │ +9FC83 Extra Length          0018 (24)
│ │ │ │ +9FC85 Comment Length        0000 (0)
│ │ │ │ +9FC87 Disk Start            0000 (0)
│ │ │ │ +9FC89 Int File Attributes   0000 (0)
│ │ │ │ +      [Bit 0]               0 'Binary Data'
│ │ │ │ +9FC8B Ext File Attributes   01A40000 (27525120)
│ │ │ │ +      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ +9FC8F Local Header Offset   0009DAC5 (645829)
│ │ │ │ +9FC93 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x9FC93: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +9FCC0 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +9FCC2   Length              0005 (5)
│ │ │ │ +9FCC4   Flags               01 (1) 'Modification'
│ │ │ │ +9FCC5   Modification Time   68A8E689 (1755899529) 'Fri Aug 22 21:52:09 2025'
│ │ │ │ +9FCC9 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +9FCCB   Length              000B (11)
│ │ │ │ +9FCCD   Version             01 (1)
│ │ │ │ +9FCCE   UID Size            04 (4)
│ │ │ │ +9FCCF   UID                 00000000 (0)
│ │ │ │ +9FCD3   GID Size            04 (4)
│ │ │ │ +9FCD4   GID                 00000000 (0)
│ │ │ │ +
│ │ │ │ +9FCD8 END CENTRAL HEADER    06054B50 (101010256)
│ │ │ │ +9FCDC Number of this disk   0000 (0)
│ │ │ │ +9FCDE Central Dir Disk no   0000 (0)
│ │ │ │ +9FCE0 Entries in this disk  005B (91)
│ │ │ │ +9FCE2 Total Entries         005B (91)
│ │ │ │ +9FCE4 Size of Central Dir   00002135 (8501)
│ │ │ │ +9FCE8 Offset to Central Dir 0009DBA3 (646051)
│ │ │ │ +9FCEC Comment Length        0000 (0)
│ │ │ │  #
│ │ │ │  # Warning Count: 182
│ │ │ │  #
│ │ │ │  # Done
│ │ │ ├── filetype from file(1)
│ │ │ │ @@ -1 +1 @@
│ │ │ │ -Zip archive data, made by v6.1 UNIX, extract using at least v1.0, last modified Jul 08 2025 08:11:06, uncompressed size 20, method=store
│ │ │ │ +Zip archive data, made by v6.1 UNIX, extract using at least v1.0, last modified Aug 22 2025 21:52:08, uncompressed size 20, method=store
│ │ │ ├── OEBPS/typespec.xhtml
│ │ │ │ @@ -143,122 +143,122 @@
│ │ │ │  and optional <code class="inline">(=&gt;)</code> association types. If an association type is mandatory, an
│ │ │ │  association with that type needs to be present. In the case of an optional
│ │ │ │  association type it is not required for the key type to be present.</p><p>The notation <code class="inline">#{}</code> specifies the singleton type for the empty map. Note that
│ │ │ │  this notation is not a shorthand for the <a href="../../../lib/../erts/doc/html/erlang.html#t:map/0"><code class="inline">map/0</code></a> type.</p><p>For convenience, the following types are also built-in. They can be thought as
│ │ │ │  predefined aliases for the type unions also shown in the table.</p><p><a href="" id="builtin_types"></a></p><table><thead><tr><th style="text-align: left;"><em>Built-in type</em></th><th style="text-align: left;"><em>Defined as</em></th></tr></thead><tbody><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:term/0"><code class="inline">term/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:any/0"><code class="inline">any/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:binary/0"><code class="inline">binary/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:_*8&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nonempty_binary/0"><code class="inline">nonempty_binary/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:8, _:_*8&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:bitstring/0"><code class="inline">bitstring/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:_*1&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nonempty_bitstring/0"><code class="inline">nonempty_bitstring/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:1, _:_*1&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:boolean/0"><code class="inline">boolean/0</code></a></td><td style="text-align: left;"><code class="inline">'false'</code> | <code class="inline">'true'</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:byte/0"><code class="inline">byte/0</code></a></td><td style="text-align: left;"><code class="inline">0..255</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:char/0"><code class="inline">char/0</code></a></td><td style="text-align: left;"><code class="inline">0..16#10ffff</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nil/0"><code class="inline">nil/0</code></a></td><td style="text-align: left;"><code class="inline">[]</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:number/0"><code class="inline">number/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:integer/0"><code class="inline">integer/0</code></a> | <a href="../../../lib/../erts/doc/html/erlang.html#t:float/0"><code class="inline">float/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:list/0"><code class="inline">list/0</code></a></td><td style="text-align: left;"><code class="inline">[any()]</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:maybe_improper_list/0"><code class="inline">maybe_improper_list/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:maybe_improper_list/2"><code class="inline">maybe_improper_list(any(), any())</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nonempty_list/0"><code class="inline">nonempty_list/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nonempty_list/1"><code class="inline">nonempty_list(any())</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:string/0"><code class="inline">string/0</code></a></td><td style="text-align: left;"><code class="inline">[char()]</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nonempty_string/0"><code class="inline">nonempty_string/0</code></a></td><td style="text-align: left;"><code class="inline">[char(),...]</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:iodata/0"><code class="inline">iodata/0</code></a></td><td style="text-align: left;"><code class="inline">iolist()</code> | <code class="inline">binary()</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:iolist/0"><code class="inline">iolist/0</code></a></td><td style="text-align: left;"><code class="inline">maybe_improper_list(byte()</code> | <code class="inline">binary()</code> | <code class="inline">iolist(), binary()</code> | <code class="inline">[])</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:map/0"><code class="inline">map/0</code></a></td><td style="text-align: left;"><code class="inline">#{any() =&gt; any()}</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:function/0"><code class="inline">function/0</code></a></td><td style="text-align: left;"><code class="inline">fun()</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:module/0"><code class="inline">module/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:atom/0"><code class="inline">atom/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:mfa/0"><code class="inline">mfa/0</code></a></td><td style="text-align: left;"><code class="inline">{module(),atom(),arity()}</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:arity/0"><code class="inline">arity/0</code></a></td><td style="text-align: left;"><code class="inline">0..255</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:identifier/0"><code class="inline">identifier/0</code></a></td><td style="text-align: left;"><code class="inline">pid()</code> | <code class="inline">port()</code> | <code class="inline">reference()</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#node/0"><code class="inline">node/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:atom/0"><code class="inline">atom/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:timeout/0"><code class="inline">timeout/0</code></a></td><td style="text-align: left;"><code class="inline">'infinity'</code> | <code class="inline">non_neg_integer()</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:none/0"><code class="inline">none/0</code></a></td></tr></tbody></table><p><em>Table: Built-in types, predefined aliases</em></p><p>In addition, the following three built-in types exist and can be thought as
│ │ │ │  defined below, though strictly their &quot;type definition&quot; is not valid syntax
│ │ │ │  according to the type language defined above.</p><table><thead><tr><th style="text-align: left;"><em>Built-in type</em></th><th style="text-align: left;"><em>Can be thought defined by the syntax</em></th></tr></thead><tbody><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:non_neg_integer/0"><code class="inline">non_neg_integer/0</code></a></td><td style="text-align: left;"><code class="inline">0..</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:pos_integer/0"><code class="inline">pos_integer/0</code></a></td><td style="text-align: left;"><code class="inline">1..</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:neg_integer/0"><code class="inline">neg_integer/0</code></a></td><td style="text-align: left;"><code class="inline">..-1</code></td></tr></tbody></table><p><em>Table: Additional built-in types</em></p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The following built-in list types also exist, but they are expected to be
│ │ │ │ -rarely used. Hence, they have long names:</p></section><pre><code class="makeup erlang" translate="no"><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="0421746982-1">(</span><span class="p" data-group-id="0421746982-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="0421746982-2">(</span><span class="nf">any</span><span class="p" data-group-id="0421746982-3">(</span><span class="p" data-group-id="0421746982-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="0421746982-4">(</span><span class="p" data-group-id="0421746982-4">)</span><span class="p" data-group-id="0421746982-2">)</span><span class="w">
│ │ │ │ -</span><span class="nf">nonempty_improper_list</span><span class="p" data-group-id="0421746982-5">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="0421746982-5">)</span><span class="w">
│ │ │ │ -</span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="0421746982-6">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="0421746982-6">)</span></code></pre><p>where the last two types define the set of Erlang terms one would expect.</p><p>Also for convenience, record notation is allowed to be used. Records are
│ │ │ │ -shorthands for the corresponding tuples:</p><pre><code class="makeup erlang" translate="no"><span class="n">Record</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="1627044824-1">{</span><span class="p" data-group-id="1627044824-1">}</span><span class="w">
│ │ │ │ -        </span><span class="p">|</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="1627044824-2">{</span><span class="n">Fields</span><span class="p" data-group-id="1627044824-2">}</span></code></pre><p>Records are extended to possibly contain type information. This is described in
│ │ │ │ +rarely used. Hence, they have long names:</p></section><pre><code class="makeup erlang" translate="no"><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="4199892554-1">(</span><span class="p" data-group-id="4199892554-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="4199892554-2">(</span><span class="nf">any</span><span class="p" data-group-id="4199892554-3">(</span><span class="p" data-group-id="4199892554-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="4199892554-4">(</span><span class="p" data-group-id="4199892554-4">)</span><span class="p" data-group-id="4199892554-2">)</span><span class="w">
│ │ │ │ +</span><span class="nf">nonempty_improper_list</span><span class="p" data-group-id="4199892554-5">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="4199892554-5">)</span><span class="w">
│ │ │ │ +</span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="4199892554-6">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="4199892554-6">)</span></code></pre><p>where the last two types define the set of Erlang terms one would expect.</p><p>Also for convenience, record notation is allowed to be used. Records are
│ │ │ │ +shorthands for the corresponding tuples:</p><pre><code class="makeup erlang" translate="no"><span class="n">Record</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="3041923264-1">{</span><span class="p" data-group-id="3041923264-1">}</span><span class="w">
│ │ │ │ +        </span><span class="p">|</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="3041923264-2">{</span><span class="n">Fields</span><span class="p" data-group-id="3041923264-2">}</span></code></pre><p>Records are extended to possibly contain type information. This is described in
│ │ │ │  <a href="typespec.xhtml#typeinrecords">Type Information in Record Declarations</a>.</p><h3 id="redefining-built-in-types" class="section-heading">
│ │ │ │    <a href="#redefining-built-in-types" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Redefining built-in types</span>
│ │ │ │  </h3>
│ │ │ │  <section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Starting from Erlang/OTP 26, it is permitted to define a type having the same
│ │ │ │  name as a built-in type.</p></section><p>It is recommended to avoid deliberately reusing built-in names because it can be
│ │ │ │  confusing. However, when an Erlang/OTP release introduces a new type, code that
│ │ │ │  happened to define its own type having the same name will continue to work.</p><p>As an example, imagine that the Erlang/OTP 42 release introduces a new type
│ │ │ │ -<code class="inline">gadget()</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="4482983515-1">(</span><span class="p" data-group-id="4482983515-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4482983515-2">{</span><span class="ss">&#39;gadget&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">reference</span><span class="p" data-group-id="4482983515-3">(</span><span class="p" data-group-id="4482983515-3">)</span><span class="p" data-group-id="4482983515-2">}</span><span class="p">.</span></code></pre><p>Further imagine that some code has its own (different) definition of <code class="inline">gadget()</code>,
│ │ │ │ -for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="1644536698-1">(</span><span class="p" data-group-id="1644536698-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1644536698-2">#{</span><span class="p" data-group-id="1644536698-2">}</span><span class="p">.</span></code></pre><p>Since redefinitions are allowed, the code will still compile (but with a
│ │ │ │ +<code class="inline">gadget()</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="0521204542-1">(</span><span class="p" data-group-id="0521204542-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0521204542-2">{</span><span class="ss">&#39;gadget&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">reference</span><span class="p" data-group-id="0521204542-3">(</span><span class="p" data-group-id="0521204542-3">)</span><span class="p" data-group-id="0521204542-2">}</span><span class="p">.</span></code></pre><p>Further imagine that some code has its own (different) definition of <code class="inline">gadget()</code>,
│ │ │ │ +for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="7194138349-1">(</span><span class="p" data-group-id="7194138349-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="7194138349-2">#{</span><span class="p" data-group-id="7194138349-2">}</span><span class="p">.</span></code></pre><p>Since redefinitions are allowed, the code will still compile (but with a
│ │ │ │  warning), and Dialyzer will not emit any additional warnings.</p><h2 id="type-declarations-of-user-defined-types" class="section-heading">
│ │ │ │    <a href="#type-declarations-of-user-defined-types" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Type Declarations of User-Defined Types</span>
│ │ │ │  </h2>
│ │ │ │  <p>As seen, the basic syntax of a type is an atom followed by closed parentheses.
│ │ │ │  New types are declared using <code class="inline">-type</code> and <code class="inline">-opaque</code> attributes as in the
│ │ │ │ -following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_struct_type</span><span class="p" data-group-id="7426205305-1">(</span><span class="p" data-group-id="7426205305-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">my_opaq_type</span><span class="p" data-group-id="7426205305-2">(</span><span class="p" data-group-id="7426205305-2">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span></code></pre><p>The type name is the atom <code class="inline">my_struct_type</code>, followed by parentheses. <code class="inline">Type</code> is a
│ │ │ │ +following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_struct_type</span><span class="p" data-group-id="9464183930-1">(</span><span class="p" data-group-id="9464183930-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">my_opaq_type</span><span class="p" data-group-id="9464183930-2">(</span><span class="p" data-group-id="9464183930-2">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span></code></pre><p>The type name is the atom <code class="inline">my_struct_type</code>, followed by parentheses. <code class="inline">Type</code> is a
│ │ │ │  type as defined in the previous section. A current restriction is that <code class="inline">Type</code>
│ │ │ │  can contain only predefined types, or user-defined types which are either of the
│ │ │ │  following:</p><ul><li>Module-local type, that is, with a definition that is present in the code of
│ │ │ │  the module</li><li>Remote type, that is, type defined in, and exported by, other modules; more
│ │ │ │  about this soon.</li></ul><p>For module-local types, the restriction that their definition exists in the
│ │ │ │  module is enforced by the compiler and results in a compilation error. (A
│ │ │ │  similar restriction currently exists for records.)</p><p>Type declarations can also be parameterized by including type variables between
│ │ │ │  the parentheses. The syntax of type variables is the same as Erlang variables,
│ │ │ │  that is, starts with an upper-case letter. These variables is to
│ │ │ │ -appear on the RHS of the definition. A concrete example follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">orddict</span><span class="p" data-group-id="8802932354-1">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="8802932354-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="8802932354-2">[</span><span class="p" data-group-id="8802932354-3">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="8802932354-3">}</span><span class="p" data-group-id="8802932354-2">]</span><span class="p">.</span></code></pre><p>A module can export some types to declare that other modules are allowed to
│ │ │ │ -refer to them as <em>remote types</em>. This declaration has the following form:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="1546048993-1">(</span><span class="p" data-group-id="1546048993-2">[</span><span class="n">T1</span><span class="o">/</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Tk</span><span class="o">/</span><span class="n">Ak</span><span class="p" data-group-id="1546048993-2">]</span><span class="p" data-group-id="1546048993-1">)</span><span class="p">.</span></code></pre><p>Here the <code class="inline">Ti</code>s are atoms (the name of the type) and the <code class="inline">Ai</code>s are their arguments.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="8650745833-1">(</span><span class="p" data-group-id="8650745833-2">[</span><span class="ss">my_struct_type</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">orddict</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8650745833-2">]</span><span class="p" data-group-id="8650745833-1">)</span><span class="p">.</span></code></pre><p>Assuming that these types are exported from module <code class="inline">'mod'</code>, you can refer to
│ │ │ │ -them from other modules using remote type expressions like the following:</p><pre><code class="makeup erlang" translate="no"><span class="nc">mod</span><span class="p">:</span><span class="nf">my_struct_type</span><span class="p" data-group-id="7962535241-1">(</span><span class="p" data-group-id="7962535241-1">)</span><span class="w">
│ │ │ │ -</span><span class="nc">mod</span><span class="p">:</span><span class="nf">orddict</span><span class="p" data-group-id="7962535241-2">(</span><span class="nf">atom</span><span class="p" data-group-id="7962535241-3">(</span><span class="p" data-group-id="7962535241-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7962535241-4">(</span><span class="p" data-group-id="7962535241-4">)</span><span class="p" data-group-id="7962535241-2">)</span></code></pre><p>It is not allowed to refer to types that are not declared as exported.</p><p>Types declared as <code class="inline">opaque</code> represent sets of terms whose structure is not
│ │ │ │ +appear on the RHS of the definition. A concrete example follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">orddict</span><span class="p" data-group-id="5022096918-1">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="5022096918-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="5022096918-2">[</span><span class="p" data-group-id="5022096918-3">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="5022096918-3">}</span><span class="p" data-group-id="5022096918-2">]</span><span class="p">.</span></code></pre><p>A module can export some types to declare that other modules are allowed to
│ │ │ │ +refer to them as <em>remote types</em>. This declaration has the following form:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="0966412194-1">(</span><span class="p" data-group-id="0966412194-2">[</span><span class="n">T1</span><span class="o">/</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Tk</span><span class="o">/</span><span class="n">Ak</span><span class="p" data-group-id="0966412194-2">]</span><span class="p" data-group-id="0966412194-1">)</span><span class="p">.</span></code></pre><p>Here the <code class="inline">Ti</code>s are atoms (the name of the type) and the <code class="inline">Ai</code>s are their arguments.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="1817348739-1">(</span><span class="p" data-group-id="1817348739-2">[</span><span class="ss">my_struct_type</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">orddict</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1817348739-2">]</span><span class="p" data-group-id="1817348739-1">)</span><span class="p">.</span></code></pre><p>Assuming that these types are exported from module <code class="inline">'mod'</code>, you can refer to
│ │ │ │ +them from other modules using remote type expressions like the following:</p><pre><code class="makeup erlang" translate="no"><span class="nc">mod</span><span class="p">:</span><span class="nf">my_struct_type</span><span class="p" data-group-id="1065188976-1">(</span><span class="p" data-group-id="1065188976-1">)</span><span class="w">
│ │ │ │ +</span><span class="nc">mod</span><span class="p">:</span><span class="nf">orddict</span><span class="p" data-group-id="1065188976-2">(</span><span class="nf">atom</span><span class="p" data-group-id="1065188976-3">(</span><span class="p" data-group-id="1065188976-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="1065188976-4">(</span><span class="p" data-group-id="1065188976-4">)</span><span class="p" data-group-id="1065188976-2">)</span></code></pre><p>It is not allowed to refer to types that are not declared as exported.</p><p>Types declared as <code class="inline">opaque</code> represent sets of terms whose structure is not
│ │ │ │  supposed to be visible from outside of their defining module. That is, only the
│ │ │ │  module defining them is allowed to depend on their term structure. Consequently,
│ │ │ │  such types do not make much sense as module local - module local types are not
│ │ │ │  accessible by other modules anyway - and is always to be exported.</p><p>Read more on <a href="opaques.xhtml">Opaques</a></p><p><a href="" id="typeinrecords"></a></p><h2 id="type-information-in-record-declarations" class="section-heading">
│ │ │ │    <a href="#type-information-in-record-declarations" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Type Information in Record Declarations</span>
│ │ │ │  </h2>
│ │ │ │  <p>The types of record fields can be specified in the declaration of the record.
│ │ │ │ -The syntax for this is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8222005372-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8222005372-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="8222005372-2">}</span><span class="p" data-group-id="8222005372-1">)</span><span class="p">.</span></code></pre><p>For fields without type annotations, their type defaults to <code class="inline">any()</code>. That is, the
│ │ │ │ -previous example is a shorthand for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0981042144-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0981042144-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="0981042144-3">(</span><span class="p" data-group-id="0981042144-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="0981042144-2">}</span><span class="p" data-group-id="0981042144-1">)</span><span class="p">.</span></code></pre><p>In the presence of initial values for fields, the type must be declared after
│ │ │ │ -the initialization, as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5602325207-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5602325207-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5602325207-3">[</span><span class="p" data-group-id="5602325207-3">]</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="5602325207-2">}</span><span class="p" data-group-id="5602325207-1">)</span><span class="p">.</span></code></pre><p>The initial values for fields are to be compatible with (that is, a member of)
│ │ │ │ +The syntax for this is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3430570154-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3430570154-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="3430570154-2">}</span><span class="p" data-group-id="3430570154-1">)</span><span class="p">.</span></code></pre><p>For fields without type annotations, their type defaults to <code class="inline">any()</code>. That is, the
│ │ │ │ +previous example is a shorthand for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9418681898-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9418681898-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="9418681898-3">(</span><span class="p" data-group-id="9418681898-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="9418681898-2">}</span><span class="p" data-group-id="9418681898-1">)</span><span class="p">.</span></code></pre><p>In the presence of initial values for fields, the type must be declared after
│ │ │ │ +the initialization, as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9651413332-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9651413332-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9651413332-3">[</span><span class="p" data-group-id="9651413332-3">]</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="9651413332-2">}</span><span class="p" data-group-id="9651413332-1">)</span><span class="p">.</span></code></pre><p>The initial values for fields are to be compatible with (that is, a member of)
│ │ │ │  the corresponding types. This is checked by the compiler and results in a
│ │ │ │  compilation error if a violation is detected.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 19, for fields without initial values, the singleton type
│ │ │ │  <code class="inline">'undefined'</code> was added to all declared types. In other words, the following
│ │ │ │ -two record declarations had identical effects:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2369988679-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2369988679-2">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="2369988679-3">(</span><span class="p" data-group-id="2369988679-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="2369988679-4">(</span><span class="p" data-group-id="2369988679-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="2369988679-2">}</span><span class="p" data-group-id="2369988679-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +two record declarations had identical effects:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7989008584-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7989008584-2">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="7989008584-3">(</span><span class="p" data-group-id="7989008584-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="7989008584-4">(</span><span class="p" data-group-id="7989008584-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="7989008584-2">}</span><span class="p" data-group-id="7989008584-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2369988679-5">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2369988679-6">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="2369988679-7">(</span><span class="p" data-group-id="2369988679-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="2369988679-8">(</span><span class="p" data-group-id="2369988679-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="2369988679-6">}</span><span class="p" data-group-id="2369988679-5">)</span><span class="p">.</span></code></pre><p>This is no longer the case. If you require <code class="inline">'undefined'</code> in your record field
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7989008584-5">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7989008584-6">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="7989008584-7">(</span><span class="p" data-group-id="7989008584-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="7989008584-8">(</span><span class="p" data-group-id="7989008584-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="7989008584-6">}</span><span class="p" data-group-id="7989008584-5">)</span><span class="p">.</span></code></pre><p>This is no longer the case. If you require <code class="inline">'undefined'</code> in your record field
│ │ │ │  type, you must explicitly add it to the typespec, as in the 2nd example.</p></section><p>Any record, containing type information or not, once defined, can be used as a
│ │ │ │  type using the following syntax:</p><pre><code class="text">#rec{}</code></pre><p>In addition, the record fields can be further specified when using a record type
│ │ │ │  by adding type information about the field as follows:</p><pre><code class="text">#rec{some_field :: Type}</code></pre><p>Any unspecified fields are assumed to have the type in the original record
│ │ │ │  declaration.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>When records are used to create patterns for ETS and Mnesia match functions,
│ │ │ │ -Dialyzer may need some help not to emit bad warnings. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="6943825193-1">(</span><span class="p" data-group-id="6943825193-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="6943825193-2">(</span><span class="p" data-group-id="6943825193-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6943825193-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6943825193-4">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="6943825193-5">(</span><span class="p" data-group-id="6943825193-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="6943825193-6">(</span><span class="p" data-group-id="6943825193-6">)</span><span class="p" data-group-id="6943825193-4">}</span><span class="p" data-group-id="6943825193-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +Dialyzer may need some help not to emit bad warnings. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="7467019626-1">(</span><span class="p" data-group-id="7467019626-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="7467019626-2">(</span><span class="p" data-group-id="7467019626-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7467019626-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7467019626-4">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="7467019626-5">(</span><span class="p" data-group-id="7467019626-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="7467019626-6">(</span><span class="p" data-group-id="7467019626-6">)</span><span class="p" data-group-id="7467019626-4">}</span><span class="p" data-group-id="7467019626-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="6943825193-7">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="6943825193-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="6943825193-8">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6943825193-9">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6943825193-9">}</span><span class="p" data-group-id="6943825193-8">)</span><span class="p">.</span></code></pre><p>Dialyzer will emit a warning since <code class="inline">'_'</code> is not in the type of record field
│ │ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="7467019626-7">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="7467019626-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="7467019626-8">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7467019626-9">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="7467019626-9">}</span><span class="p" data-group-id="7467019626-8">)</span><span class="p">.</span></code></pre><p>Dialyzer will emit a warning since <code class="inline">'_'</code> is not in the type of record field
│ │ │ │  <code class="inline">height</code>.</p><p>The recommended way of dealing with this is to declare the smallest record
│ │ │ │  field types to accommodate all your needs, and then create refinements as
│ │ │ │ -needed. The modified example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2896535487-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2896535487-2">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="2896535487-3">(</span><span class="p" data-group-id="2896535487-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="2896535487-4">(</span><span class="p" data-group-id="2896535487-4">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="2896535487-2">}</span><span class="p" data-group-id="2896535487-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +needed. The modified example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7916574871-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7916574871-2">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="7916574871-3">(</span><span class="p" data-group-id="7916574871-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="7916574871-4">(</span><span class="p" data-group-id="7916574871-4">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="7916574871-2">}</span><span class="p" data-group-id="7916574871-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">person</span><span class="p" data-group-id="2896535487-5">(</span><span class="p" data-group-id="2896535487-5">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2896535487-6">{</span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="2896535487-7">(</span><span class="p" data-group-id="2896535487-7">)</span><span class="p" data-group-id="2896535487-6">}</span><span class="p">.</span></code></pre><p>In specifications and type declarations the type <code class="inline">person()</code> is to be preferred
│ │ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">person</span><span class="p" data-group-id="7916574871-5">(</span><span class="p" data-group-id="7916574871-5">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7916574871-6">{</span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="7916574871-7">(</span><span class="p" data-group-id="7916574871-7">)</span><span class="p" data-group-id="7916574871-6">}</span><span class="p">.</span></code></pre><p>In specifications and type declarations the type <code class="inline">person()</code> is to be preferred
│ │ │ │  before <code class="inline">#person{}</code>.</p></section><h2 id="specifications-for-functions" class="section-heading">
│ │ │ │    <a href="#specifications-for-functions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Specifications for Functions</span>
│ │ │ │  </h2>
│ │ │ │  <p>A specification (or contract) for a function is given using the <code class="inline">-spec</code>
│ │ │ │  attribute. The general format is as follows:</p><pre><code class="text">-spec Function(ArgType1, ..., ArgTypeN) -&gt; ReturnType.</code></pre><p>An implementation of the function with the same name <code class="inline">Function</code> must exist in
│ │ │ │  the current module, and the arity of the function must match the number of
│ │ │ │  arguments, otherwise the compilation fails.</p><p>The following longer format with module name is also valid as long as <code class="inline">Module</code>
│ │ │ │  is the name of the current module. This can be useful for documentation
│ │ │ │  purposes.</p><pre><code class="text">-spec Module:Function(ArgType1, ..., ArgTypeN) -&gt; ReturnType.</code></pre><p>Also, for documentation purposes, argument names can be given:</p><pre><code class="text">-spec Function(ArgName1 :: Type1, ..., ArgNameN :: TypeN) -&gt; RT.</code></pre><p>A function specification can be overloaded. That is, it can have several types,
│ │ │ │ -separated by a semicolon (<code class="inline">;</code>). For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="7089773728-1">(</span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="7089773728-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T3</span><span class="p">;</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="7089773728-2">(</span><span class="n">T4</span><span class="p">,</span><span class="w"> </span><span class="n">T5</span><span class="p" data-group-id="7089773728-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T6</span><span class="p">.</span></code></pre><p>A current restriction, which currently results in a warning by Dialyzer, is that
│ │ │ │ +separated by a semicolon (<code class="inline">;</code>). For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="1229119574-1">(</span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="1229119574-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T3</span><span class="p">;</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="1229119574-2">(</span><span class="n">T4</span><span class="p">,</span><span class="w"> </span><span class="n">T5</span><span class="p" data-group-id="1229119574-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T6</span><span class="p">.</span></code></pre><p>A current restriction, which currently results in a warning by Dialyzer, is that
│ │ │ │  the domains of the argument types cannot overlap. For example, the following
│ │ │ │ -specification results in a warning:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="0130516479-1">(</span><span class="nf">pos_integer</span><span class="p" data-group-id="0130516479-2">(</span><span class="p" data-group-id="0130516479-2">)</span><span class="p" data-group-id="0130516479-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="0130516479-3">(</span><span class="p" data-group-id="0130516479-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="0130516479-4">(</span><span class="nf">integer</span><span class="p" data-group-id="0130516479-5">(</span><span class="p" data-group-id="0130516479-5">)</span><span class="p" data-group-id="0130516479-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0130516479-6">(</span><span class="p" data-group-id="0130516479-6">)</span><span class="p">.</span></code></pre><p>Type variables can be used in specifications to specify relations for the input
│ │ │ │ +specification results in a warning:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="0963245998-1">(</span><span class="nf">pos_integer</span><span class="p" data-group-id="0963245998-2">(</span><span class="p" data-group-id="0963245998-2">)</span><span class="p" data-group-id="0963245998-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="0963245998-3">(</span><span class="p" data-group-id="0963245998-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="0963245998-4">(</span><span class="nf">integer</span><span class="p" data-group-id="0963245998-5">(</span><span class="p" data-group-id="0963245998-5">)</span><span class="p" data-group-id="0963245998-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0963245998-6">(</span><span class="p" data-group-id="0963245998-6">)</span><span class="p">.</span></code></pre><p>Type variables can be used in specifications to specify relations for the input
│ │ │ │  and output arguments of a function. For example, the following specification
│ │ │ │  defines the type of a polymorphic identity function:</p><pre><code class="text">-spec id(X) -&gt; X.</code></pre><p>Notice that the above specification does not restrict the input and output type
│ │ │ │  in any way. These types can be constrained by guard-like subtype constraints and
│ │ │ │ -provide bounded quantification:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="7702189350-1">(</span><span class="n">X</span><span class="p" data-group-id="7702189350-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="7702189350-2">(</span><span class="p" data-group-id="7702189350-2">)</span><span class="p">.</span></code></pre><p>Currently, the <code class="inline">::</code> constraint (read as &quot;is a subtype of&quot;) is the only guard
│ │ │ │ +provide bounded quantification:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="9507685384-1">(</span><span class="n">X</span><span class="p" data-group-id="9507685384-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="9507685384-2">(</span><span class="p" data-group-id="9507685384-2">)</span><span class="p">.</span></code></pre><p>Currently, the <code class="inline">::</code> constraint (read as &quot;is a subtype of&quot;) is the only guard
│ │ │ │  constraint that can be used in the <code class="inline">when</code> part of a <code class="inline">-spec</code> attribute.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The above function specification uses multiple occurrences of the same type
│ │ │ │  variable. That provides more type information than the following function
│ │ │ │ -specification, where the type variables are missing:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="1039528047-1">(</span><span class="nf">tuple</span><span class="p" data-group-id="1039528047-2">(</span><span class="p" data-group-id="1039528047-2">)</span><span class="p" data-group-id="1039528047-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="1039528047-3">(</span><span class="p" data-group-id="1039528047-3">)</span><span class="p">.</span></code></pre><p>The latter specification says that the function takes some tuple and returns
│ │ │ │ +specification, where the type variables are missing:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="0926145592-1">(</span><span class="nf">tuple</span><span class="p" data-group-id="0926145592-2">(</span><span class="p" data-group-id="0926145592-2">)</span><span class="p" data-group-id="0926145592-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="0926145592-3">(</span><span class="p" data-group-id="0926145592-3">)</span><span class="p">.</span></code></pre><p>The latter specification says that the function takes some tuple and returns
│ │ │ │  some tuple. The specification with the <code class="inline">X</code> type variable specifies that the
│ │ │ │  function takes a tuple and returns <em>the same</em> tuple.</p><p>However, it is up to the tools that process the specifications to choose
│ │ │ │  whether to take this extra information into account or not.</p></section><p>The scope of a <code class="inline">::</code> constraint is the <code class="inline">(...) -&gt; RetType</code> specification after
│ │ │ │  which it appears. To avoid confusion, it is suggested that different variables
│ │ │ │  are used in different constituents of an overloaded contract, as shown in the
│ │ │ │ -following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="4533830333-1">(</span><span class="p" data-group-id="4533830333-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4533830333-3">(</span><span class="p" data-group-id="4533830333-3">)</span><span class="p" data-group-id="4533830333-2">}</span><span class="p" data-group-id="4533830333-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="4533830333-4">(</span><span class="p" data-group-id="4533830333-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="4533830333-5">(</span><span class="p" data-group-id="4533830333-6">[</span><span class="n">Y</span><span class="p" data-group-id="4533830333-6">]</span><span class="p" data-group-id="4533830333-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4533830333-7">(</span><span class="p" data-group-id="4533830333-7">)</span><span class="p">.</span></code></pre><p>Some functions in Erlang are not meant to return; either because they define
│ │ │ │ +following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="4170096164-1">(</span><span class="p" data-group-id="4170096164-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4170096164-3">(</span><span class="p" data-group-id="4170096164-3">)</span><span class="p" data-group-id="4170096164-2">}</span><span class="p" data-group-id="4170096164-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="4170096164-4">(</span><span class="p" data-group-id="4170096164-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="4170096164-5">(</span><span class="p" data-group-id="4170096164-6">[</span><span class="n">Y</span><span class="p" data-group-id="4170096164-6">]</span><span class="p" data-group-id="4170096164-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4170096164-7">(</span><span class="p" data-group-id="4170096164-7">)</span><span class="p">.</span></code></pre><p>Some functions in Erlang are not meant to return; either because they define
│ │ │ │  servers or because they are used to throw exceptions, as in the following
│ │ │ │ -function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_error</span><span class="p" data-group-id="7981672679-1">(</span><span class="n">Err</span><span class="p" data-group-id="7981672679-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="7981672679-2">(</span><span class="p" data-group-id="7981672679-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Err</span><span class="p" data-group-id="7981672679-3">}</span><span class="p" data-group-id="7981672679-2">)</span><span class="p">.</span></code></pre><p>For such functions, it is recommended to use the special <a href="../../../lib/../erts/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a> type
│ │ │ │ +function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_error</span><span class="p" data-group-id="2959599727-1">(</span><span class="n">Err</span><span class="p" data-group-id="2959599727-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="2959599727-2">(</span><span class="p" data-group-id="2959599727-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Err</span><span class="p" data-group-id="2959599727-3">}</span><span class="p" data-group-id="2959599727-2">)</span><span class="p">.</span></code></pre><p>For such functions, it is recommended to use the special <a href="../../../lib/../erts/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a> type
│ │ │ │  for their &quot;return&quot;, through a contract of the following form:</p><pre><code class="text">-spec my_error(term()) -&gt; no_return().</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Erlang uses the shorthand version <code class="inline">_</code> as an anonymous type variable equivalent
│ │ │ │  to <a href="../../../lib/../erts/doc/html/erlang.html#t:term/0"><code class="inline">term/0</code></a> or <a href="../../../lib/../erts/doc/html/erlang.html#t:any/0"><code class="inline">any/0</code></a>. For example, the following function</p><pre><code class="text">-spec Function(string(), _) -&gt; string().</code></pre><p>is equivalent to:</p><pre><code class="text">-spec Function(string(), any()) -&gt; string().</code></pre></section>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/tablesdatabases.xhtml
│ │ │ │ @@ -51,73 +51,73 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Deleting an Element</span>
│ │ │ │  </h3>
│ │ │ │  <p>The <code class="inline">delete</code> operation is considered successful if the element was not present
│ │ │ │  in the table. Hence all attempts to check that the element is present in the
│ │ │ │  Ets/Mnesia table before deletion are unnecessary. Here follows an example for
│ │ │ │ -Ets tables:</p><p><strong>DO</strong></p><pre><code class="text">ets:delete(Tab, Key),</code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="0565437883-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="0565437883-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0565437883-2">[</span><span class="p" data-group-id="0565437883-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +Ets tables:</p><p><strong>DO</strong></p><pre><code class="text">ets:delete(Tab, Key),</code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="9914093950-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9914093950-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9914093950-2">[</span><span class="p" data-group-id="9914093950-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0565437883-3">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="0565437883-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">ets</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="0565437883-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="0565437883-4">)</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9914093950-3">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="9914093950-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nc">ets</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="9914093950-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9914093950-4">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre><h3 id="fetching-data" class="section-heading">
│ │ │ │    <a href="#fetching-data" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Fetching Data</span>
│ │ │ │  </h3>
│ │ │ │  <p>Do not fetch data that you already have.</p><p>Consider that you have a module that handles the abstract data type <code class="inline">Person</code>.
│ │ │ │  You export the interface function <code class="inline">print_person/1</code>, which uses the internal
│ │ │ │  functions <code class="inline">print_name/1</code>, <code class="inline">print_age/1</code>, and <code class="inline">print_occupation/1</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>If the function <code class="inline">print_name/1</code>, and so on, had been interface functions, the
│ │ │ │  situation would have been different, as you do not want the user of the
│ │ │ │  interface to know about the internal data representation.</p></section><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ │ -</span><span class="nf">print_person</span><span class="p" data-group-id="1960842229-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="1960842229-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">print_person</span><span class="p" data-group-id="8790964226-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="8790964226-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Look up the person in the named table person,</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="1960842229-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="1960842229-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1960842229-3">[</span><span class="n">Person</span><span class="p" data-group-id="1960842229-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_name</span><span class="p" data-group-id="1960842229-4">(</span><span class="n">Person</span><span class="p" data-group-id="1960842229-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_age</span><span class="p" data-group-id="1960842229-5">(</span><span class="n">Person</span><span class="p" data-group-id="1960842229-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_occupation</span><span class="p" data-group-id="1960842229-6">(</span><span class="n">Person</span><span class="p" data-group-id="1960842229-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1960842229-7">[</span><span class="p" data-group-id="1960842229-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1960842229-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1960842229-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="1960842229-9">]</span><span class="p" data-group-id="1960842229-8">)</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="8790964226-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="8790964226-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8790964226-3">[</span><span class="n">Person</span><span class="p" data-group-id="8790964226-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_name</span><span class="p" data-group-id="8790964226-4">(</span><span class="n">Person</span><span class="p" data-group-id="8790964226-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_age</span><span class="p" data-group-id="8790964226-5">(</span><span class="n">Person</span><span class="p" data-group-id="8790964226-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_occupation</span><span class="p" data-group-id="8790964226-6">(</span><span class="n">Person</span><span class="p" data-group-id="8790964226-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8790964226-7">[</span><span class="p" data-group-id="8790964226-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8790964226-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8790964226-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="8790964226-9">]</span><span class="p" data-group-id="8790964226-8">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Internal functions</span><span class="w">
│ │ │ │ -</span><span class="nf">print_name</span><span class="p" data-group-id="1960842229-10">(</span><span class="n">Person</span><span class="p" data-group-id="1960842229-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1960842229-11">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1960842229-12">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="1960842229-12">]</span><span class="p" data-group-id="1960842229-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">print_name</span><span class="p" data-group-id="8790964226-10">(</span><span class="n">Person</span><span class="p" data-group-id="8790964226-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8790964226-11">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8790964226-12">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="8790964226-12">]</span><span class="p" data-group-id="8790964226-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">print_age</span><span class="p" data-group-id="1960842229-13">(</span><span class="n">Person</span><span class="p" data-group-id="1960842229-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1960842229-14">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1960842229-15">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="1960842229-15">]</span><span class="p" data-group-id="1960842229-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">print_age</span><span class="p" data-group-id="8790964226-13">(</span><span class="n">Person</span><span class="p" data-group-id="8790964226-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8790964226-14">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8790964226-15">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="8790964226-15">]</span><span class="p" data-group-id="8790964226-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">print_occupation</span><span class="p" data-group-id="1960842229-16">(</span><span class="n">Person</span><span class="p" data-group-id="1960842229-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1960842229-17">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1960842229-18">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="1960842229-18">]</span><span class="p" data-group-id="1960842229-17">)</span><span class="p">.</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ │ -</span><span class="nf">print_person</span><span class="p" data-group-id="3873865410-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="3873865410-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">print_occupation</span><span class="p" data-group-id="8790964226-16">(</span><span class="n">Person</span><span class="p" data-group-id="8790964226-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8790964226-17">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8790964226-18">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="8790964226-18">]</span><span class="p" data-group-id="8790964226-17">)</span><span class="p">.</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ │ +</span><span class="nf">print_person</span><span class="p" data-group-id="3746737535-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="3746737535-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Look up the person in the named table person,</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="3873865410-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="3873865410-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="3873865410-3">[</span><span class="n">Person</span><span class="p" data-group-id="3873865410-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_name</span><span class="p" data-group-id="3873865410-4">(</span><span class="n">PersonID</span><span class="p" data-group-id="3873865410-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_age</span><span class="p" data-group-id="3873865410-5">(</span><span class="n">PersonID</span><span class="p" data-group-id="3873865410-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_occupation</span><span class="p" data-group-id="3873865410-6">(</span><span class="n">PersonID</span><span class="p" data-group-id="3873865410-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="3873865410-7">[</span><span class="p" data-group-id="3873865410-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3873865410-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3873865410-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="3873865410-9">]</span><span class="p" data-group-id="3873865410-8">)</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="3746737535-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="3746737535-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3746737535-3">[</span><span class="n">Person</span><span class="p" data-group-id="3746737535-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_name</span><span class="p" data-group-id="3746737535-4">(</span><span class="n">PersonID</span><span class="p" data-group-id="3746737535-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_age</span><span class="p" data-group-id="3746737535-5">(</span><span class="n">PersonID</span><span class="p" data-group-id="3746737535-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_occupation</span><span class="p" data-group-id="3746737535-6">(</span><span class="n">PersonID</span><span class="p" data-group-id="3746737535-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3746737535-7">[</span><span class="p" data-group-id="3746737535-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3746737535-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3746737535-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="3746737535-9">]</span><span class="p" data-group-id="3746737535-8">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Internal functions</span><span class="w">
│ │ │ │ -</span><span class="nf">print_name</span><span class="p" data-group-id="3873865410-10">(</span><span class="n">PersonID</span><span class="p" data-group-id="3873865410-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3873865410-11">[</span><span class="n">Person</span><span class="p" data-group-id="3873865410-11">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="3873865410-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="3873865410-12">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3873865410-13">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3873865410-14">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="3873865410-14">]</span><span class="p" data-group-id="3873865410-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">print_age</span><span class="p" data-group-id="3873865410-15">(</span><span class="n">PersonID</span><span class="p" data-group-id="3873865410-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3873865410-16">[</span><span class="n">Person</span><span class="p" data-group-id="3873865410-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="3873865410-17">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="3873865410-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3873865410-18">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3873865410-19">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="3873865410-19">]</span><span class="p" data-group-id="3873865410-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">print_occupation</span><span class="p" data-group-id="3873865410-20">(</span><span class="n">PersonID</span><span class="p" data-group-id="3873865410-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3873865410-21">[</span><span class="n">Person</span><span class="p" data-group-id="3873865410-21">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="3873865410-22">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="3873865410-22">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3873865410-23">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3873865410-24">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="3873865410-24">]</span><span class="p" data-group-id="3873865410-23">)</span><span class="p">.</span></code></pre><h3 id="non-persistent-database-storage" class="section-heading">
│ │ │ │ +</span><span class="nf">print_name</span><span class="p" data-group-id="3746737535-10">(</span><span class="n">PersonID</span><span class="p" data-group-id="3746737535-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3746737535-11">[</span><span class="n">Person</span><span class="p" data-group-id="3746737535-11">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="3746737535-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="3746737535-12">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3746737535-13">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3746737535-14">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="3746737535-14">]</span><span class="p" data-group-id="3746737535-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">print_age</span><span class="p" data-group-id="3746737535-15">(</span><span class="n">PersonID</span><span class="p" data-group-id="3746737535-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3746737535-16">[</span><span class="n">Person</span><span class="p" data-group-id="3746737535-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="3746737535-17">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="3746737535-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3746737535-18">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3746737535-19">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="3746737535-19">]</span><span class="p" data-group-id="3746737535-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">print_occupation</span><span class="p" data-group-id="3746737535-20">(</span><span class="n">PersonID</span><span class="p" data-group-id="3746737535-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3746737535-21">[</span><span class="n">Person</span><span class="p" data-group-id="3746737535-21">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="3746737535-22">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="3746737535-22">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3746737535-23">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3746737535-24">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="3746737535-24">]</span><span class="p" data-group-id="3746737535-23">)</span><span class="p">.</span></code></pre><h3 id="non-persistent-database-storage" class="section-heading">
│ │ │ │    <a href="#non-persistent-database-storage" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Non-Persistent Database Storage</span>
│ │ │ │  </h3>
│ │ │ │  <p>For non-persistent database storage, prefer Ets tables over Mnesia
│ │ │ │  <code class="inline">local_content</code> tables. Even the Mnesia <code class="inline">dirty_write</code> operations carry a fixed
│ │ │ │ @@ -131,38 +131,38 @@
│ │ │ │  </h3>
│ │ │ │  <p>Assuming an Ets table that uses <code class="inline">idno</code> as key and contains the following:</p><pre><code class="text">[#person{idno = 1, name = &quot;Adam&quot;,  age = 31, occupation = &quot;mailman&quot;},
│ │ │ │   #person{idno = 2, name = &quot;Bryan&quot;, age = 31, occupation = &quot;cashier&quot;},
│ │ │ │   #person{idno = 3, name = &quot;Bryan&quot;, age = 35, occupation = &quot;banker&quot;},
│ │ │ │   #person{idno = 4, name = &quot;Carl&quot;,  age = 25, occupation = &quot;mailman&quot;}]</code></pre><p>If you <em>must</em> return all data stored in the Ets table, you can use
│ │ │ │  <a href="../../../lib/stdlib/doc/html/ets.html#tab2list/1"><code class="inline">ets:tab2list/1</code></a>. However, usually you are only interested in a subset of the
│ │ │ │  information in which case <a href="../../../lib/stdlib/doc/html/ets.html#tab2list/1"><code class="inline">ets:tab2list/1</code></a> is expensive. If you only want to
│ │ │ │ -extract one field from each record, for example, the age of every person, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="6093147796-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6093147796-2">[</span><span class="p" data-group-id="6093147796-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6093147796-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ +extract one field from each record, for example, the age of every person, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="4051134412-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4051134412-2">[</span><span class="p" data-group-id="4051134412-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4051134412-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;$1&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6093147796-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="6093147796-5">[</span><span class="p" data-group-id="6093147796-5">]</span><span class="p">,</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="6093147796-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="6093147796-6">]</span><span class="p" data-group-id="6093147796-3">}</span><span class="p" data-group-id="6093147796-2">]</span><span class="p" data-group-id="6093147796-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="0146552570-1">(</span><span class="n">Tab</span><span class="p" data-group-id="0146552570-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0146552570-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0146552570-3">(</span><span class="n">X</span><span class="p" data-group-id="0146552570-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="0146552570-2">)</span><span class="p">,</span></code></pre><p>If you are only interested in the age of all persons named &quot;Bryan&quot;, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="1062584558-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1062584558-2">[</span><span class="p" data-group-id="1062584558-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1062584558-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="4051134412-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="4051134412-5">[</span><span class="p" data-group-id="4051134412-5">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="4051134412-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="4051134412-6">]</span><span class="p" data-group-id="4051134412-3">}</span><span class="p" data-group-id="4051134412-2">]</span><span class="p" data-group-id="4051134412-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="0943293869-1">(</span><span class="n">Tab</span><span class="p" data-group-id="0943293869-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0943293869-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0943293869-3">(</span><span class="n">X</span><span class="p" data-group-id="0943293869-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="0943293869-2">)</span><span class="p">,</span></code></pre><p>If you are only interested in the age of all persons named &quot;Bryan&quot;, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="2679387051-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679387051-2">[</span><span class="p" data-group-id="2679387051-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2679387051-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Bryan&quot;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;$1&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="1062584558-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="1062584558-5">[</span><span class="p" data-group-id="1062584558-5">]</span><span class="p">,</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="1062584558-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="1062584558-6">]</span><span class="p" data-group-id="1062584558-3">}</span><span class="p" data-group-id="1062584558-2">]</span><span class="p" data-group-id="1062584558-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="9440219456-1">(</span><span class="n">Tab</span><span class="p" data-group-id="9440219456-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="9440219456-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9440219456-3">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9440219456-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="2679387051-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="2679387051-5">[</span><span class="p" data-group-id="2679387051-5">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="2679387051-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="2679387051-6">]</span><span class="p" data-group-id="2679387051-3">}</span><span class="p" data-group-id="2679387051-2">]</span><span class="p" data-group-id="2679387051-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="9277438687-1">(</span><span class="n">Tab</span><span class="p" data-group-id="9277438687-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="9277438687-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9277438687-3">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9277438687-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │                                  </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                                    </span><span class="p" data-group-id="9440219456-4">[</span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="9440219456-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ +                                    </span><span class="p" data-group-id="9277438687-4">[</span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="9277438687-4">]</span><span class="p">;</span><span class="w">
│ │ │ │                                   </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                                       </span><span class="n">Acc</span><span class="w">
│ │ │ │                             </span><span class="k">end</span><span class="w">
│ │ │ │ -             </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9440219456-5">[</span><span class="p" data-group-id="9440219456-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="9440219456-2">)</span></code></pre><p>If you need all information stored in the Ets table about persons named &quot;Bryan&quot;,
│ │ │ │ -then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="9263966817-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9263966817-2">[</span><span class="p" data-group-id="9263966817-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9263966817-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9277438687-5">[</span><span class="p" data-group-id="9277438687-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="9277438687-2">)</span></code></pre><p>If you need all information stored in the Ets table about persons named &quot;Bryan&quot;,
│ │ │ │ +then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="8963697480-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8963697480-2">[</span><span class="p" data-group-id="8963697480-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8963697480-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Bryan&quot;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="9263966817-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9263966817-5">[</span><span class="p" data-group-id="9263966817-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9263966817-6">[</span><span class="ss">&#39;$_&#39;</span><span class="p" data-group-id="9263966817-6">]</span><span class="p" data-group-id="9263966817-3">}</span><span class="p" data-group-id="9263966817-2">]</span><span class="p" data-group-id="9263966817-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="3430804301-1">(</span><span class="n">Tab</span><span class="p" data-group-id="3430804301-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="3430804301-2">(</span><span class="nf">fun</span><span class="p" data-group-id="3430804301-3">(</span><span class="n">X</span><span class="p" data-group-id="3430804301-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="3430804301-2">)</span><span class="p">,</span></code></pre><h3 id="ordered_set-tables" class="section-heading">
│ │ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="8963697480-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8963697480-5">[</span><span class="p" data-group-id="8963697480-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8963697480-6">[</span><span class="ss">&#39;$_&#39;</span><span class="p" data-group-id="8963697480-6">]</span><span class="p" data-group-id="8963697480-3">}</span><span class="p" data-group-id="8963697480-2">]</span><span class="p" data-group-id="8963697480-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="7047999516-1">(</span><span class="n">Tab</span><span class="p" data-group-id="7047999516-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="7047999516-2">(</span><span class="nf">fun</span><span class="p" data-group-id="7047999516-3">(</span><span class="n">X</span><span class="p" data-group-id="7047999516-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="7047999516-2">)</span><span class="p">,</span></code></pre><h3 id="ordered_set-tables" class="section-heading">
│ │ │ │    <a href="#ordered_set-tables" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text"><code class="inline">ordered_set</code> Tables</span>
│ │ │ │  </h3>
│ │ │ │  <p>If the data in the table is to be accessed so that the order of the keys in the
│ │ │ │  table is significant, the table type <code class="inline">ordered_set</code> can be used instead of the
│ │ │ │ @@ -198,20 +198,20 @@
│ │ │ │  Clearly, the second table would have to be kept consistent with the master
│ │ │ │  table. Mnesia can do this for you, but a home-brew index table can be very
│ │ │ │  efficient compared to the overhead involved in using Mnesia.</p><p>An index table for the table in the previous examples would have to be a bag (as
│ │ │ │  keys would appear more than once) and can have the following contents:</p><pre><code class="text">[#index_entry{name=&quot;Adam&quot;, idno=1},
│ │ │ │   #index_entry{name=&quot;Bryan&quot;, idno=2},
│ │ │ │   #index_entry{name=&quot;Bryan&quot;, idno=3},
│ │ │ │   #index_entry{name=&quot;Carl&quot;, idno=4}]</code></pre><p>Given this index table, a lookup of the <code class="inline">age</code> fields for all persons named
│ │ │ │ -&quot;Bryan&quot; can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">MatchingIDs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="1182589036-1">(</span><span class="n">IndexTable</span><span class="p">,</span><span class="s">&quot;Bryan&quot;</span><span class="p" data-group-id="1182589036-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1182589036-2">(</span><span class="nf">fun</span><span class="p" data-group-id="1182589036-3">(</span><span class="o">#</span><span class="ss">index_entry</span><span class="p" data-group-id="1182589036-4">{</span><span class="ss">idno</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="1182589036-4">}</span><span class="p" data-group-id="1182589036-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="1182589036-5">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1182589036-6">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="1182589036-6">}</span><span class="p" data-group-id="1182589036-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="1182589036-7">(</span><span class="n">PersonTable</span><span class="p">,</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="1182589036-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +&quot;Bryan&quot; can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">MatchingIDs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="9490967193-1">(</span><span class="n">IndexTable</span><span class="p">,</span><span class="s">&quot;Bryan&quot;</span><span class="p" data-group-id="9490967193-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="9490967193-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9490967193-3">(</span><span class="o">#</span><span class="ss">index_entry</span><span class="p" data-group-id="9490967193-4">{</span><span class="ss">idno</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="9490967193-4">}</span><span class="p" data-group-id="9490967193-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="9490967193-5">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9490967193-6">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="9490967193-6">}</span><span class="p" data-group-id="9490967193-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="9490967193-7">(</span><span class="n">PersonTable</span><span class="p">,</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="9490967193-7">)</span><span class="p">,</span><span class="w">
│ │ │ │                   </span><span class="n">Age</span><span class="w">
│ │ │ │            </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="n">MatchingIDs</span><span class="p" data-group-id="1182589036-2">)</span><span class="p">,</span></code></pre><p>Notice that this code does not use <a href="../../../lib/stdlib/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>, but instead uses the
│ │ │ │ +          </span><span class="n">MatchingIDs</span><span class="p" data-group-id="9490967193-2">)</span><span class="p">,</span></code></pre><p>Notice that this code does not use <a href="../../../lib/stdlib/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>, but instead uses the
│ │ │ │  <a href="../../../lib/stdlib/doc/html/ets.html#lookup/2"><code class="inline">ets:lookup/2</code></a> call. The <a href="../../../lib/stdlib/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> call is only used to traverse the <code class="inline">idno</code>s
│ │ │ │  matching the name &quot;Bryan&quot; in the table; thus the number of lookups in the master
│ │ │ │  table is minimized.</p><p>Keeping an index table introduces some overhead when inserting records in the
│ │ │ │  table. The number of operations gained from the table must therefore be compared
│ │ │ │  against the number of operations inserting objects in the table. However, notice
│ │ │ │  that the gain is significant when the key can be used to lookup elements.</p><h2 id="mnesia" class="section-heading">
│ │ │ │    <a href="#mnesia" class="hover-link">
│ │ │ │ @@ -226,47 +226,47 @@
│ │ │ │    <span class="text">Secondary Index</span>
│ │ │ │  </h3>
│ │ │ │  <p>If you frequently do lookups on a field that is not the key of the table, you
│ │ │ │  lose performance using <a href="../../../lib/mnesia/doc/html/mnesia.html#select/3">mnesia:select()</a> or
│ │ │ │  <a href="../../../lib/mnesia/doc/html/mnesia.html#match_object/1"><code class="inline">mnesia:match_object()</code></a> as these function traverse
│ │ │ │  the whole table. Instead, you can create a secondary index and use
│ │ │ │  <a href="../../../lib/mnesia/doc/html/mnesia.html#index_read/3"><code class="inline">mnesia:index_read/3</code></a> to get faster access at the expense of using more
│ │ │ │ -memory.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9688778945-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9688778945-2">{</span><span class="ss">idno</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">occupation</span><span class="p" data-group-id="9688778945-2">}</span><span class="p" data-group-id="9688778945-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +memory.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3430096026-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3430096026-2">{</span><span class="ss">idno</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">occupation</span><span class="p" data-group-id="3430096026-2">}</span><span class="p" data-group-id="3430096026-1">)</span><span class="p">.</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9688778945-3">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="9688778945-3">}</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ -</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">create_table</span><span class="p" data-group-id="9688778945-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9688778945-5">[</span><span class="p" data-group-id="9688778945-6">{</span><span class="ss">index</span><span class="p">,</span><span class="p" data-group-id="9688778945-7">[</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="9688778945-7">]</span><span class="p" data-group-id="9688778945-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                              </span><span class="p" data-group-id="9688778945-8">{</span><span class="ss">attributes</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="nf">record_info</span><span class="p" data-group-id="9688778945-9">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="9688778945-9">)</span><span class="p" data-group-id="9688778945-8">}</span><span class="p" data-group-id="9688778945-5">]</span><span class="p" data-group-id="9688778945-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9688778945-10">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="9688778945-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">add_table_index</span><span class="p" data-group-id="9688778945-11">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="9688778945-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3430096026-3">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="3430096026-3">}</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ +</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">create_table</span><span class="p" data-group-id="3430096026-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3430096026-5">[</span><span class="p" data-group-id="3430096026-6">{</span><span class="ss">index</span><span class="p">,</span><span class="p" data-group-id="3430096026-7">[</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="3430096026-7">]</span><span class="p" data-group-id="3430096026-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                              </span><span class="p" data-group-id="3430096026-8">{</span><span class="ss">attributes</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="nf">record_info</span><span class="p" data-group-id="3430096026-9">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="3430096026-9">)</span><span class="p" data-group-id="3430096026-8">}</span><span class="p" data-group-id="3430096026-5">]</span><span class="p" data-group-id="3430096026-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3430096026-10">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="3430096026-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">add_table_index</span><span class="p" data-group-id="3430096026-11">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="3430096026-11">)</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="n">PersonsAge42</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ -     </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_index_read</span><span class="p" data-group-id="9688778945-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="9688778945-12">)</span><span class="p">,</span></code></pre><h3 id="transactions" class="section-heading">
│ │ │ │ +     </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_index_read</span><span class="p" data-group-id="3430096026-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="3430096026-12">)</span><span class="p">,</span></code></pre><h3 id="transactions" class="section-heading">
│ │ │ │    <a href="#transactions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Transactions</span>
│ │ │ │  </h3>
│ │ │ │  <p>Using transactions is a way to guarantee that the distributed Mnesia database
│ │ │ │  remains consistent, even when many different processes update it in parallel.
│ │ │ │  However, if you have real-time requirements it is recommended to use dirtry
│ │ │ │  operations instead of transactions. When using dirty operations, you lose the
│ │ │ │  consistency guarantee; this is usually solved by only letting one process update
│ │ │ │  the table. Other processes must send update requests to that process.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Using transaction</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9352115188-1">(</span><span class="p" data-group-id="9352115188-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="9352115188-2">[</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="9352115188-3">(</span><span class="p" data-group-id="9352115188-4">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9352115188-4">}</span><span class="p" data-group-id="9352115188-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -           </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="9352115188-5">(</span><span class="p" data-group-id="9352115188-6">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="9352115188-6">}</span><span class="p" data-group-id="9352115188-5">)</span><span class="p" data-group-id="9352115188-2">]</span><span class="w">
│ │ │ │ +</span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="2026838403-1">(</span><span class="p" data-group-id="2026838403-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="2026838403-2">[</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="2026838403-3">(</span><span class="p" data-group-id="2026838403-4">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="2026838403-4">}</span><span class="p" data-group-id="2026838403-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +           </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="2026838403-5">(</span><span class="p" data-group-id="2026838403-6">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="2026838403-6">}</span><span class="p" data-group-id="2026838403-5">)</span><span class="p" data-group-id="2026838403-2">]</span><span class="w">
│ │ │ │        </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p" data-group-id="9352115188-7">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9352115188-8">[</span><span class="n">Result1</span><span class="p">,</span><span class="w"> </span><span class="n">Result2</span><span class="p" data-group-id="9352115188-8">]</span><span class="p" data-group-id="9352115188-7">}</span><span class="w">  </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">transaction</span><span class="p" data-group-id="9352115188-9">(</span><span class="n">Fun</span><span class="p" data-group-id="9352115188-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2026838403-7">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2026838403-8">[</span><span class="n">Result1</span><span class="p">,</span><span class="w"> </span><span class="n">Result2</span><span class="p" data-group-id="2026838403-8">]</span><span class="p" data-group-id="2026838403-7">}</span><span class="w">  </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">transaction</span><span class="p" data-group-id="2026838403-9">(</span><span class="n">Fun</span><span class="p" data-group-id="2026838403-9">)</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% Same thing using dirty operations</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Result1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="9352115188-10">(</span><span class="p" data-group-id="9352115188-11">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9352115188-11">}</span><span class="p" data-group-id="9352115188-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Result2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="9352115188-12">(</span><span class="p" data-group-id="9352115188-13">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="9352115188-13">}</span><span class="p" data-group-id="9352115188-12">)</span><span class="p">,</span></code></pre>
│ │ │ │ +</span><span class="n">Result1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="2026838403-10">(</span><span class="p" data-group-id="2026838403-11">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="2026838403-11">}</span><span class="p" data-group-id="2026838403-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Result2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="2026838403-12">(</span><span class="p" data-group-id="2026838403-13">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="2026838403-13">}</span><span class="p" data-group-id="2026838403-12">)</span><span class="p">,</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/sup_princ.xhtml
│ │ │ │ @@ -33,48 +33,48 @@
│ │ │ │  the order specified by this list, and are terminated in the reverse order.</p><h2 id="example" class="section-heading">
│ │ │ │    <a href="#example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example</span>
│ │ │ │  </h2>
│ │ │ │  <p>The callback module for a supervisor starting the server from
│ │ │ │ -<a href="gen_server_concepts.xhtml#ex">gen_server Behaviour</a> can look as follows:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3025335136-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="3025335136-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3025335136-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="3025335136-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<a href="gen_server_concepts.xhtml#ex">gen_server Behaviour</a> can look as follows:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4744272221-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="4744272221-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4744272221-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="4744272221-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3025335136-3">(</span><span class="p" data-group-id="3025335136-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3025335136-4">]</span><span class="p" data-group-id="3025335136-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3025335136-5">(</span><span class="p" data-group-id="3025335136-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3025335136-6">]</span><span class="p" data-group-id="3025335136-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4744272221-3">(</span><span class="p" data-group-id="4744272221-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4744272221-4">]</span><span class="p" data-group-id="4744272221-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4744272221-5">(</span><span class="p" data-group-id="4744272221-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4744272221-6">]</span><span class="p" data-group-id="4744272221-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="3025335136-7">(</span><span class="p" data-group-id="3025335136-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3025335136-8">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3025335136-9">[</span><span class="p" data-group-id="3025335136-9">]</span><span class="p" data-group-id="3025335136-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="4744272221-7">(</span><span class="p" data-group-id="4744272221-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4744272221-8">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4744272221-9">[</span><span class="p" data-group-id="4744272221-9">]</span><span class="p" data-group-id="4744272221-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="3025335136-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="3025335136-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3025335136-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_one</span><span class="p">,</span><span class="w"> </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="3025335136-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3025335136-12">[</span><span class="p" data-group-id="3025335136-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3025335136-14">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3025335136-15">[</span><span class="p" data-group-id="3025335136-15">]</span><span class="p" data-group-id="3025335136-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="4744272221-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="4744272221-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4744272221-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_one</span><span class="p">,</span><span class="w"> </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="4744272221-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4744272221-12">[</span><span class="p" data-group-id="4744272221-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4744272221-14">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4744272221-15">[</span><span class="p" data-group-id="4744272221-15">]</span><span class="p" data-group-id="4744272221-14">}</span><span class="p">,</span><span class="w">
│ │ │ │                      </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">permanent</span><span class="p">,</span><span class="w">
│ │ │ │                      </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w">
│ │ │ │                      </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3025335136-16">[</span><span class="ss">ch3</span><span class="p" data-group-id="3025335136-16">]</span><span class="p" data-group-id="3025335136-13">}</span><span class="p" data-group-id="3025335136-12">]</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3025335136-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3025335136-18">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="3025335136-18">}</span><span class="p" data-group-id="3025335136-17">}</span><span class="p">.</span></code></pre><p>The <code class="inline">SupFlags</code> variable in the return value from <code class="inline">init/1</code> represents the
│ │ │ │ +                    </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4744272221-16">[</span><span class="ss">ch3</span><span class="p" data-group-id="4744272221-16">]</span><span class="p" data-group-id="4744272221-13">}</span><span class="p" data-group-id="4744272221-12">]</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4744272221-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4744272221-18">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="4744272221-18">}</span><span class="p" data-group-id="4744272221-17">}</span><span class="p">.</span></code></pre><p>The <code class="inline">SupFlags</code> variable in the return value from <code class="inline">init/1</code> represents the
│ │ │ │  <a href="sup_princ.xhtml#flags">supervisor flags</a>.</p><p>The <code class="inline">ChildSpecs</code> variable in the return value from <code class="inline">init/1</code> is a list of
│ │ │ │  <a href="sup_princ.xhtml#spec">child specifications</a>.</p><p><a href="" id="flags"></a></p><h2 id="supervisor-flags" class="section-heading">
│ │ │ │    <a href="#supervisor-flags" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Supervisor Flags</span>
│ │ │ │  </h2>
│ │ │ │ -<p>This is the type definition for the supervisor flags:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sup_flags</span><span class="p" data-group-id="0029299332-1">(</span><span class="p" data-group-id="0029299332-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0029299332-2">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">strategy</span><span class="p" data-group-id="0029299332-3">(</span><span class="p" data-group-id="0029299332-3">)</span><span class="p">,</span><span class="w">           </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="0029299332-4">(</span><span class="p" data-group-id="0029299332-4">)</span><span class="p">,</span><span class="w">   </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="0029299332-5">(</span><span class="p" data-group-id="0029299332-5">)</span><span class="p">,</span><span class="w">          </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                </span><span class="ss">auto_shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="0029299332-6">(</span><span class="p" data-group-id="0029299332-6">)</span><span class="p" data-group-id="0029299332-2">}</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -    </span><span class="nf">strategy</span><span class="p" data-group-id="0029299332-7">(</span><span class="p" data-group-id="0029299332-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">one_for_all</span><span class="w">
│ │ │ │ +<p>This is the type definition for the supervisor flags:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sup_flags</span><span class="p" data-group-id="0588224755-1">(</span><span class="p" data-group-id="0588224755-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0588224755-2">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">strategy</span><span class="p" data-group-id="0588224755-3">(</span><span class="p" data-group-id="0588224755-3">)</span><span class="p">,</span><span class="w">           </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="0588224755-4">(</span><span class="p" data-group-id="0588224755-4">)</span><span class="p">,</span><span class="w">   </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="0588224755-5">(</span><span class="p" data-group-id="0588224755-5">)</span><span class="p">,</span><span class="w">          </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                </span><span class="ss">auto_shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="0588224755-6">(</span><span class="p" data-group-id="0588224755-6">)</span><span class="p" data-group-id="0588224755-2">}</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +    </span><span class="nf">strategy</span><span class="p" data-group-id="0588224755-7">(</span><span class="p" data-group-id="0588224755-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">one_for_all</span><span class="w">
│ │ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">one_for_one</span><span class="w">
│ │ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">rest_for_one</span><span class="w">
│ │ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="w">
│ │ │ │ -    </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="0029299332-8">(</span><span class="p" data-group-id="0029299332-8">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">never</span><span class="w">
│ │ │ │ +    </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="0588224755-8">(</span><span class="p" data-group-id="0588224755-8">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">never</span><span class="w">
│ │ │ │                      </span><span class="p">|</span><span class="w"> </span><span class="ss">any_significant</span><span class="w">
│ │ │ │                      </span><span class="p">|</span><span class="w"> </span><span class="ss">all_significant</span></code></pre><ul><li><code class="inline">strategy</code> specifies the <a href="sup_princ.xhtml#strategy">restart strategy</a>.</li><li><code class="inline">intensity</code> and <code class="inline">period</code> specify the
│ │ │ │  <a href="sup_princ.xhtml#max_intensity">maximum restart intensity</a>.</li><li><code class="inline">auto_shutdown</code> specifies whether and when a supervisor should
│ │ │ │  <a href="sup_princ.xhtml#automatic-shutdown">automatically shut itself down</a>.</li></ul><p><a href="" id="strategy"></a></p><h2 id="restart-strategy" class="section-heading">
│ │ │ │    <a href="#restart-strategy" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -313,28 +313,28 @@
│ │ │ │  exhaust the <a href="sup_princ.xhtml#max_intensity">Maximum Restart Intensity</a> of the
│ │ │ │  parent supervisor.</p></section><p><a href="" id="spec"></a></p><h2 id="child-specification" class="section-heading">
│ │ │ │    <a href="#child-specification" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Child Specification</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The type definition for a child specification is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">child_spec</span><span class="p" data-group-id="8826226942-1">(</span><span class="p" data-group-id="8826226942-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8826226942-2">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">child_id</span><span class="p" data-group-id="8826226942-3">(</span><span class="p" data-group-id="8826226942-3">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% mandatory</span><span class="w">
│ │ │ │ -                 </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">mfargs</span><span class="p" data-group-id="8826226942-4">(</span><span class="p" data-group-id="8826226942-4">)</span><span class="p">,</span><span class="w">            </span><span class="c1">% mandatory</span><span class="w">
│ │ │ │ -                 </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">restart</span><span class="p" data-group-id="8826226942-5">(</span><span class="p" data-group-id="8826226942-5">)</span><span class="p">,</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                 </span><span class="ss">significant</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">significant</span><span class="p" data-group-id="8826226942-6">(</span><span class="p" data-group-id="8826226942-6">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                 </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">shutdown</span><span class="p" data-group-id="8826226942-7">(</span><span class="p" data-group-id="8826226942-7">)</span><span class="p">,</span><span class="w">       </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                 </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">worker</span><span class="p" data-group-id="8826226942-8">(</span><span class="p" data-group-id="8826226942-8">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                 </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">modules</span><span class="p" data-group-id="8826226942-9">(</span><span class="p" data-group-id="8826226942-9">)</span><span class="p" data-group-id="8826226942-2">}</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -    </span><span class="nf">child_id</span><span class="p" data-group-id="8826226942-10">(</span><span class="p" data-group-id="8826226942-10">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="8826226942-11">(</span><span class="p" data-group-id="8826226942-11">)</span><span class="w">
│ │ │ │ -    </span><span class="nf">mfargs</span><span class="p" data-group-id="8826226942-12">(</span><span class="p" data-group-id="8826226942-12">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8826226942-13">{</span><span class="n">M</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">module</span><span class="p" data-group-id="8826226942-14">(</span><span class="p" data-group-id="8826226942-14">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="8826226942-15">(</span><span class="p" data-group-id="8826226942-15">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="8826226942-16">[</span><span class="nf">term</span><span class="p" data-group-id="8826226942-17">(</span><span class="p" data-group-id="8826226942-17">)</span><span class="p" data-group-id="8826226942-16">]</span><span class="p" data-group-id="8826226942-13">}</span><span class="w">
│ │ │ │ -    </span><span class="nf">modules</span><span class="p" data-group-id="8826226942-18">(</span><span class="p" data-group-id="8826226942-18">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8826226942-19">[</span><span class="nf">module</span><span class="p" data-group-id="8826226942-20">(</span><span class="p" data-group-id="8826226942-20">)</span><span class="p" data-group-id="8826226942-19">]</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">dynamic</span><span class="w">
│ │ │ │ -    </span><span class="nf">restart</span><span class="p" data-group-id="8826226942-21">(</span><span class="p" data-group-id="8826226942-21">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">permanent</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">transient</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">temporary</span><span class="w">
│ │ │ │ -    </span><span class="nf">significant</span><span class="p" data-group-id="8826226942-22">(</span><span class="p" data-group-id="8826226942-22">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="8826226942-23">(</span><span class="p" data-group-id="8826226942-23">)</span><span class="w">
│ │ │ │ -    </span><span class="nf">shutdown</span><span class="p" data-group-id="8826226942-24">(</span><span class="p" data-group-id="8826226942-24">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">timeout</span><span class="p" data-group-id="8826226942-25">(</span><span class="p" data-group-id="8826226942-25">)</span><span class="w">
│ │ │ │ -    </span><span class="nf">worker</span><span class="p" data-group-id="8826226942-26">(</span><span class="p" data-group-id="8826226942-26">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">worker</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">supervisor</span></code></pre><ul><li><p><code class="inline">id</code> is used to identify the child specification internally by the supervisor.</p><p>The <code class="inline">id</code> key is mandatory.</p><p>Note that this identifier occasionally has been called &quot;name&quot;. As far as
│ │ │ │ +<p>The type definition for a child specification is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">child_spec</span><span class="p" data-group-id="6039056691-1">(</span><span class="p" data-group-id="6039056691-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6039056691-2">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">child_id</span><span class="p" data-group-id="6039056691-3">(</span><span class="p" data-group-id="6039056691-3">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% mandatory</span><span class="w">
│ │ │ │ +                 </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">mfargs</span><span class="p" data-group-id="6039056691-4">(</span><span class="p" data-group-id="6039056691-4">)</span><span class="p">,</span><span class="w">            </span><span class="c1">% mandatory</span><span class="w">
│ │ │ │ +                 </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">restart</span><span class="p" data-group-id="6039056691-5">(</span><span class="p" data-group-id="6039056691-5">)</span><span class="p">,</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                 </span><span class="ss">significant</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">significant</span><span class="p" data-group-id="6039056691-6">(</span><span class="p" data-group-id="6039056691-6">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                 </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">shutdown</span><span class="p" data-group-id="6039056691-7">(</span><span class="p" data-group-id="6039056691-7">)</span><span class="p">,</span><span class="w">       </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                 </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">worker</span><span class="p" data-group-id="6039056691-8">(</span><span class="p" data-group-id="6039056691-8">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                 </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">modules</span><span class="p" data-group-id="6039056691-9">(</span><span class="p" data-group-id="6039056691-9">)</span><span class="p" data-group-id="6039056691-2">}</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +    </span><span class="nf">child_id</span><span class="p" data-group-id="6039056691-10">(</span><span class="p" data-group-id="6039056691-10">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="6039056691-11">(</span><span class="p" data-group-id="6039056691-11">)</span><span class="w">
│ │ │ │ +    </span><span class="nf">mfargs</span><span class="p" data-group-id="6039056691-12">(</span><span class="p" data-group-id="6039056691-12">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6039056691-13">{</span><span class="n">M</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">module</span><span class="p" data-group-id="6039056691-14">(</span><span class="p" data-group-id="6039056691-14">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="6039056691-15">(</span><span class="p" data-group-id="6039056691-15">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6039056691-16">[</span><span class="nf">term</span><span class="p" data-group-id="6039056691-17">(</span><span class="p" data-group-id="6039056691-17">)</span><span class="p" data-group-id="6039056691-16">]</span><span class="p" data-group-id="6039056691-13">}</span><span class="w">
│ │ │ │ +    </span><span class="nf">modules</span><span class="p" data-group-id="6039056691-18">(</span><span class="p" data-group-id="6039056691-18">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6039056691-19">[</span><span class="nf">module</span><span class="p" data-group-id="6039056691-20">(</span><span class="p" data-group-id="6039056691-20">)</span><span class="p" data-group-id="6039056691-19">]</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">dynamic</span><span class="w">
│ │ │ │ +    </span><span class="nf">restart</span><span class="p" data-group-id="6039056691-21">(</span><span class="p" data-group-id="6039056691-21">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">permanent</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">transient</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">temporary</span><span class="w">
│ │ │ │ +    </span><span class="nf">significant</span><span class="p" data-group-id="6039056691-22">(</span><span class="p" data-group-id="6039056691-22">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="6039056691-23">(</span><span class="p" data-group-id="6039056691-23">)</span><span class="w">
│ │ │ │ +    </span><span class="nf">shutdown</span><span class="p" data-group-id="6039056691-24">(</span><span class="p" data-group-id="6039056691-24">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">timeout</span><span class="p" data-group-id="6039056691-25">(</span><span class="p" data-group-id="6039056691-25">)</span><span class="w">
│ │ │ │ +    </span><span class="nf">worker</span><span class="p" data-group-id="6039056691-26">(</span><span class="p" data-group-id="6039056691-26">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">worker</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">supervisor</span></code></pre><ul><li><p><code class="inline">id</code> is used to identify the child specification internally by the supervisor.</p><p>The <code class="inline">id</code> key is mandatory.</p><p>Note that this identifier occasionally has been called &quot;name&quot;. As far as
│ │ │ │  possible, the terms &quot;identifier&quot; or &quot;id&quot; are now used but in order to keep
│ │ │ │  backwards compatibility, some occurrences of &quot;name&quot; can still be found, for
│ │ │ │  example in error messages.</p></li><li><p><code class="inline">start</code> defines the function call used to start the child process. It is a
│ │ │ │  module-function-arguments tuple used as <a href="../../../lib/../erts/doc/html/erlang.html#apply/3"><code class="inline">apply(M, F, A)</code></a>.</p><p>It is to be (or result in) a call to any of the following:</p><ul><li><a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link/2,3</code></a></li><li><a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/3,4</code></a></li><li><a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/3,4</code></a></li><li><a href="../../../lib/stdlib/doc/html/gen_event.html#start_link/2"><code class="inline">gen_event:start_link/0,1,2</code></a></li><li>A function compliant with these functions. For details, see
│ │ │ │  <a href="../../../lib/stdlib/doc/html/supervisor.html"><code class="inline">supervisor</code></a>.</li></ul><p>The <code class="inline">start</code> key is mandatory.</p></li><li><p><a href="" id="restart"></a> <code class="inline">restart</code> defines when a terminated child process is to be
│ │ │ │  restarted.</p><ul><li>A <code class="inline">permanent</code> child process is always restarted.</li><li>A <code class="inline">temporary</code> child process is never restarted (not even when the supervisor
│ │ │ │  restart strategy is <code class="inline">rest_for_one</code> or <code class="inline">one_for_all</code> and a sibling death
│ │ │ │ @@ -362,53 +362,53 @@
│ │ │ │  <code class="inline">supervisor</code>, the default value <code class="inline">infinity</code> will be used.</p></li><li><p><code class="inline">type</code> specifies whether the child process is a supervisor or a worker.</p><p>The <code class="inline">type</code> key is optional. If it is not given, the default value <code class="inline">worker</code>
│ │ │ │  will be used.</p></li><li><p><code class="inline">modules</code> has to be a list consisting of a single element. The value
│ │ │ │  of that element depends on the behaviour of the process:</p><ul><li>If the child process is a <code class="inline">gen_event</code>, the element has to be the atom
│ │ │ │  <code class="inline">dynamic</code>.</li><li>Otherwise, the element should be <code class="inline">Module</code>, where <code class="inline">Module</code> is the
│ │ │ │  name of the callback module.</li></ul><p>This information is used by the release handler during upgrades and
│ │ │ │  downgrades; see <a href="release_handling.xhtml">Release Handling</a>.</p><p>The <code class="inline">modules</code> key is optional. If it is not given, it defaults to <code class="inline">[M]</code>, where
│ │ │ │  <code class="inline">M</code> comes from the child's start <code class="inline">{M,F,A}</code>.</p></li></ul><p><em>Example:</em> The child specification to start the server <code class="inline">ch3</code> in the previous
│ │ │ │ -example look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9438142947-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9438142947-2">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9438142947-3">[</span><span class="p" data-group-id="9438142947-3">]</span><span class="p" data-group-id="9438142947-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +example look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1970872142-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1970872142-2">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1970872142-3">[</span><span class="p" data-group-id="1970872142-3">]</span><span class="p" data-group-id="1970872142-2">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">permanent</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9438142947-4">[</span><span class="ss">ch3</span><span class="p" data-group-id="9438142947-4">]</span><span class="p" data-group-id="9438142947-1">}</span></code></pre><p>or simplified, relying on the default values:</p><pre><code class="text">#{id =&gt; ch3,
│ │ │ │ +  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1970872142-4">[</span><span class="ss">ch3</span><span class="p" data-group-id="1970872142-4">]</span><span class="p" data-group-id="1970872142-1">}</span></code></pre><p>or simplified, relying on the default values:</p><pre><code class="text">#{id =&gt; ch3,
│ │ │ │    start =&gt; {ch3, start_link, []},
│ │ │ │    shutdown =&gt; brutal_kill}</code></pre><p>Example: A child specification to start the event manager from the chapter about
│ │ │ │ -<a href="events.xhtml#mgr">gen_event</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3659562159-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">error_man</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3659562159-2">{</span><span class="ss">gen_event</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3659562159-3">[</span><span class="p" data-group-id="3659562159-4">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="3659562159-4">}</span><span class="p" data-group-id="3659562159-3">]</span><span class="p" data-group-id="3659562159-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">dynamic</span><span class="p" data-group-id="3659562159-1">}</span></code></pre><p>Both server and event manager are registered processes which can be expected to
│ │ │ │ +<a href="events.xhtml#mgr">gen_event</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8203860409-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">error_man</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8203860409-2">{</span><span class="ss">gen_event</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8203860409-3">[</span><span class="p" data-group-id="8203860409-4">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="8203860409-4">}</span><span class="p" data-group-id="8203860409-3">]</span><span class="p" data-group-id="8203860409-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">dynamic</span><span class="p" data-group-id="8203860409-1">}</span></code></pre><p>Both server and event manager are registered processes which can be expected to
│ │ │ │  be always accessible. Thus they are specified to be <code class="inline">permanent</code>.</p><p><code class="inline">ch3</code> does not need to do any cleaning up before termination. Thus, no shutdown
│ │ │ │  time is needed, but <code class="inline">brutal_kill</code> is sufficient. <code class="inline">error_man</code> can need some time
│ │ │ │  for the event handlers to clean up, thus the shutdown time is set to 5000 ms
│ │ │ │ -(which is the default value).</p><p>Example: A child specification to start another supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7979506304-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">sup</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7979506304-2">{</span><span class="ss">sup</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7979506304-3">[</span><span class="p" data-group-id="7979506304-3">]</span><span class="p" data-group-id="7979506304-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +(which is the default value).</p><p>Example: A child specification to start another supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6084592980-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">sup</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6084592980-2">{</span><span class="ss">sup</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6084592980-3">[</span><span class="p" data-group-id="6084592980-3">]</span><span class="p" data-group-id="6084592980-2">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">transient</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7979506304-1">}</span><span class="w"> </span><span class="c1">% will cause default shutdown=&gt;infinity</span></code></pre><p><a href="" id="super_tree"></a></p><h2 id="starting-a-supervisor" class="section-heading">
│ │ │ │ +  </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="6084592980-1">}</span><span class="w"> </span><span class="c1">% will cause default shutdown=&gt;infinity</span></code></pre><p><a href="" id="super_tree"></a></p><h2 id="starting-a-supervisor" class="section-heading">
│ │ │ │    <a href="#starting-a-supervisor" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting a Supervisor</span>
│ │ │ │  </h2>
│ │ │ │  <p>In the previous example, the supervisor is started by calling
│ │ │ │ -<code class="inline">ch_sup:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="6710779839-1">(</span><span class="p" data-group-id="6710779839-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6710779839-2">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6710779839-3">[</span><span class="p" data-group-id="6710779839-3">]</span><span class="p" data-group-id="6710779839-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch_sup:start_link</code> calls function <a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/2"><code class="inline">supervisor:start_link/2</code></a>, which spawns and
│ │ │ │ +<code class="inline">ch_sup:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="8915159063-1">(</span><span class="p" data-group-id="8915159063-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8915159063-2">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8915159063-3">[</span><span class="p" data-group-id="8915159063-3">]</span><span class="p" data-group-id="8915159063-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch_sup:start_link</code> calls function <a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/2"><code class="inline">supervisor:start_link/2</code></a>, which spawns and
│ │ │ │  links to a new process, a supervisor.</p><ul><li>The first argument, <code class="inline">ch_sup</code>, is the name of the callback module, that is, the
│ │ │ │  module where the <code class="inline">init</code> callback function is located.</li><li>The second argument, <code class="inline">[]</code>, is a term that is passed as is to the callback
│ │ │ │  function <code class="inline">init</code>. Here, <code class="inline">init</code> does not need any data and ignores the argument.</li></ul><p>In this case, the supervisor is not registered. Instead its pid must be used. A
│ │ │ │  name can be specified by calling
│ │ │ │  <a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link({local, Name}, Module, Args)</code></a>
│ │ │ │  or
│ │ │ │  <a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link({global, Name}, Module, Args)</code></a>.</p><p>The new supervisor process calls the callback function <code class="inline">ch_sup:init([])</code>. <code class="inline">init</code>
│ │ │ │ -has to return <code class="inline">{ok, {SupFlags, ChildSpecs}}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5371878767-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5371878767-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5371878767-2">#{</span><span class="p" data-group-id="5371878767-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5371878767-3">[</span><span class="p" data-group-id="5371878767-4">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5371878767-5">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5371878767-6">[</span><span class="p" data-group-id="5371878767-6">]</span><span class="p" data-group-id="5371878767-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="5371878767-4">}</span><span class="p" data-group-id="5371878767-3">]</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5371878767-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5371878767-8">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="5371878767-8">}</span><span class="p" data-group-id="5371878767-7">}</span><span class="p">.</span></code></pre><p>Subsequently, the supervisor starts its child processes according to the child
│ │ │ │ +has to return <code class="inline">{ok, {SupFlags, ChildSpecs}}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6973536976-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6973536976-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6973536976-2">#{</span><span class="p" data-group-id="6973536976-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6973536976-3">[</span><span class="p" data-group-id="6973536976-4">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6973536976-5">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6973536976-6">[</span><span class="p" data-group-id="6973536976-6">]</span><span class="p" data-group-id="6973536976-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="6973536976-4">}</span><span class="p" data-group-id="6973536976-3">]</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6973536976-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6973536976-8">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="6973536976-8">}</span><span class="p" data-group-id="6973536976-7">}</span><span class="p">.</span></code></pre><p>Subsequently, the supervisor starts its child processes according to the child
│ │ │ │  specifications in the start specification. In this case there is a single child
│ │ │ │  process, called <code class="inline">ch3</code>.</p><p><a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link/3</code></a> is synchronous. It does not return until all child
│ │ │ │  processes have been started.</p><h2 id="adding-a-child-process" class="section-heading">
│ │ │ │    <a href="#adding-a-child-process" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Adding a Child Process</span>
│ │ │ │ @@ -437,31 +437,31 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Simplified one_for_one Supervisors</span>
│ │ │ │  </h2>
│ │ │ │  <p>A supervisor with restart strategy <code class="inline">simple_one_for_one</code> is a simplified
│ │ │ │  <code class="inline">one_for_one</code> supervisor, where all child processes are dynamically added
│ │ │ │  instances of the same process.</p><p>The following is an example of a callback module for a <code class="inline">simple_one_for_one</code>
│ │ │ │ -supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2763401910-1">(</span><span class="ss">simple_sup</span><span class="p" data-group-id="2763401910-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="2763401910-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="2763401910-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2396779819-1">(</span><span class="ss">simple_sup</span><span class="p" data-group-id="2396779819-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="2396779819-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="2396779819-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2763401910-3">(</span><span class="p" data-group-id="2763401910-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2763401910-4">]</span><span class="p" data-group-id="2763401910-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2763401910-5">(</span><span class="p" data-group-id="2763401910-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2763401910-6">]</span><span class="p" data-group-id="2763401910-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2396779819-3">(</span><span class="p" data-group-id="2396779819-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2396779819-4">]</span><span class="p" data-group-id="2396779819-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2396779819-5">(</span><span class="p" data-group-id="2396779819-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2396779819-6">]</span><span class="p" data-group-id="2396779819-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="2763401910-7">(</span><span class="p" data-group-id="2763401910-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2763401910-8">(</span><span class="ss">simple_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2763401910-9">[</span><span class="p" data-group-id="2763401910-9">]</span><span class="p" data-group-id="2763401910-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="2396779819-7">(</span><span class="p" data-group-id="2396779819-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2396779819-8">(</span><span class="ss">simple_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2396779819-9">[</span><span class="p" data-group-id="2396779819-9">]</span><span class="p" data-group-id="2396779819-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="2763401910-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="2763401910-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2763401910-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="2396779819-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="2396779819-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2396779819-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="p">,</span><span class="w">
│ │ │ │                   </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2763401910-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2763401910-12">[</span><span class="p" data-group-id="2763401910-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">call</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2763401910-14">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2763401910-15">[</span><span class="p" data-group-id="2763401910-15">]</span><span class="p" data-group-id="2763401910-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="2763401910-13">}</span><span class="p" data-group-id="2763401910-12">]</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2763401910-16">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2763401910-17">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="2763401910-17">}</span><span class="p" data-group-id="2763401910-16">}</span><span class="p">.</span></code></pre><p>When started, the supervisor does not start any child
│ │ │ │ +                 </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2396779819-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2396779819-12">[</span><span class="p" data-group-id="2396779819-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">call</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2396779819-14">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2396779819-15">[</span><span class="p" data-group-id="2396779819-15">]</span><span class="p" data-group-id="2396779819-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="2396779819-13">}</span><span class="p" data-group-id="2396779819-12">]</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2396779819-16">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2396779819-17">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="2396779819-17">}</span><span class="p" data-group-id="2396779819-16">}</span><span class="p">.</span></code></pre><p>When started, the supervisor does not start any child
│ │ │ │  processes. Instead, all child processes need to be added dynamically by
│ │ │ │  calling <a href="../../../lib/stdlib/doc/html/supervisor.html#start_child/2"><code class="inline">supervisor:start_child(Sup, List)</code></a>.</p><p><code class="inline">Sup</code> is the pid, or name, of the supervisor. <code class="inline">List</code> is an arbitrary list of
│ │ │ │  terms, which are added to the list of arguments specified in the child
│ │ │ │  specification. If the start function is specified as <code class="inline">{M, F, A}</code>, the child
│ │ │ │  process is started by calling <a href="../../../lib/../erts/doc/html/erlang.html#apply/3"><code class="inline">apply(M, F, A++List)</code></a>.</p><p>For example, adding a child to <code class="inline">simple_sup</code> above:</p><pre><code class="text">supervisor:start_child(Pid, [id1])</code></pre><p>The result is that the child process is started by calling
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#apply/3"><code class="inline">apply(call, start_link, []++[id1])</code></a>, or actually:</p><pre><code class="text">call:start_link(id1)</code></pre><p>A child under a <code class="inline">simple_one_for_one</code> supervisor can be terminated with the
│ │ │ │  following:</p><pre><code class="text">supervisor:terminate_child(Sup, Pid)</code></pre><p><code class="inline">Sup</code> is the pid, or name, of the supervisor and <code class="inline">Pid</code> is the pid of the child.</p><p>Because a <code class="inline">simple_one_for_one</code> supervisor can have many children, it shuts them
│ │ │ ├── OEBPS/statem.xhtml
│ │ │ │ @@ -29,15 +29,15 @@
│ │ │ │  </h2>
│ │ │ │  <p>Established Automata Theory does not deal much with how a <em>state transition</em>
│ │ │ │  is triggered, but assumes that the output is a function of the input
│ │ │ │  (and the state) and that they are some kind of values.</p><p>For an Event-Driven State Machine, the input is an <em>event</em> that triggers
│ │ │ │  a <em>state transition</em> and the output is actions executed during
│ │ │ │  the <em>state transition</em>.  Analogously to the mathematical model
│ │ │ │  of a Finite State Machine, it can be described as a set of relations
│ │ │ │ -of the following form:</p><pre><code class="makeup erlang" translate="no"><span class="n">State</span><span class="p" data-group-id="0463516220-1">(</span><span class="n">S</span><span class="p" data-group-id="0463516220-1">)</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="0463516220-2">(</span><span class="n">E</span><span class="p" data-group-id="0463516220-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Actions</span><span class="p" data-group-id="0463516220-3">(</span><span class="n">A</span><span class="p" data-group-id="0463516220-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="0463516220-4">(</span><span class="n">S</span><span class="err">&#39;</span><span class="p" data-group-id="0463516220-4">)</span></code></pre><p>These relations are interpreted as follows: if we are in state <code class="inline">S</code>,
│ │ │ │ +of the following form:</p><pre><code class="makeup erlang" translate="no"><span class="n">State</span><span class="p" data-group-id="0782391976-1">(</span><span class="n">S</span><span class="p" data-group-id="0782391976-1">)</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="0782391976-2">(</span><span class="n">E</span><span class="p" data-group-id="0782391976-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Actions</span><span class="p" data-group-id="0782391976-3">(</span><span class="n">A</span><span class="p" data-group-id="0782391976-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="0782391976-4">(</span><span class="n">S</span><span class="err">&#39;</span><span class="p" data-group-id="0782391976-4">)</span></code></pre><p>These relations are interpreted as follows: if we are in state <code class="inline">S</code>,
│ │ │ │  and event <code class="inline">E</code> occurs, we are to perform actions <code class="inline">A</code>, and make a transition
│ │ │ │  to state <code class="inline">S'</code>.  Notice that <code class="inline">S'</code> can be equal to <code class="inline">S</code>,
│ │ │ │  and that <code class="inline">A</code> can be empty.</p><p>In <code class="inline">gen_statem</code> we define a <em>state change</em> as a <em>state transition</em> in which the
│ │ │ │  new state <code class="inline">S'</code> is different from the current state <code class="inline">S</code>, where &quot;different&quot; means
│ │ │ │  Erlang's strict inequality: <code class="inline">=/=</code> also known as &quot;does not match&quot;. <code class="inline">gen_statem</code>
│ │ │ │  does more things during <em>state changes</em> than during other <em>state transitions</em>.</p><p>As <code class="inline">A</code> and <code class="inline">S'</code> depend only on <code class="inline">S</code> and <code class="inline">E</code>, the kind of state machine described
│ │ │ │  here is a Mealy machine (see, for example, the Wikipedia article
│ │ │ │ @@ -310,20 +310,20 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">State Enter Calls</span>
│ │ │ │  </h2>
│ │ │ │  <p>The <code class="inline">gen_statem</code> behaviour can, if this is enabled, regardless of <em>callback
│ │ │ │  mode</em>, automatically call the <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:state_enter/0"><em>state callback</em></a>
│ │ │ │  with special arguments whenever the state changes, so you can write
│ │ │ │  state enter actions near the rest of the <em>state transition</em> rules.
│ │ │ │ -It typically looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">StateName</span><span class="p" data-group-id="3257890593-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3257890593-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +It typically looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">StateName</span><span class="p" data-group-id="0347926697-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0347926697-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">enter</span><span class="w"> </span><span class="ss">actions</span><span class="w"> </span><span class="ss">here</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3257890593-2">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="3257890593-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="n">StateName</span><span class="p" data-group-id="3257890593-3">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3257890593-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0347926697-2">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="0347926697-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="n">StateName</span><span class="p" data-group-id="0347926697-3">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0347926697-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">actions</span><span class="w"> </span><span class="ss">here</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3257890593-4">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewStateName</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="3257890593-4">}</span><span class="p">.</span></code></pre><p>Since the <em>state enter call</em> is not an event there are restrictions on the
│ │ │ │ +    </span><span class="p" data-group-id="0347926697-4">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewStateName</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="0347926697-4">}</span><span class="p">.</span></code></pre><p>Since the <em>state enter call</em> is not an event there are restrictions on the
│ │ │ │  allowed return value and state <a href="#transition-actions"><em>transition actions</em></a>.
│ │ │ │  You must not change the state, <a href="#postponing-events">postpone</a> this non-event,
│ │ │ │  <a href="#inserted-events">insert any events</a>, or change the
│ │ │ │  <a href="#callback-module"><em>callback module</em></a>.</p><p>The first state that is entered after <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:init/1"><code class="inline">gen_statem:init/1</code></a> will get
│ │ │ │  a <em>state enter call</em> with <code class="inline">OldState</code> equal to the current state.</p><p>You may repeat the <em>state enter call</em> using the <code class="inline">{repeat_state,...}</code> return
│ │ │ │  value from the <a href="#state-callback"><em>state callback</em></a>. In this case
│ │ │ │  <code class="inline">OldState</code> will also be equal to the current state.</p><p>Depending on how your state machine is specified, this can be a very useful
│ │ │ │ @@ -404,72 +404,72 @@
│ │ │ │  
│ │ │ │      locked      --&gt; check_code : {button, Button}\n* Collect Buttons
│ │ │ │      check_code  --&gt; locked     : Incorrect code
│ │ │ │      check_code  --&gt; open       : Correct code\n* do_unlock()\n* Clear Buttons\n* Set state_timeout 10 s
│ │ │ │  
│ │ │ │      open        --&gt; open   : {button, Digit}
│ │ │ │      open        --&gt; locked : state_timeout\n* do_lock()</code></pre><p>This code lock state machine can be implemented using <a href="../../../lib/stdlib/doc/html/gen_statem.html"><code class="inline">gen_statem</code></a> with
│ │ │ │ -the following <em>callback module</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1287884438-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="1287884438-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1287884438-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="1287884438-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1287884438-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock</span><span class="p" data-group-id="1287884438-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the following <em>callback module</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0032039779-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="0032039779-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="0032039779-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="0032039779-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0032039779-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock</span><span class="p" data-group-id="0032039779-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1287884438-4">(</span><span class="p" data-group-id="1287884438-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1287884438-5">]</span><span class="p" data-group-id="1287884438-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1287884438-6">(</span><span class="p" data-group-id="1287884438-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1287884438-7">]</span><span class="p" data-group-id="1287884438-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1287884438-8">(</span><span class="p" data-group-id="1287884438-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="1287884438-9">]</span><span class="p" data-group-id="1287884438-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1287884438-10">(</span><span class="p" data-group-id="1287884438-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="1287884438-11">]</span><span class="p" data-group-id="1287884438-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="1287884438-12">(</span><span class="n">Code</span><span class="p" data-group-id="1287884438-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1287884438-13">(</span><span class="p" data-group-id="1287884438-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="1287884438-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1287884438-15">[</span><span class="p" data-group-id="1287884438-15">]</span><span class="p" data-group-id="1287884438-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="1287884438-16">(</span><span class="n">Button</span><span class="p" data-group-id="1287884438-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1287884438-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1287884438-18">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1287884438-18">}</span><span class="p" data-group-id="1287884438-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1287884438-19">(</span><span class="n">Code</span><span class="p" data-group-id="1287884438-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="1287884438-20">(</span><span class="p" data-group-id="1287884438-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1287884438-21">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="1287884438-22">(</span><span class="n">Code</span><span class="p" data-group-id="1287884438-22">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1287884438-23">[</span><span class="p" data-group-id="1287884438-23">]</span><span class="p" data-group-id="1287884438-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1287884438-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1287884438-24">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="1287884438-25">(</span><span class="p" data-group-id="1287884438-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="6727702510-1">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6727702510-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6727702510-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6727702510-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="6727702510-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6727702510-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0032039779-4">(</span><span class="p" data-group-id="0032039779-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0032039779-5">]</span><span class="p" data-group-id="0032039779-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0032039779-6">(</span><span class="p" data-group-id="0032039779-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0032039779-7">]</span><span class="p" data-group-id="0032039779-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0032039779-8">(</span><span class="p" data-group-id="0032039779-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="0032039779-9">]</span><span class="p" data-group-id="0032039779-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0032039779-10">(</span><span class="p" data-group-id="0032039779-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="0032039779-11">]</span><span class="p" data-group-id="0032039779-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="0032039779-12">(</span><span class="n">Code</span><span class="p" data-group-id="0032039779-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0032039779-13">(</span><span class="p" data-group-id="0032039779-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="0032039779-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0032039779-15">[</span><span class="p" data-group-id="0032039779-15">]</span><span class="p" data-group-id="0032039779-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="0032039779-16">(</span><span class="n">Button</span><span class="p" data-group-id="0032039779-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="0032039779-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0032039779-18">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0032039779-18">}</span><span class="p" data-group-id="0032039779-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="0032039779-19">(</span><span class="n">Code</span><span class="p" data-group-id="0032039779-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="0032039779-20">(</span><span class="p" data-group-id="0032039779-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0032039779-21">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0032039779-22">(</span><span class="n">Code</span><span class="p" data-group-id="0032039779-22">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0032039779-23">[</span><span class="p" data-group-id="0032039779-23">]</span><span class="p" data-group-id="0032039779-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0032039779-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0032039779-24">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="0032039779-25">(</span><span class="p" data-group-id="0032039779-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="3827819688-1">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3827819688-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3827819688-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3827819688-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="3827819688-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3827819688-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │          </span><span class="k">if</span><span class="w">
│ │ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="6727702510-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="6727702510-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="3827819688-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="3827819688-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="6727702510-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="6727702510-5">)</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6727702510-6">[</span><span class="n">Button</span><span class="p" data-group-id="6727702510-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="3827819688-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="3827819688-5">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="3827819688-6">[</span><span class="n">Button</span><span class="p" data-group-id="3827819688-6">]</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="6727702510-7">(</span><span class="p" data-group-id="6727702510-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="6727702510-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6727702510-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="6727702510-10">[</span><span class="p" data-group-id="6727702510-10">]</span><span class="p" data-group-id="6727702510-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="6727702510-11">[</span><span class="p" data-group-id="6727702510-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="6727702510-12">}</span><span class="p" data-group-id="6727702510-11">]</span><span class="p" data-group-id="6727702510-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3827819688-7">(</span><span class="p" data-group-id="3827819688-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="3827819688-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3827819688-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3827819688-10">[</span><span class="p" data-group-id="3827819688-10">]</span><span class="p" data-group-id="3827819688-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="3827819688-11">[</span><span class="p" data-group-id="3827819688-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3827819688-12">}</span><span class="p" data-group-id="3827819688-11">]</span><span class="p" data-group-id="3827819688-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="6727702510-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6727702510-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="6727702510-14">}</span><span class="p" data-group-id="6727702510-13">}</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="9230038403-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="9230038403-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="9230038403-2">(</span><span class="p" data-group-id="9230038403-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9230038403-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9230038403-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="9230038403-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9230038403-5">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9230038403-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9230038403-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9230038403-6">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9230038403-6">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="5862694930-1">(</span><span class="p" data-group-id="5862694930-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5862694930-2">(</span><span class="s">&quot;Lock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5862694930-3">[</span><span class="p" data-group-id="5862694930-3">]</span><span class="p" data-group-id="5862694930-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="5862694930-4">(</span><span class="p" data-group-id="5862694930-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5862694930-5">(</span><span class="s">&quot;Unlock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5862694930-6">[</span><span class="p" data-group-id="5862694930-6">]</span><span class="p" data-group-id="5862694930-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="3827819688-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3827819688-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="3827819688-14">}</span><span class="p" data-group-id="3827819688-13">}</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="9110827242-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="9110827242-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="9110827242-2">(</span><span class="p" data-group-id="9110827242-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9110827242-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9110827242-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="9110827242-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9110827242-5">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9110827242-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9110827242-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9110827242-6">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9110827242-6">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="0787367483-1">(</span><span class="p" data-group-id="0787367483-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0787367483-2">(</span><span class="s">&quot;Lock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0787367483-3">[</span><span class="p" data-group-id="0787367483-3">]</span><span class="p" data-group-id="0787367483-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="0787367483-4">(</span><span class="p" data-group-id="0787367483-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0787367483-5">(</span><span class="s">&quot;Unlock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0787367483-6">[</span><span class="p" data-group-id="0787367483-6">]</span><span class="p" data-group-id="0787367483-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="5862694930-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="5862694930-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="5862694930-8">(</span><span class="p" data-group-id="5862694930-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="0787367483-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0787367483-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="0787367483-8">(</span><span class="p" data-group-id="0787367483-8">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-gen_statem" class="section-heading">
│ │ │ │    <a href="#starting-gen_statem" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting gen_statem</span>
│ │ │ │  </h2>
│ │ │ │  <p>In the example in the previous section, <code class="inline">gen_statem</code> is started by calling
│ │ │ │ -<code class="inline">code_lock:start_link(Code)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="6089745811-1">(</span><span class="n">Code</span><span class="p" data-group-id="6089745811-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6089745811-2">(</span><span class="p" data-group-id="6089745811-3">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="6089745811-3">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6089745811-4">[</span><span class="p" data-group-id="6089745811-4">]</span><span class="p" data-group-id="6089745811-2">)</span><span class="p">.</span></code></pre><p><code class="inline">start_link/1</code> calls function <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/4</code></a>,
│ │ │ │ +<code class="inline">code_lock:start_link(Code)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="4824844099-1">(</span><span class="n">Code</span><span class="p" data-group-id="4824844099-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4824844099-2">(</span><span class="p" data-group-id="4824844099-3">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4824844099-3">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4824844099-4">[</span><span class="p" data-group-id="4824844099-4">]</span><span class="p" data-group-id="4824844099-2">)</span><span class="p">.</span></code></pre><p><code class="inline">start_link/1</code> calls function <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/4</code></a>,
│ │ │ │  which spawns and links to a new process, a <code class="inline">gen_statem</code>.</p><ul><li><p>The first argument, <code class="inline">{local,?NAME}</code>, specifies the name. In this case, the
│ │ │ │  <code class="inline">gen_statem</code> is locally registered as <code class="inline">code_lock</code> through the macro <code class="inline">?NAME</code>.</p><p>If the name is omitted, the <code class="inline">gen_statem</code> is not registered. Instead its pid
│ │ │ │  must be used. The name can also be specified as <code class="inline">{global, Name}</code>, then the
│ │ │ │  <code class="inline">gen_statem</code> is registered using <a href="../../../lib/kernel/doc/html/global.html#register_name/2"><code class="inline">global:register_name/2</code></a> in Kernel.</p></li><li><p>The second argument, <code class="inline">?MODULE</code>, is the name of the <em>callback module</em>,
│ │ │ │  that is, the module where the callback functions are located,
│ │ │ │  which is this module.</p><p>The interface functions (<code class="inline">start_link/1</code> and <code class="inline">button/1</code>) are located in the
│ │ │ │  same module as the callback functions (<code class="inline">init/1</code>, <code class="inline">locked/3</code>, and <code class="inline">open/3</code>).
│ │ │ │ @@ -479,184 +479,184 @@
│ │ │ │  see <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3</code></a>.</p></li></ul><p>If name registration succeeds, the new <code class="inline">gen_statem</code> process calls callback
│ │ │ │  function <code class="inline">code_lock:init(Code)</code>. This function is expected to return
│ │ │ │  <code class="inline">{ok, State, Data}</code>, where <code class="inline">State</code> is the initial state of the <code class="inline">gen_statem</code>,
│ │ │ │  in this case <code class="inline">locked</code>; assuming that the door is locked to begin with.
│ │ │ │  <code class="inline">Data</code> is the internal server data of the <code class="inline">gen_statem</code>. Here the server data
│ │ │ │  is a <a href="../../../lib/stdlib/doc/html/maps.html"><code class="inline">map()</code></a> with key <code class="inline">code</code> that stores the correct
│ │ │ │  button sequence, key <code class="inline">length</code> store its length, and key <code class="inline">buttons</code>
│ │ │ │ -that stores the collected buttons up to the same length.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5830308085-1">(</span><span class="n">Code</span><span class="p" data-group-id="5830308085-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="5830308085-2">(</span><span class="p" data-group-id="5830308085-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5830308085-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="5830308085-4">(</span><span class="n">Code</span><span class="p" data-group-id="5830308085-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5830308085-5">[</span><span class="p" data-group-id="5830308085-5">]</span><span class="p" data-group-id="5830308085-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5830308085-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5830308085-6">}</span><span class="p">.</span></code></pre><p>Function <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │ │ +that stores the collected buttons up to the same length.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6186439366-1">(</span><span class="n">Code</span><span class="p" data-group-id="6186439366-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="6186439366-2">(</span><span class="p" data-group-id="6186439366-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6186439366-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="6186439366-4">(</span><span class="n">Code</span><span class="p" data-group-id="6186439366-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6186439366-5">[</span><span class="p" data-group-id="6186439366-5">]</span><span class="p" data-group-id="6186439366-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6186439366-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6186439366-6">}</span><span class="p">.</span></code></pre><p>Function <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │ │  is synchronous. It does not return until the <code class="inline">gen_statem</code> is initialized
│ │ │ │  and is ready to receive events.</p><p>Function <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │ │  must be used if the <code class="inline">gen_statem</code> is part of a supervision tree, that is,
│ │ │ │  started by a supervisor.  Function,
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#start/3"><code class="inline">gen_statem:start/3,4</code></a> can be used to start
│ │ │ │  a standalone <code class="inline">gen_statem</code>, meaning it is not part of a supervision tree.</p><p>Function <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:callback_mode/0"><code class="inline">Module:callback_mode/0</code></a> selects
│ │ │ │  the <a href="#callback-modes"><code class="inline">CallbackMode</code></a> for the <em>callback module</em>,
│ │ │ │  in this case <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:callback_mode/0"><code class="inline">state_functions</code></a>.
│ │ │ │ -That is, each state has its own handler function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="2332464290-1">(</span><span class="p" data-group-id="2332464290-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +That is, each state has its own handler function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="2848184469-1">(</span><span class="p" data-group-id="2848184469-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><h2 id="handling-events" class="section-heading">
│ │ │ │    <a href="#handling-events" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Handling Events</span>
│ │ │ │  </h2>
│ │ │ │  <p>The function notifying the code lock about a button event is implemented using
│ │ │ │ -<a href="../../../lib/stdlib/doc/html/gen_statem.html#cast/2"><code class="inline">gen_statem:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">button</span><span class="p" data-group-id="4675995739-1">(</span><span class="n">Button</span><span class="p" data-group-id="4675995739-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4675995739-2">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4675995739-3">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4675995739-3">}</span><span class="p" data-group-id="4675995739-2">)</span><span class="p">.</span></code></pre><p>The first argument is the name of the <code class="inline">gen_statem</code> and must agree with
│ │ │ │ +<a href="../../../lib/stdlib/doc/html/gen_statem.html#cast/2"><code class="inline">gen_statem:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">button</span><span class="p" data-group-id="8698910591-1">(</span><span class="n">Button</span><span class="p" data-group-id="8698910591-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8698910591-2">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8698910591-3">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8698910591-3">}</span><span class="p" data-group-id="8698910591-2">)</span><span class="p">.</span></code></pre><p>The first argument is the name of the <code class="inline">gen_statem</code> and must agree with
│ │ │ │  the name used to start it. So, we use the same macro <code class="inline">?NAME</code> as when starting.
│ │ │ │  <code class="inline">{button, Button}</code> is the event content.</p><p>The event is sent to the <code class="inline">gen_statem</code>. When the event is received, the
│ │ │ │  <code class="inline">gen_statem</code> calls <code class="inline">StateName(cast, Event, Data)</code>, which is expected
│ │ │ │  to return a tuple <code class="inline">{next_state, NewStateName, NewData}</code>, or
│ │ │ │  <code class="inline">{next_state, NewStateName, NewData, Actions}</code>. <code class="inline">StateName</code> is the name
│ │ │ │  of the current state and <code class="inline">NewStateName</code> is the name of the next state.
│ │ │ │  <code class="inline">NewData</code> is a new value for the server data of the <code class="inline">gen_statem</code>,
│ │ │ │ -and <code class="inline">Actions</code> is a list of actions to be performed by the <code class="inline">gen_statem</code> engine.</p><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="8824538567-1">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8824538567-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8824538567-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8824538567-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="8824538567-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8824538567-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +and <code class="inline">Actions</code> is a list of actions to be performed by the <code class="inline">gen_statem</code> engine.</p><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="3856149857-1">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3856149857-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3856149857-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3856149857-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="3856149857-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3856149857-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │          </span><span class="k">if</span><span class="w">
│ │ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="8824538567-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="8824538567-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="3856149857-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="3856149857-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="8824538567-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="8824538567-5">)</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="8824538567-6">[</span><span class="n">Button</span><span class="p" data-group-id="8824538567-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="3856149857-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="3856149857-5">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="3856149857-6">[</span><span class="n">Button</span><span class="p" data-group-id="3856149857-6">]</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="8824538567-7">(</span><span class="p" data-group-id="8824538567-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="8824538567-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8824538567-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8824538567-10">[</span><span class="p" data-group-id="8824538567-10">]</span><span class="p" data-group-id="8824538567-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="8824538567-11">[</span><span class="p" data-group-id="8824538567-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8824538567-12">}</span><span class="p" data-group-id="8824538567-11">]</span><span class="p" data-group-id="8824538567-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3856149857-7">(</span><span class="p" data-group-id="3856149857-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="3856149857-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3856149857-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3856149857-10">[</span><span class="p" data-group-id="3856149857-10">]</span><span class="p" data-group-id="3856149857-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="3856149857-11">[</span><span class="p" data-group-id="3856149857-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3856149857-12">}</span><span class="p" data-group-id="3856149857-11">]</span><span class="p" data-group-id="3856149857-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="8824538567-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8824538567-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="8824538567-14">}</span><span class="p" data-group-id="8824538567-13">}</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="3856149857-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3856149857-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="3856149857-14">}</span><span class="p" data-group-id="3856149857-13">}</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>In state <code class="inline">locked</code>, when a button is pressed, it is collected with the
│ │ │ │  previously pressed buttons up to the length of the correct code, then
│ │ │ │  compared with the correct code. Depending on the result, the door is
│ │ │ │  either unlocked and the <code class="inline">gen_statem</code> goes to state <code class="inline">open</code>, or the door
│ │ │ │  remains in state <code class="inline">locked</code>.</p><p>When changing to state <code class="inline">open</code>, the collected buttons are reset, the lock
│ │ │ │ -unlocked, and a <em>state time-out</em> for 10 seconds is started.</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="9884991957-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9884991957-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9884991957-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9884991957-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9884991957-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9884991957-3">}</span><span class="p">.</span></code></pre><p>In state <code class="inline">open</code>, a button event is ignored by staying in the same state.
│ │ │ │ +unlocked, and a <em>state time-out</em> for 10 seconds is started.</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="3589329500-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3589329500-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3589329500-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3589329500-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3589329500-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3589329500-3">}</span><span class="p">.</span></code></pre><p>In state <code class="inline">open</code>, a button event is ignored by staying in the same state.
│ │ │ │  This can also be done by returning <code class="inline">{keep_state, Data}</code>, or in this case
│ │ │ │  since <code class="inline">Data</code> is unchanged, by returning <code class="inline">keep_state_and_data</code>.</p><h2 id="state-time-outs" class="section-heading">
│ │ │ │    <a href="#state-time-outs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">State Time-Outs</span>
│ │ │ │  </h2>
│ │ │ │  <p>When a correct code has been given, the door is unlocked and the following
│ │ │ │ -tuple is returned from <code class="inline">locked/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9386442361-1">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9386442361-2">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9386442361-3">[</span><span class="p" data-group-id="9386442361-3">]</span><span class="p" data-group-id="9386442361-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9386442361-4">[</span><span class="p" data-group-id="9386442361-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="9386442361-5">}</span><span class="p" data-group-id="9386442361-4">]</span><span class="p" data-group-id="9386442361-1">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span></code></pre><p>10,000 is a time-out value in milliseconds. After this time (10 seconds),
│ │ │ │ +tuple is returned from <code class="inline">locked/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8587390239-1">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8587390239-2">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8587390239-3">[</span><span class="p" data-group-id="8587390239-3">]</span><span class="p" data-group-id="8587390239-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8587390239-4">[</span><span class="p" data-group-id="8587390239-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8587390239-5">}</span><span class="p" data-group-id="8587390239-4">]</span><span class="p" data-group-id="8587390239-1">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span></code></pre><p>10,000 is a time-out value in milliseconds. After this time (10 seconds),
│ │ │ │  a time-out occurs. Then, <code class="inline">StateName(state_timeout, lock, Data)</code> is called.
│ │ │ │  The time-out occurs when the door has been in state <code class="inline">open</code> for 10 seconds.
│ │ │ │ -After that the door is locked again:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="0009883280-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="0009883280-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="0009883280-2">(</span><span class="p" data-group-id="0009883280-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0009883280-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0009883280-3">}</span><span class="p">;</span></code></pre><p>The timer for a <em>state time-out</em> is automatically canceled when
│ │ │ │ +After that the door is locked again:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="6529515527-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="6529515527-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="6529515527-2">(</span><span class="p" data-group-id="6529515527-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6529515527-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6529515527-3">}</span><span class="p">;</span></code></pre><p>The timer for a <em>state time-out</em> is automatically canceled when
│ │ │ │  the state machine does a <em>state change</em>.</p><p>You can restart, cancel, or update a <em>state time-out</em>. See section
│ │ │ │  <a href="#time-outs"><em>Time-Outs</em></a> for details.</p><h2 id="all-state-events" class="section-heading">
│ │ │ │    <a href="#all-state-events" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">All State Events</span>
│ │ │ │  </h2>
│ │ │ │  <p>Sometimes events can arrive in any state of the <code class="inline">gen_statem</code>. It is convenient
│ │ │ │  to handle these in a common state handler function that all state functions
│ │ │ │  call for events not specific to the state.</p><p>Consider a <code class="inline">code_length/0</code> function that returns the length
│ │ │ │  of the correct code.  We dispatch all events that are not state-specific
│ │ │ │  to the common function <code class="inline">handle_common/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1795254828-1">(</span><span class="p" data-group-id="1795254828-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1795254828-2">]</span><span class="p" data-group-id="1795254828-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5601502489-1">(</span><span class="p" data-group-id="5601502489-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5601502489-2">]</span><span class="p" data-group-id="5601502489-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="1795254828-3">(</span><span class="p" data-group-id="1795254828-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="1795254828-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="1795254828-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="5601502489-3">(</span><span class="p" data-group-id="5601502489-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="5601502489-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="5601502489-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="1795254828-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1795254828-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="1795254828-6">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1795254828-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">handle_common</span><span class="p" data-group-id="1795254828-7">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1795254828-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="5601502489-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5601502489-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="5601502489-6">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5601502489-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">handle_common</span><span class="p" data-group-id="5601502489-7">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5601502489-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="1795254828-8">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1795254828-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="1795254828-9">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1795254828-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">handle_common</span><span class="p" data-group-id="1795254828-10">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1795254828-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="1795254828-11">(</span><span class="p" data-group-id="1795254828-12">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="1795254828-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1795254828-13">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="1795254828-13">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1795254828-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1795254828-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="1795254828-15">[</span><span class="p" data-group-id="1795254828-16">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="1795254828-17">(</span><span class="n">Code</span><span class="p" data-group-id="1795254828-17">)</span><span class="p" data-group-id="1795254828-16">}</span><span class="p" data-group-id="1795254828-15">]</span><span class="p" data-group-id="1795254828-14">}</span><span class="p">.</span></code></pre><p>Another way to do it is through a convenience macro <code class="inline">?HANDLE_COMMON/0</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2238333613-1">(</span><span class="p" data-group-id="2238333613-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2238333613-2">]</span><span class="p" data-group-id="2238333613-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="5601502489-8">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5601502489-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="5601502489-9">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5601502489-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">handle_common</span><span class="p" data-group-id="5601502489-10">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5601502489-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="5601502489-11">(</span><span class="p" data-group-id="5601502489-12">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="5601502489-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5601502489-13">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="5601502489-13">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5601502489-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5601502489-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="5601502489-15">[</span><span class="p" data-group-id="5601502489-16">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="5601502489-17">(</span><span class="n">Code</span><span class="p" data-group-id="5601502489-17">)</span><span class="p" data-group-id="5601502489-16">}</span><span class="p" data-group-id="5601502489-15">]</span><span class="p" data-group-id="5601502489-14">}</span><span class="p">.</span></code></pre><p>Another way to do it is through a convenience macro <code class="inline">?HANDLE_COMMON/0</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4667592580-1">(</span><span class="p" data-group-id="4667592580-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4667592580-2">]</span><span class="p" data-group-id="4667592580-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="2238333613-3">(</span><span class="p" data-group-id="2238333613-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="2238333613-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="2238333613-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="4667592580-3">(</span><span class="p" data-group-id="4667592580-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4667592580-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="4667592580-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2238333613-5">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="2238333613-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="2238333613-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="2238333613-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="2238333613-7">)</span><span class="p" data-group-id="2238333613-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4667592580-5">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="4667592580-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="4667592580-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="4667592580-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="4667592580-7">)</span><span class="p" data-group-id="4667592580-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="2238333613-8">(</span><span class="p" data-group-id="2238333613-9">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="2238333613-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2238333613-10">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="2238333613-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2238333613-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2238333613-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="2238333613-12">[</span><span class="p" data-group-id="2238333613-13">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="2238333613-14">(</span><span class="n">Code</span><span class="p" data-group-id="2238333613-14">)</span><span class="p" data-group-id="2238333613-13">}</span><span class="p" data-group-id="2238333613-12">]</span><span class="p" data-group-id="2238333613-11">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="4667592580-8">(</span><span class="p" data-group-id="4667592580-9">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="4667592580-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4667592580-10">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="4667592580-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4667592580-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4667592580-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="4667592580-12">[</span><span class="p" data-group-id="4667592580-13">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="4667592580-14">(</span><span class="n">Code</span><span class="p" data-group-id="4667592580-14">)</span><span class="p" data-group-id="4667592580-13">}</span><span class="p" data-group-id="4667592580-12">]</span><span class="p" data-group-id="4667592580-11">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="2238333613-15">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2238333613-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="4667592580-15">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4667592580-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="2238333613-16">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2238333613-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="4667592580-16">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4667592580-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><p>This example uses <a href="../../../lib/stdlib/doc/html/gen_statem.html#call/2"><code class="inline">gen_statem:call/2</code></a>, which waits for a reply from the server.
│ │ │ │  The reply is sent with a <code class="inline">{reply, From, Reply}</code> tuple in an action list in the
│ │ │ │  <code class="inline">{keep_state, ...}</code> tuple that retains the current state. This return form is
│ │ │ │  convenient when you want to stay in the current state but do not know or care
│ │ │ │  about what it is.</p><p>If the common <em>state callback</em> needs to know the current state a function
│ │ │ │ -<code class="inline">handle_common/4</code> can be used instead:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8419190959-1">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="8419190959-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="8419190959-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="8419190959-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="8419190959-3">)</span><span class="p" data-group-id="8419190959-1">)</span><span class="p">.</span></code></pre><h2 id="one-state-callback" class="section-heading">
│ │ │ │ +<code class="inline">handle_common/4</code> can be used instead:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5934818028-1">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="5934818028-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="5934818028-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="5934818028-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="5934818028-3">)</span><span class="p" data-group-id="5934818028-1">)</span><span class="p">.</span></code></pre><h2 id="one-state-callback" class="section-heading">
│ │ │ │    <a href="#one-state-callback" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">One State Callback</span>
│ │ │ │  </h2>
│ │ │ │  <p>If <a href="#callback-modes"><em>callback mode</em></a> <code class="inline">handle_event_function</code> is used,
│ │ │ │  all events are handled in
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:handle_event/4"><code class="inline">Module:handle_event/4</code></a> and we can
│ │ │ │  (but do not have to) use an event-centered approach where we first branch
│ │ │ │  depending on event and then depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6806418342-1">(</span><span class="p" data-group-id="6806418342-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="6806418342-2">]</span><span class="p" data-group-id="6806418342-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9641973212-1">(</span><span class="p" data-group-id="9641973212-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="9641973212-2">]</span><span class="p" data-group-id="9641973212-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="6806418342-3">(</span><span class="p" data-group-id="6806418342-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="9641973212-3">(</span><span class="p" data-group-id="9641973212-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">handle_event_function</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="6806418342-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6806418342-5">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6806418342-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6806418342-6">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="6806418342-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6806418342-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="9641973212-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9641973212-5">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9641973212-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9641973212-6">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="9641973212-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9641973212-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │  	</span><span class="ss">locked</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="6806418342-7">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="6806418342-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9641973212-7">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9641973212-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │                  </span><span class="k">if</span><span class="w">
│ │ │ │ -                    </span><span class="nf">length</span><span class="p" data-group-id="6806418342-8">(</span><span class="n">Buttons</span><span class="p" data-group-id="6806418342-8">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                    </span><span class="nf">length</span><span class="p" data-group-id="9641973212-8">(</span><span class="n">Buttons</span><span class="p" data-group-id="9641973212-8">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                          </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │                      </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                        </span><span class="nf">tl</span><span class="p" data-group-id="6806418342-9">(</span><span class="n">Buttons</span><span class="p" data-group-id="6806418342-9">)</span><span class="w">
│ │ │ │ -                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6806418342-10">[</span><span class="n">Button</span><span class="p" data-group-id="6806418342-10">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                        </span><span class="nf">tl</span><span class="p" data-group-id="9641973212-9">(</span><span class="n">Buttons</span><span class="p" data-group-id="9641973212-9">)</span><span class="w">
│ │ │ │ +                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9641973212-10">[</span><span class="n">Button</span><span class="p" data-group-id="9641973212-10">]</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="k">if</span><span class="w">
│ │ │ │                  </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="6806418342-11">(</span><span class="p" data-group-id="6806418342-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="6806418342-12">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6806418342-13">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="6806418342-14">[</span><span class="p" data-group-id="6806418342-14">]</span><span class="p" data-group-id="6806418342-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                     </span><span class="p" data-group-id="6806418342-15">[</span><span class="p" data-group-id="6806418342-16">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="6806418342-16">}</span><span class="p" data-group-id="6806418342-15">]</span><span class="p" data-group-id="6806418342-12">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="9641973212-11">(</span><span class="p" data-group-id="9641973212-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="9641973212-12">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9641973212-13">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9641973212-14">[</span><span class="p" data-group-id="9641973212-14">]</span><span class="p" data-group-id="9641973212-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                     </span><span class="p" data-group-id="9641973212-15">[</span><span class="p" data-group-id="9641973212-16">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="9641973212-16">}</span><span class="p" data-group-id="9641973212-15">]</span><span class="p" data-group-id="9641973212-12">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │                  </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="6806418342-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6806418342-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="6806418342-18">}</span><span class="p" data-group-id="6806418342-17">}</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="9641973212-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9641973212-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="9641973212-18">}</span><span class="p" data-group-id="9641973212-17">}</span><span class="w">
│ │ │ │              </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">open</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="6806418342-19">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6806418342-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="6806418342-20">(</span><span class="p" data-group-id="6806418342-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6806418342-21">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6806418342-21">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="6806418342-22">(</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6806418342-23">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="6806418342-23">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6806418342-24">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="6806418342-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6806418342-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6806418342-25">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="6806418342-26">[</span><span class="p" data-group-id="6806418342-27">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="6806418342-28">(</span><span class="n">Code</span><span class="p" data-group-id="6806418342-28">)</span><span class="p" data-group-id="6806418342-27">}</span><span class="p" data-group-id="6806418342-26">]</span><span class="p" data-group-id="6806418342-25">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="9641973212-19">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9641973212-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="9641973212-20">(</span><span class="p" data-group-id="9641973212-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9641973212-21">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9641973212-21">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="9641973212-22">(</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9641973212-23">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="9641973212-23">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9641973212-24">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="9641973212-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9641973212-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9641973212-25">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="9641973212-26">[</span><span class="p" data-group-id="9641973212-27">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="9641973212-28">(</span><span class="n">Code</span><span class="p" data-group-id="9641973212-28">)</span><span class="p" data-group-id="9641973212-27">}</span><span class="p" data-group-id="9641973212-26">]</span><span class="p" data-group-id="9641973212-25">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │ │    <a href="#stopping" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Stopping</span>
│ │ │ │  </h2>
│ │ │ │ @@ -668,59 +668,59 @@
│ │ │ │  </h3>
│ │ │ │  <p>If the <code class="inline">gen_statem</code> is part of a supervision tree, no stop function is needed.
│ │ │ │  The <code class="inline">gen_statem</code> is automatically terminated by its supervisor. Exactly how
│ │ │ │  this is done is defined by a <a href="sup_princ.xhtml#shutdown">shutdown strategy</a>
│ │ │ │  set in the supervisor.</p><p>If it is necessary to clean up before termination, the shutdown strategy
│ │ │ │  must be a time-out value and the <code class="inline">gen_statem</code> must in function <code class="inline">init/1</code>
│ │ │ │  set itself to trap exit signals by calling
│ │ │ │ -<a href="../../../lib/../erts/doc/html/erlang.html#process_flag/2"><code class="inline">process_flag(trap_exit, true)</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7815600787-1">(</span><span class="n">Args</span><span class="p" data-group-id="7815600787-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="7815600787-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7815600787-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="7815600787-3">(</span><span class="p" data-group-id="7815600787-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +<a href="../../../lib/../erts/doc/html/erlang.html#process_flag/2"><code class="inline">process_flag(trap_exit, true)</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6210723547-1">(</span><span class="n">Args</span><span class="p" data-group-id="6210723547-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="6210723547-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6210723547-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="6210723547-3">(</span><span class="p" data-group-id="6210723547-3">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>When ordered to shut down, the <code class="inline">gen_statem</code> then calls callback function
│ │ │ │  <code class="inline">terminate(shutdown, State, Data)</code>.</p><p>In this example, function <code class="inline">terminate/3</code> locks the door if it is open,
│ │ │ │  so we do not accidentally leave the door open
│ │ │ │ -when the supervision tree terminates:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="7298267236-1">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="7298267236-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="7298267236-2">(</span><span class="p" data-group-id="7298267236-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +when the supervision tree terminates:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="3193874101-1">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="3193874101-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="3193874101-2">(</span><span class="p" data-group-id="3193874101-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="standalone-gen_statem" class="section-heading">
│ │ │ │    <a href="#standalone-gen_statem" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Standalone gen_statem</span>
│ │ │ │  </h3>
│ │ │ │  <p>If the <code class="inline">gen_statem</code> is not part of a supervision tree, it can be stopped
│ │ │ │  using <a href="../../../lib/stdlib/doc/html/gen_statem.html#stop/1"><code class="inline">gen_statem:stop/1</code></a>, preferably through
│ │ │ │  an API function:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7399720841-1">(</span><span class="p" data-group-id="7399720841-2">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7399720841-2">]</span><span class="p" data-group-id="7399720841-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2824154948-1">(</span><span class="p" data-group-id="2824154948-2">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2824154948-2">]</span><span class="p" data-group-id="2824154948-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="7399720841-3">(</span><span class="p" data-group-id="7399720841-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="7399720841-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="7399720841-4">)</span><span class="p">.</span></code></pre><p>This makes the <code class="inline">gen_statem</code> call callback function <code class="inline">terminate/3</code> just like
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="2824154948-3">(</span><span class="p" data-group-id="2824154948-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="2824154948-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="2824154948-4">)</span><span class="p">.</span></code></pre><p>This makes the <code class="inline">gen_statem</code> call callback function <code class="inline">terminate/3</code> just like
│ │ │ │  for a supervised server and waits for the process to terminate.</p><h2 id="event-time-outs" class="section-heading">
│ │ │ │    <a href="#event-time-outs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Event Time-Outs</span>
│ │ │ │  </h2>
│ │ │ │  <p>A time-out feature inherited from <code class="inline">gen_statem</code>'s predecessor <a href="../../../lib/stdlib/doc/html/gen_fsm.html"><code class="inline">gen_fsm</code></a>,
│ │ │ │  is an <em>event time-out</em>, that is, if an event arrives the timer is canceled.
│ │ │ │  You get either an event or a time-out, but not both.</p><p>It is ordered by the
│ │ │ │  <a href="#transition-actions"><em>transition action</em></a> <code class="inline">{timeout, Time, EventContent}</code>,
│ │ │ │  or just an integer <code class="inline">Time</code>, even without the enclosing actions list (the latter
│ │ │ │  is a form inherited from <code class="inline">gen_fsm</code>).</p><p>This type of time-out is useful, for example, to act on inactivity.
│ │ │ │  Let's restart the code sequence if no button is pressed for say 30 seconds:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="1205491614-1">(</span><span class="ss">timeout</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1205491614-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1205491614-2">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1205491614-3">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1205491614-4">[</span><span class="p" data-group-id="1205491614-4">]</span><span class="p" data-group-id="1205491614-3">}</span><span class="p" data-group-id="1205491614-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="1205491614-5">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1205491614-6">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1205491614-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1205491614-7">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="1205491614-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1205491614-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="4843826864-1">(</span><span class="ss">timeout</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4843826864-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4843826864-2">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4843826864-3">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4843826864-4">[</span><span class="p" data-group-id="4843826864-4">]</span><span class="p" data-group-id="4843826864-3">}</span><span class="p" data-group-id="4843826864-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="4843826864-5">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4843826864-6">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4843826864-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4843826864-7">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="4843826864-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4843826864-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="1205491614-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1205491614-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="1205491614-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p" data-group-id="1205491614-8">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="4843826864-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4843826864-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="4843826864-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p" data-group-id="4843826864-8">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Whenever we receive a button event we start an <em>event time-out</em> of 30 seconds,
│ │ │ │  and if we get an <em>event type</em> of <code class="inline">timeout</code> we reset the remaining
│ │ │ │  code sequence.</p><p>An <em>event time-out</em> is canceled by any other event so you either get
│ │ │ │  some other event or the time-out event. Therefore, canceling,
│ │ │ │  restarting, or updating an <em>event time-out</em> is neither possible nor
│ │ │ │  necessary. Whatever event you act on has already canceled
│ │ │ │  the <em>event time-out</em>, so there is never a running <em>event time-out</em>
│ │ │ │ @@ -739,30 +739,30 @@
│ │ │ │  another, maybe cancel the time-out without changing states, or perhaps run
│ │ │ │  multiple time-outs in parallel. All this can be accomplished with
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:generic_timeout/0"><em>generic time-outs</em></a>. They may look a little
│ │ │ │  bit like <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:event_timeout/0"><em>event time-outs</em></a> but contain
│ │ │ │  a name to allow for any number of them simultaneously and they are
│ │ │ │  not automatically canceled.</p><p>Here is how to accomplish the <em>state time-out</em> in the previous example
│ │ │ │  by instead using a <em>generic time-out</em> named for example <code class="inline">open</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="5551017485-1">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5551017485-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5551017485-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5551017485-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="5551017485-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5551017485-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="0040081658-1">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0040081658-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0040081658-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0040081658-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="0040081658-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0040081658-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="5551017485-4">(</span><span class="p" data-group-id="5551017485-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="5551017485-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5551017485-6">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="5551017485-7">[</span><span class="p" data-group-id="5551017485-7">]</span><span class="p" data-group-id="5551017485-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="5551017485-8">[</span><span class="p" data-group-id="5551017485-9">{</span><span class="p" data-group-id="5551017485-10">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="5551017485-10">}</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="5551017485-9">}</span><span class="p" data-group-id="5551017485-8">]</span><span class="p" data-group-id="5551017485-5">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="0040081658-4">(</span><span class="p" data-group-id="0040081658-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="0040081658-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0040081658-6">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="0040081658-7">[</span><span class="p" data-group-id="0040081658-7">]</span><span class="p" data-group-id="0040081658-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="0040081658-8">[</span><span class="p" data-group-id="0040081658-9">{</span><span class="p" data-group-id="0040081658-10">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="0040081658-10">}</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="0040081658-9">}</span><span class="p" data-group-id="0040081658-8">]</span><span class="p" data-group-id="0040081658-5">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="5551017485-11">(</span><span class="p" data-group-id="5551017485-12">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="5551017485-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5551017485-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="5551017485-13">(</span><span class="p" data-group-id="5551017485-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5551017485-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="5551017485-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="5551017485-15">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5551017485-16">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5551017485-16">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5551017485-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5551017485-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="5551017485-17">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="0040081658-11">(</span><span class="p" data-group-id="0040081658-12">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="0040081658-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0040081658-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="0040081658-13">(</span><span class="p" data-group-id="0040081658-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0040081658-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="0040081658-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="0040081658-15">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0040081658-16">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0040081658-16">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0040081658-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0040081658-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="0040081658-17">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Specific <em>generic time-outs</em> can just as <a href="#state-time-outs"><em>state time-outs</em></a>
│ │ │ │  be restarted or canceled by setting it to a new time or <code class="inline">infinity</code>.</p><p>In this particular case we do not need to cancel the time-out since
│ │ │ │  the time-out event is the only possible reason to do a <em>state change</em>
│ │ │ │  from <code class="inline">open</code> to <code class="inline">locked</code>.</p><p>Instead of bothering with when to cancel a time-out, a late time-out event
│ │ │ │  can be handled by ignoring it if it arrives in a state
│ │ │ │  where it is known to be late.</p><p>You can restart, cancel, or update a <em>generic time-out</em>.
│ │ │ │  See section <a href="#time-outs"><em>Time-Outs</em></a> for details.</p><h2 id="erlang-timers" class="section-heading">
│ │ │ │ @@ -774,32 +774,32 @@
│ │ │ │  <p>The most versatile way to handle time-outs is to use Erlang Timers; see
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#start_timer/4"><code class="inline">erlang:start_timer/3,4</code></a>. Most time-out tasks
│ │ │ │  can be performed with the time-out features in <a href="../../../lib/stdlib/doc/html/gen_statem.html"><code class="inline">gen_statem</code></a>,
│ │ │ │  but an example of one that cannot is if you should need the return value
│ │ │ │  from <a href="../../../lib/../erts/doc/html/erlang.html#cancel_timer/2"><code class="inline">erlang:cancel_timer(Tref)</code></a>, that is,
│ │ │ │  the remaining time of the timer.</p><p>Here is how to accomplish the <em>state time-out</em> in the previous example
│ │ │ │  by instead using an Erlang Timer:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="5100083777-1">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5100083777-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5100083777-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5100083777-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="5100083777-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5100083777-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="9938733577-1">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9938733577-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9938733577-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9938733577-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9938733577-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9938733577-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="5100083777-4">(</span><span class="p" data-group-id="5100083777-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="9938733577-4">(</span><span class="p" data-group-id="9938733577-4">)</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="n">Tref</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ -                 </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">start_timer</span><span class="p" data-group-id="5100083777-5">(</span><span class="w">
│ │ │ │ -                     </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5100083777-6">(</span><span class="p" data-group-id="5100083777-6">)</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p" data-group-id="5100083777-5">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="5100083777-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5100083777-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="5100083777-9">[</span><span class="p" data-group-id="5100083777-9">]</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="5100083777-8">}</span><span class="p" data-group-id="5100083777-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +                 </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">start_timer</span><span class="p" data-group-id="9938733577-5">(</span><span class="w">
│ │ │ │ +                     </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9938733577-6">(</span><span class="p" data-group-id="9938733577-6">)</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p" data-group-id="9938733577-5">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9938733577-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9938733577-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9938733577-9">[</span><span class="p" data-group-id="9938733577-9">]</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="9938733577-8">}</span><span class="p" data-group-id="9938733577-7">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="5100083777-10">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5100083777-11">{</span><span class="ss">timeout</span><span class="p">,</span><span class="n">Tref</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="5100083777-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5100083777-12">#{</span><span class="ss">timer</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="5100083777-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5100083777-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="5100083777-13">(</span><span class="p" data-group-id="5100083777-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5100083777-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="5100083777-15">(</span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5100083777-15">)</span><span class="p" data-group-id="5100083777-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="5100083777-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5100083777-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5100083777-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5100083777-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5100083777-18">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="5100083777-18">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="9938733577-10">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9938733577-11">{</span><span class="ss">timeout</span><span class="p">,</span><span class="n">Tref</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="9938733577-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9938733577-12">#{</span><span class="ss">timer</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="9938733577-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9938733577-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="9938733577-13">(</span><span class="p" data-group-id="9938733577-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9938733577-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="9938733577-15">(</span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9938733577-15">)</span><span class="p" data-group-id="9938733577-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="9938733577-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9938733577-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9938733577-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9938733577-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9938733577-18">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="9938733577-18">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Removing the <code class="inline">timer</code> key from the map when we do a <em>state change</em> to <code class="inline">locked</code>
│ │ │ │  is not strictly necessary since we can only get into state <code class="inline">open</code>
│ │ │ │  with an updated <code class="inline">timer</code> map value. But it can be nice to not have
│ │ │ │  outdated values in the state <code class="inline">Data</code>.</p><p>If you need to cancel a timer because of some other event, you can use
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#cancel_timer/2"><code class="inline">erlang:cancel_timer(Tref)</code></a>. Note that no time-out
│ │ │ │  message will arrive after this (because the timer has been
│ │ │ │  explicitly canceled), unless you have already postponed one earlier
│ │ │ │ @@ -815,16 +815,16 @@
│ │ │ │    <span class="text">Postponing Events</span>
│ │ │ │  </h2>
│ │ │ │  <p>If you want to ignore a particular event in the current state and handle it
│ │ │ │  in a future state, you can postpone the event. A postponed event
│ │ │ │  is retried after a <em>state change</em>, that is, <code class="inline">OldState =/= NewState</code>.</p><p>Postponing is ordered by the
│ │ │ │  <a href="#transition-actions"><em>transition action</em></a> <code class="inline">postpone</code>.</p><p>In this example, instead of ignoring button events while in the <code class="inline">open</code> state,
│ │ │ │  we can postpone them handle them later in the <code class="inline">locked</code> state:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="2218670937-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2218670937-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2218670937-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2218670937-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2218670937-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="2218670937-4">[</span><span class="ss">postpone</span><span class="p" data-group-id="2218670937-4">]</span><span class="p" data-group-id="2218670937-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="8444466652-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8444466652-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8444466652-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8444466652-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8444466652-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="8444466652-4">[</span><span class="ss">postpone</span><span class="p" data-group-id="8444466652-4">]</span><span class="p" data-group-id="8444466652-3">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Since a postponed event is only retried after a <em>state change</em>, you have to
│ │ │ │  think about where to keep a state data item. You can keep it in the server
│ │ │ │  <code class="inline">Data</code> or in the <code class="inline">State</code> itself, for example by having two more or less
│ │ │ │  identical states to keep a boolean value, or by using a complex state (see
│ │ │ │  section <a href="#complex-state"><em>Complex State</em></a>) with
│ │ │ │  <a href="#callback-modes"><em>callback mode</em></a>
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:callback_mode/0"><code class="inline">handle_event_function</code></a>. If a change
│ │ │ │ @@ -845,55 +845,55 @@
│ │ │ │    <a href="#selective-receive" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Selective Receive</span>
│ │ │ │  </h3>
│ │ │ │  <p>Erlang's selective <code class="inline">receive</code> statement is often used to describe simple state
│ │ │ │  machine examples in straightforward Erlang code. The following is a possible
│ │ │ │ -implementation of the first example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5651631263-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="5651631263-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5651631263-2">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_1</span><span class="p" data-group-id="5651631263-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5651631263-3">(</span><span class="p" data-group-id="5651631263-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5651631263-4">]</span><span class="p" data-group-id="5651631263-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="5651631263-5">(</span><span class="n">Code</span><span class="p" data-group-id="5651631263-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="5651631263-6">(</span><span class="w">
│ │ │ │ -      </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5651631263-7">(</span><span class="p" data-group-id="5651631263-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">register</span><span class="p" data-group-id="5651631263-8">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5651631263-9">(</span><span class="p" data-group-id="5651631263-9">)</span><span class="p" data-group-id="5651631263-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -	      </span><span class="nf">do_lock</span><span class="p" data-group-id="5651631263-10">(</span><span class="p" data-group-id="5651631263-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -	      </span><span class="nf">locked</span><span class="p" data-group-id="5651631263-11">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="5651631263-12">(</span><span class="n">Code</span><span class="p" data-group-id="5651631263-12">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5651631263-13">[</span><span class="p" data-group-id="5651631263-13">]</span><span class="p" data-group-id="5651631263-11">)</span><span class="w">
│ │ │ │ -      </span><span class="k">end</span><span class="p" data-group-id="5651631263-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +implementation of the first example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3640408287-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="3640408287-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3640408287-2">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_1</span><span class="p" data-group-id="3640408287-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3640408287-3">(</span><span class="p" data-group-id="3640408287-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3640408287-4">]</span><span class="p" data-group-id="3640408287-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="3640408287-5">(</span><span class="n">Code</span><span class="p" data-group-id="3640408287-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="3640408287-6">(</span><span class="w">
│ │ │ │ +      </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3640408287-7">(</span><span class="p" data-group-id="3640408287-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">register</span><span class="p" data-group-id="3640408287-8">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3640408287-9">(</span><span class="p" data-group-id="3640408287-9">)</span><span class="p" data-group-id="3640408287-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	      </span><span class="nf">do_lock</span><span class="p" data-group-id="3640408287-10">(</span><span class="p" data-group-id="3640408287-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	      </span><span class="nf">locked</span><span class="p" data-group-id="3640408287-11">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="3640408287-12">(</span><span class="n">Code</span><span class="p" data-group-id="3640408287-12">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3640408287-13">[</span><span class="p" data-group-id="3640408287-13">]</span><span class="p" data-group-id="3640408287-11">)</span><span class="w">
│ │ │ │ +      </span><span class="k">end</span><span class="p" data-group-id="3640408287-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="5651631263-14">(</span><span class="n">Button</span><span class="p" data-group-id="5651631263-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">NAME</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5651631263-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5651631263-15">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="4423684663-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="4423684663-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="3640408287-14">(</span><span class="n">Button</span><span class="p" data-group-id="3640408287-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">NAME</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3640408287-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3640408287-15">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="2143390221-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="2143390221-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4423684663-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4423684663-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2143390221-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2143390221-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │                  </span><span class="k">if</span><span class="w">
│ │ │ │ -                    </span><span class="nf">length</span><span class="p" data-group-id="4423684663-3">(</span><span class="n">Buttons</span><span class="p" data-group-id="4423684663-3">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                    </span><span class="nf">length</span><span class="p" data-group-id="2143390221-3">(</span><span class="n">Buttons</span><span class="p" data-group-id="2143390221-3">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                          </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │                      </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                        </span><span class="nf">tl</span><span class="p" data-group-id="4423684663-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="4423684663-4">)</span><span class="w">
│ │ │ │ -                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4423684663-5">[</span><span class="n">Button</span><span class="p" data-group-id="4423684663-5">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                        </span><span class="nf">tl</span><span class="p" data-group-id="2143390221-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="2143390221-4">)</span><span class="w">
│ │ │ │ +                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2143390221-5">[</span><span class="n">Button</span><span class="p" data-group-id="2143390221-5">]</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="k">if</span><span class="w">
│ │ │ │                  </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="4423684663-6">(</span><span class="p" data-group-id="4423684663-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -		    </span><span class="nf">open</span><span class="p" data-group-id="4423684663-7">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="4423684663-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="2143390221-6">(</span><span class="p" data-group-id="2143390221-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +		    </span><span class="nf">open</span><span class="p" data-group-id="2143390221-7">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="2143390221-7">)</span><span class="p">;</span><span class="w">
│ │ │ │                  </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -                    </span><span class="nf">locked</span><span class="p" data-group-id="4423684663-8">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="4423684663-8">)</span><span class="w">
│ │ │ │ +                    </span><span class="nf">locked</span><span class="p" data-group-id="2143390221-8">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="2143390221-8">)</span><span class="w">
│ │ │ │              </span><span class="k">end</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="1886841689-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="1886841689-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="9721503370-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="9721503370-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -	    </span><span class="nf">do_lock</span><span class="p" data-group-id="1886841689-2">(</span><span class="p" data-group-id="1886841689-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">locked</span><span class="p" data-group-id="1886841689-3">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1886841689-4">[</span><span class="p" data-group-id="1886841689-4">]</span><span class="p" data-group-id="1886841689-3">)</span><span class="w">
│ │ │ │ +	    </span><span class="nf">do_lock</span><span class="p" data-group-id="9721503370-2">(</span><span class="p" data-group-id="9721503370-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="nf">locked</span><span class="p" data-group-id="9721503370-3">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9721503370-4">[</span><span class="p" data-group-id="9721503370-4">]</span><span class="p" data-group-id="9721503370-3">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">do_lock</span><span class="p" data-group-id="1886841689-5">(</span><span class="p" data-group-id="1886841689-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1886841689-6">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1886841689-7">[</span><span class="p" data-group-id="1886841689-7">]</span><span class="p" data-group-id="1886841689-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="1886841689-8">(</span><span class="p" data-group-id="1886841689-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1886841689-9">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1886841689-10">[</span><span class="p" data-group-id="1886841689-10">]</span><span class="p" data-group-id="1886841689-9">)</span><span class="p">.</span></code></pre><p>The selective receive in this case causes <code class="inline">open</code> to implicitly postpone any
│ │ │ │ +</span><span class="nf">do_lock</span><span class="p" data-group-id="9721503370-5">(</span><span class="p" data-group-id="9721503370-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9721503370-6">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9721503370-7">[</span><span class="p" data-group-id="9721503370-7">]</span><span class="p" data-group-id="9721503370-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="9721503370-8">(</span><span class="p" data-group-id="9721503370-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9721503370-9">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9721503370-10">[</span><span class="p" data-group-id="9721503370-10">]</span><span class="p" data-group-id="9721503370-9">)</span><span class="p">.</span></code></pre><p>The selective receive in this case causes <code class="inline">open</code> to implicitly postpone any
│ │ │ │  events to the <code class="inline">locked</code> state.</p><p>A catch-all receive should never be used from a <code class="inline">gen_statem</code> behaviour
│ │ │ │  (or from any <code class="inline">gen_*</code> behaviour), as the receive statement is within
│ │ │ │  the <code class="inline">gen_*</code> engine itself. <a href="../../../lib/stdlib/doc/html/sys.html"><code class="inline">sys</code></a>-compatible behaviours must respond to
│ │ │ │  system messages and therefore do that in their engine receive loop,
│ │ │ │  passing non-system messages to the <em>callback module</em>. Using a catch-all
│ │ │ │  receive can result in system messages being discarded, which in turn
│ │ │ │  can lead to unexpected behaviour. If a selective receive must be used,
│ │ │ │ @@ -916,40 +916,40 @@
│ │ │ │  section), especially if only one or a few states have state enter actions,
│ │ │ │  this is a perfect use case for the built in
│ │ │ │  <a href="#state-enter-calls"><em>state enter calls</em></a>.</p><p>You return a list containing <code class="inline">state_enter</code> from your
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:callback_mode/0"><code class="inline">callback_mode/0</code></a> function and the
│ │ │ │  <code class="inline">gen_statem</code> engine will call your <em>state callback</em> once with an event
│ │ │ │  <code class="inline">(enter, OldState, ...)</code> whenever it does a <em>state change</em>. Then you
│ │ │ │  just need to handle these event-like calls in all states.</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6079218935-1">(</span><span class="n">Code</span><span class="p" data-group-id="6079218935-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="6079218935-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6079218935-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6079218935-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="6079218935-4">(</span><span class="n">Code</span><span class="p" data-group-id="6079218935-4">)</span><span class="p" data-group-id="6079218935-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6079218935-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6079218935-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="6079218935-6">(</span><span class="p" data-group-id="6079218935-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6079218935-7">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="6079218935-7">]</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="6079218935-8">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6079218935-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="6079218935-9">(</span><span class="p" data-group-id="6079218935-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6079218935-10">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="6079218935-11">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6079218935-12">[</span><span class="p" data-group-id="6079218935-12">]</span><span class="p" data-group-id="6079218935-11">}</span><span class="p" data-group-id="6079218935-10">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="6079218935-13">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6079218935-14">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6079218935-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6079218935-15">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="6079218935-15">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6079218935-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="0750737677-1">(</span><span class="n">Code</span><span class="p" data-group-id="0750737677-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="0750737677-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0750737677-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0750737677-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0750737677-4">(</span><span class="n">Code</span><span class="p" data-group-id="0750737677-4">)</span><span class="p" data-group-id="0750737677-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0750737677-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0750737677-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="0750737677-6">(</span><span class="p" data-group-id="0750737677-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0750737677-7">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="0750737677-7">]</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="0750737677-8">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0750737677-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="0750737677-9">(</span><span class="p" data-group-id="0750737677-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0750737677-10">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="0750737677-11">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0750737677-12">[</span><span class="p" data-group-id="0750737677-12">]</span><span class="p" data-group-id="0750737677-11">}</span><span class="p" data-group-id="0750737677-10">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="0750737677-13">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0750737677-14">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0750737677-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0750737677-15">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="0750737677-15">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0750737677-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="6079218935-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6079218935-16">}</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="0750737677-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0750737677-16">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="6079218935-17">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="6079218935-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="6079218935-18">(</span><span class="p" data-group-id="6079218935-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6079218935-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="6079218935-20">[</span><span class="p" data-group-id="6079218935-21">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="6079218935-21">}</span><span class="p" data-group-id="6079218935-20">]</span><span class="p" data-group-id="6079218935-19">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="6079218935-22">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6079218935-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6079218935-23">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6079218935-23">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="0750737677-17">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0750737677-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="0750737677-18">(</span><span class="p" data-group-id="0750737677-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0750737677-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="0750737677-20">[</span><span class="p" data-group-id="0750737677-21">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="0750737677-21">}</span><span class="p" data-group-id="0750737677-20">]</span><span class="p" data-group-id="0750737677-19">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="0750737677-22">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0750737677-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0750737677-23">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0750737677-23">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>You can repeat the state enter code by returning one of
│ │ │ │  <code class="inline">{repeat_state, ...}</code>,<code class="inline">{repeat_state_and_data, _}</code>,
│ │ │ │  or <code class="inline">repeat_state_and_data</code> that otherwise behaves exactly like their
│ │ │ │  <code class="inline">keep_state</code> siblings.  See the type
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:state_callback_result/2"><code class="inline">state_callback_result()</code></a>
│ │ │ │  in the Reference Manual.</p><h2 id="inserted-events" class="section-heading">
│ │ │ │    <a href="#inserted-events" class="hover-link">
│ │ │ │ @@ -971,44 +971,44 @@
│ │ │ │  to dispatch pre-processed events as internal events to the main state
│ │ │ │  machine.</p><p>Using internal events also can make it easier to synchronize the state
│ │ │ │  machines.</p><p>A variant of this is to use a <a href="#complex-state">complex state</a> with
│ │ │ │  <a href="#one-state-callback">one state callback</a>, modeling the state
│ │ │ │  with, for example, a tuple <code class="inline">{MainFSMState, SubFSMState}</code>.</p><p>To illustrate this we make up an example where the buttons instead generate
│ │ │ │  down and up (press and release) events, and the lock responds
│ │ │ │  to an up event only after the corresponding down event.</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2665025641-1">(</span><span class="p" data-group-id="2665025641-2">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2665025641-2">]</span><span class="p" data-group-id="2665025641-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6670630586-1">(</span><span class="p" data-group-id="6670630586-2">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6670630586-2">]</span><span class="p" data-group-id="6670630586-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">down</span><span class="p" data-group-id="2665025641-3">(</span><span class="n">Button</span><span class="p" data-group-id="2665025641-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="2665025641-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2665025641-5">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2665025641-5">}</span><span class="p" data-group-id="2665025641-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">down</span><span class="p" data-group-id="6670630586-3">(</span><span class="n">Button</span><span class="p" data-group-id="6670630586-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6670630586-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6670630586-5">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6670630586-5">}</span><span class="p" data-group-id="6670630586-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">up</span><span class="p" data-group-id="2665025641-6">(</span><span class="n">Button</span><span class="p" data-group-id="2665025641-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="2665025641-7">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2665025641-8">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2665025641-8">}</span><span class="p" data-group-id="2665025641-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">up</span><span class="p" data-group-id="6670630586-6">(</span><span class="n">Button</span><span class="p" data-group-id="6670630586-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6670630586-7">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6670630586-8">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6670630586-8">}</span><span class="p" data-group-id="6670630586-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="2665025641-9">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2665025641-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="2665025641-10">(</span><span class="p" data-group-id="2665025641-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2665025641-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="2665025641-12">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2665025641-13">[</span><span class="p" data-group-id="2665025641-13">]</span><span class="p" data-group-id="2665025641-12">}</span><span class="p" data-group-id="2665025641-11">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="2665025641-14">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2665025641-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2665025641-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2665025641-16">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="2665025641-16">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2665025641-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">handle_common</span><span class="p" data-group-id="7431076248-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7431076248-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7431076248-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7431076248-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7431076248-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7431076248-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="7431076248-4">}</span><span class="p" data-group-id="7431076248-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="7431076248-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7431076248-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7431076248-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7431076248-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="6670630586-9">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6670630586-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="6670630586-10">(</span><span class="p" data-group-id="6670630586-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6670630586-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="6670630586-12">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6670630586-13">[</span><span class="p" data-group-id="6670630586-13">]</span><span class="p" data-group-id="6670630586-12">}</span><span class="p" data-group-id="6670630586-11">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="6670630586-14">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6670630586-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6670630586-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6670630586-16">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="6670630586-16">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6670630586-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">handle_common</span><span class="p" data-group-id="9798777799-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9798777799-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9798777799-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9798777799-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9798777799-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9798777799-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="9798777799-4">}</span><span class="p" data-group-id="9798777799-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="9798777799-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9798777799-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9798777799-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9798777799-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7431076248-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="7431076248-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="7431076248-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="7431076248-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7431076248-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="7431076248-10">[</span><span class="p" data-group-id="7431076248-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="7431076248-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7431076248-12">}</span><span class="p" data-group-id="7431076248-11">}</span><span class="p" data-group-id="7431076248-10">]</span><span class="p" data-group-id="7431076248-8">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7431076248-13">#{</span><span class="p" data-group-id="7431076248-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9798777799-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="9798777799-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9798777799-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="9798777799-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9798777799-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="9798777799-10">[</span><span class="p" data-group-id="9798777799-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="9798777799-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9798777799-12">}</span><span class="p" data-group-id="9798777799-11">}</span><span class="p" data-group-id="9798777799-10">]</span><span class="p" data-group-id="9798777799-8">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9798777799-13">#{</span><span class="p" data-group-id="9798777799-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="7431076248-14">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7431076248-15">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7431076248-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7431076248-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7431076248-16">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="7431076248-17">[</span><span class="ss">postpone</span><span class="p" data-group-id="7431076248-17">]</span><span class="p" data-group-id="7431076248-16">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="9798777799-14">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9798777799-15">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9798777799-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9798777799-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9798777799-16">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="9798777799-17">[</span><span class="ss">postpone</span><span class="p" data-group-id="9798777799-17">]</span><span class="p" data-group-id="9798777799-16">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>If you start this program with <code class="inline">code_lock:start([17])</code> you can unlock with
│ │ │ │  <code class="inline">code_lock:down(17), code_lock:up(17).</code></p><h2 id="example-revisited" class="section-heading">
│ │ │ │    <a href="#example-revisited" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example Revisited</span>
│ │ │ │  </h2>
│ │ │ │ @@ -1036,152 +1036,152 @@
│ │ │ │  Also, the state diagram does not show that the <code class="inline">code_length/0</code> call
│ │ │ │  must be handled in every state.</p><h3 id="callback-mode-state_functions" class="section-heading">
│ │ │ │    <a href="#callback-mode-state_functions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Callback Mode: state_functions</span>
│ │ │ │  </h3>
│ │ │ │ -<p>Using state functions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3436661825-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="3436661825-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3436661825-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="3436661825-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3436661825-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_2</span><span class="p" data-group-id="3436661825-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>Using state functions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8832207974-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="8832207974-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8832207974-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="8832207974-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8832207974-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_2</span><span class="p" data-group-id="8832207974-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3436661825-4">(</span><span class="p" data-group-id="3436661825-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3436661825-5">]</span><span class="p" data-group-id="3436661825-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3436661825-6">(</span><span class="p" data-group-id="3436661825-7">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3436661825-7">]</span><span class="p" data-group-id="3436661825-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3436661825-8">(</span><span class="p" data-group-id="3436661825-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="3436661825-9">]</span><span class="p" data-group-id="3436661825-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3436661825-10">(</span><span class="p" data-group-id="3436661825-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="3436661825-11">]</span><span class="p" data-group-id="3436661825-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="3436661825-12">(</span><span class="n">Code</span><span class="p" data-group-id="3436661825-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3436661825-13">(</span><span class="p" data-group-id="3436661825-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="3436661825-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3436661825-15">[</span><span class="p" data-group-id="3436661825-15">]</span><span class="p" data-group-id="3436661825-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="3436661825-16">(</span><span class="p" data-group-id="3436661825-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="3436661825-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="3436661825-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">down</span><span class="p" data-group-id="3436661825-18">(</span><span class="n">Button</span><span class="p" data-group-id="3436661825-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="3436661825-19">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3436661825-20">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3436661825-20">}</span><span class="p" data-group-id="3436661825-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">up</span><span class="p" data-group-id="3436661825-21">(</span><span class="n">Button</span><span class="p" data-group-id="3436661825-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="3436661825-22">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3436661825-23">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3436661825-23">}</span><span class="p" data-group-id="3436661825-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="3436661825-24">(</span><span class="p" data-group-id="3436661825-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="3436661825-25">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="3436661825-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9113310413-1">(</span><span class="n">Code</span><span class="p" data-group-id="9113310413-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9113310413-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9113310413-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9113310413-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9113310413-4">(</span><span class="n">Code</span><span class="p" data-group-id="9113310413-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9113310413-5">[</span><span class="p" data-group-id="9113310413-5">]</span><span class="p" data-group-id="9113310413-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9113310413-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9113310413-6">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8832207974-4">(</span><span class="p" data-group-id="8832207974-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8832207974-5">]</span><span class="p" data-group-id="8832207974-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8832207974-6">(</span><span class="p" data-group-id="8832207974-7">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8832207974-7">]</span><span class="p" data-group-id="8832207974-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8832207974-8">(</span><span class="p" data-group-id="8832207974-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="8832207974-9">]</span><span class="p" data-group-id="8832207974-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8832207974-10">(</span><span class="p" data-group-id="8832207974-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="8832207974-11">]</span><span class="p" data-group-id="8832207974-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="8832207974-12">(</span><span class="n">Code</span><span class="p" data-group-id="8832207974-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8832207974-13">(</span><span class="p" data-group-id="8832207974-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="8832207974-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8832207974-15">[</span><span class="p" data-group-id="8832207974-15">]</span><span class="p" data-group-id="8832207974-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="8832207974-16">(</span><span class="p" data-group-id="8832207974-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="8832207974-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="8832207974-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">down</span><span class="p" data-group-id="8832207974-18">(</span><span class="n">Button</span><span class="p" data-group-id="8832207974-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8832207974-19">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8832207974-20">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8832207974-20">}</span><span class="p" data-group-id="8832207974-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">up</span><span class="p" data-group-id="8832207974-21">(</span><span class="n">Button</span><span class="p" data-group-id="8832207974-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8832207974-22">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8832207974-23">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8832207974-23">}</span><span class="p" data-group-id="8832207974-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="8832207974-24">(</span><span class="p" data-group-id="8832207974-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="8832207974-25">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="8832207974-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9716136954-1">(</span><span class="n">Code</span><span class="p" data-group-id="9716136954-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="9716136954-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9716136954-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9716136954-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9716136954-4">(</span><span class="n">Code</span><span class="p" data-group-id="9716136954-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9716136954-5">[</span><span class="p" data-group-id="9716136954-5">]</span><span class="p" data-group-id="9716136954-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9716136954-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9716136954-6">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="9113310413-7">(</span><span class="p" data-group-id="9113310413-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9113310413-8">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="9113310413-8">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="9716136954-7">(</span><span class="p" data-group-id="9716136954-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9716136954-8">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="9716136954-8">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9113310413-9">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="9113310413-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9113310413-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="9113310413-11">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9113310413-11">)</span><span class="p" data-group-id="9113310413-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9716136954-9">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="9716136954-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9716136954-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="9716136954-11">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9716136954-11">)</span><span class="p" data-group-id="9716136954-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="9113310413-12">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9113310413-13">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9113310413-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9113310413-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9113310413-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9113310413-15">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="9113310413-15">}</span><span class="p" data-group-id="9113310413-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="9113310413-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9113310413-17">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9113310413-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9113310413-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="9716136954-12">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9716136954-13">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9716136954-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9716136954-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9716136954-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9716136954-15">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="9716136954-15">}</span><span class="p" data-group-id="9716136954-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="9716136954-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9716136954-17">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9716136954-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9716136954-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9113310413-18">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="9113310413-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9113310413-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="9113310413-20">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9113310413-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="9113310413-21">[</span><span class="p" data-group-id="9113310413-22">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="9113310413-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9113310413-23">}</span><span class="p" data-group-id="9113310413-22">}</span><span class="p" data-group-id="9113310413-21">]</span><span class="p" data-group-id="9113310413-19">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9113310413-24">#{</span><span class="p" data-group-id="9113310413-24">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9716136954-18">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="9716136954-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9716136954-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="9716136954-20">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9716136954-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="9716136954-21">[</span><span class="p" data-group-id="9716136954-22">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="9716136954-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9716136954-23">}</span><span class="p" data-group-id="9716136954-22">}</span><span class="p" data-group-id="9716136954-21">]</span><span class="p" data-group-id="9716136954-19">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9716136954-24">#{</span><span class="p" data-group-id="9716136954-24">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="9113310413-25">(</span><span class="p" data-group-id="9113310413-26">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="9113310413-26">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9113310413-27">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="9113310413-27">}</span><span class="p" data-group-id="9113310413-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9113310413-28">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="9113310413-29">[</span><span class="p" data-group-id="9113310413-30">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="9113310413-31">(</span><span class="n">Code</span><span class="p" data-group-id="9113310413-31">)</span><span class="p" data-group-id="9113310413-30">}</span><span class="p" data-group-id="9113310413-29">]</span><span class="p" data-group-id="9113310413-28">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="7126449111-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7126449111-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="7126449111-2">(</span><span class="p" data-group-id="7126449111-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7126449111-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7126449111-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="7126449111-5">[</span><span class="p" data-group-id="7126449111-5">]</span><span class="p" data-group-id="7126449111-4">}</span><span class="p" data-group-id="7126449111-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="7126449111-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7126449111-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7126449111-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7126449111-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="7126449111-9">[</span><span class="p" data-group-id="7126449111-9">]</span><span class="p" data-group-id="7126449111-8">}</span><span class="p" data-group-id="7126449111-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="7126449111-10">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7126449111-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7126449111-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="7126449111-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="7126449111-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7126449111-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="9716136954-25">(</span><span class="p" data-group-id="9716136954-26">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="9716136954-26">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9716136954-27">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="9716136954-27">}</span><span class="p" data-group-id="9716136954-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9716136954-28">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="9716136954-29">[</span><span class="p" data-group-id="9716136954-30">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="9716136954-31">(</span><span class="n">Code</span><span class="p" data-group-id="9716136954-31">)</span><span class="p" data-group-id="9716136954-30">}</span><span class="p" data-group-id="9716136954-29">]</span><span class="p" data-group-id="9716136954-28">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="1271872787-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1271872787-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="1271872787-2">(</span><span class="p" data-group-id="1271872787-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1271872787-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1271872787-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1271872787-5">[</span><span class="p" data-group-id="1271872787-5">]</span><span class="p" data-group-id="1271872787-4">}</span><span class="p" data-group-id="1271872787-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="1271872787-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1271872787-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1271872787-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1271872787-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1271872787-9">[</span><span class="p" data-group-id="1271872787-9">]</span><span class="p" data-group-id="1271872787-8">}</span><span class="p" data-group-id="1271872787-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="1271872787-10">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1271872787-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1271872787-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="1271872787-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="1271872787-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1271872787-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │          </span><span class="k">if</span><span class="w">
│ │ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="7126449111-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="7126449111-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="1271872787-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="1271872787-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="7126449111-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="7126449111-14">)</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="7126449111-15">[</span><span class="n">Button</span><span class="p" data-group-id="7126449111-15">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="1271872787-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="1271872787-14">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1271872787-15">[</span><span class="n">Button</span><span class="p" data-group-id="1271872787-15">]</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="7126449111-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7126449111-16">}</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="1271872787-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1271872787-16">}</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="7126449111-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7126449111-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="7126449111-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="7126449111-19">[</span><span class="p" data-group-id="7126449111-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="7126449111-20">}</span><span class="p" data-group-id="7126449111-19">]</span><span class="p" data-group-id="7126449111-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="1271872787-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1271872787-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="1271872787-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="1271872787-19">[</span><span class="p" data-group-id="1271872787-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="1271872787-20">}</span><span class="p" data-group-id="1271872787-19">]</span><span class="p" data-group-id="1271872787-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="8189217644-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="8189217644-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="8189217644-2">(</span><span class="p" data-group-id="8189217644-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8189217644-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="8189217644-4">[</span><span class="p" data-group-id="8189217644-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8189217644-5">}</span><span class="p" data-group-id="8189217644-4">]</span><span class="p" data-group-id="8189217644-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8189217644-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8189217644-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8189217644-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8189217644-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8189217644-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8189217644-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8189217644-9">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="8189217644-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8189217644-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8189217644-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="8189217644-11">]</span><span class="p" data-group-id="8189217644-10">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="0944530534-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0944530534-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="0944530534-2">(</span><span class="p" data-group-id="0944530534-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0944530534-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="0944530534-4">[</span><span class="p" data-group-id="0944530534-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="0944530534-5">}</span><span class="p" data-group-id="0944530534-4">]</span><span class="p" data-group-id="0944530534-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="0944530534-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0944530534-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0944530534-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0944530534-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="0944530534-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0944530534-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0944530534-9">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="0944530534-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0944530534-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0944530534-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="0944530534-11">]</span><span class="p" data-group-id="0944530534-10">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">do_lock</span><span class="p" data-group-id="8189217644-12">(</span><span class="p" data-group-id="8189217644-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8189217644-13">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8189217644-14">[</span><span class="p" data-group-id="8189217644-14">]</span><span class="p" data-group-id="8189217644-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="8189217644-15">(</span><span class="p" data-group-id="8189217644-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8189217644-16">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8189217644-17">[</span><span class="p" data-group-id="8189217644-17">]</span><span class="p" data-group-id="8189217644-16">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">do_lock</span><span class="p" data-group-id="0944530534-12">(</span><span class="p" data-group-id="0944530534-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0944530534-13">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0944530534-14">[</span><span class="p" data-group-id="0944530534-14">]</span><span class="p" data-group-id="0944530534-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="0944530534-15">(</span><span class="p" data-group-id="0944530534-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0944530534-16">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0944530534-17">[</span><span class="p" data-group-id="0944530534-17">]</span><span class="p" data-group-id="0944530534-16">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="8189217644-18">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="8189217644-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="8189217644-19">(</span><span class="p" data-group-id="8189217644-19">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="0944530534-18">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0944530534-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="0944530534-19">(</span><span class="p" data-group-id="0944530534-19">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="callback-mode-handle_event_function" class="section-heading">
│ │ │ │    <a href="#callback-mode-handle_event_function" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Callback Mode: handle_event_function</span>
│ │ │ │  </h3>
│ │ │ │  <p>This section describes what to change in the example to use one
│ │ │ │  <code class="inline">handle_event/4</code> function.  The previously used approach to first branch
│ │ │ │  depending on event does not work that well here because of
│ │ │ │ -the <em>state enter calls</em>, so this example first branches depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2958707169-1">(</span><span class="p" data-group-id="2958707169-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="2958707169-2">]</span><span class="p" data-group-id="2958707169-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="1307372707-1">(</span><span class="p" data-group-id="1307372707-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1307372707-2">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="1307372707-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │ +the <em>state enter calls</em>, so this example first branches depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8813890022-1">(</span><span class="p" data-group-id="8813890022-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="8813890022-2">]</span><span class="p" data-group-id="8813890022-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="7229123486-1">(</span><span class="p" data-group-id="7229123486-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7229123486-2">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="7229123486-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% State: locked</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9876277011-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9876277011-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="9876277011-2">(</span><span class="p" data-group-id="9876277011-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9876277011-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9876277011-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9876277011-5">[</span><span class="p" data-group-id="9876277011-5">]</span><span class="p" data-group-id="9876277011-4">}</span><span class="p" data-group-id="9876277011-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9876277011-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9876277011-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9876277011-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9876277011-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9876277011-9">[</span><span class="p" data-group-id="9876277011-9">]</span><span class="p" data-group-id="9876277011-8">}</span><span class="p" data-group-id="9876277011-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9876277011-10">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9876277011-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9876277011-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9876277011-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9876277011-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9876277011-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="1784072188-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1784072188-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="1784072188-2">(</span><span class="p" data-group-id="1784072188-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1784072188-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1784072188-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1784072188-5">[</span><span class="p" data-group-id="1784072188-5">]</span><span class="p" data-group-id="1784072188-4">}</span><span class="p" data-group-id="1784072188-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="1784072188-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1784072188-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1784072188-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1784072188-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1784072188-9">[</span><span class="p" data-group-id="1784072188-9">]</span><span class="p" data-group-id="1784072188-8">}</span><span class="p" data-group-id="1784072188-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="1784072188-10">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1784072188-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1784072188-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="1784072188-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="1784072188-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1784072188-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │          </span><span class="k">if</span><span class="w">
│ │ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="9876277011-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="9876277011-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="1784072188-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="1784072188-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="9876277011-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="9876277011-14">)</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9876277011-15">[</span><span class="n">Button</span><span class="p" data-group-id="9876277011-15">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="1784072188-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="1784072188-14">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1784072188-15">[</span><span class="n">Button</span><span class="p" data-group-id="1784072188-15">]</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9876277011-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9876277011-16">}</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="1784072188-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1784072188-16">}</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9876277011-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9876277011-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="9876277011-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="9876277011-19">[</span><span class="p" data-group-id="9876277011-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="9876277011-20">}</span><span class="p" data-group-id="9876277011-19">]</span><span class="p" data-group-id="9876277011-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="1784072188-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1784072188-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="1784072188-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="1784072188-19">[</span><span class="p" data-group-id="1784072188-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="1784072188-20">}</span><span class="p" data-group-id="1784072188-19">]</span><span class="p" data-group-id="1784072188-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1201310620-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="1201310620-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="1201310620-2">(</span><span class="p" data-group-id="1201310620-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1201310620-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="1201310620-4">[</span><span class="p" data-group-id="1201310620-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="1201310620-5">}</span><span class="p" data-group-id="1201310620-4">]</span><span class="p" data-group-id="1201310620-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1201310620-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1201310620-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1201310620-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1201310620-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1201310620-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1201310620-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1201310620-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1201310620-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1201310620-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="1201310620-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="1201310620-11">]</span><span class="p" data-group-id="1201310620-10">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%% Common events</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="3591981310-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3591981310-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3591981310-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3591981310-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3591981310-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3591981310-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="3591981310-4">}</span><span class="p" data-group-id="3591981310-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="3591981310-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3591981310-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3591981310-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3591981310-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="0342214018-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0342214018-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="0342214018-2">(</span><span class="p" data-group-id="0342214018-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0342214018-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="0342214018-4">[</span><span class="p" data-group-id="0342214018-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="0342214018-5">}</span><span class="p" data-group-id="0342214018-4">]</span><span class="p" data-group-id="0342214018-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="0342214018-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0342214018-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0342214018-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0342214018-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="0342214018-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0342214018-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0342214018-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="0342214018-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0342214018-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="0342214018-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="0342214018-11">]</span><span class="p" data-group-id="0342214018-10">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%% Common events</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2459272519-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2459272519-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2459272519-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2459272519-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2459272519-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2459272519-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="2459272519-4">}</span><span class="p" data-group-id="2459272519-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2459272519-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2459272519-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2459272519-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2459272519-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="3591981310-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="3591981310-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="3591981310-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="3591981310-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3591981310-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="3591981310-10">[</span><span class="p" data-group-id="3591981310-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="3591981310-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3591981310-12">}</span><span class="p" data-group-id="3591981310-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="3591981310-13">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="3591981310-13">}</span><span class="p" data-group-id="3591981310-10">]</span><span class="p" data-group-id="3591981310-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="3591981310-14">#{</span><span class="p" data-group-id="3591981310-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2459272519-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="2459272519-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="2459272519-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="2459272519-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2459272519-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="2459272519-10">[</span><span class="p" data-group-id="2459272519-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="2459272519-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2459272519-12">}</span><span class="p" data-group-id="2459272519-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="2459272519-13">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="2459272519-13">}</span><span class="p" data-group-id="2459272519-10">]</span><span class="p" data-group-id="2459272519-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2459272519-14">#{</span><span class="p" data-group-id="2459272519-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="3591981310-15">(</span><span class="p" data-group-id="3591981310-16">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="3591981310-16">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3591981310-17">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="3591981310-17">}</span><span class="p" data-group-id="3591981310-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3591981310-18">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="3591981310-19">[</span><span class="p" data-group-id="3591981310-20">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">Length</span><span class="p" data-group-id="3591981310-20">}</span><span class="p" data-group-id="3591981310-19">]</span><span class="p" data-group-id="3591981310-18">}</span><span class="p">.</span></code></pre><p>Notice that postponing buttons from the <code class="inline">open</code> state to the <code class="inline">locked</code> state
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2459272519-15">(</span><span class="p" data-group-id="2459272519-16">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="2459272519-16">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2459272519-17">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="2459272519-17">}</span><span class="p" data-group-id="2459272519-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2459272519-18">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="2459272519-19">[</span><span class="p" data-group-id="2459272519-20">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">Length</span><span class="p" data-group-id="2459272519-20">}</span><span class="p" data-group-id="2459272519-19">]</span><span class="p" data-group-id="2459272519-18">}</span><span class="p">.</span></code></pre><p>Notice that postponing buttons from the <code class="inline">open</code> state to the <code class="inline">locked</code> state
│ │ │ │  seems like a strange thing to do for a code lock, but it at least
│ │ │ │  illustrates event postponing.</p><h2 id="filter-the-state" class="section-heading">
│ │ │ │    <a href="#filter-the-state" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Filter the State</span>
│ │ │ │  </h2>
│ │ │ │ @@ -1191,30 +1191,30 @@
│ │ │ │  and which digits that remain to unlock.</p><p>This state data can be regarded as sensitive, and maybe not what you want
│ │ │ │  in the error log because of some unpredictable event.</p><p>Another reason to filter the state can be that the state is too large to print,
│ │ │ │  as it fills the error log with uninteresting details.</p><p>To avoid this, you can format the internal state that gets in the error log
│ │ │ │  and gets returned from <a href="../../../lib/stdlib/doc/html/sys.html#get_status/1"><code class="inline">sys:get_status/1,2</code></a>
│ │ │ │  by implementing function
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:format_status/2"><code class="inline">Module:format_status/2</code></a>,
│ │ │ │  for example like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5368912170-1">(</span><span class="p" data-group-id="5368912170-2">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">format_status</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5368912170-2">]</span><span class="p" data-group-id="5368912170-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4853031272-1">(</span><span class="p" data-group-id="4853031272-2">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">format_status</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4853031272-2">]</span><span class="p" data-group-id="4853031272-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">format_status</span><span class="p" data-group-id="5368912170-3">(</span><span class="n">Opt</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5368912170-4">[</span><span class="p">_</span><span class="n">PDict</span><span class="p">,</span><span class="n">State</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="5368912170-4">]</span><span class="p" data-group-id="5368912170-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">format_status</span><span class="p" data-group-id="4853031272-3">(</span><span class="n">Opt</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4853031272-4">[</span><span class="p">_</span><span class="n">PDict</span><span class="p">,</span><span class="n">State</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="4853031272-4">]</span><span class="p" data-group-id="4853031272-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">StateData</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="5368912170-5">{</span><span class="n">State</span><span class="p">,</span><span class="w">
│ │ │ │ -	 </span><span class="nc">maps</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="5368912170-6">(</span><span class="w">
│ │ │ │ -	   </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5368912170-7">(</span><span class="ss">code</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="5368912170-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="p">;</span><span class="w">
│ │ │ │ -	       </span><span class="p" data-group-id="5368912170-8">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="5368912170-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="4853031272-5">{</span><span class="n">State</span><span class="p">,</span><span class="w">
│ │ │ │ +	 </span><span class="nc">maps</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="4853031272-6">(</span><span class="w">
│ │ │ │ +	   </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4853031272-7">(</span><span class="ss">code</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="4853031272-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="p">;</span><span class="w">
│ │ │ │ +	       </span><span class="p" data-group-id="4853031272-8">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="4853031272-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="w">
│ │ │ │  	   </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -	   </span><span class="n">Data</span><span class="p" data-group-id="5368912170-6">)</span><span class="p" data-group-id="5368912170-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	   </span><span class="n">Data</span><span class="p" data-group-id="4853031272-6">)</span><span class="p" data-group-id="4853031272-5">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Opt</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │  	</span><span class="ss">terminate</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">StateData</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">normal</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="p" data-group-id="5368912170-9">[</span><span class="p" data-group-id="5368912170-10">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="5368912170-11">[</span><span class="p" data-group-id="5368912170-12">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="n">StateData</span><span class="p" data-group-id="5368912170-12">}</span><span class="p" data-group-id="5368912170-11">]</span><span class="p" data-group-id="5368912170-10">}</span><span class="p" data-group-id="5368912170-9">]</span><span class="w">
│ │ │ │ +	    </span><span class="p" data-group-id="4853031272-9">[</span><span class="p" data-group-id="4853031272-10">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="4853031272-11">[</span><span class="p" data-group-id="4853031272-12">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="n">StateData</span><span class="p" data-group-id="4853031272-12">}</span><span class="p" data-group-id="4853031272-11">]</span><span class="p" data-group-id="4853031272-10">}</span><span class="p" data-group-id="4853031272-9">]</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>It is not mandatory to implement a
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:format_status/2"><code class="inline">Module:format_status/2</code></a> function.
│ │ │ │  If you do not, a default implementation is used that does the same
│ │ │ │  as this example function without filtering the <code class="inline">Data</code> term, that is,
│ │ │ │  <code class="inline">StateData = {State, Data}</code>, in this example containing sensitive information.</p><h2 id="complex-state" class="section-heading">
│ │ │ │    <a href="#complex-state" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -1227,104 +1227,104 @@
│ │ │ │  like a tuple.</p><p>One reason to use this is when you have a state item that when changed
│ │ │ │  should cancel the <a href="#state-time-outs"><em>state time-out</em></a>, or one that affects
│ │ │ │  the event handling in combination with postponing events. We will go for
│ │ │ │  the latter and complicate the previous example by introducing
│ │ │ │  a configurable lock button (this is the state item in question),
│ │ │ │  which in the <code class="inline">open</code> state immediately locks the door, and an API function
│ │ │ │  <code class="inline">set_lock_button/1</code> to set the lock button.</p><p>Suppose now that we call <code class="inline">set_lock_button</code> while the door is open,
│ │ │ │ -and we have already postponed a button event that was the new lock button:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5424563287-1">(</span><span class="p" data-group-id="5424563287-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5424563287-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">x</span><span class="p" data-group-id="5424563287-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5424563287-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.666</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5424563287-3">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5424563287-4">(</span><span class="ss">a</span><span class="p" data-group-id="5424563287-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +and we have already postponed a button event that was the new lock button:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4476566801-1">(</span><span class="p" data-group-id="4476566801-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4476566801-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">x</span><span class="p" data-group-id="4476566801-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4476566801-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.666</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4476566801-3">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="4476566801-4">(</span><span class="ss">a</span><span class="p" data-group-id="4476566801-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5424563287-5">(</span><span class="ss">b</span><span class="p" data-group-id="5424563287-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="4476566801-5">(</span><span class="ss">b</span><span class="p" data-group-id="4476566801-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5424563287-6">(</span><span class="ss">c</span><span class="p" data-group-id="5424563287-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="4476566801-6">(</span><span class="ss">c</span><span class="p" data-group-id="4476566801-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="n">Open</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5424563287-7">(</span><span class="ss">y</span><span class="p" data-group-id="5424563287-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="4476566801-7">(</span><span class="ss">y</span><span class="p" data-group-id="4476566801-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">set_lock_button</span><span class="p" data-group-id="5424563287-8">(</span><span class="ss">y</span><span class="p" data-group-id="5424563287-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">set_lock_button</span><span class="p" data-group-id="4476566801-8">(</span><span class="ss">y</span><span class="p" data-group-id="4476566801-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">x</span><span class="w">
│ │ │ │  </span><span class="c1">% What should happen here?  Immediate lock or nothing?</span></code></pre><p>We could say that the button was pressed too early so it should not be
│ │ │ │  recognized as the lock button. Or we can make the lock button part of
│ │ │ │  the state so when we then change the lock button in the locked state,
│ │ │ │  the change becomes a <em>state change</em> and all postponed events are retried,
│ │ │ │  therefore the lock is immediately locked!</p><p>We define the state as <code class="inline">{StateName, LockButton}</code>, where <code class="inline">StateName</code>
│ │ │ │ -is as before and <code class="inline">LockButton</code> is the current lock button:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3184901689-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="3184901689-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3184901689-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="3184901689-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3184901689-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_3</span><span class="p" data-group-id="3184901689-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +is as before and <code class="inline">LockButton</code> is the current lock button:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1168375256-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="1168375256-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1168375256-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="1168375256-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1168375256-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_3</span><span class="p" data-group-id="1168375256-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3184901689-4">(</span><span class="p" data-group-id="3184901689-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3184901689-5">]</span><span class="p" data-group-id="3184901689-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3184901689-6">(</span><span class="p" data-group-id="3184901689-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">set_lock_button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3184901689-7">]</span><span class="p" data-group-id="3184901689-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3184901689-8">(</span><span class="p" data-group-id="3184901689-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="3184901689-9">]</span><span class="p" data-group-id="3184901689-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3184901689-10">(</span><span class="p" data-group-id="3184901689-11">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="3184901689-11">]</span><span class="p" data-group-id="3184901689-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="3184901689-12">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">LockButton</span><span class="p" data-group-id="3184901689-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3184901689-13">(</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="3184901689-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="3184901689-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3184901689-15">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="3184901689-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3184901689-16">[</span><span class="p" data-group-id="3184901689-16">]</span><span class="p" data-group-id="3184901689-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="3184901689-17">(</span><span class="p" data-group-id="3184901689-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="3184901689-18">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="3184901689-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="3184901689-19">(</span><span class="n">Button</span><span class="p" data-group-id="3184901689-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="3184901689-20">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3184901689-21">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3184901689-21">}</span><span class="p" data-group-id="3184901689-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">set_lock_button</span><span class="p" data-group-id="3184901689-22">(</span><span class="n">LockButton</span><span class="p" data-group-id="3184901689-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="3184901689-23">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3184901689-24">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="3184901689-24">}</span><span class="p" data-group-id="3184901689-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4281099580-1">(</span><span class="p" data-group-id="4281099580-2">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="4281099580-2">}</span><span class="p" data-group-id="4281099580-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="4281099580-3">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4281099580-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4281099580-4">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="4281099580-5">(</span><span class="n">Code</span><span class="p" data-group-id="4281099580-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4281099580-6">[</span><span class="p" data-group-id="4281099580-6">]</span><span class="p" data-group-id="4281099580-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4281099580-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4281099580-8">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="4281099580-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4281099580-7">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1168375256-4">(</span><span class="p" data-group-id="1168375256-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1168375256-5">]</span><span class="p" data-group-id="1168375256-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1168375256-6">(</span><span class="p" data-group-id="1168375256-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">set_lock_button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1168375256-7">]</span><span class="p" data-group-id="1168375256-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1168375256-8">(</span><span class="p" data-group-id="1168375256-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="1168375256-9">]</span><span class="p" data-group-id="1168375256-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1168375256-10">(</span><span class="p" data-group-id="1168375256-11">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="1168375256-11">]</span><span class="p" data-group-id="1168375256-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="1168375256-12">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">LockButton</span><span class="p" data-group-id="1168375256-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1168375256-13">(</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="1168375256-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="1168375256-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1168375256-15">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1168375256-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1168375256-16">[</span><span class="p" data-group-id="1168375256-16">]</span><span class="p" data-group-id="1168375256-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="1168375256-17">(</span><span class="p" data-group-id="1168375256-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="1168375256-18">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="1168375256-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="1168375256-19">(</span><span class="n">Button</span><span class="p" data-group-id="1168375256-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1168375256-20">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1168375256-21">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1168375256-21">}</span><span class="p" data-group-id="1168375256-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">set_lock_button</span><span class="p" data-group-id="1168375256-22">(</span><span class="n">LockButton</span><span class="p" data-group-id="1168375256-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="1168375256-23">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1168375256-24">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1168375256-24">}</span><span class="p" data-group-id="1168375256-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="2869976149-1">(</span><span class="p" data-group-id="2869976149-2">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2869976149-2">}</span><span class="p" data-group-id="2869976149-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="2869976149-3">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2869976149-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2869976149-4">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="2869976149-5">(</span><span class="n">Code</span><span class="p" data-group-id="2869976149-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2869976149-6">[</span><span class="p" data-group-id="2869976149-6">]</span><span class="p" data-group-id="2869976149-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2869976149-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2869976149-8">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2869976149-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2869976149-7">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="4281099580-9">(</span><span class="p" data-group-id="4281099580-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4281099580-10">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="4281099580-10">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="2869976149-9">(</span><span class="p" data-group-id="2869976149-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2869976149-10">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="2869976149-10">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% State: locked</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4281099580-11">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4281099580-12">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4281099580-12">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4281099580-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="4281099580-13">(</span><span class="p" data-group-id="4281099580-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4281099580-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4281099580-15">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4281099580-16">[</span><span class="p" data-group-id="4281099580-16">]</span><span class="p" data-group-id="4281099580-15">}</span><span class="p" data-group-id="4281099580-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4281099580-17">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4281099580-18">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4281099580-18">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4281099580-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4281099580-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4281099580-20">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4281099580-21">[</span><span class="p" data-group-id="4281099580-21">]</span><span class="p" data-group-id="4281099580-20">}</span><span class="p" data-group-id="4281099580-19">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4281099580-22">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4281099580-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4281099580-23">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4281099580-24">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="4281099580-24">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4281099580-25">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="4281099580-25">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4281099580-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2869976149-11">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2869976149-12">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2869976149-12">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2869976149-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="2869976149-13">(</span><span class="p" data-group-id="2869976149-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2869976149-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2869976149-15">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="2869976149-16">[</span><span class="p" data-group-id="2869976149-16">]</span><span class="p" data-group-id="2869976149-15">}</span><span class="p" data-group-id="2869976149-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2869976149-17">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2869976149-18">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2869976149-18">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2869976149-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2869976149-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2869976149-20">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="2869976149-21">[</span><span class="p" data-group-id="2869976149-21">]</span><span class="p" data-group-id="2869976149-20">}</span><span class="p" data-group-id="2869976149-19">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2869976149-22">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2869976149-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2869976149-23">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2869976149-24">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2869976149-24">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="2869976149-25">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="2869976149-25">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2869976149-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │          </span><span class="k">if</span><span class="w">
│ │ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="4281099580-26">(</span><span class="n">Buttons</span><span class="p" data-group-id="4281099580-26">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="2869976149-26">(</span><span class="n">Buttons</span><span class="p" data-group-id="2869976149-26">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="4281099580-27">(</span><span class="n">Buttons</span><span class="p" data-group-id="4281099580-27">)</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4281099580-28">[</span><span class="n">Button</span><span class="p" data-group-id="4281099580-28">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="2869976149-27">(</span><span class="n">Buttons</span><span class="p" data-group-id="2869976149-27">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2869976149-28">[</span><span class="n">Button</span><span class="p" data-group-id="2869976149-28">]</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="4281099580-29">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4281099580-30">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="4281099580-30">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4281099580-29">}</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="2869976149-29">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2869976149-30">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2869976149-30">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2869976149-29">}</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="4281099580-31">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4281099580-32">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="4281099580-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="4281099580-33">[</span><span class="p" data-group-id="4281099580-34">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="4281099580-34">}</span><span class="p" data-group-id="4281099580-33">]</span><span class="p" data-group-id="4281099580-31">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="2869976149-31">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2869976149-32">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="2869976149-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="2869976149-33">[</span><span class="p" data-group-id="2869976149-34">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="2869976149-34">}</span><span class="p" data-group-id="2869976149-33">]</span><span class="p" data-group-id="2869976149-31">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="0418925595-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0418925595-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0418925595-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0418925595-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="0418925595-3">(</span><span class="p" data-group-id="0418925595-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0418925595-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="0418925595-5">[</span><span class="p" data-group-id="0418925595-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="0418925595-6">}</span><span class="p" data-group-id="0418925595-5">]</span><span class="p" data-group-id="0418925595-4">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="0418925595-7">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0418925595-8">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="0418925595-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0418925595-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0418925595-9">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0418925595-10">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="0418925595-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0418925595-9">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="0418925595-11">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0418925595-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="0418925595-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0418925595-13">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="0418925595-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0418925595-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0418925595-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0418925595-15">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="0418925595-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0418925595-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="0418925595-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0418925595-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0418925595-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0418925595-18">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0418925595-18">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0418925595-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0418925595-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="0418925595-20">[</span><span class="ss">postpone</span><span class="p" data-group-id="0418925595-20">]</span><span class="p" data-group-id="0418925595-19">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="6235608580-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6235608580-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6235608580-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="6235608580-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="6235608580-3">(</span><span class="p" data-group-id="6235608580-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6235608580-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="6235608580-5">[</span><span class="p" data-group-id="6235608580-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="6235608580-6">}</span><span class="p" data-group-id="6235608580-5">]</span><span class="p" data-group-id="6235608580-4">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="6235608580-7">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6235608580-8">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6235608580-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6235608580-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6235608580-9">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6235608580-10">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6235608580-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6235608580-9">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="6235608580-11">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6235608580-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6235608580-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6235608580-13">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6235608580-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6235608580-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6235608580-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6235608580-15">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6235608580-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6235608580-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="6235608580-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6235608580-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6235608580-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6235608580-18">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6235608580-18">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="6235608580-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6235608580-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="6235608580-20">[</span><span class="ss">postpone</span><span class="p" data-group-id="6235608580-20">]</span><span class="p" data-group-id="6235608580-19">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% Common events</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="3597766882-1">(</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="3597766882-2">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="3597766882-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3597766882-3">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="3597766882-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="3597766882-4">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="3597766882-4">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3597766882-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3597766882-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3597766882-6">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="3597766882-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="3597766882-7">[</span><span class="p" data-group-id="3597766882-8">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="3597766882-8">}</span><span class="p" data-group-id="3597766882-7">]</span><span class="p" data-group-id="3597766882-5">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="1404554128-1">(</span><span class="p" data-group-id="1404554128-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1404554128-2">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1404554128-3">[</span><span class="p" data-group-id="1404554128-3">]</span><span class="p" data-group-id="1404554128-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="1404554128-4">(</span><span class="p" data-group-id="1404554128-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1404554128-5">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1404554128-6">[</span><span class="p" data-group-id="1404554128-6">]</span><span class="p" data-group-id="1404554128-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3887308174-1">(</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3887308174-2">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="3887308174-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3887308174-3">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="3887308174-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3887308174-4">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="3887308174-4">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3887308174-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3887308174-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3887308174-6">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="3887308174-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="3887308174-7">[</span><span class="p" data-group-id="3887308174-8">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="3887308174-8">}</span><span class="p" data-group-id="3887308174-7">]</span><span class="p" data-group-id="3887308174-5">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="5553811781-1">(</span><span class="p" data-group-id="5553811781-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5553811781-2">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5553811781-3">[</span><span class="p" data-group-id="5553811781-3">]</span><span class="p" data-group-id="5553811781-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="5553811781-4">(</span><span class="p" data-group-id="5553811781-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5553811781-5">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5553811781-6">[</span><span class="p" data-group-id="5553811781-6">]</span><span class="p" data-group-id="5553811781-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="1404554128-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="1404554128-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="1404554128-8">(</span><span class="p" data-group-id="1404554128-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="5553811781-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="5553811781-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="5553811781-8">(</span><span class="p" data-group-id="5553811781-8">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h2 id="hibernation" class="section-heading">
│ │ │ │    <a href="#hibernation" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Hibernation</span>
│ │ │ │  </h2>
│ │ │ │  <p>If you have many servers in one node and they have some state(s) in their
│ │ │ │ @@ -1333,19 +1333,19 @@
│ │ │ │  footprint of a server can be minimized by hibernating it through
│ │ │ │  <a href="../../../lib/stdlib/doc/html/proc_lib.html#hibernate/3"><code class="inline">proc_lib:hibernate/3</code></a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>It is rather costly to hibernate a process; see <a href="../../../lib/../erts/doc/html/erlang.html#hibernate/3"><code class="inline">erlang:hibernate/3</code></a>. It is
│ │ │ │  not something you want to do after every event.</p></section><p>We can in this example hibernate in the <code class="inline">{open, _}</code> state,
│ │ │ │  because what normally occurs in that state is that the <em>state time-out</em>
│ │ │ │  after a while triggers a transition to <code class="inline">{locked, _}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4247785621-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4247785621-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4247785621-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="4247785621-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="4247785621-3">(</span><span class="p" data-group-id="4247785621-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4247785621-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="4247785621-5">[</span><span class="p" data-group-id="4247785621-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="4247785621-6">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -      </span><span class="ss">hibernate</span><span class="p" data-group-id="4247785621-5">]</span><span class="p" data-group-id="4247785621-4">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3461460528-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3461460528-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3461460528-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="3461460528-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3461460528-3">(</span><span class="p" data-group-id="3461460528-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3461460528-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="3461460528-5">[</span><span class="p" data-group-id="3461460528-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3461460528-6">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +      </span><span class="ss">hibernate</span><span class="p" data-group-id="3461460528-5">]</span><span class="p" data-group-id="3461460528-4">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The atom <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:hibernate/0"><code class="inline">hibernate</code></a> in the action list on the
│ │ │ │  last line when entering the <code class="inline">{open, _}</code> state is the only change. If any event
│ │ │ │  arrives in the <code class="inline">{open, _},</code> state, we do not bother to rehibernate,
│ │ │ │  so the server stays awake after any event.</p><p>To change that we would need to insert action <code class="inline">hibernate</code> in more places.
│ │ │ │  For example, the state-independent <code class="inline">set_lock_button</code> operation
│ │ │ │  would have to use <code class="inline">hibernate</code> but only in the <code class="inline">{open, _}</code> state,
│ │ │ │  which would clutter the code.</p><p>Another not uncommon scenario is to use the
│ │ │ ├── OEBPS/spec_proc.xhtml
│ │ │ │ @@ -28,72 +28,72 @@
│ │ │ │    <a href="#simple-debugging" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Simple Debugging</span>
│ │ │ │  </h2>
│ │ │ │  <p>The <a href="../../../lib/stdlib/doc/html/sys.html"><code class="inline">sys</code></a> module has functions for simple debugging of processes implemented
│ │ │ │  using behaviours. The <code class="inline">code_lock</code> example from
│ │ │ │ -<a href="statem.xhtml#example">gen_statem Behaviour</a> is used to illustrate this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="2217947586-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="2217947586-1">]</span><span class="w"> </span><span class="p" data-group-id="2217947586-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="2217947586-2">]</span><span class="w"> </span><span class="p" data-group-id="2217947586-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="2217947586-3">]</span><span class="w"> </span><span class="p" data-group-id="2217947586-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="2217947586-4">]</span><span class="w"> </span><span class="p" data-group-id="2217947586-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2217947586-5">]</span><span class="w"> </span><span class="p" data-group-id="2217947586-6">[</span><span class="ss">jit</span><span class="p" data-group-id="2217947586-6">]</span><span class="w">
│ │ │ │ +<a href="statem.xhtml#example">gen_statem Behaviour</a> is used to illustrate this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="5692709471-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="5692709471-1">]</span><span class="w"> </span><span class="p" data-group-id="5692709471-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="5692709471-2">]</span><span class="w"> </span><span class="p" data-group-id="5692709471-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="5692709471-3">]</span><span class="w"> </span><span class="p" data-group-id="5692709471-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="5692709471-4">]</span><span class="w"> </span><span class="p" data-group-id="5692709471-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5692709471-5">]</span><span class="w"> </span><span class="p" data-group-id="5692709471-6">[</span><span class="ss">jit</span><span class="p" data-group-id="5692709471-6">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="2217947586-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="2217947586-8">(</span><span class="p" data-group-id="2217947586-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="2217947586-7">)</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2217947586-9">(</span><span class="p" data-group-id="2217947586-10">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2217947586-10">]</span><span class="p" data-group-id="2217947586-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="5692709471-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="5692709471-8">(</span><span class="p" data-group-id="5692709471-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="5692709471-7">)</span><span class="gp unselectable">
│ │ │ │ +1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5692709471-9">(</span><span class="p" data-group-id="5692709471-10">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5692709471-10">]</span><span class="p" data-group-id="5692709471-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">Lock</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2217947586-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2217947586-11">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="2217947586-12">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2217947586-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5692709471-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5692709471-11">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5692709471-12">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5692709471-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="2217947586-13">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2217947586-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="5692709471-13">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5692709471-13">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="2217947586-14">(</span><span class="mi">1</span><span class="p" data-group-id="2217947586-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="2217947586-15">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2217947586-15">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5692709471-14">(</span><span class="mi">1</span><span class="p" data-group-id="5692709471-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5692709471-15">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5692709471-15">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="2217947586-16">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2217947586-16">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="2217947586-17">(</span><span class="mi">2</span><span class="p" data-group-id="2217947586-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="2217947586-18">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2217947586-18">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5692709471-16">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5692709471-16">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ │ +5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5692709471-17">(</span><span class="mi">2</span><span class="p" data-group-id="5692709471-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5692709471-18">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5692709471-18">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="2217947586-19">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2217947586-19">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="2217947586-20">(</span><span class="mi">3</span><span class="p" data-group-id="2217947586-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="2217947586-21">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2217947586-21">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5692709471-19">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5692709471-19">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ │ +6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5692709471-20">(</span><span class="mi">3</span><span class="p" data-group-id="5692709471-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5692709471-21">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5692709471-21">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="2217947586-22">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2217947586-22">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ │ -7&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="2217947586-23">(</span><span class="mi">4</span><span class="p" data-group-id="2217947586-23">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="2217947586-24">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2217947586-24">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5692709471-22">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5692709471-22">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ │ +7&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5692709471-23">(</span><span class="mi">4</span><span class="p" data-group-id="5692709471-23">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5692709471-24">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5692709471-24">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="n">Unlock</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="2217947586-25">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2217947586-25">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="nb">start_timer</span><span class="w"> </span><span class="p" data-group-id="2217947586-26">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10000</span><span class="p">,</span><span class="ss">lock</span><span class="p">,</span><span class="p" data-group-id="2217947586-27">[</span><span class="p" data-group-id="2217947586-27">]</span><span class="p" data-group-id="2217947586-26">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5692709471-25">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5692709471-25">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="nb">start_timer</span><span class="w"> </span><span class="p" data-group-id="5692709471-26">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10000</span><span class="p">,</span><span class="ss">lock</span><span class="p">,</span><span class="p" data-group-id="5692709471-27">[</span><span class="p" data-group-id="5692709471-27">]</span><span class="p" data-group-id="5692709471-26">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ │  </span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">state_timeout</span><span class="w"> </span><span class="ss">lock</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ │  </span><span class="n">Lock</span><span class="w">
│ │ │ │  </span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">state_timeout</span><span class="w"> </span><span class="ss">lock</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ │ -8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="2217947586-28">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="2217947586-28">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2217947586-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="2217947586-30">[</span><span class="p" data-group-id="2217947586-31">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="2217947586-32">{</span><span class="p" data-group-id="2217947586-33">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2217947586-33">}</span><span class="p">,</span><span class="p" data-group-id="2217947586-34">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2217947586-34">}</span><span class="p" data-group-id="2217947586-32">}</span><span class="p" data-group-id="2217947586-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="2217947586-35">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="2217947586-36">{</span><span class="p" data-group-id="2217947586-37">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2217947586-37">}</span><span class="p">,</span><span class="p" data-group-id="2217947586-38">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">48</span><span class="p" data-group-id="2217947586-38">}</span><span class="p" data-group-id="2217947586-36">}</span><span class="p" data-group-id="2217947586-35">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="2217947586-39">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">4098</span><span class="p" data-group-id="2217947586-39">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="2217947586-40">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2217947586-40">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="2217947586-41">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="2217947586-41">}</span><span class="p" data-group-id="2217947586-30">]</span><span class="p" data-group-id="2217947586-29">}</span><span class="gp unselectable">
│ │ │ │ -9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="2217947586-42">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="2217947586-42">)</span><span class="p">.</span><span class="w">
│ │ │ │ +8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5692709471-28">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="5692709471-28">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5692709471-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="5692709471-30">[</span><span class="p" data-group-id="5692709471-31">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="5692709471-32">{</span><span class="p" data-group-id="5692709471-33">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5692709471-33">}</span><span class="p">,</span><span class="p" data-group-id="5692709471-34">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5692709471-34">}</span><span class="p" data-group-id="5692709471-32">}</span><span class="p" data-group-id="5692709471-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="5692709471-35">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="5692709471-36">{</span><span class="p" data-group-id="5692709471-37">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5692709471-37">}</span><span class="p">,</span><span class="p" data-group-id="5692709471-38">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">48</span><span class="p" data-group-id="5692709471-38">}</span><span class="p" data-group-id="5692709471-36">}</span><span class="p" data-group-id="5692709471-35">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="5692709471-39">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">4098</span><span class="p" data-group-id="5692709471-39">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="5692709471-40">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5692709471-40">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="5692709471-41">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="5692709471-41">}</span><span class="p" data-group-id="5692709471-30">]</span><span class="p" data-group-id="5692709471-29">}</span><span class="gp unselectable">
│ │ │ │ +9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5692709471-42">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="5692709471-42">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -10&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="2217947586-43">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="2217947586-43">)</span><span class="p">.</span><span class="w">
│ │ │ │ +10&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="5692709471-43">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="5692709471-43">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -11&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="2217947586-44">(</span><span class="ss">code_lock</span><span class="p" data-group-id="2217947586-44">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2217947586-45">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2217947586-46">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">gen_statem</span><span class="p" data-group-id="2217947586-46">}</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2217947586-47">[</span><span class="p" data-group-id="2217947586-48">[</span><span class="p" data-group-id="2217947586-49">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="2217947586-50">{</span><span class="ss">code_lock</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2217947586-50">}</span><span class="p" data-group-id="2217947586-49">}</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="2217947586-51">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="2217947586-52">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2217947586-52">]</span><span class="p" data-group-id="2217947586-51">}</span><span class="p" data-group-id="2217947586-48">]</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="2217947586-53">[</span><span class="p" data-group-id="2217947586-53">]</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="2217947586-54">[</span><span class="p" data-group-id="2217947586-55">{</span><span class="ss">header</span><span class="p">,</span><span class="s">&quot;Status for state machine code_lock&quot;</span><span class="p" data-group-id="2217947586-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="2217947586-56">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="2217947586-57">[</span><span class="p" data-group-id="2217947586-58">{</span><span class="s">&quot;Status&quot;</span><span class="p">,</span><span class="ss">running</span><span class="p" data-group-id="2217947586-58">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="2217947586-59">{</span><span class="s">&quot;Parent&quot;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2217947586-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="2217947586-60">{</span><span class="s">&quot;Modules&quot;</span><span class="p">,</span><span class="p" data-group-id="2217947586-61">[</span><span class="ss">code_lock</span><span class="p" data-group-id="2217947586-61">]</span><span class="p" data-group-id="2217947586-60">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="2217947586-62">{</span><span class="s">&quot;Time-outs&quot;</span><span class="p">,</span><span class="p" data-group-id="2217947586-63">{</span><span class="mi">0</span><span class="p">,</span><span class="p" data-group-id="2217947586-64">[</span><span class="p" data-group-id="2217947586-64">]</span><span class="p" data-group-id="2217947586-63">}</span><span class="p" data-group-id="2217947586-62">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="2217947586-65">{</span><span class="s">&quot;Logged Events&quot;</span><span class="p">,</span><span class="p" data-group-id="2217947586-66">[</span><span class="p" data-group-id="2217947586-66">]</span><span class="p" data-group-id="2217947586-65">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="2217947586-67">{</span><span class="s">&quot;Postponed&quot;</span><span class="p">,</span><span class="p" data-group-id="2217947586-68">[</span><span class="p" data-group-id="2217947586-68">]</span><span class="p" data-group-id="2217947586-67">}</span><span class="p" data-group-id="2217947586-57">]</span><span class="p" data-group-id="2217947586-56">}</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="2217947586-69">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="2217947586-70">[</span><span class="p" data-group-id="2217947586-71">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -                  </span><span class="p" data-group-id="2217947586-72">{</span><span class="ss">locked</span><span class="p">,</span><span class="p" data-group-id="2217947586-73">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2217947586-74">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2217947586-74">]</span><span class="p">,</span><span class="w">
│ │ │ │ -                            </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2217947586-75">[</span><span class="p" data-group-id="2217947586-75">]</span><span class="p" data-group-id="2217947586-73">}</span><span class="p" data-group-id="2217947586-72">}</span><span class="p" data-group-id="2217947586-71">}</span><span class="p" data-group-id="2217947586-70">]</span><span class="p" data-group-id="2217947586-69">}</span><span class="p" data-group-id="2217947586-54">]</span><span class="p" data-group-id="2217947586-47">]</span><span class="p" data-group-id="2217947586-45">}</span></code></pre><h2 id="special-processes" class="section-heading">
│ │ │ │ +11&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="5692709471-44">(</span><span class="ss">code_lock</span><span class="p" data-group-id="5692709471-44">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5692709471-45">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="5692709471-46">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">gen_statem</span><span class="p" data-group-id="5692709471-46">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="5692709471-47">[</span><span class="p" data-group-id="5692709471-48">[</span><span class="p" data-group-id="5692709471-49">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="5692709471-50">{</span><span class="ss">code_lock</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5692709471-50">}</span><span class="p" data-group-id="5692709471-49">}</span><span class="p">,</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="5692709471-51">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="5692709471-52">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5692709471-52">]</span><span class="p" data-group-id="5692709471-51">}</span><span class="p" data-group-id="5692709471-48">]</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="5692709471-53">[</span><span class="p" data-group-id="5692709471-53">]</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="5692709471-54">[</span><span class="p" data-group-id="5692709471-55">{</span><span class="ss">header</span><span class="p">,</span><span class="s">&quot;Status for state machine code_lock&quot;</span><span class="p" data-group-id="5692709471-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="5692709471-56">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="5692709471-57">[</span><span class="p" data-group-id="5692709471-58">{</span><span class="s">&quot;Status&quot;</span><span class="p">,</span><span class="ss">running</span><span class="p" data-group-id="5692709471-58">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="5692709471-59">{</span><span class="s">&quot;Parent&quot;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5692709471-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="5692709471-60">{</span><span class="s">&quot;Modules&quot;</span><span class="p">,</span><span class="p" data-group-id="5692709471-61">[</span><span class="ss">code_lock</span><span class="p" data-group-id="5692709471-61">]</span><span class="p" data-group-id="5692709471-60">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="5692709471-62">{</span><span class="s">&quot;Time-outs&quot;</span><span class="p">,</span><span class="p" data-group-id="5692709471-63">{</span><span class="mi">0</span><span class="p">,</span><span class="p" data-group-id="5692709471-64">[</span><span class="p" data-group-id="5692709471-64">]</span><span class="p" data-group-id="5692709471-63">}</span><span class="p" data-group-id="5692709471-62">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="5692709471-65">{</span><span class="s">&quot;Logged Events&quot;</span><span class="p">,</span><span class="p" data-group-id="5692709471-66">[</span><span class="p" data-group-id="5692709471-66">]</span><span class="p" data-group-id="5692709471-65">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="5692709471-67">{</span><span class="s">&quot;Postponed&quot;</span><span class="p">,</span><span class="p" data-group-id="5692709471-68">[</span><span class="p" data-group-id="5692709471-68">]</span><span class="p" data-group-id="5692709471-67">}</span><span class="p" data-group-id="5692709471-57">]</span><span class="p" data-group-id="5692709471-56">}</span><span class="p">,</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="5692709471-69">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="5692709471-70">[</span><span class="p" data-group-id="5692709471-71">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +                  </span><span class="p" data-group-id="5692709471-72">{</span><span class="ss">locked</span><span class="p">,</span><span class="p" data-group-id="5692709471-73">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5692709471-74">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5692709471-74">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                            </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5692709471-75">[</span><span class="p" data-group-id="5692709471-75">]</span><span class="p" data-group-id="5692709471-73">}</span><span class="p" data-group-id="5692709471-72">}</span><span class="p" data-group-id="5692709471-71">}</span><span class="p" data-group-id="5692709471-70">]</span><span class="p" data-group-id="5692709471-69">}</span><span class="p" data-group-id="5692709471-54">]</span><span class="p" data-group-id="5692709471-47">]</span><span class="p" data-group-id="5692709471-45">}</span></code></pre><h2 id="special-processes" class="section-heading">
│ │ │ │    <a href="#special-processes" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Special Processes</span>
│ │ │ │  </h2>
│ │ │ │  <p>This section describes how to write a process that complies to the OTP design
│ │ │ │  principles, without using a standard behaviour. Such a process is to:</p><ul><li>Be started in a way that makes the process fit into a supervision tree</li><li>Support the <code class="inline">sys</code> <a href="spec_proc.xhtml#debug">debug facilities</a></li><li>Take care of <a href="spec_proc.xhtml#msg">system messages</a>.</li></ul><p>System messages are messages with a special meaning, used in the supervision
│ │ │ │ @@ -103,238 +103,238 @@
│ │ │ │    <a href="#example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example</span>
│ │ │ │  </h3>
│ │ │ │  <p>Here follows the simple server from
│ │ │ │  <a href="design_principles.xhtml#ch1">Overview</a>,
│ │ │ │ -implemented using <code class="inline">sys</code> and <code class="inline">proc_lib</code> to fit into a supervision tree:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6987729430-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="6987729430-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6987729430-2">(</span><span class="p" data-group-id="6987729430-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6987729430-3">]</span><span class="p" data-group-id="6987729430-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6987729430-4">(</span><span class="p" data-group-id="6987729430-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6987729430-5">]</span><span class="p" data-group-id="6987729430-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6987729430-6">(</span><span class="p" data-group-id="6987729430-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6987729430-7">]</span><span class="p" data-group-id="6987729430-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6987729430-8">(</span><span class="p" data-group-id="6987729430-9">[</span><span class="ss">system_continue</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">system_terminate</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w">
│ │ │ │ +implemented using <code class="inline">sys</code> and <code class="inline">proc_lib</code> to fit into a supervision tree:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4024991866-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="4024991866-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4024991866-2">(</span><span class="p" data-group-id="4024991866-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4024991866-3">]</span><span class="p" data-group-id="4024991866-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4024991866-4">(</span><span class="p" data-group-id="4024991866-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4024991866-5">]</span><span class="p" data-group-id="4024991866-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4024991866-6">(</span><span class="p" data-group-id="4024991866-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4024991866-7">]</span><span class="p" data-group-id="4024991866-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4024991866-8">(</span><span class="p" data-group-id="4024991866-9">[</span><span class="ss">system_continue</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">system_terminate</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w">
│ │ │ │           </span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="ss">system_get_state</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">system_replace_state</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6987729430-9">]</span><span class="p" data-group-id="6987729430-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +         </span><span class="ss">system_get_state</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">system_replace_state</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4024991866-9">]</span><span class="p" data-group-id="4024991866-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="6987729430-10">(</span><span class="p" data-group-id="6987729430-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6987729430-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6987729430-12">[</span><span class="nf">self</span><span class="p" data-group-id="6987729430-13">(</span><span class="p" data-group-id="6987729430-13">)</span><span class="p" data-group-id="6987729430-12">]</span><span class="p" data-group-id="6987729430-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="4024991866-10">(</span><span class="p" data-group-id="4024991866-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4024991866-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4024991866-12">[</span><span class="nf">self</span><span class="p" data-group-id="4024991866-13">(</span><span class="p" data-group-id="4024991866-13">)</span><span class="p" data-group-id="4024991866-12">]</span><span class="p" data-group-id="4024991866-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="6987729430-14">(</span><span class="p" data-group-id="6987729430-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6987729430-15">{</span><span class="nf">self</span><span class="p" data-group-id="6987729430-16">(</span><span class="p" data-group-id="6987729430-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="6987729430-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="4024991866-14">(</span><span class="p" data-group-id="4024991866-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4024991866-15">{</span><span class="nf">self</span><span class="p" data-group-id="4024991866-16">(</span><span class="p" data-group-id="4024991866-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="4024991866-15">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6987729430-17">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="6987729430-17">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4024991866-17">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="4024991866-17">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">Res</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="6987729430-18">(</span><span class="n">Ch</span><span class="p" data-group-id="6987729430-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6987729430-19">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6987729430-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="4024991866-18">(</span><span class="n">Ch</span><span class="p" data-group-id="4024991866-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4024991866-19">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4024991866-19">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6987729430-20">(</span><span class="n">Parent</span><span class="p" data-group-id="6987729430-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="6987729430-21">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6987729430-22">(</span><span class="p" data-group-id="6987729430-22">)</span><span class="p" data-group-id="6987729430-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="6987729430-23">(</span><span class="p" data-group-id="6987729430-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="6987729430-24">(</span><span class="p" data-group-id="6987729430-25">[</span><span class="p" data-group-id="6987729430-25">]</span><span class="p" data-group-id="6987729430-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="6987729430-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6987729430-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6987729430-28">(</span><span class="p" data-group-id="6987729430-28">)</span><span class="p" data-group-id="6987729430-27">}</span><span class="p" data-group-id="6987729430-26">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="6987729430-29">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="6987729430-29">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="4024991866-20">(</span><span class="n">Parent</span><span class="p" data-group-id="4024991866-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="4024991866-21">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4024991866-22">(</span><span class="p" data-group-id="4024991866-22">)</span><span class="p" data-group-id="4024991866-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="4024991866-23">(</span><span class="p" data-group-id="4024991866-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="4024991866-24">(</span><span class="p" data-group-id="4024991866-25">[</span><span class="p" data-group-id="4024991866-25">]</span><span class="p" data-group-id="4024991866-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="4024991866-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4024991866-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4024991866-28">(</span><span class="p" data-group-id="4024991866-28">)</span><span class="p" data-group-id="4024991866-27">}</span><span class="p" data-group-id="4024991866-26">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="4024991866-29">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="4024991866-29">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="6987729430-30">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="6987729430-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="4024991866-30">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="4024991866-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6987729430-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="6987729430-31">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="6987729430-32">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6987729430-33">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="6987729430-33">}</span><span class="p" data-group-id="6987729430-32">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="6987729430-34">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6987729430-34">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="6987729430-35">(</span><span class="n">Chs</span><span class="p" data-group-id="6987729430-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6987729430-36">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6987729430-36">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="6987729430-37">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6987729430-38">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6987729430-39">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6987729430-39">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="6987729430-38">}</span><span class="p" data-group-id="6987729430-37">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="6987729430-40">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="6987729430-40">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6987729430-41">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6987729430-41">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="6987729430-42">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6987729430-43">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6987729430-44">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6987729430-44">}</span><span class="p" data-group-id="6987729430-43">}</span><span class="p" data-group-id="6987729430-42">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="6987729430-45">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6987729430-45">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="6987729430-46">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="6987729430-46">)</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -        </span><span class="p" data-group-id="6987729430-47">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="6987729430-47">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="6987729430-48">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ │ -                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6987729430-48">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4024991866-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="4024991866-31">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="4024991866-32">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4024991866-33">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="4024991866-33">}</span><span class="p" data-group-id="4024991866-32">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="4024991866-34">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="4024991866-34">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="4024991866-35">(</span><span class="n">Chs</span><span class="p" data-group-id="4024991866-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4024991866-36">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4024991866-36">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="4024991866-37">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4024991866-38">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4024991866-39">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4024991866-39">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="4024991866-38">}</span><span class="p" data-group-id="4024991866-37">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="4024991866-40">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="4024991866-40">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4024991866-41">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4024991866-41">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="4024991866-42">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4024991866-43">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4024991866-44">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4024991866-44">}</span><span class="p" data-group-id="4024991866-43">}</span><span class="p" data-group-id="4024991866-42">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="4024991866-45">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4024991866-45">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="4024991866-46">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="4024991866-46">)</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +        </span><span class="p" data-group-id="4024991866-47">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="4024991866-47">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="4024991866-48">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ │ +                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4024991866-48">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_continue</span><span class="p" data-group-id="6987729430-49">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6987729430-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="6987729430-50">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="6987729430-50">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_continue</span><span class="p" data-group-id="4024991866-49">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4024991866-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="4024991866-50">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="4024991866-50">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_terminate</span><span class="p" data-group-id="6987729430-51">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Chs</span><span class="p" data-group-id="6987729430-51">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="6987729430-52">(</span><span class="n">Reason</span><span class="p" data-group-id="6987729430-52">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_terminate</span><span class="p" data-group-id="4024991866-51">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Chs</span><span class="p" data-group-id="4024991866-51">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="4024991866-52">(</span><span class="n">Reason</span><span class="p" data-group-id="4024991866-52">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_get_state</span><span class="p" data-group-id="6987729430-53">(</span><span class="n">Chs</span><span class="p" data-group-id="6987729430-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6987729430-54">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6987729430-54">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_get_state</span><span class="p" data-group-id="4024991866-53">(</span><span class="n">Chs</span><span class="p" data-group-id="4024991866-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4024991866-54">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4024991866-54">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_replace_state</span><span class="p" data-group-id="6987729430-55">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6987729430-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="6987729430-56">(</span><span class="n">Chs</span><span class="p" data-group-id="6987729430-56">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6987729430-57">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="6987729430-57">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_replace_state</span><span class="p" data-group-id="4024991866-55">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4024991866-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="4024991866-56">(</span><span class="n">Chs</span><span class="p" data-group-id="4024991866-56">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4024991866-57">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="4024991866-57">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">write_debug</span><span class="p" data-group-id="6987729430-58">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6987729430-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6987729430-59">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6987729430-60">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="6987729430-60">]</span><span class="p" data-group-id="6987729430-59">)</span><span class="p">.</span></code></pre><p id="ex">As it is not relevant to the example, the channel handling functions have been
│ │ │ │ +</span><span class="nf">write_debug</span><span class="p" data-group-id="4024991866-58">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4024991866-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4024991866-59">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4024991866-60">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="4024991866-60">]</span><span class="p" data-group-id="4024991866-59">)</span><span class="p">.</span></code></pre><p id="ex">As it is not relevant to the example, the channel handling functions have been
│ │ │ │  omitted. To compile this example, the
│ │ │ │  <a href="design_principles.xhtml#channels-implementation">implementation of channel handling</a>
│ │ │ │  needs to be added to the module.</p><p>Here is an example showing how the debugging functions in the <code class="inline">sys</code>
│ │ │ │  module can be used for <code class="inline">ch4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="7267959045-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="7267959045-1">]</span><span class="w"> </span><span class="p" data-group-id="7267959045-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="7267959045-2">]</span><span class="w"> </span><span class="p" data-group-id="7267959045-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="7267959045-3">]</span><span class="w"> </span><span class="p" data-group-id="7267959045-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="7267959045-4">]</span><span class="w"> </span><span class="p" data-group-id="7267959045-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="7267959045-5">]</span><span class="w"> </span><span class="p" data-group-id="7267959045-6">[</span><span class="ss">jit</span><span class="p" data-group-id="7267959045-6">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="7368531603-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="7368531603-1">]</span><span class="w"> </span><span class="p" data-group-id="7368531603-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="7368531603-2">]</span><span class="w"> </span><span class="p" data-group-id="7368531603-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="7368531603-3">]</span><span class="w"> </span><span class="p" data-group-id="7368531603-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="7368531603-4">]</span><span class="w"> </span><span class="p" data-group-id="7368531603-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="7368531603-5">]</span><span class="w"> </span><span class="p" data-group-id="7368531603-6">[</span><span class="ss">jit</span><span class="p" data-group-id="7368531603-6">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="7267959045-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="7267959045-8">(</span><span class="p" data-group-id="7267959045-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="7267959045-7">)</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="7267959045-9">(</span><span class="p" data-group-id="7267959045-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7267959045-10">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7267959045-10">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="7267959045-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7267959045-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="7368531603-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="7368531603-8">(</span><span class="p" data-group-id="7368531603-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="7368531603-7">)</span><span class="gp unselectable">
│ │ │ │ +1&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="7368531603-9">(</span><span class="p" data-group-id="7368531603-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7368531603-10">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7368531603-10">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="7368531603-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7368531603-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="7267959045-12">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7267959045-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="7368531603-12">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7368531603-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">alloc</span><span class="p" data-group-id="7267959045-13">(</span><span class="p" data-group-id="7267959045-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7267959045-14">{</span><span class="ss">in</span><span class="p">,</span><span class="ss">alloc</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7267959045-14">}</span><span class="w">
│ │ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7267959045-15">{</span><span class="ss">out</span><span class="p">,</span><span class="p" data-group-id="7267959045-16">{</span><span class="ss">ch4</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7267959045-16">}</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7267959045-15">}</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">alloc</span><span class="p" data-group-id="7368531603-13">(</span><span class="p" data-group-id="7368531603-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7368531603-14">{</span><span class="ss">in</span><span class="p">,</span><span class="ss">alloc</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7368531603-14">}</span><span class="w">
│ │ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7368531603-15">{</span><span class="ss">out</span><span class="p">,</span><span class="p" data-group-id="7368531603-16">{</span><span class="ss">ch4</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7368531603-16">}</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7368531603-15">}</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">free</span><span class="p" data-group-id="7267959045-17">(</span><span class="ss">ch1</span><span class="p" data-group-id="7267959045-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7267959045-18">{</span><span class="ss">in</span><span class="p">,</span><span class="p" data-group-id="7267959045-19">{</span><span class="ss">free</span><span class="p">,</span><span class="ss">ch1</span><span class="p" data-group-id="7267959045-19">}</span><span class="p" data-group-id="7267959045-18">}</span><span class="w">
│ │ │ │ +5&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">free</span><span class="p" data-group-id="7368531603-17">(</span><span class="ss">ch1</span><span class="p" data-group-id="7368531603-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7368531603-18">{</span><span class="ss">in</span><span class="p">,</span><span class="p" data-group-id="7368531603-19">{</span><span class="ss">free</span><span class="p">,</span><span class="ss">ch1</span><span class="p" data-group-id="7368531603-19">}</span><span class="p" data-group-id="7368531603-18">}</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="7267959045-20">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="7267959045-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7267959045-21">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="7267959045-22">[</span><span class="p" data-group-id="7267959045-23">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="7267959045-24">{</span><span class="p" data-group-id="7267959045-25">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7267959045-25">}</span><span class="p">,</span><span class="p" data-group-id="7267959045-26">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="7267959045-26">}</span><span class="p" data-group-id="7267959045-24">}</span><span class="p" data-group-id="7267959045-23">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="7267959045-27">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="7267959045-28">{</span><span class="p" data-group-id="7267959045-29">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7267959045-29">}</span><span class="p">,</span><span class="p" data-group-id="7267959045-30">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">49</span><span class="p" data-group-id="7267959045-30">}</span><span class="p" data-group-id="7267959045-28">}</span><span class="p" data-group-id="7267959045-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="7267959045-31">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">202</span><span class="p" data-group-id="7267959045-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="7267959045-32">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7267959045-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="7267959045-33">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7267959045-33">}</span><span class="p" data-group-id="7267959045-22">]</span><span class="p" data-group-id="7267959045-21">}</span><span class="gp unselectable">
│ │ │ │ -7&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="7267959045-34">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="7267959045-34">)</span><span class="p">.</span><span class="w">
│ │ │ │ +6&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="7368531603-20">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="7368531603-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7368531603-21">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="7368531603-22">[</span><span class="p" data-group-id="7368531603-23">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="7368531603-24">{</span><span class="p" data-group-id="7368531603-25">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7368531603-25">}</span><span class="p">,</span><span class="p" data-group-id="7368531603-26">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="7368531603-26">}</span><span class="p" data-group-id="7368531603-24">}</span><span class="p" data-group-id="7368531603-23">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="7368531603-27">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="7368531603-28">{</span><span class="p" data-group-id="7368531603-29">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7368531603-29">}</span><span class="p">,</span><span class="p" data-group-id="7368531603-30">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">49</span><span class="p" data-group-id="7368531603-30">}</span><span class="p" data-group-id="7368531603-28">}</span><span class="p" data-group-id="7368531603-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="7368531603-31">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">202</span><span class="p" data-group-id="7368531603-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="7368531603-32">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7368531603-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="7368531603-33">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7368531603-33">}</span><span class="p" data-group-id="7368531603-22">]</span><span class="p" data-group-id="7368531603-21">}</span><span class="gp unselectable">
│ │ │ │ +7&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="7368531603-34">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="7368531603-34">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="7267959045-35">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="7267959045-35">)</span><span class="p">.</span><span class="w">
│ │ │ │ +8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="7368531603-35">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="7368531603-35">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="7267959045-36">(</span><span class="ss">ch4</span><span class="p" data-group-id="7267959045-36">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7267959045-37">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7267959045-38">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">ch4</span><span class="p" data-group-id="7267959045-38">}</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7267959045-39">[</span><span class="p" data-group-id="7267959045-40">[</span><span class="p" data-group-id="7267959045-41">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="7267959045-42">{</span><span class="ss">ch4</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7267959045-42">}</span><span class="p" data-group-id="7267959045-41">}</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="7267959045-43">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="7267959045-44">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7267959045-44">]</span><span class="p" data-group-id="7267959045-43">}</span><span class="p" data-group-id="7267959045-40">]</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="7267959045-45">[</span><span class="p" data-group-id="7267959045-45">]</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="7267959045-46">{</span><span class="p" data-group-id="7267959045-47">[</span><span class="mi">1</span><span class="p" data-group-id="7267959045-47">]</span><span class="p">,</span><span class="p" data-group-id="7267959045-48">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">18</span><span class="p">,</span><span class="mi">19</span><span class="p">|</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7267959045-48">]</span><span class="p" data-group-id="7267959045-46">}</span><span class="p" data-group-id="7267959045-39">]</span><span class="p" data-group-id="7267959045-37">}</span></code></pre><h3 id="starting-the-process" class="section-heading">
│ │ │ │ +9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="7368531603-36">(</span><span class="ss">ch4</span><span class="p" data-group-id="7368531603-36">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7368531603-37">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7368531603-38">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">ch4</span><span class="p" data-group-id="7368531603-38">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7368531603-39">[</span><span class="p" data-group-id="7368531603-40">[</span><span class="p" data-group-id="7368531603-41">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="7368531603-42">{</span><span class="ss">ch4</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7368531603-42">}</span><span class="p" data-group-id="7368531603-41">}</span><span class="p">,</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="7368531603-43">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="7368531603-44">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7368531603-44">]</span><span class="p" data-group-id="7368531603-43">}</span><span class="p" data-group-id="7368531603-40">]</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="7368531603-45">[</span><span class="p" data-group-id="7368531603-45">]</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="7368531603-46">{</span><span class="p" data-group-id="7368531603-47">[</span><span class="mi">1</span><span class="p" data-group-id="7368531603-47">]</span><span class="p">,</span><span class="p" data-group-id="7368531603-48">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">18</span><span class="p">,</span><span class="mi">19</span><span class="p">|</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7368531603-48">]</span><span class="p" data-group-id="7368531603-46">}</span><span class="p" data-group-id="7368531603-39">]</span><span class="p" data-group-id="7368531603-37">}</span></code></pre><h3 id="starting-the-process" class="section-heading">
│ │ │ │    <a href="#starting-the-process" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting the Process</span>
│ │ │ │  </h3>
│ │ │ │  <p>A function in the <a href="../../../lib/stdlib/doc/html/proc_lib.html"><code class="inline">proc_lib</code></a> module is to be used to start the process. Several
│ │ │ │  functions are available, for example,
│ │ │ │  <a href="../../../lib/stdlib/doc/html/proc_lib.html#spawn_link/4"><code class="inline">proc_lib:spawn_link/3,4</code></a>
│ │ │ │  for asynchronous start and
│ │ │ │  <a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/5"><code class="inline">proc_lib:start_link/3,4,5</code></a> for synchronous start.</p><p>Information necessary for a process within a supervision tree, such as
│ │ │ │  details on ancestors and the initial call, is stored when a process
│ │ │ │  is started through one of these functions.</p><p>If the process terminates with a reason other than <code class="inline">normal</code> or <code class="inline">shutdown</code>, a
│ │ │ │  crash report is generated. For more information about the crash report, see
│ │ │ │  <a href="../../../lib/kernel/doc/html/logger_chapter.xhtml">Logging</a> in Kernel User's Guide.</p><p>In the example, synchronous start is used. The process starts by calling
│ │ │ │ -<code class="inline">ch4:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="5944709118-1">(</span><span class="p" data-group-id="5944709118-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5944709118-2">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5944709118-3">[</span><span class="nf">self</span><span class="p" data-group-id="5944709118-4">(</span><span class="p" data-group-id="5944709118-4">)</span><span class="p" data-group-id="5944709118-3">]</span><span class="p" data-group-id="5944709118-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch4:start_link/0</code> calls <a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>, which takes a module
│ │ │ │ +<code class="inline">ch4:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="8769359262-1">(</span><span class="p" data-group-id="8769359262-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8769359262-2">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8769359262-3">[</span><span class="nf">self</span><span class="p" data-group-id="8769359262-4">(</span><span class="p" data-group-id="8769359262-4">)</span><span class="p" data-group-id="8769359262-3">]</span><span class="p" data-group-id="8769359262-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch4:start_link/0</code> calls <a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>, which takes a module
│ │ │ │  name, a function name, and an argument list as arguments. It then
│ │ │ │  spawns a new process and establishes a link. The new process starts
│ │ │ │  by executing the given function, here <code class="inline">ch4:init(Pid)</code>, where <code class="inline">Pid</code> is
│ │ │ │  the pid of the parent process (obtained by the call to
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self()</code></a> in the call to <a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>).</p><p>All initialization, including name registration, is done in <code class="inline">init/1</code>. The new
│ │ │ │ -process has to acknowledge that it has been started to the parent:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="3091478465-1">(</span><span class="n">Parent</span><span class="p" data-group-id="3091478465-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +process has to acknowledge that it has been started to the parent:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="0358833465-1">(</span><span class="n">Parent</span><span class="p" data-group-id="0358833465-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="3091478465-2">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3091478465-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3091478465-4">(</span><span class="p" data-group-id="3091478465-4">)</span><span class="p" data-group-id="3091478465-3">}</span><span class="p" data-group-id="3091478465-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="3091478465-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3091478465-5">)</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a> is synchronous and does not return until
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="0358833465-2">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0358833465-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0358833465-4">(</span><span class="p" data-group-id="0358833465-4">)</span><span class="p" data-group-id="0358833465-3">}</span><span class="p" data-group-id="0358833465-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="0358833465-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0358833465-5">)</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a> is synchronous and does not return until
│ │ │ │  <a href="../../../lib/stdlib/doc/html/proc_lib.html#init_ack/2"><code class="inline">proc_lib:init_ack/1,2</code></a> or
│ │ │ │  <a href="../../../lib/stdlib/doc/html/proc_lib.html#init_fail/3"><code class="inline">proc_lib:init_fail/2,3</code></a> has been called,
│ │ │ │  or the process has exited.</p><p><a href="" id="debug"></a></p><h3 id="debugging" class="section-heading">
│ │ │ │    <a href="#debugging" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Debugging</span>
│ │ │ │  </h3>
│ │ │ │  <p>To support the debug facilities in <code class="inline">sys</code>, a <em>debug structure</em> is needed. The
│ │ │ │ -<code class="inline">Deb</code> term is initialized using <a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7281850033-1">(</span><span class="n">Parent</span><span class="p" data-group-id="7281850033-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +<code class="inline">Deb</code> term is initialized using <a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4793192650-1">(</span><span class="n">Parent</span><span class="p" data-group-id="4793192650-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="7281850033-2">(</span><span class="p" data-group-id="7281850033-3">[</span><span class="p" data-group-id="7281850033-3">]</span><span class="p" data-group-id="7281850033-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="4793192650-2">(</span><span class="p" data-group-id="4793192650-3">[</span><span class="p" data-group-id="4793192650-3">]</span><span class="p" data-group-id="4793192650-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="7281850033-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="7281850033-4">)</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a> takes a list of options. Given an empty list as in this
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="4793192650-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="4793192650-4">)</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a> takes a list of options. Given an empty list as in this
│ │ │ │  example means that debugging is initially disabled. For information about the
│ │ │ │  possible options, see <a href="../../../lib/stdlib/doc/html/sys.html"><code class="inline">sys</code></a> in STDLIB.</p><p>For each <em>system event</em> to be logged or traced, the following function
│ │ │ │ -is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="7757044261-1">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Func</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="7757044261-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Deb1</span></code></pre><p>The arguments have the follow meaning:</p><ul><li><code class="inline">Deb</code> is the debug structure as returned from <a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>.</li><li><code class="inline">Func</code> is a fun specifying a (user-defined) function used to format trace
│ │ │ │ +is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="6461393189-1">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Func</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="6461393189-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Deb1</span></code></pre><p>The arguments have the follow meaning:</p><ul><li><code class="inline">Deb</code> is the debug structure as returned from <a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>.</li><li><code class="inline">Func</code> is a fun specifying a (user-defined) function used to format trace
│ │ │ │  output. For each system event, the format function is called as
│ │ │ │  <code class="inline">Func(Dev, Event, Info)</code>, where:<ul><li><code class="inline">Dev</code> is the I/O device to which the output is to be printed. See <a href="../../../lib/stdlib/doc/html/io.html"><code class="inline">io</code></a>
│ │ │ │  in STDLIB.</li><li><code class="inline">Event</code> and <code class="inline">Info</code> are passed as-is from the call to <a href="../../../lib/stdlib/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a>.</li></ul></li><li><code class="inline">Info</code> is used to pass more information to <code class="inline">Func</code>. It can be any term, and it
│ │ │ │  is passed as-is.</li><li><code class="inline">Event</code> is the system event. It is up to the user to define what a system
│ │ │ │  event is and how it is to be represented. Typically, at least incoming and
│ │ │ │  outgoing messages are considered system events and represented by the tuples
│ │ │ │  <code class="inline">{in,Msg[,From]}</code> and <code class="inline">{out,Msg,To[,State]}</code>, respectively.</li></ul><p><a href="../../../lib/stdlib/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a> returns an updated debug structure <code class="inline">Deb1</code>.</p><p>In the example, <a href="../../../lib/stdlib/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a> is called for each incoming and
│ │ │ │  outgoing message. The format function <code class="inline">Func</code> is the function
│ │ │ │ -<code class="inline">ch4:write_debug/3</code>, which prints the message using <a href="../../../lib/stdlib/doc/html/io.html#format/3"><code class="inline">io:format/3</code></a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="3314775252-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="3314775252-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +<code class="inline">ch4:write_debug/3</code>, which prints the message using <a href="../../../lib/stdlib/doc/html/io.html#format/3"><code class="inline">io:format/3</code></a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="0090826584-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0090826584-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="3314775252-2">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="3314775252-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="3314775252-3">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314775252-4">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="3314775252-4">}</span><span class="p" data-group-id="3314775252-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="3314775252-5">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="3314775252-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="3314775252-6">(</span><span class="n">Chs</span><span class="p" data-group-id="3314775252-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3314775252-7">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3314775252-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="3314775252-8">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314775252-9">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314775252-10">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3314775252-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="3314775252-9">}</span><span class="p" data-group-id="3314775252-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="3314775252-11">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="3314775252-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="3314775252-12">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3314775252-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="3314775252-13">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314775252-14">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314775252-15">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3314775252-15">}</span><span class="p" data-group-id="3314775252-14">}</span><span class="p" data-group-id="3314775252-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="3314775252-16">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3314775252-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="3314775252-17">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="3314775252-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0090826584-2">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0090826584-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0090826584-3">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0090826584-4">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="0090826584-4">}</span><span class="p" data-group-id="0090826584-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="0090826584-5">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="0090826584-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="0090826584-6">(</span><span class="n">Chs</span><span class="p" data-group-id="0090826584-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0090826584-7">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0090826584-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0090826584-8">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0090826584-9">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0090826584-10">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0090826584-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="0090826584-9">}</span><span class="p" data-group-id="0090826584-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="0090826584-11">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="0090826584-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0090826584-12">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0090826584-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0090826584-13">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0090826584-14">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0090826584-15">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0090826584-15">}</span><span class="p" data-group-id="0090826584-14">}</span><span class="p" data-group-id="0090826584-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="0090826584-16">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0090826584-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="0090826584-17">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="0090826584-17">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">write_debug</span><span class="p" data-group-id="3314775252-18">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3314775252-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3314775252-19">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314775252-20">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="3314775252-20">]</span><span class="p" data-group-id="3314775252-19">)</span><span class="p">.</span></code></pre><p><a href="" id="msg"></a></p><h3 id="handling-system-messages" class="section-heading">
│ │ │ │ +</span><span class="nf">write_debug</span><span class="p" data-group-id="0090826584-18">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0090826584-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0090826584-19">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0090826584-20">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="0090826584-20">]</span><span class="p" data-group-id="0090826584-19">)</span><span class="p">.</span></code></pre><p><a href="" id="msg"></a></p><h3 id="handling-system-messages" class="section-heading">
│ │ │ │    <a href="#handling-system-messages" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Handling System Messages</span>
│ │ │ │  </h3>
│ │ │ │  <p><em>System messages</em> are received as:</p><pre><code class="text">{system, From, Request}</code></pre><p>The content and meaning of these messages are not to be interpreted by the
│ │ │ │ -process. Instead the following function is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="9046280644-1">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9046280644-1">)</span></code></pre><p>The arguments have the following meaning:</p><ul><li><code class="inline">Request</code> and <code class="inline">From</code> from the received system message are to be
│ │ │ │ +process. Instead the following function is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="5096274733-1">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5096274733-1">)</span></code></pre><p>The arguments have the following meaning:</p><ul><li><code class="inline">Request</code> and <code class="inline">From</code> from the received system message are to be
│ │ │ │  passed as-is to the call to <a href="../../../lib/stdlib/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a>.</li><li><code class="inline">Parent</code> is the pid of the parent process.</li><li><code class="inline">Module</code> is the name of the module implementing the speciall process.</li><li><code class="inline">Deb</code> is the debug structure.</li><li><code class="inline">State</code> is a term describing the internal state and is passed on to
│ │ │ │  <code class="inline">Module:system_continue/3</code>, <code class="inline">Module:system_terminate/4</code>/
│ │ │ │  <code class="inline">Module:system_get_state/1</code>, and <code class="inline">Module:system_replace_state/2</code>.</li></ul><p><a href="../../../lib/stdlib/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a> does not return. It handles the system
│ │ │ │  message and <em>eventually</em> calls either of the following functions:</p><ul><li><p><code class="inline">Module:system_continue(Parent, Deb, State)</code> - if process execution is to
│ │ │ │  continue.</p></li><li><p><code class="inline">Module:system_terminate(Reason, Parent, Deb, State)</code> - if the
│ │ │ │  process is to terminate.</p></li></ul><p>While handling the system message, <a href="../../../lib/stdlib/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a> can call
│ │ │ │  one of the following functions:</p><ul><li><p><code class="inline">Module:system_get_state(State)</code> - if the process is to return its state.</p></li><li><p><code class="inline">Module:system_replace_state(StateFun, State)</code> - if the process is
│ │ │ │  to replace its state using the fun <code class="inline">StateFun</code> fun. See <a href="../../../lib/stdlib/doc/html/sys.html#replace_state/3"><code class="inline">sys:replace_state/3</code></a>
│ │ │ │  for more information.</p></li><li><p><code class="inline">system_code_change(Misc, Module, OldVsn, Extra)</code> - if the process is to
│ │ │ │  perform a code change.</p></li></ul><p>A process in a supervision tree is expected to terminate with the same reason as
│ │ │ │ -its parent.</p><p>In the example, system messages are handed by the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="2109179142-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="2109179142-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +its parent.</p><p>In the example, system messages are handed by the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="3396149072-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="3396149072-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -        </span><span class="p" data-group-id="2109179142-2">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="2109179142-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="2109179142-3">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ │ -                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2109179142-3">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3396149072-2">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="3396149072-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="3396149072-3">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ │ +                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3396149072-3">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_continue</span><span class="p" data-group-id="2109179142-4">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2109179142-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="2109179142-5">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="2109179142-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_continue</span><span class="p" data-group-id="3396149072-4">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3396149072-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="3396149072-5">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="3396149072-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_terminate</span><span class="p" data-group-id="2109179142-6">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2109179142-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="2109179142-7">(</span><span class="n">Reason</span><span class="p" data-group-id="2109179142-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_terminate</span><span class="p" data-group-id="3396149072-6">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3396149072-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="3396149072-7">(</span><span class="n">Reason</span><span class="p" data-group-id="3396149072-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_get_state</span><span class="p" data-group-id="2109179142-8">(</span><span class="n">Chs</span><span class="p" data-group-id="2109179142-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2109179142-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2109179142-9">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_get_state</span><span class="p" data-group-id="3396149072-8">(</span><span class="n">Chs</span><span class="p" data-group-id="3396149072-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3396149072-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3396149072-9">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_replace_state</span><span class="p" data-group-id="2109179142-10">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2109179142-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="2109179142-11">(</span><span class="n">Chs</span><span class="p" data-group-id="2109179142-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2109179142-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="2109179142-12">}</span><span class="p">.</span></code></pre><p>If a special process is configured to trap exits, it must take notice
│ │ │ │ +</span><span class="nf">system_replace_state</span><span class="p" data-group-id="3396149072-10">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3396149072-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="3396149072-11">(</span><span class="n">Chs</span><span class="p" data-group-id="3396149072-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3396149072-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="3396149072-12">}</span><span class="p">.</span></code></pre><p>If a special process is configured to trap exits, it must take notice
│ │ │ │  of 'EXIT' messages from its parent process and terminate using the
│ │ │ │ -same exit reason once the parent process has terminated.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5227487660-1">(</span><span class="n">Parent</span><span class="p" data-group-id="5227487660-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +same exit reason once the parent process has terminated.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6112216308-1">(</span><span class="n">Parent</span><span class="p" data-group-id="6112216308-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="5227487660-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5227487660-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="6112216308-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6112216308-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="5227487660-3">(</span><span class="n">Parent</span><span class="p" data-group-id="5227487660-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="6112216308-3">(</span><span class="n">Parent</span><span class="p" data-group-id="6112216308-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="5227487660-4">(</span><span class="n">Parent</span><span class="p" data-group-id="5227487660-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="6112216308-4">(</span><span class="n">Parent</span><span class="p" data-group-id="6112216308-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="5227487660-5">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5227487660-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6112216308-5">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="6112216308-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="c1">%% Clean up here, if needed.</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="5227487660-6">(</span><span class="n">Reason</span><span class="p" data-group-id="5227487660-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="6112216308-6">(</span><span class="n">Reason</span><span class="p" data-group-id="6112216308-6">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="user-defined-behaviours" class="section-heading">
│ │ │ │    <a href="#user-defined-behaviours" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">User-Defined Behaviours</span>
│ │ │ │  </h2>
│ │ │ │ @@ -353,69 +353,69 @@
│ │ │ │  function. Note that the <code class="inline">-optional_callbacks</code> attribute is to be used together
│ │ │ │  with the <code class="inline">-callback</code> attribute; it cannot be combined with the
│ │ │ │  <code class="inline">behaviour_info()</code> function described below.</p><p>Tools that need to know about optional callback functions can call
│ │ │ │  <code class="inline">Behaviour:behaviour_info(optional_callbacks)</code> to get a list of all optional
│ │ │ │  callback functions.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>We recommend using the <code class="inline">-callback</code> attribute rather than the
│ │ │ │  <code class="inline">behaviour_info()</code> function. The reason is that the extra type information can
│ │ │ │  be used by tools to produce documentation or find discrepancies.</p></section><p>As an alternative to the <code class="inline">-callback</code> and <code class="inline">-optional_callbacks</code> attributes you
│ │ │ │ -may directly implement and export <code class="inline">behaviour_info()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="5365322432-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="5365322432-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5365322432-2">[</span><span class="p" data-group-id="5365322432-3">{</span><span class="n">Name1</span><span class="p">,</span><span class="w"> </span><span class="n">Arity1</span><span class="p" data-group-id="5365322432-3">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="p" data-group-id="5365322432-4">{</span><span class="n">NameN</span><span class="p">,</span><span class="w"> </span><span class="n">ArityN</span><span class="p" data-group-id="5365322432-4">}</span><span class="p" data-group-id="5365322432-2">]</span><span class="p">.</span></code></pre><p>where each <code class="inline">{Name, Arity}</code> specifies the name and arity of a callback function.
│ │ │ │ +may directly implement and export <code class="inline">behaviour_info()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="0219287369-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="0219287369-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0219287369-2">[</span><span class="p" data-group-id="0219287369-3">{</span><span class="n">Name1</span><span class="p">,</span><span class="w"> </span><span class="n">Arity1</span><span class="p" data-group-id="0219287369-3">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="p" data-group-id="0219287369-4">{</span><span class="n">NameN</span><span class="p">,</span><span class="w"> </span><span class="n">ArityN</span><span class="p" data-group-id="0219287369-4">}</span><span class="p" data-group-id="0219287369-2">]</span><span class="p">.</span></code></pre><p>where each <code class="inline">{Name, Arity}</code> specifies the name and arity of a callback function.
│ │ │ │  This function is otherwise automatically generated by the compiler using the
│ │ │ │  <code class="inline">-callback</code> attributes.</p><p>When the compiler encounters the module attribute <code class="inline">-behaviour(Behaviour).</code> in a
│ │ │ │  module <code class="inline">Mod</code>, it calls <code class="inline">Behaviour:behaviour_info(callbacks)</code> and compares the
│ │ │ │  result with the set of functions actually exported from <code class="inline">Mod</code>, and issues a
│ │ │ │  warning if any callback function is missing.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">%% User-defined behaviour module</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3538664784-1">(</span><span class="ss">simple_server</span><span class="p" data-group-id="3538664784-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3538664784-2">(</span><span class="p" data-group-id="3538664784-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3538664784-3">]</span><span class="p" data-group-id="3538664784-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2968108563-1">(</span><span class="ss">simple_server</span><span class="p" data-group-id="2968108563-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2968108563-2">(</span><span class="p" data-group-id="2968108563-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2968108563-3">]</span><span class="p" data-group-id="2968108563-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">init</span><span class="p" data-group-id="3538664784-4">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3538664784-5">(</span><span class="p" data-group-id="3538664784-5">)</span><span class="p" data-group-id="3538664784-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="3538664784-6">(</span><span class="n">Req</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3538664784-7">(</span><span class="p" data-group-id="3538664784-7">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3538664784-8">(</span><span class="p" data-group-id="3538664784-8">)</span><span class="p" data-group-id="3538664784-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3538664784-9">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3538664784-10">(</span><span class="p" data-group-id="3538664784-10">)</span><span class="p" data-group-id="3538664784-9">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">terminate</span><span class="p" data-group-id="3538664784-11">(</span><span class="p" data-group-id="3538664784-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">format_state</span><span class="p" data-group-id="3538664784-12">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3538664784-13">(</span><span class="p" data-group-id="3538664784-13">)</span><span class="p" data-group-id="3538664784-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3538664784-14">(</span><span class="p" data-group-id="3538664784-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">init</span><span class="p" data-group-id="2968108563-4">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2968108563-5">(</span><span class="p" data-group-id="2968108563-5">)</span><span class="p" data-group-id="2968108563-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="2968108563-6">(</span><span class="n">Req</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2968108563-7">(</span><span class="p" data-group-id="2968108563-7">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2968108563-8">(</span><span class="p" data-group-id="2968108563-8">)</span><span class="p" data-group-id="2968108563-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2968108563-9">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2968108563-10">(</span><span class="p" data-group-id="2968108563-10">)</span><span class="p" data-group-id="2968108563-9">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">terminate</span><span class="p" data-group-id="2968108563-11">(</span><span class="p" data-group-id="2968108563-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">format_state</span><span class="p" data-group-id="2968108563-12">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2968108563-13">(</span><span class="p" data-group-id="2968108563-13">)</span><span class="p" data-group-id="2968108563-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2968108563-14">(</span><span class="p" data-group-id="2968108563-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">optional_callbacks</span><span class="p" data-group-id="3538664784-15">(</span><span class="p" data-group-id="3538664784-16">[</span><span class="ss">format_state</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3538664784-16">]</span><span class="p" data-group-id="3538664784-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">optional_callbacks</span><span class="p" data-group-id="2968108563-15">(</span><span class="p" data-group-id="2968108563-16">[</span><span class="ss">format_state</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2968108563-16">]</span><span class="p" data-group-id="2968108563-15">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% Alternatively you may define:</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% -export([behaviour_info/1]).</span><span class="w">
│ │ │ │  </span><span class="c1">%% behaviour_info(callbacks) -&gt;</span><span class="w">
│ │ │ │  </span><span class="c1">%%     [{init,1},</span><span class="w">
│ │ │ │  </span><span class="c1">%%      {handle_req,2},</span><span class="w">
│ │ │ │  </span><span class="c1">%%      {terminate,0}].</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="3538664784-17">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="3538664784-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3538664784-18">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3538664784-19">[</span><span class="nf">self</span><span class="p" data-group-id="3538664784-20">(</span><span class="p" data-group-id="3538664784-20">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="3538664784-19">]</span><span class="p" data-group-id="3538664784-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="2968108563-17">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2968108563-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2968108563-18">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2968108563-19">[</span><span class="nf">self</span><span class="p" data-group-id="2968108563-20">(</span><span class="p" data-group-id="2968108563-20">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2968108563-19">]</span><span class="p" data-group-id="2968108563-18">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="3538664784-21">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="3538664784-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="3538664784-22">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3538664784-23">(</span><span class="p" data-group-id="3538664784-23">)</span><span class="p" data-group-id="3538664784-22">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="2968108563-21">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2968108563-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="2968108563-22">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2968108563-23">(</span><span class="p" data-group-id="2968108563-23">)</span><span class="p" data-group-id="2968108563-22">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Dbg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="3538664784-24">(</span><span class="p" data-group-id="3538664784-25">[</span><span class="p" data-group-id="3538664784-25">]</span><span class="p" data-group-id="3538664784-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="3538664784-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3538664784-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3538664784-28">(</span><span class="p" data-group-id="3538664784-28">)</span><span class="p" data-group-id="3538664784-27">}</span><span class="p" data-group-id="3538664784-26">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="3538664784-29">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3538664784-29">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="n">Dbg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="2968108563-24">(</span><span class="p" data-group-id="2968108563-25">[</span><span class="p" data-group-id="2968108563-25">]</span><span class="p" data-group-id="2968108563-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="2968108563-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2968108563-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2968108563-28">(</span><span class="p" data-group-id="2968108563-28">)</span><span class="p" data-group-id="2968108563-27">}</span><span class="p" data-group-id="2968108563-26">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="2968108563-29">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2968108563-29">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>In a callback module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7707800821-1">(</span><span class="ss">db</span><span class="p" data-group-id="7707800821-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="7707800821-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="7707800821-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>In a callback module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5271917316-1">(</span><span class="ss">db</span><span class="p" data-group-id="5271917316-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5271917316-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="5271917316-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7707800821-3">(</span><span class="p" data-group-id="7707800821-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7707800821-4">]</span><span class="p" data-group-id="7707800821-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5271917316-3">(</span><span class="p" data-group-id="5271917316-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5271917316-4">]</span><span class="p" data-group-id="5271917316-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The contracts specified with <code class="inline">-callback</code> attributes in behaviour modules can be
│ │ │ │  further refined by adding <code class="inline">-spec</code> attributes in callback modules. This can be
│ │ │ │  useful as <code class="inline">-callback</code> contracts are usually generic. The same callback module
│ │ │ │ -with contracts for the callbacks:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0483897828-1">(</span><span class="ss">db</span><span class="p" data-group-id="0483897828-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="0483897828-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="0483897828-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +with contracts for the callbacks:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7724216256-1">(</span><span class="ss">db</span><span class="p" data-group-id="7724216256-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="7724216256-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="7724216256-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0483897828-3">(</span><span class="p" data-group-id="0483897828-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0483897828-4">]</span><span class="p" data-group-id="0483897828-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7724216256-3">(</span><span class="p" data-group-id="7724216256-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7724216256-4">]</span><span class="p" data-group-id="7724216256-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0483897828-5">(</span><span class="ss">state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0483897828-6">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0483897828-7">[</span><span class="nf">atom</span><span class="p" data-group-id="0483897828-8">(</span><span class="p" data-group-id="0483897828-8">)</span><span class="p" data-group-id="0483897828-7">]</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0483897828-9">(</span><span class="p" data-group-id="0483897828-9">)</span><span class="p" data-group-id="0483897828-6">}</span><span class="p" data-group-id="0483897828-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7724216256-5">(</span><span class="ss">state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7724216256-6">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="7724216256-7">[</span><span class="nf">atom</span><span class="p" data-group-id="7724216256-8">(</span><span class="p" data-group-id="7724216256-8">)</span><span class="p" data-group-id="7724216256-7">]</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="7724216256-9">(</span><span class="p" data-group-id="7724216256-9">)</span><span class="p" data-group-id="7724216256-6">}</span><span class="p" data-group-id="7724216256-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="0483897828-10">(</span><span class="p" data-group-id="0483897828-10">)</span><span class="w">   </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="0483897828-11">{</span><span class="p" data-group-id="0483897828-11">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">request</span><span class="p" data-group-id="0483897828-12">(</span><span class="p" data-group-id="0483897828-12">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0483897828-13">{</span><span class="ss">&#39;store&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0483897828-14">(</span><span class="p" data-group-id="0483897828-14">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0483897828-15">(</span><span class="p" data-group-id="0483897828-15">)</span><span class="p" data-group-id="0483897828-13">}</span><span class="p">;</span><span class="w">
│ │ │ │ -                   </span><span class="p" data-group-id="0483897828-16">{</span><span class="ss">&#39;lookup&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0483897828-17">(</span><span class="p" data-group-id="0483897828-17">)</span><span class="p" data-group-id="0483897828-16">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="7724216256-10">(</span><span class="p" data-group-id="7724216256-10">)</span><span class="w">   </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="7724216256-11">{</span><span class="p" data-group-id="7724216256-11">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">request</span><span class="p" data-group-id="7724216256-12">(</span><span class="p" data-group-id="7724216256-12">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="7724216256-13">{</span><span class="ss">&#39;store&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7724216256-14">(</span><span class="p" data-group-id="7724216256-14">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7724216256-15">(</span><span class="p" data-group-id="7724216256-15">)</span><span class="p" data-group-id="7724216256-13">}</span><span class="p">;</span><span class="w">
│ │ │ │ +                   </span><span class="p" data-group-id="7724216256-16">{</span><span class="ss">&#39;lookup&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7724216256-17">(</span><span class="p" data-group-id="7724216256-17">)</span><span class="p" data-group-id="7724216256-16">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="0483897828-18">(</span><span class="nf">request</span><span class="p" data-group-id="0483897828-19">(</span><span class="p" data-group-id="0483897828-19">)</span><span class="p">,</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="0483897828-20">(</span><span class="p" data-group-id="0483897828-20">)</span><span class="p" data-group-id="0483897828-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0483897828-21">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0483897828-22">(</span><span class="p" data-group-id="0483897828-22">)</span><span class="p" data-group-id="0483897828-21">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="7724216256-18">(</span><span class="nf">request</span><span class="p" data-group-id="7724216256-19">(</span><span class="p" data-group-id="7724216256-19">)</span><span class="p">,</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="7724216256-20">(</span><span class="p" data-group-id="7724216256-20">)</span><span class="p" data-group-id="7724216256-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7724216256-21">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7724216256-22">(</span><span class="p" data-group-id="7724216256-22">)</span><span class="p" data-group-id="7724216256-21">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Each <code class="inline">-spec</code> contract is to be a subtype of the respective <code class="inline">-callback</code> contract.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/seq_prog.xhtml
│ │ │ │ @@ -41,293 +41,293 @@
│ │ │ │  </span><span class="mi">7</span><span class="gp unselectable">
│ │ │ │  2&gt; </span></code></pre><p>As shown, the Erlang shell numbers the lines that can be entered, (as 1&gt; 2&gt;) and
│ │ │ │  that it correctly says that 2 + 5 is 7. If you make writing mistakes in the
│ │ │ │  shell, you can delete with the backspace key, as in most shells. There are many
│ │ │ │  more editing commands in the shell (see
│ │ │ │  <a href="../../../lib/../erts/doc/html/tty.xhtml">tty - A command line interface</a> in ERTS User's Guide).</p><p>(Notice that many line numbers given by the shell in the following examples are
│ │ │ │  out of sequence. This is because this tutorial was written and code-tested in
│ │ │ │ -separate sessions).</p><p>Here is a bit more complex calculation:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="3093612901-1">(</span><span class="mi">42</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">77</span><span class="p" data-group-id="3093612901-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">66</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │ +separate sessions).</p><p>Here is a bit more complex calculation:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="6871147634-1">(</span><span class="mi">42</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">77</span><span class="p" data-group-id="6871147634-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">66</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">2618.0</span></code></pre><p>Notice the use of brackets, the multiplication operator <code class="inline">*</code>, and the division
│ │ │ │  operator <code class="inline">/</code>, as in normal arithmetic (see
│ │ │ │  <a href="../../../lib/../system/doc/html/expressions.xhtml">Expressions</a>).</p><p>Press Control-C to shut down the Erlang system and the Erlang shell.</p><p>The following output is shown:</p><pre><code class="text">BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
│ │ │ │         (v)ersion (k)ill (D)b-tables (d)istribution
│ │ │ │  a
│ │ │ │ -$</code></pre><p>Type <code class="inline">a</code> to leave the Erlang system.</p><p>Another way to shut down the Erlang system is by entering <a href="../../../lib/../erts/doc/html/erlang.html#halt/0"><code class="inline">halt/0</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">halt</span><span class="p" data-group-id="0805030683-1">(</span><span class="p" data-group-id="0805030683-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +$</code></pre><p>Type <code class="inline">a</code> to leave the Erlang system.</p><p>Another way to shut down the Erlang system is by entering <a href="../../../lib/../erts/doc/html/erlang.html#halt/0"><code class="inline">halt/0</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">halt</span><span class="p" data-group-id="6580395048-1">(</span><span class="p" data-group-id="6580395048-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="err">$</span></code></pre><h2 id="modules-and-functions" class="section-heading">
│ │ │ │    <a href="#modules-and-functions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Modules and Functions</span>
│ │ │ │  </h2>
│ │ │ │  <p>A programming language is not much use if you only can run code from the shell.
│ │ │ │  So here is a small Erlang program. Enter it into a file named <code class="inline">tut.erl</code> using a
│ │ │ │  suitable text editor. The file name <code class="inline">tut.erl</code> is important, and also that it is
│ │ │ │  in the same directory as the one where you started <code class="inline">erl</code>). If you are lucky your
│ │ │ │  editor has an Erlang mode that makes it easier for you to enter and format your
│ │ │ │  code nicely (see <a href="../../../lib/tools/doc/html/erlang_mode_chapter.xhtml">The Erlang mode for Emacs</a>
│ │ │ │  in Tools User's Guide), but you can manage perfectly well without. Here is the
│ │ │ │ -code to enter:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4126716780-1">(</span><span class="ss">tut</span><span class="p" data-group-id="4126716780-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4126716780-2">(</span><span class="p" data-group-id="4126716780-3">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4126716780-3">]</span><span class="p" data-group-id="4126716780-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +code to enter:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6502960127-1">(</span><span class="ss">tut</span><span class="p" data-group-id="6502960127-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6502960127-2">(</span><span class="p" data-group-id="6502960127-3">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6502960127-3">]</span><span class="p" data-group-id="6502960127-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="4126716780-4">(</span><span class="n">X</span><span class="p" data-group-id="4126716780-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="6502960127-4">(</span><span class="n">X</span><span class="p" data-group-id="6502960127-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="p">.</span></code></pre><p>It is not hard to guess that this program doubles the value of numbers. The
│ │ │ │  first two lines of the code are described later. Let us compile the program.
│ │ │ │ -This can be done in an Erlang shell as follows, where <code class="inline">c</code> means compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">c</span><span class="p" data-group-id="7378400390-1">(</span><span class="ss">tut</span><span class="p" data-group-id="7378400390-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7378400390-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut</span><span class="p" data-group-id="7378400390-2">}</span></code></pre><p>The <code class="inline">{ok,tut}</code> means that the compilation is OK. If it says <code class="inline">error</code> it means
│ │ │ │ +This can be done in an Erlang shell as follows, where <code class="inline">c</code> means compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">c</span><span class="p" data-group-id="7871074718-1">(</span><span class="ss">tut</span><span class="p" data-group-id="7871074718-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7871074718-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut</span><span class="p" data-group-id="7871074718-2">}</span></code></pre><p>The <code class="inline">{ok,tut}</code> means that the compilation is OK. If it says <code class="inline">error</code> it means
│ │ │ │  that there is some mistake in the text that you entered. Additional error
│ │ │ │  messages gives an idea to what is wrong so you can modify the text and then try
│ │ │ │ -to compile the program again.</p><p>Now run the program:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="3363307572-1">(</span><span class="mi">10</span><span class="p" data-group-id="3363307572-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +to compile the program again.</p><p>Now run the program:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="6827421117-1">(</span><span class="mi">10</span><span class="p" data-group-id="6827421117-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">20</span></code></pre><p>As expected, double of 10 is 20.</p><p>Now let us get back to the first two lines of the code. Erlang programs are
│ │ │ │  written in files. Each file contains an Erlang <em>module</em>. The first line of code
│ │ │ │ -in the module is the module name (see <a href="../../../lib/../system/doc/html/modules.xhtml">Modules</a>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3750354449-1">(</span><span class="ss">tut</span><span class="p" data-group-id="3750354449-1">)</span><span class="p">.</span></code></pre><p>Thus, the module is called <em>tut</em>. Notice the full stop <code class="inline">.</code> at the end of the
│ │ │ │ +in the module is the module name (see <a href="../../../lib/../system/doc/html/modules.xhtml">Modules</a>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9133433377-1">(</span><span class="ss">tut</span><span class="p" data-group-id="9133433377-1">)</span><span class="p">.</span></code></pre><p>Thus, the module is called <em>tut</em>. Notice the full stop <code class="inline">.</code> at the end of the
│ │ │ │  line. The files which are used to store the module must have the same name as
│ │ │ │  the module but with the extension <code class="inline">.erl</code>. In this case the file name is
│ │ │ │  <code class="inline">tut.erl</code>. When using a function in another module, the syntax
│ │ │ │  <code class="inline">module_name:function_name(arguments)</code> is used. So the following means call
│ │ │ │ -function <code class="inline">double</code> in module <code class="inline">tut</code> with argument <code class="inline">10</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="2170565432-1">(</span><span class="mi">10</span><span class="p" data-group-id="2170565432-1">)</span><span class="p">.</span></code></pre><p>The second line says that the module <code class="inline">tut</code> contains a function called <code class="inline">double</code>,
│ │ │ │ -which takes one argument (<code class="inline">X</code> in our example):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0376685450-1">(</span><span class="p" data-group-id="0376685450-2">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0376685450-2">]</span><span class="p" data-group-id="0376685450-1">)</span><span class="p">.</span></code></pre><p>The second line also says that this function can be called from outside the
│ │ │ │ +function <code class="inline">double</code> in module <code class="inline">tut</code> with argument <code class="inline">10</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="8147626664-1">(</span><span class="mi">10</span><span class="p" data-group-id="8147626664-1">)</span><span class="p">.</span></code></pre><p>The second line says that the module <code class="inline">tut</code> contains a function called <code class="inline">double</code>,
│ │ │ │ +which takes one argument (<code class="inline">X</code> in our example):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1300683008-1">(</span><span class="p" data-group-id="1300683008-2">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1300683008-2">]</span><span class="p" data-group-id="1300683008-1">)</span><span class="p">.</span></code></pre><p>The second line also says that this function can be called from outside the
│ │ │ │  module <code class="inline">tut</code>. More about this later. Again, notice the <code class="inline">.</code> at the end of the
│ │ │ │  line.</p><p>Now for a more complicated example, the factorial of a number. For example, the
│ │ │ │ -factorial of 4 is 4 <em> 3 </em> 2 * 1, which equals 24.</p><p>Enter the following code in a file named <code class="inline">tut1.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7226139051-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="7226139051-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7226139051-2">(</span><span class="p" data-group-id="7226139051-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7226139051-3">]</span><span class="p" data-group-id="7226139051-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +factorial of 4 is 4 <em> 3 </em> 2 * 1, which equals 24.</p><p>Enter the following code in a file named <code class="inline">tut1.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7639227613-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="7639227613-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7639227613-2">(</span><span class="p" data-group-id="7639227613-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7639227613-3">]</span><span class="p" data-group-id="7639227613-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="7226139051-4">(</span><span class="mi">1</span><span class="p" data-group-id="7226139051-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="7639227613-4">(</span><span class="mi">1</span><span class="p" data-group-id="7639227613-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="7226139051-5">(</span><span class="n">N</span><span class="p" data-group-id="7226139051-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="7226139051-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7226139051-6">)</span><span class="p">.</span></code></pre><p>So this is a module, called <code class="inline">tut1</code> that contains a function called <code class="inline">fac&gt;</code>, which
│ │ │ │ -takes one argument, <code class="inline">N</code>.</p><p>The first part says that the factorial of 1 is 1.:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="2198652651-1">(</span><span class="mi">1</span><span class="p" data-group-id="2198652651-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="7639227613-5">(</span><span class="n">N</span><span class="p" data-group-id="7639227613-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="7639227613-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7639227613-6">)</span><span class="p">.</span></code></pre><p>So this is a module, called <code class="inline">tut1</code> that contains a function called <code class="inline">fac&gt;</code>, which
│ │ │ │ +takes one argument, <code class="inline">N</code>.</p><p>The first part says that the factorial of 1 is 1.:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="0369827476-1">(</span><span class="mi">1</span><span class="p" data-group-id="0369827476-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">;</span></code></pre><p>Notice that this part ends with a semicolon <code class="inline">;</code> that indicates that there is
│ │ │ │  more of the function <code class="inline">fac&gt;</code> to come.</p><p>The second part says that the factorial of N is N multiplied by the factorial of
│ │ │ │ -N - 1:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="4175368590-1">(</span><span class="n">N</span><span class="p" data-group-id="4175368590-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="4175368590-2">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4175368590-2">)</span><span class="p">.</span></code></pre><p>Notice that this part ends with a <code class="inline">.</code> saying that there are no more parts of
│ │ │ │ -this function.</p><p>Compile the file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="9605994513-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="9605994513-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9605994513-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="9605994513-2">}</span></code></pre><p>And now calculate the factorial of 4.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">6&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">fac</span><span class="p" data-group-id="0863811708-1">(</span><span class="mi">4</span><span class="p" data-group-id="0863811708-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +N - 1:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="9267393169-1">(</span><span class="n">N</span><span class="p" data-group-id="9267393169-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="9267393169-2">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9267393169-2">)</span><span class="p">.</span></code></pre><p>Notice that this part ends with a <code class="inline">.</code> saying that there are no more parts of
│ │ │ │ +this function.</p><p>Compile the file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="8499220489-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="8499220489-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8499220489-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="8499220489-2">}</span></code></pre><p>And now calculate the factorial of 4.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">6&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">fac</span><span class="p" data-group-id="8814567236-1">(</span><span class="mi">4</span><span class="p" data-group-id="8814567236-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">24</span></code></pre><p>Here the function <code class="inline">fac&gt;</code> in module <code class="inline">tut1</code> is called with argument <code class="inline">4</code>.</p><p>A function can have many arguments. Let us expand the module <code class="inline">tut1</code> with the
│ │ │ │ -function to multiply two numbers:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6928365931-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="6928365931-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6928365931-2">(</span><span class="p" data-group-id="6928365931-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">mult</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6928365931-3">]</span><span class="p" data-group-id="6928365931-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +function to multiply two numbers:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1605638356-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="1605638356-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1605638356-2">(</span><span class="p" data-group-id="1605638356-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">mult</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1605638356-3">]</span><span class="p" data-group-id="1605638356-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="6928365931-4">(</span><span class="mi">1</span><span class="p" data-group-id="6928365931-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="1605638356-4">(</span><span class="mi">1</span><span class="p" data-group-id="1605638356-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="6928365931-5">(</span><span class="n">N</span><span class="p" data-group-id="6928365931-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="6928365931-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6928365931-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="1605638356-5">(</span><span class="n">N</span><span class="p" data-group-id="1605638356-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="1605638356-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1605638356-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">mult</span><span class="p" data-group-id="6928365931-7">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6928365931-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">mult</span><span class="p" data-group-id="1605638356-7">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1605638356-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>Notice that it is also required to expand the <code class="inline">-export</code> line with the
│ │ │ │ -information that there is another function <code class="inline">mult</code> with two arguments.</p><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nf">c</span><span class="p" data-group-id="8772223139-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="8772223139-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8772223139-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="8772223139-2">}</span></code></pre><p>Try out the new function <code class="inline">mult</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">8&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">mult</span><span class="p" data-group-id="5901133207-1">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5901133207-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +information that there is another function <code class="inline">mult</code> with two arguments.</p><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nf">c</span><span class="p" data-group-id="0027251483-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="0027251483-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0027251483-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="0027251483-2">}</span></code></pre><p>Try out the new function <code class="inline">mult</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">8&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">mult</span><span class="p" data-group-id="2687133776-1">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2687133776-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">12</span></code></pre><p>In this example the numbers are integers and the arguments in the functions in
│ │ │ │  the code <code class="inline">N</code>, <code class="inline">X</code>, and <code class="inline">Y</code> are called variables. Variables must start with a
│ │ │ │  capital letter (see <a href="../../../lib/../system/doc/html/expressions.xhtml">Variables</a>). Examples of
│ │ │ │  variables are <code class="inline">Number</code>, <code class="inline">ShoeSize</code>, and <code class="inline">Age</code>.</p><h2 id="atoms" class="section-heading">
│ │ │ │    <a href="#atoms" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Atoms</span>
│ │ │ │  </h2>
│ │ │ │  <p>Atom is another data type in Erlang. Atoms start with a small letter (see
│ │ │ │  <a href="../../../lib/../system/doc/html/data_types.xhtml">Atom</a>), for example, <code class="inline">charles</code>, <code class="inline">centimeter</code>, and
│ │ │ │  <code class="inline">inch</code>. Atoms are simply names, nothing else. They are not like variables, which
│ │ │ │  can have a value.</p><p>Enter the next program in a file named <code class="inline">tut2.erl</code>). It can be useful for
│ │ │ │ -converting from inches to centimeters and conversely:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6740366112-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="6740366112-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6740366112-2">(</span><span class="p" data-group-id="6740366112-3">[</span><span class="ss">convert</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6740366112-3">]</span><span class="p" data-group-id="6740366112-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +converting from inches to centimeters and conversely:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1902683550-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="1902683550-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1902683550-2">(</span><span class="p" data-group-id="1902683550-3">[</span><span class="ss">convert</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1902683550-3">]</span><span class="p" data-group-id="1902683550-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert</span><span class="p" data-group-id="6740366112-4">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="6740366112-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert</span><span class="p" data-group-id="1902683550-4">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="1902683550-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">M</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert</span><span class="p" data-group-id="6740366112-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="6740366112-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p">.</span></code></pre><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nf">c</span><span class="p" data-group-id="6866821443-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="6866821443-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6866821443-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut2</span><span class="p" data-group-id="6866821443-2">}</span></code></pre><p>Test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">10&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="7668774473-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="7668774473-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">convert</span><span class="p" data-group-id="1902683550-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="1902683550-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p">.</span></code></pre><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nf">c</span><span class="p" data-group-id="8398513231-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="8398513231-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8398513231-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut2</span><span class="p" data-group-id="8398513231-2">}</span></code></pre><p>Test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">10&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="8745737393-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="8745737393-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">1.1811023622047243</span><span class="gp unselectable">
│ │ │ │ -11&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="7668774473-2">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="7668774473-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +11&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="8745737393-2">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="8745737393-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">17.78</span></code></pre><p>Notice the introduction of decimals (floating point numbers) without any
│ │ │ │  explanation. Hopefully you can cope with that.</p><p>Let us see what happens if something other than <code class="inline">centimeter</code> or <code class="inline">inch</code> is
│ │ │ │ -entered in the <code class="inline">convert</code> function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">12&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="8868108821-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">miles</span><span class="p" data-group-id="8868108821-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +entered in the <code class="inline">convert</code> function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">12&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="0179042544-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">miles</span><span class="p" data-group-id="0179042544-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no function clause matching tut2:convert(3,miles) (tut2.erl, line 4)</span></code></pre><p>The two parts of the <code class="inline">convert</code> function are called its clauses. As shown,
│ │ │ │  <code class="inline">miles</code> is not part of either of the clauses. The Erlang system cannot <em>match</em>
│ │ │ │  either of the clauses so an error message <code class="inline">function_clause</code> is returned. The
│ │ │ │  shell formats the error message nicely, but the error tuple is saved in the
│ │ │ │ -shell's history list and can be output by the shell command <code class="inline">v/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">13&gt; </span><span class="nf">v</span><span class="p" data-group-id="4405967490-1">(</span><span class="mi">12</span><span class="p" data-group-id="4405967490-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4405967490-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="4405967490-3">{</span><span class="ss">function_clause</span><span class="p">,</span><span class="p" data-group-id="4405967490-4">[</span><span class="p" data-group-id="4405967490-5">{</span><span class="ss">tut2</span><span class="p">,</span><span class="ss">convert</span><span class="p">,</span><span class="w">
│ │ │ │ -                                </span><span class="p" data-group-id="4405967490-6">[</span><span class="mi">3</span><span class="p">,</span><span class="ss">miles</span><span class="p" data-group-id="4405967490-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ -                                </span><span class="p" data-group-id="4405967490-7">[</span><span class="p" data-group-id="4405967490-8">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;tut2.erl&quot;</span><span class="p" data-group-id="4405967490-8">}</span><span class="p">,</span><span class="p" data-group-id="4405967490-9">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4405967490-9">}</span><span class="p" data-group-id="4405967490-7">]</span><span class="p" data-group-id="4405967490-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="p" data-group-id="4405967490-10">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="p" data-group-id="4405967490-11">[</span><span class="p" data-group-id="4405967490-12">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="4405967490-12">}</span><span class="p">,</span><span class="p" data-group-id="4405967490-13">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">677</span><span class="p" data-group-id="4405967490-13">}</span><span class="p" data-group-id="4405967490-11">]</span><span class="p" data-group-id="4405967490-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="p" data-group-id="4405967490-14">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="4405967490-15">[</span><span class="p" data-group-id="4405967490-16">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="4405967490-16">}</span><span class="p">,</span><span class="p" data-group-id="4405967490-17">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">687</span><span class="p" data-group-id="4405967490-17">}</span><span class="p" data-group-id="4405967490-15">]</span><span class="p" data-group-id="4405967490-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="p" data-group-id="4405967490-18">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="4405967490-19">[</span><span class="p" data-group-id="4405967490-20">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="4405967490-20">}</span><span class="p">,</span><span class="p" data-group-id="4405967490-21">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">642</span><span class="p" data-group-id="4405967490-21">}</span><span class="p" data-group-id="4405967490-19">]</span><span class="p" data-group-id="4405967490-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="p" data-group-id="4405967490-22">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_loop</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                 </span><span class="p" data-group-id="4405967490-23">[</span><span class="p" data-group-id="4405967490-24">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="4405967490-24">}</span><span class="p">,</span><span class="p" data-group-id="4405967490-25">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">627</span><span class="p" data-group-id="4405967490-25">}</span><span class="p" data-group-id="4405967490-23">]</span><span class="p" data-group-id="4405967490-22">}</span><span class="p" data-group-id="4405967490-4">]</span><span class="p" data-group-id="4405967490-3">}</span><span class="p" data-group-id="4405967490-2">}</span></code></pre><h2 id="tuples" class="section-heading">
│ │ │ │ +shell's history list and can be output by the shell command <code class="inline">v/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">13&gt; </span><span class="nf">v</span><span class="p" data-group-id="8767059198-1">(</span><span class="mi">12</span><span class="p" data-group-id="8767059198-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8767059198-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="8767059198-3">{</span><span class="ss">function_clause</span><span class="p">,</span><span class="p" data-group-id="8767059198-4">[</span><span class="p" data-group-id="8767059198-5">{</span><span class="ss">tut2</span><span class="p">,</span><span class="ss">convert</span><span class="p">,</span><span class="w">
│ │ │ │ +                                </span><span class="p" data-group-id="8767059198-6">[</span><span class="mi">3</span><span class="p">,</span><span class="ss">miles</span><span class="p" data-group-id="8767059198-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                                </span><span class="p" data-group-id="8767059198-7">[</span><span class="p" data-group-id="8767059198-8">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;tut2.erl&quot;</span><span class="p" data-group-id="8767059198-8">}</span><span class="p">,</span><span class="p" data-group-id="8767059198-9">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8767059198-9">}</span><span class="p" data-group-id="8767059198-7">]</span><span class="p" data-group-id="8767059198-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="p" data-group-id="8767059198-10">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="p" data-group-id="8767059198-11">[</span><span class="p" data-group-id="8767059198-12">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="8767059198-12">}</span><span class="p">,</span><span class="p" data-group-id="8767059198-13">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">677</span><span class="p" data-group-id="8767059198-13">}</span><span class="p" data-group-id="8767059198-11">]</span><span class="p" data-group-id="8767059198-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="p" data-group-id="8767059198-14">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="8767059198-15">[</span><span class="p" data-group-id="8767059198-16">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="8767059198-16">}</span><span class="p">,</span><span class="p" data-group-id="8767059198-17">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">687</span><span class="p" data-group-id="8767059198-17">}</span><span class="p" data-group-id="8767059198-15">]</span><span class="p" data-group-id="8767059198-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="p" data-group-id="8767059198-18">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="8767059198-19">[</span><span class="p" data-group-id="8767059198-20">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="8767059198-20">}</span><span class="p">,</span><span class="p" data-group-id="8767059198-21">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">642</span><span class="p" data-group-id="8767059198-21">}</span><span class="p" data-group-id="8767059198-19">]</span><span class="p" data-group-id="8767059198-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="p" data-group-id="8767059198-22">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_loop</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                 </span><span class="p" data-group-id="8767059198-23">[</span><span class="p" data-group-id="8767059198-24">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="8767059198-24">}</span><span class="p">,</span><span class="p" data-group-id="8767059198-25">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">627</span><span class="p" data-group-id="8767059198-25">}</span><span class="p" data-group-id="8767059198-23">]</span><span class="p" data-group-id="8767059198-22">}</span><span class="p" data-group-id="8767059198-4">]</span><span class="p" data-group-id="8767059198-3">}</span><span class="p" data-group-id="8767059198-2">}</span></code></pre><h2 id="tuples" class="section-heading">
│ │ │ │    <a href="#tuples" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Tuples</span>
│ │ │ │  </h2>
│ │ │ │ -<p>Now the <code class="inline">tut2</code> program is hardly good programming style. Consider:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="7505152458-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="7505152458-1">)</span><span class="p">.</span></code></pre><p>Does this mean that 3 is in inches? Or does it mean that 3 is in centimeters and
│ │ │ │ +<p>Now the <code class="inline">tut2</code> program is hardly good programming style. Consider:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="0664377103-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="0664377103-1">)</span><span class="p">.</span></code></pre><p>Does this mean that 3 is in inches? Or does it mean that 3 is in centimeters and
│ │ │ │  is to be converted to inches? Erlang has a way to group things together to make
│ │ │ │  things more understandable. These are called <em>tuples</em> and are surrounded by
│ │ │ │  curly brackets, <code class="inline">{</code> and <code class="inline">}</code>.</p><p>So, <code class="inline">{inch,3}</code> denotes 3 inches and <code class="inline">{centimeter,5}</code> denotes 5 centimeters. Now
│ │ │ │  let us write a new program that converts centimeters to inches and conversely.
│ │ │ │ -Enter the following code in a file called <code class="inline">tut3.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1840925644-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="1840925644-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1840925644-2">(</span><span class="p" data-group-id="1840925644-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1840925644-3">]</span><span class="p" data-group-id="1840925644-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +Enter the following code in a file called <code class="inline">tut3.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6278741193-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="6278741193-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6278741193-2">(</span><span class="p" data-group-id="6278741193-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6278741193-3">]</span><span class="p" data-group-id="6278741193-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="1840925644-4">(</span><span class="p" data-group-id="1840925644-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1840925644-5">}</span><span class="p" data-group-id="1840925644-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1840925644-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="1840925644-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="1840925644-7">(</span><span class="p" data-group-id="1840925644-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1840925644-8">}</span><span class="p" data-group-id="1840925644-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1840925644-9">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="1840925644-9">}</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">14&gt; </span><span class="nf">c</span><span class="p" data-group-id="0644570124-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="0644570124-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0644570124-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut3</span><span class="p" data-group-id="0644570124-2">}</span><span class="gp unselectable">
│ │ │ │ -15&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="0644570124-3">(</span><span class="p" data-group-id="0644570124-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="0644570124-4">}</span><span class="p" data-group-id="0644570124-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0644570124-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">12.7</span><span class="p" data-group-id="0644570124-5">}</span><span class="gp unselectable">
│ │ │ │ -16&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="0644570124-6">(</span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="0644570124-7">(</span><span class="p" data-group-id="0644570124-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="0644570124-8">}</span><span class="p" data-group-id="0644570124-7">)</span><span class="p" data-group-id="0644570124-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0644570124-9">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">5.0</span><span class="p" data-group-id="0644570124-9">}</span></code></pre><p>Notice on line 16 that 5 inches is converted to centimeters and back again and
│ │ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="6278741193-4">(</span><span class="p" data-group-id="6278741193-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6278741193-5">}</span><span class="p" data-group-id="6278741193-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6278741193-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="6278741193-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="6278741193-7">(</span><span class="p" data-group-id="6278741193-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6278741193-8">}</span><span class="p" data-group-id="6278741193-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6278741193-9">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="6278741193-9">}</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">14&gt; </span><span class="nf">c</span><span class="p" data-group-id="2751264058-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="2751264058-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2751264058-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut3</span><span class="p" data-group-id="2751264058-2">}</span><span class="gp unselectable">
│ │ │ │ +15&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="2751264058-3">(</span><span class="p" data-group-id="2751264058-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="2751264058-4">}</span><span class="p" data-group-id="2751264058-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2751264058-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">12.7</span><span class="p" data-group-id="2751264058-5">}</span><span class="gp unselectable">
│ │ │ │ +16&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="2751264058-6">(</span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="2751264058-7">(</span><span class="p" data-group-id="2751264058-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="2751264058-8">}</span><span class="p" data-group-id="2751264058-7">)</span><span class="p" data-group-id="2751264058-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2751264058-9">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">5.0</span><span class="p" data-group-id="2751264058-9">}</span></code></pre><p>Notice on line 16 that 5 inches is converted to centimeters and back again and
│ │ │ │  reassuringly get back to the original value. That is, the argument to a function
│ │ │ │  can be the result of another function. Consider how line 16 (above) works. The
│ │ │ │  argument given to the function <code class="inline">{inch,5}</code> is first matched against the first
│ │ │ │  head clause of <code class="inline">convert_length</code>, that is, <code class="inline">convert_length({centimeter,X})</code>. It
│ │ │ │  can be seen that <code class="inline">{centimeter,X}</code> does not match <code class="inline">{inch,5}</code> (the head is the bit
│ │ │ │  before the <code class="inline">-&gt;</code>). This having failed, let us try the head of the next clause
│ │ │ │  that is, <code class="inline">convert_length({inch,Y})</code>. This matches, and <code class="inline">Y</code> gets the value 5.</p><p>Tuples can have more than two parts, in fact as many parts as you want, and
│ │ │ │  contain any valid Erlang <em>term</em>. For example, to represent the temperature of
│ │ │ │ -various cities of the world:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5624295862-1">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5624295862-2">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="5624295862-2">}</span><span class="p" data-group-id="5624295862-1">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5624295862-3">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5624295862-4">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="5624295862-4">}</span><span class="p" data-group-id="5624295862-3">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5624295862-5">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5624295862-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="5624295862-6">}</span><span class="p" data-group-id="5624295862-5">}</span></code></pre><p>Tuples have a fixed number of items in them. Each item in a tuple is called an
│ │ │ │ +various cities of the world:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1645227190-1">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1645227190-2">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="1645227190-2">}</span><span class="p" data-group-id="1645227190-1">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1645227190-3">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1645227190-4">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="1645227190-4">}</span><span class="p" data-group-id="1645227190-3">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1645227190-5">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1645227190-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="1645227190-6">}</span><span class="p" data-group-id="1645227190-5">}</span></code></pre><p>Tuples have a fixed number of items in them. Each item in a tuple is called an
│ │ │ │  <em>element</em>. In the tuple <code class="inline">{moscow,{c,-10}}</code>, element 1 is <code class="inline">moscow</code> and element 2
│ │ │ │  is <code class="inline">{c,-10}</code>. Here <code class="inline">c</code> represents Celsius and <code class="inline">f</code> Fahrenheit.</p><h2 id="lists" class="section-heading">
│ │ │ │    <a href="#lists" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Lists</span>
│ │ │ │  </h2>
│ │ │ │  <p>Whereas tuples group things together, it is also needed to represent lists of
│ │ │ │  things. Lists in Erlang are surrounded by square brackets, <code class="inline">[</code> and <code class="inline">]</code>. For
│ │ │ │ -example, a list of the temperatures of various cities in the world can be:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8183538384-1">[</span><span class="p" data-group-id="8183538384-2">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8183538384-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8183538384-3">}</span><span class="p" data-group-id="8183538384-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8183538384-4">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8183538384-5">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="8183538384-5">}</span><span class="p" data-group-id="8183538384-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8183538384-6">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8183538384-7">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8183538384-7">}</span><span class="p" data-group-id="8183538384-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8183538384-8">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8183538384-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8183538384-9">}</span><span class="p" data-group-id="8183538384-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8183538384-10">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8183538384-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="8183538384-11">}</span><span class="p" data-group-id="8183538384-10">}</span><span class="p" data-group-id="8183538384-1">]</span></code></pre><p>Notice that this list was so long that it did not fit on one line. This does not
│ │ │ │ +example, a list of the temperatures of various cities in the world can be:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4117643267-1">[</span><span class="p" data-group-id="4117643267-2">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4117643267-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4117643267-3">}</span><span class="p" data-group-id="4117643267-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4117643267-4">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4117643267-5">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4117643267-5">}</span><span class="p" data-group-id="4117643267-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4117643267-6">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4117643267-7">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4117643267-7">}</span><span class="p" data-group-id="4117643267-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4117643267-8">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4117643267-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4117643267-9">}</span><span class="p" data-group-id="4117643267-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4117643267-10">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4117643267-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4117643267-11">}</span><span class="p" data-group-id="4117643267-10">}</span><span class="p" data-group-id="4117643267-1">]</span></code></pre><p>Notice that this list was so long that it did not fit on one line. This does not
│ │ │ │  matter, Erlang allows line breaks at all &quot;sensible places&quot; but not, for example,
│ │ │ │  in the middle of atoms, integers, and others.</p><p>A useful way of looking at parts of lists, is by using <code class="inline">|</code>. This is best
│ │ │ │ -explained by an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">17&gt; </span><span class="p" data-group-id="5500810359-1">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="n">TheRest</span><span class="p" data-group-id="5500810359-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5500810359-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5500810359-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5500810359-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5500810359-3">]</span><span class="gp unselectable">
│ │ │ │ +explained by an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">17&gt; </span><span class="p" data-group-id="5933083103-1">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="n">TheRest</span><span class="p" data-group-id="5933083103-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5933083103-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5933083103-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5933083103-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5933083103-3">]</span><span class="gp unselectable">
│ │ │ │  18&gt; </span><span class="n">First</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="gp unselectable">
│ │ │ │  19&gt; </span><span class="n">TheRest</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5500810359-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5500810359-4">]</span></code></pre><p>To separate the first elements of the list from the rest of the list, <code class="inline">|</code> is
│ │ │ │ -used. <code class="inline">First</code> has got value <code class="inline">1</code> and <code class="inline">TheRest</code> has got the value <code class="inline">[2,3,4,5]</code>.</p><p>Another example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">20&gt; </span><span class="p" data-group-id="0104725731-1">[</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">R</span><span class="p" data-group-id="0104725731-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0104725731-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="0104725731-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0104725731-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="0104725731-3">]</span><span class="gp unselectable">
│ │ │ │ +</span><span class="p" data-group-id="5933083103-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5933083103-4">]</span></code></pre><p>To separate the first elements of the list from the rest of the list, <code class="inline">|</code> is
│ │ │ │ +used. <code class="inline">First</code> has got value <code class="inline">1</code> and <code class="inline">TheRest</code> has got the value <code class="inline">[2,3,4,5]</code>.</p><p>Another example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">20&gt; </span><span class="p" data-group-id="3622434969-1">[</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">R</span><span class="p" data-group-id="3622434969-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3622434969-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3622434969-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3622434969-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3622434969-3">]</span><span class="gp unselectable">
│ │ │ │  21&gt; </span><span class="n">E1</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="gp unselectable">
│ │ │ │  22&gt; </span><span class="n">E2</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">2</span><span class="gp unselectable">
│ │ │ │  23&gt; </span><span class="n">R</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0104725731-4">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="0104725731-4">]</span></code></pre><p>Here you see the use of <code class="inline">|</code> to get the first two elements from the list. If you
│ │ │ │ +</span><span class="p" data-group-id="3622434969-4">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3622434969-4">]</span></code></pre><p>Here you see the use of <code class="inline">|</code> to get the first two elements from the list. If you
│ │ │ │  try to get more elements from the list than there are elements in the list, an
│ │ │ │  error is returned. Notice also the special case of the list with no elements,
│ │ │ │ -<code class="inline">[]</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">24&gt; </span><span class="p" data-group-id="3734170573-1">[</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="3734170573-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3734170573-2">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3734170573-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3734170573-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3734170573-3">]</span><span class="gp unselectable">
│ │ │ │ +<code class="inline">[]</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">24&gt; </span><span class="p" data-group-id="2200632336-1">[</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="2200632336-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2200632336-2">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2200632336-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2200632336-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2200632336-3">]</span><span class="gp unselectable">
│ │ │ │  25&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="gp unselectable">
│ │ │ │  26&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">2</span><span class="gp unselectable">
│ │ │ │  27&gt; </span><span class="n">C</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3734170573-4">[</span><span class="p" data-group-id="3734170573-4">]</span></code></pre><p>In the previous examples, new variable names are used, instead of reusing the
│ │ │ │ +</span><span class="p" data-group-id="2200632336-4">[</span><span class="p" data-group-id="2200632336-4">]</span></code></pre><p>In the previous examples, new variable names are used, instead of reusing the
│ │ │ │  old ones: <code class="inline">First</code>, <code class="inline">TheRest</code>, <code class="inline">E1</code>, <code class="inline">E2</code>, <code class="inline">R</code>, <code class="inline">A</code>, <code class="inline">B</code>, and <code class="inline">C</code>. The reason for
│ │ │ │  this is that a variable can only be given a value once in its context (scope).
│ │ │ │  More about this later.</p><p>The following example shows how to find the length of a list. Enter the
│ │ │ │ -following code in a file named <code class="inline">tut4.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4450039285-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="4450039285-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +following code in a file named <code class="inline">tut4.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8636242978-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="8636242978-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4450039285-2">(</span><span class="p" data-group-id="4450039285-3">[</span><span class="ss">list_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4450039285-3">]</span><span class="p" data-group-id="4450039285-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8636242978-2">(</span><span class="p" data-group-id="8636242978-3">[</span><span class="ss">list_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8636242978-3">]</span><span class="p" data-group-id="8636242978-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">list_length</span><span class="p" data-group-id="4450039285-4">(</span><span class="p" data-group-id="4450039285-5">[</span><span class="p" data-group-id="4450039285-5">]</span><span class="p" data-group-id="4450039285-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">list_length</span><span class="p" data-group-id="8636242978-4">(</span><span class="p" data-group-id="8636242978-5">[</span><span class="p" data-group-id="8636242978-5">]</span><span class="p" data-group-id="8636242978-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">list_length</span><span class="p" data-group-id="4450039285-6">(</span><span class="p" data-group-id="4450039285-7">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4450039285-7">]</span><span class="p" data-group-id="4450039285-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="4450039285-8">(</span><span class="n">Rest</span><span class="p" data-group-id="4450039285-8">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">28&gt; </span><span class="nf">c</span><span class="p" data-group-id="5887858083-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="5887858083-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5887858083-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut4</span><span class="p" data-group-id="5887858083-2">}</span><span class="gp unselectable">
│ │ │ │ -29&gt; </span><span class="nc">tut4</span><span class="p">:</span><span class="nf">list_length</span><span class="p" data-group-id="5887858083-3">(</span><span class="p" data-group-id="5887858083-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="5887858083-4">]</span><span class="p" data-group-id="5887858083-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="mi">7</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="9825301201-1">(</span><span class="p" data-group-id="9825301201-2">[</span><span class="p" data-group-id="9825301201-2">]</span><span class="p" data-group-id="9825301201-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="mi">0</span><span class="p">;</span></code></pre><p>The length of an empty list is obviously 0.</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="5100204955-1">(</span><span class="p" data-group-id="5100204955-2">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="5100204955-2">]</span><span class="p" data-group-id="5100204955-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="5100204955-3">(</span><span class="n">Rest</span><span class="p" data-group-id="5100204955-3">)</span><span class="p">.</span></code></pre><p>The length of a list with the first element <code class="inline">First</code> and the remaining elements
│ │ │ │ +</span><span class="nf">list_length</span><span class="p" data-group-id="8636242978-6">(</span><span class="p" data-group-id="8636242978-7">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8636242978-7">]</span><span class="p" data-group-id="8636242978-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="8636242978-8">(</span><span class="n">Rest</span><span class="p" data-group-id="8636242978-8">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">28&gt; </span><span class="nf">c</span><span class="p" data-group-id="7316246254-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="7316246254-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7316246254-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut4</span><span class="p" data-group-id="7316246254-2">}</span><span class="gp unselectable">
│ │ │ │ +29&gt; </span><span class="nc">tut4</span><span class="p">:</span><span class="nf">list_length</span><span class="p" data-group-id="7316246254-3">(</span><span class="p" data-group-id="7316246254-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7316246254-4">]</span><span class="p" data-group-id="7316246254-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="mi">7</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="8639885244-1">(</span><span class="p" data-group-id="8639885244-2">[</span><span class="p" data-group-id="8639885244-2">]</span><span class="p" data-group-id="8639885244-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="mi">0</span><span class="p">;</span></code></pre><p>The length of an empty list is obviously 0.</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="9544298632-1">(</span><span class="p" data-group-id="9544298632-2">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9544298632-2">]</span><span class="p" data-group-id="9544298632-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="9544298632-3">(</span><span class="n">Rest</span><span class="p" data-group-id="9544298632-3">)</span><span class="p">.</span></code></pre><p>The length of a list with the first element <code class="inline">First</code> and the remaining elements
│ │ │ │  <code class="inline">Rest</code> is 1 + the length of <code class="inline">Rest</code>.</p><p>(Advanced readers only: This is not tail recursive, there is a better way to
│ │ │ │  write this function.)</p><p>In general, tuples are used where &quot;records&quot; or &quot;structs&quot; are used in other
│ │ │ │  languages. Also, lists are used when representing things with varying sizes,
│ │ │ │  that is, where linked lists are used in other languages.</p><p>Erlang does not have a string data type. Instead, strings can be represented by
│ │ │ │  lists of Unicode characters. This implies for example that the list <code class="inline">[97,98,99]</code>
│ │ │ │  is equivalent to <code class="inline">&quot;abc&quot;</code>. The Erlang shell is &quot;clever&quot; and guesses what list you
│ │ │ │ -mean and outputs it in what it thinks is the most appropriate form, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">30&gt; </span><span class="p" data-group-id="4464650737-1">[</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="4464650737-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +mean and outputs it in what it thinks is the most appropriate form, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">30&gt; </span><span class="p" data-group-id="5609489630-1">[</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="5609489630-1">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;abc&quot;</span></code></pre><h2 id="maps" class="section-heading">
│ │ │ │    <a href="#maps" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Maps</span>
│ │ │ │  </h2>
│ │ │ │  <p>Maps are a set of key to value associations. These associations are encapsulated
│ │ │ │ -with <code class="inline">#{</code> and <code class="inline">}</code>. To create an association from <code class="inline">&quot;key&quot;</code> to value <code class="inline">42</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="9580914006-1">#{</span><span class="w"> </span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p" data-group-id="9580914006-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9580914006-2">#{</span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="9580914006-2">}</span></code></pre><p>Let us jump straight into the deep end with an example using some interesting
│ │ │ │ +with <code class="inline">#{</code> and <code class="inline">}</code>. To create an association from <code class="inline">&quot;key&quot;</code> to value <code class="inline">42</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="0675200005-1">#{</span><span class="w"> </span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p" data-group-id="0675200005-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0675200005-2">#{</span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="0675200005-2">}</span></code></pre><p>Let us jump straight into the deep end with an example using some interesting
│ │ │ │  features.</p><p>The following example shows how to calculate alpha blending using maps to
│ │ │ │ -reference color and alpha channels. Enter the code in a file named <code class="inline">color.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5309459283-1">(</span><span class="ss">color</span><span class="p" data-group-id="5309459283-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +reference color and alpha channels. Enter the code in a file named <code class="inline">color.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0782791506-1">(</span><span class="ss">color</span><span class="p" data-group-id="0782791506-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5309459283-2">(</span><span class="p" data-group-id="5309459283-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="ss">blend</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5309459283-3">]</span><span class="p" data-group-id="5309459283-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0782791506-2">(</span><span class="p" data-group-id="0782791506-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="ss">blend</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0782791506-3">]</span><span class="p" data-group-id="0782791506-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5309459283-4">(</span><span class="nf">is_channel</span><span class="p" data-group-id="5309459283-5">(</span><span class="n">V</span><span class="p" data-group-id="5309459283-5">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5309459283-6">(</span><span class="nf">is_float</span><span class="p" data-group-id="5309459283-7">(</span><span class="n">V</span><span class="p" data-group-id="5309459283-7">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="5309459283-6">)</span><span class="p" data-group-id="5309459283-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0782791506-4">(</span><span class="nf">is_channel</span><span class="p" data-group-id="0782791506-5">(</span><span class="n">V</span><span class="p" data-group-id="0782791506-5">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0782791506-6">(</span><span class="nf">is_float</span><span class="p" data-group-id="0782791506-7">(</span><span class="n">V</span><span class="p" data-group-id="0782791506-7">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="0782791506-6">)</span><span class="p" data-group-id="0782791506-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">new</span><span class="p" data-group-id="5309459283-8">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="5309459283-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="5309459283-9">(</span><span class="n">R</span><span class="p" data-group-id="5309459283-9">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="5309459283-10">(</span><span class="n">G</span><span class="p" data-group-id="5309459283-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="5309459283-11">(</span><span class="n">B</span><span class="p" data-group-id="5309459283-11">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="5309459283-12">(</span><span class="n">A</span><span class="p" data-group-id="5309459283-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5309459283-13">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="5309459283-13">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="5309459283-14">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="5309459283-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">blend</span><span class="p" data-group-id="5309459283-15">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="nf">alpha</span><span class="p" data-group-id="5309459283-16">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="5309459283-16">)</span><span class="p" data-group-id="5309459283-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="5309459283-17">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="5309459283-17">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="5309459283-18">#{</span><span class="w">
│ │ │ │ -        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="5309459283-19">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="5309459283-19">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="5309459283-20">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="5309459283-20">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="5309459283-21">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="5309459283-21">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">new</span><span class="p" data-group-id="0782791506-8">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="0782791506-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0782791506-9">(</span><span class="n">R</span><span class="p" data-group-id="0782791506-9">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0782791506-10">(</span><span class="n">G</span><span class="p" data-group-id="0782791506-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0782791506-11">(</span><span class="n">B</span><span class="p" data-group-id="0782791506-11">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0782791506-12">(</span><span class="n">A</span><span class="p" data-group-id="0782791506-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0782791506-13">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="0782791506-13">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="0782791506-14">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0782791506-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">blend</span><span class="p" data-group-id="0782791506-15">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="nf">alpha</span><span class="p" data-group-id="0782791506-16">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0782791506-16">)</span><span class="p" data-group-id="0782791506-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="0782791506-17">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="0782791506-17">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="0782791506-18">#{</span><span class="w">
│ │ │ │ +        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="0782791506-19">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0782791506-19">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="0782791506-20">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0782791506-20">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="0782791506-21">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0782791506-21">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Alpha</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5309459283-18">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="5309459283-22">(</span><span class="p">_</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5309459283-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="5309459283-23">#{</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0782791506-18">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="0782791506-22">(</span><span class="p">_</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0782791506-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="0782791506-23">#{</span><span class="w">
│ │ │ │          </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5309459283-23">}</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0782791506-23">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alpha</span><span class="p" data-group-id="5309459283-24">(</span><span class="p" data-group-id="5309459283-25">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="5309459283-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5309459283-26">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="5309459283-26">}</span><span class="p" data-group-id="5309459283-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="5309459283-27">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="5309459283-27">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">alpha</span><span class="p" data-group-id="0782791506-24">(</span><span class="p" data-group-id="0782791506-25">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0782791506-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0782791506-26">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0782791506-26">}</span><span class="p" data-group-id="0782791506-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0782791506-27">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0782791506-27">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">red</span><span class="p" data-group-id="5309459283-28">(</span><span class="p" data-group-id="5309459283-29">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="5309459283-29">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5309459283-30">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="5309459283-30">}</span><span class="p" data-group-id="5309459283-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="5309459283-31">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="5309459283-31">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">green</span><span class="p" data-group-id="5309459283-32">(</span><span class="p" data-group-id="5309459283-33">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="5309459283-33">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5309459283-34">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="5309459283-34">}</span><span class="p" data-group-id="5309459283-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="5309459283-35">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="5309459283-35">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">blue</span><span class="p" data-group-id="5309459283-36">(</span><span class="p" data-group-id="5309459283-37">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="5309459283-37">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5309459283-38">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="5309459283-38">}</span><span class="p" data-group-id="5309459283-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="5309459283-39">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="5309459283-39">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">c</span><span class="p" data-group-id="8648636753-1">(</span><span class="ss">color</span><span class="p" data-group-id="8648636753-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8648636753-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">color</span><span class="p" data-group-id="8648636753-2">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="n">C1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="8648636753-3">(</span><span class="mf">0.3</span><span class="p">,</span><span class="mf">0.4</span><span class="p">,</span><span class="mf">0.5</span><span class="p">,</span><span class="mf">1.0</span><span class="p" data-group-id="8648636753-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8648636753-4">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="8648636753-4">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="n">C2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="8648636753-5">(</span><span class="mf">1.0</span><span class="p">,</span><span class="mf">0.8</span><span class="p">,</span><span class="mf">0.1</span><span class="p">,</span><span class="mf">0.3</span><span class="p" data-group-id="8648636753-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8648636753-6">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.1</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.8</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="8648636753-6">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="8648636753-7">(</span><span class="n">C1</span><span class="p">,</span><span class="n">C2</span><span class="p" data-group-id="8648636753-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8648636753-8">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="8648636753-8">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="8648636753-9">(</span><span class="n">C2</span><span class="p">,</span><span class="n">C1</span><span class="p" data-group-id="8648636753-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8648636753-10">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.38</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.52</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.51</span><span class="p" data-group-id="8648636753-10">}</span></code></pre><p>This example warrants some explanation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1618765818-1">(</span><span class="nf">is_channel</span><span class="p" data-group-id="1618765818-2">(</span><span class="n">V</span><span class="p" data-group-id="1618765818-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1618765818-3">(</span><span class="nf">is_float</span><span class="p" data-group-id="1618765818-4">(</span><span class="n">V</span><span class="p" data-group-id="1618765818-4">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="1618765818-3">)</span><span class="p" data-group-id="1618765818-1">)</span><span class="p">.</span></code></pre><p>First a macro <code class="inline">is_channel</code> is defined to help with the guard tests. This is only
│ │ │ │ +</span><span class="nf">red</span><span class="p" data-group-id="0782791506-28">(</span><span class="p" data-group-id="0782791506-29">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0782791506-29">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0782791506-30">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0782791506-30">}</span><span class="p" data-group-id="0782791506-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0782791506-31">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0782791506-31">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">green</span><span class="p" data-group-id="0782791506-32">(</span><span class="p" data-group-id="0782791506-33">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0782791506-33">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0782791506-34">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0782791506-34">}</span><span class="p" data-group-id="0782791506-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0782791506-35">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0782791506-35">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">blue</span><span class="p" data-group-id="0782791506-36">(</span><span class="p" data-group-id="0782791506-37">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0782791506-37">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0782791506-38">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0782791506-38">}</span><span class="p" data-group-id="0782791506-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0782791506-39">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0782791506-39">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">c</span><span class="p" data-group-id="1102272025-1">(</span><span class="ss">color</span><span class="p" data-group-id="1102272025-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1102272025-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">color</span><span class="p" data-group-id="1102272025-2">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="n">C1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="1102272025-3">(</span><span class="mf">0.3</span><span class="p">,</span><span class="mf">0.4</span><span class="p">,</span><span class="mf">0.5</span><span class="p">,</span><span class="mf">1.0</span><span class="p" data-group-id="1102272025-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1102272025-4">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="1102272025-4">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="n">C2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="1102272025-5">(</span><span class="mf">1.0</span><span class="p">,</span><span class="mf">0.8</span><span class="p">,</span><span class="mf">0.1</span><span class="p">,</span><span class="mf">0.3</span><span class="p" data-group-id="1102272025-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1102272025-6">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.1</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.8</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="1102272025-6">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="1102272025-7">(</span><span class="n">C1</span><span class="p">,</span><span class="n">C2</span><span class="p" data-group-id="1102272025-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1102272025-8">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="1102272025-8">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="1102272025-9">(</span><span class="n">C2</span><span class="p">,</span><span class="n">C1</span><span class="p" data-group-id="1102272025-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1102272025-10">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.38</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.52</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.51</span><span class="p" data-group-id="1102272025-10">}</span></code></pre><p>This example warrants some explanation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3605059290-1">(</span><span class="nf">is_channel</span><span class="p" data-group-id="3605059290-2">(</span><span class="n">V</span><span class="p" data-group-id="3605059290-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3605059290-3">(</span><span class="nf">is_float</span><span class="p" data-group-id="3605059290-4">(</span><span class="n">V</span><span class="p" data-group-id="3605059290-4">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="3605059290-3">)</span><span class="p" data-group-id="3605059290-1">)</span><span class="p">.</span></code></pre><p>First a macro <code class="inline">is_channel</code> is defined to help with the guard tests. This is only
│ │ │ │  here for convenience and to reduce syntax cluttering. For more information about
│ │ │ │ -macros, see <a href="../../../lib/../system/doc/html/macros.xhtml">The Preprocessor</a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="9785735120-1">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="9785735120-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="9785735120-2">(</span><span class="n">R</span><span class="p" data-group-id="9785735120-2">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="9785735120-3">(</span><span class="n">G</span><span class="p" data-group-id="9785735120-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="9785735120-4">(</span><span class="n">B</span><span class="p" data-group-id="9785735120-4">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="9785735120-5">(</span><span class="n">A</span><span class="p" data-group-id="9785735120-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9785735120-6">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="9785735120-6">}</span><span class="p">.</span></code></pre><p>The function <code class="inline">new/4</code> creates a new map term and lets the keys <code class="inline">red</code>, <code class="inline">green</code>,
│ │ │ │ +macros, see <a href="../../../lib/../system/doc/html/macros.xhtml">The Preprocessor</a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="6654401422-1">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="6654401422-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="6654401422-2">(</span><span class="n">R</span><span class="p" data-group-id="6654401422-2">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="6654401422-3">(</span><span class="n">G</span><span class="p" data-group-id="6654401422-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="6654401422-4">(</span><span class="n">B</span><span class="p" data-group-id="6654401422-4">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="6654401422-5">(</span><span class="n">A</span><span class="p" data-group-id="6654401422-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6654401422-6">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="6654401422-6">}</span><span class="p">.</span></code></pre><p>The function <code class="inline">new/4</code> creates a new map term and lets the keys <code class="inline">red</code>, <code class="inline">green</code>,
│ │ │ │  <code class="inline">blue</code>, and <code class="inline">alpha</code> be associated with an initial value. In this case, only
│ │ │ │  float values between and including 0.0 and 1.0 are allowed, as ensured by the
│ │ │ │  <code class="inline">?is_channel/1</code> macro for each argument. Only the <code class="inline">=&gt;</code> operator is allowed when
│ │ │ │  creating a new map.</p><p>By calling <code class="inline">blend/2</code> on any color term created by <code class="inline">new/4</code>, the resulting color
│ │ │ │ -can be calculated as determined by the two map terms.</p><p>The first thing <code class="inline">blend/2</code> does is to calculate the resulting alpha channel:</p><pre><code class="makeup erlang" translate="no"><span class="nf">alpha</span><span class="p" data-group-id="0908857772-1">(</span><span class="p" data-group-id="0908857772-2">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0908857772-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0908857772-3">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0908857772-3">}</span><span class="p" data-group-id="0908857772-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0908857772-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0908857772-4">)</span><span class="p">.</span></code></pre><p>The value associated with key <code class="inline">alpha</code> is fetched for both arguments using the
│ │ │ │ +can be calculated as determined by the two map terms.</p><p>The first thing <code class="inline">blend/2</code> does is to calculate the resulting alpha channel:</p><pre><code class="makeup erlang" translate="no"><span class="nf">alpha</span><span class="p" data-group-id="7231419501-1">(</span><span class="p" data-group-id="7231419501-2">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7231419501-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7231419501-3">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="7231419501-3">}</span><span class="p" data-group-id="7231419501-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="7231419501-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7231419501-4">)</span><span class="p">.</span></code></pre><p>The value associated with key <code class="inline">alpha</code> is fetched for both arguments using the
│ │ │ │  <code class="inline">:=</code> operator. The other keys in the map are ignored, only the key <code class="inline">alpha</code> is
│ │ │ │ -required and checked for.</p><p>This is also the case for functions <code class="inline">red/2</code>, <code class="inline">blue/2</code>, and <code class="inline">green/2</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">red</span><span class="p" data-group-id="1449862350-1">(</span><span class="p" data-group-id="1449862350-2">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="1449862350-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1449862350-3">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="1449862350-3">}</span><span class="p" data-group-id="1449862350-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="1449862350-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="1449862350-4">)</span><span class="p">.</span></code></pre><p>The difference here is that a check is made for two keys in each map argument.
│ │ │ │ -The other keys are ignored.</p><p>Finally, let us return the resulting color in <code class="inline">blend/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">blend</span><span class="p" data-group-id="8530820397-1">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="8530820397-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="8530820397-2">#{</span><span class="w">
│ │ │ │ -        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="8530820397-3">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="8530820397-3">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="8530820397-4">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="8530820397-4">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="8530820397-5">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="8530820397-5">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +required and checked for.</p><p>This is also the case for functions <code class="inline">red/2</code>, <code class="inline">blue/2</code>, and <code class="inline">green/2</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">red</span><span class="p" data-group-id="8082176025-1">(</span><span class="p" data-group-id="8082176025-2">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="8082176025-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8082176025-3">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="8082176025-3">}</span><span class="p" data-group-id="8082176025-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="8082176025-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="8082176025-4">)</span><span class="p">.</span></code></pre><p>The difference here is that a check is made for two keys in each map argument.
│ │ │ │ +The other keys are ignored.</p><p>Finally, let us return the resulting color in <code class="inline">blend/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">blend</span><span class="p" data-group-id="0979925578-1">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="0979925578-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="0979925578-2">#{</span><span class="w">
│ │ │ │ +        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="0979925578-3">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0979925578-3">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="0979925578-4">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0979925578-4">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="0979925578-5">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0979925578-5">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Alpha</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8530820397-2">}</span><span class="p">;</span></code></pre><p>The <code class="inline">Dst</code> map is updated with new channel values. The syntax for updating an
│ │ │ │ +    </span><span class="p" data-group-id="0979925578-2">}</span><span class="p">;</span></code></pre><p>The <code class="inline">Dst</code> map is updated with new channel values. The syntax for updating an
│ │ │ │  existing key with a new value is with the <code class="inline">:=</code> operator.</p><h2 id="standard-modules-and-manual-pages" class="section-heading">
│ │ │ │    <a href="#standard-modules-and-manual-pages" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Standard Modules and Manual Pages</span>
│ │ │ │  </h2>
│ │ │ │  <p>Erlang has many standard modules to help you do things. For example, the module
│ │ │ │ @@ -347,24 +347,24 @@
│ │ │ │    <a href="#writing-output-to-a-terminal" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Writing Output to a Terminal</span>
│ │ │ │  </h2>
│ │ │ │  <p>It is nice to be able to do formatted output in examples, so the next example
│ │ │ │  shows a simple way to use the <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function. Like all other exported
│ │ │ │ -functions, you can test the <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">31&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8596088292-1">(</span><span class="s">&quot;hello world</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8596088292-2">[</span><span class="p" data-group-id="8596088292-2">]</span><span class="p" data-group-id="8596088292-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +functions, you can test the <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">31&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7986615449-1">(</span><span class="s">&quot;hello world</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7986615449-2">[</span><span class="p" data-group-id="7986615449-2">]</span><span class="p" data-group-id="7986615449-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w"> </span><span class="ss">world</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -32&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8596088292-3">(</span><span class="s">&quot;this outputs one Erlang term: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8596088292-4">[</span><span class="ss">hello</span><span class="p" data-group-id="8596088292-4">]</span><span class="p" data-group-id="8596088292-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +32&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7986615449-3">(</span><span class="s">&quot;this outputs one Erlang term: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7986615449-4">[</span><span class="ss">hello</span><span class="p" data-group-id="7986615449-4">]</span><span class="p" data-group-id="7986615449-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">one</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">term</span><span class="p">:</span><span class="w"> </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -33&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8596088292-5">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8596088292-6">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="8596088292-6">]</span><span class="p" data-group-id="8596088292-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +33&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7986615449-5">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7986615449-6">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="7986615449-6">]</span><span class="p" data-group-id="7986615449-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">two</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">terms</span><span class="p">:</span><span class="w"> </span><span class="ss">helloworld</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -34&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8596088292-7">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8596088292-8">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="8596088292-8">]</span><span class="p" data-group-id="8596088292-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +34&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7986615449-7">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7986615449-8">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="7986615449-8">]</span><span class="p" data-group-id="7986615449-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">two</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">terms</span><span class="p">:</span><span class="w"> </span><span class="ss">hello</span><span class="w"> </span><span class="ss">world</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>The function <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> (that is, <code class="inline">format</code> with two arguments) takes two lists.
│ │ │ │  The first one is nearly always a list written between <code class="inline">&quot; &quot;</code>. This list is printed
│ │ │ │  out as it is, except that each <code class="inline">~w</code> is replaced by a term taken in order from the
│ │ │ │  second list. Each ~n is replaced by a new line. The <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function
│ │ │ │  itself returns the atom <code class="inline">ok</code> if everything goes as planned. Like other functions
│ │ │ │  in Erlang, it crashes if an error occurs. This is not a fault in Erlang, it is a
│ │ │ │ @@ -378,34 +378,34 @@
│ │ │ │    <span class="text">A Larger Example</span>
│ │ │ │  </h2>
│ │ │ │  <p>Now for a larger example to consolidate what you have learnt so far. Assume that
│ │ │ │  you have a list of temperature readings from a number of cities in the world.
│ │ │ │  Some of them are in Celsius and some in Fahrenheit (as in the previous list).
│ │ │ │  First let us convert them all to Celsius, then let us print the data neatly.</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% This module is in file tut5.erl</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9995358432-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="9995358432-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9995358432-2">(</span><span class="p" data-group-id="9995358432-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9995358432-3">]</span><span class="p" data-group-id="9995358432-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7634735047-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="7634735047-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7634735047-2">(</span><span class="p" data-group-id="7634735047-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7634735047-3">]</span><span class="p" data-group-id="7634735047-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% Only this function is exported</span><span class="w">
│ │ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="9995358432-4">(</span><span class="p" data-group-id="9995358432-5">[</span><span class="p" data-group-id="9995358432-5">]</span><span class="p" data-group-id="9995358432-4">)</span><span class="p">-&gt;</span><span class="w">                        </span><span class="c1">% No output for an empty list</span><span class="w">
│ │ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="7634735047-4">(</span><span class="p" data-group-id="7634735047-5">[</span><span class="p" data-group-id="7634735047-5">]</span><span class="p" data-group-id="7634735047-4">)</span><span class="p">-&gt;</span><span class="w">                        </span><span class="c1">% No output for an empty list</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="9995358432-6">(</span><span class="p" data-group-id="9995358432-7">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9995358432-7">]</span><span class="p" data-group-id="9995358432-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="9995358432-8">(</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="9995358432-9">(</span><span class="n">City</span><span class="p" data-group-id="9995358432-9">)</span><span class="p" data-group-id="9995358432-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">format_temps</span><span class="p" data-group-id="9995358432-10">(</span><span class="n">Rest</span><span class="p" data-group-id="9995358432-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="9995358432-11">(</span><span class="p" data-group-id="9995358432-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9995358432-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9995358432-13">}</span><span class="p" data-group-id="9995358432-12">}</span><span class="p" data-group-id="9995358432-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% No conversion needed</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9995358432-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9995358432-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9995358432-15">}</span><span class="p" data-group-id="9995358432-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="9995358432-16">(</span><span class="p" data-group-id="9995358432-17">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9995358432-18">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9995358432-18">}</span><span class="p" data-group-id="9995358432-17">}</span><span class="p" data-group-id="9995358432-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Do the conversion</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9995358432-19">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9995358432-20">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9995358432-21">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="9995358432-21">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="9995358432-20">}</span><span class="p" data-group-id="9995358432-19">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="9995358432-22">(</span><span class="p" data-group-id="9995358432-23">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9995358432-24">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9995358432-24">}</span><span class="p" data-group-id="9995358432-23">}</span><span class="p" data-group-id="9995358432-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9995358432-25">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9995358432-26">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9995358432-26">]</span><span class="p" data-group-id="9995358432-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">35&gt; </span><span class="nf">c</span><span class="p" data-group-id="1928059661-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="1928059661-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1928059661-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut5</span><span class="p" data-group-id="1928059661-2">}</span><span class="gp unselectable">
│ │ │ │ -36&gt; </span><span class="nc">tut5</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="1928059661-3">(</span><span class="p" data-group-id="1928059661-4">[</span><span class="p" data-group-id="1928059661-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1928059661-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="1928059661-6">}</span><span class="p" data-group-id="1928059661-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1928059661-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1928059661-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="1928059661-8">}</span><span class="p" data-group-id="1928059661-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1928059661-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1928059661-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="1928059661-10">}</span><span class="p" data-group-id="1928059661-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1928059661-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1928059661-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="1928059661-12">}</span><span class="p" data-group-id="1928059661-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1928059661-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1928059661-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="1928059661-14">}</span><span class="p" data-group-id="1928059661-13">}</span><span class="p" data-group-id="1928059661-4">]</span><span class="p" data-group-id="1928059661-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="7634735047-6">(</span><span class="p" data-group-id="7634735047-7">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7634735047-7">]</span><span class="p" data-group-id="7634735047-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="7634735047-8">(</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="7634735047-9">(</span><span class="n">City</span><span class="p" data-group-id="7634735047-9">)</span><span class="p" data-group-id="7634735047-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">format_temps</span><span class="p" data-group-id="7634735047-10">(</span><span class="n">Rest</span><span class="p" data-group-id="7634735047-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="7634735047-11">(</span><span class="p" data-group-id="7634735047-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7634735047-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7634735047-13">}</span><span class="p" data-group-id="7634735047-12">}</span><span class="p" data-group-id="7634735047-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% No conversion needed</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7634735047-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7634735047-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7634735047-15">}</span><span class="p" data-group-id="7634735047-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="7634735047-16">(</span><span class="p" data-group-id="7634735047-17">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7634735047-18">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7634735047-18">}</span><span class="p" data-group-id="7634735047-17">}</span><span class="p" data-group-id="7634735047-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Do the conversion</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7634735047-19">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7634735047-20">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7634735047-21">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="7634735047-21">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="7634735047-20">}</span><span class="p" data-group-id="7634735047-19">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="7634735047-22">(</span><span class="p" data-group-id="7634735047-23">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7634735047-24">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7634735047-24">}</span><span class="p" data-group-id="7634735047-23">}</span><span class="p" data-group-id="7634735047-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7634735047-25">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7634735047-26">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7634735047-26">]</span><span class="p" data-group-id="7634735047-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">35&gt; </span><span class="nf">c</span><span class="p" data-group-id="6061620297-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="6061620297-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6061620297-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut5</span><span class="p" data-group-id="6061620297-2">}</span><span class="gp unselectable">
│ │ │ │ +36&gt; </span><span class="nc">tut5</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="6061620297-3">(</span><span class="p" data-group-id="6061620297-4">[</span><span class="p" data-group-id="6061620297-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6061620297-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6061620297-6">}</span><span class="p" data-group-id="6061620297-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6061620297-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6061620297-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6061620297-8">}</span><span class="p" data-group-id="6061620297-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6061620297-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6061620297-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6061620297-10">}</span><span class="p" data-group-id="6061620297-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6061620297-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6061620297-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6061620297-12">}</span><span class="p" data-group-id="6061620297-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6061620297-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6061620297-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="6061620297-14">}</span><span class="p" data-group-id="6061620297-13">}</span><span class="p" data-group-id="6061620297-4">]</span><span class="p" data-group-id="6061620297-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>Before looking at how this program works, notice that a few comments are added
│ │ │ │  to the code. A comment starts with a %-character and goes on to the end of the
│ │ │ │ @@ -433,28 +433,28 @@
│ │ │ │    <a href="#matching-guards-and-scope-of-variables" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Matching, Guards, and Scope of Variables</span>
│ │ │ │  </h2>
│ │ │ │  <p>It can be useful to find the maximum and minimum temperature in lists like this.
│ │ │ │  Before extending the program to do this, let us look at functions for finding
│ │ │ │ -the maximum value of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5773686280-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="5773686280-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5773686280-2">(</span><span class="p" data-group-id="5773686280-3">[</span><span class="ss">list_max</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5773686280-3">]</span><span class="p" data-group-id="5773686280-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the maximum value of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2483016892-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="2483016892-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2483016892-2">(</span><span class="p" data-group-id="2483016892-3">[</span><span class="ss">list_max</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2483016892-3">]</span><span class="p" data-group-id="2483016892-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="5773686280-4">(</span><span class="p" data-group-id="5773686280-5">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="5773686280-5">]</span><span class="p" data-group-id="5773686280-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="nf">list_max</span><span class="p" data-group-id="5773686280-6">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="5773686280-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="2483016892-4">(</span><span class="p" data-group-id="2483016892-5">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="2483016892-5">]</span><span class="p" data-group-id="2483016892-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="nf">list_max</span><span class="p" data-group-id="2483016892-6">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="2483016892-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="5773686280-7">(</span><span class="p" data-group-id="5773686280-8">[</span><span class="p" data-group-id="5773686280-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="5773686280-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="2483016892-7">(</span><span class="p" data-group-id="2483016892-8">[</span><span class="p" data-group-id="2483016892-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="2483016892-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Res</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="5773686280-9">(</span><span class="p" data-group-id="5773686280-10">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="5773686280-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="5773686280-9">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="5773686280-11">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="5773686280-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="5773686280-12">(</span><span class="p" data-group-id="5773686280-13">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="5773686280-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="5773686280-12">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="5773686280-14">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="5773686280-14">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">37&gt; </span><span class="nf">c</span><span class="p" data-group-id="3306667931-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="3306667931-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3306667931-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut6</span><span class="p" data-group-id="3306667931-2">}</span><span class="gp unselectable">
│ │ │ │ -38&gt; </span><span class="nc">tut6</span><span class="p">:</span><span class="nf">list_max</span><span class="p" data-group-id="3306667931-3">(</span><span class="p" data-group-id="3306667931-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3306667931-4">]</span><span class="p" data-group-id="3306667931-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="2483016892-9">(</span><span class="p" data-group-id="2483016892-10">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="2483016892-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="2483016892-9">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="2483016892-11">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="2483016892-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="2483016892-12">(</span><span class="p" data-group-id="2483016892-13">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="2483016892-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="2483016892-12">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="2483016892-14">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="2483016892-14">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">37&gt; </span><span class="nf">c</span><span class="p" data-group-id="3904553853-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="3904553853-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3904553853-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut6</span><span class="p" data-group-id="3904553853-2">}</span><span class="gp unselectable">
│ │ │ │ +38&gt; </span><span class="nc">tut6</span><span class="p">:</span><span class="nf">list_max</span><span class="p" data-group-id="3904553853-3">(</span><span class="p" data-group-id="3904553853-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3904553853-4">]</span><span class="p" data-group-id="3904553853-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">7</span></code></pre><p>First notice that two functions have the same name, <code class="inline">list_max</code>. However, each of
│ │ │ │  these takes a different number of arguments (parameters). In Erlang these are
│ │ │ │  regarded as completely different functions. Where you need to distinguish
│ │ │ │  between these functions, you write Name/Arity, where Name is the function name
│ │ │ │  and Arity is the number of arguments, in this case <code class="inline">list_max/1</code> and
│ │ │ │  <code class="inline">list_max/2</code>.</p><p>In this example you walk through a list &quot;carrying&quot; a value, in this case
│ │ │ │  <code class="inline">Result_so_far</code>. <code class="inline">list_max/1</code> simply assumes that the max value of the list is
│ │ │ │ @@ -483,180 +483,180 @@
│ │ │ │  </span><span class="mi">5</span><span class="gp unselectable">
│ │ │ │  40&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value 6</span><span class="gp unselectable">
│ │ │ │  41&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value 6</span><span class="gp unselectable">
│ │ │ │  42&gt; </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">6</span></code></pre><p>The use of the match operator is particularly useful for pulling apart Erlang
│ │ │ │ -terms and creating new ones.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">43&gt; </span><span class="p" data-group-id="9334769559-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9334769559-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9334769559-2">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9334769559-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="9334769559-3">}</span><span class="p" data-group-id="9334769559-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9334769559-4">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="9334769559-5">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="9334769559-5">}</span><span class="p" data-group-id="9334769559-4">}</span><span class="gp unselectable">
│ │ │ │ +terms and creating new ones.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">43&gt; </span><span class="p" data-group-id="5010316287-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5010316287-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5010316287-2">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5010316287-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="5010316287-3">}</span><span class="p" data-group-id="5010316287-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5010316287-4">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="5010316287-5">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="5010316287-5">}</span><span class="p" data-group-id="5010316287-4">}</span><span class="gp unselectable">
│ │ │ │  44&gt; </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="gp unselectable">
│ │ │ │  45&gt; </span><span class="n">Y</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9334769559-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="9334769559-6">}</span></code></pre><p>Here <code class="inline">X</code> gets the value <code class="inline">paris</code> and <code class="inline">Y</code> the value <code class="inline">{f,28}</code>.</p><p>If you try to do the same again with another city, an error is returned:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">46&gt; </span><span class="p" data-group-id="3900639745-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3900639745-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3900639745-2">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3900639745-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="3900639745-3">}</span><span class="p" data-group-id="3900639745-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5010316287-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="5010316287-6">}</span></code></pre><p>Here <code class="inline">X</code> gets the value <code class="inline">paris</code> and <code class="inline">Y</code> the value <code class="inline">{f,28}</code>.</p><p>If you try to do the same again with another city, an error is returned:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">46&gt; </span><span class="p" data-group-id="1121345644-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1121345644-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1121345644-2">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1121345644-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="1121345644-3">}</span><span class="p" data-group-id="1121345644-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value {london,{f,36}}</span></code></pre><p>Variables can also be used to improve the readability of programs. For example,
│ │ │ │ -in function <code class="inline">list_max/2</code> above, you can write:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_max</span><span class="p" data-group-id="2009481884-1">(</span><span class="p" data-group-id="2009481884-2">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="2009481884-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="2009481884-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +in function <code class="inline">list_max/2</code> above, you can write:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_max</span><span class="p" data-group-id="6978304768-1">(</span><span class="p" data-group-id="6978304768-2">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="6978304768-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="6978304768-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">New_result_far</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Head</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="2009481884-3">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">New_result_far</span><span class="p" data-group-id="2009481884-3">)</span><span class="p">;</span></code></pre><p>This is possibly a little clearer.</p><h2 id="more-about-lists" class="section-heading">
│ │ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="6978304768-3">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">New_result_far</span><span class="p" data-group-id="6978304768-3">)</span><span class="p">;</span></code></pre><p>This is possibly a little clearer.</p><h2 id="more-about-lists" class="section-heading">
│ │ │ │    <a href="#more-about-lists" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">More About Lists</span>
│ │ │ │  </h2>
│ │ │ │ -<p>Remember that the <code class="inline">|</code> operator can be used to get the head of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">47&gt; </span><span class="p" data-group-id="7492223107-1">[</span><span class="n">M1</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="7492223107-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7492223107-2">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="ss">rome</span><span class="p" data-group-id="7492223107-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7492223107-3">[</span><span class="ss">paris</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="7492223107-3">]</span><span class="gp unselectable">
│ │ │ │ +<p>Remember that the <code class="inline">|</code> operator can be used to get the head of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">47&gt; </span><span class="p" data-group-id="0207546988-1">[</span><span class="n">M1</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="0207546988-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0207546988-2">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="ss">rome</span><span class="p" data-group-id="0207546988-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0207546988-3">[</span><span class="ss">paris</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="0207546988-3">]</span><span class="gp unselectable">
│ │ │ │  48&gt; </span><span class="n">M1</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="gp unselectable">
│ │ │ │  49&gt; </span><span class="n">T1</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7492223107-4">[</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="7492223107-4">]</span></code></pre><p>The <code class="inline">|</code> operator can also be used to add a head to a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">50&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7760644842-1">[</span><span class="ss">madrid</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="7760644842-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7760644842-2">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="7760644842-2">]</span><span class="gp unselectable">
│ │ │ │ +</span><span class="p" data-group-id="0207546988-4">[</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="0207546988-4">]</span></code></pre><p>The <code class="inline">|</code> operator can also be used to add a head to a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">50&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1529453185-1">[</span><span class="ss">madrid</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="1529453185-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1529453185-2">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="1529453185-2">]</span><span class="gp unselectable">
│ │ │ │  51&gt; </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7760644842-3">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="7760644842-3">]</span></code></pre><p>Now an example of this when working with lists - reversing the order of a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7272640181-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="7272640181-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1529453185-3">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="1529453185-3">]</span></code></pre><p>Now an example of this when working with lists - reversing the order of a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8194547509-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="8194547509-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7272640181-2">(</span><span class="p" data-group-id="7272640181-3">[</span><span class="ss">reverse</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7272640181-3">]</span><span class="p" data-group-id="7272640181-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8194547509-2">(</span><span class="p" data-group-id="8194547509-3">[</span><span class="ss">reverse</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8194547509-3">]</span><span class="p" data-group-id="8194547509-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="7272640181-4">(</span><span class="n">List</span><span class="p" data-group-id="7272640181-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="7272640181-5">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7272640181-6">[</span><span class="p" data-group-id="7272640181-6">]</span><span class="p" data-group-id="7272640181-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="8194547509-4">(</span><span class="n">List</span><span class="p" data-group-id="8194547509-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="8194547509-5">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8194547509-6">[</span><span class="p" data-group-id="8194547509-6">]</span><span class="p" data-group-id="8194547509-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="7272640181-7">(</span><span class="p" data-group-id="7272640181-8">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7272640181-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="7272640181-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="7272640181-9">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7272640181-10">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="7272640181-10">]</span><span class="p" data-group-id="7272640181-9">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="7272640181-11">(</span><span class="p" data-group-id="7272640181-12">[</span><span class="p" data-group-id="7272640181-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="7272640181-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Reversed_List</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">52&gt; </span><span class="nf">c</span><span class="p" data-group-id="1557447766-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="1557447766-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1557447766-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut8</span><span class="p" data-group-id="1557447766-2">}</span><span class="gp unselectable">
│ │ │ │ -53&gt; </span><span class="nc">tut8</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="1557447766-3">(</span><span class="p" data-group-id="1557447766-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1557447766-4">]</span><span class="p" data-group-id="1557447766-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1557447766-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1557447766-5">]</span></code></pre><p>Consider how <code class="inline">Reversed_List</code> is built. It starts as [], then successively the
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="8194547509-7">(</span><span class="p" data-group-id="8194547509-8">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8194547509-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="8194547509-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="8194547509-9">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8194547509-10">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="8194547509-10">]</span><span class="p" data-group-id="8194547509-9">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="8194547509-11">(</span><span class="p" data-group-id="8194547509-12">[</span><span class="p" data-group-id="8194547509-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="8194547509-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Reversed_List</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">52&gt; </span><span class="nf">c</span><span class="p" data-group-id="4942731096-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="4942731096-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4942731096-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut8</span><span class="p" data-group-id="4942731096-2">}</span><span class="gp unselectable">
│ │ │ │ +53&gt; </span><span class="nc">tut8</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="4942731096-3">(</span><span class="p" data-group-id="4942731096-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4942731096-4">]</span><span class="p" data-group-id="4942731096-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4942731096-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4942731096-5">]</span></code></pre><p>Consider how <code class="inline">Reversed_List</code> is built. It starts as [], then successively the
│ │ │ │  heads are taken off of the list to be reversed and added to the the
│ │ │ │ -<code class="inline">Reversed_List</code>, as shown in the following:</p><pre><code class="makeup erlang" translate="no"><span class="nf">reverse</span><span class="p" data-group-id="3053496492-1">(</span><span class="p" data-group-id="3053496492-2">[</span><span class="mi">1</span><span class="p">|</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3053496492-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3053496492-3">[</span><span class="p" data-group-id="3053496492-3">]</span><span class="p" data-group-id="3053496492-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="3053496492-4">(</span><span class="p" data-group-id="3053496492-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3053496492-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3053496492-6">[</span><span class="mi">1</span><span class="p">|</span><span class="p" data-group-id="3053496492-7">[</span><span class="p" data-group-id="3053496492-7">]</span><span class="p" data-group-id="3053496492-6">]</span><span class="p" data-group-id="3053496492-4">)</span><span class="w">
│ │ │ │ +<code class="inline">Reversed_List</code>, as shown in the following:</p><pre><code class="makeup erlang" translate="no"><span class="nf">reverse</span><span class="p" data-group-id="1730397147-1">(</span><span class="p" data-group-id="1730397147-2">[</span><span class="mi">1</span><span class="p">|</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1730397147-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1730397147-3">[</span><span class="p" data-group-id="1730397147-3">]</span><span class="p" data-group-id="1730397147-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="1730397147-4">(</span><span class="p" data-group-id="1730397147-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1730397147-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1730397147-6">[</span><span class="mi">1</span><span class="p">|</span><span class="p" data-group-id="1730397147-7">[</span><span class="p" data-group-id="1730397147-7">]</span><span class="p" data-group-id="1730397147-6">]</span><span class="p" data-group-id="1730397147-4">)</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="3053496492-8">(</span><span class="p" data-group-id="3053496492-9">[</span><span class="mi">2</span><span class="p">|</span><span class="mi">3</span><span class="p" data-group-id="3053496492-9">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3053496492-10">[</span><span class="mi">1</span><span class="p" data-group-id="3053496492-10">]</span><span class="p" data-group-id="3053496492-8">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="3053496492-11">(</span><span class="p" data-group-id="3053496492-12">[</span><span class="mi">3</span><span class="p" data-group-id="3053496492-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3053496492-13">[</span><span class="mi">2</span><span class="p">|</span><span class="p" data-group-id="3053496492-14">[</span><span class="mi">1</span><span class="p" data-group-id="3053496492-14">]</span><span class="p">)</span><span class="w">
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="1730397147-8">(</span><span class="p" data-group-id="1730397147-9">[</span><span class="mi">2</span><span class="p">|</span><span class="mi">3</span><span class="p" data-group-id="1730397147-9">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1730397147-10">[</span><span class="mi">1</span><span class="p" data-group-id="1730397147-10">]</span><span class="p" data-group-id="1730397147-8">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="1730397147-11">(</span><span class="p" data-group-id="1730397147-12">[</span><span class="mi">3</span><span class="p" data-group-id="1730397147-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1730397147-13">[</span><span class="mi">2</span><span class="p">|</span><span class="p" data-group-id="1730397147-14">[</span><span class="mi">1</span><span class="p" data-group-id="1730397147-14">]</span><span class="p">)</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="3053496492-15">(</span><span class="p" data-group-id="3053496492-16">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="3053496492-17">[</span><span class="p" data-group-id="3053496492-17">]</span><span class="p" data-group-id="3053496492-16">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3053496492-18">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3053496492-18">]</span><span class="p" data-group-id="3053496492-15">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="3053496492-19">(</span><span class="p" data-group-id="3053496492-20">[</span><span class="p" data-group-id="3053496492-20">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3053496492-21">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="3053496492-22">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3053496492-22">]</span><span class="p" data-group-id="3053496492-21">]</span><span class="p" data-group-id="3053496492-19">)</span><span class="w">
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="1730397147-15">(</span><span class="p" data-group-id="1730397147-16">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="1730397147-17">[</span><span class="p" data-group-id="1730397147-17">]</span><span class="p" data-group-id="1730397147-16">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1730397147-18">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1730397147-18">]</span><span class="p" data-group-id="1730397147-15">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="1730397147-19">(</span><span class="p" data-group-id="1730397147-20">[</span><span class="p" data-group-id="1730397147-20">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1730397147-21">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="1730397147-22">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1730397147-22">]</span><span class="p" data-group-id="1730397147-21">]</span><span class="p" data-group-id="1730397147-19">)</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="3053496492-23">(</span><span class="p" data-group-id="3053496492-24">[</span><span class="p" data-group-id="3053496492-24">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3053496492-25">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3053496492-25">]</span><span class="p" data-group-id="3053496492-23">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3053496492-26">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3053496492-26">]</span></code></pre><p>The module <code class="inline">lists</code> contains many functions for manipulating lists, for example,
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="1730397147-23">(</span><span class="p" data-group-id="1730397147-24">[</span><span class="p" data-group-id="1730397147-24">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1730397147-25">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1730397147-25">]</span><span class="p" data-group-id="1730397147-23">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1730397147-26">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1730397147-26">]</span></code></pre><p>The module <code class="inline">lists</code> contains many functions for manipulating lists, for example,
│ │ │ │  for reversing them. So before writing a list-manipulating function it is a good
│ │ │ │  idea to check if one not already is written for you (see the <a href="../../../lib/stdlib/doc/html/lists.html"><code class="inline">lists</code></a> manual
│ │ │ │  page in STDLIB).</p><p>Now let us get back to the cities and temperatures, but take a more structured
│ │ │ │ -approach this time. First let us convert the whole list to Celsius as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1665169954-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="1665169954-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1665169954-2">(</span><span class="p" data-group-id="1665169954-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1665169954-3">]</span><span class="p" data-group-id="1665169954-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +approach this time. First let us convert the whole list to Celsius as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8886609417-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="8886609417-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8886609417-2">(</span><span class="p" data-group-id="8886609417-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8886609417-3">]</span><span class="p" data-group-id="8886609417-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="1665169954-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="1665169954-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1665169954-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="1665169954-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="8886609417-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="8886609417-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8886609417-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="8886609417-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1665169954-6">(</span><span class="p" data-group-id="1665169954-7">[</span><span class="p" data-group-id="1665169954-8">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1665169954-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="1665169954-9">}</span><span class="p" data-group-id="1665169954-8">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1665169954-7">]</span><span class="p" data-group-id="1665169954-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1665169954-10">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1665169954-11">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1665169954-12">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="1665169954-12">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1665169954-11">}</span><span class="p" data-group-id="1665169954-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1665169954-13">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1665169954-14">(</span><span class="n">Rest</span><span class="p" data-group-id="1665169954-14">)</span><span class="p" data-group-id="1665169954-13">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1665169954-15">(</span><span class="p" data-group-id="1665169954-16">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1665169954-16">]</span><span class="p" data-group-id="1665169954-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1665169954-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1665169954-18">(</span><span class="n">Rest</span><span class="p" data-group-id="1665169954-18">)</span><span class="p" data-group-id="1665169954-17">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1665169954-19">(</span><span class="p" data-group-id="1665169954-20">[</span><span class="p" data-group-id="1665169954-20">]</span><span class="p" data-group-id="1665169954-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1665169954-21">[</span><span class="p" data-group-id="1665169954-21">]</span><span class="p">.</span></code></pre><p>Test the function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">54&gt; </span><span class="nf">c</span><span class="p" data-group-id="9825294024-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="9825294024-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9825294024-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="9825294024-2">}</span><span class="p">.</span><span class="gp unselectable">
│ │ │ │ -55&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="9825294024-3">(</span><span class="p" data-group-id="9825294024-4">[</span><span class="p" data-group-id="9825294024-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9825294024-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="9825294024-6">}</span><span class="p" data-group-id="9825294024-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9825294024-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9825294024-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="9825294024-8">}</span><span class="p" data-group-id="9825294024-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9825294024-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9825294024-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="9825294024-10">}</span><span class="p" data-group-id="9825294024-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9825294024-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9825294024-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="9825294024-12">}</span><span class="p" data-group-id="9825294024-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9825294024-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9825294024-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="9825294024-14">}</span><span class="p" data-group-id="9825294024-13">}</span><span class="p" data-group-id="9825294024-4">]</span><span class="p" data-group-id="9825294024-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9825294024-15">[</span><span class="p" data-group-id="9825294024-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="9825294024-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="9825294024-17">}</span><span class="p" data-group-id="9825294024-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9825294024-18">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="9825294024-19">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">21.11111111111111</span><span class="p" data-group-id="9825294024-19">}</span><span class="p" data-group-id="9825294024-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9825294024-20">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="9825294024-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="9825294024-21">}</span><span class="p" data-group-id="9825294024-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9825294024-22">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="9825294024-23">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="9825294024-23">}</span><span class="p" data-group-id="9825294024-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9825294024-24">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="9825294024-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="9825294024-25">}</span><span class="p" data-group-id="9825294024-24">}</span><span class="p" data-group-id="9825294024-15">]</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">format_temps</span><span class="p" data-group-id="6969004810-1">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="6969004810-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6969004810-2">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="6969004810-2">)</span><span class="p">.</span></code></pre><p>Here <code class="inline">format_temps/1</code> calls <code class="inline">convert_list_to_c/1</code>. <code class="inline">convert_list_to_c/1</code> takes
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8886609417-6">(</span><span class="p" data-group-id="8886609417-7">[</span><span class="p" data-group-id="8886609417-8">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8886609417-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="8886609417-9">}</span><span class="p" data-group-id="8886609417-8">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8886609417-7">]</span><span class="p" data-group-id="8886609417-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8886609417-10">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8886609417-11">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8886609417-12">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="8886609417-12">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="8886609417-11">}</span><span class="p" data-group-id="8886609417-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8886609417-13">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8886609417-14">(</span><span class="n">Rest</span><span class="p" data-group-id="8886609417-14">)</span><span class="p" data-group-id="8886609417-13">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8886609417-15">(</span><span class="p" data-group-id="8886609417-16">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8886609417-16">]</span><span class="p" data-group-id="8886609417-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8886609417-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8886609417-18">(</span><span class="n">Rest</span><span class="p" data-group-id="8886609417-18">)</span><span class="p" data-group-id="8886609417-17">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8886609417-19">(</span><span class="p" data-group-id="8886609417-20">[</span><span class="p" data-group-id="8886609417-20">]</span><span class="p" data-group-id="8886609417-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8886609417-21">[</span><span class="p" data-group-id="8886609417-21">]</span><span class="p">.</span></code></pre><p>Test the function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">54&gt; </span><span class="nf">c</span><span class="p" data-group-id="8416964863-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="8416964863-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8416964863-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="8416964863-2">}</span><span class="p">.</span><span class="gp unselectable">
│ │ │ │ +55&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="8416964863-3">(</span><span class="p" data-group-id="8416964863-4">[</span><span class="p" data-group-id="8416964863-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8416964863-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8416964863-6">}</span><span class="p" data-group-id="8416964863-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8416964863-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8416964863-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="8416964863-8">}</span><span class="p" data-group-id="8416964863-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8416964863-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8416964863-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8416964863-10">}</span><span class="p" data-group-id="8416964863-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8416964863-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8416964863-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8416964863-12">}</span><span class="p" data-group-id="8416964863-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8416964863-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8416964863-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="8416964863-14">}</span><span class="p" data-group-id="8416964863-13">}</span><span class="p" data-group-id="8416964863-4">]</span><span class="p" data-group-id="8416964863-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8416964863-15">[</span><span class="p" data-group-id="8416964863-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="8416964863-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8416964863-17">}</span><span class="p" data-group-id="8416964863-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8416964863-18">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="8416964863-19">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">21.11111111111111</span><span class="p" data-group-id="8416964863-19">}</span><span class="p" data-group-id="8416964863-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8416964863-20">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="8416964863-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8416964863-21">}</span><span class="p" data-group-id="8416964863-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8416964863-22">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="8416964863-23">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="8416964863-23">}</span><span class="p" data-group-id="8416964863-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8416964863-24">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="8416964863-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="8416964863-25">}</span><span class="p" data-group-id="8416964863-24">}</span><span class="p" data-group-id="8416964863-15">]</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">format_temps</span><span class="p" data-group-id="3950163004-1">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="3950163004-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3950163004-2">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="3950163004-2">)</span><span class="p">.</span></code></pre><p>Here <code class="inline">format_temps/1</code> calls <code class="inline">convert_list_to_c/1</code>. <code class="inline">convert_list_to_c/1</code> takes
│ │ │ │  off the head of the <code class="inline">List_of_cities</code>, converts it to Celsius if needed. The <code class="inline">|</code>
│ │ │ │ -operator is used to add the (maybe) converted to the converted rest of the list:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7262982499-1">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7262982499-2">(</span><span class="n">Rest</span><span class="p" data-group-id="7262982499-2">)</span><span class="p" data-group-id="7262982499-1">]</span><span class="p">;</span></code></pre><p>or:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4453036848-1">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4453036848-2">(</span><span class="n">Rest</span><span class="p" data-group-id="4453036848-2">)</span><span class="p" data-group-id="4453036848-1">]</span><span class="p">;</span></code></pre><p>This is done until the end of the list is reached, that is, the list is empty:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8613767544-1">(</span><span class="p" data-group-id="8613767544-2">[</span><span class="p" data-group-id="8613767544-2">]</span><span class="p" data-group-id="8613767544-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8613767544-3">[</span><span class="p" data-group-id="8613767544-3">]</span><span class="p">.</span></code></pre><p>Now when the list is converted, a function to print it is added:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9716294777-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="9716294777-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9716294777-2">(</span><span class="p" data-group-id="9716294777-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9716294777-3">]</span><span class="p" data-group-id="9716294777-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="9716294777-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="9716294777-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9716294777-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="9716294777-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="9716294777-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="9716294777-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9716294777-7">(</span><span class="p" data-group-id="9716294777-8">[</span><span class="p" data-group-id="9716294777-9">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9716294777-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="9716294777-10">}</span><span class="p" data-group-id="9716294777-9">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9716294777-8">]</span><span class="p" data-group-id="9716294777-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9716294777-11">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9716294777-12">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9716294777-13">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="9716294777-13">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="9716294777-12">}</span><span class="p" data-group-id="9716294777-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9716294777-14">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9716294777-15">(</span><span class="n">Rest</span><span class="p" data-group-id="9716294777-15">)</span><span class="p" data-group-id="9716294777-14">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9716294777-16">(</span><span class="p" data-group-id="9716294777-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9716294777-17">]</span><span class="p" data-group-id="9716294777-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9716294777-18">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9716294777-19">(</span><span class="n">Rest</span><span class="p" data-group-id="9716294777-19">)</span><span class="p" data-group-id="9716294777-18">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9716294777-20">(</span><span class="p" data-group-id="9716294777-21">[</span><span class="p" data-group-id="9716294777-21">]</span><span class="p" data-group-id="9716294777-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9716294777-22">[</span><span class="p" data-group-id="9716294777-22">]</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="9716294777-23">(</span><span class="p" data-group-id="9716294777-24">[</span><span class="p" data-group-id="9716294777-25">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9716294777-26">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9716294777-26">}</span><span class="p" data-group-id="9716294777-25">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9716294777-24">]</span><span class="p" data-group-id="9716294777-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9716294777-27">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9716294777-28">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9716294777-28">]</span><span class="p" data-group-id="9716294777-27">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="9716294777-29">(</span><span class="n">Rest</span><span class="p" data-group-id="9716294777-29">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="9716294777-30">(</span><span class="p" data-group-id="9716294777-31">[</span><span class="p" data-group-id="9716294777-31">]</span><span class="p" data-group-id="9716294777-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">56&gt; </span><span class="nf">c</span><span class="p" data-group-id="9601365084-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="9601365084-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9601365084-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut7</span><span class="p" data-group-id="9601365084-2">}</span><span class="gp unselectable">
│ │ │ │ -57&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="9601365084-3">(</span><span class="p" data-group-id="9601365084-4">[</span><span class="p" data-group-id="9601365084-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601365084-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="9601365084-6">}</span><span class="p" data-group-id="9601365084-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601365084-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601365084-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="9601365084-8">}</span><span class="p" data-group-id="9601365084-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9601365084-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601365084-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="9601365084-10">}</span><span class="p" data-group-id="9601365084-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601365084-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601365084-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="9601365084-12">}</span><span class="p" data-group-id="9601365084-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601365084-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601365084-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="9601365084-14">}</span><span class="p" data-group-id="9601365084-13">}</span><span class="p" data-group-id="9601365084-4">]</span><span class="p" data-group-id="9601365084-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +operator is used to add the (maybe) converted to the converted rest of the list:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3778904626-1">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3778904626-2">(</span><span class="n">Rest</span><span class="p" data-group-id="3778904626-2">)</span><span class="p" data-group-id="3778904626-1">]</span><span class="p">;</span></code></pre><p>or:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1798784975-1">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1798784975-2">(</span><span class="n">Rest</span><span class="p" data-group-id="1798784975-2">)</span><span class="p" data-group-id="1798784975-1">]</span><span class="p">;</span></code></pre><p>This is done until the end of the list is reached, that is, the list is empty:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4145725955-1">(</span><span class="p" data-group-id="4145725955-2">[</span><span class="p" data-group-id="4145725955-2">]</span><span class="p" data-group-id="4145725955-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4145725955-3">[</span><span class="p" data-group-id="4145725955-3">]</span><span class="p">.</span></code></pre><p>Now when the list is converted, a function to print it is added:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4065556233-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="4065556233-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4065556233-2">(</span><span class="p" data-group-id="4065556233-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4065556233-3">]</span><span class="p" data-group-id="4065556233-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="4065556233-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="4065556233-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4065556233-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="4065556233-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="4065556233-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="4065556233-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4065556233-7">(</span><span class="p" data-group-id="4065556233-8">[</span><span class="p" data-group-id="4065556233-9">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4065556233-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="4065556233-10">}</span><span class="p" data-group-id="4065556233-9">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4065556233-8">]</span><span class="p" data-group-id="4065556233-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4065556233-11">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4065556233-12">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4065556233-13">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="4065556233-13">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="4065556233-12">}</span><span class="p" data-group-id="4065556233-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4065556233-14">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4065556233-15">(</span><span class="n">Rest</span><span class="p" data-group-id="4065556233-15">)</span><span class="p" data-group-id="4065556233-14">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4065556233-16">(</span><span class="p" data-group-id="4065556233-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4065556233-17">]</span><span class="p" data-group-id="4065556233-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4065556233-18">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4065556233-19">(</span><span class="n">Rest</span><span class="p" data-group-id="4065556233-19">)</span><span class="p" data-group-id="4065556233-18">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4065556233-20">(</span><span class="p" data-group-id="4065556233-21">[</span><span class="p" data-group-id="4065556233-21">]</span><span class="p" data-group-id="4065556233-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4065556233-22">[</span><span class="p" data-group-id="4065556233-22">]</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="4065556233-23">(</span><span class="p" data-group-id="4065556233-24">[</span><span class="p" data-group-id="4065556233-25">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4065556233-26">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4065556233-26">}</span><span class="p" data-group-id="4065556233-25">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4065556233-24">]</span><span class="p" data-group-id="4065556233-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4065556233-27">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4065556233-28">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4065556233-28">]</span><span class="p" data-group-id="4065556233-27">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="4065556233-29">(</span><span class="n">Rest</span><span class="p" data-group-id="4065556233-29">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="4065556233-30">(</span><span class="p" data-group-id="4065556233-31">[</span><span class="p" data-group-id="4065556233-31">]</span><span class="p" data-group-id="4065556233-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">56&gt; </span><span class="nf">c</span><span class="p" data-group-id="4917320727-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="4917320727-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4917320727-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut7</span><span class="p" data-group-id="4917320727-2">}</span><span class="gp unselectable">
│ │ │ │ +57&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="4917320727-3">(</span><span class="p" data-group-id="4917320727-4">[</span><span class="p" data-group-id="4917320727-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4917320727-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4917320727-6">}</span><span class="p" data-group-id="4917320727-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4917320727-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4917320727-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4917320727-8">}</span><span class="p" data-group-id="4917320727-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4917320727-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4917320727-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4917320727-10">}</span><span class="p" data-group-id="4917320727-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4917320727-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4917320727-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4917320727-12">}</span><span class="p" data-group-id="4917320727-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4917320727-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4917320727-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4917320727-14">}</span><span class="p" data-group-id="4917320727-13">}</span><span class="p" data-group-id="4917320727-4">]</span><span class="p" data-group-id="4917320727-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>Now a function has to be added to find the cities with the maximum and minimum
│ │ │ │  temperatures. The following program is not the most efficient way of doing this
│ │ │ │  as you walk through the list of cities four times. But it is better to first
│ │ │ │  strive for clarity and correctness and to make programs efficient only if
│ │ │ │ -needed.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3446202504-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="3446202504-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3446202504-2">(</span><span class="p" data-group-id="3446202504-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3446202504-3">]</span><span class="p" data-group-id="3446202504-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +needed.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8627664552-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="8627664552-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8627664552-2">(</span><span class="p" data-group-id="8627664552-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8627664552-3">]</span><span class="p" data-group-id="8627664552-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="3446202504-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="3446202504-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3446202504-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="3446202504-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="3446202504-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="3446202504-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3446202504-7">{</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="3446202504-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3446202504-8">(</span><span class="n">Converted_List</span><span class="p" data-group-id="3446202504-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_max_and_min</span><span class="p" data-group-id="3446202504-9">(</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="3446202504-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3446202504-10">(</span><span class="p" data-group-id="3446202504-11">[</span><span class="p" data-group-id="3446202504-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-13">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3446202504-13">}</span><span class="p" data-group-id="3446202504-12">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3446202504-11">]</span><span class="p" data-group-id="3446202504-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3446202504-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-16">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="3446202504-16">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="3446202504-15">}</span><span class="p" data-group-id="3446202504-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3446202504-17">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3446202504-18">(</span><span class="n">Rest</span><span class="p" data-group-id="3446202504-18">)</span><span class="p" data-group-id="3446202504-17">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3446202504-19">(</span><span class="p" data-group-id="3446202504-20">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3446202504-20">]</span><span class="p" data-group-id="3446202504-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3446202504-21">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3446202504-22">(</span><span class="n">Rest</span><span class="p" data-group-id="3446202504-22">)</span><span class="p" data-group-id="3446202504-21">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3446202504-23">(</span><span class="p" data-group-id="3446202504-24">[</span><span class="p" data-group-id="3446202504-24">]</span><span class="p" data-group-id="3446202504-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3446202504-25">[</span><span class="p" data-group-id="3446202504-25">]</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="3446202504-26">(</span><span class="p" data-group-id="3446202504-27">[</span><span class="p" data-group-id="3446202504-28">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-29">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3446202504-29">}</span><span class="p" data-group-id="3446202504-28">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3446202504-27">]</span><span class="p" data-group-id="3446202504-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3446202504-30">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-31">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3446202504-31">]</span><span class="p" data-group-id="3446202504-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="3446202504-32">(</span><span class="n">Rest</span><span class="p" data-group-id="3446202504-32">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="3446202504-33">(</span><span class="p" data-group-id="3446202504-34">[</span><span class="p" data-group-id="3446202504-34">]</span><span class="p" data-group-id="3446202504-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="8627664552-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="8627664552-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8627664552-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="8627664552-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="8627664552-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="8627664552-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8627664552-7">{</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="8627664552-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8627664552-8">(</span><span class="n">Converted_List</span><span class="p" data-group-id="8627664552-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_max_and_min</span><span class="p" data-group-id="8627664552-9">(</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="8627664552-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8627664552-10">(</span><span class="p" data-group-id="8627664552-11">[</span><span class="p" data-group-id="8627664552-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-13">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8627664552-13">}</span><span class="p" data-group-id="8627664552-12">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8627664552-11">]</span><span class="p" data-group-id="8627664552-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8627664552-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-16">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="8627664552-16">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="8627664552-15">}</span><span class="p" data-group-id="8627664552-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8627664552-17">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8627664552-18">(</span><span class="n">Rest</span><span class="p" data-group-id="8627664552-18">)</span><span class="p" data-group-id="8627664552-17">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8627664552-19">(</span><span class="p" data-group-id="8627664552-20">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8627664552-20">]</span><span class="p" data-group-id="8627664552-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8627664552-21">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8627664552-22">(</span><span class="n">Rest</span><span class="p" data-group-id="8627664552-22">)</span><span class="p" data-group-id="8627664552-21">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8627664552-23">(</span><span class="p" data-group-id="8627664552-24">[</span><span class="p" data-group-id="8627664552-24">]</span><span class="p" data-group-id="8627664552-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8627664552-25">[</span><span class="p" data-group-id="8627664552-25">]</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="8627664552-26">(</span><span class="p" data-group-id="8627664552-27">[</span><span class="p" data-group-id="8627664552-28">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-29">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8627664552-29">}</span><span class="p" data-group-id="8627664552-28">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8627664552-27">]</span><span class="p" data-group-id="8627664552-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8627664552-30">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-31">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8627664552-31">]</span><span class="p" data-group-id="8627664552-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="8627664552-32">(</span><span class="n">Rest</span><span class="p" data-group-id="8627664552-32">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="8627664552-33">(</span><span class="p" data-group-id="8627664552-34">[</span><span class="p" data-group-id="8627664552-34">]</span><span class="p" data-group-id="8627664552-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3446202504-35">(</span><span class="p" data-group-id="3446202504-36">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3446202504-36">]</span><span class="p" data-group-id="3446202504-35">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3446202504-37">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p" data-group-id="3446202504-37">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8627664552-35">(</span><span class="p" data-group-id="8627664552-36">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8627664552-36">]</span><span class="p" data-group-id="8627664552-35">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8627664552-37">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p" data-group-id="8627664552-37">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3446202504-38">(</span><span class="p" data-group-id="3446202504-39">[</span><span class="p" data-group-id="3446202504-40">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-41">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3446202504-41">}</span><span class="p" data-group-id="3446202504-40">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3446202504-39">]</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="3446202504-42">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-43">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="3446202504-43">}</span><span class="p" data-group-id="3446202504-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="3446202504-44">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-45">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="3446202504-45">}</span><span class="p" data-group-id="3446202504-44">}</span><span class="p" data-group-id="3446202504-38">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8627664552-38">(</span><span class="p" data-group-id="8627664552-39">[</span><span class="p" data-group-id="8627664552-40">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-41">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8627664552-41">}</span><span class="p" data-group-id="8627664552-40">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8627664552-39">]</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="8627664552-42">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-43">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="8627664552-43">}</span><span class="p" data-group-id="8627664552-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="8627664552-44">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-45">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="8627664552-45">}</span><span class="p" data-group-id="8627664552-44">}</span><span class="p" data-group-id="8627664552-38">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">Temp</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Max_Temp</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3446202504-46">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-47">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3446202504-47">}</span><span class="p" data-group-id="3446202504-46">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ │ +            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8627664552-46">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-47">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8627664552-47">}</span><span class="p" data-group-id="8627664552-46">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3446202504-48">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-49">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="3446202504-49">}</span><span class="p" data-group-id="3446202504-48">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ │ +            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8627664552-48">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-49">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="8627664552-49">}</span><span class="p" data-group-id="8627664552-48">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │           </span><span class="n">Temp</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Min_Temp</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3446202504-50">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-51">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3446202504-51">}</span><span class="p" data-group-id="3446202504-50">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ │ +            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8627664552-50">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-51">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8627664552-51">}</span><span class="p" data-group-id="8627664552-50">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3446202504-52">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-53">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="3446202504-53">}</span><span class="p" data-group-id="3446202504-52">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ │ +            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8627664552-52">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-53">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="8627664552-53">}</span><span class="p" data-group-id="8627664552-52">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3446202504-54">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="3446202504-54">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8627664552-54">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="8627664552-54">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3446202504-55">(</span><span class="p" data-group-id="3446202504-56">[</span><span class="p" data-group-id="3446202504-56">]</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="3446202504-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3446202504-57">{</span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="3446202504-57">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8627664552-55">(</span><span class="p" data-group-id="8627664552-56">[</span><span class="p" data-group-id="8627664552-56">]</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="8627664552-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8627664552-57">{</span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="8627664552-57">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">print_max_and_min</span><span class="p" data-group-id="3446202504-58">(</span><span class="p" data-group-id="3446202504-59">{</span><span class="n">Max_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-60">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_temp</span><span class="p" data-group-id="3446202504-60">}</span><span class="p" data-group-id="3446202504-59">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-61">{</span><span class="n">Min_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-62">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_temp</span><span class="p" data-group-id="3446202504-62">}</span><span class="p" data-group-id="3446202504-61">}</span><span class="p" data-group-id="3446202504-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3446202504-63">(</span><span class="s">&quot;Max temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-64">[</span><span class="n">Max_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Max_name</span><span class="p" data-group-id="3446202504-64">]</span><span class="p" data-group-id="3446202504-63">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3446202504-65">(</span><span class="s">&quot;Min temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3446202504-66">[</span><span class="n">Min_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Min_name</span><span class="p" data-group-id="3446202504-66">]</span><span class="p" data-group-id="3446202504-65">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">58&gt; </span><span class="nf">c</span><span class="p" data-group-id="8314099120-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="8314099120-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8314099120-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="8314099120-2">}</span><span class="gp unselectable">
│ │ │ │ -59&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="8314099120-3">(</span><span class="p" data-group-id="8314099120-4">[</span><span class="p" data-group-id="8314099120-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8314099120-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8314099120-6">}</span><span class="p" data-group-id="8314099120-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8314099120-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8314099120-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="8314099120-8">}</span><span class="p" data-group-id="8314099120-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8314099120-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8314099120-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8314099120-10">}</span><span class="p" data-group-id="8314099120-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8314099120-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8314099120-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8314099120-12">}</span><span class="p" data-group-id="8314099120-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8314099120-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8314099120-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="8314099120-14">}</span><span class="p" data-group-id="8314099120-13">}</span><span class="p" data-group-id="8314099120-4">]</span><span class="p" data-group-id="8314099120-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">print_max_and_min</span><span class="p" data-group-id="8627664552-58">(</span><span class="p" data-group-id="8627664552-59">{</span><span class="n">Max_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-60">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_temp</span><span class="p" data-group-id="8627664552-60">}</span><span class="p" data-group-id="8627664552-59">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-61">{</span><span class="n">Min_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-62">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_temp</span><span class="p" data-group-id="8627664552-62">}</span><span class="p" data-group-id="8627664552-61">}</span><span class="p" data-group-id="8627664552-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8627664552-63">(</span><span class="s">&quot;Max temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-64">[</span><span class="n">Max_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Max_name</span><span class="p" data-group-id="8627664552-64">]</span><span class="p" data-group-id="8627664552-63">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8627664552-65">(</span><span class="s">&quot;Min temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8627664552-66">[</span><span class="n">Min_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Min_name</span><span class="p" data-group-id="8627664552-66">]</span><span class="p" data-group-id="8627664552-65">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">58&gt; </span><span class="nf">c</span><span class="p" data-group-id="1902335213-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="1902335213-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1902335213-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="1902335213-2">}</span><span class="gp unselectable">
│ │ │ │ +59&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="1902335213-3">(</span><span class="p" data-group-id="1902335213-4">[</span><span class="p" data-group-id="1902335213-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1902335213-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="1902335213-6">}</span><span class="p" data-group-id="1902335213-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1902335213-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1902335213-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="1902335213-8">}</span><span class="p" data-group-id="1902335213-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1902335213-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1902335213-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="1902335213-10">}</span><span class="p" data-group-id="1902335213-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1902335213-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1902335213-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="1902335213-12">}</span><span class="p" data-group-id="1902335213-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1902335213-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1902335213-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="1902335213-14">}</span><span class="p" data-group-id="1902335213-13">}</span><span class="p" data-group-id="1902335213-4">]</span><span class="p" data-group-id="1902335213-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="n">Max</span><span class="w"> </span><span class="ss">temperature</span><span class="w"> </span><span class="ss">was</span><span class="w"> </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">cape_town</span><span class="w">
│ │ │ │  </span><span class="n">Min</span><span class="w"> </span><span class="ss">temperature</span><span class="w"> </span><span class="ss">was</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">moscow</span><span class="w">
│ │ │ │ @@ -678,88 +678,88 @@
│ │ │ │          Action 4
│ │ │ │  end</code></pre><p>Notice that there is no <code class="inline">;</code> before <code class="inline">end</code>. Conditions do the same as guards, that
│ │ │ │  is, tests that succeed or fail. Erlang starts at the top and tests until it
│ │ │ │  finds a condition that succeeds. Then it evaluates (performs) the action
│ │ │ │  following the condition and ignores all other conditions and actions before the
│ │ │ │  <code class="inline">end</code>. If no condition matches, a run-time failure occurs. A condition that
│ │ │ │  always succeeds is the atom <code class="inline">true</code>. This is often used last in an <code class="inline">if</code>, meaning,
│ │ │ │ -do the action following the <code class="inline">true</code> if all other conditions have failed.</p><p>The following is a short program to show the workings of <code class="inline">if</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2831947005-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="2831947005-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2831947005-2">(</span><span class="p" data-group-id="2831947005-3">[</span><span class="ss">test_if</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2831947005-3">]</span><span class="p" data-group-id="2831947005-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +do the action following the <code class="inline">true</code> if all other conditions have failed.</p><p>The following is a short program to show the workings of <code class="inline">if</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3162027856-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="3162027856-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3162027856-2">(</span><span class="p" data-group-id="3162027856-3">[</span><span class="ss">test_if</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3162027856-3">]</span><span class="p" data-group-id="3162027856-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">test_if</span><span class="p" data-group-id="2831947005-4">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2831947005-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">test_if</span><span class="p" data-group-id="3162027856-4">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="3162027856-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2831947005-5">(</span><span class="s">&quot;A == 5</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2831947005-6">[</span><span class="p" data-group-id="2831947005-6">]</span><span class="p" data-group-id="2831947005-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3162027856-5">(</span><span class="s">&quot;A == 5</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3162027856-6">[</span><span class="p" data-group-id="3162027856-6">]</span><span class="p" data-group-id="3162027856-5">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="ss">a_equals_5</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2831947005-7">(</span><span class="s">&quot;B == 6</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2831947005-8">[</span><span class="p" data-group-id="2831947005-8">]</span><span class="p" data-group-id="2831947005-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3162027856-7">(</span><span class="s">&quot;B == 6</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3162027856-8">[</span><span class="p" data-group-id="3162027856-8">]</span><span class="p" data-group-id="3162027856-7">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="ss">b_equals_6</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">                      </span><span class="c1">%That is A equals 2 and B equals 3</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2831947005-9">(</span><span class="s">&quot;A == 2, B == 3</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2831947005-10">[</span><span class="p" data-group-id="2831947005-10">]</span><span class="p" data-group-id="2831947005-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3162027856-9">(</span><span class="s">&quot;A == 2, B == 3</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3162027856-10">[</span><span class="p" data-group-id="3162027856-10">]</span><span class="p" data-group-id="3162027856-9">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="ss">a_equals_2_b_equals_3</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">                     </span><span class="c1">%That is A equals 1 or B equals 7</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2831947005-11">(</span><span class="s">&quot;A == 1 ; B == 7</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2831947005-12">[</span><span class="p" data-group-id="2831947005-12">]</span><span class="p" data-group-id="2831947005-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3162027856-11">(</span><span class="s">&quot;A == 1 ; B == 7</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3162027856-12">[</span><span class="p" data-group-id="3162027856-12">]</span><span class="p" data-group-id="3162027856-11">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Testing this program gives:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">60&gt; </span><span class="nf">c</span><span class="p" data-group-id="4276678705-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="4276678705-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4276678705-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut9</span><span class="p" data-group-id="4276678705-2">}</span><span class="gp unselectable">
│ │ │ │ -61&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4276678705-3">(</span><span class="mi">5</span><span class="p">,</span><span class="mi">33</span><span class="p" data-group-id="4276678705-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Testing this program gives:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">60&gt; </span><span class="nf">c</span><span class="p" data-group-id="7386231124-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="7386231124-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7386231124-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut9</span><span class="p" data-group-id="7386231124-2">}</span><span class="gp unselectable">
│ │ │ │ +61&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="7386231124-3">(</span><span class="mi">5</span><span class="p">,</span><span class="mi">33</span><span class="p" data-group-id="7386231124-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ │  </span><span class="ss">a_equals_5</span><span class="gp unselectable">
│ │ │ │ -62&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4276678705-4">(</span><span class="mi">33</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4276678705-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +62&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="7386231124-4">(</span><span class="mi">33</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7386231124-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">6</span><span class="w">
│ │ │ │  </span><span class="ss">b_equals_6</span><span class="gp unselectable">
│ │ │ │ -63&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4276678705-5">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4276678705-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +63&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="7386231124-5">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7386231124-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="w">
│ │ │ │  </span><span class="ss">a_equals_2_b_equals_3</span><span class="gp unselectable">
│ │ │ │ -64&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4276678705-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="4276678705-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +64&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="7386231124-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="7386231124-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w">
│ │ │ │  </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="gp unselectable">
│ │ │ │ -65&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4276678705-7">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="4276678705-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +65&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="7386231124-7">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="7386231124-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w">
│ │ │ │  </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="gp unselectable">
│ │ │ │ -66&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4276678705-8">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="4276678705-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +66&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="7386231124-8">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="7386231124-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no true branch found when evaluating an if expression
│ │ │ │       in function  tut9:test_if/2 (tut9.erl, line 5)</span></code></pre><p>Notice that <code class="inline">tut9:test_if(33,33)</code> does not cause any condition to succeed. This
│ │ │ │  leads to the run time error <code class="inline">if_clause</code>, here nicely formatted by the shell. See
│ │ │ │  <a href="../../../lib/../system/doc/html/expressions.xhtml">Guard Sequences</a> for details of the many guard tests
│ │ │ │  available.</p><p><code class="inline">case</code> is another construct in Erlang. Recall that the <code class="inline">convert_length</code> function
│ │ │ │ -was written as:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_length</span><span class="p" data-group-id="1426041725-1">(</span><span class="p" data-group-id="1426041725-2">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1426041725-2">}</span><span class="p" data-group-id="1426041725-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1426041725-3">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="1426041725-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="1426041725-4">(</span><span class="p" data-group-id="1426041725-5">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1426041725-5">}</span><span class="p" data-group-id="1426041725-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1426041725-6">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="1426041725-6">}</span><span class="p">.</span></code></pre><p>The same program can also be written as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0709046216-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="0709046216-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0709046216-2">(</span><span class="p" data-group-id="0709046216-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0709046216-3">]</span><span class="p" data-group-id="0709046216-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +was written as:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_length</span><span class="p" data-group-id="7885116900-1">(</span><span class="p" data-group-id="7885116900-2">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7885116900-2">}</span><span class="p" data-group-id="7885116900-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7885116900-3">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="7885116900-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="7885116900-4">(</span><span class="p" data-group-id="7885116900-5">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7885116900-5">}</span><span class="p" data-group-id="7885116900-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7885116900-6">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="7885116900-6">}</span><span class="p">.</span></code></pre><p>The same program can also be written as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5727852565-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="5727852565-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5727852565-2">(</span><span class="p" data-group-id="5727852565-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5727852565-3">]</span><span class="p" data-group-id="5727852565-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="0709046216-4">(</span><span class="n">Length</span><span class="p" data-group-id="0709046216-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="5727852565-4">(</span><span class="n">Length</span><span class="p" data-group-id="5727852565-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0709046216-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0709046216-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="0709046216-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="0709046216-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0709046216-7">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0709046216-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="0709046216-8">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="0709046216-8">}</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">67&gt; </span><span class="nf">c</span><span class="p" data-group-id="7833701803-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="7833701803-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7833701803-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut10</span><span class="p" data-group-id="7833701803-2">}</span><span class="gp unselectable">
│ │ │ │ -68&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="7833701803-3">(</span><span class="p" data-group-id="7833701803-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="7833701803-4">}</span><span class="p" data-group-id="7833701803-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7833701803-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">15.24</span><span class="p" data-group-id="7833701803-5">}</span><span class="gp unselectable">
│ │ │ │ -69&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="7833701803-6">(</span><span class="p" data-group-id="7833701803-7">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="mf">2.5</span><span class="p" data-group-id="7833701803-7">}</span><span class="p" data-group-id="7833701803-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7833701803-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">0.984251968503937</span><span class="p" data-group-id="7833701803-8">}</span></code></pre><p>Both <code class="inline">case</code> and <code class="inline">if</code> have <em>return values</em>, that is, in the above example <code class="inline">case</code>
│ │ │ │ +        </span><span class="p" data-group-id="5727852565-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5727852565-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="5727852565-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="5727852565-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="5727852565-7">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5727852565-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="5727852565-8">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="5727852565-8">}</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">67&gt; </span><span class="nf">c</span><span class="p" data-group-id="9893643921-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="9893643921-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9893643921-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut10</span><span class="p" data-group-id="9893643921-2">}</span><span class="gp unselectable">
│ │ │ │ +68&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="9893643921-3">(</span><span class="p" data-group-id="9893643921-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="9893643921-4">}</span><span class="p" data-group-id="9893643921-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9893643921-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">15.24</span><span class="p" data-group-id="9893643921-5">}</span><span class="gp unselectable">
│ │ │ │ +69&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="9893643921-6">(</span><span class="p" data-group-id="9893643921-7">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="mf">2.5</span><span class="p" data-group-id="9893643921-7">}</span><span class="p" data-group-id="9893643921-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9893643921-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">0.984251968503937</span><span class="p" data-group-id="9893643921-8">}</span></code></pre><p>Both <code class="inline">case</code> and <code class="inline">if</code> have <em>return values</em>, that is, in the above example <code class="inline">case</code>
│ │ │ │  returned either <code class="inline">{inch,X/2.54}</code> or <code class="inline">{centimeter,Y*2.54}</code>. The behaviour of
│ │ │ │  <code class="inline">case</code> can also be modified by using guards. The following example clarifies
│ │ │ │  this. It tells us the length of a month, given the year. The year must be known,
│ │ │ │ -since February has 29 days in a leap year.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6615203693-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="6615203693-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6615203693-2">(</span><span class="p" data-group-id="6615203693-3">[</span><span class="ss">month_length</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6615203693-3">]</span><span class="p" data-group-id="6615203693-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +since February has 29 days in a leap year.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7100068842-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="7100068842-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7100068842-2">(</span><span class="p" data-group-id="7100068842-3">[</span><span class="ss">month_length</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7100068842-3">]</span><span class="p" data-group-id="7100068842-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">month_length</span><span class="p" data-group-id="6615203693-4">(</span><span class="n">Year</span><span class="p">,</span><span class="w"> </span><span class="n">Month</span><span class="p" data-group-id="6615203693-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">month_length</span><span class="p" data-group-id="7100068842-4">(</span><span class="n">Year</span><span class="p">,</span><span class="w"> </span><span class="n">Month</span><span class="p" data-group-id="7100068842-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% All years divisible by 400 are leap</span><span class="w">
│ │ │ │      </span><span class="c1">%% Years divisible by 100 are not leap (except the 400 rule above)</span><span class="w">
│ │ │ │      </span><span class="c1">%% Years divisible by 4 are leap (except the 100 rule above)</span><span class="w">
│ │ │ │      </span><span class="n">Leap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">if</span><span class="w">
│ │ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="6615203693-5">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="6615203693-5">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="7100068842-5">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="7100068842-5">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">leap</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="6615203693-6">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="6615203693-6">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">100</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="7100068842-6">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="7100068842-6">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">100</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">not_leap</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="6615203693-7">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="6615203693-7">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="7100068842-7">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="7100068842-7">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">leap</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">not_leap</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Month</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">sep</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">30</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">apr</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">30</span><span class="p">;</span><span class="w">
│ │ │ │ @@ -770,151 +770,151 @@
│ │ │ │          </span><span class="ss">jan</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">mar</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">may</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">jul</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">aug</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">oct</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">dec</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">70&gt; </span><span class="nf">c</span><span class="p" data-group-id="0238590333-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="0238590333-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0238590333-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut11</span><span class="p" data-group-id="0238590333-2">}</span><span class="gp unselectable">
│ │ │ │ -71&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="0238590333-3">(</span><span class="mi">2004</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="0238590333-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">70&gt; </span><span class="nf">c</span><span class="p" data-group-id="2070937270-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="2070937270-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2070937270-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut11</span><span class="p" data-group-id="2070937270-2">}</span><span class="gp unselectable">
│ │ │ │ +71&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="2070937270-3">(</span><span class="mi">2004</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="2070937270-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">29</span><span class="gp unselectable">
│ │ │ │ -72&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="0238590333-4">(</span><span class="mi">2003</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="0238590333-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +72&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="2070937270-4">(</span><span class="mi">2003</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="2070937270-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">28</span><span class="gp unselectable">
│ │ │ │ -73&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="0238590333-5">(</span><span class="mi">1947</span><span class="p">,</span><span class="w"> </span><span class="ss">aug</span><span class="p" data-group-id="0238590333-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +73&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="2070937270-5">(</span><span class="mi">1947</span><span class="p">,</span><span class="w"> </span><span class="ss">aug</span><span class="p" data-group-id="2070937270-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">31</span></code></pre><h2 id="built-in-functions-bifs" class="section-heading">
│ │ │ │    <a href="#built-in-functions-bifs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Built-In Functions (BIFs)</span>
│ │ │ │  </h2>
│ │ │ │  <p>BIFs are functions that for some reason are built-in to the Erlang virtual
│ │ │ │  machine. BIFs often implement functionality that is impossible or is too
│ │ │ │  inefficient to implement in Erlang. Some BIFs can be called using the function
│ │ │ │  name only but they are by default belonging to the <code class="inline">erlang</code> module. For example,
│ │ │ │  the call to the BIF <code class="inline">trunc</code> below is equivalent to a call to <code class="inline">erlang:trunc</code>.</p><p>As shown, first it is checked if a year is leap. If a year is divisible by 400,
│ │ │ │  it is a leap year. To determine this, first divide the year by 400 and use the
│ │ │ │  BIF <code class="inline">trunc</code> (more about this later) to cut off any decimals. Then multiply by
│ │ │ │  400 again and see if the same value is returned again. For example, year 2004:</p><pre><code class="makeup erlang" translate="no"><span class="mi">2004</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">5.01</span><span class="w">
│ │ │ │ -</span><span class="nf">trunc</span><span class="p" data-group-id="8589480571-1">(</span><span class="mf">5.01</span><span class="p" data-group-id="8589480571-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ │ +</span><span class="nf">trunc</span><span class="p" data-group-id="9783453719-1">(</span><span class="mf">5.01</span><span class="p" data-group-id="9783453719-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ │  </span><span class="mi">5</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2000</span></code></pre><p>2000 is not the same as 2004, so 2004 is not divisible by 400. Year 2000:</p><pre><code class="makeup erlang" translate="no"><span class="mi">2000</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">5.0</span><span class="w">
│ │ │ │ -</span><span class="nf">trunc</span><span class="p" data-group-id="7760336541-1">(</span><span class="mf">5.0</span><span class="p" data-group-id="7760336541-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ │ +</span><span class="nf">trunc</span><span class="p" data-group-id="8033181563-1">(</span><span class="mf">5.0</span><span class="p" data-group-id="8033181563-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ │  </span><span class="mi">5</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2000</span></code></pre><p>That is, a leap year. The next two <code class="inline">trunc</code>-tests evaluate if the year is
│ │ │ │  divisible by 100 or 4 in the same way. The first <code class="inline">if</code> returns <code class="inline">leap</code> or
│ │ │ │  <code class="inline">not_leap</code>, which lands up in the variable <code class="inline">Leap</code>. This variable is used in the
│ │ │ │  guard for <code class="inline">feb</code> in the following <code class="inline">case</code> that tells us how long the month is.</p><p>This example showed the use of <code class="inline">trunc</code>. It is easier to use the Erlang operator
│ │ │ │  <code class="inline">rem</code> that gives the remainder after division, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">74&gt; </span><span class="mi">2004</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">400</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="mi">4</span></code></pre><p>So instead of writing:</p><pre><code class="makeup erlang" translate="no"><span class="nf">trunc</span><span class="p" data-group-id="4767131610-1">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="4767131610-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="mi">4</span></code></pre><p>So instead of writing:</p><pre><code class="makeup erlang" translate="no"><span class="nf">trunc</span><span class="p" data-group-id="7611619333-1">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="7611619333-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">leap</span><span class="p">;</span></code></pre><p>it can be written:</p><pre><code class="makeup erlang" translate="no"><span class="n">Year</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">leap</span><span class="p">;</span></code></pre><p>There are many other BIFs such as <code class="inline">trunc</code>. Only a few BIFs can be used in
│ │ │ │  guards, and you cannot use functions you have defined yourself in guards. (see
│ │ │ │  <a href="../../../lib/../system/doc/html/expressions.xhtml">Guard Sequences</a>) (For advanced readers: This is to
│ │ │ │  ensure that guards do not have side effects.) Let us play with a few of these
│ │ │ │ -functions in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">75&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="6418714502-1">(</span><span class="mf">5.6</span><span class="p" data-group-id="6418714502-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +functions in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">75&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="4010692871-1">(</span><span class="mf">5.6</span><span class="p" data-group-id="4010692871-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">5</span><span class="gp unselectable">
│ │ │ │ -76&gt; </span><span class="nf">round</span><span class="p" data-group-id="6418714502-2">(</span><span class="mf">5.6</span><span class="p" data-group-id="6418714502-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +76&gt; </span><span class="nf">round</span><span class="p" data-group-id="4010692871-2">(</span><span class="mf">5.6</span><span class="p" data-group-id="4010692871-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">6</span><span class="gp unselectable">
│ │ │ │ -77&gt; </span><span class="nf">length</span><span class="p" data-group-id="6418714502-3">(</span><span class="p" data-group-id="6418714502-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="6418714502-4">]</span><span class="p" data-group-id="6418714502-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +77&gt; </span><span class="nf">length</span><span class="p" data-group-id="4010692871-3">(</span><span class="p" data-group-id="4010692871-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="4010692871-4">]</span><span class="p" data-group-id="4010692871-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ │ -78&gt; </span><span class="nf">float</span><span class="p" data-group-id="6418714502-5">(</span><span class="mi">5</span><span class="p" data-group-id="6418714502-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +78&gt; </span><span class="nf">float</span><span class="p" data-group-id="4010692871-5">(</span><span class="mi">5</span><span class="p" data-group-id="4010692871-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">5.0</span><span class="gp unselectable">
│ │ │ │ -79&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="6418714502-6">(</span><span class="ss">hello</span><span class="p" data-group-id="6418714502-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +79&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="4010692871-6">(</span><span class="ss">hello</span><span class="p" data-group-id="4010692871-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -80&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="6418714502-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6418714502-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +80&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="4010692871-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4010692871-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ │ -81&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="6418714502-8">(</span><span class="p" data-group-id="6418714502-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6418714502-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="6418714502-10">}</span><span class="p" data-group-id="6418714502-9">}</span><span class="p" data-group-id="6418714502-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +81&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="4010692871-8">(</span><span class="p" data-group-id="4010692871-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4010692871-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="4010692871-10">}</span><span class="p" data-group-id="4010692871-9">}</span><span class="p" data-group-id="4010692871-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -82&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="6418714502-11">(</span><span class="p" data-group-id="6418714502-12">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6418714502-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="6418714502-13">}</span><span class="p" data-group-id="6418714502-12">]</span><span class="p" data-group-id="6418714502-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +82&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="4010692871-11">(</span><span class="p" data-group-id="4010692871-12">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4010692871-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="4010692871-13">}</span><span class="p" data-group-id="4010692871-12">]</span><span class="p" data-group-id="4010692871-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span></code></pre><p>All of these can be used in guards. Now for some BIFs that cannot be used in
│ │ │ │ -guards:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">83&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="6693808781-1">(</span><span class="ss">hello</span><span class="p" data-group-id="6693808781-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +guards:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">83&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="9119808480-1">(</span><span class="ss">hello</span><span class="p" data-group-id="9119808480-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;hello&quot;</span><span class="gp unselectable">
│ │ │ │ -84&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="6693808781-2">(</span><span class="s">&quot;goodbye&quot;</span><span class="p" data-group-id="6693808781-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +84&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="9119808480-2">(</span><span class="s">&quot;goodbye&quot;</span><span class="p" data-group-id="9119808480-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">goodbye</span><span class="gp unselectable">
│ │ │ │ -85&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="6693808781-3">(</span><span class="mi">22</span><span class="p" data-group-id="6693808781-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +85&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="9119808480-3">(</span><span class="mi">22</span><span class="p" data-group-id="9119808480-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;22&quot;</span></code></pre><p>These three BIFs do conversions that would be difficult (or impossible) to do in
│ │ │ │  Erlang.</p><h2 id="higher-order-functions-funs" class="section-heading">
│ │ │ │    <a href="#higher-order-functions-funs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Higher-Order Functions (Funs)</span>
│ │ │ │  </h2>
│ │ │ │  <p>Erlang, like most modern functional programming languages, has higher-order
│ │ │ │ -functions. Here is an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">86&gt; </span><span class="n">Xf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9036763721-1">(</span><span class="n">X</span><span class="p" data-group-id="9036763721-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +functions. Here is an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">86&gt; </span><span class="n">Xf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="7071637268-1">(</span><span class="n">X</span><span class="p" data-group-id="7071637268-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -87&gt; </span><span class="n">Xf</span><span class="p" data-group-id="9036763721-2">(</span><span class="mi">5</span><span class="p" data-group-id="9036763721-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +87&gt; </span><span class="n">Xf</span><span class="p" data-group-id="7071637268-2">(</span><span class="mi">5</span><span class="p" data-group-id="7071637268-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">10</span></code></pre><p>Here is defined a function that doubles the value of a number and assigned this
│ │ │ │  function to a variable. Thus <code class="inline">Xf(5)</code> returns value 10. Two useful functions when
│ │ │ │ -working with lists are <code class="inline">foreach</code> and <code class="inline">map</code>, which are defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="0828953885-1">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0828953885-2">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0828953885-2">]</span><span class="p" data-group-id="0828953885-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Fun</span><span class="p" data-group-id="0828953885-3">(</span><span class="n">First</span><span class="p" data-group-id="0828953885-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="0828953885-4">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0828953885-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="0828953885-5">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0828953885-6">[</span><span class="p" data-group-id="0828953885-6">]</span><span class="p" data-group-id="0828953885-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +working with lists are <code class="inline">foreach</code> and <code class="inline">map</code>, which are defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="5340072293-1">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5340072293-2">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="5340072293-2">]</span><span class="p" data-group-id="5340072293-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Fun</span><span class="p" data-group-id="5340072293-3">(</span><span class="n">First</span><span class="p" data-group-id="5340072293-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="5340072293-4">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="5340072293-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="5340072293-5">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5340072293-6">[</span><span class="p" data-group-id="5340072293-6">]</span><span class="p" data-group-id="5340072293-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="0828953885-7">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0828953885-8">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0828953885-8">]</span><span class="p" data-group-id="0828953885-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0828953885-9">[</span><span class="n">Fun</span><span class="p" data-group-id="0828953885-10">(</span><span class="n">First</span><span class="p" data-group-id="0828953885-10">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="0828953885-11">(</span><span class="n">Fun</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="0828953885-11">)</span><span class="p" data-group-id="0828953885-9">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="0828953885-12">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0828953885-13">[</span><span class="p" data-group-id="0828953885-13">]</span><span class="p" data-group-id="0828953885-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0828953885-14">[</span><span class="p" data-group-id="0828953885-14">]</span><span class="p">.</span></code></pre><p>These two functions are provided in the standard module <code class="inline">lists</code>. <code class="inline">foreach</code> takes
│ │ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="5340072293-7">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5340072293-8">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="5340072293-8">]</span><span class="p" data-group-id="5340072293-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5340072293-9">[</span><span class="n">Fun</span><span class="p" data-group-id="5340072293-10">(</span><span class="n">First</span><span class="p" data-group-id="5340072293-10">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="5340072293-11">(</span><span class="n">Fun</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="5340072293-11">)</span><span class="p" data-group-id="5340072293-9">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="5340072293-12">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5340072293-13">[</span><span class="p" data-group-id="5340072293-13">]</span><span class="p" data-group-id="5340072293-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5340072293-14">[</span><span class="p" data-group-id="5340072293-14">]</span><span class="p">.</span></code></pre><p>These two functions are provided in the standard module <code class="inline">lists</code>. <code class="inline">foreach</code> takes
│ │ │ │  a list and applies a fun to every element in the list. <code class="inline">map</code> creates a new list
│ │ │ │  by applying a fun to every element in a list. Going back to the shell, <code class="inline">map</code> is
│ │ │ │ -used and a fun to add 3 to every element of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">88&gt; </span><span class="n">Add_3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0005612056-1">(</span><span class="n">X</span><span class="p" data-group-id="0005612056-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +used and a fun to add 3 to every element of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">88&gt; </span><span class="n">Add_3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1636843327-1">(</span><span class="n">X</span><span class="p" data-group-id="1636843327-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -89&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0005612056-2">(</span><span class="n">Add_3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0005612056-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0005612056-3">]</span><span class="p" data-group-id="0005612056-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0005612056-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="0005612056-4">]</span></code></pre><p>Let us (again) print the temperatures in a list of cities:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">90&gt; </span><span class="n">Print_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="8095977932-1">(</span><span class="p" data-group-id="8095977932-2">{</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8095977932-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8095977932-3">}</span><span class="p" data-group-id="8095977932-2">}</span><span class="p" data-group-id="8095977932-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8095977932-4">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8095977932-5">[</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8095977932-5">]</span><span class="p" data-group-id="8095977932-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +89&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1636843327-2">(</span><span class="n">Add_3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1636843327-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1636843327-3">]</span><span class="p" data-group-id="1636843327-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1636843327-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1636843327-4">]</span></code></pre><p>Let us (again) print the temperatures in a list of cities:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">90&gt; </span><span class="n">Print_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4607771477-1">(</span><span class="p" data-group-id="4607771477-2">{</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4607771477-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4607771477-3">}</span><span class="p" data-group-id="4607771477-2">}</span><span class="p" data-group-id="4607771477-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4607771477-4">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4607771477-5">[</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4607771477-5">]</span><span class="p" data-group-id="4607771477-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -91&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="8095977932-6">(</span><span class="n">Print_City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8095977932-7">[</span><span class="p" data-group-id="8095977932-8">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8095977932-9">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8095977932-9">}</span><span class="p" data-group-id="8095977932-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8095977932-10">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8095977932-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="8095977932-11">}</span><span class="p" data-group-id="8095977932-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8095977932-12">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8095977932-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8095977932-13">}</span><span class="p" data-group-id="8095977932-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8095977932-14">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8095977932-15">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8095977932-15">}</span><span class="p" data-group-id="8095977932-14">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8095977932-16">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8095977932-17">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="8095977932-17">}</span><span class="p" data-group-id="8095977932-16">}</span><span class="p" data-group-id="8095977932-7">]</span><span class="p" data-group-id="8095977932-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +91&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="4607771477-6">(</span><span class="n">Print_City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4607771477-7">[</span><span class="p" data-group-id="4607771477-8">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4607771477-9">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4607771477-9">}</span><span class="p" data-group-id="4607771477-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4607771477-10">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4607771477-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4607771477-11">}</span><span class="p" data-group-id="4607771477-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4607771477-12">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4607771477-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4607771477-13">}</span><span class="p" data-group-id="4607771477-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4607771477-14">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4607771477-15">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4607771477-15">}</span><span class="p" data-group-id="4607771477-14">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4607771477-16">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4607771477-17">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4607771477-17">}</span><span class="p" data-group-id="4607771477-16">}</span><span class="p" data-group-id="4607771477-7">]</span><span class="p" data-group-id="4607771477-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="ss">c</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="w">
│ │ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="ss">f</span><span class="w"> </span><span class="mi">70</span><span class="w">
│ │ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="ss">c</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="ss">f</span><span class="w"> </span><span class="mi">28</span><span class="w">
│ │ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="ss">f</span><span class="w"> </span><span class="mi">36</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>Let us now define a fun that can be used to go through a list of cities and
│ │ │ │ -temperatures and transform them all to Celsius.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3925926763-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="3925926763-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +temperatures and transform them all to Celsius.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2810534311-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="2810534311-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3925926763-2">(</span><span class="p" data-group-id="3925926763-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3925926763-3">]</span><span class="p" data-group-id="3925926763-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2810534311-2">(</span><span class="p" data-group-id="2810534311-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2810534311-3">]</span><span class="p" data-group-id="2810534311-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="3925926763-4">(</span><span class="p" data-group-id="3925926763-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3925926763-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3925926763-6">}</span><span class="p" data-group-id="3925926763-5">}</span><span class="p" data-group-id="3925926763-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3925926763-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3925926763-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="3925926763-9">(</span><span class="p" data-group-id="3925926763-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="3925926763-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="3925926763-9">)</span><span class="p" data-group-id="3925926763-8">}</span><span class="p" data-group-id="3925926763-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="3925926763-11">(</span><span class="p" data-group-id="3925926763-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3925926763-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3925926763-13">}</span><span class="p" data-group-id="3925926763-12">}</span><span class="p" data-group-id="3925926763-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3925926763-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3925926763-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3925926763-15">}</span><span class="p" data-group-id="3925926763-14">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3925926763-16">(</span><span class="n">List</span><span class="p" data-group-id="3925926763-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="3925926763-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3925926763-17">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">92&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4450308817-1">(</span><span class="p" data-group-id="4450308817-2">[</span><span class="p" data-group-id="4450308817-3">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4450308817-4">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4450308817-4">}</span><span class="p" data-group-id="4450308817-3">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4450308817-5">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4450308817-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4450308817-6">}</span><span class="p" data-group-id="4450308817-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4450308817-7">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4450308817-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4450308817-8">}</span><span class="p" data-group-id="4450308817-7">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4450308817-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4450308817-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4450308817-10">}</span><span class="p" data-group-id="4450308817-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4450308817-11">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4450308817-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4450308817-12">}</span><span class="p" data-group-id="4450308817-11">}</span><span class="p" data-group-id="4450308817-2">]</span><span class="p" data-group-id="4450308817-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4450308817-13">[</span><span class="p" data-group-id="4450308817-14">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="4450308817-15">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4450308817-15">}</span><span class="p" data-group-id="4450308817-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4450308817-16">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="4450308817-17">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="4450308817-17">}</span><span class="p" data-group-id="4450308817-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4450308817-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="4450308817-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4450308817-19">}</span><span class="p" data-group-id="4450308817-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4450308817-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="4450308817-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="4450308817-21">}</span><span class="p" data-group-id="4450308817-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4450308817-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="4450308817-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4450308817-23">}</span><span class="p" data-group-id="4450308817-22">}</span><span class="p" data-group-id="4450308817-13">]</span></code></pre><p>The <code class="inline">convert_to_c</code> function is the same as before, but here it is used as a fun:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7098144127-1">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7098144127-1">)</span></code></pre><p>When a function defined elsewhere is used as a fun, it can be referred to as
│ │ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="2810534311-4">(</span><span class="p" data-group-id="2810534311-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2810534311-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2810534311-6">}</span><span class="p" data-group-id="2810534311-5">}</span><span class="p" data-group-id="2810534311-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2810534311-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2810534311-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="2810534311-9">(</span><span class="p" data-group-id="2810534311-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="2810534311-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="2810534311-9">)</span><span class="p" data-group-id="2810534311-8">}</span><span class="p" data-group-id="2810534311-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="2810534311-11">(</span><span class="p" data-group-id="2810534311-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2810534311-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2810534311-13">}</span><span class="p" data-group-id="2810534311-12">}</span><span class="p" data-group-id="2810534311-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2810534311-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2810534311-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2810534311-15">}</span><span class="p" data-group-id="2810534311-14">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2810534311-16">(</span><span class="n">List</span><span class="p" data-group-id="2810534311-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="2810534311-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="2810534311-17">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">92&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3645763090-1">(</span><span class="p" data-group-id="3645763090-2">[</span><span class="p" data-group-id="3645763090-3">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3645763090-4">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="3645763090-4">}</span><span class="p" data-group-id="3645763090-3">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3645763090-5">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3645763090-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="3645763090-6">}</span><span class="p" data-group-id="3645763090-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3645763090-7">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3645763090-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="3645763090-8">}</span><span class="p" data-group-id="3645763090-7">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3645763090-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3645763090-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="3645763090-10">}</span><span class="p" data-group-id="3645763090-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3645763090-11">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3645763090-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="3645763090-12">}</span><span class="p" data-group-id="3645763090-11">}</span><span class="p" data-group-id="3645763090-2">]</span><span class="p" data-group-id="3645763090-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3645763090-13">[</span><span class="p" data-group-id="3645763090-14">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="3645763090-15">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="3645763090-15">}</span><span class="p" data-group-id="3645763090-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3645763090-16">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="3645763090-17">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="3645763090-17">}</span><span class="p" data-group-id="3645763090-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3645763090-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="3645763090-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="3645763090-19">}</span><span class="p" data-group-id="3645763090-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3645763090-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="3645763090-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="3645763090-21">}</span><span class="p" data-group-id="3645763090-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3645763090-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="3645763090-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3645763090-23">}</span><span class="p" data-group-id="3645763090-22">}</span><span class="p" data-group-id="3645763090-13">]</span></code></pre><p>The <code class="inline">convert_to_c</code> function is the same as before, but here it is used as a fun:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="6620846337-1">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6620846337-1">)</span></code></pre><p>When a function defined elsewhere is used as a fun, it can be referred to as
│ │ │ │  <code class="inline">Function/Arity</code> (remember that <code class="inline">Arity</code> = number of arguments). So in the
│ │ │ │  <code class="inline">map</code>-call <code class="inline">lists:map(fun convert_to_c/1, List)</code> is written. As shown,
│ │ │ │  <code class="inline">convert_list_to_c</code> becomes much shorter and easier to understand.</p><p>The standard module <code class="inline">lists</code> also contains a function <code class="inline">sort(Fun, List)</code> where
│ │ │ │  <code class="inline">Fun</code> is a fun with two arguments. This fun returns <code class="inline">true</code> if the first argument
│ │ │ │  is less than the second argument, or else <code class="inline">false</code>. Sorting is added to the
│ │ │ │ -<code class="inline">convert_list_to_c</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1349772473-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="1349772473-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">convert_list_to_c</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7078838787-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="7078838787-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1349772473-2">(</span><span class="p" data-group-id="1349772473-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1349772473-3">]</span><span class="p" data-group-id="1349772473-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7078838787-2">(</span><span class="p" data-group-id="7078838787-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7078838787-3">]</span><span class="p" data-group-id="7078838787-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="1349772473-4">(</span><span class="p" data-group-id="1349772473-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1349772473-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1349772473-6">}</span><span class="p" data-group-id="1349772473-5">}</span><span class="p" data-group-id="1349772473-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1349772473-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1349772473-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="1349772473-9">(</span><span class="p" data-group-id="1349772473-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="1349772473-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1349772473-9">)</span><span class="p" data-group-id="1349772473-8">}</span><span class="p" data-group-id="1349772473-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="1349772473-11">(</span><span class="p" data-group-id="1349772473-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1349772473-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1349772473-13">}</span><span class="p" data-group-id="1349772473-12">}</span><span class="p" data-group-id="1349772473-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1349772473-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1349772473-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1349772473-15">}</span><span class="p" data-group-id="1349772473-14">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1349772473-16">(</span><span class="n">List</span><span class="p" data-group-id="1349772473-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">New_list</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1349772473-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1349772473-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="1349772473-18">(</span><span class="nf">fun</span><span class="p" data-group-id="1349772473-19">(</span><span class="p" data-group-id="1349772473-20">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1349772473-21">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="1349772473-21">}</span><span class="p" data-group-id="1349772473-20">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1349772473-22">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1349772473-23">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="1349772473-23">}</span><span class="p" data-group-id="1349772473-22">}</span><span class="p" data-group-id="1349772473-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                       </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">New_list</span><span class="p" data-group-id="1349772473-18">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">93&gt; </span><span class="nf">c</span><span class="p" data-group-id="8177117493-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="8177117493-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8177117493-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut13</span><span class="p" data-group-id="8177117493-2">}</span><span class="gp unselectable">
│ │ │ │ -94&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8177117493-3">(</span><span class="p" data-group-id="8177117493-4">[</span><span class="p" data-group-id="8177117493-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8177117493-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8177117493-6">}</span><span class="p" data-group-id="8177117493-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8177117493-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8177117493-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="8177117493-8">}</span><span class="p" data-group-id="8177117493-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8177117493-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8177117493-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8177117493-10">}</span><span class="p" data-group-id="8177117493-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8177117493-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8177117493-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8177117493-12">}</span><span class="p" data-group-id="8177117493-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8177117493-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8177117493-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="8177117493-14">}</span><span class="p" data-group-id="8177117493-13">}</span><span class="p" data-group-id="8177117493-4">]</span><span class="p" data-group-id="8177117493-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8177117493-15">[</span><span class="p" data-group-id="8177117493-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="8177117493-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8177117493-17">}</span><span class="p" data-group-id="8177117493-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8177117493-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="8177117493-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8177117493-19">}</span><span class="p" data-group-id="8177117493-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8177117493-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="8177117493-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="8177117493-21">}</span><span class="p" data-group-id="8177117493-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8177117493-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="8177117493-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8177117493-23">}</span><span class="p" data-group-id="8177117493-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8177117493-24">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="8177117493-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="8177117493-25">}</span><span class="p" data-group-id="8177117493-24">}</span><span class="p" data-group-id="8177117493-15">]</span></code></pre><p>In <code class="inline">sort</code> the fun is used:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="p" data-group-id="6732995249-1">(</span><span class="p" data-group-id="6732995249-2">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6732995249-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="6732995249-3">}</span><span class="p" data-group-id="6732995249-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6732995249-4">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6732995249-5">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="6732995249-5">}</span><span class="p" data-group-id="6732995249-4">}</span><span class="p" data-group-id="6732995249-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span></code></pre><p>Here the concept of an <em>anonymous variable</em> <code class="inline">_</code> is introduced. This is simply
│ │ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="7078838787-4">(</span><span class="p" data-group-id="7078838787-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7078838787-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7078838787-6">}</span><span class="p" data-group-id="7078838787-5">}</span><span class="p" data-group-id="7078838787-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7078838787-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7078838787-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="7078838787-9">(</span><span class="p" data-group-id="7078838787-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="7078838787-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="7078838787-9">)</span><span class="p" data-group-id="7078838787-8">}</span><span class="p" data-group-id="7078838787-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="7078838787-11">(</span><span class="p" data-group-id="7078838787-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7078838787-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7078838787-13">}</span><span class="p" data-group-id="7078838787-12">}</span><span class="p" data-group-id="7078838787-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7078838787-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7078838787-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7078838787-15">}</span><span class="p" data-group-id="7078838787-14">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7078838787-16">(</span><span class="n">List</span><span class="p" data-group-id="7078838787-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">New_list</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7078838787-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7078838787-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="7078838787-18">(</span><span class="nf">fun</span><span class="p" data-group-id="7078838787-19">(</span><span class="p" data-group-id="7078838787-20">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7078838787-21">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="7078838787-21">}</span><span class="p" data-group-id="7078838787-20">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7078838787-22">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7078838787-23">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="7078838787-23">}</span><span class="p" data-group-id="7078838787-22">}</span><span class="p" data-group-id="7078838787-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                       </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">New_list</span><span class="p" data-group-id="7078838787-18">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">93&gt; </span><span class="nf">c</span><span class="p" data-group-id="2493858132-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="2493858132-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2493858132-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut13</span><span class="p" data-group-id="2493858132-2">}</span><span class="gp unselectable">
│ │ │ │ +94&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2493858132-3">(</span><span class="p" data-group-id="2493858132-4">[</span><span class="p" data-group-id="2493858132-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2493858132-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2493858132-6">}</span><span class="p" data-group-id="2493858132-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2493858132-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2493858132-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="2493858132-8">}</span><span class="p" data-group-id="2493858132-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2493858132-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2493858132-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2493858132-10">}</span><span class="p" data-group-id="2493858132-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2493858132-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2493858132-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="2493858132-12">}</span><span class="p" data-group-id="2493858132-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2493858132-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2493858132-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="2493858132-14">}</span><span class="p" data-group-id="2493858132-13">}</span><span class="p" data-group-id="2493858132-4">]</span><span class="p" data-group-id="2493858132-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2493858132-15">[</span><span class="p" data-group-id="2493858132-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="2493858132-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2493858132-17">}</span><span class="p" data-group-id="2493858132-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2493858132-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="2493858132-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2493858132-19">}</span><span class="p" data-group-id="2493858132-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2493858132-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="2493858132-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="2493858132-21">}</span><span class="p" data-group-id="2493858132-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2493858132-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="2493858132-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2493858132-23">}</span><span class="p" data-group-id="2493858132-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2493858132-24">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="2493858132-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="2493858132-25">}</span><span class="p" data-group-id="2493858132-24">}</span><span class="p" data-group-id="2493858132-15">]</span></code></pre><p>In <code class="inline">sort</code> the fun is used:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="p" data-group-id="4557677478-1">(</span><span class="p" data-group-id="4557677478-2">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4557677478-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="4557677478-3">}</span><span class="p" data-group-id="4557677478-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4557677478-4">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4557677478-5">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="4557677478-5">}</span><span class="p" data-group-id="4557677478-4">}</span><span class="p" data-group-id="4557677478-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span></code></pre><p>Here the concept of an <em>anonymous variable</em> <code class="inline">_</code> is introduced. This is simply
│ │ │ │  shorthand for a variable that gets a value, but the value is ignored. This can
│ │ │ │  be used anywhere suitable, not just in funs. <code class="inline">Temp1 &lt; Temp2</code> returns <code class="inline">true</code> if
│ │ │ │  <code class="inline">Temp1</code> is less than <code class="inline">Temp2</code>.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/robustness.xhtml
│ │ │ │ @@ -33,68 +33,68 @@
│ │ │ │  </h2>
│ │ │ │  <p>Before improving the messenger program, let us look at some general principles,
│ │ │ │  using the ping pong program as an example. Recall that when &quot;ping&quot; finishes, it
│ │ │ │  tells &quot;pong&quot; that it has done so by sending the atom <code class="inline">finished</code> as a message to
│ │ │ │  &quot;pong&quot; so that &quot;pong&quot; can also finish. Another way to let &quot;pong&quot; finish is to
│ │ │ │  make &quot;pong&quot; exit if it does not receive a message from ping within a certain
│ │ │ │  time. This can be done by adding a <em>time-out</em> to <code class="inline">pong</code> as shown in the
│ │ │ │ -following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9033769991-1">(</span><span class="ss">tut19</span><span class="p" data-group-id="9033769991-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4364583899-1">(</span><span class="ss">tut19</span><span class="p" data-group-id="4364583899-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9033769991-2">(</span><span class="p" data-group-id="9033769991-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9033769991-3">]</span><span class="p" data-group-id="9033769991-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4364583899-2">(</span><span class="p" data-group-id="4364583899-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4364583899-3">]</span><span class="p" data-group-id="4364583899-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="9033769991-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9033769991-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9033769991-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9033769991-6">[</span><span class="p" data-group-id="9033769991-6">]</span><span class="p" data-group-id="9033769991-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="4364583899-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="4364583899-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4364583899-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4364583899-6">[</span><span class="p" data-group-id="4364583899-6">]</span><span class="p" data-group-id="4364583899-5">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="9033769991-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9033769991-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9033769991-8">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9033769991-8">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9033769991-9">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9033769991-10">(</span><span class="p" data-group-id="9033769991-10">)</span><span class="p" data-group-id="9033769991-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="4364583899-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="4364583899-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4364583899-8">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="4364583899-8">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4364583899-9">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4364583899-10">(</span><span class="p" data-group-id="4364583899-10">)</span><span class="p" data-group-id="4364583899-9">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9033769991-11">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9033769991-12">[</span><span class="p" data-group-id="9033769991-12">]</span><span class="p" data-group-id="9033769991-11">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4364583899-11">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4364583899-12">[</span><span class="p" data-group-id="4364583899-12">]</span><span class="p" data-group-id="4364583899-11">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="9033769991-13">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9033769991-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="4364583899-13">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="4364583899-13">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="9033769991-14">(</span><span class="p" data-group-id="9033769991-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="4364583899-14">(</span><span class="p" data-group-id="4364583899-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9033769991-15">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9033769991-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9033769991-16">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9033769991-17">[</span><span class="p" data-group-id="9033769991-17">]</span><span class="p" data-group-id="9033769991-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4364583899-15">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="4364583899-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4364583899-16">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4364583899-17">[</span><span class="p" data-group-id="4364583899-17">]</span><span class="p" data-group-id="4364583899-16">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="9033769991-18">(</span><span class="p" data-group-id="9033769991-18">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="4364583899-18">(</span><span class="p" data-group-id="4364583899-18">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9033769991-19">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9033769991-20">[</span><span class="p" data-group-id="9033769991-20">]</span><span class="p" data-group-id="9033769991-19">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4364583899-19">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4364583899-20">[</span><span class="p" data-group-id="4364583899-20">]</span><span class="p" data-group-id="4364583899-19">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_pong</span><span class="p" data-group-id="9033769991-21">(</span><span class="p" data-group-id="9033769991-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9033769991-22">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9033769991-23">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9033769991-24">[</span><span class="p" data-group-id="9033769991-24">]</span><span class="p" data-group-id="9033769991-23">)</span><span class="p" data-group-id="9033769991-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_pong</span><span class="p" data-group-id="4364583899-21">(</span><span class="p" data-group-id="4364583899-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="4364583899-22">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="4364583899-23">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4364583899-24">[</span><span class="p" data-group-id="4364583899-24">]</span><span class="p" data-group-id="4364583899-23">)</span><span class="p" data-group-id="4364583899-22">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_ping</span><span class="p" data-group-id="9033769991-25">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="9033769991-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9033769991-26">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9033769991-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9033769991-27">]</span><span class="p" data-group-id="9033769991-26">)</span><span class="p">.</span></code></pre><p>After this is compiled and the file <code class="inline">tut19.beam</code> is copied to the necessary
│ │ │ │ +</span><span class="nf">start_ping</span><span class="p" data-group-id="4364583899-25">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="4364583899-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="4364583899-26">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4364583899-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="4364583899-27">]</span><span class="p" data-group-id="4364583899-26">)</span><span class="p">.</span></code></pre><p>After this is compiled and the file <code class="inline">tut19.beam</code> is copied to the necessary
│ │ │ │  directories, the following is seen on (pong@kosken):</p><pre><code class="text">(pong@kosken)1&gt; tut19:start_pong().
│ │ │ │  true
│ │ │ │  Pong received ping
│ │ │ │  Pong received ping
│ │ │ │  Pong received ping
│ │ │ │  Pong timed out</code></pre><p>And the following is seen on (ping@gollum):</p><pre><code class="text">(ping@gollum)1&gt; tut19:start_ping(pong@kosken).
│ │ │ │  &lt;0.36.0&gt;
│ │ │ │  Ping received pong
│ │ │ │  Ping received pong
│ │ │ │  Ping received pong
│ │ │ │ -ping finished</code></pre><p>The time-out is set in:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pong</span><span class="p" data-group-id="3272688011-1">(</span><span class="p" data-group-id="3272688011-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +ping finished</code></pre><p>The time-out is set in:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pong</span><span class="p" data-group-id="4529052405-1">(</span><span class="p" data-group-id="4529052405-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="3272688011-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="3272688011-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3272688011-3">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3272688011-4">[</span><span class="p" data-group-id="3272688011-4">]</span><span class="p" data-group-id="3272688011-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4529052405-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="4529052405-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4529052405-3">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4529052405-4">[</span><span class="p" data-group-id="4529052405-4">]</span><span class="p" data-group-id="4529052405-3">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="3272688011-5">(</span><span class="p" data-group-id="3272688011-5">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="4529052405-5">(</span><span class="p" data-group-id="4529052405-5">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3272688011-6">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3272688011-7">[</span><span class="p" data-group-id="3272688011-7">]</span><span class="p" data-group-id="3272688011-6">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4529052405-6">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4529052405-7">[</span><span class="p" data-group-id="4529052405-7">]</span><span class="p" data-group-id="4529052405-6">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The time-out (<code class="inline">after 5000</code>) is started when <code class="inline">receive</code> is entered. The time-out
│ │ │ │  is canceled if <code class="inline">{ping,Ping_PID}</code> is received. If <code class="inline">{ping,Ping_PID}</code> is not
│ │ │ │  received, the actions following the time-out are done after 5000 milliseconds.
│ │ │ │  <code class="inline">after</code> must be last in the <code class="inline">receive</code>, that is, preceded by all other message
│ │ │ │  reception specifications in the <code class="inline">receive</code>. It is also possible to call a
│ │ │ │ -function that returned an integer for the time-out:</p><pre><code class="makeup erlang" translate="no"><span class="k">after</span><span class="w"> </span><span class="nf">pong_timeout</span><span class="p" data-group-id="4745624849-1">(</span><span class="p" data-group-id="4745624849-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>In general, there are better ways than using time-outs to supervise parts of a
│ │ │ │ +function that returned an integer for the time-out:</p><pre><code class="makeup erlang" translate="no"><span class="k">after</span><span class="w"> </span><span class="nf">pong_timeout</span><span class="p" data-group-id="2110794383-1">(</span><span class="p" data-group-id="2110794383-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>In general, there are better ways than using time-outs to supervise parts of a
│ │ │ │  distributed Erlang system. Time-outs are usually appropriate to supervise
│ │ │ │  external events, for example, if you have expected a message from some external
│ │ │ │  system within a specified time. For example, a time-out can be used to log a
│ │ │ │  user out of the messenger system if they have not accessed it for, say, ten
│ │ │ │  minutes.</p><h2 id="error-handling" class="section-heading">
│ │ │ │    <a href="#error-handling" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -114,96 +114,96 @@
│ │ │ │  something called a <em>signal</em> to all the processes it has links to.</p><p>The signal carries information about the pid it was sent from and the exit
│ │ │ │  reason.</p><p>The default behaviour of a process that receives a normal exit is to ignore the
│ │ │ │  signal.</p><p>The default behaviour in the two other cases (that is, abnormal exit) above is
│ │ │ │  to:</p><ul><li>Bypass all messages to the receiving process.</li><li>Kill the receiving process.</li><li>Propagate the same error signal to the links of the killed process.</li></ul><p>In this way you can connect all processes in a transaction together using links.
│ │ │ │  If one of the processes exits abnormally, all the processes in the transaction
│ │ │ │  are killed. As it is often wanted to create a process and link to it at the same
│ │ │ │  time, there is a special BIF, <a href="../../../lib/../erts/doc/html/erlang.html#spawn_link/1">spawn_link</a> that does the
│ │ │ │ -same as <code class="inline">spawn</code>, but also creates a link to the spawned process.</p><p>Now an example of the ping pong example using links to terminate &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8750202671-1">(</span><span class="ss">tut20</span><span class="p" data-group-id="8750202671-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +same as <code class="inline">spawn</code>, but also creates a link to the spawned process.</p><p>Now an example of the ping pong example using links to terminate &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9985232346-1">(</span><span class="ss">tut20</span><span class="p" data-group-id="9985232346-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8750202671-2">(</span><span class="p" data-group-id="8750202671-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8750202671-3">]</span><span class="p" data-group-id="8750202671-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9985232346-2">(</span><span class="p" data-group-id="9985232346-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9985232346-3">]</span><span class="p" data-group-id="9985232346-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="8750202671-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="8750202671-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">link</span><span class="p" data-group-id="8750202671-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="8750202671-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="8750202671-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="8750202671-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="9985232346-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="9985232346-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">link</span><span class="p" data-group-id="9985232346-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="9985232346-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="9985232346-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="9985232346-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="8750202671-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="8750202671-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="8750202671-8">(</span><span class="ss">ping</span><span class="p" data-group-id="8750202671-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="9985232346-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9985232346-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="9985232346-8">(</span><span class="ss">ping</span><span class="p" data-group-id="9985232346-8">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="8750202671-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="8750202671-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8750202671-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8750202671-11">(</span><span class="p" data-group-id="8750202671-11">)</span><span class="p" data-group-id="8750202671-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="9985232346-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="9985232346-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9985232346-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9985232346-11">(</span><span class="p" data-group-id="9985232346-11">)</span><span class="p" data-group-id="9985232346-10">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8750202671-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8750202671-13">[</span><span class="p" data-group-id="8750202671-13">]</span><span class="p" data-group-id="8750202671-12">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9985232346-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9985232346-13">[</span><span class="p" data-group-id="9985232346-13">]</span><span class="p" data-group-id="9985232346-12">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="8750202671-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="8750202671-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="9985232346-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="9985232346-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="8750202671-15">(</span><span class="p" data-group-id="8750202671-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="9985232346-15">(</span><span class="p" data-group-id="9985232346-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8750202671-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="8750202671-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8750202671-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8750202671-18">[</span><span class="p" data-group-id="8750202671-18">]</span><span class="p" data-group-id="8750202671-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9985232346-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9985232346-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9985232346-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9985232346-18">[</span><span class="p" data-group-id="9985232346-18">]</span><span class="p" data-group-id="9985232346-17">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="8750202671-19">(</span><span class="p" data-group-id="8750202671-19">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="9985232346-19">(</span><span class="p" data-group-id="9985232346-19">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="8750202671-20">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="8750202671-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="8750202671-21">(</span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8750202671-22">[</span><span class="p" data-group-id="8750202671-22">]</span><span class="p" data-group-id="8750202671-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="8750202671-23">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8750202671-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="8750202671-24">]</span><span class="p" data-group-id="8750202671-23">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)3&gt; tut20:start(s2@kosken).
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="9985232346-20">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="9985232346-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9985232346-21">(</span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9985232346-22">[</span><span class="p" data-group-id="9985232346-22">]</span><span class="p" data-group-id="9985232346-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9985232346-23">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9985232346-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="9985232346-24">]</span><span class="p" data-group-id="9985232346-23">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)3&gt; tut20:start(s2@kosken).
│ │ │ │  Pong received ping
│ │ │ │  &lt;3820.41.0&gt;
│ │ │ │  Ping received pong
│ │ │ │  Pong received ping
│ │ │ │  Ping received pong
│ │ │ │  Pong received ping
│ │ │ │  Ping received pong</code></pre><p>This is a slight modification of the ping pong program where both processes are
│ │ │ │  spawned from the same <code class="inline">start/1</code> function, and the &quot;ping&quot; process can be spawned
│ │ │ │  on a separate node. Notice the use of the <code class="inline">link</code> BIF. &quot;Ping&quot; calls
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit(ping)</code></a> when it finishes and this causes an exit signal to be
│ │ │ │  sent to &quot;pong&quot;, which also terminates.</p><p>It is possible to modify the default behaviour of a process so that it does not
│ │ │ │  get killed when it receives abnormal exit signals. Instead, all signals are
│ │ │ │  turned into normal messages on the format <code class="inline">{'EXIT',FromPID,Reason}</code> and added to
│ │ │ │ -the end of the receiving process' message queue. This behaviour is set by:</p><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="5740739689-1">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5740739689-1">)</span></code></pre><p>There are several other process flags, see <a href="../../../lib/../erts/doc/html/erlang.html#process_flag/2">erlang(3)</a>.
│ │ │ │ +the end of the receiving process' message queue. This behaviour is set by:</p><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="9190320026-1">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9190320026-1">)</span></code></pre><p>There are several other process flags, see <a href="../../../lib/../erts/doc/html/erlang.html#process_flag/2">erlang(3)</a>.
│ │ │ │  Changing the default behaviour of a process in this way is usually not done in
│ │ │ │  standard user programs, but is left to the supervisory programs in OTP. However,
│ │ │ │ -the ping pong program is modified to illustrate exit trapping.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5120741542-1">(</span><span class="ss">tut21</span><span class="p" data-group-id="5120741542-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the ping pong program is modified to illustrate exit trapping.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3917395905-1">(</span><span class="ss">tut21</span><span class="p" data-group-id="3917395905-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5120741542-2">(</span><span class="p" data-group-id="5120741542-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5120741542-3">]</span><span class="p" data-group-id="5120741542-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3917395905-2">(</span><span class="p" data-group-id="3917395905-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3917395905-3">]</span><span class="p" data-group-id="3917395905-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="5120741542-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="5120741542-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">link</span><span class="p" data-group-id="5120741542-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="5120741542-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="5120741542-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="5120741542-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="3917395905-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="3917395905-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">link</span><span class="p" data-group-id="3917395905-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="3917395905-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="3917395905-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="3917395905-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="5120741542-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="5120741542-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="5120741542-8">(</span><span class="ss">ping</span><span class="p" data-group-id="5120741542-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="3917395905-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3917395905-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="3917395905-8">(</span><span class="ss">ping</span><span class="p" data-group-id="3917395905-8">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="5120741542-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="5120741542-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5120741542-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5120741542-11">(</span><span class="p" data-group-id="5120741542-11">)</span><span class="p" data-group-id="5120741542-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="3917395905-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="3917395905-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3917395905-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3917395905-11">(</span><span class="p" data-group-id="3917395905-11">)</span><span class="p" data-group-id="3917395905-10">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5120741542-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5120741542-13">[</span><span class="p" data-group-id="5120741542-13">]</span><span class="p" data-group-id="5120741542-12">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3917395905-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3917395905-13">[</span><span class="p" data-group-id="3917395905-13">]</span><span class="p" data-group-id="3917395905-12">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="5120741542-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="5120741542-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="3917395905-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="3917395905-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="5120741542-15">(</span><span class="p" data-group-id="5120741542-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="5120741542-16">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5120741542-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">pong1</span><span class="p" data-group-id="5120741542-17">(</span><span class="p" data-group-id="5120741542-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="3917395905-15">(</span><span class="p" data-group-id="3917395905-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="3917395905-16">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="3917395905-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">pong1</span><span class="p" data-group-id="3917395905-17">(</span><span class="p" data-group-id="3917395905-17">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong1</span><span class="p" data-group-id="5120741542-18">(</span><span class="p" data-group-id="5120741542-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong1</span><span class="p" data-group-id="3917395905-18">(</span><span class="p" data-group-id="3917395905-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="5120741542-19">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="5120741542-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5120741542-20">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5120741542-21">[</span><span class="p" data-group-id="5120741542-21">]</span><span class="p" data-group-id="5120741542-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3917395905-19">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="3917395905-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3917395905-20">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3917395905-21">[</span><span class="p" data-group-id="3917395905-21">]</span><span class="p" data-group-id="3917395905-20">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong1</span><span class="p" data-group-id="5120741542-22">(</span><span class="p" data-group-id="5120741542-22">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="5120741542-23">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5120741542-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5120741542-24">(</span><span class="s">&quot;pong exiting, got </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5120741542-25">[</span><span class="p" data-group-id="5120741542-26">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5120741542-26">}</span><span class="p" data-group-id="5120741542-25">]</span><span class="p" data-group-id="5120741542-24">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong1</span><span class="p" data-group-id="3917395905-22">(</span><span class="p" data-group-id="3917395905-22">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3917395905-23">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="3917395905-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3917395905-24">(</span><span class="s">&quot;pong exiting, got </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3917395905-25">[</span><span class="p" data-group-id="3917395905-26">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="3917395905-26">}</span><span class="p" data-group-id="3917395905-25">]</span><span class="p" data-group-id="3917395905-24">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="5120741542-27">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="5120741542-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="5120741542-28">(</span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5120741542-29">[</span><span class="p" data-group-id="5120741542-29">]</span><span class="p" data-group-id="5120741542-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="5120741542-30">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5120741542-31">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="5120741542-31">]</span><span class="p" data-group-id="5120741542-30">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)1&gt; tut21:start(s2@gollum).
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="3917395905-27">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="3917395905-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="3917395905-28">(</span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3917395905-29">[</span><span class="p" data-group-id="3917395905-29">]</span><span class="p" data-group-id="3917395905-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="3917395905-30">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3917395905-31">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="3917395905-31">]</span><span class="p" data-group-id="3917395905-30">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)1&gt; tut21:start(s2@gollum).
│ │ │ │  &lt;3820.39.0&gt;
│ │ │ │  Pong received ping
│ │ │ │  Ping received pong
│ │ │ │  Pong received ping
│ │ │ │  Ping received pong
│ │ │ │  Pong received ping
│ │ │ │  Ping received pong
│ │ │ │ @@ -256,135 +256,135 @@
│ │ │ │  </span><span class="c1">%%% Started: messenger:client(Server_Node, Name)</span><span class="w">
│ │ │ │  </span><span class="c1">%%% To client: logoff</span><span class="w">
│ │ │ │  </span><span class="c1">%%% To client: {message_to, ToName, Message}</span><span class="w">
│ │ │ │  </span><span class="c1">%%%</span><span class="w">
│ │ │ │  </span><span class="c1">%%% Configuration: change the server_node() function to return the</span><span class="w">
│ │ │ │  </span><span class="c1">%%% name of the node where the messenger server runs</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7225610988-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="7225610988-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7225610988-2">(</span><span class="p" data-group-id="7225610988-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7225610988-3">]</span><span class="p" data-group-id="7225610988-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0029906099-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="0029906099-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0029906099-2">(</span><span class="p" data-group-id="0029906099-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0029906099-3">]</span><span class="p" data-group-id="0029906099-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Change the function below to return the name of the node where the</span><span class="w">
│ │ │ │  </span><span class="c1">%%% messenger server runs</span><span class="w">
│ │ │ │ -</span><span class="nf">server_node</span><span class="p" data-group-id="7225610988-4">(</span><span class="p" data-group-id="7225610988-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_node</span><span class="p" data-group-id="0029906099-4">(</span><span class="p" data-group-id="0029906099-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">messenger@super</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% This is the server process for the &quot;messenger&quot;</span><span class="w">
│ │ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="7225610988-5">(</span><span class="p" data-group-id="7225610988-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="7225610988-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7225610988-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="7225610988-7">(</span><span class="p" data-group-id="7225610988-8">[</span><span class="p" data-group-id="7225610988-8">]</span><span class="p" data-group-id="7225610988-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="0029906099-5">(</span><span class="p" data-group-id="0029906099-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="0029906099-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0029906099-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="0029906099-7">(</span><span class="p" data-group-id="0029906099-8">[</span><span class="p" data-group-id="0029906099-8">]</span><span class="p" data-group-id="0029906099-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="7225610988-9">(</span><span class="n">User_List</span><span class="p" data-group-id="7225610988-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="0029906099-9">(</span><span class="n">User_List</span><span class="p" data-group-id="0029906099-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7225610988-10">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7225610988-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="7225610988-11">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="7225610988-12">(</span><span class="n">New_User_List</span><span class="p" data-group-id="7225610988-12">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7225610988-13">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7225610988-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="7225610988-14">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="7225610988-15">(</span><span class="n">New_User_List</span><span class="p" data-group-id="7225610988-15">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7225610988-16">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7225610988-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="7225610988-17">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7225610988-18">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7225610988-19">[</span><span class="n">User_List</span><span class="p" data-group-id="7225610988-19">]</span><span class="p" data-group-id="7225610988-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="7225610988-20">(</span><span class="n">User_List</span><span class="p" data-group-id="7225610988-20">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0029906099-10">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0029906099-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="0029906099-11">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="0029906099-12">(</span><span class="n">New_User_List</span><span class="p" data-group-id="0029906099-12">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0029906099-13">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="0029906099-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="0029906099-14">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="0029906099-15">(</span><span class="n">New_User_List</span><span class="p" data-group-id="0029906099-15">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0029906099-16">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0029906099-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="0029906099-17">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0029906099-18">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0029906099-19">[</span><span class="n">User_List</span><span class="p" data-group-id="0029906099-19">]</span><span class="p" data-group-id="0029906099-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="0029906099-20">(</span><span class="n">User_List</span><span class="p" data-group-id="0029906099-20">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="7225610988-21">(</span><span class="p" data-group-id="7225610988-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="7225610988-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7225610988-23">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7225610988-24">[</span><span class="p" data-group-id="7225610988-24">]</span><span class="p" data-group-id="7225610988-23">)</span><span class="p" data-group-id="7225610988-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="0029906099-21">(</span><span class="p" data-group-id="0029906099-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="0029906099-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0029906099-23">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0029906099-24">[</span><span class="p" data-group-id="0029906099-24">]</span><span class="p" data-group-id="0029906099-23">)</span><span class="p" data-group-id="0029906099-22">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="7225610988-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="0029906099-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="7225610988-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="0029906099-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7225610988-27">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="7225610988-27">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0029906099-27">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="0029906099-27">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7225610988-28">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="7225610988-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">link</span><span class="p" data-group-id="7225610988-29">(</span><span class="n">From</span><span class="p" data-group-id="7225610988-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="7225610988-30">[</span><span class="p" data-group-id="7225610988-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7225610988-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0029906099-28">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="0029906099-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">link</span><span class="p" data-group-id="0029906099-29">(</span><span class="n">From</span><span class="p" data-group-id="0029906099-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="0029906099-30">[</span><span class="p" data-group-id="0029906099-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0029906099-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="7225610988-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="7225610988-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-33">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="0029906099-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="0029906099-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-33">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="7225610988-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="0029906099-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="7225610988-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="0029906099-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7225610988-36">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="7225610988-36">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7225610988-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7225610988-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7225610988-38">}</span><span class="p" data-group-id="7225610988-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="7225610988-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-39">)</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0029906099-36">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="0029906099-36">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0029906099-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0029906099-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0029906099-38">}</span><span class="p" data-group-id="0029906099-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="0029906099-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-39">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="7225610988-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="0029906099-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="7225610988-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7225610988-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="0029906099-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0029906099-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7225610988-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="7225610988-42">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7225610988-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7225610988-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="7225610988-44">}</span><span class="p" data-group-id="7225610988-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7225610988-45">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7225610988-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7225610988-46">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="7225610988-46">}</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0029906099-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="0029906099-42">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0029906099-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0029906099-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="0029906099-44">}</span><span class="p" data-group-id="0029906099-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0029906099-45">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0029906099-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0029906099-46">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="0029906099-46">}</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% User Commands</span><span class="w">
│ │ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="7225610988-47">(</span><span class="n">Name</span><span class="p" data-group-id="7225610988-47">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="7225610988-48">(</span><span class="ss">mess_client</span><span class="p" data-group-id="7225610988-48">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="0029906099-47">(</span><span class="n">Name</span><span class="p" data-group-id="0029906099-47">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="0029906099-48">(</span><span class="ss">mess_client</span><span class="p" data-group-id="0029906099-48">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="7225610988-49">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="7225610988-50">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7225610988-51">[</span><span class="nf">server_node</span><span class="p" data-group-id="7225610988-52">(</span><span class="p" data-group-id="7225610988-52">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7225610988-51">]</span><span class="p" data-group-id="7225610988-50">)</span><span class="p" data-group-id="7225610988-49">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="0029906099-49">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="0029906099-50">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0029906099-51">[</span><span class="nf">server_node</span><span class="p" data-group-id="0029906099-52">(</span><span class="p" data-group-id="0029906099-52">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0029906099-51">]</span><span class="p" data-group-id="0029906099-50">)</span><span class="p" data-group-id="0029906099-49">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="7225610988-53">(</span><span class="p" data-group-id="7225610988-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="0029906099-53">(</span><span class="p" data-group-id="0029906099-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="7225610988-54">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7225610988-54">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="7225610988-55">(</span><span class="ss">mess_client</span><span class="p" data-group-id="7225610988-55">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="0029906099-54">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0029906099-54">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="0029906099-55">(</span><span class="ss">mess_client</span><span class="p" data-group-id="0029906099-55">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7225610988-56">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7225610988-56">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0029906099-56">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0029906099-56">}</span><span class="p">,</span><span class="w">
│ │ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% The client process which runs on each user node</span><span class="w">
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="7225610988-57">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7225610988-57">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7225610988-58">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="7225610988-58">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7225610988-59">{</span><span class="nf">self</span><span class="p" data-group-id="7225610988-60">(</span><span class="p" data-group-id="7225610988-60">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7225610988-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="7225610988-61">(</span><span class="p" data-group-id="7225610988-61">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="7225610988-62">(</span><span class="n">Server_Node</span><span class="p" data-group-id="7225610988-62">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="0029906099-57">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0029906099-57">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0029906099-58">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="0029906099-58">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0029906099-59">{</span><span class="nf">self</span><span class="p" data-group-id="0029906099-60">(</span><span class="p" data-group-id="0029906099-60">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0029906099-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="0029906099-61">(</span><span class="p" data-group-id="0029906099-61">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="0029906099-62">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0029906099-62">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="7225610988-63">(</span><span class="n">Server_Node</span><span class="p" data-group-id="7225610988-63">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="0029906099-63">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0029906099-63">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="7225610988-64">(</span><span class="ss">normal</span><span class="p" data-group-id="7225610988-64">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7225610988-65">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7225610988-65">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="7225610988-66">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="7225610988-66">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7225610988-67">{</span><span class="nf">self</span><span class="p" data-group-id="7225610988-68">(</span><span class="p" data-group-id="7225610988-68">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7225610988-67">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="7225610988-69">(</span><span class="p" data-group-id="7225610988-69">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7225610988-70">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7225610988-70">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7225610988-71">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7225610988-72">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7225610988-72">]</span><span class="p" data-group-id="7225610988-71">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="0029906099-64">(</span><span class="ss">normal</span><span class="p" data-group-id="0029906099-64">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0029906099-65">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0029906099-65">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="0029906099-66">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="0029906099-66">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0029906099-67">{</span><span class="nf">self</span><span class="p" data-group-id="0029906099-68">(</span><span class="p" data-group-id="0029906099-68">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0029906099-67">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="0029906099-69">(</span><span class="p" data-group-id="0029906099-69">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0029906099-70">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0029906099-70">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0029906099-71">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0029906099-72">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0029906099-72">]</span><span class="p" data-group-id="0029906099-71">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="7225610988-73">(</span><span class="n">Server_Node</span><span class="p" data-group-id="7225610988-73">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="0029906099-73">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0029906099-73">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="7225610988-74">(</span><span class="p" data-group-id="7225610988-74">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="0029906099-74">(</span><span class="p" data-group-id="0029906099-74">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7225610988-75">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="7225610988-75">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7225610988-76">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7225610988-77">[</span><span class="n">Why</span><span class="p" data-group-id="7225610988-77">]</span><span class="p" data-group-id="7225610988-76">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="7225610988-78">(</span><span class="ss">normal</span><span class="p" data-group-id="7225610988-78">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7225610988-79">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="7225610988-79">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7225610988-80">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7225610988-81">[</span><span class="n">What</span><span class="p" data-group-id="7225610988-81">]</span><span class="p" data-group-id="7225610988-80">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0029906099-75">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="0029906099-75">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0029906099-76">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0029906099-77">[</span><span class="n">Why</span><span class="p" data-group-id="0029906099-77">]</span><span class="p" data-group-id="0029906099-76">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="0029906099-78">(</span><span class="ss">normal</span><span class="p" data-group-id="0029906099-78">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0029906099-79">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="0029906099-79">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0029906099-80">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0029906099-81">[</span><span class="n">What</span><span class="p" data-group-id="0029906099-81">]</span><span class="p" data-group-id="0029906099-80">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7225610988-82">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7225610988-83">[</span><span class="p" data-group-id="7225610988-83">]</span><span class="p" data-group-id="7225610988-82">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="7225610988-84">(</span><span class="ss">timeout</span><span class="p" data-group-id="7225610988-84">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0029906099-82">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0029906099-83">[</span><span class="p" data-group-id="0029906099-83">]</span><span class="p" data-group-id="0029906099-82">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="0029906099-84">(</span><span class="ss">timeout</span><span class="p" data-group-id="0029906099-84">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The following changes are added:</p><p>The messenger server traps exits. If it receives an exit signal,
│ │ │ │  <code class="inline">{'EXIT',From,Reason}</code>, this means that a client process has terminated or is
│ │ │ │  unreachable for one of the following reasons:</p><ul><li>The user has logged off (the &quot;logoff&quot; message is removed).</li><li>The network connection to the client is broken.</li><li>The node on which the client process resides has gone down.</li><li>The client processes has done some illegal operation.</li></ul><p>If an exit signal is received as above, the tuple <code class="inline">{From,Name}</code> is deleted from
│ │ │ │  the servers <code class="inline">User_List</code> using the <code class="inline">server_logoff</code> function. If the node on which
│ │ │ │  the server runs goes down, an exit signal (automatically generated by the
│ │ │ │  system) is sent to all of the client processes:
│ │ │ │  <code class="inline">{'EXIT',MessengerPID,noconnection}</code> causing all the client processes to
│ │ │ ├── OEBPS/release_structure.xhtml
│ │ │ │ @@ -41,37 +41,37 @@
│ │ │ │    <a href="#release-resource-file" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Release Resource File</span>
│ │ │ │  </h2>
│ │ │ │  <p>To define a release, create a <em>release resource file</em>, or in short a <code class="inline">.rel</code>
│ │ │ │  file. In the file, specify the name and version of the release, which ERTS
│ │ │ │ -version it is based on, and which applications it consists of:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2880490587-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2880490587-2">{</span><span class="n">Name</span><span class="p">,</span><span class="n">Vsn</span><span class="p" data-group-id="2880490587-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2880490587-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">EVsn</span><span class="p" data-group-id="2880490587-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2880490587-4">[</span><span class="p" data-group-id="2880490587-5">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsn1</span><span class="p" data-group-id="2880490587-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +version it is based on, and which applications it consists of:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6433578364-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6433578364-2">{</span><span class="n">Name</span><span class="p">,</span><span class="n">Vsn</span><span class="p" data-group-id="6433578364-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6433578364-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">EVsn</span><span class="p" data-group-id="6433578364-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6433578364-4">[</span><span class="p" data-group-id="6433578364-5">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsn1</span><span class="p" data-group-id="6433578364-5">}</span><span class="p">,</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2880490587-6">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsnN</span><span class="p" data-group-id="2880490587-6">}</span><span class="p" data-group-id="2880490587-4">]</span><span class="p" data-group-id="2880490587-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Name</code>, <code class="inline">Vsn</code>, <code class="inline">EVsn</code>, and <code class="inline">AppVsn</code> are strings.</p><p>The file must be named <code class="inline">Rel.rel</code>, where <code class="inline">Rel</code> is a unique name.</p><p>Each <code class="inline">Application</code> (atom) and <code class="inline">AppVsn</code> is the name and version of an application
│ │ │ │ +  </span><span class="p" data-group-id="6433578364-6">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsnN</span><span class="p" data-group-id="6433578364-6">}</span><span class="p" data-group-id="6433578364-4">]</span><span class="p" data-group-id="6433578364-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Name</code>, <code class="inline">Vsn</code>, <code class="inline">EVsn</code>, and <code class="inline">AppVsn</code> are strings.</p><p>The file must be named <code class="inline">Rel.rel</code>, where <code class="inline">Rel</code> is a unique name.</p><p>Each <code class="inline">Application</code> (atom) and <code class="inline">AppVsn</code> is the name and version of an application
│ │ │ │  included in the release. The minimal release based on Erlang/OTP consists of the
│ │ │ │  Kernel and STDLIB applications, so these applications must be included in the
│ │ │ │  list.</p><p>If the release is to be upgraded, it must also include the SASL application.</p><p><a href="" id="ch_rel"></a></p><p>Here is an example showing the <code class="inline">.app</code> file for a release of <code class="inline">ch_app</code> from
│ │ │ │ -the <a href="applications.xhtml#ch_app">Applications</a> section:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7425250140-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7425250140-2">[</span><span class="p" data-group-id="7425250140-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="7425250140-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="7425250140-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="7425250140-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="7425250140-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7425250140-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7425250140-6">]</span><span class="p" data-group-id="7425250140-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="7425250140-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7425250140-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="7425250140-8">]</span><span class="p" data-group-id="7425250140-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="7425250140-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7425250140-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="7425250140-10">]</span><span class="p" data-group-id="7425250140-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="7425250140-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7425250140-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="7425250140-13">[</span><span class="p" data-group-id="7425250140-13">]</span><span class="p" data-group-id="7425250140-12">}</span><span class="p" data-group-id="7425250140-11">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7425250140-2">]</span><span class="p" data-group-id="7425250140-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">.rel</code> file must also contain <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code>, as these
│ │ │ │ -applications are required by <code class="inline">ch_app</code>. The file is called <code class="inline">ch_rel-1.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8411452996-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8411452996-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;A&quot;</span><span class="p" data-group-id="8411452996-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8411452996-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="8411452996-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8411452996-4">[</span><span class="p" data-group-id="8411452996-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="8411452996-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8411452996-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="8411452996-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8411452996-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="8411452996-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8411452996-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="8411452996-8">}</span><span class="p" data-group-id="8411452996-4">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8411452996-1">}</span><span class="p">.</span></code></pre><p><a href="" id="boot"></a></p><h2 id="generating-boot-scripts" class="section-heading">
│ │ │ │ +the <a href="applications.xhtml#ch_app">Applications</a> section:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9469636397-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9469636397-2">[</span><span class="p" data-group-id="9469636397-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="9469636397-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9469636397-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="9469636397-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9469636397-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9469636397-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="9469636397-6">]</span><span class="p" data-group-id="9469636397-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9469636397-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9469636397-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="9469636397-8">]</span><span class="p" data-group-id="9469636397-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9469636397-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9469636397-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="9469636397-10">]</span><span class="p" data-group-id="9469636397-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9469636397-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9469636397-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="9469636397-13">[</span><span class="p" data-group-id="9469636397-13">]</span><span class="p" data-group-id="9469636397-12">}</span><span class="p" data-group-id="9469636397-11">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9469636397-2">]</span><span class="p" data-group-id="9469636397-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">.rel</code> file must also contain <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code>, as these
│ │ │ │ +applications are required by <code class="inline">ch_app</code>. The file is called <code class="inline">ch_rel-1.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0014973695-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0014973695-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;A&quot;</span><span class="p" data-group-id="0014973695-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0014973695-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="0014973695-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0014973695-4">[</span><span class="p" data-group-id="0014973695-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="0014973695-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0014973695-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="0014973695-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0014973695-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="0014973695-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0014973695-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="0014973695-8">}</span><span class="p" data-group-id="0014973695-4">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0014973695-1">}</span><span class="p">.</span></code></pre><p><a href="" id="boot"></a></p><h2 id="generating-boot-scripts" class="section-heading">
│ │ │ │    <a href="#generating-boot-scripts" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Generating Boot Scripts</span>
│ │ │ │  </h2>
│ │ │ │  <p><a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a> in the SASL application includes tools to build and check
│ │ │ │  releases. The functions read the <code class="inline">.rel</code> and <code class="inline">.app</code> files and perform
│ │ │ │ @@ -95,17 +95,17 @@
│ │ │ │    <a href="#creating-a-release-package" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating a Release Package</span>
│ │ │ │  </h2>
│ │ │ │  <p>The <a href="../../../lib/sasl/doc/html/systools.html#make_tar/2"><code class="inline">systools:make_tar/1,2</code></a> function takes a
│ │ │ │  <code class="inline">.rel</code> file as input and creates a zipped tar file with the code for
│ │ │ │ -the specified applications, a <em>release package</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="9542454531-1">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="9542454531-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the specified applications, a <em>release package</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="7661468475-1">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="7661468475-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="9542454531-2">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="9542454531-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="7661468475-2">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="7661468475-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>The release package by default contains:</p><ul><li>The <code class="inline">.app</code> files</li><li>The <code class="inline">.rel</code> file</li><li>The object code for all applications, structured according to the
│ │ │ │  <a href="applications.xhtml#app_dir">application directory structure</a></li><li>The binary boot script renamed to <code class="inline">start.boot</code></li></ul><pre><code class="text">% tar tf ch_rel-1.tar
│ │ │ │  lib/kernel-9.2.4/ebin/kernel.app
│ │ │ │  lib/kernel-9.2.4/ebin/application.beam
│ │ │ │  ...
│ │ │ │  lib/stdlib-5.2.3/ebin/stdlib.app
│ │ │ │  lib/stdlib-5.2.3/ebin/argparse.beam
│ │ │ ├── OEBPS/release_handling.xhtml
│ │ │ │ @@ -128,38 +128,38 @@
│ │ │ │    <span class="text">update</span>
│ │ │ │  </h3>
│ │ │ │  <p>If a more complex change has been made, for example, a change to the format of
│ │ │ │  the internal state of a <a href="../../../lib/stdlib/doc/html/gen_server.html"><code class="inline">gen_server</code></a>, simple code replacement is not sufficient.
│ │ │ │  Instead, it is necessary to:</p><ul><li>Suspend the processes using the module (to avoid that they try to handle any
│ │ │ │  requests before the code replacement is completed).</li><li>Ask them to transform the internal state format and switch to the new version
│ │ │ │  of the module.</li><li>Remove the old version.</li><li>Resume the processes.</li></ul><p>This is called <em>synchronized code replacement</em> and for this the following
│ │ │ │ -instructions are used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0032093782-1">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0032093782-2">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="0032093782-2">}</span><span class="p" data-group-id="0032093782-1">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0032093782-3">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0032093782-3">}</span></code></pre><p><code class="inline">update</code> with argument <code class="inline">{advanced,Extra}</code> is used when changing the internal
│ │ │ │ +instructions are used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2641488722-1">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2641488722-2">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="2641488722-2">}</span><span class="p" data-group-id="2641488722-1">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2641488722-3">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="2641488722-3">}</span></code></pre><p><code class="inline">update</code> with argument <code class="inline">{advanced,Extra}</code> is used when changing the internal
│ │ │ │  state of a behaviour as described above. It causes behaviour processes to call
│ │ │ │  the callback function <code class="inline">code_change/3</code>, passing the term <code class="inline">Extra</code> and some other
│ │ │ │  information as arguments. See the manual pages for the respective behaviours and
│ │ │ │  <a href="appup_cookbook.xhtml#int_state">Appup Cookbook</a>.</p><p><code class="inline">update</code> with argument <code class="inline">supervisor</code> is used when changing the start
│ │ │ │  specification of a supervisor. See <a href="appup_cookbook.xhtml#sup">Appup Cookbook</a>.</p><p>When a module is to be updated, the release handler finds which processes that
│ │ │ │  are <em>using</em> the module by traversing the supervision tree of each running
│ │ │ │ -application and checking all the child specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1986198501-1">{</span><span class="n">Id</span><span class="p">,</span><span class="w"> </span><span class="n">StartFunc</span><span class="p">,</span><span class="w"> </span><span class="n">Restart</span><span class="p">,</span><span class="w"> </span><span class="n">Shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Modules</span><span class="p" data-group-id="1986198501-1">}</span></code></pre><p>A process uses a module if the name is listed in <code class="inline">Modules</code> in the child
│ │ │ │ +application and checking all the child specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4518091592-1">{</span><span class="n">Id</span><span class="p">,</span><span class="w"> </span><span class="n">StartFunc</span><span class="p">,</span><span class="w"> </span><span class="n">Restart</span><span class="p">,</span><span class="w"> </span><span class="n">Shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Modules</span><span class="p" data-group-id="4518091592-1">}</span></code></pre><p>A process uses a module if the name is listed in <code class="inline">Modules</code> in the child
│ │ │ │  specification for the process.</p><p>If <code class="inline">Modules=dynamic</code>, which is the case for event managers, the event manager
│ │ │ │  process informs the release handler about the list of currently installed event
│ │ │ │  handlers (<code class="inline">gen_event</code>), and it is checked if the module name is in this list
│ │ │ │  instead.</p><p>The release handler suspends, asks for code change, and resumes processes by
│ │ │ │  calling the functions <code class="inline">sys:suspend/1,2</code>, <code class="inline">sys:change_code/4,5</code>, and
│ │ │ │  <code class="inline">sys:resume/1,2</code>, respectively.</p><h3 id="add_module-and-delete_module" class="section-heading">
│ │ │ │    <a href="#add_module-and-delete_module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">add_module and delete_module</span>
│ │ │ │  </h3>
│ │ │ │ -<p>If a new module is introduced, the following instruction is used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1210843613-1">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="1210843613-1">}</span></code></pre><p>This instruction loads module <code class="inline">Module</code>. When running Erlang in
│ │ │ │ +<p>If a new module is introduced, the following instruction is used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2369414098-1">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2369414098-1">}</span></code></pre><p>This instruction loads module <code class="inline">Module</code>. When running Erlang in
│ │ │ │  embedded mode it is necessary to use this this instruction. It is not
│ │ │ │  strictly required when running Erlang in interactive mode, since the
│ │ │ │ -code server automatically searches for and loads unloaded modules.</p><p>The opposite of <code class="inline">add_module</code> is <code class="inline">delete_module</code>, which unloads a module:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7643235548-1">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="7643235548-1">}</span></code></pre><p>Any process, in any application, with <code class="inline">Module</code> as residence module, is
│ │ │ │ +code server automatically searches for and loads unloaded modules.</p><p>The opposite of <code class="inline">add_module</code> is <code class="inline">delete_module</code>, which unloads a module:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3620663766-1">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="3620663766-1">}</span></code></pre><p>Any process, in any application, with <code class="inline">Module</code> as residence module, is
│ │ │ │  killed when the instruction is evaluated. Therefore, the user must
│ │ │ │  ensure that all such processes are terminated before deleting module
│ │ │ │  <code class="inline">Module</code> to avoid a situation with failing supervisor restarts.</p><h3 id="application-instructions" class="section-heading">
│ │ │ │    <a href="#application-instructions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Application Instructions</span>
│ │ │ │ @@ -246,60 +246,60 @@
│ │ │ │  <code class="inline">.app</code> file.</li><li>Each <code class="inline">UpFromVsn</code> is a previous version of the application to upgrade from.</li><li>Each <code class="inline">DownToVsn</code> is a previous version of the application to downgrade to.</li><li>Each <code class="inline">Instructions</code> is a list of release handling instructions.</li></ul><p><code class="inline">UpFromVsn</code> and <code class="inline">DownToVsn</code> can also be specified as regular expressions. For
│ │ │ │  more information about the syntax and contents of the <code class="inline">.appup</code> file, see
│ │ │ │  <a href="../../../lib/sasl/doc/html/appup.xhtml"><code class="inline">appup</code></a> in SASL.</p><p><a href="appup_cookbook.xhtml">Appup Cookbook</a> includes examples of <code class="inline">.appup</code> files for
│ │ │ │  typical upgrade/downgrade cases.</p><p><em>Example:</em> Consider the release <code class="inline">ch_rel-1</code> from
│ │ │ │  <a href="release_structure.xhtml#ch_rel">Releases</a>. Assume you want to add a function
│ │ │ │  <code class="inline">available/0</code> to server <code class="inline">ch3</code>, which returns the number of available channels
│ │ │ │  (when trying out the example, make the change in a copy of the original
│ │ │ │ -directory, to ensure that the first version is still available):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6569015157-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="6569015157-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="6569015157-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="6569015157-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +directory, to ensure that the first version is still available):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3725819746-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="3725819746-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3725819746-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="3725819746-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6569015157-3">(</span><span class="p" data-group-id="6569015157-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6569015157-4">]</span><span class="p" data-group-id="6569015157-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6569015157-5">(</span><span class="p" data-group-id="6569015157-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6569015157-6">]</span><span class="p" data-group-id="6569015157-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6569015157-7">(</span><span class="p" data-group-id="6569015157-8">[</span><span class="ss">available</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6569015157-8">]</span><span class="p" data-group-id="6569015157-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6569015157-9">(</span><span class="p" data-group-id="6569015157-10">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6569015157-10">]</span><span class="p" data-group-id="6569015157-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3725819746-3">(</span><span class="p" data-group-id="3725819746-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3725819746-4">]</span><span class="p" data-group-id="3725819746-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3725819746-5">(</span><span class="p" data-group-id="3725819746-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3725819746-6">]</span><span class="p" data-group-id="3725819746-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3725819746-7">(</span><span class="p" data-group-id="3725819746-8">[</span><span class="ss">available</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3725819746-8">]</span><span class="p" data-group-id="3725819746-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3725819746-9">(</span><span class="p" data-group-id="3725819746-10">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3725819746-10">]</span><span class="p" data-group-id="3725819746-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="6569015157-11">(</span><span class="p" data-group-id="6569015157-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6569015157-12">(</span><span class="p" data-group-id="6569015157-13">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6569015157-13">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6569015157-14">[</span><span class="p" data-group-id="6569015157-14">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6569015157-15">[</span><span class="p" data-group-id="6569015157-15">]</span><span class="p" data-group-id="6569015157-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="3725819746-11">(</span><span class="p" data-group-id="3725819746-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3725819746-12">(</span><span class="p" data-group-id="3725819746-13">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="3725819746-13">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3725819746-14">[</span><span class="p" data-group-id="3725819746-14">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3725819746-15">[</span><span class="p" data-group-id="3725819746-15">]</span><span class="p" data-group-id="3725819746-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="6569015157-16">(</span><span class="p" data-group-id="6569015157-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="6569015157-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="6569015157-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="3725819746-16">(</span><span class="p" data-group-id="3725819746-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="3725819746-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="3725819746-17">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="6569015157-18">(</span><span class="n">Ch</span><span class="p" data-group-id="6569015157-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6569015157-19">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6569015157-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6569015157-20">}</span><span class="p" data-group-id="6569015157-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="3725819746-18">(</span><span class="n">Ch</span><span class="p" data-group-id="3725819746-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="3725819746-19">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3725819746-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3725819746-20">}</span><span class="p" data-group-id="3725819746-19">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">available</span><span class="p" data-group-id="6569015157-21">(</span><span class="p" data-group-id="6569015157-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="6569015157-22">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">available</span><span class="p" data-group-id="6569015157-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">available</span><span class="p" data-group-id="3725819746-21">(</span><span class="p" data-group-id="3725819746-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="3725819746-22">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">available</span><span class="p" data-group-id="3725819746-22">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6569015157-23">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6569015157-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6569015157-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="6569015157-25">(</span><span class="p" data-group-id="6569015157-25">)</span><span class="p" data-group-id="6569015157-24">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="3725819746-23">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="3725819746-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3725819746-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="3725819746-25">(</span><span class="p" data-group-id="3725819746-25">)</span><span class="p" data-group-id="3725819746-24">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="6569015157-26">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6569015157-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6569015157-27">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6569015157-27">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="6569015157-28">(</span><span class="n">Chs</span><span class="p" data-group-id="6569015157-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6569015157-29">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6569015157-29">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="6569015157-30">(</span><span class="ss">available</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6569015157-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">available</span><span class="p" data-group-id="6569015157-31">(</span><span class="n">Chs</span><span class="p" data-group-id="6569015157-31">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6569015157-32">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6569015157-32">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="3725819746-26">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3725819746-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3725819746-27">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="3725819746-27">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="3725819746-28">(</span><span class="n">Chs</span><span class="p" data-group-id="3725819746-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3725819746-29">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="3725819746-29">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="3725819746-30">(</span><span class="ss">available</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3725819746-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">available</span><span class="p" data-group-id="3725819746-31">(</span><span class="n">Chs</span><span class="p" data-group-id="3725819746-31">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3725819746-32">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3725819746-32">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="6569015157-33">(</span><span class="p" data-group-id="6569015157-34">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6569015157-34">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6569015157-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="6569015157-35">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6569015157-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6569015157-36">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6569015157-36">}</span><span class="p">.</span></code></pre><p>A new version of the <code class="inline">ch_app.app</code> file must now be created, where the version is
│ │ │ │ -updated:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5418740927-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5418740927-2">[</span><span class="p" data-group-id="5418740927-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="5418740927-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5418740927-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="5418740927-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5418740927-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5418740927-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="5418740927-6">]</span><span class="p" data-group-id="5418740927-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5418740927-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5418740927-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="5418740927-8">]</span><span class="p" data-group-id="5418740927-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5418740927-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5418740927-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="5418740927-10">]</span><span class="p" data-group-id="5418740927-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5418740927-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5418740927-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="5418740927-13">[</span><span class="p" data-group-id="5418740927-13">]</span><span class="p" data-group-id="5418740927-12">}</span><span class="p" data-group-id="5418740927-11">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5418740927-2">]</span><span class="p" data-group-id="5418740927-1">}</span><span class="p">.</span></code></pre><p>To upgrade <code class="inline">ch_app</code> from <code class="inline">&quot;1&quot;</code> to <code class="inline">&quot;2&quot;</code> (and to downgrade from <code class="inline">&quot;2&quot;</code> to <code class="inline">&quot;1&quot;</code>),
│ │ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="3725819746-33">(</span><span class="p" data-group-id="3725819746-34">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3725819746-34">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3725819746-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="3725819746-35">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3725819746-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3725819746-36">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="3725819746-36">}</span><span class="p">.</span></code></pre><p>A new version of the <code class="inline">ch_app.app</code> file must now be created, where the version is
│ │ │ │ +updated:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7356303584-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7356303584-2">[</span><span class="p" data-group-id="7356303584-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="7356303584-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7356303584-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="7356303584-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7356303584-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7356303584-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7356303584-6">]</span><span class="p" data-group-id="7356303584-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7356303584-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7356303584-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="7356303584-8">]</span><span class="p" data-group-id="7356303584-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7356303584-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7356303584-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="7356303584-10">]</span><span class="p" data-group-id="7356303584-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7356303584-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7356303584-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="7356303584-13">[</span><span class="p" data-group-id="7356303584-13">]</span><span class="p" data-group-id="7356303584-12">}</span><span class="p" data-group-id="7356303584-11">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7356303584-2">]</span><span class="p" data-group-id="7356303584-1">}</span><span class="p">.</span></code></pre><p>To upgrade <code class="inline">ch_app</code> from <code class="inline">&quot;1&quot;</code> to <code class="inline">&quot;2&quot;</code> (and to downgrade from <code class="inline">&quot;2&quot;</code> to <code class="inline">&quot;1&quot;</code>),
│ │ │ │  you only need to load the new (old) version of the <code class="inline">ch3</code> callback module. Create
│ │ │ │ -the application upgrade file <code class="inline">ch_app.appup</code> in the <code class="inline">ebin</code> directory:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3155030564-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3155030564-2">[</span><span class="p" data-group-id="3155030564-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3155030564-4">[</span><span class="p" data-group-id="3155030564-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="3155030564-5">}</span><span class="p" data-group-id="3155030564-4">]</span><span class="p" data-group-id="3155030564-3">}</span><span class="p" data-group-id="3155030564-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3155030564-6">[</span><span class="p" data-group-id="3155030564-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3155030564-8">[</span><span class="p" data-group-id="3155030564-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="3155030564-9">}</span><span class="p" data-group-id="3155030564-8">]</span><span class="p" data-group-id="3155030564-7">}</span><span class="p" data-group-id="3155030564-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3155030564-1">}</span><span class="p">.</span></code></pre><p><a href="" id="relup"></a></p><h2 id="release-upgrade-file" class="section-heading">
│ │ │ │ +the application upgrade file <code class="inline">ch_app.appup</code> in the <code class="inline">ebin</code> directory:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0600634563-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0600634563-2">[</span><span class="p" data-group-id="0600634563-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0600634563-4">[</span><span class="p" data-group-id="0600634563-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0600634563-5">}</span><span class="p" data-group-id="0600634563-4">]</span><span class="p" data-group-id="0600634563-3">}</span><span class="p" data-group-id="0600634563-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0600634563-6">[</span><span class="p" data-group-id="0600634563-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0600634563-8">[</span><span class="p" data-group-id="0600634563-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0600634563-9">}</span><span class="p" data-group-id="0600634563-8">]</span><span class="p" data-group-id="0600634563-7">}</span><span class="p" data-group-id="0600634563-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0600634563-1">}</span><span class="p">.</span></code></pre><p><a href="" id="relup"></a></p><h2 id="release-upgrade-file" class="section-heading">
│ │ │ │    <a href="#release-upgrade-file" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Release Upgrade File</span>
│ │ │ │  </h2>
│ │ │ │  <p>To define how to upgrade/downgrade between the new version and previous versions
│ │ │ │  of a release, a <em>release upgrade file</em>, or in short <code class="inline">.relup</code> file, is to be
│ │ │ │ @@ -310,22 +310,22 @@
│ │ │ │  are to be added and deleted, and which applications that must be upgraded and/or
│ │ │ │  downgraded. The instructions for this are fetched from the <code class="inline">.appup</code> files and
│ │ │ │  transformed into a single list of low-level instructions in the right order.</p><p>If the <code class="inline">relup</code> file is relatively simple, it can be created manually. It is only
│ │ │ │  to contain low-level instructions.</p><p>For details about the syntax and contents of the release upgrade file, see
│ │ │ │  <a href="../../../lib/sasl/doc/html/relup.xhtml"><code class="inline">relup</code></a> in SASL.</p><p><em>Example, continued from the previous section:</em> You have a new version &quot;2&quot; of
│ │ │ │  <code class="inline">ch_app</code> and an <code class="inline">.appup</code> file. A new version of the <code class="inline">.rel</code> file is also needed.
│ │ │ │  This time the file is called <code class="inline">ch_rel-2.rel</code> and the release version string is
│ │ │ │ -changed from &quot;A&quot; to &quot;B&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6982877327-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6982877327-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="6982877327-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6982877327-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="6982877327-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6982877327-4">[</span><span class="p" data-group-id="6982877327-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="6982877327-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6982877327-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="6982877327-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6982877327-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="6982877327-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6982877327-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="6982877327-8">}</span><span class="p" data-group-id="6982877327-4">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6982877327-1">}</span><span class="p">.</span></code></pre><p>Now the <code class="inline">relup</code> file can be generated:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;]).
│ │ │ │ +changed from &quot;A&quot; to &quot;B&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9593118296-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9593118296-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="9593118296-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9593118296-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="9593118296-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9593118296-4">[</span><span class="p" data-group-id="9593118296-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="9593118296-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9593118296-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="9593118296-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9593118296-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="9593118296-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9593118296-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="9593118296-8">}</span><span class="p" data-group-id="9593118296-4">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9593118296-1">}</span><span class="p">.</span></code></pre><p>Now the <code class="inline">relup</code> file can be generated:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;]).
│ │ │ │  ok</code></pre><p>This generates a <code class="inline">relup</code> file with instructions for how to upgrade from version
│ │ │ │  &quot;A&quot; (&quot;ch_rel-1&quot;) to version &quot;B&quot; (&quot;ch_rel-2&quot;) and how to downgrade from version
│ │ │ │  &quot;B&quot; to version &quot;A&quot;.</p><p>Both the old and new versions of the <code class="inline">.app</code> and <code class="inline">.rel</code> files must be in the code
│ │ │ │  path, as well as the <code class="inline">.appup</code> and (new) <code class="inline">.beam</code> files. The code path can be
│ │ │ │  extended by using the option <code class="inline">path</code>:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;],
│ │ │ │  [{path,[&quot;../ch_rel-1&quot;,
│ │ │ │  &quot;../ch_rel-1/lib/ch_app-1/ebin&quot;]}]).
│ │ │ │ @@ -338,25 +338,25 @@
│ │ │ │  <p>When you have made a new version of a release, a release package can be created
│ │ │ │  with this new version and transferred to the target environment.</p><p>To install the new version of the release in runtime, the <em>release
│ │ │ │  handler</em> is used. This is a process belonging to the SASL application,
│ │ │ │  which handles unpacking, installation, and removal of release
│ │ │ │  packages. The <a href="../../../lib/sasl/doc/html/release_handler.html"><code class="inline">release_handler</code></a> module communicates with this process.</p><p>Assuming there is an operational target system with installation root directory
│ │ │ │  <code class="inline">$ROOT</code>, the release package with the new version of the release is to be copied
│ │ │ │  to <code class="inline">$ROOT/releases</code>.</p><p>First, <em>unpack</em> the release package. The files are then extracted from the
│ │ │ │ -package:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="0563021925-1">(</span><span class="n">ReleaseName</span><span class="p" data-group-id="0563021925-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0563021925-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p" data-group-id="0563021925-2">}</span></code></pre><ul><li><code class="inline">ReleaseName</code> is the name of the release package except the <code class="inline">.tar.gz</code>
│ │ │ │ +package:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="2665322098-1">(</span><span class="n">ReleaseName</span><span class="p" data-group-id="2665322098-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2665322098-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p" data-group-id="2665322098-2">}</span></code></pre><ul><li><code class="inline">ReleaseName</code> is the name of the release package except the <code class="inline">.tar.gz</code>
│ │ │ │  extension.</li><li><code class="inline">Vsn</code> is the version of the unpacked release, as defined in its <code class="inline">.rel</code> file.</li></ul><p>A directory <code class="inline">$ROOT/lib/releases/Vsn</code> is created, where the <code class="inline">.rel</code> file, the boot
│ │ │ │  script <code class="inline">start.boot</code>, the system configuration file <code class="inline">sys.config</code>, and <code class="inline">relup</code> are
│ │ │ │  placed. For applications with new version numbers, the application directories
│ │ │ │  are placed under <code class="inline">$ROOT/lib</code>. Unchanged applications are not affected.</p><p>An unpacked release can be <em>installed</em>. The release handler then evaluates the
│ │ │ │ -instructions in <code class="inline">relup</code>, step by step:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="0889258179-1">(</span><span class="n">Vsn</span><span class="p" data-group-id="0889258179-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0889258179-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FromVsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0889258179-3">[</span><span class="p" data-group-id="0889258179-3">]</span><span class="p" data-group-id="0889258179-2">}</span></code></pre><p>If an error occurs during the installation, the system is rebooted using the old
│ │ │ │ +instructions in <code class="inline">relup</code>, step by step:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="4583033366-1">(</span><span class="n">Vsn</span><span class="p" data-group-id="4583033366-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4583033366-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FromVsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4583033366-3">[</span><span class="p" data-group-id="4583033366-3">]</span><span class="p" data-group-id="4583033366-2">}</span></code></pre><p>If an error occurs during the installation, the system is rebooted using the old
│ │ │ │  version of the release. If installation succeeds, the system is afterwards using
│ │ │ │  the new version of the release, but if anything happens and the system is
│ │ │ │  rebooted, it starts using the previous version again.</p><p>To be made the default version, the newly installed release must be made
│ │ │ │  <em>permanent</em>, which means the previous version becomes <em>old</em>:</p><pre><code class="text">release_handler:make_permanent(Vsn) =&gt; ok</code></pre><p>The system keeps information about which versions are old and permanent in the
│ │ │ │ -files <code class="inline">$ROOT/releases/RELEASES</code> and <code class="inline">$ROOT/releases/start_erl.data</code>.</p><p>To downgrade from <code class="inline">Vsn</code> to <code class="inline">FromVsn</code>, <code class="inline">install_release</code> must be called again:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="6800837743-1">(</span><span class="n">FromVsn</span><span class="p" data-group-id="6800837743-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6800837743-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6800837743-3">[</span><span class="p" data-group-id="6800837743-3">]</span><span class="p" data-group-id="6800837743-2">}</span></code></pre><p>An installed, but not permanent, release can be <em>removed</em>. Information about the
│ │ │ │ +files <code class="inline">$ROOT/releases/RELEASES</code> and <code class="inline">$ROOT/releases/start_erl.data</code>.</p><p>To downgrade from <code class="inline">Vsn</code> to <code class="inline">FromVsn</code>, <code class="inline">install_release</code> must be called again:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="5371310273-1">(</span><span class="n">FromVsn</span><span class="p" data-group-id="5371310273-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5371310273-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5371310273-3">[</span><span class="p" data-group-id="5371310273-3">]</span><span class="p" data-group-id="5371310273-2">}</span></code></pre><p>An installed, but not permanent, release can be <em>removed</em>. Information about the
│ │ │ │  release is then deleted from <code class="inline">$ROOT/releases/RELEASES</code> and the release-specific
│ │ │ │  code, that is, the new application directories and the <code class="inline">$ROOT/releases/Vsn</code>
│ │ │ │  directory, are removed.</p><pre><code class="text">release_handler:remove_release(Vsn) =&gt; ok</code></pre><h3 id="example-continued-from-the-previous-sections" class="section-heading">
│ │ │ │    <a href="#example-continued-from-the-previous-sections" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example (continued from the previous sections)</span>
│ │ │ │ @@ -367,17 +367,17 @@
│ │ │ │  is needed, the file is to contain the empty list:</p><pre><code class="text">[].</code></pre><p><em>Step 2)</em> Start the system as a simple target system. In reality, it is to be
│ │ │ │  started as an embedded system. However, using <code class="inline">erl</code> with the correct boot script
│ │ │ │  and config file is enough for illustration purposes:</p><pre><code class="text">% cd $ROOT
│ │ │ │  % bin/erl -boot $ROOT/releases/A/start -config $ROOT/releases/A/sys
│ │ │ │  ...</code></pre><p><code class="inline">$ROOT</code> is the installation directory of the target system.</p><p><em>Step 3)</em> In another Erlang shell, generate start scripts and create a release
│ │ │ │  package for the new version <code class="inline">&quot;B&quot;</code>. Remember to include (a possible updated)
│ │ │ │  <code class="inline">sys.config</code> and the <code class="inline">relup</code> file. For more information, see
│ │ │ │ -<a href="release_handling.xhtml#relup">Release Upgrade File</a>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="1015888697-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="1015888697-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<a href="release_handling.xhtml#relup">Release Upgrade File</a>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="6295444469-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="6295444469-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="1015888697-2">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="1015888697-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="6295444469-2">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="6295444469-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>The new release package now also contains version &quot;2&quot; of <code class="inline">ch_app</code> and the
│ │ │ │  <code class="inline">relup</code> file:</p><pre><code class="text">% tar tf ch_rel-2.tar
│ │ │ │  lib/kernel-9.2.4/ebin/kernel.app
│ │ │ │  lib/kernel-9.2.4/ebin/application.beam
│ │ │ │  ...
│ │ │ │  lib/stdlib-5.2.3/ebin/stdlib.app
│ │ │ │  lib/stdlib-5.2.3/ebin/argparse.beam
│ │ │ │ @@ -390,31 +390,31 @@
│ │ │ │  lib/ch_app-2/ebin/ch_sup.beam
│ │ │ │  lib/ch_app-2/ebin/ch3.beam
│ │ │ │  releases/B/start.boot
│ │ │ │  releases/B/relup
│ │ │ │  releases/B/sys.config
│ │ │ │  releases/B/ch_rel-2.rel
│ │ │ │  releases/ch_rel-2.rel</code></pre><p><em>Step 4)</em> Copy the release package <code class="inline">ch_rel-2.tar.gz</code> to the <code class="inline">$ROOT/releases</code>
│ │ │ │ -directory.</p><p><em>Step 5)</em> In the running target system, unpack the release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="0512461263-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="0512461263-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0512461263-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="0512461263-2">}</span></code></pre><p>The new application version <code class="inline">ch_app-2</code> is installed under <code class="inline">$ROOT/lib</code> next to
│ │ │ │ +directory.</p><p><em>Step 5)</em> In the running target system, unpack the release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="4432645228-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="4432645228-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4432645228-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="4432645228-2">}</span></code></pre><p>The new application version <code class="inline">ch_app-2</code> is installed under <code class="inline">$ROOT/lib</code> next to
│ │ │ │  <code class="inline">ch_app-1</code>. The <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code> directories are not affected, as
│ │ │ │  they have not changed.</p><p>Under <code class="inline">$ROOT/releases</code>, a new directory <code class="inline">B</code> is created, containing
│ │ │ │ -<code class="inline">ch_rel-2.rel</code>, <code class="inline">start.boot</code>, <code class="inline">sys.config</code>, and <code class="inline">relup</code>.</p><p><em>Step 6)</em> Check if the function <code class="inline">ch3:available/0</code> is available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="9052968779-1">(</span><span class="p" data-group-id="9052968779-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">ch_rel-2.rel</code>, <code class="inline">start.boot</code>, <code class="inline">sys.config</code>, and <code class="inline">relup</code>.</p><p><em>Step 6)</em> Check if the function <code class="inline">ch3:available/0</code> is available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="4855733963-1">(</span><span class="p" data-group-id="4855733963-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: undefined function ch3:available/0</span></code></pre><p><em>Step 7)</em> Install the new release. The instructions in <code class="inline">$ROOT/releases/B/relup</code>
│ │ │ │  are executed one by one, resulting in the new version of <code class="inline">ch3</code> being loaded. The
│ │ │ │ -function <code class="inline">ch3:available/0</code> is now available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="3225855128-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="3225855128-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3225855128-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="p" data-group-id="3225855128-3">[</span><span class="p" data-group-id="3225855128-3">]</span><span class="p" data-group-id="3225855128-2">}</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="3225855128-4">(</span><span class="p" data-group-id="3225855128-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +function <code class="inline">ch3:available/0</code> is now available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="3358929664-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="3358929664-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3358929664-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="p" data-group-id="3358929664-3">[</span><span class="p" data-group-id="3358929664-3">]</span><span class="p" data-group-id="3358929664-2">}</span><span class="gp unselectable">
│ │ │ │ +4&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="3358929664-4">(</span><span class="p" data-group-id="3358929664-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="3225855128-5">(</span><span class="ss">ch3</span><span class="p" data-group-id="3225855128-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="3358929664-5">(</span><span class="ss">ch3</span><span class="p" data-group-id="3358929664-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;.../lib/ch_app-2/ebin/ch3.beam&quot;</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="3225855128-6">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="3225855128-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +6&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="3358929664-6">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="3358929664-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;.../lib/ch_app-1/ebin/ch_sup.beam&quot;</span></code></pre><p>Processes in <code class="inline">ch_app</code> for which code have not been updated, for example, the
│ │ │ │  supervisor, are still evaluating code from <code class="inline">ch_app-1</code>.</p><p><em>Step 8)</em> If the target system is now rebooted, it uses version &quot;A&quot; again. The
│ │ │ │ -&quot;B&quot; version must be made permanent, to be used when the system is rebooted.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">make_permanent</span><span class="p" data-group-id="3818250637-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="3818250637-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&quot;B&quot; version must be made permanent, to be used when the system is rebooted.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">make_permanent</span><span class="p" data-group-id="6132439978-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="6132439978-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p><a href="" id="sys"></a></p><h2 id="updating-application-specifications" class="section-heading">
│ │ │ │    <a href="#updating-application-specifications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Updating Application Specifications</span>
│ │ │ │  </h2>
│ │ │ │  <p>When a new version of a release is installed, the application specifications are
│ │ │ │ @@ -423,14 +423,14 @@
│ │ │ │  boot script is generated from the same <code class="inline">.rel</code> file as is used to build the
│ │ │ │  release package itself.</p></section><p>Specifically, the application configuration parameters are automatically updated
│ │ │ │  according to (in increasing priority order):</p><ul><li>The data in the boot script, fetched from the new application resource file
│ │ │ │  <code class="inline">App.app</code></li><li>The new <code class="inline">sys.config</code></li><li>Command-line arguments <code class="inline">-App Par Val</code></li></ul><p>This means that parameter values set in the other system configuration files and
│ │ │ │  values set using <a href="../../../lib/kernel/doc/html/application.html#set_env/3"><code class="inline">application:set_env/3</code></a> are disregarded.</p><p>When an installed release is made permanent, the system process <code class="inline">init</code> is set to
│ │ │ │  point out the new <code class="inline">sys.config</code>.</p><p>After the installation, the application controller compares the old and new
│ │ │ │  configuration parameters for all running applications and call the callback
│ │ │ │ -function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">config_change</span><span class="p" data-group-id="1900259475-1">(</span><span class="n">Changed</span><span class="p">,</span><span class="w"> </span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">Removed</span><span class="p" data-group-id="1900259475-1">)</span></code></pre><ul><li><code class="inline">Module</code> is the application callback module as defined by the <code class="inline">mod</code> key in the
│ │ │ │ +function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">config_change</span><span class="p" data-group-id="0187832920-1">(</span><span class="n">Changed</span><span class="p">,</span><span class="w"> </span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">Removed</span><span class="p" data-group-id="0187832920-1">)</span></code></pre><ul><li><code class="inline">Module</code> is the application callback module as defined by the <code class="inline">mod</code> key in the
│ │ │ │  <code class="inline">.app</code> file.</li><li><code class="inline">Changed</code> and <code class="inline">New</code> are lists of <code class="inline">{Par,Val}</code> for all changed and added
│ │ │ │  configuration parameters, respectively.</li><li><code class="inline">Removed</code> is a list of all parameters <code class="inline">Par</code> that have been removed.</li></ul><p>The function is optional and can be omitted when implementing an application
│ │ │ │  callback module.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/ref_man_records.xhtml
│ │ │ │ @@ -28,17 +28,17 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Defining Records</span>
│ │ │ │  </h2>
│ │ │ │  <p>A record definition consists of the name of the record, followed by the field
│ │ │ │  names of the record. Record and field names must be atoms. Each field can be
│ │ │ │  given an optional default value. If no default value is supplied, <code class="inline">undefined</code> is
│ │ │ │ -used.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3084202384-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3084202384-2">{</span><span class="n">Field1</span><span class="w"> </span><span class="p" data-group-id="3084202384-3">[</span><span class="o">=</span><span class="w"> </span><span class="n">Expr1</span><span class="p" data-group-id="3084202384-3">]</span><span class="p">,</span><span class="w">
│ │ │ │ +used.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6692727420-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6692727420-2">{</span><span class="n">Field1</span><span class="w"> </span><span class="p" data-group-id="6692727420-3">[</span><span class="o">=</span><span class="w"> </span><span class="n">Expr1</span><span class="p" data-group-id="6692727420-3">]</span><span class="p">,</span><span class="w">
│ │ │ │                 </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -               </span><span class="n">FieldN</span><span class="w"> </span><span class="p" data-group-id="3084202384-4">[</span><span class="o">=</span><span class="w"> </span><span class="n">ExprN</span><span class="p" data-group-id="3084202384-4">]</span><span class="p" data-group-id="3084202384-2">}</span><span class="p" data-group-id="3084202384-1">)</span><span class="p">.</span></code></pre><p>The default value for a field is an arbitrary expression, except that it must
│ │ │ │ +               </span><span class="n">FieldN</span><span class="w"> </span><span class="p" data-group-id="6692727420-4">[</span><span class="o">=</span><span class="w"> </span><span class="n">ExprN</span><span class="p" data-group-id="6692727420-4">]</span><span class="p" data-group-id="6692727420-2">}</span><span class="p" data-group-id="6692727420-1">)</span><span class="p">.</span></code></pre><p>The default value for a field is an arbitrary expression, except that it must
│ │ │ │  not use any variables.</p><p>A record definition can be placed anywhere among the attributes and function
│ │ │ │  declarations of a module, but the definition must come before any usage of the
│ │ │ │  record.</p><p>If a record is used in several modules, it is recommended that the record
│ │ │ │  definition is placed in an include file.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Starting from Erlang/OTP 26, records can be defined in the Erlang shell
│ │ │ │  using the syntax described in this section. In earlier releases, it was
│ │ │ │  necessary to use the <a href="../../../lib/stdlib/doc/html/shell.html"><code class="inline">shell</code></a> built-in function <code class="inline">rd/2</code>.</p></section><h2 id="creating-records" class="section-heading">
│ │ │ │    <a href="#creating-records" class="hover-link">
│ │ │ │ @@ -48,32 +48,32 @@
│ │ │ │  </h2>
│ │ │ │  <p>The following expression creates a new <code class="inline">Name</code> record where the value of each
│ │ │ │  field <code class="inline">FieldI</code> is the value of evaluating the corresponding expression <code class="inline">ExprI</code>:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p>The fields can be in any order, not necessarily the same order as in the record
│ │ │ │  definition, and fields can be omitted. Omitted fields get their respective
│ │ │ │  default value instead.</p><p>If several fields are to be assigned the same value, the following construction
│ │ │ │  can be used:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK, _=ExprL}</code></pre><p>Omitted fields then get the value of evaluating <code class="inline">ExprL</code> instead of their default
│ │ │ │  values. This feature is primarily intended to be used to create patterns for ETS
│ │ │ │ -and Mnesia match functions.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0979196293-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0979196293-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="0979196293-2">}</span><span class="p" data-group-id="0979196293-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +and Mnesia match functions.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0088810696-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0088810696-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="0088810696-2">}</span><span class="p" data-group-id="0088810696-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="0979196293-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="0979196293-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="0979196293-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0979196293-5">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="0979196293-5">}</span><span class="p" data-group-id="0979196293-4">)</span><span class="p">.</span></code></pre><h2 id="accessing-record-fields" class="section-heading">
│ │ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="0088810696-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="0088810696-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="0088810696-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0088810696-5">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="0088810696-5">}</span><span class="p" data-group-id="0088810696-4">)</span><span class="p">.</span></code></pre><h2 id="accessing-record-fields" class="section-heading">
│ │ │ │    <a href="#accessing-record-fields" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Accessing Record Fields</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="text">Expr#Name.Field</code></pre><p>Returns the value of the specified field. <code class="inline">Expr</code> is to evaluate to a <code class="inline">Name</code>
│ │ │ │ -record.</p><p><em>Example</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7514721951-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7514721951-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="7514721951-2">}</span><span class="p" data-group-id="7514721951-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +record.</p><p><em>Example</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0214258042-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0214258042-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="0214258042-2">}</span><span class="p" data-group-id="0214258042-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">get_person_name</span><span class="p" data-group-id="7514721951-3">(</span><span class="n">Person</span><span class="p" data-group-id="7514721951-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">get_person_name</span><span class="p" data-group-id="0214258042-3">(</span><span class="n">Person</span><span class="p" data-group-id="0214258042-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">.</span></code></pre><p>The following expression returns the position of the specified field in the
│ │ │ │ -tuple representation of the record:</p><pre><code class="text">#Name.Field</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1625929485-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1625929485-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="1625929485-2">}</span><span class="p" data-group-id="1625929485-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +tuple representation of the record:</p><pre><code class="text">#Name.Field</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3997166176-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3997166176-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="3997166176-2">}</span><span class="p" data-group-id="3997166176-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="1625929485-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1625929485-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="1625929485-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1625929485-4">)</span><span class="p">.</span></code></pre><h2 id="updating-records" class="section-heading">
│ │ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="3997166176-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3997166176-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="3997166176-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3997166176-4">)</span><span class="p">.</span></code></pre><h2 id="updating-records" class="section-heading">
│ │ │ │    <a href="#updating-records" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Updating Records</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="text">Expr#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p><code class="inline">Expr</code> is to evaluate to a <code class="inline">Name</code> record. A copy of this record is returned,
│ │ │ │  with the value of each specified field <code class="inline">FieldI</code> changed to the value of
│ │ │ │ @@ -83,48 +83,48 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Records in Guards</span>
│ │ │ │  </h2>
│ │ │ │  <p>Since record expressions are expanded to tuple expressions, creating
│ │ │ │  records and accessing record fields are allowed in guards. However,
│ │ │ │  all subexpressions (for initializing fields), must be valid guard
│ │ │ │ -expressions as well.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="5776004384-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5776004384-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Msg</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">#</span><span class="ss">msg</span><span class="p" data-group-id="5776004384-2">{</span><span class="ss">to</span><span class="o">=</span><span class="ss">void</span><span class="p">,</span><span class="w"> </span><span class="ss">no</span><span class="o">=</span><span class="mi">3</span><span class="p" data-group-id="5776004384-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +expressions as well.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="4786360029-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4786360029-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Msg</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">#</span><span class="ss">msg</span><span class="p" data-group-id="4786360029-2">{</span><span class="ss">to</span><span class="o">=</span><span class="ss">void</span><span class="p">,</span><span class="w"> </span><span class="ss">no</span><span class="o">=</span><span class="mi">3</span><span class="p" data-group-id="4786360029-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle</span><span class="p" data-group-id="5776004384-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5776004384-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">running</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>There is also a type test BIF <a href="../../../lib/../erts/doc/html/erlang.html#is_record/2"><code class="inline">is_record(Term, RecordTag)</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_person</span><span class="p" data-group-id="3693149419-1">(</span><span class="n">P</span><span class="p" data-group-id="3693149419-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="3693149419-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="3693149419-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle</span><span class="p" data-group-id="4786360029-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4786360029-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">running</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>There is also a type test BIF <a href="../../../lib/../erts/doc/html/erlang.html#is_record/2"><code class="inline">is_record(Term, RecordTag)</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_person</span><span class="p" data-group-id="5848705540-1">(</span><span class="n">P</span><span class="p" data-group-id="5848705540-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="5848705540-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="5848705540-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">is_person</span><span class="p" data-group-id="3693149419-3">(</span><span class="p">_</span><span class="n">P</span><span class="p" data-group-id="3693149419-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">is_person</span><span class="p" data-group-id="5848705540-3">(</span><span class="p">_</span><span class="n">P</span><span class="p" data-group-id="5848705540-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">false</span><span class="p">.</span></code></pre><h2 id="records-in-patterns" class="section-heading">
│ │ │ │    <a href="#records-in-patterns" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Records in Patterns</span>
│ │ │ │  </h2>
│ │ │ │  <p>A pattern that matches a certain record is created in the same way as a record
│ │ │ │  is created:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p>In this case, one or more of <code class="inline">Expr1</code> ... <code class="inline">ExprK</code> can be unbound variables.</p><h2 id="nested-records" class="section-heading">
│ │ │ │    <a href="#nested-records" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Nested Records</span>
│ │ │ │  </h2>
│ │ │ │ -<p>Assume the following record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8852158475-1">(</span><span class="ss">nrec0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8852158475-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested0&quot;</span><span class="p" data-group-id="8852158475-2">}</span><span class="p" data-group-id="8852158475-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8852158475-3">(</span><span class="ss">nrec1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8852158475-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec0</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec0</span><span class="p" data-group-id="8852158475-5">{</span><span class="p" data-group-id="8852158475-5">}</span><span class="p" data-group-id="8852158475-4">}</span><span class="p" data-group-id="8852158475-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8852158475-6">(</span><span class="ss">nrec2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8852158475-7">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested2&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec1</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec1</span><span class="p" data-group-id="8852158475-8">{</span><span class="p" data-group-id="8852158475-8">}</span><span class="p" data-group-id="8852158475-7">}</span><span class="p" data-group-id="8852158475-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>Assume the following record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8098363721-1">(</span><span class="ss">nrec0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8098363721-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested0&quot;</span><span class="p" data-group-id="8098363721-2">}</span><span class="p" data-group-id="8098363721-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8098363721-3">(</span><span class="ss">nrec1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8098363721-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec0</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec0</span><span class="p" data-group-id="8098363721-5">{</span><span class="p" data-group-id="8098363721-5">}</span><span class="p" data-group-id="8098363721-4">}</span><span class="p" data-group-id="8098363721-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8098363721-6">(</span><span class="ss">nrec2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8098363721-7">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested2&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec1</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec1</span><span class="p" data-group-id="8098363721-8">{</span><span class="p" data-group-id="8098363721-8">}</span><span class="p" data-group-id="8098363721-7">}</span><span class="p" data-group-id="8098363721-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">N2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">nrec2</span><span class="p" data-group-id="8852158475-9">{</span><span class="p" data-group-id="8852158475-9">}</span><span class="p">,</span></code></pre><p>Accessing or updating nested records can be written without parentheses:</p><pre><code class="text">&quot;nested0&quot; = N2#nrec2.nrec1#nrec1.nrec0#nrec0.name,
│ │ │ │ +</span><span class="n">N2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">nrec2</span><span class="p" data-group-id="8098363721-9">{</span><span class="p" data-group-id="8098363721-9">}</span><span class="p">,</span></code></pre><p>Accessing or updating nested records can be written without parentheses:</p><pre><code class="text">&quot;nested0&quot; = N2#nrec2.nrec1#nrec1.nrec0#nrec0.name,
│ │ │ │      N0n = N2#nrec2.nrec1#nrec1.nrec0#nrec0{name = &quot;nested0a&quot;},</code></pre><p>which is equivalent to:</p><pre><code class="text">&quot;nested0&quot; = ((N2#nrec2.nrec1)#nrec1.nrec0)#nrec0.name,
│ │ │ │  N0n = ((N2#nrec2.nrec1)#nrec1.nrec0)#nrec0{name = &quot;nested0a&quot;},</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R14, parentheses were necessary when accessing or updating
│ │ │ │  nested records.</p></section><h2 id="internal-representation-of-records" class="section-heading">
│ │ │ │    <a href="#internal-representation-of-records" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Internal Representation of Records</span>
│ │ │ │  </h2>
│ │ │ │  <p>Record expressions are translated to tuple expressions during compilation. A
│ │ │ │ -record defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5596488958-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5596488958-2">{</span><span class="n">Field1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">FieldN</span><span class="p" data-group-id="5596488958-2">}</span><span class="p" data-group-id="5596488958-1">)</span><span class="p">.</span></code></pre><p>is internally represented by the tuple:</p><pre><code class="text">{Name, Value1, ..., ValueN}</code></pre><p>Here each <code class="inline">ValueI</code> is the default value for <code class="inline">FieldI</code>.</p><p>To each module using records, a pseudo function is added during compilation to
│ │ │ │ -obtain information about records:</p><pre><code class="makeup erlang" translate="no"><span class="nf">record_info</span><span class="p" data-group-id="0445135776-1">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="0445135776-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0445135776-2">[</span><span class="n">Field</span><span class="p" data-group-id="0445135776-2">]</span><span class="w">
│ │ │ │ -</span><span class="nf">record_info</span><span class="p" data-group-id="0445135776-3">(</span><span class="nb">size</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="0445135776-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Size</span></code></pre><p><code class="inline">Size</code> is the size of the tuple representation, that is, one more than the
│ │ │ │ +record defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7102288252-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7102288252-2">{</span><span class="n">Field1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">FieldN</span><span class="p" data-group-id="7102288252-2">}</span><span class="p" data-group-id="7102288252-1">)</span><span class="p">.</span></code></pre><p>is internally represented by the tuple:</p><pre><code class="text">{Name, Value1, ..., ValueN}</code></pre><p>Here each <code class="inline">ValueI</code> is the default value for <code class="inline">FieldI</code>.</p><p>To each module using records, a pseudo function is added during compilation to
│ │ │ │ +obtain information about records:</p><pre><code class="makeup erlang" translate="no"><span class="nf">record_info</span><span class="p" data-group-id="7535104013-1">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="7535104013-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7535104013-2">[</span><span class="n">Field</span><span class="p" data-group-id="7535104013-2">]</span><span class="w">
│ │ │ │ +</span><span class="nf">record_info</span><span class="p" data-group-id="7535104013-3">(</span><span class="nb">size</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="7535104013-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Size</span></code></pre><p><code class="inline">Size</code> is the size of the tuple representation, that is, one more than the
│ │ │ │  number of fields.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/ref_man_processes.xhtml
│ │ │ │ @@ -30,18 +30,18 @@
│ │ │ │  (grow and shrink dynamically) with small memory footprint, fast to create and
│ │ │ │  terminate, and the scheduling overhead is low.</p><h2 id="process-creation" class="section-heading">
│ │ │ │    <a href="#process-creation" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Process Creation</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A process is created by calling <a href="../../../lib/../erts/doc/html/erlang.html#spawn/3"><code class="inline">spawn()</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="1140804513-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="1140804513-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pid</span><span class="p" data-group-id="1140804513-2">(</span><span class="p" data-group-id="1140804513-2">)</span><span class="w">
│ │ │ │ -  </span><span class="n">Module</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="1140804513-3">(</span><span class="p" data-group-id="1140804513-3">)</span><span class="w">
│ │ │ │ -  </span><span class="n">Args</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1140804513-4">[</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="1140804513-4">]</span><span class="w">
│ │ │ │ -    </span><span class="n">ArgI</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="1140804513-5">(</span><span class="p" data-group-id="1140804513-5">)</span></code></pre><p><code class="inline">spawn()</code> creates a new process and returns the pid.</p><p>The new process starts executing in <code class="inline">Module:Name(Arg1,...,ArgN)</code> where the
│ │ │ │ +<p>A process is created by calling <a href="../../../lib/../erts/doc/html/erlang.html#spawn/3"><code class="inline">spawn()</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="7394995069-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="7394995069-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pid</span><span class="p" data-group-id="7394995069-2">(</span><span class="p" data-group-id="7394995069-2">)</span><span class="w">
│ │ │ │ +  </span><span class="n">Module</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="7394995069-3">(</span><span class="p" data-group-id="7394995069-3">)</span><span class="w">
│ │ │ │ +  </span><span class="n">Args</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7394995069-4">[</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="7394995069-4">]</span><span class="w">
│ │ │ │ +    </span><span class="n">ArgI</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7394995069-5">(</span><span class="p" data-group-id="7394995069-5">)</span></code></pre><p><code class="inline">spawn()</code> creates a new process and returns the pid.</p><p>The new process starts executing in <code class="inline">Module:Name(Arg1,...,ArgN)</code> where the
│ │ │ │  arguments are the elements of the (possible empty) <code class="inline">Args</code> argument list.</p><p>There exist a number of different <code class="inline">spawn</code> BIFs:</p><ul><li><a href="../../../lib/../erts/doc/html/erlang.html#spawn/4"><code class="inline">spawn/1,2,3,4</code></a></li><li><a href="../../../lib/../erts/doc/html/erlang.html#spawn_link/4"><code class="inline">spawn_link/1,2,3,4</code></a></li><li><a href="../../../lib/../erts/doc/html/erlang.html#spawn_monitor/4"><code class="inline">spawn_monitor/1,2,3,4</code></a></li><li><a href="../../../lib/../erts/doc/html/erlang.html#spawn_opt/5"><code class="inline">spawn_opt/2,3,4,5</code></a></li><li><a href="../../../lib/../erts/doc/html/erlang.html#spawn_request/5"><code class="inline">spawn_request/1,2,3,4,5</code></a></li></ul><h2 id="registered-processes" class="section-heading">
│ │ │ │    <a href="#registered-processes" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Registered Processes</span>
│ │ │ │  </h2>
│ │ │ │  <p>Besides addressing a process by using its pid, there are also BIFs for
│ │ │ ├── OEBPS/ref_man_functions.xhtml
│ │ │ │ @@ -25,51 +25,51 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Function Declaration Syntax</span>
│ │ │ │  </h2>
│ │ │ │  <p>A <em>function declaration</em> is a sequence of function clauses separated by
│ │ │ │  semicolons, and terminated by a period (<code class="inline">.</code>).</p><p>A <em>function clause</em> consists of a <em>clause head</em> and a <em>clause body</em>, separated by
│ │ │ │  <code class="inline">-&gt;</code>.</p><p>A clause <em>head</em> consists of the function name, an argument list, and an optional
│ │ │ │ -guard sequence beginning with the keyword <code class="inline">when</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="p" data-group-id="9569868708-1">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="9569868708-1">)</span><span class="w"> </span><span class="p" data-group-id="9569868708-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9569868708-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +guard sequence beginning with the keyword <code class="inline">when</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="p" data-group-id="0586240811-1">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="0586240811-1">)</span><span class="w"> </span><span class="p" data-group-id="0586240811-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="0586240811-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="n">Name</span><span class="p" data-group-id="9569868708-3">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="9569868708-3">)</span><span class="w"> </span><span class="p" data-group-id="9569868708-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="9569868708-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="n">Name</span><span class="p" data-group-id="0586240811-3">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="0586240811-3">)</span><span class="w"> </span><span class="p" data-group-id="0586240811-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="0586240811-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">BodyK</span><span class="p">.</span></code></pre><p>The function name is an atom. Each argument is a pattern.</p><p>The number of arguments <code class="inline">N</code> is the <em>arity</em> of the function. A function is
│ │ │ │  uniquely defined by the module name, function name, and arity. That is, two
│ │ │ │  functions with the same name and in the same module, but with different arities
│ │ │ │  are two different functions.</p><p>A function named <code class="inline">f</code> in module <code class="inline">mod</code> and with arity <code class="inline">N</code> is often denoted as
│ │ │ │  <code class="inline">mod:f/N</code>.</p><p>A clause <em>body</em> consists of a sequence of expressions separated by comma (<code class="inline">,</code>):</p><pre><code class="text">Expr1,
│ │ │ │  ...,
│ │ │ │  ExprN</code></pre><p>Valid Erlang expressions and guard sequences are described in
│ │ │ │ -<a href="expressions.xhtml">Expressions</a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">fact</span><span class="p" data-group-id="1202602873-1">(</span><span class="n">N</span><span class="p" data-group-id="1202602873-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% first clause head</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="1202602873-2">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="1202602873-2">)</span><span class="p">;</span><span class="w">     </span><span class="c1">% first clause body</span><span class="w">
│ │ │ │ +<a href="expressions.xhtml">Expressions</a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">fact</span><span class="p" data-group-id="9459675543-1">(</span><span class="n">N</span><span class="p" data-group-id="9459675543-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% first clause head</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="9459675543-2">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="9459675543-2">)</span><span class="p">;</span><span class="w">     </span><span class="c1">% first clause body</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="1202602873-3">(</span><span class="mi">0</span><span class="p" data-group-id="1202602873-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">             </span><span class="c1">% second clause head</span><span class="w">
│ │ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="9459675543-3">(</span><span class="mi">0</span><span class="p" data-group-id="9459675543-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">             </span><span class="c1">% second clause head</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">.</span><span class="w">                 </span><span class="c1">% second clause body</span></code></pre><p><a href="" id="eval"></a></p><h2 id="function-evaluation" class="section-heading">
│ │ │ │    <a href="#function-evaluation" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Function Evaluation</span>
│ │ │ │  </h2>
│ │ │ │  <p>When a function <code class="inline">M:F/N</code> is called, first the code for the function is located.
│ │ │ │  If the function cannot be found, an <code class="inline">undef</code> runtime error occurs. Notice that
│ │ │ │  the function must be exported to be visible outside the module it is defined in.</p><p>If the function is found, the function clauses are scanned sequentially until a
│ │ │ │  clause is found that fulfills both of the following two conditions:</p><ol><li>The patterns in the clause head can be successfully matched against the given
│ │ │ │  arguments.</li><li>The guard sequence, if any, is true.</li></ol><p>If such a clause cannot be found, a <code class="inline">function_clause</code> runtime error occurs.</p><p>If such a clause is found, the corresponding clause body is evaluated. That is,
│ │ │ │  the expressions in the body are evaluated sequentially and the value of the last
│ │ │ │ -expression is returned.</p><p>Consider the function <code class="inline">fact</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7913551085-1">(</span><span class="ss">mod</span><span class="p" data-group-id="7913551085-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7913551085-2">(</span><span class="p" data-group-id="7913551085-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7913551085-3">]</span><span class="p" data-group-id="7913551085-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +expression is returned.</p><p>Consider the function <code class="inline">fact</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9441918709-1">(</span><span class="ss">mod</span><span class="p" data-group-id="9441918709-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9441918709-2">(</span><span class="p" data-group-id="9441918709-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9441918709-3">]</span><span class="p" data-group-id="9441918709-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="7913551085-4">(</span><span class="n">N</span><span class="p" data-group-id="7913551085-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="7913551085-5">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7913551085-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="7913551085-6">(</span><span class="mi">0</span><span class="p" data-group-id="7913551085-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="9441918709-4">(</span><span class="n">N</span><span class="p" data-group-id="9441918709-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="9441918709-5">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9441918709-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="9441918709-6">(</span><span class="mi">0</span><span class="p" data-group-id="9441918709-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">.</span></code></pre><p>Assume that you want to calculate the factorial for 1:</p><pre><code class="text">1&gt; mod:fact(1).</code></pre><p>Evaluation starts at the first clause. The pattern <code class="inline">N</code> is matched against
│ │ │ │  argument 1. The matching succeeds and the guard (<code class="inline">N &gt; 0</code>) is true, thus <code class="inline">N</code> is
│ │ │ │ -bound to 1, and the corresponding body is evaluated:</p><pre><code class="makeup erlang" translate="no"><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="4574393302-1">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="4574393302-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4574393302-2">(</span><span class="n">N</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">bound</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4574393302-2">)</span><span class="w">
│ │ │ │ -</span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="4574393302-3">(</span><span class="mi">0</span><span class="p" data-group-id="4574393302-3">)</span></code></pre><p>Now, <code class="inline">fact(0)</code> is called, and the function clauses are scanned
│ │ │ │ +bound to 1, and the corresponding body is evaluated:</p><pre><code class="makeup erlang" translate="no"><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="1253596419-1">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="1253596419-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1253596419-2">(</span><span class="n">N</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">bound</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1253596419-2">)</span><span class="w">
│ │ │ │ +</span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="1253596419-3">(</span><span class="mi">0</span><span class="p" data-group-id="1253596419-3">)</span></code></pre><p>Now, <code class="inline">fact(0)</code> is called, and the function clauses are scanned
│ │ │ │  sequentially again. First, the pattern <code class="inline">N</code> is matched against 0. The
│ │ │ │  matching succeeds, but the guard (<code class="inline">N &gt; 0</code>) is false. Second, the
│ │ │ │  pattern <code class="inline">0</code> is matched against the argument <code class="inline">0</code>. The matching succeeds
│ │ │ │  and the body is evaluated:</p><pre><code class="text">1 * fact(0) =&gt;
│ │ │ │  1 * 1 =&gt;
│ │ │ │  1</code></pre><p>Evaluation has succeed and <code class="inline">mod:fact(1)</code> returns 1.</p><p>If <code class="inline">mod:fact/1</code> is called with a negative number as argument, no clause head
│ │ │ │  matches. A <code class="inline">function_clause</code> runtime error occurs.</p><h2 id="tail-recursion" class="section-heading">
│ │ │ │ @@ -78,17 +78,17 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Tail recursion</span>
│ │ │ │  </h2>
│ │ │ │  <p>If the last expression of a function body is a function call, a
│ │ │ │  <em>tail-recursive call</em> is done. This is to ensure that no system
│ │ │ │  resources, for example, call stack, are consumed. This means that an
│ │ │ │  infinite loop using tail-recursive calls will not exhaust the call
│ │ │ │ -stack and can (in principle) run forever.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="6194021798-1">(</span><span class="n">N</span><span class="p" data-group-id="6194021798-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6194021798-2">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194021798-3">[</span><span class="n">N</span><span class="p" data-group-id="6194021798-3">]</span><span class="p" data-group-id="6194021798-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="6194021798-4">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="6194021798-4">)</span><span class="p">.</span></code></pre><p>The earlier factorial example is a counter-example. It is not
│ │ │ │ +stack and can (in principle) run forever.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="0403058603-1">(</span><span class="n">N</span><span class="p" data-group-id="0403058603-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0403058603-2">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0403058603-3">[</span><span class="n">N</span><span class="p" data-group-id="0403058603-3">]</span><span class="p" data-group-id="0403058603-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="0403058603-4">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="0403058603-4">)</span><span class="p">.</span></code></pre><p>The earlier factorial example is a counter-example. It is not
│ │ │ │  tail-recursive, since a multiplication is done on the result of the recursive
│ │ │ │  call to <code class="inline">fact(N-1)</code>.</p><h2 id="built-in-functions-bifs" class="section-heading">
│ │ │ │    <a href="#built-in-functions-bifs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Built-In Functions (BIFs)</span>
│ │ │ │  </h2>
│ │ │ │ @@ -96,14 +96,14 @@
│ │ │ │  system. BIFs do things that are difficult or impossible to implement
│ │ │ │  in Erlang. Most of the BIFs belong to module <a href="../../../lib/../erts/doc/html/erlang.html"><code class="inline">erlang</code></a>, but there
│ │ │ │  are also BIFs belonging to a few other modules, for example <a href="../../../lib/stdlib/doc/html/lists.html"><code class="inline">lists</code></a>
│ │ │ │  and <a href="../../../lib/stdlib/doc/html/ets.html"><code class="inline">ets</code></a>.</p><p>The most commonly used BIFs belonging to <a href="../../../lib/../erts/doc/html/erlang.html"><code class="inline">erlang</code></a> are <em>auto-imported</em>. They do
│ │ │ │  not need to be prefixed with the module name. Which BIFs that are auto-imported
│ │ │ │  is specified in the <a href="../../../lib/../erts/doc/html/erlang.html"><code class="inline">erlang</code></a> module in ERTS. For example, standard-type
│ │ │ │  conversion BIFs like <code class="inline">atom_to_list</code> and BIFs allowed in guards can be called
│ │ │ │ -without specifying the module name.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="1097951938-1">(</span><span class="p" data-group-id="1097951938-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1097951938-2">}</span><span class="p" data-group-id="1097951938-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +without specifying the module name.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="1146625027-1">(</span><span class="p" data-group-id="1146625027-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1146625027-2">}</span><span class="p" data-group-id="1146625027-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="1097951938-3">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="1097951938-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="1146625027-3">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="1146625027-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;Erlang&quot;</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/records_macros.xhtml
│ │ │ │ @@ -29,40 +29,40 @@
│ │ │ │  </h2>
│ │ │ │  <p>To illustrate this, the messenger example from the previous section is divided
│ │ │ │  into the following five files:</p><ul><li><p><code class="inline">mess_config.hrl</code></p><p>Header file for configuration data</p></li><li><p><code class="inline">mess_interface.hrl</code></p><p>Interface definitions between the client and the messenger</p></li><li><p><code class="inline">user_interface.erl</code></p><p>Functions for the user interface</p></li><li><p><code class="inline">mess_client.erl</code></p><p>Functions for the client side of the messenger</p></li><li><p><code class="inline">mess_server.erl</code></p><p>Functions for the server side of the messenger</p></li></ul><p>While doing this, the message passing interface between the shell, the client,
│ │ │ │  and the server is cleaned up and is defined using <em>records</em>. Also, <em>macros</em> are
│ │ │ │  introduced:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_config.hrl----</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Configure the location of the server node,</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2535063834-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="2535063834-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2207751278-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="2207751278-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_interface.hrl----</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Message interface between client and server and client shell for</span><span class="w">
│ │ │ │  </span><span class="c1">%%% messenger program</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%Messages from Client to server received in server/1 function.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1898720213-1">(</span><span class="ss">logon</span><span class="p">,</span><span class="p" data-group-id="1898720213-2">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="p" data-group-id="1898720213-2">}</span><span class="p" data-group-id="1898720213-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1898720213-3">(</span><span class="ss">message</span><span class="p">,</span><span class="p" data-group-id="1898720213-4">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="1898720213-4">}</span><span class="p" data-group-id="1898720213-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1641288278-1">(</span><span class="ss">logon</span><span class="p">,</span><span class="p" data-group-id="1641288278-2">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="p" data-group-id="1641288278-2">}</span><span class="p" data-group-id="1641288278-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1641288278-3">(</span><span class="ss">message</span><span class="p">,</span><span class="p" data-group-id="1641288278-4">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="1641288278-4">}</span><span class="p" data-group-id="1641288278-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% {&#39;EXIT&#39;, ClientPid, Reason}  (client terminated or unreachable.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Messages from Server to Client, received in await_result/0 function</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1898720213-5">(</span><span class="ss">abort_client</span><span class="p">,</span><span class="p" data-group-id="1898720213-6">{</span><span class="ss">message</span><span class="p" data-group-id="1898720213-6">}</span><span class="p" data-group-id="1898720213-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1641288278-5">(</span><span class="ss">abort_client</span><span class="p">,</span><span class="p" data-group-id="1641288278-6">{</span><span class="ss">message</span><span class="p" data-group-id="1641288278-6">}</span><span class="p" data-group-id="1641288278-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% Messages are: user_exists_at_other_node,</span><span class="w">
│ │ │ │  </span><span class="c1">%%%               you_are_not_logged_on</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1898720213-7">(</span><span class="ss">server_reply</span><span class="p">,</span><span class="p" data-group-id="1898720213-8">{</span><span class="ss">message</span><span class="p" data-group-id="1898720213-8">}</span><span class="p" data-group-id="1898720213-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1641288278-7">(</span><span class="ss">server_reply</span><span class="p">,</span><span class="p" data-group-id="1641288278-8">{</span><span class="ss">message</span><span class="p" data-group-id="1641288278-8">}</span><span class="p" data-group-id="1641288278-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% Messages are: logged_on</span><span class="w">
│ │ │ │  </span><span class="c1">%%%               receiver_not_found</span><span class="w">
│ │ │ │  </span><span class="c1">%%%               sent  (Message has been sent (no guarantee)</span><span class="w">
│ │ │ │  </span><span class="c1">%%% Messages from Server to Client received in client/1 function</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1898720213-9">(</span><span class="ss">message_from</span><span class="p">,</span><span class="p" data-group-id="1898720213-10">{</span><span class="ss">from_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="1898720213-10">}</span><span class="p" data-group-id="1898720213-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1641288278-9">(</span><span class="ss">message_from</span><span class="p">,</span><span class="p" data-group-id="1641288278-10">{</span><span class="ss">from_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="1641288278-10">}</span><span class="p" data-group-id="1641288278-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Messages from shell to Client received in client/1 function</span><span class="w">
│ │ │ │  </span><span class="c1">%%% spawn(mess_client, client, [server_node(), Name])</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1898720213-11">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="1898720213-12">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="1898720213-12">}</span><span class="p" data-group-id="1898720213-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1641288278-11">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="1641288278-12">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="1641288278-12">}</span><span class="p" data-group-id="1641288278-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% logoff</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE user_interface.erl----</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% User interface to the messenger program</span><span class="w">
│ │ │ │  </span><span class="c1">%%% login(Name)</span><span class="w">
│ │ │ │  </span><span class="c1">%%%     One user at a time can log in from each Erlang node in the</span><span class="w">
│ │ │ │ @@ -75,177 +75,177 @@
│ │ │ │  </span><span class="c1">%%%     Logs off anybody at that node</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% message(ToName, Message)</span><span class="w">
│ │ │ │  </span><span class="c1">%%%     sends Message to ToName. Error messages if the user of this</span><span class="w">
│ │ │ │  </span><span class="c1">%%%     function is not logged on or if ToName is not logged on at</span><span class="w">
│ │ │ │  </span><span class="c1">%%%     any node.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4161865466-1">(</span><span class="ss">user_interface</span><span class="p" data-group-id="4161865466-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4161865466-2">(</span><span class="p" data-group-id="4161865466-3">[</span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4161865466-3">]</span><span class="p" data-group-id="4161865466-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4161865466-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="4161865466-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4161865466-5">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="4161865466-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5168626654-1">(</span><span class="ss">user_interface</span><span class="p" data-group-id="5168626654-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5168626654-2">(</span><span class="p" data-group-id="5168626654-3">[</span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5168626654-3">]</span><span class="p" data-group-id="5168626654-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5168626654-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="5168626654-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5168626654-5">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="5168626654-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="4161865466-6">(</span><span class="n">Name</span><span class="p" data-group-id="4161865466-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="4161865466-7">(</span><span class="ss">mess_client</span><span class="p" data-group-id="4161865466-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="5168626654-6">(</span><span class="n">Name</span><span class="p" data-group-id="5168626654-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="5168626654-7">(</span><span class="ss">mess_client</span><span class="p" data-group-id="5168626654-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="4161865466-8">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="4161865466-9">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161865466-10">[</span><span class="o">?</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4161865466-10">]</span><span class="p" data-group-id="4161865466-9">)</span><span class="p" data-group-id="4161865466-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="5168626654-8">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="5168626654-9">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5168626654-10">[</span><span class="o">?</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="5168626654-10">]</span><span class="p" data-group-id="5168626654-9">)</span><span class="p" data-group-id="5168626654-8">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="4161865466-11">(</span><span class="p" data-group-id="4161865466-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="5168626654-11">(</span><span class="p" data-group-id="5168626654-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="4161865466-12">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4161865466-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="4161865466-13">(</span><span class="ss">mess_client</span><span class="p" data-group-id="4161865466-13">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="5168626654-12">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5168626654-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="5168626654-13">(</span><span class="ss">mess_client</span><span class="p" data-group-id="5168626654-13">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="4161865466-14">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="4161865466-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="5168626654-14">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="5168626654-14">}</span><span class="p">,</span><span class="w">
│ │ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_client.erl----</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% The client process which runs on each user node</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0212296476-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="0212296476-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0212296476-2">(</span><span class="p" data-group-id="0212296476-3">[</span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0212296476-3">]</span><span class="p" data-group-id="0212296476-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="0212296476-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="0212296476-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="0212296476-5">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0212296476-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0212296476-6">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="0212296476-6">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="0212296476-7">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="0212296476-8">(</span><span class="p" data-group-id="0212296476-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="0212296476-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="0212296476-9">(</span><span class="p" data-group-id="0212296476-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="0212296476-10">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0212296476-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8054564156-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="8054564156-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8054564156-2">(</span><span class="p" data-group-id="8054564156-3">[</span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8054564156-3">]</span><span class="p" data-group-id="8054564156-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="8054564156-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="8054564156-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="8054564156-5">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8054564156-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8054564156-6">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="8054564156-6">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="8054564156-7">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="8054564156-8">(</span><span class="p" data-group-id="8054564156-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="8054564156-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="8054564156-9">(</span><span class="p" data-group-id="8054564156-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="8054564156-10">(</span><span class="n">Server_Node</span><span class="p" data-group-id="8054564156-10">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="0212296476-11">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0212296476-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="8054564156-11">(</span><span class="n">Server_Node</span><span class="p" data-group-id="8054564156-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="0212296476-12">(</span><span class="ss">normal</span><span class="p" data-group-id="0212296476-12">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="0212296476-13">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="0212296476-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="0212296476-14">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="0212296476-14">}</span><span class="w"> </span><span class="o">!</span><span class="w">
│ │ │ │ -                </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="0212296476-15">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="0212296476-16">(</span><span class="p" data-group-id="0212296476-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="0212296476-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="0212296476-17">(</span><span class="p" data-group-id="0212296476-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0212296476-18">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0212296476-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0212296476-19">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0212296476-20">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0212296476-20">]</span><span class="p" data-group-id="0212296476-19">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="8054564156-12">(</span><span class="ss">normal</span><span class="p" data-group-id="8054564156-12">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="8054564156-13">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="8054564156-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="8054564156-14">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="8054564156-14">}</span><span class="w"> </span><span class="o">!</span><span class="w">
│ │ │ │ +                </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="8054564156-15">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="8054564156-16">(</span><span class="p" data-group-id="8054564156-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="8054564156-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="8054564156-17">(</span><span class="p" data-group-id="8054564156-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8054564156-18">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8054564156-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8054564156-19">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8054564156-20">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8054564156-20">]</span><span class="p" data-group-id="8054564156-19">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="0212296476-21">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0212296476-21">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="8054564156-21">(</span><span class="n">Server_Node</span><span class="p" data-group-id="8054564156-21">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="0212296476-22">(</span><span class="p" data-group-id="0212296476-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="8054564156-22">(</span><span class="p" data-group-id="8054564156-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="0212296476-23">{</span><span class="ss">message</span><span class="o">=</span><span class="n">Why</span><span class="p" data-group-id="0212296476-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0212296476-24">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0212296476-25">[</span><span class="n">Why</span><span class="p" data-group-id="0212296476-25">]</span><span class="p" data-group-id="0212296476-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="0212296476-26">(</span><span class="ss">normal</span><span class="p" data-group-id="0212296476-26">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="0212296476-27">{</span><span class="ss">message</span><span class="o">=</span><span class="n">What</span><span class="p" data-group-id="0212296476-27">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0212296476-28">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0212296476-29">[</span><span class="n">What</span><span class="p" data-group-id="0212296476-29">]</span><span class="p" data-group-id="0212296476-28">)</span><span class="w">
│ │ │ │ +        </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="8054564156-23">{</span><span class="ss">message</span><span class="o">=</span><span class="n">Why</span><span class="p" data-group-id="8054564156-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8054564156-24">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8054564156-25">[</span><span class="n">Why</span><span class="p" data-group-id="8054564156-25">]</span><span class="p" data-group-id="8054564156-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="8054564156-26">(</span><span class="ss">normal</span><span class="p" data-group-id="8054564156-26">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="8054564156-27">{</span><span class="ss">message</span><span class="o">=</span><span class="n">What</span><span class="p" data-group-id="8054564156-27">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8054564156-28">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8054564156-29">[</span><span class="n">What</span><span class="p" data-group-id="8054564156-29">]</span><span class="p" data-group-id="8054564156-28">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0212296476-30">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0212296476-31">[</span><span class="p" data-group-id="0212296476-31">]</span><span class="p" data-group-id="0212296476-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="0212296476-32">(</span><span class="ss">timeout</span><span class="p" data-group-id="0212296476-32">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8054564156-30">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8054564156-31">[</span><span class="p" data-group-id="8054564156-31">]</span><span class="p" data-group-id="8054564156-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="8054564156-32">(</span><span class="ss">timeout</span><span class="p" data-group-id="8054564156-32">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%----END FILE---</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_server.erl----</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% This is the server process of the messenger service</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9550852607-1">(</span><span class="ss">mess_server</span><span class="p" data-group-id="9550852607-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9550852607-2">(</span><span class="p" data-group-id="9550852607-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9550852607-3">]</span><span class="p" data-group-id="9550852607-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="9550852607-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="9550852607-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="9550852607-5">(</span><span class="p" data-group-id="9550852607-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9550852607-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9550852607-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="9550852607-7">(</span><span class="p" data-group-id="9550852607-8">[</span><span class="p" data-group-id="9550852607-8">]</span><span class="p" data-group-id="9550852607-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3688564104-1">(</span><span class="ss">mess_server</span><span class="p" data-group-id="3688564104-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3688564104-2">(</span><span class="p" data-group-id="3688564104-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3688564104-3">]</span><span class="p" data-group-id="3688564104-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3688564104-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="3688564104-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="3688564104-5">(</span><span class="p" data-group-id="3688564104-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="3688564104-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="3688564104-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="3688564104-7">(</span><span class="p" data-group-id="3688564104-8">[</span><span class="p" data-group-id="3688564104-8">]</span><span class="p" data-group-id="3688564104-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="9550852607-9">(</span><span class="n">User_List</span><span class="p" data-group-id="9550852607-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9550852607-10">(</span><span class="s">&quot;User list = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9550852607-11">[</span><span class="n">User_List</span><span class="p" data-group-id="9550852607-11">]</span><span class="p" data-group-id="9550852607-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="3688564104-9">(</span><span class="n">User_List</span><span class="p" data-group-id="3688564104-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3688564104-10">(</span><span class="s">&quot;User list = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3688564104-11">[</span><span class="n">User_List</span><span class="p" data-group-id="3688564104-11">]</span><span class="p" data-group-id="3688564104-10">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="9550852607-12">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="9550852607-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="9550852607-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9550852607-14">(</span><span class="n">New_User_List</span><span class="p" data-group-id="9550852607-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9550852607-15">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9550852607-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="9550852607-16">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9550852607-17">(</span><span class="n">New_User_List</span><span class="p" data-group-id="9550852607-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="9550852607-18">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="9550852607-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="9550852607-19">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-19">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9550852607-20">(</span><span class="n">User_List</span><span class="p" data-group-id="9550852607-20">)</span><span class="w">
│ │ │ │ +        </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="3688564104-12">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="3688564104-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="3688564104-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="3688564104-14">(</span><span class="n">New_User_List</span><span class="p" data-group-id="3688564104-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3688564104-15">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3688564104-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="3688564104-16">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="3688564104-17">(</span><span class="n">New_User_List</span><span class="p" data-group-id="3688564104-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="3688564104-18">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="3688564104-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="3688564104-19">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-19">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="3688564104-20">(</span><span class="n">User_List</span><span class="p" data-group-id="3688564104-20">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="9550852607-21">(</span><span class="p" data-group-id="9550852607-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9550852607-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9550852607-23">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9550852607-24">[</span><span class="p" data-group-id="9550852607-24">]</span><span class="p" data-group-id="9550852607-23">)</span><span class="p" data-group-id="9550852607-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="3688564104-21">(</span><span class="p" data-group-id="3688564104-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="3688564104-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="3688564104-23">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3688564104-24">[</span><span class="p" data-group-id="3688564104-24">]</span><span class="p" data-group-id="3688564104-23">)</span><span class="p" data-group-id="3688564104-22">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="9550852607-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="3688564104-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="9550852607-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="3688564104-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="9550852607-27">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="9550852607-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="3688564104-27">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="3688564104-27">}</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="9550852607-28">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">logged_on</span><span class="p" data-group-id="9550852607-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">link</span><span class="p" data-group-id="9550852607-29">(</span><span class="n">From</span><span class="p" data-group-id="9550852607-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9550852607-30">[</span><span class="p" data-group-id="9550852607-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9550852607-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="3688564104-28">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">logged_on</span><span class="p" data-group-id="3688564104-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">link</span><span class="p" data-group-id="3688564104-29">(</span><span class="n">From</span><span class="p" data-group-id="3688564104-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="3688564104-30">[</span><span class="p" data-group-id="3688564104-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3688564104-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="9550852607-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="9550852607-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-33">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="3688564104-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="3688564104-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-33">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="9550852607-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="3688564104-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9550852607-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3688564104-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="9550852607-36">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="9550852607-36">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9550852607-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9550852607-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9550852607-38">}</span><span class="p" data-group-id="9550852607-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="9550852607-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-39">)</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="3688564104-36">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="3688564104-36">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3688564104-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3688564104-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3688564104-38">}</span><span class="p" data-group-id="3688564104-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="3688564104-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-39">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="9550852607-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="3688564104-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9550852607-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9550852607-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3688564104-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688564104-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="9550852607-42">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">receiver_not_found</span><span class="p" data-group-id="9550852607-42">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9550852607-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9550852607-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="9550852607-44">}</span><span class="p" data-group-id="9550852607-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_from</span><span class="p" data-group-id="9550852607-45">{</span><span class="ss">from_name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="9550852607-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="9550852607-46">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">sent</span><span class="p" data-group-id="9550852607-46">}</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="3688564104-42">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">receiver_not_found</span><span class="p" data-group-id="3688564104-42">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3688564104-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3688564104-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="3688564104-44">}</span><span class="p" data-group-id="3688564104-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_from</span><span class="p" data-group-id="3688564104-45">{</span><span class="ss">from_name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="3688564104-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="3688564104-46">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">sent</span><span class="p" data-group-id="3688564104-46">}</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%----END FILE---</span></code></pre><h2 id="header-files" class="section-heading">
│ │ │ │    <a href="#header-files" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Header Files</span>
│ │ │ │  </h2>
│ │ │ │  <p>As shown above, some files have extension <code class="inline">.hrl</code>. These are header files that
│ │ │ │ -are included in the <code class="inline">.erl</code> files by:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4409395013-1">(</span><span class="s">&quot;File_Name&quot;</span><span class="p" data-group-id="4409395013-1">)</span><span class="p">.</span></code></pre><p>for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5008104224-1">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="5008104224-1">)</span><span class="p">.</span></code></pre><p>In the case above the file is fetched from the same directory as all the other
│ │ │ │ +are included in the <code class="inline">.erl</code> files by:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1110046101-1">(</span><span class="s">&quot;File_Name&quot;</span><span class="p" data-group-id="1110046101-1">)</span><span class="p">.</span></code></pre><p>for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3635510790-1">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="3635510790-1">)</span><span class="p">.</span></code></pre><p>In the case above the file is fetched from the same directory as all the other
│ │ │ │  files in the messenger example. (<em>manual</em>).</p><p>.hrl files can contain any valid Erlang code but are most often used for record
│ │ │ │  and macro definitions.</p><h2 id="records" class="section-heading">
│ │ │ │    <a href="#records" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Records</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A record is defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7371708331-1">(</span><span class="ss">name_of_record</span><span class="p">,</span><span class="p" data-group-id="7371708331-2">{</span><span class="ss">field_name1</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name2</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7371708331-2">}</span><span class="p" data-group-id="7371708331-1">)</span><span class="p">.</span></code></pre><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6821787874-1">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="6821787874-2">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="6821787874-2">}</span><span class="p" data-group-id="6821787874-1">)</span><span class="p">.</span></code></pre><p>This is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2604817174-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To_Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2604817174-1">}</span></code></pre><p>Creating a record is best illustrated by an example:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="2331590709-1">{</span><span class="ss">message</span><span class="o">=</span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="ss">fred</span><span class="p">)</span></code></pre><p>This creates:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8843154035-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8843154035-1">}</span></code></pre><p>Notice that you do not have to worry about the order you assign values to the
│ │ │ │ +<p>A record is defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7021807225-1">(</span><span class="ss">name_of_record</span><span class="p">,</span><span class="p" data-group-id="7021807225-2">{</span><span class="ss">field_name1</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name2</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7021807225-2">}</span><span class="p" data-group-id="7021807225-1">)</span><span class="p">.</span></code></pre><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3664166470-1">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="3664166470-2">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="3664166470-2">}</span><span class="p" data-group-id="3664166470-1">)</span><span class="p">.</span></code></pre><p>This is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3448006152-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To_Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3448006152-1">}</span></code></pre><p>Creating a record is best illustrated by an example:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="0665764748-1">{</span><span class="ss">message</span><span class="o">=</span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="ss">fred</span><span class="p">)</span></code></pre><p>This creates:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8940739165-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8940739165-1">}</span></code></pre><p>Notice that you do not have to worry about the order you assign values to the
│ │ │ │  various parts of the records when you create it. The advantage of using records
│ │ │ │  is that by placing their definitions in header files you can conveniently define
│ │ │ │  interfaces that are easy to change. For example, if you want to add a new field
│ │ │ │  to the record, you only have to change the code where the new field is used and
│ │ │ │  not at every place the record is referred to. If you leave out a field when
│ │ │ │  creating a record, it gets the value of the atom <code class="inline">undefined</code>. (<em>manual</em>)</p><p>Pattern matching with records is very similar to creating records. For example,
│ │ │ │ -inside a <code class="inline">case</code> or <code class="inline">receive</code>:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="2512307030-1">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="2512307030-1">}</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>This is the same as:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8913946315-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8913946315-1">}</span></code></pre><h2 id="macros" class="section-heading">
│ │ │ │ +inside a <code class="inline">case</code> or <code class="inline">receive</code>:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="4929777377-1">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="4929777377-1">}</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>This is the same as:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6980358471-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6980358471-1">}</span></code></pre><h2 id="macros" class="section-heading">
│ │ │ │    <a href="#macros" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Macros</span>
│ │ │ │  </h2>
│ │ │ │  <p>Another thing that has been added to the messenger is a macro. The file
│ │ │ │  <code class="inline">mess_config.hrl</code> contains the definition:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Configure the location of the server node,</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8838476195-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="8838476195-1">)</span><span class="p">.</span></code></pre><p>This file is included in <code class="inline">mess_server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2846677947-1">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="2846677947-1">)</span><span class="p">.</span></code></pre><p>Every occurrence of <code class="inline">?server_node</code> in <code class="inline">mess_server.erl</code> is now replaced by
│ │ │ │ -<code class="inline">messenger@super</code>.</p><p>A macro is also used when spawning the server process:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="7413130835-1">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7413130835-2">[</span><span class="p" data-group-id="7413130835-2">]</span><span class="p" data-group-id="7413130835-1">)</span></code></pre><p>This is a standard macro (that is, defined by the system, not by the user).
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9895075116-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="9895075116-1">)</span><span class="p">.</span></code></pre><p>This file is included in <code class="inline">mess_server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="8804078524-1">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="8804078524-1">)</span><span class="p">.</span></code></pre><p>Every occurrence of <code class="inline">?server_node</code> in <code class="inline">mess_server.erl</code> is now replaced by
│ │ │ │ +<code class="inline">messenger@super</code>.</p><p>A macro is also used when spawning the server process:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="6859580918-1">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6859580918-2">[</span><span class="p" data-group-id="6859580918-2">]</span><span class="p" data-group-id="6859580918-1">)</span></code></pre><p>This is a standard macro (that is, defined by the system, not by the user).
│ │ │ │  <code class="inline">?MODULE</code> is always replaced by the name of the current module (that is, the
│ │ │ │  <code class="inline">-module</code> definition near the start of the file). There are more advanced ways
│ │ │ │  of using macros with, for example, <a href="macros.xhtml#defining-and-using-macros">parameters</a>.</p><p>The three Erlang (<code class="inline">.erl</code>) files in the messenger example are individually
│ │ │ │  compiled into object code file (<code class="inline">.beam</code>). The Erlang system loads and links
│ │ │ │  these files into the system when they are referred to during execution of the
│ │ │ │  code. In this case, they are simply put in our current working directory (that
│ │ │ │  is, the place you have done &quot;cd&quot; to). There are ways of putting the <code class="inline">.beam</code>
│ │ │ ├── OEBPS/prog_ex_records.xhtml
│ │ │ │ @@ -27,105 +27,105 @@
│ │ │ │    <span class="text">Records and Tuples</span>
│ │ │ │  </h2>
│ │ │ │  <p>The main advantage of using records rather than tuples is that fields in a
│ │ │ │  record are accessed by name, whereas fields in a tuple are accessed by position.
│ │ │ │  To illustrate these differences, suppose that you want to represent a person
│ │ │ │  with the tuple <code class="inline">{Name, Address, Phone}</code>.</p><p>To write functions that manipulate this data, remember the following:</p><ul><li>The <code class="inline">Name</code> field is the first element of the tuple.</li><li>The <code class="inline">Address</code> field is the second element.</li><li>The <code class="inline">Phone</code> field is the third element.</li></ul><p>For example, to extract data from a variable <code class="inline">P</code> that contains such a tuple, you
│ │ │ │  can write the following code and then use pattern matching to extract the
│ │ │ │ -relevant fields:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="5261051482-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="5261051482-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="5261051482-2">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="5261051482-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +relevant fields:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="4987960007-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="4987960007-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="4987960007-2">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="4987960007-2">)</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Such code is difficult to read and understand, and errors occur if the numbering
│ │ │ │  of the elements in the tuple is wrong. If the data representation of the fields
│ │ │ │  is changed, by re-ordering, adding, or removing fields, all references to the
│ │ │ │  person tuple must be checked and possibly modified.</p><p>Records allow references to the fields by name, instead of by position. In the
│ │ │ │ -following example, a record instead of a tuple is used to store the data:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1893018125-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1893018125-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="1893018125-2">}</span><span class="p" data-group-id="1893018125-1">)</span><span class="p">.</span></code></pre><p>This enables references to the fields of the record by name. For example, if <code class="inline">P</code>
│ │ │ │ +following example, a record instead of a tuple is used to store the data:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5175982226-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5175982226-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="5175982226-2">}</span><span class="p" data-group-id="5175982226-1">)</span><span class="p">.</span></code></pre><p>This enables references to the fields of the record by name. For example, if <code class="inline">P</code>
│ │ │ │  is a variable whose value is a <code class="inline">person</code> record, the following code access the
│ │ │ │  name and address fields of the records:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">address</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Internally, records are represented using tagged tuples:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6614417509-1">{</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p" data-group-id="6614417509-1">}</span></code></pre><h2 id="defining-a-record" class="section-heading">
│ │ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Internally, records are represented using tagged tuples:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6787792947-1">{</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p" data-group-id="6787792947-1">}</span></code></pre><h2 id="defining-a-record" class="section-heading">
│ │ │ │    <a href="#defining-a-record" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Defining a Record</span>
│ │ │ │  </h2>
│ │ │ │  <p>This following definition of a <code class="inline">person</code> is used in several examples in this
│ │ │ │  section. Three fields are included, <code class="inline">name</code>, <code class="inline">phone</code>, and <code class="inline">address</code>. The default
│ │ │ │  values for <code class="inline">name</code> and <code class="inline">phone</code> is &quot;&quot; and [], respectively. The default value for
│ │ │ │  <code class="inline">address</code> is the atom <code class="inline">undefined</code>, since no default value is supplied for this
│ │ │ │ -field:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7632786972-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7632786972-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7632786972-3">[</span><span class="p" data-group-id="7632786972-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="7632786972-2">}</span><span class="p" data-group-id="7632786972-1">)</span><span class="p">.</span></code></pre><p>The record must be defined in the shell to enable use of the record syntax in
│ │ │ │ -the examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">rd</span><span class="p" data-group-id="3467136419-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3467136419-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3467136419-3">[</span><span class="p" data-group-id="3467136419-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="3467136419-2">}</span><span class="p" data-group-id="3467136419-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +field:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6267192158-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6267192158-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6267192158-3">[</span><span class="p" data-group-id="6267192158-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="6267192158-2">}</span><span class="p" data-group-id="6267192158-1">)</span><span class="p">.</span></code></pre><p>The record must be defined in the shell to enable use of the record syntax in
│ │ │ │ +the examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">rd</span><span class="p" data-group-id="0657676101-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0657676101-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0657676101-3">[</span><span class="p" data-group-id="0657676101-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="0657676101-2">}</span><span class="p" data-group-id="0657676101-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">person</span></code></pre><p>This is because record definitions are only available at compile time, not at
│ │ │ │  runtime. For details on records in the shell, see the <a href="../../../lib/stdlib/doc/html/shell.html"><code class="inline">shell</code></a> manual page in
│ │ │ │  STDLIB.</p><h2 id="creating-a-record" class="section-heading">
│ │ │ │    <a href="#creating-a-record" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating a Record</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A new <code class="inline">person</code> record is created as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7481792496-1">{</span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="7481792496-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7481792496-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="7481792496-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7481792496-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7481792496-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7481792496-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="7481792496-3">}</span></code></pre><p>As the <code class="inline">address</code> field was omitted, its default value is used.</p><p>From Erlang 5.1/OTP R8B, a value to all fields in a record can be set with the
│ │ │ │ -special field <code class="inline">_</code>. <code class="inline">_</code> means &quot;all fields not explicitly specified&quot;.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0818059023-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="0818059023-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0818059023-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="0818059023-2">}</span></code></pre><p>It is primarily intended to be used in <a href="../../../lib/stdlib/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a> and
│ │ │ │ +<p>A new <code class="inline">person</code> record is created as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7991492333-1">{</span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="7991492333-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7991492333-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="7991492333-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7991492333-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7991492333-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7991492333-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="7991492333-3">}</span></code></pre><p>As the <code class="inline">address</code> field was omitted, its default value is used.</p><p>From Erlang 5.1/OTP R8B, a value to all fields in a record can be set with the
│ │ │ │ +special field <code class="inline">_</code>. <code class="inline">_</code> means &quot;all fields not explicitly specified&quot;.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4868631648-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="4868631648-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4868631648-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="4868631648-2">}</span></code></pre><p>It is primarily intended to be used in <a href="../../../lib/stdlib/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a> and
│ │ │ │  <a href="../../../lib/mnesia/doc/html/mnesia.html#match_object/3"><code class="inline">mnesia:match_object/3</code></a>, to set record fields to the atom <code class="inline">'_'</code>. (This is a
│ │ │ │  wildcard in <a href="../../../lib/stdlib/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>.)</p><h2 id="accessing-a-record-field" class="section-heading">
│ │ │ │    <a href="#accessing-a-record-field" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Accessing a Record Field</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The following example shows how to access a record field:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8619096193-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8619096193-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8619096193-2">]</span><span class="p" data-group-id="8619096193-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8619096193-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8619096193-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8619096193-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="8619096193-3">}</span><span class="gp unselectable">
│ │ │ │ +<p>The following example shows how to access a record field:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8664624514-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8664624514-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8664624514-2">]</span><span class="p" data-group-id="8664624514-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8664624514-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8664624514-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8664624514-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="8664624514-3">}</span><span class="gp unselectable">
│ │ │ │  &gt; </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;Joe&quot;</span></code></pre><h2 id="updating-a-record" class="section-heading">
│ │ │ │    <a href="#updating-a-record" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Updating a Record</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The following example shows how to update a record:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3872114235-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="3872114235-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3872114235-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="3872114235-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3872114235-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3872114235-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3872114235-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="3872114235-3">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P1</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3872114235-5">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="3872114235-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3872114235-6">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3872114235-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3872114235-7">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="3872114235-6">}</span></code></pre><h2 id="type-testing" class="section-heading">
│ │ │ │ +<p>The following example shows how to update a record:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1828442669-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="1828442669-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1828442669-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1828442669-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1828442669-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1828442669-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1828442669-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1828442669-3">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P1</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1828442669-5">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="1828442669-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1828442669-6">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1828442669-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1828442669-7">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1828442669-6">}</span></code></pre><h2 id="type-testing" class="section-heading">
│ │ │ │    <a href="#type-testing" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Type Testing</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following example shows that the guard succeeds if <code class="inline">P</code> is record of type
│ │ │ │ -<code class="inline">person</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="3677897077-1">(</span><span class="n">P</span><span class="p" data-group-id="3677897077-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="3677897077-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="3677897077-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">a_person</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="3677897077-3">(</span><span class="p">_</span><span class="p" data-group-id="3677897077-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">not_a_person</span><span class="p">.</span></code></pre><h2 id="pattern-matching" class="section-heading">
│ │ │ │ +<code class="inline">person</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="2519287909-1">(</span><span class="n">P</span><span class="p" data-group-id="2519287909-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="2519287909-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="2519287909-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">a_person</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="2519287909-3">(</span><span class="p">_</span><span class="p" data-group-id="2519287909-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">not_a_person</span><span class="p">.</span></code></pre><h2 id="pattern-matching" class="section-heading">
│ │ │ │    <a href="#pattern-matching" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Pattern Matching</span>
│ │ │ │  </h2>
│ │ │ │  <p>Matching can be used in combination with records, as shown in the following
│ │ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6433065310-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="6433065310-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="6433065310-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="6433065310-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6433065310-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6433065310-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="6433065310-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="6433065310-3">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6433065310-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6433065310-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P3</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">.</span><span class="w">
│ │ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4609193603-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="4609193603-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4609193603-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="4609193603-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4609193603-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4609193603-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4609193603-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="4609193603-3">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4609193603-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4609193603-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P3</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;Joe&quot;</span></code></pre><p>The following function takes a list of <code class="inline">person</code> records and searches for the
│ │ │ │ -phone number of a person with a particular name:</p><pre><code class="makeup erlang" translate="no"><span class="nf">find_phone</span><span class="p" data-group-id="7530788907-1">(</span><span class="p" data-group-id="7530788907-2">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7530788907-3">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="n">Phone</span><span class="p" data-group-id="7530788907-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7530788907-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7530788907-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7530788907-4">{</span><span class="ss">found</span><span class="p">,</span><span class="w">  </span><span class="n">Phone</span><span class="p" data-group-id="7530788907-4">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">find_phone</span><span class="p" data-group-id="7530788907-5">(</span><span class="p" data-group-id="7530788907-6">[</span><span class="p">_</span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="7530788907-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7530788907-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">find_phone</span><span class="p" data-group-id="7530788907-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7530788907-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">find_phone</span><span class="p" data-group-id="7530788907-8">(</span><span class="p" data-group-id="7530788907-9">[</span><span class="p" data-group-id="7530788907-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7530788907-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +phone number of a person with a particular name:</p><pre><code class="makeup erlang" translate="no"><span class="nf">find_phone</span><span class="p" data-group-id="2648447232-1">(</span><span class="p" data-group-id="2648447232-2">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2648447232-3">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="n">Phone</span><span class="p" data-group-id="2648447232-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2648447232-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2648447232-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2648447232-4">{</span><span class="ss">found</span><span class="p">,</span><span class="w">  </span><span class="n">Phone</span><span class="p" data-group-id="2648447232-4">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">find_phone</span><span class="p" data-group-id="2648447232-5">(</span><span class="p" data-group-id="2648447232-6">[</span><span class="p">_</span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2648447232-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2648447232-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">find_phone</span><span class="p" data-group-id="2648447232-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2648447232-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">find_phone</span><span class="p" data-group-id="2648447232-8">(</span><span class="p" data-group-id="2648447232-9">[</span><span class="p" data-group-id="2648447232-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2648447232-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">not_found</span><span class="p">.</span></code></pre><p>The fields referred to in the pattern can be given in any order.</p><h2 id="nested-records" class="section-heading">
│ │ │ │    <a href="#nested-records" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Nested Records</span>
│ │ │ │  </h2>
│ │ │ │  <p>The value of a field in a record can be an instance of a record. Retrieval of
│ │ │ │  nested data can be done stepwise, or in a single step, as shown in the following
│ │ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5568386895-1">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5568386895-2">{</span><span class="ss">first</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">last</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Ericsson&quot;</span><span class="p" data-group-id="5568386895-2">}</span><span class="p" data-group-id="5568386895-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5568386895-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5568386895-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="5568386895-5">{</span><span class="p" data-group-id="5568386895-5">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p" data-group-id="5568386895-4">}</span><span class="p" data-group-id="5568386895-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9997092554-1">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9997092554-2">{</span><span class="ss">first</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">last</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Ericsson&quot;</span><span class="p" data-group-id="9997092554-2">}</span><span class="p" data-group-id="9997092554-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9997092554-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9997092554-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="9997092554-5">{</span><span class="p" data-group-id="9997092554-5">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p" data-group-id="9997092554-4">}</span><span class="p" data-group-id="9997092554-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">demo</span><span class="p" data-group-id="5568386895-6">(</span><span class="p" data-group-id="5568386895-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5568386895-7">{</span><span class="ss">name</span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="5568386895-8">{</span><span class="ss">first</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">last</span><span class="o">=</span><span class="s">&quot;Virding&quot;</span><span class="p" data-group-id="5568386895-8">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="mi">123</span><span class="p" data-group-id="5568386895-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="n">First</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5568386895-9">(</span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="5568386895-9">)</span><span class="o">#</span><span class="ss">name</span><span class="p">.</span><span class="ss">first</span><span class="p">.</span></code></pre><p>Here, <code class="inline">demo()</code> evaluates to <code class="inline">&quot;Robert&quot;</code>.</p><h2 id="a-longer-example" class="section-heading">
│ │ │ │ +</span><span class="nf">demo</span><span class="p" data-group-id="9997092554-6">(</span><span class="p" data-group-id="9997092554-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9997092554-7">{</span><span class="ss">name</span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="9997092554-8">{</span><span class="ss">first</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">last</span><span class="o">=</span><span class="s">&quot;Virding&quot;</span><span class="p" data-group-id="9997092554-8">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="mi">123</span><span class="p" data-group-id="9997092554-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="n">First</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9997092554-9">(</span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="9997092554-9">)</span><span class="o">#</span><span class="ss">name</span><span class="p">.</span><span class="ss">first</span><span class="p">.</span></code></pre><p>Here, <code class="inline">demo()</code> evaluates to <code class="inline">&quot;Robert&quot;</code>.</p><h2 id="a-longer-example" class="section-heading">
│ │ │ │    <a href="#a-longer-example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">A Longer Example</span>
│ │ │ │  </h2>
│ │ │ │  <p>Comments are embedded in the following example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% File: person.hrl</span><span class="w">
│ │ │ │  
│ │ │ │ @@ -135,44 +135,44 @@
│ │ │ │  </span><span class="c1">%%    name:  A string (default is undefined).</span><span class="w">
│ │ │ │  </span><span class="c1">%%    age:   An integer (default is undefined).</span><span class="w">
│ │ │ │  </span><span class="c1">%%    phone: A list of integers (default is []).</span><span class="w">
│ │ │ │  </span><span class="c1">%%    dict:  A dictionary containing various information</span><span class="w">
│ │ │ │  </span><span class="c1">%%           about the person.</span><span class="w">
│ │ │ │  </span><span class="c1">%%           A {Key, Value} list (default is the empty list).</span><span class="w">
│ │ │ │  </span><span class="c1">%%------------------------------------------------------------</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6832626332-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6832626332-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6832626332-3">[</span><span class="p" data-group-id="6832626332-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6832626332-4">[</span><span class="p" data-group-id="6832626332-4">]</span><span class="p" data-group-id="6832626332-2">}</span><span class="p" data-group-id="6832626332-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0481734427-1">(</span><span class="ss">person</span><span class="p" data-group-id="0481734427-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="0481734427-2">(</span><span class="s">&quot;person.hrl&quot;</span><span class="p" data-group-id="0481734427-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="0481734427-3">(</span><span class="ss">export_all</span><span class="p" data-group-id="0481734427-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% For test purposes only.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3117562577-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3117562577-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3117562577-3">[</span><span class="p" data-group-id="3117562577-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3117562577-4">[</span><span class="p" data-group-id="3117562577-4">]</span><span class="p" data-group-id="3117562577-2">}</span><span class="p" data-group-id="3117562577-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3556686379-1">(</span><span class="ss">person</span><span class="p" data-group-id="3556686379-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3556686379-2">(</span><span class="s">&quot;person.hrl&quot;</span><span class="p" data-group-id="3556686379-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="3556686379-3">(</span><span class="ss">export_all</span><span class="p" data-group-id="3556686379-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% For test purposes only.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% This creates an instance of a person.</span><span class="w">
│ │ │ │  </span><span class="c1">%%   Note: The phone number is not supplied so the</span><span class="w">
│ │ │ │  </span><span class="c1">%%         default value [] will be used.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="0481734427-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="0481734427-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0481734427-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ │ -           </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0481734427-6">[</span><span class="p" data-group-id="0481734427-7">{</span><span class="ss">computer_knowledge</span><span class="p">,</span><span class="w"> </span><span class="ss">excellent</span><span class="p" data-group-id="0481734427-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                   </span><span class="p" data-group-id="0481734427-8">{</span><span class="ss">drinks</span><span class="p">,</span><span class="w"> </span><span class="ss">coke</span><span class="p" data-group-id="0481734427-8">}</span><span class="p" data-group-id="0481734427-6">]</span><span class="p" data-group-id="0481734427-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="3556686379-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="3556686379-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3556686379-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ │ +           </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3556686379-6">[</span><span class="p" data-group-id="3556686379-7">{</span><span class="ss">computer_knowledge</span><span class="p">,</span><span class="w"> </span><span class="ss">excellent</span><span class="p" data-group-id="3556686379-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                   </span><span class="p" data-group-id="3556686379-8">{</span><span class="ss">drinks</span><span class="p">,</span><span class="w"> </span><span class="ss">coke</span><span class="p" data-group-id="3556686379-8">}</span><span class="p" data-group-id="3556686379-6">]</span><span class="p" data-group-id="3556686379-5">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% This demonstrates matching in arguments</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">print</span><span class="p" data-group-id="0481734427-9">(</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0481734427-10">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="0481734427-10">}</span><span class="p" data-group-id="0481734427-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0481734427-11">(</span><span class="s">&quot;Name: </span><span class="si">~s</span><span class="s">, Age: </span><span class="si">~w</span><span class="s">, Phone: </span><span class="si">~w</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="w">
│ │ │ │ -            </span><span class="s">&quot;Dictionary: </span><span class="si">~w</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0481734427-12">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="0481734427-12">]</span><span class="p" data-group-id="0481734427-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">print</span><span class="p" data-group-id="3556686379-9">(</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3556686379-10">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="3556686379-10">}</span><span class="p" data-group-id="3556686379-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3556686379-11">(</span><span class="s">&quot;Name: </span><span class="si">~s</span><span class="s">, Age: </span><span class="si">~w</span><span class="s">, Phone: </span><span class="si">~w</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="w">
│ │ │ │ +            </span><span class="s">&quot;Dictionary: </span><span class="si">~w</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3556686379-12">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="3556686379-12">]</span><span class="p" data-group-id="3556686379-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% Demonstrates type testing, selector, updating.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">birthday</span><span class="p" data-group-id="0481734427-13">(</span><span class="n">P</span><span class="p" data-group-id="0481734427-13">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="0481734427-14">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="0481734427-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0481734427-15">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0481734427-15">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">birthday</span><span class="p" data-group-id="3556686379-13">(</span><span class="n">P</span><span class="p" data-group-id="3556686379-13">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="3556686379-14">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="3556686379-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3556686379-15">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3556686379-15">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">register_two_hackers</span><span class="p" data-group-id="0481734427-16">(</span><span class="p" data-group-id="0481734427-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="n">Hacker1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="0481734427-17">(</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">29</span><span class="p" data-group-id="0481734427-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="n">OldHacker</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">birthday</span><span class="p" data-group-id="0481734427-18">(</span><span class="n">Hacker1</span><span class="p" data-group-id="0481734427-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">register_two_hackers</span><span class="p" data-group-id="3556686379-16">(</span><span class="p" data-group-id="3556686379-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="n">Hacker1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="3556686379-17">(</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">29</span><span class="p" data-group-id="3556686379-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="n">OldHacker</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">birthday</span><span class="p" data-group-id="3556686379-18">(</span><span class="n">Hacker1</span><span class="p" data-group-id="3556686379-18">)</span><span class="p">,</span><span class="w">
│ │ │ │     </span><span class="c1">% The central_register_server should have</span><span class="w">
│ │ │ │     </span><span class="c1">% an interface function for this.</span><span class="w">
│ │ │ │ -   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0481734427-19">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w"> </span><span class="n">Hacker1</span><span class="p" data-group-id="0481734427-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0481734427-20">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="n">OldHacker</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0481734427-21">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -                              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0481734427-22">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0481734427-22">]</span><span class="p" data-group-id="0481734427-21">}</span><span class="p" data-group-id="0481734427-20">}</span><span class="p">.</span></code></pre>
│ │ │ │ +   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3556686379-19">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w"> </span><span class="n">Hacker1</span><span class="p" data-group-id="3556686379-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3556686379-20">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="n">OldHacker</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3556686379-21">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +                              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3556686379-22">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3556686379-22">]</span><span class="p" data-group-id="3556686379-21">}</span><span class="p" data-group-id="3556686379-20">}</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/patterns.xhtml
│ │ │ │ @@ -33,16 +33,16 @@
│ │ │ │  succeeds, any unbound variables in the pattern become bound. If the matching
│ │ │ │  fails, an exception is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** 1:1: variable &#39;X&#39; is unbound **</span><span class="gp unselectable">
│ │ │ │  2&gt; </span><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">2</span><span class="gp unselectable">
│ │ │ │  3&gt; </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="p" data-group-id="3327512790-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3327512790-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3327512790-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3327512790-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="p" data-group-id="7363458926-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7363458926-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7363458926-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7363458926-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value {1,2}</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="p" data-group-id="3327512790-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3327512790-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3327512790-4">{</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3327512790-4">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3327512790-5">{</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3327512790-5">}</span><span class="gp unselectable">
│ │ │ │ +5&gt; </span><span class="p" data-group-id="7363458926-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7363458926-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7363458926-4">{</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7363458926-4">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7363458926-5">{</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7363458926-5">}</span><span class="gp unselectable">
│ │ │ │  6&gt; </span><span class="n">Y</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/otp-patch-apply.xhtml
│ │ │ │ @@ -106,13 +106,13 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Sanity check</span>
│ │ │ │  </h2>
│ │ │ │  <p>The application dependencies can be checked using the Erlang shell.
│ │ │ │  Application dependencies are verified among installed applications by
│ │ │ │  <code class="inline">otp_patch_apply</code>, but these are not necessarily those actually loaded.
│ │ │ │  By calling <code class="inline">system_information:sanity_check()</code> one can validate
│ │ │ │ -dependencies among applications actually loaded.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">system_information</span><span class="p">:</span><span class="nf">sanity_check</span><span class="p" data-group-id="7783517986-1">(</span><span class="p" data-group-id="7783517986-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +dependencies among applications actually loaded.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">system_information</span><span class="p">:</span><span class="nf">sanity_check</span><span class="p" data-group-id="0040169443-1">(</span><span class="p" data-group-id="0040169443-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>Please take a look at the reference of <a href="../../../lib/runtime_tools/doc/html/system_information.html#sanity_check/0" title="">sanity_check()</a> for more
│ │ │ │  information.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/opaques.xhtml
│ │ │ │ @@ -27,24 +27,24 @@
│ │ │ │    <span class="text">Opaque Type Aliases</span>
│ │ │ │  </h2>
│ │ │ │  <p>The main use case for opacity in Erlang is to hide the implementation of a data
│ │ │ │  type, enabling evolving the API while minimizing the risk of breaking consumers.
│ │ │ │  The runtime does not check opacity. Dialyzer provides some opacity-checking, but
│ │ │ │  the rest is up to convention.</p><p>This document explains what Erlang opacity is (and the trade-offs involved) via
│ │ │ │  the example of the <a href="../../../lib/stdlib/doc/html/sets.html#t:set/0"><code class="inline">sets:set()</code></a> data type. This type <em>was</em>
│ │ │ │ -defined in the <code class="inline">sets</code> module like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="6140851677-1">(</span><span class="n">Element</span><span class="p" data-group-id="6140851677-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="6140851677-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="6140851677-3">(</span><span class="n">Element</span><span class="p" data-group-id="6140851677-3">)</span><span class="p" data-group-id="6140851677-2">}</span><span class="p">.</span></code></pre><p>OTP 24 changed the definition to the following in
│ │ │ │ -<a href="https://github.com/erlang/otp/commit/e66941e8d7c47b973dff94c0308ea85a6be1958e">this commit</a>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="7354617701-1">(</span><span class="n">Element</span><span class="p" data-group-id="7354617701-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="7354617701-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="7354617701-3">(</span><span class="n">Element</span><span class="p" data-group-id="7354617701-3">)</span><span class="p" data-group-id="7354617701-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="7354617701-4">#{</span><span class="n">Element</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VALUE</span><span class="p" data-group-id="7354617701-4">}</span><span class="p">.</span></code></pre><p>And this change was safer and more backwards-compatible than if the type had
│ │ │ │ +defined in the <code class="inline">sets</code> module like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="5520956140-1">(</span><span class="n">Element</span><span class="p" data-group-id="5520956140-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="5520956140-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="5520956140-3">(</span><span class="n">Element</span><span class="p" data-group-id="5520956140-3">)</span><span class="p" data-group-id="5520956140-2">}</span><span class="p">.</span></code></pre><p>OTP 24 changed the definition to the following in
│ │ │ │ +<a href="https://github.com/erlang/otp/commit/e66941e8d7c47b973dff94c0308ea85a6be1958e">this commit</a>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="6119598816-1">(</span><span class="n">Element</span><span class="p" data-group-id="6119598816-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="6119598816-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="6119598816-3">(</span><span class="n">Element</span><span class="p" data-group-id="6119598816-3">)</span><span class="p" data-group-id="6119598816-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="6119598816-4">#{</span><span class="n">Element</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VALUE</span><span class="p" data-group-id="6119598816-4">}</span><span class="p">.</span></code></pre><p>And this change was safer and more backwards-compatible than if the type had
│ │ │ │  been defined with <code class="inline">-type</code> instead of <code class="inline">-opaque</code>. Here is why: when a module
│ │ │ │  defines an <code class="inline">-opaque</code>, the contract is that only the defining module should rely
│ │ │ │  on the definition of the type: no other modules should rely on the definition.</p><p>This means that code that pattern-matched on <code class="inline">set</code> as a record/tuple technically
│ │ │ │  broke the contract, and opted in to being potentially broken when the definition
│ │ │ │  of <code class="inline">set()</code> changed. Before OTP 24, this code printed <code class="inline">ok</code>. In OTP 24 it may
│ │ │ │ -error:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="8222561913-1">(</span><span class="p" data-group-id="8222561913-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="n">Set</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_tuple</span><span class="p" data-group-id="8222561913-2">(</span><span class="n">Set</span><span class="p" data-group-id="8222561913-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8222561913-3">(</span><span class="s">&quot;ok&quot;</span><span class="p" data-group-id="8222561913-3">)</span><span class="w">
│ │ │ │ +error:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="3892835234-1">(</span><span class="p" data-group-id="3892835234-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="n">Set</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_tuple</span><span class="p" data-group-id="3892835234-2">(</span><span class="n">Set</span><span class="p" data-group-id="3892835234-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3892835234-3">(</span><span class="s">&quot;ok&quot;</span><span class="p" data-group-id="3892835234-3">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p><strong>When working with an opaque defined in another module, here are some
│ │ │ │  recommendations:</strong></p><ul><li>Don't examine the underlying type using pattern-matching, guards, or functions
│ │ │ │  that reveal the type, such as <a href="../../../lib/../erts/doc/html/erlang.html#tuple_size/1"><code class="inline">tuple_size/1</code></a> .</li><li>Instead, use functions provided by the module for working with the type. For
│ │ │ │  example, <code class="inline">sets</code> module provides <a href="../../../lib/stdlib/doc/html/sets.html#new/0"><code class="inline">sets:new/0</code></a>, <a href="../../../lib/stdlib/doc/html/sets.html#add_element/2"><code class="inline">sets:add_element/2</code></a>,
│ │ │ │  <a href="../../../lib/stdlib/doc/html/sets.html#is_element/2"><code class="inline">sets:is_element/2</code></a>, and so on.</li><li><p><a href="../../../lib/stdlib/doc/html/sets.html#t:set/1"><code class="inline">sets:set(a)</code></a> is a subtype of <code class="inline">sets:set(a | b)</code> and not the
│ │ │ │  other way around. Generally, you can rely on the property that <code class="inline">the_opaque(T)</code>
│ │ │ │  is a subtype of <code class="inline">the_opaque(U)</code> when T is a subtype of U.</p></li></ul><p><strong>When defining your own opaques, here are some recommendations:</strong></p><ul><li>Since consumers are expected to not rely on the definition of the opaque type,
│ │ │ ├── OEBPS/nif.xhtml
│ │ │ │ @@ -38,26 +38,26 @@
│ │ │ │    <span class="text">Erlang Program</span>
│ │ │ │  </h2>
│ │ │ │  <p>Even if all functions of a module are NIFs, an Erlang module is still needed for
│ │ │ │  two reasons:</p><ul><li>The NIF library must be explicitly loaded by Erlang code in the same module.</li><li>All NIFs of a module must have an Erlang implementation as well.</li></ul><p>Normally these are minimal stub implementations that throw an exception. But
│ │ │ │  they can also be used as fallback implementations for functions that do not have
│ │ │ │  native implementations on some architectures.</p><p>NIF libraries are loaded by calling <a href="../../../lib/../erts/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a>, with the name of the
│ │ │ │  shared library as argument. The second argument can be any term that will be
│ │ │ │ -passed on to the library and used for initialization:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0569707356-1">(</span><span class="ss">complex6</span><span class="p" data-group-id="0569707356-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0569707356-2">(</span><span class="p" data-group-id="0569707356-3">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0569707356-3">]</span><span class="p" data-group-id="0569707356-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">nifs</span><span class="p" data-group-id="0569707356-4">(</span><span class="p" data-group-id="0569707356-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0569707356-5">]</span><span class="p" data-group-id="0569707356-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="0569707356-6">(</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0569707356-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="0569707356-7">(</span><span class="p" data-group-id="0569707356-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="0569707356-8">(</span><span class="s">&quot;./complex6_nif&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0569707356-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="0569707356-9">(</span><span class="p">_</span><span class="n">X</span><span class="p" data-group-id="0569707356-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="0569707356-10">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="0569707356-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="0569707356-11">(</span><span class="p">_</span><span class="n">Y</span><span class="p" data-group-id="0569707356-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="0569707356-12">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="0569707356-12">)</span><span class="p">.</span></code></pre><p>Here, the directive <code class="inline">on_load</code> is used to get function <code class="inline">init</code> to be automatically
│ │ │ │ +passed on to the library and used for initialization:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4184368205-1">(</span><span class="ss">complex6</span><span class="p" data-group-id="4184368205-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4184368205-2">(</span><span class="p" data-group-id="4184368205-3">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4184368205-3">]</span><span class="p" data-group-id="4184368205-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">nifs</span><span class="p" data-group-id="4184368205-4">(</span><span class="p" data-group-id="4184368205-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4184368205-5">]</span><span class="p" data-group-id="4184368205-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="4184368205-6">(</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4184368205-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="4184368205-7">(</span><span class="p" data-group-id="4184368205-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="4184368205-8">(</span><span class="s">&quot;./complex6_nif&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4184368205-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="4184368205-9">(</span><span class="p">_</span><span class="n">X</span><span class="p" data-group-id="4184368205-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="4184368205-10">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="4184368205-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="4184368205-11">(</span><span class="p">_</span><span class="n">Y</span><span class="p" data-group-id="4184368205-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="4184368205-12">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="4184368205-12">)</span><span class="p">.</span></code></pre><p>Here, the directive <code class="inline">on_load</code> is used to get function <code class="inline">init</code> to be automatically
│ │ │ │  called when the module is loaded. If <code class="inline">init</code> returns anything other than <code class="inline">ok</code>,
│ │ │ │  such when the loading of the NIF library fails in this example, the module is
│ │ │ │  unloaded and calls to functions within it, fail.</p><p>Loading the NIF library overrides the stub implementations and cause calls to
│ │ │ │  <code class="inline">foo</code> and <code class="inline">bar</code> to be dispatched to the NIF implementations instead.</p><h2 id="nif-library-code" class="section-heading">
│ │ │ │    <a href="#nif-library-code" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -114,22 +114,22 @@
│ │ │ │    <a href="#running-the-example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Running the Example</span>
│ │ │ │  </h2>
│ │ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">unix&gt; gcc -o complex6_nif.so -fpic -shared complex.c complex6_nif.c
│ │ │ │  windows&gt; cl -LD -MD -Fe complex6_nif.dll complex.c complex6_nif.c</code></pre><p><em>Step 2:</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="ss">erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="n">R13B04</span><span class="w"> </span><span class="p" data-group-id="9532042361-1">(</span><span class="ss">erts</span><span class="o">-</span><span class="mf">5.7</span><span class="p">.</span><span class="mi">5</span><span class="p" data-group-id="9532042361-1">)</span><span class="w"> </span><span class="p" data-group-id="9532042361-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="9532042361-2">]</span><span class="w"> </span><span class="p" data-group-id="9532042361-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="9532042361-3">]</span><span class="w"> </span><span class="p" data-group-id="9532042361-4">[</span><span class="nc">rq</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="9532042361-4">]</span><span class="w"> </span><span class="p" data-group-id="9532042361-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="9532042361-5">]</span><span class="w"> </span><span class="p" data-group-id="9532042361-6">[</span><span class="ss">kernel</span><span class="o">-</span><span class="nc">poll</span><span class="p">:</span><span class="ss">false</span><span class="p" data-group-id="9532042361-6">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="n">R13B04</span><span class="w"> </span><span class="p" data-group-id="0507387816-1">(</span><span class="ss">erts</span><span class="o">-</span><span class="mf">5.7</span><span class="p">.</span><span class="mi">5</span><span class="p" data-group-id="0507387816-1">)</span><span class="w"> </span><span class="p" data-group-id="0507387816-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0507387816-2">]</span><span class="w"> </span><span class="p" data-group-id="0507387816-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="0507387816-3">]</span><span class="w"> </span><span class="p" data-group-id="0507387816-4">[</span><span class="nc">rq</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="0507387816-4">]</span><span class="w"> </span><span class="p" data-group-id="0507387816-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="0507387816-5">]</span><span class="w"> </span><span class="p" data-group-id="0507387816-6">[</span><span class="ss">kernel</span><span class="o">-</span><span class="nc">poll</span><span class="p">:</span><span class="ss">false</span><span class="p" data-group-id="0507387816-6">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">7.5</span><span class="w">  </span><span class="p" data-group-id="9532042361-7">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="9532042361-7">)</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="nf">c</span><span class="p" data-group-id="9532042361-8">(</span><span class="ss">complex6</span><span class="p" data-group-id="9532042361-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9532042361-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex6</span><span class="p" data-group-id="9532042361-9">}</span></code></pre><p><em>Step 3:</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="2896850410-1">(</span><span class="mi">3</span><span class="p" data-group-id="2896850410-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">7.5</span><span class="w">  </span><span class="p" data-group-id="0507387816-7">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="0507387816-7">)</span><span class="gp unselectable">
│ │ │ │ +1&gt; </span><span class="nf">c</span><span class="p" data-group-id="0507387816-8">(</span><span class="ss">complex6</span><span class="p" data-group-id="0507387816-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0507387816-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex6</span><span class="p" data-group-id="0507387816-9">}</span></code></pre><p><em>Step 3:</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="1267125592-1">(</span><span class="mi">3</span><span class="p" data-group-id="1267125592-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="2896850410-2">(</span><span class="mi">5</span><span class="p" data-group-id="2896850410-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="1267125592-2">(</span><span class="mi">5</span><span class="p" data-group-id="1267125592-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">10</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="2896850410-3">(</span><span class="s">&quot;not an integer&quot;</span><span class="p" data-group-id="2896850410-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="1267125592-3">(</span><span class="s">&quot;not an integer&quot;</span><span class="p" data-group-id="1267125592-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: bad argument
│ │ │ │       in function  complex6:foo/1
│ │ │ │          called as comlpex6:foo(&quot;not an integer&quot;)</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/modules.xhtml
│ │ │ │ @@ -23,20 +23,20 @@
│ │ │ │  <h2 id="module-syntax" class="section-heading">
│ │ │ │    <a href="#module-syntax" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Module Syntax</span>
│ │ │ │  </h2>
│ │ │ │  <p>Erlang code is divided into <em>modules</em>. A module consists of a sequence of
│ │ │ │ -attributes and function declarations, each terminated by a period (<code class="inline">.</code>).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2305147970-1">(</span><span class="ss">m</span><span class="p" data-group-id="2305147970-1">)</span><span class="p">.</span><span class="w">          </span><span class="c1">% module attribute</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2305147970-2">(</span><span class="p" data-group-id="2305147970-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2305147970-3">]</span><span class="p" data-group-id="2305147970-2">)</span><span class="p">.</span><span class="w">   </span><span class="c1">% module attribute</span><span class="w">
│ │ │ │ +attributes and function declarations, each terminated by a period (<code class="inline">.</code>).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4457288246-1">(</span><span class="ss">m</span><span class="p" data-group-id="4457288246-1">)</span><span class="p">.</span><span class="w">          </span><span class="c1">% module attribute</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4457288246-2">(</span><span class="p" data-group-id="4457288246-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4457288246-3">]</span><span class="p" data-group-id="4457288246-2">)</span><span class="p">.</span><span class="w">   </span><span class="c1">% module attribute</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="2305147970-4">(</span><span class="n">N</span><span class="p" data-group-id="2305147970-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% beginning of function declaration</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="2305147970-5">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="2305147970-5">)</span><span class="p">;</span><span class="w">   </span><span class="c1">%  |</span><span class="w">
│ │ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="2305147970-6">(</span><span class="mi">0</span><span class="p" data-group-id="2305147970-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">           </span><span class="c1">%  |</span><span class="w">
│ │ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="4457288246-4">(</span><span class="n">N</span><span class="p" data-group-id="4457288246-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% beginning of function declaration</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="4457288246-5">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="4457288246-5">)</span><span class="p">;</span><span class="w">   </span><span class="c1">%  |</span><span class="w">
│ │ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="4457288246-6">(</span><span class="mi">0</span><span class="p" data-group-id="4457288246-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">           </span><span class="c1">%  |</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">.</span><span class="w">               </span><span class="c1">% end of function declaration</span></code></pre><p>For a description of function declarations, see
│ │ │ │  <a href="ref_man_functions.xhtml">Function Declaration Syntax</a>.</p><h2 id="module-attributes" class="section-heading">
│ │ │ │    <a href="#module-attributes" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Module Attributes</span>
│ │ │ │  </h2>
│ │ │ │ @@ -81,71 +81,71 @@
│ │ │ │  meaning.</p></section></li></ul><h3 id="behaviour-module-attribute" class="section-heading">
│ │ │ │    <a href="#behaviour-module-attribute" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Behaviour Module Attribute</span>
│ │ │ │  </h3>
│ │ │ │  <p>It is possible to specify that the module is the callback module for a
│ │ │ │ -<em>behaviour</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3614202238-1">(</span><span class="n">Behaviour</span><span class="p" data-group-id="3614202238-1">)</span><span class="p">.</span></code></pre><p>The atom <code class="inline">Behaviour</code> gives the name of the behaviour, which can be a
│ │ │ │ +<em>behaviour</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="7291866297-1">(</span><span class="n">Behaviour</span><span class="p" data-group-id="7291866297-1">)</span><span class="p">.</span></code></pre><p>The atom <code class="inline">Behaviour</code> gives the name of the behaviour, which can be a
│ │ │ │  user-defined behaviour or one of the following OTP standard behaviours:</p><ul><li><code class="inline">gen_server</code></li><li><code class="inline">gen_statem</code></li><li><code class="inline">gen_event</code></li><li><code class="inline">supervisor</code></li></ul><p>The spelling <code class="inline">behavior</code> is also accepted.</p><p>The callback functions of the module can be specified either directly by the
│ │ │ │ -exported function <code class="inline">behaviour_info/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="1923755217-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="1923755217-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Callbacks</span><span class="p">.</span></code></pre><p>or by a <code class="inline">-callback</code> attribute for each callback function:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="1446902445-1">(</span><span class="n">Arguments</span><span class="p" data-group-id="1446902445-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="p">.</span></code></pre><p>Here, <code class="inline">Arguments</code> is a list of zero or more arguments. The <code class="inline">-callback</code> attribute
│ │ │ │ +exported function <code class="inline">behaviour_info/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="3366410551-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="3366410551-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Callbacks</span><span class="p">.</span></code></pre><p>or by a <code class="inline">-callback</code> attribute for each callback function:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2452419177-1">(</span><span class="n">Arguments</span><span class="p" data-group-id="2452419177-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="p">.</span></code></pre><p>Here, <code class="inline">Arguments</code> is a list of zero or more arguments. The <code class="inline">-callback</code> attribute
│ │ │ │  is to be preferred since the extra type information can be used by tools to
│ │ │ │  produce documentation or find discrepancies.</p><p>Read more about behaviours and callback modules in
│ │ │ │  <a href="../../../lib/../system/doc/html/spec_proc.xhtml#behaviours">OTP Design Principles</a>.</p><h3 id="record-definitions" class="section-heading">
│ │ │ │    <a href="#record-definitions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Record Definitions</span>
│ │ │ │  </h3>
│ │ │ │ -<p>The same syntax as for module attributes is used for record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2571326813-1">(</span><span class="n">Record</span><span class="p">,</span><span class="w"> </span><span class="n">Fields</span><span class="p" data-group-id="2571326813-1">)</span><span class="p">.</span></code></pre><p>Record definitions are allowed anywhere in a module, also among the function
│ │ │ │ +<p>The same syntax as for module attributes is used for record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8705312614-1">(</span><span class="n">Record</span><span class="p">,</span><span class="w"> </span><span class="n">Fields</span><span class="p" data-group-id="8705312614-1">)</span><span class="p">.</span></code></pre><p>Record definitions are allowed anywhere in a module, also among the function
│ │ │ │  declarations. Read more in <a href="ref_man_records.xhtml">Records</a>.</p><h3 id="preprocessor" class="section-heading">
│ │ │ │    <a href="#preprocessor" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Preprocessor</span>
│ │ │ │  </h3>
│ │ │ │  <p>The same syntax as for module attributes is used by the preprocessor, which
│ │ │ │ -supports file inclusion, macros, and conditional compilation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4524215136-1">(</span><span class="s">&quot;SomeFile.hrl&quot;</span><span class="p" data-group-id="4524215136-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4524215136-2">(</span><span class="n">Macro</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="4524215136-2">)</span><span class="p">.</span></code></pre><p>Read more in <a href="macros.xhtml">Preprocessor</a>.</p><h3 id="setting-file-and-line" class="section-heading">
│ │ │ │ +supports file inclusion, macros, and conditional compilation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5344734522-1">(</span><span class="s">&quot;SomeFile.hrl&quot;</span><span class="p" data-group-id="5344734522-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5344734522-2">(</span><span class="n">Macro</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="5344734522-2">)</span><span class="p">.</span></code></pre><p>Read more in <a href="macros.xhtml">Preprocessor</a>.</p><h3 id="setting-file-and-line" class="section-heading">
│ │ │ │    <a href="#setting-file-and-line" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Setting File and Line</span>
│ │ │ │  </h3>
│ │ │ │  <p>The same syntax as for module attributes is used for changing the pre-defined
│ │ │ │ -macros <code class="inline">?FILE</code> and <code class="inline">?LINE</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">file</span><span class="p" data-group-id="1127682350-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">Line</span><span class="p" data-group-id="1127682350-1">)</span><span class="p">.</span></code></pre><p>This attribute is used by tools, such as Yecc, to inform the compiler that the
│ │ │ │ +macros <code class="inline">?FILE</code> and <code class="inline">?LINE</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">file</span><span class="p" data-group-id="4947827841-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">Line</span><span class="p" data-group-id="4947827841-1">)</span><span class="p">.</span></code></pre><p>This attribute is used by tools, such as Yecc, to inform the compiler that the
│ │ │ │  source program is generated by another tool. It also indicates the
│ │ │ │  correspondence of source files to lines of the original user-written file, from
│ │ │ │  which the source program is produced.</p><h3 id="types-and-function-specifications" class="section-heading">
│ │ │ │    <a href="#types-and-function-specifications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Types and function specifications</span>
│ │ │ │  </h3>
│ │ │ │  <p>A similar syntax as for module attributes is used for specifying types and
│ │ │ │ -function specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_type</span><span class="p" data-group-id="1230573768-1">(</span><span class="p" data-group-id="1230573768-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="1230573768-2">(</span><span class="p" data-group-id="1230573768-2">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1230573768-3">(</span><span class="p" data-group-id="1230573768-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">my_function</span><span class="p" data-group-id="1230573768-4">(</span><span class="nf">integer</span><span class="p" data-group-id="1230573768-5">(</span><span class="p" data-group-id="1230573768-5">)</span><span class="p" data-group-id="1230573768-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1230573768-6">(</span><span class="p" data-group-id="1230573768-6">)</span><span class="p">.</span></code></pre><p>Read more in <a href="typespec.xhtml">Types and Function specifications</a>.</p><p>The description is based on
│ │ │ │ +function specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_type</span><span class="p" data-group-id="9569910326-1">(</span><span class="p" data-group-id="9569910326-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="9569910326-2">(</span><span class="p" data-group-id="9569910326-2">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="9569910326-3">(</span><span class="p" data-group-id="9569910326-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">my_function</span><span class="p" data-group-id="9569910326-4">(</span><span class="nf">integer</span><span class="p" data-group-id="9569910326-5">(</span><span class="p" data-group-id="9569910326-5">)</span><span class="p" data-group-id="9569910326-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="9569910326-6">(</span><span class="p" data-group-id="9569910326-6">)</span><span class="p">.</span></code></pre><p>Read more in <a href="typespec.xhtml">Types and Function specifications</a>.</p><p>The description is based on
│ │ │ │  <a href="http://www.erlang.org/eeps/eep-0008.html">EEP8 - Types and function specifications</a>,
│ │ │ │  which is not to be further updated.</p><h3 id="documentation-attributes" class="section-heading">
│ │ │ │    <a href="#documentation-attributes" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Documentation attributes</span>
│ │ │ │  </h3>
│ │ │ │  <p>The module attribute <code class="inline">-doc(Documentation)</code> is used to provide user documentation
│ │ │ │ -for a function/type/callback:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="5208940070-1">(</span><span class="s">&quot;Example documentation&quot;</span><span class="p" data-group-id="5208940070-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="5208940070-2">(</span><span class="p" data-group-id="5208940070-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The attribute should be placed just before the entity it documents.The
│ │ │ │ +for a function/type/callback:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="8410506437-1">(</span><span class="s">&quot;Example documentation&quot;</span><span class="p" data-group-id="8410506437-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="8410506437-2">(</span><span class="p" data-group-id="8410506437-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The attribute should be placed just before the entity it documents.The
│ │ │ │  parenthesis are optional around <code class="inline">Documentation</code>. The allowed values for
│ │ │ │  <code class="inline">Documentation</code> are:</p><ul><li><p><strong><a href="data_types.xhtml#string">literal string</a> or
│ │ │ │  <a href="expressions.xhtml#unicode-segments">utf-8 encoded binary string</a></strong> - The string
│ │ │ │  documenting the entity. Any literal string is allowed, so both
│ │ │ │  <a href="data_types.xhtml#tqstring">triple quoted strings</a> and
│ │ │ │  <a href="data_types.xhtml#sigil">sigils</a> that translate to literal strings can be used.
│ │ │ │ -The following examples are equivalent:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7420779806-1">(</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="p" data-group-id="7420779806-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7420779806-2">(</span><span class="p" data-group-id="7420779806-3">&lt;&lt;</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="7420779806-3">&gt;&gt;</span><span class="p" data-group-id="7420779806-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +The following examples are equivalent:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="4245120634-1">(</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="p" data-group-id="4245120634-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="4245120634-2">(</span><span class="p" data-group-id="4245120634-3">&lt;&lt;</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="4245120634-3">&gt;&gt;</span><span class="p" data-group-id="4245120634-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">~S/Example &quot;docs&quot;/</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="s">&quot;
│ │ │ │     Example &quot;</span><span class="ss">docs</span><span class="s">&quot;
│ │ │ │     &quot;</span><span class="s">&quot;&quot;</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">~B|Example &quot;docs&quot;|</span><span class="p">.</span></code></pre><p>For clarity it is recommended to use either normal <code class="inline">&quot;strings&quot;</code> or triple
│ │ │ │  quoted strings for documentation attributes.</p></li><li><p><strong><code class="inline">{file,</code> <a href="../../../lib/kernel/doc/html/file.html#t:name/0"><code class="inline">file:name/0</code></a> <code class="inline">}</code></strong> - Read the contents of filename and use
│ │ │ │  that as the documentation string.</p></li><li><p><strong><code class="inline">false</code></strong> - Set the current entity as hidden, that is, it should not be
│ │ │ │ @@ -158,15 +158,15 @@
│ │ │ │    <a href="#the-feature-directive" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">The feature directive</span>
│ │ │ │  </h2>
│ │ │ │  <p>While not a module attribute, but rather a directive (since it might affect
│ │ │ │  syntax), there is the <code class="inline">-feature(..)</code> directive used for enabling and disabling
│ │ │ │ -<a href="../../../lib/../system/doc/html/features.xhtml#features">features</a>.</p><p>The syntax is similar to that of an attribute, but has two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">feature</span><span class="p" data-group-id="3526332187-1">(</span><span class="n">FeatureName</span><span class="p">,</span><span class="w"> </span><span class="ss">enable</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">disable</span><span class="p" data-group-id="3526332187-1">)</span><span class="p">.</span></code></pre><p>Note that the <a href="macros.xhtml#feature-directive">feature directive</a> can only appear
│ │ │ │ +<a href="../../../lib/../system/doc/html/features.xhtml#features">features</a>.</p><p>The syntax is similar to that of an attribute, but has two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">feature</span><span class="p" data-group-id="5868311638-1">(</span><span class="n">FeatureName</span><span class="p">,</span><span class="w"> </span><span class="ss">enable</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">disable</span><span class="p" data-group-id="5868311638-1">)</span><span class="p">.</span></code></pre><p>Note that the <a href="macros.xhtml#feature-directive">feature directive</a> can only appear
│ │ │ │  in a prefix of the module.</p><h2 id="comments" class="section-heading">
│ │ │ │    <a href="#comments" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Comments</span>
│ │ │ │  </h2>
│ │ │ │  <p>Comments can be placed anywhere in a module except within strings and
│ │ │ ├── OEBPS/maps.xhtml
│ │ │ │ @@ -53,16 +53,16 @@
│ │ │ │  single function that constructs the map using the map syntax and always use
│ │ │ │  it.</p></li><li><p>Always update the map using the <code class="inline">:=</code> operator (that is, requiring that an
│ │ │ │  element with that key already exists). The <code class="inline">:=</code> operator is slightly more
│ │ │ │  efficient, and it helps catching mispellings of keys.</p></li><li><p>Whenever possible, match multiple map elements at once.</p></li><li><p>Whenever possible, update multiple map elements at once.</p></li><li><p>Avoid default values and the <a href="../../../lib/stdlib/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> function. If there are default
│ │ │ │  values, sharing of keys between different instances of the map will be less
│ │ │ │  effective, and it is not possible to match multiple elements having default
│ │ │ │  values in one go.</p></li><li><p>To avoid having to deal with a map that may lack some keys, <a href="../../../lib/stdlib/doc/html/maps.html#merge/2"><code class="inline">maps:merge/2</code></a> can
│ │ │ │ -efficiently add multiple default values. For example:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8610097354-1">#{</span><span class="ss">shoe_size</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="ss">editor</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">emacs</span><span class="p" data-group-id="8610097354-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="8610097354-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="8610097354-2">)</span></code></pre></li></ul><h2 id="using-maps-as-dictionaries" class="section-heading">
│ │ │ │ +efficiently add multiple default values. For example:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1040401080-1">#{</span><span class="ss">shoe_size</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="ss">editor</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">emacs</span><span class="p" data-group-id="1040401080-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="1040401080-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="1040401080-2">)</span></code></pre></li></ul><h2 id="using-maps-as-dictionaries" class="section-heading">
│ │ │ │    <a href="#using-maps-as-dictionaries" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Using Maps as Dictionaries</span>
│ │ │ │  </h2>
│ │ │ │  <p>Using a map as a dictionary implies the following usage pattern:</p><ul><li>Keys are usually variables not known at compile-time.</li><li>There can be any number of elements in the map.</li><li>Usually, no more than one element is looked up or updated at once.</li></ul><p>Given that usage pattern, the difference in performance between using the map
│ │ │ │  syntax and the maps module is usually small. Therefore, which one to use is
│ │ │ │ @@ -72,18 +72,18 @@
│ │ │ │  choice.</li></ul><h2 id="using-maps-as-sets" class="section-heading">
│ │ │ │    <a href="#using-maps-as-sets" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Using Maps as Sets</span>
│ │ │ │  </h2>
│ │ │ │  <p>Starting in OTP 24, the <a href="../../../lib/stdlib/doc/html/sets.html"><code class="inline">sets</code></a> module has an option to represent sets as maps.
│ │ │ │ -Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="3189625133-1">(</span><span class="p" data-group-id="3189625133-2">[</span><span class="p" data-group-id="3189625133-3">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3189625133-3">}</span><span class="p" data-group-id="3189625133-2">]</span><span class="p" data-group-id="3189625133-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3189625133-4">#{</span><span class="p" data-group-id="3189625133-4">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">from_list</span><span class="p" data-group-id="3189625133-5">(</span><span class="p" data-group-id="3189625133-6">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="3189625133-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3189625133-7">[</span><span class="p" data-group-id="3189625133-8">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3189625133-8">}</span><span class="p" data-group-id="3189625133-7">]</span><span class="p" data-group-id="3189625133-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3189625133-9">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3189625133-10">[</span><span class="p" data-group-id="3189625133-10">]</span><span class="p">,</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3189625133-11">[</span><span class="p" data-group-id="3189625133-11">]</span><span class="p">,</span><span class="ss">z</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3189625133-12">[</span><span class="p" data-group-id="3189625133-12">]</span><span class="p" data-group-id="3189625133-9">}</span></code></pre><p><code class="inline">sets</code> backed by maps is generally the most efficient set representation, with a
│ │ │ │ +Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="7882983688-1">(</span><span class="p" data-group-id="7882983688-2">[</span><span class="p" data-group-id="7882983688-3">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7882983688-3">}</span><span class="p" data-group-id="7882983688-2">]</span><span class="p" data-group-id="7882983688-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7882983688-4">#{</span><span class="p" data-group-id="7882983688-4">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">from_list</span><span class="p" data-group-id="7882983688-5">(</span><span class="p" data-group-id="7882983688-6">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="7882983688-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7882983688-7">[</span><span class="p" data-group-id="7882983688-8">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7882983688-8">}</span><span class="p" data-group-id="7882983688-7">]</span><span class="p" data-group-id="7882983688-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7882983688-9">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7882983688-10">[</span><span class="p" data-group-id="7882983688-10">]</span><span class="p">,</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7882983688-11">[</span><span class="p" data-group-id="7882983688-11">]</span><span class="p">,</span><span class="ss">z</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7882983688-12">[</span><span class="p" data-group-id="7882983688-12">]</span><span class="p" data-group-id="7882983688-9">}</span></code></pre><p><code class="inline">sets</code> backed by maps is generally the most efficient set representation, with a
│ │ │ │  few possible exceptions:</p><ul><li><a href="../../../lib/stdlib/doc/html/ordsets.html#intersection/2"><code class="inline">ordsets:intersection/2</code></a> can be more efficient than <a href="../../../lib/stdlib/doc/html/sets.html#intersection/2"><code class="inline">sets:intersection/2</code></a>. If
│ │ │ │  the intersection operation is frequently used and operations that operate on a
│ │ │ │  single element in a set (such as <code class="inline">is_element/2</code>) are avoided, <a href="../../../lib/stdlib/doc/html/ordsets.html"><code class="inline">ordsets</code></a> can
│ │ │ │  be a better choice than <a href="../../../lib/stdlib/doc/html/sets.html"><code class="inline">sets</code></a>.</li><li>If the intersection operation is frequently used and operations that operate
│ │ │ │  on a single element in a set (such as <code class="inline">is_element/2</code>) must also be efficient,
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gb_sets.html"><code class="inline">gb_sets</code></a> can potentially be a better choice than <a href="../../../lib/stdlib/doc/html/sets.html"><code class="inline">sets</code></a>.</li><li>If the elements of the set are integers in a fairly compact range, the set can
│ │ │ │  be represented as an integer where each bit represents an element in the set.
│ │ │ │ @@ -108,18 +108,18 @@
│ │ │ │  for the runtime system).</p></li><li><p><strong>N</strong> - The number of elements in the map.</p></li><li><p><strong>Keys</strong> - A tuple with keys of the map: <code class="inline">{Key1,...,KeyN}</code>. The keys are
│ │ │ │  sorted.</p></li><li><p><strong>Value1</strong> - The value corresponding to the first key in the key tuple.</p></li><li><p><strong>ValueN</strong> - The value corresponding to the last key in the key tuple.</p></li></ul><p>As an example, let us look at how the map <code class="inline">#{a =&gt; foo, z =&gt; bar}</code> is
│ │ │ │  represented:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: left;">4</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>2</em></td><td style="text-align: center;"><code class="inline">{a,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: left;"><code class="inline">bar</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, z =&gt; bar}</em></p><p>Let us update the map: <code class="inline">M#{q =&gt; baz}</code>. The map now looks like this:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: center;">4</th><th style="text-align: center;">5</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>3</em></td><td style="text-align: center;"><code class="inline">{a,q,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: center;"><code class="inline">baz</code></td><td style="text-align: center;"><code class="inline">bar</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, q =&gt; baz, z =&gt; bar}</em></p><p>Finally, change the value of one element: <code class="inline">M#{z := bird}</code>. The map now looks
│ │ │ │  like this:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: center;">4</th><th style="text-align: center;">5</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>3</em></td><td style="text-align: center;"><code class="inline">{a,q,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: center;"><code class="inline">baz</code></td><td style="text-align: center;"><code class="inline">bird</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, q =&gt; baz, z =&gt; bird}</em></p><p>When the value for an existing key is updated, the key tuple is not updated,
│ │ │ │  allowing the key tuple to be shared with other instances of the map that have
│ │ │ │  the same keys. In fact, the key tuple can be shared between all maps with the
│ │ │ │  same keys with some care. To arrange that, define a function that returns a map.
│ │ │ │ -For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="9317148986-1">(</span><span class="p" data-group-id="9317148986-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9317148986-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p" data-group-id="9317148986-2">}</span><span class="p">.</span></code></pre><p>Defined like this, the key tuple <code class="inline">{a,b,c}</code> will be a global literal. To ensure
│ │ │ │ +For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="5124628232-1">(</span><span class="p" data-group-id="5124628232-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5124628232-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p" data-group-id="5124628232-2">}</span><span class="p">.</span></code></pre><p>Defined like this, the key tuple <code class="inline">{a,b,c}</code> will be a global literal. To ensure
│ │ │ │  that the key tuple is shared when creating an instance of the map, always call
│ │ │ │ -<code class="inline">new()</code> and modify the returned map:</p><pre><code class="makeup erlang" translate="no"><span class="w">    </span><span class="p" data-group-id="3773693093-1">(</span><span class="n">SOME_MODULE</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="3773693093-2">(</span><span class="p" data-group-id="3773693093-2">)</span><span class="p" data-group-id="3773693093-1">)</span><span class="p" data-group-id="3773693093-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="3773693093-3">}</span><span class="p">.</span></code></pre><p>Using the map syntax with small maps is particularly efficient. As long as the
│ │ │ │ +<code class="inline">new()</code> and modify the returned map:</p><pre><code class="makeup erlang" translate="no"><span class="w">    </span><span class="p" data-group-id="5384992448-1">(</span><span class="n">SOME_MODULE</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="5384992448-2">(</span><span class="p" data-group-id="5384992448-2">)</span><span class="p" data-group-id="5384992448-1">)</span><span class="p" data-group-id="5384992448-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="5384992448-3">}</span><span class="p">.</span></code></pre><p>Using the map syntax with small maps is particularly efficient. As long as the
│ │ │ │  keys are known at compile-time, the map is updated in one go, making the time to
│ │ │ │  update a map essentially constant regardless of the number of keys updated. The
│ │ │ │  same goes for matching. (When the keys are variables, one or more of the keys
│ │ │ │  could be identical, so the operations need to be performed sequentially from
│ │ │ │  left to right.)</p><p>The memory size for a small map is the size of all keys and values plus 5 words.
│ │ │ │  See <a href="memory.xhtml">Memory</a> for more information about memory sizes.</p><h3 id="how-large-maps-are-implemented" class="section-heading">
│ │ │ │    <a href="#how-large-maps-are-implemented" class="hover-link">
│ │ │ │ @@ -146,21 +146,21 @@
│ │ │ │    <a href="#using-the-map-syntax" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Using the Map Syntax</span>
│ │ │ │  </h2>
│ │ │ │  <p>Using the map syntax is usually slightly more efficient than using the
│ │ │ │  corresponding function in the <a href="../../../lib/stdlib/doc/html/maps.html"><code class="inline">maps</code></a> module.</p><p>The gain in efficiency for the map syntax is more noticeable for the following
│ │ │ │ -operations that can only be achieved using the map syntax:</p><ul><li>Matching multiple literal keys</li><li>Updating multiple literal keys</li><li>Adding multiple literal keys to a map</li></ul><p>For example:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="2709672401-1">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="ss">z</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="2709672401-1">}</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="2911238451-1">(</span><span class="ss">x</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="2911238451-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="2911238451-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="2911238451-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="2911238451-3">(</span><span class="ss">z</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p">,</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="2911238451-3">)</span></code></pre><p>If the map is a small map, the first example runs roughly three times as fast.</p><p>Note that for variable keys, the elements are updated sequentially from left to
│ │ │ │ -right. For example, given the following update with variable keys:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="4572760312-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="4572760312-1">}</span></code></pre><p>the compiler rewrites it like this to ensure that the updates are applied from
│ │ │ │ -left to right:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="0605248392-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0605248392-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="0605248392-2">#{</span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0605248392-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="0605248392-3">#{</span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="0605248392-3">}</span></code></pre><p>If a key is known to exist in a map, using the <code class="inline">:=</code> operator is slightly more
│ │ │ │ +operations that can only be achieved using the map syntax:</p><ul><li>Matching multiple literal keys</li><li>Updating multiple literal keys</li><li>Adding multiple literal keys to a map</li></ul><p>For example:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="0822660235-1">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="ss">z</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="0822660235-1">}</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="0693767869-1">(</span><span class="ss">x</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="0693767869-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="0693767869-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="0693767869-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="0693767869-3">(</span><span class="ss">z</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p">,</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="0693767869-3">)</span></code></pre><p>If the map is a small map, the first example runs roughly three times as fast.</p><p>Note that for variable keys, the elements are updated sequentially from left to
│ │ │ │ +right. For example, given the following update with variable keys:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="6965472623-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="6965472623-1">}</span></code></pre><p>the compiler rewrites it like this to ensure that the updates are applied from
│ │ │ │ +left to right:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="3862919864-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3862919864-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="3862919864-2">#{</span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3862919864-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="3862919864-3">#{</span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="3862919864-3">}</span></code></pre><p>If a key is known to exist in a map, using the <code class="inline">:=</code> operator is slightly more
│ │ │ │  efficient than using the <code class="inline">=&gt;</code> operator for a small map.</p><h2 id="using-the-functions-in-the-maps-module" class="section-heading">
│ │ │ │    <a href="#using-the-functions-in-the-maps-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Using the Functions in the maps Module</span>
│ │ │ │  </h2>
│ │ │ │  <p>Here follows some notes about most of the functions in the <code class="inline">maps</code> module. For
│ │ │ │ @@ -211,23 +211,23 @@
│ │ │ │    <a href="#maps-get-3" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">maps:get/3</span>
│ │ │ │  </h3>
│ │ │ │  <p>As an optimization, the compiler will rewrite a call to <a href="../../../lib/stdlib/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> to Erlang
│ │ │ │  code similar to the following:</p><pre><code class="makeup erlang" translate="no"><span class="n">Result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">Map</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="7499043089-1">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="7499043089-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="p">;</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="7499043089-2">#{</span><span class="p" data-group-id="7499043089-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Default</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="1931159252-1">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="1931159252-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="p">;</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="1931159252-2">#{</span><span class="p" data-group-id="1931159252-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Default</span><span class="w">
│ │ │ │           </span><span class="k">end</span></code></pre><p>This is reasonably efficient, but if a small map is used as an alternative to
│ │ │ │  using a record it is often better not to rely on default values as it prevents
│ │ │ │  sharing of keys, which may in the end use more memory than what you save from
│ │ │ │  not storing default values in the map.</p><p>If default values are nevertheless required, instead of calling <a href="../../../lib/stdlib/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a>
│ │ │ │  multiple times, consider putting the default values in a map and merging that
│ │ │ │ -map with the other map:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0525824586-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">KeyN</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueN</span><span class="p" data-group-id="0525824586-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="0525824586-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="0525824586-2">)</span></code></pre><p>This helps share keys between the default map and the one you applied defaults
│ │ │ │ +map with the other map:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4410330265-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">KeyN</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueN</span><span class="p" data-group-id="4410330265-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="4410330265-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="4410330265-2">)</span></code></pre><p>This helps share keys between the default map and the one you applied defaults
│ │ │ │  to, as long as the default map contains <em>all</em> the keys that will ever be used
│ │ │ │  and not just the ones with default values. Whether this is faster than calling
│ │ │ │  <a href="../../../lib/stdlib/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> multiple times depends on the size of the map and the number of
│ │ │ │  default values.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before OTP 26.0 <a href="../../../lib/stdlib/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> was implemented by calling the function instead
│ │ │ │  of rewriting it as an Erlang expression. It is now slightly faster but can no
│ │ │ │  longer be traced.</p></section><h3 id="maps-intersect-2-maps-intersect_with-3" class="section-heading">
│ │ │ │    <a href="#maps-intersect-2-maps-intersect_with-3" class="hover-link">
│ │ │ ├── OEBPS/macros.xhtml
│ │ │ │ @@ -22,56 +22,56 @@
│ │ │ │      </h1>
│ │ │ │  <h2 id="file-inclusion" class="section-heading">
│ │ │ │    <a href="#file-inclusion" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">File Inclusion</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A file can be included as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2955816732-1">(</span><span class="n">File</span><span class="p" data-group-id="2955816732-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="2955816732-2">(</span><span class="n">File</span><span class="p" data-group-id="2955816732-2">)</span><span class="p">.</span></code></pre><p><code class="inline">File</code>, a string, is to point out a file. The contents of this file are included
│ │ │ │ +<p>A file can be included as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="9010499906-1">(</span><span class="n">File</span><span class="p" data-group-id="9010499906-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="9010499906-2">(</span><span class="n">File</span><span class="p" data-group-id="9010499906-2">)</span><span class="p">.</span></code></pre><p><code class="inline">File</code>, a string, is to point out a file. The contents of this file are included
│ │ │ │  as is, at the position of the directive.</p><p>Include files are typically used for record and macro definitions that are
│ │ │ │  shared by several modules. It is recommended to use the file name extension
│ │ │ │  <code class="inline">.hrl</code> for include files.</p><p><code class="inline">File</code> can start with a path component <code class="inline">$VAR</code>, for some string <code class="inline">VAR</code>. If that is
│ │ │ │  the case, the value of the environment variable <code class="inline">VAR</code> as returned by
│ │ │ │  <code class="inline">os:getenv(VAR)</code> is substituted for <code class="inline">$VAR</code>. If <code class="inline">os:getenv(VAR)</code> returns <code class="inline">false</code>,
│ │ │ │  <code class="inline">$VAR</code> is left as is.</p><p>If the filename <code class="inline">File</code> is absolute (possibly after variable substitution), the
│ │ │ │  include file with that name is included. Otherwise, the specified file is
│ │ │ │  searched for in the following directories, and in this order:</p><ol><li>The current working directory</li><li>The directory where the module is being compiled</li><li>The directories given by the <code class="inline">include</code> option</li></ol><p>For details, see <a href="../../../lib/../erts/doc/html/erlc_cmd.xhtml">erlc</a> in ERTS and
│ │ │ │ -<a href="../../../lib/compiler/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1658249413-1">(</span><span class="s">&quot;my_records.hrl&quot;</span><span class="p" data-group-id="1658249413-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1658249413-2">(</span><span class="s">&quot;incdir/my_records.hrl&quot;</span><span class="p" data-group-id="1658249413-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1658249413-3">(</span><span class="s">&quot;/home/user/proj/my_records.hrl&quot;</span><span class="p" data-group-id="1658249413-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1658249413-4">(</span><span class="s">&quot;$PROJ_ROOT/my_records.hrl&quot;</span><span class="p" data-group-id="1658249413-4">)</span><span class="p">.</span></code></pre><p><code class="inline">include_lib</code> is similar to <code class="inline">include</code>, but is not to point out an absolute file.
│ │ │ │ +<a href="../../../lib/compiler/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4809962197-1">(</span><span class="s">&quot;my_records.hrl&quot;</span><span class="p" data-group-id="4809962197-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4809962197-2">(</span><span class="s">&quot;incdir/my_records.hrl&quot;</span><span class="p" data-group-id="4809962197-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4809962197-3">(</span><span class="s">&quot;/home/user/proj/my_records.hrl&quot;</span><span class="p" data-group-id="4809962197-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4809962197-4">(</span><span class="s">&quot;$PROJ_ROOT/my_records.hrl&quot;</span><span class="p" data-group-id="4809962197-4">)</span><span class="p">.</span></code></pre><p><code class="inline">include_lib</code> is similar to <code class="inline">include</code>, but is not to point out an absolute file.
│ │ │ │  Instead, the first path component (possibly after variable substitution) is
│ │ │ │ -assumed to be the name of an application.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="8442657439-1">(</span><span class="s">&quot;kernel/include/file.hrl&quot;</span><span class="p" data-group-id="8442657439-1">)</span><span class="p">.</span></code></pre><p>The code server uses <code class="inline">code:lib_dir(kernel)</code> to find the directory of the current
│ │ │ │ +assumed to be the name of an application.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="1132914046-1">(</span><span class="s">&quot;kernel/include/file.hrl&quot;</span><span class="p" data-group-id="1132914046-1">)</span><span class="p">.</span></code></pre><p>The code server uses <code class="inline">code:lib_dir(kernel)</code> to find the directory of the current
│ │ │ │  (latest) version of Kernel, and then the subdirectory <code class="inline">include</code> is searched for
│ │ │ │  the file <code class="inline">file.hrl</code>.</p><h2 id="defining-and-using-macros" class="section-heading">
│ │ │ │    <a href="#defining-and-using-macros" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Defining and Using Macros</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A macro is defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5271567651-1">(</span><span class="n">Const</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="5271567651-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5271567651-2">(</span><span class="n">Func</span><span class="p" data-group-id="5271567651-3">(</span><span class="n">Var1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">VarN</span><span class="p" data-group-id="5271567651-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="5271567651-2">)</span><span class="p">.</span></code></pre><p>A macro definition can be placed anywhere among the attributes and function
│ │ │ │ +<p>A macro is defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2337561462-1">(</span><span class="n">Const</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="2337561462-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2337561462-2">(</span><span class="n">Func</span><span class="p" data-group-id="2337561462-3">(</span><span class="n">Var1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">VarN</span><span class="p" data-group-id="2337561462-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="2337561462-2">)</span><span class="p">.</span></code></pre><p>A macro definition can be placed anywhere among the attributes and function
│ │ │ │  declarations of a module, but the definition must come before any usage of the
│ │ │ │  macro.</p><p>If a macro is used in several modules, it is recommended that the macro
│ │ │ │  definition is placed in an include file.</p><p>A macro is used as follows:</p><pre><code class="text">?Const
│ │ │ │  ?Func(Arg1,...,ArgN)</code></pre><p>Macros are expanded during compilation. A simple macro <code class="inline">?Const</code> is replaced with
│ │ │ │ -<code class="inline">Replacement</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9615939026-1">(</span><span class="n">TIMEOUT</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="9615939026-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">Replacement</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5416050123-1">(</span><span class="n">TIMEOUT</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="5416050123-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">call</span><span class="p" data-group-id="9615939026-2">(</span><span class="n">Request</span><span class="p" data-group-id="9615939026-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="9615939026-3">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">TIMEOUT</span><span class="p" data-group-id="9615939026-3">)</span><span class="p">.</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">call</span><span class="p" data-group-id="6626546662-1">(</span><span class="n">Request</span><span class="p" data-group-id="6626546662-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="6626546662-2">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="6626546662-2">)</span><span class="p">.</span></code></pre><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> is replaced with <code class="inline">Replacement</code>, where all
│ │ │ │ +</span><span class="nf">call</span><span class="p" data-group-id="5416050123-2">(</span><span class="n">Request</span><span class="p" data-group-id="5416050123-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="5416050123-3">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">TIMEOUT</span><span class="p" data-group-id="5416050123-3">)</span><span class="p">.</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">call</span><span class="p" data-group-id="2918325308-1">(</span><span class="n">Request</span><span class="p" data-group-id="2918325308-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="2918325308-2">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="2918325308-2">)</span><span class="p">.</span></code></pre><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> is replaced with <code class="inline">Replacement</code>, where all
│ │ │ │  occurrences of a variable <code class="inline">Var</code> from the macro definition are replaced with the
│ │ │ │ -corresponding argument <code class="inline">Arg</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9270542265-1">(</span><span class="n">MACRO1</span><span class="p" data-group-id="9270542265-2">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9270542265-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9270542265-3">{</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9270542265-3">}</span><span class="p" data-group-id="9270542265-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +corresponding argument <code class="inline">Arg</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6402265919-1">(</span><span class="n">MACRO1</span><span class="p" data-group-id="6402265919-2">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6402265919-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6402265919-3">{</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6402265919-3">}</span><span class="p" data-group-id="6402265919-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="9270542265-4">(</span><span class="n">X</span><span class="p" data-group-id="9270542265-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="9270542265-5">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="9270542265-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="9270542265-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="p" data-group-id="9270542265-6">)</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="8886695262-1">(</span><span class="n">X</span><span class="p" data-group-id="8886695262-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8886695262-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8886695262-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8886695262-3">{</span><span class="ss">a</span><span class="p">,</span><span class="n">X</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">123</span><span class="p" data-group-id="8886695262-3">}</span><span class="p">.</span></code></pre><p>It is good programming practice, but not mandatory, to ensure that a macro
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="6402265919-4">(</span><span class="n">X</span><span class="p" data-group-id="6402265919-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="6402265919-5">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="6402265919-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="6402265919-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="p" data-group-id="6402265919-6">)</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="8244297201-1">(</span><span class="n">X</span><span class="p" data-group-id="8244297201-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8244297201-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8244297201-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8244297201-3">{</span><span class="ss">a</span><span class="p">,</span><span class="n">X</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">123</span><span class="p" data-group-id="8244297201-3">}</span><span class="p">.</span></code></pre><p>It is good programming practice, but not mandatory, to ensure that a macro
│ │ │ │  definition is a valid Erlang syntactic form.</p><p>To view the result of macro expansion, a module can be compiled with the <code class="inline">'P'</code>
│ │ │ │  option. <code class="inline">compile:file(File, ['P'])</code>. This produces a listing of the parsed code
│ │ │ │  after preprocessing and parse transforms, in the file <code class="inline">File.P</code>.</p><h2 id="predefined-macros" class="section-heading">
│ │ │ │    <a href="#predefined-macros" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Predefined Macros</span>
│ │ │ │ @@ -90,29 +90,29 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Macros Overloading</span>
│ │ │ │  </h2>
│ │ │ │  <p>It is possible to overload macros, except for predefined macros. An overloaded
│ │ │ │  macro has more than one definition, each with a different number of arguments.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Support for overloading of macros was added in Erlang 5.7.5/OTP R13B04.</p></section><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> with a (possibly empty) list of arguments results
│ │ │ │  in an error message if there is at least one definition of <code class="inline">Func</code> with
│ │ │ │ -arguments, but none with N arguments.</p><p>Assuming these definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5531156528-1">(</span><span class="n">F0</span><span class="p" data-group-id="5531156528-2">(</span><span class="p" data-group-id="5531156528-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="5531156528-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5531156528-3">(</span><span class="n">F1</span><span class="p" data-group-id="5531156528-4">(</span><span class="n">A</span><span class="p" data-group-id="5531156528-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="5531156528-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5531156528-5">(</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="nc">m</span><span class="p">:</span><span class="ss">f</span><span class="p" data-group-id="5531156528-5">)</span><span class="p">.</span></code></pre><p>the following does not work:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f0</span><span class="p" data-group-id="6224580185-1">(</span><span class="p" data-group-id="6224580185-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +arguments, but none with N arguments.</p><p>Assuming these definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2288510985-1">(</span><span class="n">F0</span><span class="p" data-group-id="2288510985-2">(</span><span class="p" data-group-id="2288510985-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="2288510985-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2288510985-3">(</span><span class="n">F1</span><span class="p" data-group-id="2288510985-4">(</span><span class="n">A</span><span class="p" data-group-id="2288510985-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2288510985-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2288510985-5">(</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="nc">m</span><span class="p">:</span><span class="ss">f</span><span class="p" data-group-id="2288510985-5">)</span><span class="p">.</span></code></pre><p>the following does not work:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f0</span><span class="p" data-group-id="2116764936-1">(</span><span class="p" data-group-id="2116764936-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="o">?</span><span class="n">F0</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, an empty list of arguments expected.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">f1</span><span class="p" data-group-id="6224580185-2">(</span><span class="n">A</span><span class="p" data-group-id="6224580185-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">F1</span><span class="p" data-group-id="6224580185-3">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="6224580185-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, exactly one argument expected.</span></code></pre><p>On the other hand,</p><pre><code class="text">f() -&gt;
│ │ │ │ -    ?C().</code></pre><p>is expanded to</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="8947310538-1">(</span><span class="p" data-group-id="8947310538-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">m</span><span class="p">:</span><span class="nf">f</span><span class="p" data-group-id="8947310538-2">(</span><span class="p" data-group-id="8947310538-2">)</span><span class="p">.</span></code></pre><h2 id="removing-a-macro-definition" class="section-heading">
│ │ │ │ +</span><span class="nf">f1</span><span class="p" data-group-id="2116764936-2">(</span><span class="n">A</span><span class="p" data-group-id="2116764936-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">F1</span><span class="p" data-group-id="2116764936-3">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2116764936-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, exactly one argument expected.</span></code></pre><p>On the other hand,</p><pre><code class="text">f() -&gt;
│ │ │ │ +    ?C().</code></pre><p>is expanded to</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="2436967847-1">(</span><span class="p" data-group-id="2436967847-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">m</span><span class="p">:</span><span class="nf">f</span><span class="p" data-group-id="2436967847-2">(</span><span class="p" data-group-id="2436967847-2">)</span><span class="p">.</span></code></pre><h2 id="removing-a-macro-definition" class="section-heading">
│ │ │ │    <a href="#removing-a-macro-definition" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Removing a macro definition</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A definition of macro can be removed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">undef</span><span class="p" data-group-id="4254849763-1">(</span><span class="n">Macro</span><span class="p" data-group-id="4254849763-1">)</span><span class="p">.</span></code></pre><h2 id="conditional-compilation" class="section-heading">
│ │ │ │ +<p>A definition of macro can be removed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">undef</span><span class="p" data-group-id="9913384096-1">(</span><span class="n">Macro</span><span class="p" data-group-id="9913384096-1">)</span><span class="p">.</span></code></pre><h2 id="conditional-compilation" class="section-heading">
│ │ │ │    <a href="#conditional-compilation" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Conditional Compilation</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following macro directives support conditional compilation:</p><ul><li><p><strong><code class="inline">-ifdef(Macro).</code></strong> - Evaluate the following lines only if <code class="inline">Macro</code> is
│ │ │ │  defined.</p></li><li><p><strong><code class="inline">-ifndef(Macro).</code></strong> - Evaluate the following lines only if <code class="inline">Macro</code> is not
│ │ │ │ @@ -124,43 +124,43 @@
│ │ │ │  true, and the <code class="inline">Condition</code> evaluates to true, the lines following the <code class="inline">elif</code>
│ │ │ │  are evaluated instead.</p></li><li><p><strong><code class="inline">-endif.</code></strong> - Specifies the end of a series of control flow directives.</p></li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Macro directives cannot be used inside functions.</p></section><p>Syntactically, the <code class="inline">Condition</code> in <code class="inline">if</code> and <code class="inline">elif</code> must be a
│ │ │ │  <a href="expressions.xhtml#guard-expressions">guard expression</a>. Other constructs (such as
│ │ │ │  a <code class="inline">case</code> expression) result in a compilation error.</p><p>As opposed to the standard guard expressions, an expression in an <code class="inline">if</code> and
│ │ │ │  <code class="inline">elif</code> also supports calling the psuedo-function <code class="inline">defined(Name)</code>, which tests
│ │ │ │  whether the <code class="inline">Name</code> argument is the name of a previously defined macro.
│ │ │ │  <code class="inline">defined(Name)</code> evaluates to <code class="inline">true</code> if the macro is defined and <code class="inline">false</code>
│ │ │ │ -otherwise. An attempt to call other functions results in a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6513752406-1">(</span><span class="ss">m</span><span class="p" data-group-id="6513752406-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +otherwise. An attempt to call other functions results in a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8514930707-1">(</span><span class="ss">m</span><span class="p" data-group-id="8514930707-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="6513752406-2">(</span><span class="ss">debug</span><span class="p" data-group-id="6513752406-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6513752406-3">(</span><span class="n">LOG</span><span class="p" data-group-id="6513752406-4">(</span><span class="n">X</span><span class="p" data-group-id="6513752406-4">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6513752406-5">(</span><span class="s">&quot;{</span><span class="si">~p</span><span class="s">,</span><span class="si">~p</span><span class="s">}: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6513752406-6">[</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="o">?</span><span class="n">LINE</span><span class="p">,</span><span class="n">X</span><span class="p" data-group-id="6513752406-6">]</span><span class="p" data-group-id="6513752406-5">)</span><span class="p" data-group-id="6513752406-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="8514930707-2">(</span><span class="ss">debug</span><span class="p" data-group-id="8514930707-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8514930707-3">(</span><span class="n">LOG</span><span class="p" data-group-id="8514930707-4">(</span><span class="n">X</span><span class="p" data-group-id="8514930707-4">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8514930707-5">(</span><span class="s">&quot;{</span><span class="si">~p</span><span class="s">,</span><span class="si">~p</span><span class="s">}: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8514930707-6">[</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="o">?</span><span class="n">LINE</span><span class="p">,</span><span class="n">X</span><span class="p" data-group-id="8514930707-6">]</span><span class="p" data-group-id="8514930707-5">)</span><span class="p" data-group-id="8514930707-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6513752406-7">(</span><span class="n">LOG</span><span class="p" data-group-id="6513752406-8">(</span><span class="n">X</span><span class="p" data-group-id="6513752406-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6513752406-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8514930707-7">(</span><span class="n">LOG</span><span class="p" data-group-id="8514930707-8">(</span><span class="n">X</span><span class="p" data-group-id="8514930707-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8514930707-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>When trace output is desired, <code class="inline">debug</code> is to be defined when the module <code class="inline">m</code> is
│ │ │ │  compiled:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erlc -Ddebug m.erl</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="ow">or</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="0016854266-1">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0016854266-2">{</span><span class="ss">d</span><span class="p">,</span><span class="w"> </span><span class="ss">debug</span><span class="p" data-group-id="0016854266-2">}</span><span class="p" data-group-id="0016854266-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0016854266-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">m</span><span class="p" data-group-id="0016854266-3">}</span></code></pre><p><code class="inline">?LOG(Arg)</code> is then expanded to a call to <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> and provide the user
│ │ │ │ -with some simple trace output.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1816856661-1">(</span><span class="ss">m</span><span class="p" data-group-id="1816856661-1">)</span><span class="w">
│ │ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="1395228301-1">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1395228301-2">{</span><span class="ss">d</span><span class="p">,</span><span class="w"> </span><span class="ss">debug</span><span class="p" data-group-id="1395228301-2">}</span><span class="p" data-group-id="1395228301-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1395228301-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">m</span><span class="p" data-group-id="1395228301-3">}</span></code></pre><p><code class="inline">?LOG(Arg)</code> is then expanded to a call to <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> and provide the user
│ │ │ │ +with some simple trace output.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1344585680-1">(</span><span class="ss">m</span><span class="p" data-group-id="1344585680-1">)</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="1816856661-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">25</span><span class="p" data-group-id="1816856661-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="1344585680-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">25</span><span class="p" data-group-id="1344585680-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Code that will work in OTP 25 or higher</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">elif</span><span class="p" data-group-id="1816856661-3">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="p" data-group-id="1816856661-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">elif</span><span class="p" data-group-id="1344585680-3">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="p" data-group-id="1344585680-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Code that will work in OTP 26 or higher</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Code that will work in OTP 24 or lower.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This code uses the <code class="inline">OTP_RELEASE</code> macro to conditionally select code depending on
│ │ │ │ -release.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2568256262-1">(</span><span class="ss">m</span><span class="p" data-group-id="2568256262-1">)</span><span class="w">
│ │ │ │ +release.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9874755571-1">(</span><span class="ss">m</span><span class="p" data-group-id="9874755571-1">)</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="2568256262-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">defined</span><span class="p" data-group-id="2568256262-3">(</span><span class="ss">debug</span><span class="p" data-group-id="2568256262-3">)</span><span class="p" data-group-id="2568256262-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="9874755571-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">defined</span><span class="p" data-group-id="9874755571-3">(</span><span class="ss">debug</span><span class="p" data-group-id="9874755571-3">)</span><span class="p" data-group-id="9874755571-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Debugging code that requires OTP 26 or later.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Non-debug code that works in any release.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This code uses the <code class="inline">OTP_RELEASE</code> macro and <code class="inline">defined(debug)</code> to compile debug
│ │ │ │  code only for OTP 26 or later.</p><h2 id="the-feature-directive" class="section-heading">
│ │ │ │    <a href="#the-feature-directive" class="hover-link">
│ │ │ │ @@ -175,40 +175,40 @@
│ │ │ │  used. In practice this means it should appear before any <code class="inline">-export(..)</code> or record
│ │ │ │  definitions.</p><h2 id="error-and-warning-directives" class="section-heading">
│ │ │ │    <a href="#error-and-warning-directives" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">-error() and -warning() directives</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The directive <code class="inline">-error(Term)</code> causes a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2212318291-1">(</span><span class="ss">t</span><span class="p" data-group-id="2212318291-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2212318291-2">(</span><span class="p" data-group-id="2212318291-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2212318291-3">]</span><span class="p" data-group-id="2212318291-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>The directive <code class="inline">-error(Term)</code> causes a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5552636833-1">(</span><span class="ss">t</span><span class="p" data-group-id="5552636833-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5552636833-2">(</span><span class="p" data-group-id="5552636833-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5552636833-3">]</span><span class="p" data-group-id="5552636833-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="2212318291-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="2212318291-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="2212318291-5">(</span><span class="p" data-group-id="2212318291-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="5552636833-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="5552636833-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="5552636833-5">(</span><span class="p" data-group-id="5552636833-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">error</span><span class="p" data-group-id="2212318291-6">(</span><span class="s">&quot;Macro VERSION must be defined.&quot;</span><span class="p" data-group-id="2212318291-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="2212318291-7">(</span><span class="p" data-group-id="2212318291-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">error</span><span class="p" data-group-id="5552636833-6">(</span><span class="s">&quot;Macro VERSION must be defined.&quot;</span><span class="p" data-group-id="5552636833-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="5552636833-7">(</span><span class="p" data-group-id="5552636833-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span></code></pre><p>The error message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │ │ -t.erl:7: -error(&quot;Macro VERSION must be defined.&quot;).</code></pre><p>The directive <code class="inline">-warning(Term)</code> causes a compilation warning.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3527470209-1">(</span><span class="ss">t</span><span class="p" data-group-id="3527470209-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3527470209-2">(</span><span class="p" data-group-id="3527470209-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3527470209-3">]</span><span class="p" data-group-id="3527470209-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +t.erl:7: -error(&quot;Macro VERSION must be defined.&quot;).</code></pre><p>The directive <code class="inline">-warning(Term)</code> causes a compilation warning.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1851559313-1">(</span><span class="ss">t</span><span class="p" data-group-id="1851559313-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1851559313-2">(</span><span class="p" data-group-id="1851559313-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1851559313-3">]</span><span class="p" data-group-id="1851559313-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">ifndef</span><span class="p" data-group-id="3527470209-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="3527470209-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">warning</span><span class="p" data-group-id="3527470209-5">(</span><span class="s">&quot;Macro VERSION not defined -- using default version.&quot;</span><span class="p" data-group-id="3527470209-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3527470209-6">(</span><span class="n">VERSION</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;0&quot;</span><span class="p" data-group-id="3527470209-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">ifndef</span><span class="p" data-group-id="1851559313-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="1851559313-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">warning</span><span class="p" data-group-id="1851559313-5">(</span><span class="s">&quot;Macro VERSION not defined -- using default version.&quot;</span><span class="p" data-group-id="1851559313-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1851559313-6">(</span><span class="n">VERSION</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;0&quot;</span><span class="p" data-group-id="1851559313-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="3527470209-7">(</span><span class="p" data-group-id="3527470209-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span></code></pre><p>The warning message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="1851559313-7">(</span><span class="p" data-group-id="1851559313-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span></code></pre><p>The warning message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │ │  t.erl:5: Warning: -warning(&quot;Macro VERSION not defined -- using default version.&quot;).</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>The <code class="inline">-error()</code> and <code class="inline">-warning()</code> directives were added in Erlang/OTP 19.</p></section><h2 id="stringifying-macro-arguments" class="section-heading">
│ │ │ │    <a href="#stringifying-macro-arguments" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Stringifying Macro Arguments</span>
│ │ │ │  </h2>
│ │ │ │  <p>The construction <code class="inline">??Arg</code>, where <code class="inline">Arg</code> is a macro argument, is expanded to a
│ │ │ │  string containing the tokens of the argument. This is similar to the <code class="inline">#arg</code>
│ │ │ │ -stringifying construction in C.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0145822957-1">(</span><span class="n">TESTCALL</span><span class="p" data-group-id="0145822957-2">(</span><span class="n">Call</span><span class="p" data-group-id="0145822957-2">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0145822957-3">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0145822957-4">[</span><span class="o">?</span><span class="o">?</span><span class="n">Call</span><span class="p">,</span><span class="w"> </span><span class="n">Call</span><span class="p" data-group-id="0145822957-4">]</span><span class="p" data-group-id="0145822957-3">)</span><span class="p" data-group-id="0145822957-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +stringifying construction in C.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2776920772-1">(</span><span class="n">TESTCALL</span><span class="p" data-group-id="2776920772-2">(</span><span class="n">Call</span><span class="p" data-group-id="2776920772-2">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2776920772-3">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2776920772-4">[</span><span class="o">?</span><span class="o">?</span><span class="n">Call</span><span class="p">,</span><span class="w"> </span><span class="n">Call</span><span class="p" data-group-id="2776920772-4">]</span><span class="p" data-group-id="2776920772-3">)</span><span class="p" data-group-id="2776920772-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="0145822957-5">(</span><span class="nf">myfunction</span><span class="p" data-group-id="0145822957-6">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0145822957-6">)</span><span class="p" data-group-id="0145822957-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="0145822957-7">(</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="0145822957-8">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0145822957-8">)</span><span class="p" data-group-id="0145822957-7">)</span><span class="p">.</span></code></pre><p>results in</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0728436654-1">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="0728436654-2">[</span><span class="s">&quot;myfunction ( 1 , 2 )&quot;</span><span class="p">,</span><span class="nf">myfunction</span><span class="p" data-group-id="0728436654-3">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0728436654-3">)</span><span class="p" data-group-id="0728436654-2">]</span><span class="p" data-group-id="0728436654-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0728436654-4">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="0728436654-5">[</span><span class="s">&quot;you : function ( 2 , 1 )&quot;</span><span class="p">,</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="0728436654-6">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0728436654-6">)</span><span class="p" data-group-id="0728436654-5">]</span><span class="p" data-group-id="0728436654-4">)</span><span class="p">.</span></code></pre><p>That is, a trace output, with both the function called and the resulting value.</p>
│ │ │ │ +</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="2776920772-5">(</span><span class="nf">myfunction</span><span class="p" data-group-id="2776920772-6">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2776920772-6">)</span><span class="p" data-group-id="2776920772-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="2776920772-7">(</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="2776920772-8">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2776920772-8">)</span><span class="p" data-group-id="2776920772-7">)</span><span class="p">.</span></code></pre><p>results in</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6057876949-1">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="6057876949-2">[</span><span class="s">&quot;myfunction ( 1 , 2 )&quot;</span><span class="p">,</span><span class="nf">myfunction</span><span class="p" data-group-id="6057876949-3">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6057876949-3">)</span><span class="p" data-group-id="6057876949-2">]</span><span class="p" data-group-id="6057876949-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6057876949-4">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="6057876949-5">[</span><span class="s">&quot;you : function ( 2 , 1 )&quot;</span><span class="p">,</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="6057876949-6">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6057876949-6">)</span><span class="p" data-group-id="6057876949-5">]</span><span class="p" data-group-id="6057876949-4">)</span><span class="p">.</span></code></pre><p>That is, a trace output, with both the function called and the resulting value.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/listhandling.xhtml
│ │ │ │ @@ -25,101 +25,101 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating a List</span>
│ │ │ │  </h2>
│ │ │ │  <p>Lists can only be built starting from the end and attaching list elements at the
│ │ │ │  beginning. If you use the <code class="inline">++</code> operator as follows, a new list is created that
│ │ │ │  is a copy of the elements in <code class="inline">List1</code>, followed by <code class="inline">List2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">List1</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">List2</span></code></pre><p>Looking at how <a href="../../../lib/stdlib/doc/html/lists.html#append/2"><code class="inline">lists:append/2</code></a> or <code class="inline">++</code> would be implemented in plain Erlang,
│ │ │ │ -clearly the first list is copied:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="1991751995-1">(</span><span class="p" data-group-id="1991751995-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1991751995-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1991751995-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1991751995-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">append</span><span class="p" data-group-id="1991751995-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1991751995-4">)</span><span class="p" data-group-id="1991751995-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">append</span><span class="p" data-group-id="1991751995-5">(</span><span class="p" data-group-id="1991751995-6">[</span><span class="p" data-group-id="1991751995-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1991751995-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +clearly the first list is copied:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="1502361167-1">(</span><span class="p" data-group-id="1502361167-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1502361167-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1502361167-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1502361167-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">append</span><span class="p" data-group-id="1502361167-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1502361167-4">)</span><span class="p" data-group-id="1502361167-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">append</span><span class="p" data-group-id="1502361167-5">(</span><span class="p" data-group-id="1502361167-6">[</span><span class="p" data-group-id="1502361167-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1502361167-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>When recursing and building a list, it is important to ensure that you attach
│ │ │ │  the new elements to the beginning of the list. In this way, you will build <em>one</em>
│ │ │ │ -list, not hundreds or thousands of copies of the growing result list.</p><p>Let us first see how it is not to be done:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">bad_fib</span><span class="p" data-group-id="6907519038-1">(</span><span class="n">N</span><span class="p" data-group-id="6907519038-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">bad_fib</span><span class="p" data-group-id="6907519038-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6907519038-3">[</span><span class="p" data-group-id="6907519038-3">]</span><span class="p" data-group-id="6907519038-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +list, not hundreds or thousands of copies of the growing result list.</p><p>Let us first see how it is not to be done:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">bad_fib</span><span class="p" data-group-id="1569118266-1">(</span><span class="n">N</span><span class="p" data-group-id="1569118266-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">bad_fib</span><span class="p" data-group-id="1569118266-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1569118266-3">[</span><span class="p" data-group-id="1569118266-3">]</span><span class="p" data-group-id="1569118266-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">bad_fib</span><span class="p" data-group-id="6907519038-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="6907519038-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">bad_fib</span><span class="p" data-group-id="1569118266-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="1569118266-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Fibs</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">bad_fib</span><span class="p" data-group-id="6907519038-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="6907519038-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">bad_fib</span><span class="p" data-group-id="6907519038-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6907519038-7">[</span><span class="n">Current</span><span class="p" data-group-id="6907519038-7">]</span><span class="p" data-group-id="6907519038-6">)</span><span class="p">.</span></code></pre><p>Here more than one list is built. In each iteration step a new list is created
│ │ │ │ +</span><span class="nf">bad_fib</span><span class="p" data-group-id="1569118266-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="1569118266-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">bad_fib</span><span class="p" data-group-id="1569118266-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1569118266-7">[</span><span class="n">Current</span><span class="p" data-group-id="1569118266-7">]</span><span class="p" data-group-id="1569118266-6">)</span><span class="p">.</span></code></pre><p>Here more than one list is built. In each iteration step a new list is created
│ │ │ │  that is one element longer than the new previous list.</p><p>To avoid copying the result in each iteration, build the list in reverse order
│ │ │ │ -and reverse the list when you are done:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8027360468-1">(</span><span class="n">N</span><span class="p" data-group-id="8027360468-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8027360468-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8027360468-3">[</span><span class="p" data-group-id="8027360468-3">]</span><span class="p" data-group-id="8027360468-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +and reverse the list when you are done:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="0087690217-1">(</span><span class="n">N</span><span class="p" data-group-id="0087690217-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="0087690217-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0087690217-3">[</span><span class="p" data-group-id="0087690217-3">]</span><span class="p" data-group-id="0087690217-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8027360468-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="8027360468-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="8027360468-5">(</span><span class="n">Fibs</span><span class="p" data-group-id="8027360468-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8027360468-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="8027360468-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8027360468-7">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8027360468-8">[</span><span class="n">Current</span><span class="p">|</span><span class="n">Fibs</span><span class="p" data-group-id="8027360468-8">]</span><span class="p" data-group-id="8027360468-7">)</span><span class="p">.</span></code></pre><h2 id="list-comprehensions" class="section-heading">
│ │ │ │ +</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="0087690217-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="0087690217-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="0087690217-5">(</span><span class="n">Fibs</span><span class="p" data-group-id="0087690217-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="0087690217-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="0087690217-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="0087690217-7">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0087690217-8">[</span><span class="n">Current</span><span class="p">|</span><span class="n">Fibs</span><span class="p" data-group-id="0087690217-8">]</span><span class="p" data-group-id="0087690217-7">)</span><span class="p">.</span></code></pre><h2 id="list-comprehensions" class="section-heading">
│ │ │ │    <a href="#list-comprehensions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">List Comprehensions</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A list comprehension:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3435072804-1">[</span><span class="n">Expr</span><span class="p" data-group-id="3435072804-2">(</span><span class="n">E</span><span class="p" data-group-id="3435072804-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3435072804-1">]</span></code></pre><p>is basically translated to a local function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5848801070-1">(</span><span class="p" data-group-id="5848801070-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="5848801070-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="5848801070-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5848801070-3">[</span><span class="n">Expr</span><span class="p" data-group-id="5848801070-4">(</span><span class="n">E</span><span class="p" data-group-id="5848801070-4">)</span><span class="p">|</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5848801070-5">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="5848801070-5">)</span><span class="p" data-group-id="5848801070-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5848801070-6">(</span><span class="p" data-group-id="5848801070-7">[</span><span class="p" data-group-id="5848801070-7">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="5848801070-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5848801070-8">[</span><span class="p" data-group-id="5848801070-8">]</span><span class="p">.</span></code></pre><p>If the result of the list comprehension will <em>obviously</em> not be used, a list
│ │ │ │ -will not be constructed. For example, in this code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2356185983-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="2356185983-2">(</span><span class="n">E</span><span class="p" data-group-id="2356185983-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="2356185983-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ +<p>A list comprehension:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2125695557-1">[</span><span class="n">Expr</span><span class="p" data-group-id="2125695557-2">(</span><span class="n">E</span><span class="p" data-group-id="2125695557-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="2125695557-1">]</span></code></pre><p>is basically translated to a local function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="8108936099-1">(</span><span class="p" data-group-id="8108936099-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="8108936099-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="8108936099-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8108936099-3">[</span><span class="n">Expr</span><span class="p" data-group-id="8108936099-4">(</span><span class="n">E</span><span class="p" data-group-id="8108936099-4">)</span><span class="p">|</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="8108936099-5">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="8108936099-5">)</span><span class="p" data-group-id="8108936099-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="8108936099-6">(</span><span class="p" data-group-id="8108936099-7">[</span><span class="p" data-group-id="8108936099-7">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="8108936099-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8108936099-8">[</span><span class="p" data-group-id="8108936099-8">]</span><span class="p">.</span></code></pre><p>If the result of the list comprehension will <em>obviously</em> not be used, a list
│ │ │ │ +will not be constructed. For example, in this code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8746995999-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="8746995999-2">(</span><span class="n">E</span><span class="p" data-group-id="8746995999-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="8746995999-1">]</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>or in this code:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">Var</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2818341499-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="2818341499-2">(</span><span class="n">E</span><span class="p" data-group-id="2818341499-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="2818341499-1">]</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7056031249-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="7056031249-2">(</span><span class="n">E</span><span class="p" data-group-id="7056031249-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7056031249-1">]</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nf">some_function</span><span class="p" data-group-id="2818341499-3">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2818341499-3">)</span><span class="p">,</span></code></pre><p>the value is not assigned to a variable, not passed to another function, and not
│ │ │ │ +</span><span class="nf">some_function</span><span class="p" data-group-id="7056031249-3">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7056031249-3">)</span><span class="p">,</span></code></pre><p>the value is not assigned to a variable, not passed to another function, and not
│ │ │ │  returned. This means that there is no need to construct a list and the compiler
│ │ │ │ -will simplify the code for the list comprehension to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="2386248281-1">(</span><span class="p" data-group-id="2386248281-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="2386248281-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="2386248281-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Expr</span><span class="p" data-group-id="2386248281-3">(</span><span class="n">E</span><span class="p" data-group-id="2386248281-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="2386248281-4">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="2386248281-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="2386248281-5">(</span><span class="p" data-group-id="2386248281-6">[</span><span class="p" data-group-id="2386248281-6">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="2386248281-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2386248281-7">[</span><span class="p" data-group-id="2386248281-7">]</span><span class="p">.</span></code></pre><p>The compiler also understands that assigning to <code class="inline">_</code> means that the value will
│ │ │ │ -not be used. Therefore, the code in the following example will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8953917394-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="8953917394-2">(</span><span class="n">E</span><span class="p" data-group-id="8953917394-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="8953917394-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ +will simplify the code for the list comprehension to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="7915309018-1">(</span><span class="p" data-group-id="7915309018-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="7915309018-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="7915309018-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Expr</span><span class="p" data-group-id="7915309018-3">(</span><span class="n">E</span><span class="p" data-group-id="7915309018-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="7915309018-4">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="7915309018-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="7915309018-5">(</span><span class="p" data-group-id="7915309018-6">[</span><span class="p" data-group-id="7915309018-6">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="7915309018-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7915309018-7">[</span><span class="p" data-group-id="7915309018-7">]</span><span class="p">.</span></code></pre><p>The compiler also understands that assigning to <code class="inline">_</code> means that the value will
│ │ │ │ +not be used. Therefore, the code in the following example will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9467635483-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="9467635483-2">(</span><span class="n">E</span><span class="p" data-group-id="9467635483-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9467635483-1">]</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="p">.</span></code></pre><h2 id="deep-and-flat-lists" class="section-heading">
│ │ │ │    <a href="#deep-and-flat-lists" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Deep and Flat Lists</span>
│ │ │ │  </h2>
│ │ │ │  <p><a href="../../../lib/stdlib/doc/html/lists.html#flatten/1"><code class="inline">lists:flatten/1</code></a> builds an entirely new list. It is therefore expensive, and
│ │ │ │  even <em>more</em> expensive than the <code class="inline">++</code> operator (which copies its left argument,
│ │ │ │  but not its right argument).</p><p>In the following situations it is unnecessary to call <a href="../../../lib/stdlib/doc/html/lists.html#flatten/1"><code class="inline">lists:flatten/1</code></a>:</p><ul><li>When sending data to a port. Ports understand deep lists so there is no reason
│ │ │ │  to flatten the list before sending it to the port.</li><li>When calling BIFs that accept deep lists, such as
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a> or
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#iolist_to_binary/1"><code class="inline">iolist_to_binary/1</code></a>.</li><li>When you know that your list is only one level deep. Use <a href="../../../lib/stdlib/doc/html/lists.html#append/1"><code class="inline">lists:append/1</code></a>
│ │ │ │ -instead.</li></ul><p><em>Examples:</em></p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="1720273287-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">DeepList</span><span class="p" data-group-id="1720273287-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="1897041651-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="1897041651-2">(</span><span class="n">DeepList</span><span class="p" data-group-id="1897041651-2">)</span><span class="p" data-group-id="1897041651-1">)</span></code></pre><p>A common way to send a zero-terminated string to a port is the following:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6571657687-1">[</span><span class="mi">0</span><span class="p" data-group-id="6571657687-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nf">port_command</span><span class="p" data-group-id="6571657687-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="6571657687-2">)</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0191212590-1">[</span><span class="n">String</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0191212590-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nf">port_command</span><span class="p" data-group-id="0191212590-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="0191212590-2">)</span></code></pre><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">append</span><span class="p" data-group-id="3942308863-1">(</span><span class="p" data-group-id="3942308863-2">[</span><span class="p" data-group-id="3942308863-3">[</span><span class="mi">1</span><span class="p" data-group-id="3942308863-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3942308863-4">[</span><span class="mi">2</span><span class="p" data-group-id="3942308863-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3942308863-5">[</span><span class="mi">3</span><span class="p" data-group-id="3942308863-5">]</span><span class="p" data-group-id="3942308863-2">]</span><span class="p" data-group-id="3942308863-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3942308863-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3942308863-6">]</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="0424418911-1">(</span><span class="p" data-group-id="0424418911-2">[</span><span class="p" data-group-id="0424418911-3">[</span><span class="mi">1</span><span class="p" data-group-id="0424418911-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0424418911-4">[</span><span class="mi">2</span><span class="p" data-group-id="0424418911-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0424418911-5">[</span><span class="mi">3</span><span class="p" data-group-id="0424418911-5">]</span><span class="p" data-group-id="0424418911-2">]</span><span class="p" data-group-id="0424418911-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0424418911-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0424418911-6">]</span></code></pre><h2 id="recursive-list-functions" class="section-heading">
│ │ │ │ +instead.</li></ul><p><em>Examples:</em></p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="2683747495-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">DeepList</span><span class="p" data-group-id="2683747495-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="4412057828-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="4412057828-2">(</span><span class="n">DeepList</span><span class="p" data-group-id="4412057828-2">)</span><span class="p" data-group-id="4412057828-1">)</span></code></pre><p>A common way to send a zero-terminated string to a port is the following:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="8955030576-1">[</span><span class="mi">0</span><span class="p" data-group-id="8955030576-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">port_command</span><span class="p" data-group-id="8955030576-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="8955030576-2">)</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0935562061-1">[</span><span class="n">String</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0935562061-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">port_command</span><span class="p" data-group-id="0935562061-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="0935562061-2">)</span></code></pre><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">append</span><span class="p" data-group-id="2937698362-1">(</span><span class="p" data-group-id="2937698362-2">[</span><span class="p" data-group-id="2937698362-3">[</span><span class="mi">1</span><span class="p" data-group-id="2937698362-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2937698362-4">[</span><span class="mi">2</span><span class="p" data-group-id="2937698362-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2937698362-5">[</span><span class="mi">3</span><span class="p" data-group-id="2937698362-5">]</span><span class="p" data-group-id="2937698362-2">]</span><span class="p" data-group-id="2937698362-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2937698362-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2937698362-6">]</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="1895892133-1">(</span><span class="p" data-group-id="1895892133-2">[</span><span class="p" data-group-id="1895892133-3">[</span><span class="mi">1</span><span class="p" data-group-id="1895892133-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1895892133-4">[</span><span class="mi">2</span><span class="p" data-group-id="1895892133-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1895892133-5">[</span><span class="mi">3</span><span class="p" data-group-id="1895892133-5">]</span><span class="p" data-group-id="1895892133-2">]</span><span class="p" data-group-id="1895892133-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1895892133-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1895892133-6">]</span></code></pre><h2 id="recursive-list-functions" class="section-heading">
│ │ │ │    <a href="#recursive-list-functions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Recursive List Functions</span>
│ │ │ │  </h2>
│ │ │ │  <p>There are two basic ways to write a function that traverses a list and
│ │ │ │  produces a new list.</p><p>The first way is writing a <em>body-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ │ -</span><span class="nf">add_42_body</span><span class="p" data-group-id="8080013808-1">(</span><span class="p" data-group-id="8080013808-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8080013808-2">]</span><span class="p" data-group-id="8080013808-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8080013808-3">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">add_42_body</span><span class="p" data-group-id="8080013808-4">(</span><span class="n">T</span><span class="p" data-group-id="8080013808-4">)</span><span class="p" data-group-id="8080013808-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">add_42_body</span><span class="p" data-group-id="8080013808-5">(</span><span class="p" data-group-id="8080013808-6">[</span><span class="p" data-group-id="8080013808-6">]</span><span class="p" data-group-id="8080013808-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8080013808-7">[</span><span class="p" data-group-id="8080013808-7">]</span><span class="p">.</span></code></pre><p>The second way is writing a <em>tail-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="9816019289-1">(</span><span class="n">List</span><span class="p" data-group-id="9816019289-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="9816019289-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9816019289-3">[</span><span class="p" data-group-id="9816019289-3">]</span><span class="p" data-group-id="9816019289-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add_42_body</span><span class="p" data-group-id="4731387367-1">(</span><span class="p" data-group-id="4731387367-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4731387367-2">]</span><span class="p" data-group-id="4731387367-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4731387367-3">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">add_42_body</span><span class="p" data-group-id="4731387367-4">(</span><span class="n">T</span><span class="p" data-group-id="4731387367-4">)</span><span class="p" data-group-id="4731387367-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">add_42_body</span><span class="p" data-group-id="4731387367-5">(</span><span class="p" data-group-id="4731387367-6">[</span><span class="p" data-group-id="4731387367-6">]</span><span class="p" data-group-id="4731387367-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4731387367-7">[</span><span class="p" data-group-id="4731387367-7">]</span><span class="p">.</span></code></pre><p>The second way is writing a <em>tail-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="3140855446-1">(</span><span class="n">List</span><span class="p" data-group-id="3140855446-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="3140855446-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3140855446-3">[</span><span class="p" data-group-id="3140855446-3">]</span><span class="p" data-group-id="3140855446-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="9816019289-4">(</span><span class="p" data-group-id="9816019289-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9816019289-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9816019289-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="9816019289-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9816019289-7">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9816019289-7">]</span><span class="p" data-group-id="9816019289-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="9816019289-8">(</span><span class="p" data-group-id="9816019289-9">[</span><span class="p" data-group-id="9816019289-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9816019289-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="9816019289-10">(</span><span class="n">Acc</span><span class="p" data-group-id="9816019289-10">)</span><span class="p">.</span></code></pre><p>In early version of Erlang the tail-recursive function would typically
│ │ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="3140855446-4">(</span><span class="p" data-group-id="3140855446-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3140855446-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3140855446-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="3140855446-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3140855446-7">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3140855446-7">]</span><span class="p" data-group-id="3140855446-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="3140855446-8">(</span><span class="p" data-group-id="3140855446-9">[</span><span class="p" data-group-id="3140855446-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3140855446-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="3140855446-10">(</span><span class="n">Acc</span><span class="p" data-group-id="3140855446-10">)</span><span class="p">.</span></code></pre><p>In early version of Erlang the tail-recursive function would typically
│ │ │ │  be more efficient. In modern versions of Erlang, there is usually not
│ │ │ │  much difference in performance between a body-recursive list function and
│ │ │ │  tail-recursive function that reverses the list at the end. Therefore,
│ │ │ │  concentrate on writing beautiful code and forget about the performance
│ │ │ │  of your list functions. In the time-critical parts of your code,
│ │ │ │  <em>measure</em> before rewriting your code.</p><p>For a thorough discussion about tail and body recursion, see
│ │ │ │  <a href="http://ferd.ca/erlang-s-tail-recursion-is-not-a-silver-bullet.html">Erlang's Tail Recursion is Not a Silver Bullet</a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>This section is about list functions that <em>construct</em> lists. A tail-recursive
│ │ │ │  function that does not construct a list runs in constant space, while the
│ │ │ │  corresponding body-recursive function uses stack space proportional to the
│ │ │ │  length of the list.</p></section><p>For example, a function that sums a list of integers, is <em>not</em> to be written as
│ │ │ │ -follows:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">recursive_sum</span><span class="p" data-group-id="5756083482-1">(</span><span class="p" data-group-id="5756083482-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5756083482-2">]</span><span class="p" data-group-id="5756083482-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">H</span><span class="o">+</span><span class="nf">recursive_sum</span><span class="p" data-group-id="5756083482-3">(</span><span class="n">T</span><span class="p" data-group-id="5756083482-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">recursive_sum</span><span class="p" data-group-id="5756083482-4">(</span><span class="p" data-group-id="5756083482-5">[</span><span class="p" data-group-id="5756083482-5">]</span><span class="p" data-group-id="5756083482-4">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">sum</span><span class="p" data-group-id="7030348967-1">(</span><span class="n">L</span><span class="p" data-group-id="7030348967-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="7030348967-2">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7030348967-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +follows:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">recursive_sum</span><span class="p" data-group-id="0071279438-1">(</span><span class="p" data-group-id="0071279438-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0071279438-2">]</span><span class="p" data-group-id="0071279438-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">H</span><span class="o">+</span><span class="nf">recursive_sum</span><span class="p" data-group-id="0071279438-3">(</span><span class="n">T</span><span class="p" data-group-id="0071279438-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">recursive_sum</span><span class="p" data-group-id="0071279438-4">(</span><span class="p" data-group-id="0071279438-5">[</span><span class="p" data-group-id="0071279438-5">]</span><span class="p" data-group-id="0071279438-4">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">sum</span><span class="p" data-group-id="6873151445-1">(</span><span class="n">L</span><span class="p" data-group-id="6873151445-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="6873151445-2">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6873151445-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">sum</span><span class="p" data-group-id="7030348967-3">(</span><span class="p" data-group-id="7030348967-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7030348967-4">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="7030348967-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="7030348967-5">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">H</span><span class="p" data-group-id="7030348967-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">sum</span><span class="p" data-group-id="7030348967-6">(</span><span class="p" data-group-id="7030348967-7">[</span><span class="p" data-group-id="7030348967-7">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="7030348967-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Sum</span><span class="p">.</span></code></pre>
│ │ │ │ +</span><span class="nf">sum</span><span class="p" data-group-id="6873151445-3">(</span><span class="p" data-group-id="6873151445-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6873151445-4">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="6873151445-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="6873151445-5">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">H</span><span class="p" data-group-id="6873151445-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">sum</span><span class="p" data-group-id="6873151445-6">(</span><span class="p" data-group-id="6873151445-7">[</span><span class="p" data-group-id="6873151445-7">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="6873151445-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Sum</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/list_comprehensions.xhtml
│ │ │ │ @@ -22,33 +22,33 @@
│ │ │ │      </h1>
│ │ │ │  <h2 id="simple-examples" class="section-heading">
│ │ │ │    <a href="#simple-examples" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Simple Examples</span>
│ │ │ │  </h2>
│ │ │ │ -<p>This section starts with a simple example, showing a generator and a filter:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="7749926677-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7749926677-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7749926677-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7749926677-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7749926677-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7749926677-3">]</span></code></pre><p>This is read as follows: The list of X such that X is taken from the list
│ │ │ │ +<p>This section starts with a simple example, showing a generator and a filter:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="5796553058-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="5796553058-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5796553058-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5796553058-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5796553058-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5796553058-3">]</span></code></pre><p>This is read as follows: The list of X such that X is taken from the list
│ │ │ │  <code class="inline">[1,2,a,...]</code> and X is greater than 3.</p><p>The notation <code class="inline">X &lt;- [1,2,a,...]</code> is a generator and the expression <code class="inline">X &gt; 3</code> is a
│ │ │ │  filter.</p><p>An additional filter, <a href="../../../lib/../erts/doc/html/erlang.html#is_integer/1"><code class="inline">is_integer(X)</code></a>, can be added to
│ │ │ │ -restrict the result to integers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="1810896339-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="1810896339-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1810896339-2">]</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="1810896339-3">(</span><span class="n">X</span><span class="p" data-group-id="1810896339-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1810896339-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1810896339-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1810896339-4">]</span></code></pre><p>Generators can be combined. For example, the Cartesian product of two lists can
│ │ │ │ -be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="7302773086-1">[</span><span class="p" data-group-id="7302773086-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7302773086-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7302773086-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7302773086-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7302773086-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7302773086-4">]</span><span class="p" data-group-id="7302773086-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7302773086-5">[</span><span class="p" data-group-id="7302773086-6">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7302773086-6">}</span><span class="p">,</span><span class="p" data-group-id="7302773086-7">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7302773086-7">}</span><span class="p">,</span><span class="p" data-group-id="7302773086-8">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7302773086-8">}</span><span class="p">,</span><span class="p" data-group-id="7302773086-9">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7302773086-9">}</span><span class="p">,</span><span class="p" data-group-id="7302773086-10">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7302773086-10">}</span><span class="p">,</span><span class="p" data-group-id="7302773086-11">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7302773086-11">}</span><span class="p" data-group-id="7302773086-5">]</span></code></pre><h2 id="quick-sort" class="section-heading">
│ │ │ │ +restrict the result to integers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="4288960710-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4288960710-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4288960710-2">]</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="4288960710-3">(</span><span class="n">X</span><span class="p" data-group-id="4288960710-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4288960710-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4288960710-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4288960710-4">]</span></code></pre><p>Generators can be combined. For example, the Cartesian product of two lists can
│ │ │ │ +be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="8614008704-1">[</span><span class="p" data-group-id="8614008704-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8614008704-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="8614008704-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8614008704-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="8614008704-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8614008704-4">]</span><span class="p" data-group-id="8614008704-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8614008704-5">[</span><span class="p" data-group-id="8614008704-6">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="8614008704-6">}</span><span class="p">,</span><span class="p" data-group-id="8614008704-7">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8614008704-7">}</span><span class="p">,</span><span class="p" data-group-id="8614008704-8">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="8614008704-8">}</span><span class="p">,</span><span class="p" data-group-id="8614008704-9">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8614008704-9">}</span><span class="p">,</span><span class="p" data-group-id="8614008704-10">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="8614008704-10">}</span><span class="p">,</span><span class="p" data-group-id="8614008704-11">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8614008704-11">}</span><span class="p" data-group-id="8614008704-5">]</span></code></pre><h2 id="quick-sort" class="section-heading">
│ │ │ │    <a href="#quick-sort" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Quick Sort</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The well-known quick sort routine can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sort</span><span class="p" data-group-id="7330452084-1">(</span><span class="p" data-group-id="7330452084-2">[</span><span class="p" data-group-id="7330452084-2">]</span><span class="p" data-group-id="7330452084-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7330452084-3">[</span><span class="p" data-group-id="7330452084-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">sort</span><span class="p" data-group-id="7330452084-4">(</span><span class="p" data-group-id="7330452084-5">[</span><span class="p">_</span><span class="p" data-group-id="7330452084-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7330452084-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">L</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">sort</span><span class="p" data-group-id="7330452084-6">(</span><span class="p" data-group-id="7330452084-7">[</span><span class="n">Pivot</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7330452084-7">]</span><span class="p" data-group-id="7330452084-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">sort</span><span class="p" data-group-id="7330452084-8">(</span><span class="p" data-group-id="7330452084-9">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="7330452084-9">]</span><span class="p" data-group-id="7330452084-8">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7330452084-10">[</span><span class="n">Pivot</span><span class="p" data-group-id="7330452084-10">]</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ │ -    </span><span class="nf">sort</span><span class="p" data-group-id="7330452084-11">(</span><span class="p" data-group-id="7330452084-12">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="7330452084-12">]</span><span class="p" data-group-id="7330452084-11">)</span><span class="p">.</span></code></pre><p>The expression <code class="inline">[X || X &lt;- T, X &lt; Pivot]</code> is the list of all elements in <code class="inline">T</code>
│ │ │ │ +<p>The well-known quick sort routine can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sort</span><span class="p" data-group-id="2416784516-1">(</span><span class="p" data-group-id="2416784516-2">[</span><span class="p" data-group-id="2416784516-2">]</span><span class="p" data-group-id="2416784516-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2416784516-3">[</span><span class="p" data-group-id="2416784516-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">sort</span><span class="p" data-group-id="2416784516-4">(</span><span class="p" data-group-id="2416784516-5">[</span><span class="p">_</span><span class="p" data-group-id="2416784516-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2416784516-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">L</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">sort</span><span class="p" data-group-id="2416784516-6">(</span><span class="p" data-group-id="2416784516-7">[</span><span class="n">Pivot</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2416784516-7">]</span><span class="p" data-group-id="2416784516-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">sort</span><span class="p" data-group-id="2416784516-8">(</span><span class="p" data-group-id="2416784516-9">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="2416784516-9">]</span><span class="p" data-group-id="2416784516-8">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2416784516-10">[</span><span class="n">Pivot</span><span class="p" data-group-id="2416784516-10">]</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ │ +    </span><span class="nf">sort</span><span class="p" data-group-id="2416784516-11">(</span><span class="p" data-group-id="2416784516-12">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="2416784516-12">]</span><span class="p" data-group-id="2416784516-11">)</span><span class="p">.</span></code></pre><p>The expression <code class="inline">[X || X &lt;- T, X &lt; Pivot]</code> is the list of all elements in <code class="inline">T</code>
│ │ │ │  that are less than <code class="inline">Pivot</code>.</p><p><code class="inline">[X || X &lt;- T, X &gt;= Pivot]</code> is the list of all elements in <code class="inline">T</code> that are greater
│ │ │ │  than or equal to <code class="inline">Pivot</code>.</p><p>With the algorithm above, a list is sorted as follows:</p><ul><li>A list with zero or one element is trivially sorted.</li><li>For lists with more than one element:<ol><li>The first element in the list is isolated as the pivot element.</li><li>The remaining list is partitioned into two sublists, such that:</li></ol><ul><li>The first sublist contains all elements that are smaller than the pivot
│ │ │ │  element.</li><li>The second sublist contains all elements that are greater than or equal to
│ │ │ │  the pivot element.</li></ul><ol><li>The sublists are recursively sorted by the same algorithm and the results
│ │ │ │  are combined, resulting in a list consisting of:</li></ol><ul><li>All elements from the first sublist, that is all elements smaller than the
│ │ │ │  pivot element, in sorted order.</li><li>The pivot element.</li><li>All elements from the second sublist, that is all elements greater than or
│ │ │ │  equal to the pivot element, in sorted order.</li></ul></li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>While the sorting algorithm as shown above serves as a nice example to
│ │ │ │ @@ -56,90 +56,90 @@
│ │ │ │  <a href="../../../lib/stdlib/doc/html/lists.html"><code class="inline">lists</code></a> module contains sorting functions that are implemented in a more
│ │ │ │  efficient way.</p></section><h2 id="permutations" class="section-heading">
│ │ │ │    <a href="#permutations" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Permutations</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The following example generates all permutations of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">perms</span><span class="p" data-group-id="3637779197-1">(</span><span class="p" data-group-id="3637779197-2">[</span><span class="p" data-group-id="3637779197-2">]</span><span class="p" data-group-id="3637779197-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3637779197-3">[</span><span class="p" data-group-id="3637779197-4">[</span><span class="p" data-group-id="3637779197-4">]</span><span class="p" data-group-id="3637779197-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">perms</span><span class="p" data-group-id="3637779197-5">(</span><span class="n">L</span><span class="p" data-group-id="3637779197-5">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3637779197-6">[</span><span class="p" data-group-id="3637779197-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3637779197-7">]</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nf">perms</span><span class="p" data-group-id="3637779197-8">(</span><span class="n">L</span><span class="o">--</span><span class="p" data-group-id="3637779197-9">[</span><span class="n">H</span><span class="p" data-group-id="3637779197-9">]</span><span class="p" data-group-id="3637779197-8">)</span><span class="p" data-group-id="3637779197-6">]</span><span class="p">.</span></code></pre><p>This takes <code class="inline">H</code> from <code class="inline">L</code> in all possible ways. The result is the set of all lists
│ │ │ │ +<p>The following example generates all permutations of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">perms</span><span class="p" data-group-id="2504446103-1">(</span><span class="p" data-group-id="2504446103-2">[</span><span class="p" data-group-id="2504446103-2">]</span><span class="p" data-group-id="2504446103-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2504446103-3">[</span><span class="p" data-group-id="2504446103-4">[</span><span class="p" data-group-id="2504446103-4">]</span><span class="p" data-group-id="2504446103-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">perms</span><span class="p" data-group-id="2504446103-5">(</span><span class="n">L</span><span class="p" data-group-id="2504446103-5">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2504446103-6">[</span><span class="p" data-group-id="2504446103-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2504446103-7">]</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nf">perms</span><span class="p" data-group-id="2504446103-8">(</span><span class="n">L</span><span class="o">--</span><span class="p" data-group-id="2504446103-9">[</span><span class="n">H</span><span class="p" data-group-id="2504446103-9">]</span><span class="p" data-group-id="2504446103-8">)</span><span class="p" data-group-id="2504446103-6">]</span><span class="p">.</span></code></pre><p>This takes <code class="inline">H</code> from <code class="inline">L</code> in all possible ways. The result is the set of all lists
│ │ │ │  <code class="inline">[H|T]</code>, where <code class="inline">T</code> is the set of all possible permutations of <code class="inline">L</code>, with <code class="inline">H</code>
│ │ │ │ -removed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">perms</span><span class="p" data-group-id="3711847266-1">(</span><span class="p" data-group-id="3711847266-2">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="3711847266-2">]</span><span class="p" data-group-id="3711847266-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3711847266-3">[</span><span class="p" data-group-id="3711847266-4">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="3711847266-4">]</span><span class="p">,</span><span class="p" data-group-id="3711847266-5">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="3711847266-5">]</span><span class="p">,</span><span class="p" data-group-id="3711847266-6">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="3711847266-6">]</span><span class="p">,</span><span class="p" data-group-id="3711847266-7">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3711847266-7">]</span><span class="p">,</span><span class="p" data-group-id="3711847266-8">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="3711847266-8">]</span><span class="p">,</span><span class="p" data-group-id="3711847266-9">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3711847266-9">]</span><span class="p" data-group-id="3711847266-3">]</span></code></pre><h2 id="pythagorean-triplets" class="section-heading">
│ │ │ │ +removed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">perms</span><span class="p" data-group-id="8558927188-1">(</span><span class="p" data-group-id="8558927188-2">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="8558927188-2">]</span><span class="p" data-group-id="8558927188-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8558927188-3">[</span><span class="p" data-group-id="8558927188-4">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="8558927188-4">]</span><span class="p">,</span><span class="p" data-group-id="8558927188-5">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="8558927188-5">]</span><span class="p">,</span><span class="p" data-group-id="8558927188-6">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="8558927188-6">]</span><span class="p">,</span><span class="p" data-group-id="8558927188-7">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8558927188-7">]</span><span class="p">,</span><span class="p" data-group-id="8558927188-8">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="8558927188-8">]</span><span class="p">,</span><span class="p" data-group-id="8558927188-9">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8558927188-9">]</span><span class="p" data-group-id="8558927188-3">]</span></code></pre><h2 id="pythagorean-triplets" class="section-heading">
│ │ │ │    <a href="#pythagorean-triplets" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Pythagorean Triplets</span>
│ │ │ │  </h2>
│ │ │ │  <p>Pythagorean triplets are sets of integers <code class="inline">{A,B,C}</code> such that
│ │ │ │  <code class="inline">A**2 + B**2 = C**2</code>.</p><p>The function <code class="inline">pyth(N)</code> generates a list of all integers <code class="inline">{A,B,C}</code> such that
│ │ │ │  <code class="inline">A**2 + B**2 = C**2</code> and where the sum of the sides is equal to, or less than,
│ │ │ │ -<code class="inline">N</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth</span><span class="p" data-group-id="8449390342-1">(</span><span class="n">N</span><span class="p" data-group-id="8449390342-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8449390342-2">[</span><span class="w"> </span><span class="p" data-group-id="8449390342-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="8449390342-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ │ -        </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="8449390342-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="8449390342-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="8449390342-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="8449390342-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="8449390342-6">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="8449390342-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +<code class="inline">N</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth</span><span class="p" data-group-id="1439017313-1">(</span><span class="n">N</span><span class="p" data-group-id="1439017313-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1439017313-2">[</span><span class="w"> </span><span class="p" data-group-id="1439017313-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="1439017313-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ │ +        </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1439017313-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="1439017313-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1439017313-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="1439017313-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1439017313-6">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="1439017313-6">)</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">+</span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8449390342-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="5725072087-1">(</span><span class="mi">3</span><span class="p" data-group-id="5725072087-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5725072087-2">[</span><span class="p" data-group-id="5725072087-2">]</span><span class="p">.</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="5725072087-3">(</span><span class="mi">11</span><span class="p" data-group-id="5725072087-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5725072087-4">[</span><span class="p" data-group-id="5725072087-4">]</span><span class="p">.</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="5725072087-5">(</span><span class="mi">12</span><span class="p" data-group-id="5725072087-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5725072087-6">[</span><span class="p" data-group-id="5725072087-7">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5725072087-7">}</span><span class="p">,</span><span class="p" data-group-id="5725072087-8">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5725072087-8">}</span><span class="p" data-group-id="5725072087-6">]</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="5725072087-9">(</span><span class="mi">50</span><span class="p" data-group-id="5725072087-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5725072087-10">[</span><span class="p" data-group-id="5725072087-11">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5725072087-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-12">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5725072087-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-13">{</span><span class="mi">5</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="5725072087-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-14">{</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="5725072087-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-15">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="5725072087-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-16">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="5725072087-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-17">{</span><span class="mi">9</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="5725072087-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-18">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="5725072087-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-19">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="5725072087-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-20">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="5725072087-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-21">{</span><span class="mi">15</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="5725072087-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5725072087-22">{</span><span class="mi">16</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="5725072087-22">}</span><span class="p" data-group-id="5725072087-10">]</span></code></pre><p>The following code reduces the search space and is more efficient:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth1</span><span class="p" data-group-id="4288916038-1">(</span><span class="n">N</span><span class="p" data-group-id="4288916038-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4288916038-2">[</span><span class="p" data-group-id="4288916038-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="4288916038-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ │ -       </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="4288916038-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="4288916038-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -       </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="4288916038-5">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="4288916038-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -       </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="4288916038-6">(</span><span class="n">B</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="4288916038-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1439017313-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="8867884737-1">(</span><span class="mi">3</span><span class="p" data-group-id="8867884737-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8867884737-2">[</span><span class="p" data-group-id="8867884737-2">]</span><span class="p">.</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="8867884737-3">(</span><span class="mi">11</span><span class="p" data-group-id="8867884737-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8867884737-4">[</span><span class="p" data-group-id="8867884737-4">]</span><span class="p">.</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="8867884737-5">(</span><span class="mi">12</span><span class="p" data-group-id="8867884737-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8867884737-6">[</span><span class="p" data-group-id="8867884737-7">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8867884737-7">}</span><span class="p">,</span><span class="p" data-group-id="8867884737-8">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8867884737-8">}</span><span class="p" data-group-id="8867884737-6">]</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="8867884737-9">(</span><span class="mi">50</span><span class="p" data-group-id="8867884737-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8867884737-10">[</span><span class="p" data-group-id="8867884737-11">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8867884737-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-12">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8867884737-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-13">{</span><span class="mi">5</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="8867884737-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-14">{</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="8867884737-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-15">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="8867884737-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-16">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="8867884737-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-17">{</span><span class="mi">9</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="8867884737-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-18">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="8867884737-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-19">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="8867884737-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-20">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="8867884737-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-21">{</span><span class="mi">15</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="8867884737-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8867884737-22">{</span><span class="mi">16</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="8867884737-22">}</span><span class="p" data-group-id="8867884737-10">]</span></code></pre><p>The following code reduces the search space and is more efficient:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth1</span><span class="p" data-group-id="5033483387-1">(</span><span class="n">N</span><span class="p" data-group-id="5033483387-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="5033483387-2">[</span><span class="p" data-group-id="5033483387-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="5033483387-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ │ +       </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5033483387-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="5033483387-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +       </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5033483387-5">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5033483387-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +       </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5033483387-6">(</span><span class="n">B</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="5033483387-6">)</span><span class="p">,</span><span class="w">
│ │ │ │         </span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">+</span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w">
│ │ │ │ -       </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w"> </span><span class="p" data-group-id="4288916038-2">]</span><span class="p">.</span></code></pre><h2 id="simplifications-with-list-comprehensions" class="section-heading">
│ │ │ │ +       </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w"> </span><span class="p" data-group-id="5033483387-2">]</span><span class="p">.</span></code></pre><h2 id="simplifications-with-list-comprehensions" class="section-heading">
│ │ │ │    <a href="#simplifications-with-list-comprehensions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Simplifications With List Comprehensions</span>
│ │ │ │  </h2>
│ │ │ │  <p>As an example, list comprehensions can be used to simplify some of the functions
│ │ │ │ -in <code class="inline">lists.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="1761913994-1">(</span><span class="n">L</span><span class="p" data-group-id="1761913994-1">)</span><span class="w">   </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="1761913994-2">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">L1</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="1761913994-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="1761913994-3">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1761913994-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1761913994-4">[</span><span class="n">Fun</span><span class="p" data-group-id="1761913994-5">(</span><span class="n">X</span><span class="p" data-group-id="1761913994-5">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1761913994-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">filter</span><span class="p" data-group-id="1761913994-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1761913994-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1761913994-7">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="1761913994-8">(</span><span class="n">X</span><span class="p" data-group-id="1761913994-8">)</span><span class="p" data-group-id="1761913994-7">]</span><span class="p">.</span></code></pre><h2 id="variable-bindings-in-list-comprehensions" class="section-heading">
│ │ │ │ +in <code class="inline">lists.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="2435589852-1">(</span><span class="n">L</span><span class="p" data-group-id="2435589852-1">)</span><span class="w">   </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="2435589852-2">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">L1</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="2435589852-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="2435589852-3">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2435589852-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2435589852-4">[</span><span class="n">Fun</span><span class="p" data-group-id="2435589852-5">(</span><span class="n">X</span><span class="p" data-group-id="2435589852-5">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2435589852-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">filter</span><span class="p" data-group-id="2435589852-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2435589852-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2435589852-7">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="2435589852-8">(</span><span class="n">X</span><span class="p" data-group-id="2435589852-8">)</span><span class="p" data-group-id="2435589852-7">]</span><span class="p">.</span></code></pre><h2 id="variable-bindings-in-list-comprehensions" class="section-heading">
│ │ │ │    <a href="#variable-bindings-in-list-comprehensions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Variable Bindings in List Comprehensions</span>
│ │ │ │  </h2>
│ │ │ │  <p>The scope rules for variables that occur in list comprehensions are as follows:</p><ul><li>All variables that occur in a generator pattern are assumed to be &quot;fresh&quot;
│ │ │ │  variables.</li><li>Any variables that are defined before the list comprehension, and that are
│ │ │ │  used in filters, have the values they had before the list comprehension.</li><li>Variables cannot be exported from a list comprehension.</li></ul><p>As an example of these rules, suppose you want to write the function <code class="inline">select</code>,
│ │ │ │  which selects certain elements from a list of tuples. Suppose you write
│ │ │ │  <code class="inline">select(X, L) -&gt; [Y || {X, Y} &lt;- L].</code> with the intention of extracting all
│ │ │ │  tuples from <code class="inline">L</code>, where the first item is <code class="inline">X</code>.</p><p>Compiling this gives the following diagnostic:</p><pre><code class="text">./FileName.erl:Line: Warning: variable 'X' shadowed in generate</code></pre><p>This diagnostic warns that the variable <code class="inline">X</code> in the pattern is not the same as
│ │ │ │ -the variable <code class="inline">X</code> that occurs in the function head.</p><p>Evaluating <code class="inline">select</code> gives the following result:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="2787508196-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="2787508196-2">[</span><span class="p" data-group-id="2787508196-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2787508196-3">}</span><span class="p">,</span><span class="p" data-group-id="2787508196-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2787508196-4">}</span><span class="p">,</span><span class="p" data-group-id="2787508196-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2787508196-5">}</span><span class="p">,</span><span class="p" data-group-id="2787508196-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="2787508196-6">}</span><span class="p" data-group-id="2787508196-2">]</span><span class="p" data-group-id="2787508196-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2787508196-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="2787508196-7">]</span></code></pre><p>This is not the wanted result. To achieve the desired effect, <code class="inline">select</code> must be
│ │ │ │ -written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="3434383953-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="3434383953-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="3434383953-2">[</span><span class="n">Y</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="3434383953-3">{</span><span class="n">X1</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3434383953-3">}</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">X1</span><span class="p" data-group-id="3434383953-2">]</span><span class="p">.</span></code></pre><p>The generator now contains unbound variables and the test has been moved into
│ │ │ │ -the filter.</p><p>This now works as expected:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="4597475171-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="4597475171-2">[</span><span class="p" data-group-id="4597475171-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4597475171-3">}</span><span class="p">,</span><span class="p" data-group-id="4597475171-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4597475171-4">}</span><span class="p">,</span><span class="p" data-group-id="4597475171-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4597475171-5">}</span><span class="p">,</span><span class="p" data-group-id="4597475171-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4597475171-6">}</span><span class="p" data-group-id="4597475171-2">]</span><span class="p" data-group-id="4597475171-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4597475171-7">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4597475171-7">]</span></code></pre><p>Also note that a variable in a generator pattern will shadow a variable with the
│ │ │ │ -same name bound in a previous generator pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="4833769492-1">[</span><span class="p" data-group-id="4833769492-2">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p" data-group-id="4833769492-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4833769492-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4833769492-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="o">=</span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4833769492-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4833769492-4">]</span><span class="p" data-group-id="4833769492-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4833769492-5">[</span><span class="p" data-group-id="4833769492-6">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4833769492-6">}</span><span class="p">,</span><span class="p" data-group-id="4833769492-7">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4833769492-7">}</span><span class="p">,</span><span class="p" data-group-id="4833769492-8">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4833769492-8">}</span><span class="p">,</span><span class="p" data-group-id="4833769492-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4833769492-9">}</span><span class="p">,</span><span class="p" data-group-id="4833769492-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4833769492-10">}</span><span class="p">,</span><span class="p" data-group-id="4833769492-11">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4833769492-11">}</span><span class="p">,</span><span class="p" data-group-id="4833769492-12">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4833769492-12">}</span><span class="p">,</span><span class="p" data-group-id="4833769492-13">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4833769492-13">}</span><span class="p">,</span><span class="p" data-group-id="4833769492-14">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4833769492-14">}</span><span class="p" data-group-id="4833769492-5">]</span></code></pre><p>A consequence of the rules for importing variables into a list comprehensions is
│ │ │ │ +the variable <code class="inline">X</code> that occurs in the function head.</p><p>Evaluating <code class="inline">select</code> gives the following result:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="1300601393-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="1300601393-2">[</span><span class="p" data-group-id="1300601393-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1300601393-3">}</span><span class="p">,</span><span class="p" data-group-id="1300601393-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1300601393-4">}</span><span class="p">,</span><span class="p" data-group-id="1300601393-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1300601393-5">}</span><span class="p">,</span><span class="p" data-group-id="1300601393-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="1300601393-6">}</span><span class="p" data-group-id="1300601393-2">]</span><span class="p" data-group-id="1300601393-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1300601393-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="1300601393-7">]</span></code></pre><p>This is not the wanted result. To achieve the desired effect, <code class="inline">select</code> must be
│ │ │ │ +written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="7159747153-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7159747153-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="7159747153-2">[</span><span class="n">Y</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="7159747153-3">{</span><span class="n">X1</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7159747153-3">}</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">X1</span><span class="p" data-group-id="7159747153-2">]</span><span class="p">.</span></code></pre><p>The generator now contains unbound variables and the test has been moved into
│ │ │ │ +the filter.</p><p>This now works as expected:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="3722593598-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="3722593598-2">[</span><span class="p" data-group-id="3722593598-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3722593598-3">}</span><span class="p">,</span><span class="p" data-group-id="3722593598-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3722593598-4">}</span><span class="p">,</span><span class="p" data-group-id="3722593598-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3722593598-5">}</span><span class="p">,</span><span class="p" data-group-id="3722593598-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3722593598-6">}</span><span class="p" data-group-id="3722593598-2">]</span><span class="p" data-group-id="3722593598-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3722593598-7">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3722593598-7">]</span></code></pre><p>Also note that a variable in a generator pattern will shadow a variable with the
│ │ │ │ +same name bound in a previous generator pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="6250110159-1">[</span><span class="p" data-group-id="6250110159-2">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p" data-group-id="6250110159-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="6250110159-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6250110159-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="o">=</span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="6250110159-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6250110159-4">]</span><span class="p" data-group-id="6250110159-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6250110159-5">[</span><span class="p" data-group-id="6250110159-6">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="6250110159-6">}</span><span class="p">,</span><span class="p" data-group-id="6250110159-7">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6250110159-7">}</span><span class="p">,</span><span class="p" data-group-id="6250110159-8">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6250110159-8">}</span><span class="p">,</span><span class="p" data-group-id="6250110159-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="6250110159-9">}</span><span class="p">,</span><span class="p" data-group-id="6250110159-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6250110159-10">}</span><span class="p">,</span><span class="p" data-group-id="6250110159-11">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6250110159-11">}</span><span class="p">,</span><span class="p" data-group-id="6250110159-12">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="6250110159-12">}</span><span class="p">,</span><span class="p" data-group-id="6250110159-13">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6250110159-13">}</span><span class="p">,</span><span class="p" data-group-id="6250110159-14">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6250110159-14">}</span><span class="p" data-group-id="6250110159-5">]</span></code></pre><p>A consequence of the rules for importing variables into a list comprehensions is
│ │ │ │  that certain pattern matching operations must be moved into the filters and
│ │ │ │ -cannot be written directly in the generators.</p><p>To illustrate this, do <em>not</em> write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="9866961429-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9866961429-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +cannot be written directly in the generators.</p><p>To illustrate this, do <em>not</em> write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="7835089069-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7835089069-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9866961429-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9866961429-2">]</span><span class="w">
│ │ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Instead, write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="1056079264-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1056079264-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7835089069-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7835089069-2">]</span><span class="w">
│ │ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Instead, write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="2182713174-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2182713174-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1056079264-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y1</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1056079264-2">]</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2182713174-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y1</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2182713174-2">]</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/install-win32.xhtml
│ │ │ │ @@ -200,15 +200,15 @@
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">cd erts/emulator
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make debug
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">cd ../etc
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make debug
│ │ │ │  </span></code></pre><p>and sometimes</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make local_setup
│ │ │ │  </span></code></pre><p>So now when you run <code class="inline">$ERL_TOP/erl.exe</code>, you should have a debug compiled
│ │ │ │ -emulator, which you will see if you do a:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="1074086991-1">(</span><span class="ss">system_version</span><span class="p" data-group-id="1074086991-1">)</span><span class="p">.</span></code></pre><p>in the erlang shell. If the returned string contains <code class="inline">[debug]</code>, you
│ │ │ │ +emulator, which you will see if you do a:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="4887787284-1">(</span><span class="ss">system_version</span><span class="p" data-group-id="4887787284-1">)</span><span class="p">.</span></code></pre><p>in the erlang shell. If the returned string contains <code class="inline">[debug]</code>, you
│ │ │ │  got a debug compiled emulator.</p><p>To hack the erlang libraries, you simply do a <code class="inline">make opt</code> in the
│ │ │ │  specific &quot;applications&quot; directory, like:</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make opt
│ │ │ │  </span></code></pre><p>or even in the source directory...</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib/src
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make opt
│ │ │ │  </span></code></pre><p>Note that you're expected to have a fresh Erlang in your path when
│ │ │ │  doing this, preferably the plain 27 you have built in the previous
│ │ │ │ @@ -223,19 +223,19 @@
│ │ │ │  </span><span class="">:$ERL_TOP/erts/etc/win32/wsl_tools:$ERL_TOP/bootstrap/bin:$PATH
│ │ │ │  </span></code></pre><p>That should make it possible to rebuild any library without hassle...</p><p>If you want to copy a library (an application) newly built, to a
│ │ │ │  release area, you do like with the emulator:</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make TESTROOT=/tmp/erlang_release release
│ │ │ │  </span></code></pre><p>Remember that:</p><ul><li><p>  Windows specific C-code goes in the <code class="inline">$ERL_TOP/erts/emulator/sys/win32</code>,
│ │ │ │  <code class="inline">$ERL_TOP/erts/emulator/drivers/win32</code> or <code class="inline">$ERL_TOP/erts/etc/win32</code>.</p></li><li><p>  Windows specific erlang code should be used conditionally and the
│ │ │ │  host OS tested in <em>runtime</em>, the exactly same beam files should be
│ │ │ │ -distributed for every platform! So write code like:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">os</span><span class="p">:</span><span class="nf">type</span><span class="p" data-group-id="3287545764-1">(</span><span class="p" data-group-id="3287545764-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3287545764-2">{</span><span class="ss">win32</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3287545764-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nf">do_windows_specific</span><span class="p" data-group-id="3287545764-3">(</span><span class="p" data-group-id="3287545764-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +distributed for every platform! So write code like:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">os</span><span class="p">:</span><span class="nf">type</span><span class="p" data-group-id="6624970032-1">(</span><span class="p" data-group-id="6624970032-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6624970032-2">{</span><span class="ss">win32</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6624970032-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nf">do_windows_specific</span><span class="p" data-group-id="6624970032-3">(</span><span class="p" data-group-id="6624970032-3">)</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="n">Other</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nf">do_fallback_or_exit</span><span class="p" data-group-id="3287545764-4">(</span><span class="p" data-group-id="3287545764-4">)</span><span class="w">
│ │ │ │ +        </span><span class="nf">do_fallback_or_exit</span><span class="p" data-group-id="6624970032-4">(</span><span class="p" data-group-id="6624970032-4">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre></li></ul><p>That's basically all you need to get going.</p><h2 id="frequently-asked-questions" class="section-heading">
│ │ │ │    <a href="#frequently-asked-questions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Frequently Asked Questions</span>
│ │ │ │  </h2>
│ │ │ │  <ul><li><p>  Q: So, now I can build Erlang using GCC on Windows?</p><p>A: No, unfortunately not. You'll need Microsoft's Visual C++
│ │ │ ├── OEBPS/included_applications.xhtml
│ │ │ │ @@ -66,72 +66,72 @@
│ │ │ │  belonging to the primary application.</p><h2 id="specifying-included-applications" class="section-heading">
│ │ │ │    <a href="#specifying-included-applications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Specifying Included Applications</span>
│ │ │ │  </h2>
│ │ │ │  <p>Which applications to include is defined by the <code class="inline">included_applications</code> key in
│ │ │ │ -the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4764525823-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4764525823-2">[</span><span class="p" data-group-id="4764525823-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="4764525823-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4764525823-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="4764525823-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4764525823-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4764525823-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="4764525823-6">]</span><span class="p" data-group-id="4764525823-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4764525823-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4764525823-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="4764525823-8">]</span><span class="p" data-group-id="4764525823-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4764525823-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4764525823-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="4764525823-10">]</span><span class="p" data-group-id="4764525823-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4764525823-11">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4764525823-12">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="4764525823-12">]</span><span class="p" data-group-id="4764525823-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4764525823-13">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4764525823-14">{</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="4764525823-15">[</span><span class="p" data-group-id="4764525823-15">]</span><span class="p" data-group-id="4764525823-14">}</span><span class="p" data-group-id="4764525823-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4764525823-16">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4764525823-17">[</span><span class="p" data-group-id="4764525823-18">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="4764525823-18">}</span><span class="p" data-group-id="4764525823-17">]</span><span class="p" data-group-id="4764525823-16">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4764525823-2">]</span><span class="p" data-group-id="4764525823-1">}</span><span class="p">.</span></code></pre><h2 id="synchronizing-processes-during-startup" class="section-heading">
│ │ │ │ +the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5169803000-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5169803000-2">[</span><span class="p" data-group-id="5169803000-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="5169803000-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5169803000-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="5169803000-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5169803000-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5169803000-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="5169803000-6">]</span><span class="p" data-group-id="5169803000-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5169803000-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5169803000-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="5169803000-8">]</span><span class="p" data-group-id="5169803000-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5169803000-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5169803000-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="5169803000-10">]</span><span class="p" data-group-id="5169803000-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5169803000-11">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5169803000-12">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="5169803000-12">]</span><span class="p" data-group-id="5169803000-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5169803000-13">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5169803000-14">{</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="5169803000-15">[</span><span class="p" data-group-id="5169803000-15">]</span><span class="p" data-group-id="5169803000-14">}</span><span class="p" data-group-id="5169803000-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5169803000-16">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5169803000-17">[</span><span class="p" data-group-id="5169803000-18">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="5169803000-18">}</span><span class="p" data-group-id="5169803000-17">]</span><span class="p" data-group-id="5169803000-16">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5169803000-2">]</span><span class="p" data-group-id="5169803000-1">}</span><span class="p">.</span></code></pre><h2 id="synchronizing-processes-during-startup" class="section-heading">
│ │ │ │    <a href="#synchronizing-processes-during-startup" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Synchronizing Processes during Startup</span>
│ │ │ │  </h2>
│ │ │ │  <p>The supervisor tree of an included application is started as part of the
│ │ │ │  supervisor tree of the including application. If there is a need for
│ │ │ │  synchronization between processes in the including and included applications,
│ │ │ │  this can be achieved by using <em>start phases</em>.</p><p>Start phases are defined by the <code class="inline">start_phases</code> key in the <code class="inline">.app</code> file as a list
│ │ │ │  of tuples <code class="inline">{Phase,PhaseArgs}</code>, where <code class="inline">Phase</code> is an atom and <code class="inline">PhaseArgs</code> is a
│ │ │ │  term.</p><p>The value of the <code class="inline">mod</code> key of the including application must be set to
│ │ │ │  <code class="inline">{application_starter,[Module,StartArgs]}</code>, where <code class="inline">Module</code> as usual is the
│ │ │ │  application callback module. <code class="inline">StartArgs</code> is a term provided as argument to the
│ │ │ │ -callback function <code class="inline">Module:start/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1053374889-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="1053374889-2">[</span><span class="p" data-group-id="1053374889-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="1053374889-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="1053374889-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="1053374889-6">]</span><span class="p" data-group-id="1053374889-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="1053374889-8">]</span><span class="p" data-group-id="1053374889-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="1053374889-10">]</span><span class="p" data-group-id="1053374889-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-11">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-12">[</span><span class="p" data-group-id="1053374889-13">{</span><span class="ss">init</span><span class="p">,</span><span class="p" data-group-id="1053374889-14">[</span><span class="p" data-group-id="1053374889-14">]</span><span class="p" data-group-id="1053374889-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-15">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="1053374889-16">[</span><span class="p" data-group-id="1053374889-16">]</span><span class="p" data-group-id="1053374889-15">}</span><span class="p" data-group-id="1053374889-12">]</span><span class="p" data-group-id="1053374889-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-17">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-18">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="1053374889-18">]</span><span class="p" data-group-id="1053374889-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-19">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-20">{</span><span class="ss">application_starter</span><span class="p">,</span><span class="p" data-group-id="1053374889-21">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="1053374889-22">[</span><span class="p" data-group-id="1053374889-22">]</span><span class="p" data-group-id="1053374889-21">]</span><span class="p" data-group-id="1053374889-20">}</span><span class="p" data-group-id="1053374889-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-23">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-24">[</span><span class="p" data-group-id="1053374889-25">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="1053374889-25">}</span><span class="p" data-group-id="1053374889-24">]</span><span class="p" data-group-id="1053374889-23">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="1053374889-2">]</span><span class="p" data-group-id="1053374889-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +callback function <code class="inline">Module:start/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0683354397-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0683354397-2">[</span><span class="p" data-group-id="0683354397-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="0683354397-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="0683354397-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="0683354397-6">]</span><span class="p" data-group-id="0683354397-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="0683354397-8">]</span><span class="p" data-group-id="0683354397-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="0683354397-10">]</span><span class="p" data-group-id="0683354397-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-11">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-12">[</span><span class="p" data-group-id="0683354397-13">{</span><span class="ss">init</span><span class="p">,</span><span class="p" data-group-id="0683354397-14">[</span><span class="p" data-group-id="0683354397-14">]</span><span class="p" data-group-id="0683354397-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-15">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="0683354397-16">[</span><span class="p" data-group-id="0683354397-16">]</span><span class="p" data-group-id="0683354397-15">}</span><span class="p" data-group-id="0683354397-12">]</span><span class="p" data-group-id="0683354397-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-17">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-18">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="0683354397-18">]</span><span class="p" data-group-id="0683354397-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-19">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-20">{</span><span class="ss">application_starter</span><span class="p">,</span><span class="p" data-group-id="0683354397-21">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="0683354397-22">[</span><span class="p" data-group-id="0683354397-22">]</span><span class="p" data-group-id="0683354397-21">]</span><span class="p" data-group-id="0683354397-20">}</span><span class="p" data-group-id="0683354397-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-23">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-24">[</span><span class="p" data-group-id="0683354397-25">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="0683354397-25">}</span><span class="p" data-group-id="0683354397-24">]</span><span class="p" data-group-id="0683354397-23">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0683354397-2">]</span><span class="p" data-group-id="0683354397-1">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p" data-group-id="1053374889-26">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="1053374889-27">[</span><span class="p" data-group-id="1053374889-28">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Included application&quot;</span><span class="p" data-group-id="1053374889-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-29">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="1053374889-29">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-30">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-31">[</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_server</span><span class="p" data-group-id="1053374889-31">]</span><span class="p" data-group-id="1053374889-30">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-32">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-33">[</span><span class="p" data-group-id="1053374889-33">]</span><span class="p" data-group-id="1053374889-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-34">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-35">[</span><span class="p" data-group-id="1053374889-36">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="1053374889-37">[</span><span class="p" data-group-id="1053374889-37">]</span><span class="p" data-group-id="1053374889-36">}</span><span class="p" data-group-id="1053374889-35">]</span><span class="p" data-group-id="1053374889-34">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-38">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-39">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="1053374889-39">]</span><span class="p" data-group-id="1053374889-38">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="1053374889-40">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1053374889-41">{</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="p" data-group-id="1053374889-42">[</span><span class="p" data-group-id="1053374889-42">]</span><span class="p" data-group-id="1053374889-41">}</span><span class="p" data-group-id="1053374889-40">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="1053374889-27">]</span><span class="p" data-group-id="1053374889-26">}</span><span class="p">.</span></code></pre><p>When starting a primary application with included applications, the primary
│ │ │ │ +</span><span class="p" data-group-id="0683354397-26">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0683354397-27">[</span><span class="p" data-group-id="0683354397-28">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Included application&quot;</span><span class="p" data-group-id="0683354397-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-29">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="0683354397-29">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-30">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-31">[</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_server</span><span class="p" data-group-id="0683354397-31">]</span><span class="p" data-group-id="0683354397-30">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-32">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-33">[</span><span class="p" data-group-id="0683354397-33">]</span><span class="p" data-group-id="0683354397-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-34">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-35">[</span><span class="p" data-group-id="0683354397-36">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="0683354397-37">[</span><span class="p" data-group-id="0683354397-37">]</span><span class="p" data-group-id="0683354397-36">}</span><span class="p" data-group-id="0683354397-35">]</span><span class="p" data-group-id="0683354397-34">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-38">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-39">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="0683354397-39">]</span><span class="p" data-group-id="0683354397-38">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0683354397-40">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0683354397-41">{</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="p" data-group-id="0683354397-42">[</span><span class="p" data-group-id="0683354397-42">]</span><span class="p" data-group-id="0683354397-41">}</span><span class="p" data-group-id="0683354397-40">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0683354397-27">]</span><span class="p" data-group-id="0683354397-26">}</span><span class="p">.</span></code></pre><p>When starting a primary application with included applications, the primary
│ │ │ │  application is started the normal way, that is:</p><ul><li>The application controller creates an application master for the application</li><li>The application master calls <code class="inline">Module:start(normal, StartArgs)</code> to start the
│ │ │ │  top supervisor.</li></ul><p>Then, for the primary application and each included application in top-down,
│ │ │ │  left-to-right order, the application master calls
│ │ │ │  <code class="inline">Module:start_phase(Phase, Type, PhaseArgs)</code> for each phase defined for the
│ │ │ │  primary application, in that order. If a phase is not defined for an included
│ │ │ │  application, the function is not called for this phase and application.</p><p>The following requirements apply to the <code class="inline">.app</code> file for an included application:</p><ul><li>The <code class="inline">{mod, {Module,StartArgs}}</code> option must be included. This option is used
│ │ │ │  to find the callback module <code class="inline">Module</code> of the application. <code class="inline">StartArgs</code> is
│ │ │ │  ignored, as <code class="inline">Module:start/2</code> is called only for the primary application.</li><li>If the included application itself contains included applications, instead the
│ │ │ │  <code class="inline">{mod, {application_starter, [Module,StartArgs]}}</code> option must be included.</li><li>The <code class="inline">{start_phases, [{Phase,PhaseArgs}]}</code> option must be included, and the set
│ │ │ │  of specified phases must be a subset of the set of phases specified for the
│ │ │ │  primary application.</li></ul><p>When starting <code class="inline">prim_app</code> as defined above, the application controller calls the
│ │ │ │  following callback functions before <code class="inline">application:start(prim_app)</code> returns a
│ │ │ │ -value:</p><pre><code class="makeup erlang" translate="no"><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3018295042-1">(</span><span class="ss">prim_app</span><span class="p" data-group-id="3018295042-1">)</span><span class="w">
│ │ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3018295042-2">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3018295042-3">[</span><span class="p" data-group-id="3018295042-3">]</span><span class="p" data-group-id="3018295042-2">)</span><span class="w">
│ │ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="3018295042-4">(</span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3018295042-5">[</span><span class="p" data-group-id="3018295042-5">]</span><span class="p" data-group-id="3018295042-4">)</span><span class="w">
│ │ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="3018295042-6">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3018295042-7">[</span><span class="p" data-group-id="3018295042-7">]</span><span class="p" data-group-id="3018295042-6">)</span><span class="w">
│ │ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">incl_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="3018295042-8">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3018295042-9">[</span><span class="p" data-group-id="3018295042-9">]</span><span class="p" data-group-id="3018295042-8">)</span><span class="w">
│ │ │ │ +value:</p><pre><code class="makeup erlang" translate="no"><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8755051440-1">(</span><span class="ss">prim_app</span><span class="p" data-group-id="8755051440-1">)</span><span class="w">
│ │ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8755051440-2">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8755051440-3">[</span><span class="p" data-group-id="8755051440-3">]</span><span class="p" data-group-id="8755051440-2">)</span><span class="w">
│ │ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="8755051440-4">(</span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8755051440-5">[</span><span class="p" data-group-id="8755051440-5">]</span><span class="p" data-group-id="8755051440-4">)</span><span class="w">
│ │ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="8755051440-6">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8755051440-7">[</span><span class="p" data-group-id="8755051440-7">]</span><span class="p" data-group-id="8755051440-6">)</span><span class="w">
│ │ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">incl_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="8755051440-8">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8755051440-9">[</span><span class="p" data-group-id="8755051440-9">]</span><span class="p" data-group-id="8755051440-8">)</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/gen_server_concepts.xhtml
│ │ │ │ @@ -62,63 +62,63 @@
│ │ │ │    <a href="#example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example</span>
│ │ │ │  </h2>
│ │ │ │  <p>An example of a simple server written in plain Erlang is provided in
│ │ │ │  <a href="design_principles.xhtml#ch1">Overview</a>. The server can be reimplemented using
│ │ │ │ -<code class="inline">gen_server</code>, resulting in this callback module:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1035052718-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="1035052718-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1035052718-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="1035052718-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">gen_server</code>, resulting in this callback module:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6336009828-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="6336009828-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="6336009828-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="6336009828-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1035052718-3">(</span><span class="p" data-group-id="1035052718-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1035052718-4">]</span><span class="p" data-group-id="1035052718-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1035052718-5">(</span><span class="p" data-group-id="1035052718-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1035052718-6">]</span><span class="p" data-group-id="1035052718-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1035052718-7">(</span><span class="p" data-group-id="1035052718-8">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1035052718-8">]</span><span class="p" data-group-id="1035052718-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6336009828-3">(</span><span class="p" data-group-id="6336009828-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6336009828-4">]</span><span class="p" data-group-id="6336009828-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6336009828-5">(</span><span class="p" data-group-id="6336009828-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6336009828-6">]</span><span class="p" data-group-id="6336009828-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6336009828-7">(</span><span class="p" data-group-id="6336009828-8">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6336009828-8">]</span><span class="p" data-group-id="6336009828-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="1035052718-9">(</span><span class="p" data-group-id="1035052718-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1035052718-10">(</span><span class="p" data-group-id="1035052718-11">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="1035052718-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1035052718-12">[</span><span class="p" data-group-id="1035052718-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1035052718-13">[</span><span class="p" data-group-id="1035052718-13">]</span><span class="p" data-group-id="1035052718-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="6336009828-9">(</span><span class="p" data-group-id="6336009828-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6336009828-10">(</span><span class="p" data-group-id="6336009828-11">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6336009828-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6336009828-12">[</span><span class="p" data-group-id="6336009828-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6336009828-13">[</span><span class="p" data-group-id="6336009828-13">]</span><span class="p" data-group-id="6336009828-10">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="1035052718-14">(</span><span class="p" data-group-id="1035052718-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="1035052718-15">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="1035052718-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="6336009828-14">(</span><span class="p" data-group-id="6336009828-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="6336009828-15">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="6336009828-15">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="1035052718-16">(</span><span class="n">Ch</span><span class="p" data-group-id="1035052718-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1035052718-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1035052718-18">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="1035052718-18">}</span><span class="p" data-group-id="1035052718-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="6336009828-16">(</span><span class="n">Ch</span><span class="p" data-group-id="6336009828-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6336009828-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6336009828-18">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6336009828-18">}</span><span class="p" data-group-id="6336009828-17">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1035052718-19">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="1035052718-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1035052718-20">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="1035052718-21">(</span><span class="p" data-group-id="1035052718-21">)</span><span class="p" data-group-id="1035052718-20">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="6336009828-19">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6336009828-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6336009828-20">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="6336009828-21">(</span><span class="p" data-group-id="6336009828-21">)</span><span class="p" data-group-id="6336009828-20">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="1035052718-22">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1035052718-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1035052718-23">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1035052718-23">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="1035052718-24">(</span><span class="n">Chs</span><span class="p" data-group-id="1035052718-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1035052718-25">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1035052718-25">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="6336009828-22">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6336009828-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6336009828-23">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6336009828-23">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="6336009828-24">(</span><span class="n">Chs</span><span class="p" data-group-id="6336009828-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6336009828-25">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6336009828-25">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="1035052718-26">(</span><span class="p" data-group-id="1035052718-27">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="1035052718-27">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1035052718-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="1035052718-28">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1035052718-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1035052718-29">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1035052718-29">}</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-a-gen_server" class="section-heading">
│ │ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="6336009828-26">(</span><span class="p" data-group-id="6336009828-27">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6336009828-27">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6336009828-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="6336009828-28">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6336009828-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6336009828-29">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6336009828-29">}</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-a-gen_server" class="section-heading">
│ │ │ │    <a href="#starting-a-gen_server" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting a Gen_Server</span>
│ │ │ │  </h2>
│ │ │ │  <p>In the example in the previous section, <code class="inline">gen_server</code> is started by calling
│ │ │ │ -<code class="inline">ch3:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="9570140196-1">(</span><span class="p" data-group-id="9570140196-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="9570140196-2">(</span><span class="p" data-group-id="9570140196-3">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="9570140196-3">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9570140196-4">[</span><span class="p" data-group-id="9570140196-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9570140196-5">[</span><span class="p" data-group-id="9570140196-5">]</span><span class="p" data-group-id="9570140196-2">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9570140196-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="9570140196-6">}</span></code></pre><p><code class="inline">start_link/0</code> calls function <a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a>.  This function
│ │ │ │ +<code class="inline">ch3:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="0621510657-1">(</span><span class="p" data-group-id="0621510657-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0621510657-2">(</span><span class="p" data-group-id="0621510657-3">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0621510657-3">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0621510657-4">[</span><span class="p" data-group-id="0621510657-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0621510657-5">[</span><span class="p" data-group-id="0621510657-5">]</span><span class="p" data-group-id="0621510657-2">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0621510657-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="0621510657-6">}</span></code></pre><p><code class="inline">start_link/0</code> calls function <a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a>.  This function
│ │ │ │  spawns and links to a new process, a <code class="inline">gen_server</code>.</p><ul><li><p>The first argument, <code class="inline">{local, ch3}</code>, specifies the name.
│ │ │ │  The gen_server is then locally registered as <code class="inline">ch3</code>.</p><p>If the name is omitted, the <code class="inline">gen_server</code> is not registered. Instead its pid
│ │ │ │  must be used. The name can also be given as <code class="inline">{global, Name}</code>, in which case
│ │ │ │  the <code class="inline">gen_server</code> is registered using <a href="../../../lib/kernel/doc/html/global.html#register_name/2"><code class="inline">global:register_name/2</code></a>.</p></li><li><p>The second argument, <code class="inline">ch3</code>, is the name of the callback module, which is
│ │ │ │  the module where the callback functions are located.</p><p>The interface functions (<code class="inline">start_link/0</code>, <code class="inline">alloc/0</code>, and <code class="inline">free/1</code>) are located
│ │ │ │  in the same module as the callback functions (<code class="inline">init/1</code>, <code class="inline">handle_call/3</code>, and
│ │ │ │  <code class="inline">handle_cast/2</code>). It is usually good programming practice to have the code
│ │ │ │  corresponding to one process contained in a single module.</p></li><li><p>The third argument, <code class="inline">[]</code>, is a term that is passed as is to the callback
│ │ │ │  function <code class="inline">init</code>. Here, <code class="inline">init</code> does not need any indata and ignores the
│ │ │ │  argument.</p></li><li><p>The fourth argument, <code class="inline">[]</code>, is a list of options. See <a href="../../../lib/stdlib/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │ │  for the available options.</p></li></ul><p>If name registration succeeds, the new <code class="inline">gen_server</code> process calls the callback
│ │ │ │  function <code class="inline">ch3:init([])</code>. <code class="inline">init</code> is expected to return <code class="inline">{ok, State}</code>, where
│ │ │ │  <code class="inline">State</code> is the internal state of the <code class="inline">gen_server</code>. In this case, the state is
│ │ │ │ -the available channels.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5931254382-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5931254382-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5931254382-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="5931254382-3">(</span><span class="p" data-group-id="5931254382-3">)</span><span class="p" data-group-id="5931254382-2">}</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> is synchronous. It does not return until the
│ │ │ │ +the available channels.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6601991513-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6601991513-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6601991513-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="6601991513-3">(</span><span class="p" data-group-id="6601991513-3">)</span><span class="p" data-group-id="6601991513-2">}</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> is synchronous. It does not return until the
│ │ │ │  <code class="inline">gen_server</code> has been initialized and is ready to receive requests.</p><p><a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> must be used if the <code class="inline">gen_server</code> is part of
│ │ │ │  a supervision tree, meaning that it was started by a supervisor. There
│ │ │ │  is another function, <a href="../../../lib/stdlib/doc/html/gen_server.html#start/4"><code class="inline">gen_server:start/4</code></a>, to start a standalone
│ │ │ │  <code class="inline">gen_server</code> that is not part of a supervision tree.</p><h2 id="synchronous-requests-call" class="section-heading">
│ │ │ │    <a href="#synchronous-requests-call" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -126,32 +126,32 @@
│ │ │ │  </h2>
│ │ │ │  <p>The synchronous request <code class="inline">alloc()</code> is implemented using <a href="../../../lib/stdlib/doc/html/gen_server.html#call/2"><code class="inline">gen_server:call/2</code></a>:</p><pre><code class="text">alloc() -&gt;
│ │ │ │      gen_server:call(ch3, alloc).</code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code> and must agree with the name
│ │ │ │  used to start it. <code class="inline">alloc</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │ │  When the request is received, the <code class="inline">gen_server</code> calls
│ │ │ │  <code class="inline">handle_call(Request, From, State)</code>, which is expected to return
│ │ │ │  a tuple <code class="inline">{reply,Reply,State1}</code>. <code class="inline">Reply</code> is the reply that is to be sent back
│ │ │ │ -to the client, and <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="1915863517-1">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1915863517-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1915863517-2">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1915863517-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="1915863517-3">(</span><span class="n">Chs</span><span class="p" data-group-id="1915863517-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1915863517-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1915863517-4">}</span><span class="p">.</span></code></pre><p>In this case, the reply is the allocated channel <code class="inline">Ch</code> and the new state is the
│ │ │ │ +to the client, and <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="2519606803-1">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2519606803-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2519606803-2">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="2519606803-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="2519606803-3">(</span><span class="n">Chs</span><span class="p" data-group-id="2519606803-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2519606803-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="2519606803-4">}</span><span class="p">.</span></code></pre><p>In this case, the reply is the allocated channel <code class="inline">Ch</code> and the new state is the
│ │ │ │  set of remaining available channels <code class="inline">Chs2</code>.</p><p>Thus, the call <code class="inline">ch3:alloc()</code> returns the allocated channel <code class="inline">Ch</code> and the
│ │ │ │  <code class="inline">gen_server</code> then waits for new requests, now with an updated list of
│ │ │ │  available channels.</p><h2 id="asynchronous-requests-cast" class="section-heading">
│ │ │ │    <a href="#asynchronous-requests-cast" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Asynchronous Requests - Cast</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The asynchronous request <code class="inline">free(Ch)</code> is implemented using <a href="../../../lib/stdlib/doc/html/gen_server.html#cast/2"><code class="inline">gen_server:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">free</span><span class="p" data-group-id="8432984606-1">(</span><span class="n">Ch</span><span class="p" data-group-id="8432984606-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8432984606-2">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8432984606-3">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8432984606-3">}</span><span class="p" data-group-id="8432984606-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code>. <code class="inline">{free, Ch}</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │ │ +<p>The asynchronous request <code class="inline">free(Ch)</code> is implemented using <a href="../../../lib/stdlib/doc/html/gen_server.html#cast/2"><code class="inline">gen_server:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">free</span><span class="p" data-group-id="5515853003-1">(</span><span class="n">Ch</span><span class="p" data-group-id="5515853003-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="5515853003-2">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5515853003-3">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5515853003-3">}</span><span class="p" data-group-id="5515853003-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code>. <code class="inline">{free, Ch}</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │ │  <code class="inline">cast</code>, and thus <code class="inline">free</code>, then returns <code class="inline">ok</code>.</p><p>When the request is received, the <code class="inline">gen_server</code> calls
│ │ │ │  <code class="inline">handle_cast(Request, State)</code>, which is expected to return a tuple
│ │ │ │ -<code class="inline">{noreply,State1}</code>. <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_cast</span><span class="p" data-group-id="1859944913-1">(</span><span class="p" data-group-id="1859944913-2">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="1859944913-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1859944913-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="1859944913-3">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1859944913-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1859944913-4">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1859944913-4">}</span><span class="p">.</span></code></pre><p>In this case, the new state is the updated list of available channels <code class="inline">Chs2</code>.
│ │ │ │ +<code class="inline">{noreply,State1}</code>. <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_cast</span><span class="p" data-group-id="7727537331-1">(</span><span class="p" data-group-id="7727537331-2">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7727537331-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7727537331-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="7727537331-3">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7727537331-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7727537331-4">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="7727537331-4">}</span><span class="p">.</span></code></pre><p>In this case, the new state is the updated list of available channels <code class="inline">Chs2</code>.
│ │ │ │  The <code class="inline">gen_server</code> is now ready for new requests.</p><h2 id="stopping" class="section-heading">
│ │ │ │    <a href="#stopping" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Stopping</span>
│ │ │ │  </h2>
│ │ │ │  <h3 id="in-a-supervision-tree" class="section-heading">
│ │ │ │ @@ -162,65 +162,65 @@
│ │ │ │  </h3>
│ │ │ │  <p>If the <code class="inline">gen_server</code> is part of a supervision tree, no stop function is needed.
│ │ │ │  The <code class="inline">gen_server</code> is automatically terminated by its supervisor.  Exactly how
│ │ │ │  this is done is defined by a <a href="sup_princ.xhtml#shutdown">shutdown strategy</a>
│ │ │ │  set in the supervisor.</p><p>If it is necessary to clean up before termination, the shutdown strategy
│ │ │ │  must be a time-out value and the <code class="inline">gen_server</code> must be set to trap exit signals
│ │ │ │  in function <code class="inline">init</code>. When ordered to shutdown, the <code class="inline">gen_server</code> then calls
│ │ │ │ -the callback function <code class="inline">terminate(shutdown, State)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1662537951-1">(</span><span class="n">Args</span><span class="p" data-group-id="1662537951-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +the callback function <code class="inline">terminate(shutdown, State)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7032301293-1">(</span><span class="n">Args</span><span class="p" data-group-id="7032301293-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="1662537951-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1662537951-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="7032301293-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7032301293-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1662537951-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1662537951-3">}</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7032301293-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7032301293-3">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="1662537951-4">(</span><span class="ss">shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1662537951-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="7032301293-4">(</span><span class="ss">shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7032301293-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Code for cleaning up here</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="standalone-gen_servers" class="section-heading">
│ │ │ │    <a href="#standalone-gen_servers" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Standalone Gen_Servers</span>
│ │ │ │  </h3>
│ │ │ │  <p>If the <code class="inline">gen_server</code> is not part of a supervision tree, a stop function
│ │ │ │  can be useful, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">export</span><span class="p" data-group-id="7957504241-1">(</span><span class="p" data-group-id="7957504241-2">[</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7957504241-2">]</span><span class="p" data-group-id="7957504241-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">export</span><span class="p" data-group-id="6180138341-1">(</span><span class="p" data-group-id="6180138341-2">[</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6180138341-2">]</span><span class="p" data-group-id="6180138341-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="7957504241-3">(</span><span class="p" data-group-id="7957504241-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="7957504241-4">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p" data-group-id="7957504241-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="6180138341-3">(</span><span class="p" data-group-id="6180138341-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6180138341-4">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p" data-group-id="6180138341-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="7957504241-5">(</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7957504241-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7957504241-6">{</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7957504241-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="7957504241-7">(</span><span class="p" data-group-id="7957504241-8">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7957504241-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7957504241-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="6180138341-5">(</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6180138341-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6180138341-6">{</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6180138341-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="6180138341-7">(</span><span class="p" data-group-id="6180138341-8">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6180138341-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6180138341-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="7957504241-9">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7957504241-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="6180138341-9">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6180138341-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The callback function handling the <code class="inline">stop</code> request returns a tuple
│ │ │ │  <code class="inline">{stop,normal,State1}</code>, where <code class="inline">normal</code> specifies that it is
│ │ │ │  a normal termination and <code class="inline">State1</code> is a new value for the state
│ │ │ │  of the <code class="inline">gen_server</code>.  This causes the <code class="inline">gen_server</code> to call
│ │ │ │  <code class="inline">terminate(normal, State1)</code> and then it terminates gracefully.</p><h2 id="handling-other-messages" class="section-heading">
│ │ │ │    <a href="#handling-other-messages" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Handling Other Messages</span>
│ │ │ │  </h2>
│ │ │ │  <p>If the <code class="inline">gen_server</code> is to be able to receive other messages than requests,
│ │ │ │  the callback function <code class="inline">handle_info(Info, State)</code> must be implemented
│ │ │ │  to handle them.  Examples of other messages are exit messages,
│ │ │ │  if the <code class="inline">gen_server</code> is linked to other processes than the supervisor
│ │ │ │ -and it is trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="5795406263-1">(</span><span class="p" data-group-id="5795406263-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5795406263-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5795406263-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +and it is trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="7176745275-1">(</span><span class="p" data-group-id="7176745275-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="7176745275-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7176745275-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Code to handle exits here.</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5795406263-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="5795406263-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="3670193317-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="3670193317-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7176745275-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="7176745275-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="9408076406-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="9408076406-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Code to convert state (and more) during code change.</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3670193317-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="3670193317-2">}</span><span class="p">.</span></code></pre>
│ │ │ │ +    </span><span class="p" data-group-id="9408076406-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="9408076406-2">}</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/funs.xhtml
│ │ │ │ @@ -22,399 +22,399 @@
│ │ │ │      </h1>
│ │ │ │  <h2 id="map" class="section-heading">
│ │ │ │    <a href="#map" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">map</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The following function, <code class="inline">double</code>, doubles every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="6956420161-1">(</span><span class="p" data-group-id="6956420161-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6956420161-2">]</span><span class="p" data-group-id="6956420161-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6956420161-3">[</span><span class="mi">2</span><span class="o">*</span><span class="n">H</span><span class="p">|</span><span class="nf">double</span><span class="p" data-group-id="6956420161-4">(</span><span class="n">T</span><span class="p" data-group-id="6956420161-4">)</span><span class="p" data-group-id="6956420161-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="6956420161-5">(</span><span class="p" data-group-id="6956420161-6">[</span><span class="p" data-group-id="6956420161-6">]</span><span class="p" data-group-id="6956420161-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6956420161-7">[</span><span class="p" data-group-id="6956420161-7">]</span><span class="p">.</span></code></pre><p>Hence, the argument entered as input is doubled as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">double</span><span class="p" data-group-id="3166873828-1">(</span><span class="p" data-group-id="3166873828-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3166873828-2">]</span><span class="p" data-group-id="3166873828-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3166873828-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p" data-group-id="3166873828-3">]</span></code></pre><p>The following function, <code class="inline">add_one</code>, adds one to every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add_one</span><span class="p" data-group-id="2784562541-1">(</span><span class="p" data-group-id="2784562541-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2784562541-2">]</span><span class="p" data-group-id="2784562541-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2784562541-3">[</span><span class="n">H</span><span class="o">+</span><span class="mi">1</span><span class="p">|</span><span class="nf">add_one</span><span class="p" data-group-id="2784562541-4">(</span><span class="n">T</span><span class="p" data-group-id="2784562541-4">)</span><span class="p" data-group-id="2784562541-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">add_one</span><span class="p" data-group-id="2784562541-5">(</span><span class="p" data-group-id="2784562541-6">[</span><span class="p" data-group-id="2784562541-6">]</span><span class="p" data-group-id="2784562541-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2784562541-7">[</span><span class="p" data-group-id="2784562541-7">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> have a similar structure. This can be used
│ │ │ │ -by writing a function <code class="inline">map</code> that expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="4839713088-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4839713088-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4839713088-2">]</span><span class="p" data-group-id="4839713088-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4839713088-3">[</span><span class="n">F</span><span class="p" data-group-id="4839713088-4">(</span><span class="n">H</span><span class="p" data-group-id="4839713088-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="4839713088-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4839713088-5">)</span><span class="p" data-group-id="4839713088-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="4839713088-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4839713088-7">[</span><span class="p" data-group-id="4839713088-7">]</span><span class="p" data-group-id="4839713088-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4839713088-8">[</span><span class="p" data-group-id="4839713088-8">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> can now be expressed in terms of <code class="inline">map</code> as
│ │ │ │ -follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="7832311344-1">(</span><span class="n">L</span><span class="p" data-group-id="7832311344-1">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="7832311344-2">(</span><span class="nf">fun</span><span class="p" data-group-id="7832311344-3">(</span><span class="n">X</span><span class="p" data-group-id="7832311344-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7832311344-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add_one</span><span class="p" data-group-id="7832311344-4">(</span><span class="n">L</span><span class="p" data-group-id="7832311344-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="7832311344-5">(</span><span class="nf">fun</span><span class="p" data-group-id="7832311344-6">(</span><span class="n">X</span><span class="p" data-group-id="7832311344-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7832311344-5">)</span><span class="p">.</span></code></pre><p><code class="inline">map(F, List)</code> is a function that takes a function <code class="inline">F</code> and a list <code class="inline">L</code> as
│ │ │ │ +<p>The following function, <code class="inline">double</code>, doubles every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="8633988800-1">(</span><span class="p" data-group-id="8633988800-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8633988800-2">]</span><span class="p" data-group-id="8633988800-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8633988800-3">[</span><span class="mi">2</span><span class="o">*</span><span class="n">H</span><span class="p">|</span><span class="nf">double</span><span class="p" data-group-id="8633988800-4">(</span><span class="n">T</span><span class="p" data-group-id="8633988800-4">)</span><span class="p" data-group-id="8633988800-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="8633988800-5">(</span><span class="p" data-group-id="8633988800-6">[</span><span class="p" data-group-id="8633988800-6">]</span><span class="p" data-group-id="8633988800-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8633988800-7">[</span><span class="p" data-group-id="8633988800-7">]</span><span class="p">.</span></code></pre><p>Hence, the argument entered as input is doubled as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">double</span><span class="p" data-group-id="0110817870-1">(</span><span class="p" data-group-id="0110817870-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0110817870-2">]</span><span class="p" data-group-id="0110817870-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0110817870-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p" data-group-id="0110817870-3">]</span></code></pre><p>The following function, <code class="inline">add_one</code>, adds one to every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add_one</span><span class="p" data-group-id="3662012137-1">(</span><span class="p" data-group-id="3662012137-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3662012137-2">]</span><span class="p" data-group-id="3662012137-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3662012137-3">[</span><span class="n">H</span><span class="o">+</span><span class="mi">1</span><span class="p">|</span><span class="nf">add_one</span><span class="p" data-group-id="3662012137-4">(</span><span class="n">T</span><span class="p" data-group-id="3662012137-4">)</span><span class="p" data-group-id="3662012137-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">add_one</span><span class="p" data-group-id="3662012137-5">(</span><span class="p" data-group-id="3662012137-6">[</span><span class="p" data-group-id="3662012137-6">]</span><span class="p" data-group-id="3662012137-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3662012137-7">[</span><span class="p" data-group-id="3662012137-7">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> have a similar structure. This can be used
│ │ │ │ +by writing a function <code class="inline">map</code> that expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="6411468791-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6411468791-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6411468791-2">]</span><span class="p" data-group-id="6411468791-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6411468791-3">[</span><span class="n">F</span><span class="p" data-group-id="6411468791-4">(</span><span class="n">H</span><span class="p" data-group-id="6411468791-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="6411468791-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6411468791-5">)</span><span class="p" data-group-id="6411468791-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="6411468791-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6411468791-7">[</span><span class="p" data-group-id="6411468791-7">]</span><span class="p" data-group-id="6411468791-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6411468791-8">[</span><span class="p" data-group-id="6411468791-8">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> can now be expressed in terms of <code class="inline">map</code> as
│ │ │ │ +follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="9185623508-1">(</span><span class="n">L</span><span class="p" data-group-id="9185623508-1">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="9185623508-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9185623508-3">(</span><span class="n">X</span><span class="p" data-group-id="9185623508-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="9185623508-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add_one</span><span class="p" data-group-id="9185623508-4">(</span><span class="n">L</span><span class="p" data-group-id="9185623508-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="9185623508-5">(</span><span class="nf">fun</span><span class="p" data-group-id="9185623508-6">(</span><span class="n">X</span><span class="p" data-group-id="9185623508-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="9185623508-5">)</span><span class="p">.</span></code></pre><p><code class="inline">map(F, List)</code> is a function that takes a function <code class="inline">F</code> and a list <code class="inline">L</code> as
│ │ │ │  arguments and returns a new list, obtained by applying <code class="inline">F</code> to each of the
│ │ │ │  elements in <code class="inline">L</code>.</p><p>The process of abstracting out the common features of a number of different
│ │ │ │  programs is called <em>procedural abstraction</em>. Procedural abstraction can be used
│ │ │ │  to write several different functions that have a similar structure, but differ
│ │ │ │  in some minor detail. This is done as follows:</p><ol><li><em>Step 1.</em> Write one function that represents the common features of these
│ │ │ │  functions.</li><li><em>Step 2.</em> Parameterize the difference in terms of functions that are passed
│ │ │ │  as arguments to the common function.</li></ol><h2 id="foreach" class="section-heading">
│ │ │ │    <a href="#foreach" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">foreach</span>
│ │ │ │  </h2>
│ │ │ │  <p>This section illustrates procedural abstraction. Initially, the following two
│ │ │ │ -examples are written as conventional functions.</p><p>This function prints all elements of a list onto a stream:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="3754707048-1">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3754707048-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3754707048-2">]</span><span class="p" data-group-id="3754707048-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3754707048-3">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3754707048-4">[</span><span class="n">H</span><span class="p" data-group-id="3754707048-4">]</span><span class="p" data-group-id="3754707048-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_list</span><span class="p" data-group-id="3754707048-5">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3754707048-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">print_list</span><span class="p" data-group-id="3754707048-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3754707048-7">[</span><span class="p" data-group-id="3754707048-7">]</span><span class="p" data-group-id="3754707048-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>This function broadcasts a message to a list of processes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">broadcast</span><span class="p" data-group-id="3882968023-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3882968023-2">[</span><span class="n">Pid</span><span class="p">|</span><span class="n">Pids</span><span class="p" data-group-id="3882968023-2">]</span><span class="p" data-group-id="3882968023-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +examples are written as conventional functions.</p><p>This function prints all elements of a list onto a stream:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="0458743833-1">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0458743833-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0458743833-2">]</span><span class="p" data-group-id="0458743833-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0458743833-3">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0458743833-4">[</span><span class="n">H</span><span class="p" data-group-id="0458743833-4">]</span><span class="p" data-group-id="0458743833-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_list</span><span class="p" data-group-id="0458743833-5">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="0458743833-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">print_list</span><span class="p" data-group-id="0458743833-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0458743833-7">[</span><span class="p" data-group-id="0458743833-7">]</span><span class="p" data-group-id="0458743833-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>This function broadcasts a message to a list of processes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">broadcast</span><span class="p" data-group-id="3436532561-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3436532561-2">[</span><span class="n">Pid</span><span class="p">|</span><span class="n">Pids</span><span class="p" data-group-id="3436532561-2">]</span><span class="p" data-group-id="3436532561-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Msg</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">broadcast</span><span class="p" data-group-id="3882968023-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">Pids</span><span class="p" data-group-id="3882968023-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">broadcast</span><span class="p" data-group-id="3882968023-4">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3882968023-5">[</span><span class="p" data-group-id="3882968023-5">]</span><span class="p" data-group-id="3882968023-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">broadcast</span><span class="p" data-group-id="3436532561-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">Pids</span><span class="p" data-group-id="3436532561-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">broadcast</span><span class="p" data-group-id="3436532561-4">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3436532561-5">[</span><span class="p" data-group-id="3436532561-5">]</span><span class="p" data-group-id="3436532561-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">true</span><span class="p">.</span></code></pre><p>These two functions have a similar structure. They both iterate over a list and
│ │ │ │  do something to each element in the list. The &quot;something&quot; is passed on as an
│ │ │ │ -extra argument to the function that does this.</p><p>The function <code class="inline">foreach</code> expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="4442350796-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4442350796-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4442350796-2">]</span><span class="p" data-group-id="4442350796-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">F</span><span class="p" data-group-id="4442350796-3">(</span><span class="n">H</span><span class="p" data-group-id="4442350796-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="4442350796-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4442350796-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="4442350796-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4442350796-6">[</span><span class="p" data-group-id="4442350796-6">]</span><span class="p" data-group-id="4442350796-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">print_list</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="7949661548-1">(</span><span class="nf">fun</span><span class="p" data-group-id="7949661548-2">(</span><span class="n">H</span><span class="p" data-group-id="7949661548-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7949661548-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="7949661548-4">[</span><span class="n">H</span><span class="p" data-group-id="7949661548-4">]</span><span class="p" data-group-id="7949661548-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7949661548-1">)</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">broadcast</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="5587742901-1">(</span><span class="nf">fun</span><span class="p" data-group-id="5587742901-2">(</span><span class="n">Pid</span><span class="p" data-group-id="5587742901-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5587742901-1">)</span></code></pre><p><code class="inline">foreach</code> is evaluated for its side-effect and not its value. <code class="inline">foreach(Fun ,L)</code>
│ │ │ │ +extra argument to the function that does this.</p><p>The function <code class="inline">foreach</code> expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="9239621931-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9239621931-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9239621931-2">]</span><span class="p" data-group-id="9239621931-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">F</span><span class="p" data-group-id="9239621931-3">(</span><span class="n">H</span><span class="p" data-group-id="9239621931-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="9239621931-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9239621931-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="9239621931-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9239621931-6">[</span><span class="p" data-group-id="9239621931-6">]</span><span class="p" data-group-id="9239621931-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">print_list</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="8105653900-1">(</span><span class="nf">fun</span><span class="p" data-group-id="8105653900-2">(</span><span class="n">H</span><span class="p" data-group-id="8105653900-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8105653900-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="8105653900-4">[</span><span class="n">H</span><span class="p" data-group-id="8105653900-4">]</span><span class="p" data-group-id="8105653900-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="8105653900-1">)</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">broadcast</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="3553351427-1">(</span><span class="nf">fun</span><span class="p" data-group-id="3553351427-2">(</span><span class="n">Pid</span><span class="p" data-group-id="3553351427-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="3553351427-1">)</span></code></pre><p><code class="inline">foreach</code> is evaluated for its side-effect and not its value. <code class="inline">foreach(Fun ,L)</code>
│ │ │ │  calls <code class="inline">Fun(X)</code> for each element <code class="inline">X</code> in <code class="inline">L</code> and the processing occurs in the
│ │ │ │  order that the elements were defined in <code class="inline">L</code>. <code class="inline">map</code> does not define the order in
│ │ │ │  which its elements are processed.</p><h2 id="syntax-of-funs" class="section-heading">
│ │ │ │    <a href="#syntax-of-funs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Syntax of Funs</span>
│ │ │ │  </h2>
│ │ │ │  <p>Funs are written with the following syntax (see
│ │ │ │ -<a href="../../../lib/../system/doc/html/expressions.xhtml#fun-expressions">Fun Expressions </a>for full description):</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5937273632-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">ArgN</span><span class="p" data-group-id="5937273632-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +<a href="../../../lib/../system/doc/html/expressions.xhtml#fun-expressions">Fun Expressions </a>for full description):</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2973262174-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">ArgN</span><span class="p" data-group-id="2973262174-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">end</span></code></pre><p>This creates an anonymous function of <code class="inline">N</code> arguments and binds it to the variable
│ │ │ │  <code class="inline">F</code>.</p><p>Another function, <code class="inline">FunctionName</code>, written in the same module, can be passed as
│ │ │ │  an argument, using the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>With this form of function reference, the function that is referred to does not
│ │ │ │  need to be exported from the module.</p><p>It is also possible to refer to a function defined in a different module, with
│ │ │ │ -the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In this case, the function must be exported from the module in question.</p><p>The following program illustrates the different ways of creating funs:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9884868163-1">(</span><span class="ss">fun_test</span><span class="p" data-group-id="9884868163-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9884868163-2">(</span><span class="p" data-group-id="9884868163-3">[</span><span class="ss">t1</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">t2</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9884868163-3">]</span><span class="p" data-group-id="9884868163-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="9884868163-4">(</span><span class="ss">lists</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9884868163-5">[</span><span class="ss">map</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9884868163-5">]</span><span class="p" data-group-id="9884868163-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In this case, the function must be exported from the module in question.</p><p>The following program illustrates the different ways of creating funs:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5380002748-1">(</span><span class="ss">fun_test</span><span class="p" data-group-id="5380002748-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5380002748-2">(</span><span class="p" data-group-id="5380002748-3">[</span><span class="ss">t1</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">t2</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5380002748-3">]</span><span class="p" data-group-id="5380002748-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="5380002748-4">(</span><span class="ss">lists</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5380002748-5">[</span><span class="ss">map</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5380002748-5">]</span><span class="p" data-group-id="5380002748-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">t1</span><span class="p" data-group-id="9884868163-6">(</span><span class="p" data-group-id="9884868163-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="9884868163-7">(</span><span class="nf">fun</span><span class="p" data-group-id="9884868163-8">(</span><span class="n">X</span><span class="p" data-group-id="9884868163-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9884868163-9">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9884868163-9">]</span><span class="p" data-group-id="9884868163-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">t1</span><span class="p" data-group-id="5380002748-6">(</span><span class="p" data-group-id="5380002748-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="5380002748-7">(</span><span class="nf">fun</span><span class="p" data-group-id="5380002748-8">(</span><span class="n">X</span><span class="p" data-group-id="5380002748-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5380002748-9">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5380002748-9">]</span><span class="p" data-group-id="5380002748-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">t2</span><span class="p" data-group-id="9884868163-10">(</span><span class="p" data-group-id="9884868163-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="9884868163-11">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9884868163-12">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9884868163-12">]</span><span class="p" data-group-id="9884868163-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">t2</span><span class="p" data-group-id="5380002748-10">(</span><span class="p" data-group-id="5380002748-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="5380002748-11">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5380002748-12">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5380002748-12">]</span><span class="p" data-group-id="5380002748-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="9884868163-13">(</span><span class="n">X</span><span class="p" data-group-id="9884868163-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span></code></pre><p>The fun <code class="inline">F</code> can be evaluated with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="p" data-group-id="0334028317-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Argn</span><span class="p" data-group-id="0334028317-1">)</span></code></pre><p>To check whether a term is a fun, use the test
│ │ │ │ -<a href="../../../lib/../erts/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> in a guard.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="9833182111-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="9833182111-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_function</span><span class="p" data-group-id="9833182111-2">(</span><span class="n">F</span><span class="p" data-group-id="9833182111-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="nf">apply</span><span class="p" data-group-id="9833182111-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="9833182111-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="9833182111-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9833182111-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="9833182111-5">(</span><span class="n">N</span><span class="p" data-group-id="9833182111-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="5380002748-13">(</span><span class="n">X</span><span class="p" data-group-id="5380002748-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span></code></pre><p>The fun <code class="inline">F</code> can be evaluated with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="p" data-group-id="9412718885-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Argn</span><span class="p" data-group-id="9412718885-1">)</span></code></pre><p>To check whether a term is a fun, use the test
│ │ │ │ +<a href="../../../lib/../erts/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> in a guard.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="9111317009-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="9111317009-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_function</span><span class="p" data-group-id="9111317009-2">(</span><span class="n">F</span><span class="p" data-group-id="9111317009-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="nf">apply</span><span class="p" data-group-id="9111317009-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="9111317009-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="9111317009-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9111317009-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="9111317009-5">(</span><span class="n">N</span><span class="p" data-group-id="9111317009-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │     </span><span class="n">N</span><span class="p">.</span></code></pre><p>Funs are a distinct type. The BIFs <code class="inline">erlang:fun_info/1,2</code> can be used to retrieve
│ │ │ │  information about a fun, and the BIF <a href="../../../lib/../erts/doc/html/erlang.html#fun_to_list/1"><code class="inline">erlang:fun_to_list/1</code></a> returns a textual
│ │ │ │  representation of a fun. The <a href="../../../lib/../erts/doc/html/erlang.html#check_process_code/2"><code class="inline">check_process_code/2</code></a>
│ │ │ │  BIF returns <code class="inline">true</code> if the process contains funs that depend on the old version
│ │ │ │  of a module.</p><h2 id="variable-bindings-within-a-fun" class="section-heading">
│ │ │ │    <a href="#variable-bindings-within-a-fun" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Variable Bindings Within a Fun</span>
│ │ │ │  </h2>
│ │ │ │  <p>The scope rules for variables that occur in funs are as follows:</p><ul><li>All variables that occur in the head of a fun are assumed to be &quot;fresh&quot;
│ │ │ │  variables.</li><li>Variables that are defined before the fun, and that occur in function calls or
│ │ │ │ -guard tests within the fun, have the values they had outside the fun.</li><li>Variables cannot be exported from a fun.</li></ul><p>The following examples illustrate these rules:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="1528619953-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1528619953-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1528619953-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="1528619953-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="1528619953-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="1528619953-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="1528619953-4">(</span><span class="nf">fun</span><span class="p" data-group-id="1528619953-5">(</span><span class="n">X</span><span class="p" data-group-id="1528619953-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1528619953-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="1528619953-7">[</span><span class="n">X</span><span class="p" data-group-id="1528619953-7">]</span><span class="p" data-group-id="1528619953-6">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1528619953-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="1528619953-8">(</span><span class="n">Stream</span><span class="p" data-group-id="1528619953-8">)</span><span class="p">.</span></code></pre><p>Here, the variable <code class="inline">X</code>, defined in the head of the fun, is a new variable. The
│ │ │ │ +guard tests within the fun, have the values they had outside the fun.</li><li>Variables cannot be exported from a fun.</li></ul><p>The following examples illustrate these rules:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="6213644021-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6213644021-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6213644021-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="6213644021-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="6213644021-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="6213644021-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="6213644021-4">(</span><span class="nf">fun</span><span class="p" data-group-id="6213644021-5">(</span><span class="n">X</span><span class="p" data-group-id="6213644021-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6213644021-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="6213644021-7">[</span><span class="n">X</span><span class="p" data-group-id="6213644021-7">]</span><span class="p" data-group-id="6213644021-6">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6213644021-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="6213644021-8">(</span><span class="n">Stream</span><span class="p" data-group-id="6213644021-8">)</span><span class="p">.</span></code></pre><p>Here, the variable <code class="inline">X</code>, defined in the head of the fun, is a new variable. The
│ │ │ │  variable <code class="inline">Stream</code>, which is used within the fun, gets its value from the
│ │ │ │  <code class="inline">file:open</code> line.</p><p>As any variable that occurs in the head of a fun is considered a new variable,
│ │ │ │ -it is equally valid to write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="4072176226-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="4072176226-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4072176226-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="4072176226-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="4072176226-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="4072176226-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="4072176226-4">(</span><span class="nf">fun</span><span class="p" data-group-id="4072176226-5">(</span><span class="n">File</span><span class="p" data-group-id="4072176226-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4072176226-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="4072176226-7">[</span><span class="n">File</span><span class="p" data-group-id="4072176226-7">]</span><span class="p" data-group-id="4072176226-6">)</span><span class="w">
│ │ │ │ -            </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="4072176226-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="4072176226-8">(</span><span class="n">Stream</span><span class="p" data-group-id="4072176226-8">)</span><span class="p">.</span></code></pre><p>Here, <code class="inline">File</code> is used as the new variable instead of <code class="inline">X</code>. This is not so wise
│ │ │ │ +it is equally valid to write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="0621918769-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="0621918769-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0621918769-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="0621918769-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="0621918769-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="0621918769-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="0621918769-4">(</span><span class="nf">fun</span><span class="p" data-group-id="0621918769-5">(</span><span class="n">File</span><span class="p" data-group-id="0621918769-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0621918769-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="0621918769-7">[</span><span class="n">File</span><span class="p" data-group-id="0621918769-7">]</span><span class="p" data-group-id="0621918769-6">)</span><span class="w">
│ │ │ │ +            </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="0621918769-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="0621918769-8">(</span><span class="n">Stream</span><span class="p" data-group-id="0621918769-8">)</span><span class="p">.</span></code></pre><p>Here, <code class="inline">File</code> is used as the new variable instead of <code class="inline">X</code>. This is not so wise
│ │ │ │  because code in the fun body cannot refer to the variable <code class="inline">File</code>, which is
│ │ │ │  defined outside of the fun. Compiling this example gives the following
│ │ │ │  diagnostic:</p><pre><code class="text">./FileName.erl:Line: Warning: variable 'File'
│ │ │ │        shadowed in 'fun'</code></pre><p>This indicates that the variable <code class="inline">File</code>, which is defined inside the fun,
│ │ │ │  collides with the variable <code class="inline">File</code>, which is defined outside the fun.</p><p>The rules for importing variables into a fun has the consequence that certain
│ │ │ │  pattern matching operations must be moved into guard expressions and cannot be
│ │ │ │  written in the head of the fun. For example, you might write the following code
│ │ │ │  if you intend the first clause of <code class="inline">F</code> to be evaluated when the value of its
│ │ │ │ -argument is <code class="inline">Y</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="5064045976-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5064045976-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +argument is <code class="inline">Y</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="2276908644-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2276908644-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="nf">map</span><span class="p" data-group-id="5064045976-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5064045976-3">(</span><span class="n">X</span><span class="p" data-group-id="5064045976-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">map</span><span class="p" data-group-id="2276908644-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2276908644-3">(</span><span class="n">X</span><span class="p" data-group-id="2276908644-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │               </span><span class="p">;</span><span class="w">
│ │ │ │ -           </span><span class="p" data-group-id="5064045976-4">(</span><span class="p">_</span><span class="p" data-group-id="5064045976-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +           </span><span class="p" data-group-id="2276908644-4">(</span><span class="p">_</span><span class="p" data-group-id="2276908644-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │               </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5064045976-2">)</span><span class="w">
│ │ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>instead of writing the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="9445213585-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9445213585-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2276908644-2">)</span><span class="w">
│ │ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>instead of writing the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0372631448-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0372631448-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="nf">map</span><span class="p" data-group-id="9445213585-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9445213585-3">(</span><span class="n">Y</span><span class="p" data-group-id="9445213585-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">map</span><span class="p" data-group-id="0372631448-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0372631448-3">(</span><span class="n">Y</span><span class="p" data-group-id="0372631448-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │               </span><span class="p">;</span><span class="w">
│ │ │ │ -           </span><span class="p" data-group-id="9445213585-4">(</span><span class="p">_</span><span class="p" data-group-id="9445213585-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +           </span><span class="p" data-group-id="0372631448-4">(</span><span class="p">_</span><span class="p" data-group-id="0372631448-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │               </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9445213585-2">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0372631448-2">)</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="funs-and-module-lists" class="section-heading">
│ │ │ │    <a href="#funs-and-module-lists" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Funs and Module Lists</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following examples show a dialogue with the Erlang shell. All the higher
│ │ │ │  order functions discussed are exported from the module <a href="../../../lib/stdlib/doc/html/lists.html"><code class="inline">lists</code></a>.</p><h3 id="map-1" class="section-heading">
│ │ │ │    <a href="#map-1" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">map</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="5215378406-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5215378406-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5215378406-2">]</span><span class="p" data-group-id="5215378406-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5215378406-3">[</span><span class="n">F</span><span class="p" data-group-id="5215378406-4">(</span><span class="n">H</span><span class="p" data-group-id="5215378406-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="5215378406-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5215378406-5">)</span><span class="p" data-group-id="5215378406-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="5215378406-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5215378406-7">[</span><span class="p" data-group-id="5215378406-7">]</span><span class="p" data-group-id="5215378406-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5215378406-8">[</span><span class="p" data-group-id="5215378406-8">]</span><span class="p">.</span></code></pre><p>It returns the list obtained by applying the function to every argument in the
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="9382050578-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9382050578-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9382050578-2">]</span><span class="p" data-group-id="9382050578-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9382050578-3">[</span><span class="n">F</span><span class="p" data-group-id="9382050578-4">(</span><span class="n">H</span><span class="p" data-group-id="9382050578-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="9382050578-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9382050578-5">)</span><span class="p" data-group-id="9382050578-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="9382050578-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9382050578-7">[</span><span class="p" data-group-id="9382050578-7">]</span><span class="p" data-group-id="9382050578-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9382050578-8">[</span><span class="p" data-group-id="9382050578-8">]</span><span class="p">.</span></code></pre><p>It returns the list obtained by applying the function to every argument in the
│ │ │ │  list.</p><p>When a new fun is defined in the shell, the value of the fun is printed as
│ │ │ │ -<code class="inline">Fun#&lt;erl_eval&gt;</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Double</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5007924586-1">(</span><span class="n">X</span><span class="p" data-group-id="5007924586-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">Fun#&lt;erl_eval&gt;</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Double</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6549594692-1">(</span><span class="n">X</span><span class="p" data-group-id="6549594692-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="5007924586-2">(</span><span class="n">Double</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5007924586-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5007924586-3">]</span><span class="p" data-group-id="5007924586-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5007924586-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="5007924586-4">]</span></code></pre><h3 id="any" class="section-heading">
│ │ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="6549594692-2">(</span><span class="n">Double</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6549594692-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="6549594692-3">]</span><span class="p" data-group-id="6549594692-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6549594692-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="6549594692-4">]</span></code></pre><h3 id="any" class="section-heading">
│ │ │ │    <a href="#any" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">any</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#any/2"><code class="inline">lists:any/2</code></a> takes a predicate <code class="inline">P</code> of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">any</span><span class="p" data-group-id="2634179931-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2634179931-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2634179931-2">]</span><span class="p" data-group-id="2634179931-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="2634179931-3">(</span><span class="n">H</span><span class="p" data-group-id="2634179931-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#any/2"><code class="inline">lists:any/2</code></a> takes a predicate <code class="inline">P</code> of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">any</span><span class="p" data-group-id="6027945623-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6027945623-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6027945623-2">]</span><span class="p" data-group-id="6027945623-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="6027945623-3">(</span><span class="n">H</span><span class="p" data-group-id="6027945623-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">any</span><span class="p" data-group-id="2634179931-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2634179931-4">)</span><span class="w">
│ │ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">any</span><span class="p" data-group-id="6027945623-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6027945623-4">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">any</span><span class="p" data-group-id="2634179931-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2634179931-6">[</span><span class="p" data-group-id="2634179931-6">]</span><span class="p" data-group-id="2634179931-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">any</span><span class="p" data-group-id="6027945623-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6027945623-6">[</span><span class="p" data-group-id="6027945623-6">]</span><span class="p" data-group-id="6027945623-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">false</span><span class="p">.</span></code></pre><p>A predicate is a function that returns <code class="inline">true</code> or <code class="inline">false</code>. <code class="inline">any</code> is <code class="inline">true</code> if
│ │ │ │  there is a term <code class="inline">X</code> in the list such that <code class="inline">P(X)</code> is <code class="inline">true</code>.</p><p>A predicate <code class="inline">Big(X)</code> is defined, which is <code class="inline">true</code> if its argument is greater that
│ │ │ │ -10:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Big</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="7948161930-1">(</span><span class="n">X</span><span class="p" data-group-id="7948161930-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="p">;</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +10:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Big</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="4769014499-1">(</span><span class="n">X</span><span class="p" data-group-id="4769014499-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="p">;</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="7948161930-2">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7948161930-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7948161930-3">]</span><span class="p" data-group-id="7948161930-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="4769014499-2">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4769014499-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4769014499-3">]</span><span class="p" data-group-id="4769014499-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="7948161930-4">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7948161930-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7948161930-5">]</span><span class="p" data-group-id="7948161930-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="4769014499-4">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4769014499-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4769014499-5">]</span><span class="p" data-group-id="4769014499-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span></code></pre><h3 id="all" class="section-heading">
│ │ │ │    <a href="#all" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">all</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#all/2"><code class="inline">lists:all/2</code></a> has the same arguments as <code class="inline">any</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="9016855702-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9016855702-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9016855702-2">]</span><span class="p" data-group-id="9016855702-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="9016855702-3">(</span><span class="n">H</span><span class="p" data-group-id="9016855702-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">all</span><span class="p" data-group-id="9016855702-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9016855702-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#all/2"><code class="inline">lists:all/2</code></a> has the same arguments as <code class="inline">any</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="1998236870-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1998236870-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1998236870-2">]</span><span class="p" data-group-id="1998236870-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="1998236870-3">(</span><span class="n">H</span><span class="p" data-group-id="1998236870-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">all</span><span class="p" data-group-id="1998236870-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="1998236870-4">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="ss">false</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">all</span><span class="p" data-group-id="9016855702-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9016855702-6">[</span><span class="p" data-group-id="9016855702-6">]</span><span class="p" data-group-id="9016855702-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>It is <code class="inline">true</code> if the predicate applied to all elements in the list is <code class="inline">true</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="8942996715-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8942996715-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8942996715-2">]</span><span class="p" data-group-id="8942996715-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">all</span><span class="p" data-group-id="1998236870-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1998236870-6">[</span><span class="p" data-group-id="1998236870-6">]</span><span class="p" data-group-id="1998236870-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>It is <code class="inline">true</code> if the predicate applied to all elements in the list is <code class="inline">true</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="9732730601-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9732730601-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9732730601-2">]</span><span class="p" data-group-id="9732730601-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="8942996715-3">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8942996715-4">[</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="8942996715-4">]</span><span class="p" data-group-id="8942996715-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="9732730601-3">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9732730601-4">[</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="9732730601-4">]</span><span class="p" data-group-id="9732730601-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span></code></pre><h3 id="foreach-1" class="section-heading">
│ │ │ │    <a href="#foreach-1" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">foreach</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#foreach/2"><code class="inline">lists:foreach/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="3708219293-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3708219293-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3708219293-2">]</span><span class="p" data-group-id="3708219293-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">F</span><span class="p" data-group-id="3708219293-3">(</span><span class="n">H</span><span class="p" data-group-id="3708219293-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="3708219293-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3708219293-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="3708219293-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3708219293-6">[</span><span class="p" data-group-id="3708219293-6">]</span><span class="p" data-group-id="3708219293-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#foreach/2"><code class="inline">lists:foreach/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="6594231853-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6594231853-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6594231853-2">]</span><span class="p" data-group-id="6594231853-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">F</span><span class="p" data-group-id="6594231853-3">(</span><span class="n">H</span><span class="p" data-group-id="6594231853-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="6594231853-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6594231853-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="6594231853-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6594231853-6">[</span><span class="p" data-group-id="6594231853-6">]</span><span class="p" data-group-id="6594231853-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The function is applied to each argument in the list. <code class="inline">foreach</code> returns <code class="inline">ok</code>. It
│ │ │ │ -is only used for its side-effect:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="7668524594-1">(</span><span class="nf">fun</span><span class="p" data-group-id="7668524594-2">(</span><span class="n">X</span><span class="p" data-group-id="7668524594-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7668524594-3">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="7668524594-4">[</span><span class="n">X</span><span class="p" data-group-id="7668524594-4">]</span><span class="p" data-group-id="7668524594-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7668524594-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7668524594-5">]</span><span class="p" data-group-id="7668524594-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +is only used for its side-effect:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="0847295442-1">(</span><span class="nf">fun</span><span class="p" data-group-id="0847295442-2">(</span><span class="n">X</span><span class="p" data-group-id="0847295442-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0847295442-3">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="0847295442-4">[</span><span class="n">X</span><span class="p" data-group-id="0847295442-4">]</span><span class="p" data-group-id="0847295442-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0847295442-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0847295442-5">]</span><span class="p" data-group-id="0847295442-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="w">
│ │ │ │  </span><span class="mi">2</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><h3 id="foldl" class="section-heading">
│ │ │ │    <a href="#foldl" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">foldl</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> takes a function of two arguments, an accumulator and a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foldl</span><span class="p" data-group-id="1200073935-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1200073935-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="1200073935-2">]</span><span class="p" data-group-id="1200073935-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">foldl</span><span class="p" data-group-id="1200073935-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="1200073935-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="1200073935-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1200073935-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">foldl</span><span class="p" data-group-id="1200073935-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1200073935-6">[</span><span class="p" data-group-id="1200073935-6">]</span><span class="p" data-group-id="1200073935-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Accu</span><span class="p">.</span></code></pre><p>The function is called with two arguments. The first argument is the successive
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> takes a function of two arguments, an accumulator and a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foldl</span><span class="p" data-group-id="0537638248-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0537638248-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="0537638248-2">]</span><span class="p" data-group-id="0537638248-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">foldl</span><span class="p" data-group-id="0537638248-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="0537638248-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="0537638248-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="0537638248-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">foldl</span><span class="p" data-group-id="0537638248-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0537638248-6">[</span><span class="p" data-group-id="0537638248-6">]</span><span class="p" data-group-id="0537638248-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Accu</span><span class="p">.</span></code></pre><p>The function is called with two arguments. The first argument is the successive
│ │ │ │  elements in the list. The second argument is the accumulator. The function must
│ │ │ │  return a new accumulator, which is used the next time the function is called.</p><p>If you have a list of lists <code class="inline">L = [&quot;I&quot;,&quot;like&quot;,&quot;Erlang&quot;]</code>, then you can sum the
│ │ │ │ -lengths of all the strings in <code class="inline">L</code> as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0549105042-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="0549105042-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0549105042-2">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="0549105042-2">]</span><span class="gp unselectable">
│ │ │ │ -10&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="0549105042-3">(</span><span class="nf">fun</span><span class="p" data-group-id="0549105042-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="0549105042-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0549105042-5">(</span><span class="n">X</span><span class="p" data-group-id="0549105042-5">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0549105042-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="mi">11</span></code></pre><p><a href="../../../lib/stdlib/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> works like a <code class="inline">while</code> loop in an imperative language:</p><pre><code class="makeup erlang" translate="no"><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="p" data-group-id="8863530854-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="8863530854-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ +lengths of all the strings in <code class="inline">L</code> as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0700919352-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="0700919352-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0700919352-2">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="0700919352-2">]</span><span class="gp unselectable">
│ │ │ │ +10&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="0700919352-3">(</span><span class="nf">fun</span><span class="p" data-group-id="0700919352-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="0700919352-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0700919352-5">(</span><span class="n">X</span><span class="p" data-group-id="0700919352-5">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0700919352-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="mi">11</span></code></pre><p><a href="../../../lib/stdlib/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> works like a <code class="inline">while</code> loop in an imperative language:</p><pre><code class="makeup erlang" translate="no"><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="p" data-group-id="7616262317-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="7616262317-1">]</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="n">Sum</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nf">while</span><span class="p" data-group-id="8863530854-2">(</span><span class="w"> </span><span class="n">L</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8863530854-3">[</span><span class="p" data-group-id="8863530854-3">]</span><span class="p" data-group-id="8863530854-2">)</span><span class="p" data-group-id="8863530854-4">{</span><span class="w">
│ │ │ │ -    </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8863530854-5">(</span><span class="nf">head</span><span class="p" data-group-id="8863530854-6">(</span><span class="n">L</span><span class="p" data-group-id="8863530854-6">)</span><span class="p" data-group-id="8863530854-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tail</span><span class="p" data-group-id="8863530854-7">(</span><span class="n">L</span><span class="p" data-group-id="8863530854-7">)</span><span class="w">
│ │ │ │ +</span><span class="nf">while</span><span class="p" data-group-id="7616262317-2">(</span><span class="w"> </span><span class="n">L</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7616262317-3">[</span><span class="p" data-group-id="7616262317-3">]</span><span class="p" data-group-id="7616262317-2">)</span><span class="p" data-group-id="7616262317-4">{</span><span class="w">
│ │ │ │ +    </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7616262317-5">(</span><span class="nf">head</span><span class="p" data-group-id="7616262317-6">(</span><span class="n">L</span><span class="p" data-group-id="7616262317-6">)</span><span class="p" data-group-id="7616262317-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tail</span><span class="p" data-group-id="7616262317-7">(</span><span class="n">L</span><span class="p" data-group-id="7616262317-7">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><h3 id="mapfoldl" class="section-heading">
│ │ │ │    <a href="#mapfoldl" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">mapfoldl</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#mapfoldl/3"><code class="inline">lists:mapfoldl/3</code></a> simultaneously maps and folds over a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mapfoldl</span><span class="p" data-group-id="8992753049-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8992753049-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="8992753049-2">]</span><span class="p" data-group-id="8992753049-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8992753049-3">{</span><span class="n">R</span><span class="p">,</span><span class="n">Accu1</span><span class="p" data-group-id="8992753049-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="8992753049-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p" data-group-id="8992753049-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8992753049-5">{</span><span class="n">Rs</span><span class="p">,</span><span class="n">Accu2</span><span class="p" data-group-id="8992753049-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">mapfoldl</span><span class="p" data-group-id="8992753049-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu1</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="8992753049-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8992753049-7">{</span><span class="p" data-group-id="8992753049-8">[</span><span class="n">R</span><span class="p">|</span><span class="n">Rs</span><span class="p" data-group-id="8992753049-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu2</span><span class="p" data-group-id="8992753049-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">mapfoldl</span><span class="p" data-group-id="8992753049-9">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8992753049-10">[</span><span class="p" data-group-id="8992753049-10">]</span><span class="p" data-group-id="8992753049-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8992753049-11">{</span><span class="p" data-group-id="8992753049-12">[</span><span class="p" data-group-id="8992753049-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="8992753049-11">}</span><span class="p">.</span></code></pre><p>The following example shows how to change all letters in <code class="inline">L</code> to upper case and
│ │ │ │ -then count them.</p><p>First the change to upper case:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Upcase</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="2734789621-1">(</span><span class="n">X</span><span class="p" data-group-id="2734789621-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w">  </span><span class="n">X</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="sc">$a</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2734789621-2">(</span><span class="n">X</span><span class="p" data-group-id="2734789621-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w">
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#mapfoldl/3"><code class="inline">lists:mapfoldl/3</code></a> simultaneously maps and folds over a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mapfoldl</span><span class="p" data-group-id="0652574586-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0652574586-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="0652574586-2">]</span><span class="p" data-group-id="0652574586-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0652574586-3">{</span><span class="n">R</span><span class="p">,</span><span class="n">Accu1</span><span class="p" data-group-id="0652574586-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="0652574586-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p" data-group-id="0652574586-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0652574586-5">{</span><span class="n">Rs</span><span class="p">,</span><span class="n">Accu2</span><span class="p" data-group-id="0652574586-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">mapfoldl</span><span class="p" data-group-id="0652574586-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu1</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="0652574586-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0652574586-7">{</span><span class="p" data-group-id="0652574586-8">[</span><span class="n">R</span><span class="p">|</span><span class="n">Rs</span><span class="p" data-group-id="0652574586-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu2</span><span class="p" data-group-id="0652574586-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">mapfoldl</span><span class="p" data-group-id="0652574586-9">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0652574586-10">[</span><span class="p" data-group-id="0652574586-10">]</span><span class="p" data-group-id="0652574586-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0652574586-11">{</span><span class="p" data-group-id="0652574586-12">[</span><span class="p" data-group-id="0652574586-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="0652574586-11">}</span><span class="p">.</span></code></pre><p>The following example shows how to change all letters in <code class="inline">L</code> to upper case and
│ │ │ │ +then count them.</p><p>First the change to upper case:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Upcase</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="7423873694-1">(</span><span class="n">X</span><span class="p" data-group-id="7423873694-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w">  </span><span class="n">X</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="sc">$a</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7423873694-2">(</span><span class="n">X</span><span class="p" data-group-id="7423873694-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │  &gt; </span><span class="n">Upcase_word</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ -</span><span class="nf">fun</span><span class="p" data-group-id="2734789621-3">(</span><span class="n">X</span><span class="p" data-group-id="2734789621-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="2734789621-4">(</span><span class="n">Upcase</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2734789621-4">)</span><span class="w">
│ │ │ │ +</span><span class="nf">fun</span><span class="p" data-group-id="7423873694-3">(</span><span class="n">X</span><span class="p" data-group-id="7423873694-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7423873694-4">(</span><span class="n">Upcase</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7423873694-4">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="n">Upcase_word</span><span class="p" data-group-id="2734789621-5">(</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="2734789621-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&gt; </span><span class="n">Upcase_word</span><span class="p" data-group-id="7423873694-5">(</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="7423873694-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;ERLANG&quot;</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="2734789621-6">(</span><span class="n">Upcase_word</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2734789621-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2734789621-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="2734789621-7">]</span></code></pre><p>Now, the fold and the map can be done at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">mapfoldl</span><span class="p" data-group-id="2414984211-1">(</span><span class="nf">fun</span><span class="p" data-group-id="2414984211-2">(</span><span class="n">Word</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="2414984211-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2414984211-3">{</span><span class="n">Upcase_word</span><span class="p" data-group-id="2414984211-4">(</span><span class="n">Word</span><span class="p" data-group-id="2414984211-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="2414984211-5">(</span><span class="n">Word</span><span class="p" data-group-id="2414984211-5">)</span><span class="p" data-group-id="2414984211-3">}</span><span class="w">
│ │ │ │ -</span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2414984211-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2414984211-6">{</span><span class="p" data-group-id="2414984211-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="2414984211-7">]</span><span class="p">,</span><span class="mi">11</span><span class="p" data-group-id="2414984211-6">}</span></code></pre><h3 id="filter" class="section-heading">
│ │ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7423873694-6">(</span><span class="n">Upcase_word</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7423873694-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7423873694-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="7423873694-7">]</span></code></pre><p>Now, the fold and the map can be done at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">mapfoldl</span><span class="p" data-group-id="1444493350-1">(</span><span class="nf">fun</span><span class="p" data-group-id="1444493350-2">(</span><span class="n">Word</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="1444493350-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1444493350-3">{</span><span class="n">Upcase_word</span><span class="p" data-group-id="1444493350-4">(</span><span class="n">Word</span><span class="p" data-group-id="1444493350-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="1444493350-5">(</span><span class="n">Word</span><span class="p" data-group-id="1444493350-5">)</span><span class="p" data-group-id="1444493350-3">}</span><span class="w">
│ │ │ │ +</span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1444493350-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1444493350-6">{</span><span class="p" data-group-id="1444493350-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="1444493350-7">]</span><span class="p">,</span><span class="mi">11</span><span class="p" data-group-id="1444493350-6">}</span></code></pre><h3 id="filter" class="section-heading">
│ │ │ │    <a href="#filter" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">filter</span>
│ │ │ │  </h3>
│ │ │ │  <p><a href="../../../lib/stdlib/doc/html/lists.html#filter/2"><code class="inline">lists:filter/2</code></a> takes a predicate of one argument and a list and returns all elements
│ │ │ │ -in the list that satisfy the predicate:</p><pre><code class="makeup erlang" translate="no"><span class="nf">filter</span><span class="p" data-group-id="5457959489-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5457959489-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5457959489-2">]</span><span class="p" data-group-id="5457959489-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="5457959489-3">(</span><span class="n">H</span><span class="p" data-group-id="5457959489-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5457959489-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">filter</span><span class="p" data-group-id="5457959489-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5457959489-5">)</span><span class="p" data-group-id="5457959489-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="5457959489-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5457959489-6">)</span><span class="w">
│ │ │ │ +in the list that satisfy the predicate:</p><pre><code class="makeup erlang" translate="no"><span class="nf">filter</span><span class="p" data-group-id="9595284690-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9595284690-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9595284690-2">]</span><span class="p" data-group-id="9595284690-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="9595284690-3">(</span><span class="n">H</span><span class="p" data-group-id="9595284690-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9595284690-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">filter</span><span class="p" data-group-id="9595284690-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9595284690-5">)</span><span class="p" data-group-id="9595284690-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="9595284690-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9595284690-6">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">filter</span><span class="p" data-group-id="5457959489-7">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5457959489-8">[</span><span class="p" data-group-id="5457959489-8">]</span><span class="p" data-group-id="5457959489-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5457959489-9">[</span><span class="p" data-group-id="5457959489-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="4519000581-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4519000581-2">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4519000581-2">]</span><span class="p" data-group-id="4519000581-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4519000581-3">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="4519000581-3">]</span></code></pre><p>Combining maps and filters enables writing of very succinct code. For example,
│ │ │ │ +</span><span class="nf">filter</span><span class="p" data-group-id="9595284690-7">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9595284690-8">[</span><span class="p" data-group-id="9595284690-8">]</span><span class="p" data-group-id="9595284690-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9595284690-9">[</span><span class="p" data-group-id="9595284690-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="5683699831-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5683699831-2">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="5683699831-2">]</span><span class="p" data-group-id="5683699831-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5683699831-3">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="5683699831-3">]</span></code></pre><p>Combining maps and filters enables writing of very succinct code. For example,
│ │ │ │  to define a set difference function <code class="inline">diff(L1, L2)</code> to be the difference between
│ │ │ │ -the lists <code class="inline">L1</code> and <code class="inline">L2</code>, the code can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">diff</span><span class="p" data-group-id="4184617283-1">(</span><span class="n">L1</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="4184617283-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">filter</span><span class="p" data-group-id="4184617283-2">(</span><span class="nf">fun</span><span class="p" data-group-id="4184617283-3">(</span><span class="n">X</span><span class="p" data-group-id="4184617283-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="4184617283-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="4184617283-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="4184617283-2">)</span><span class="p">.</span></code></pre><p>This gives the list of all elements in L1 that are not contained in L2.</p><p>The AND intersection of the list <code class="inline">L1</code> and <code class="inline">L2</code> is also easily defined:</p><pre><code class="makeup erlang" translate="no"><span class="nf">intersection</span><span class="p" data-group-id="6284823521-1">(</span><span class="n">L1</span><span class="p">,</span><span class="n">L2</span><span class="p" data-group-id="6284823521-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="6284823521-2">(</span><span class="nf">fun</span><span class="p" data-group-id="6284823521-3">(</span><span class="n">X</span><span class="p" data-group-id="6284823521-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="6284823521-4">(</span><span class="n">X</span><span class="p">,</span><span class="n">L1</span><span class="p" data-group-id="6284823521-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="6284823521-2">)</span><span class="p">.</span></code></pre><h3 id="takewhile" class="section-heading">
│ │ │ │ +the lists <code class="inline">L1</code> and <code class="inline">L2</code>, the code can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">diff</span><span class="p" data-group-id="8895296073-1">(</span><span class="n">L1</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="8895296073-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">filter</span><span class="p" data-group-id="8895296073-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8895296073-3">(</span><span class="n">X</span><span class="p" data-group-id="8895296073-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="8895296073-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="8895296073-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="8895296073-2">)</span><span class="p">.</span></code></pre><p>This gives the list of all elements in L1 that are not contained in L2.</p><p>The AND intersection of the list <code class="inline">L1</code> and <code class="inline">L2</code> is also easily defined:</p><pre><code class="makeup erlang" translate="no"><span class="nf">intersection</span><span class="p" data-group-id="7050238682-1">(</span><span class="n">L1</span><span class="p">,</span><span class="n">L2</span><span class="p" data-group-id="7050238682-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="7050238682-2">(</span><span class="nf">fun</span><span class="p" data-group-id="7050238682-3">(</span><span class="n">X</span><span class="p" data-group-id="7050238682-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="7050238682-4">(</span><span class="n">X</span><span class="p">,</span><span class="n">L1</span><span class="p" data-group-id="7050238682-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="7050238682-2">)</span><span class="p">.</span></code></pre><h3 id="takewhile" class="section-heading">
│ │ │ │    <a href="#takewhile" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">takewhile</span>
│ │ │ │  </h3>
│ │ │ │  <p><a href="../../../lib/stdlib/doc/html/lists.html#takewhile/2"><code class="inline">lists:takewhile/2</code></a> takes elements <code class="inline">X</code> from a list <code class="inline">L</code> as long as the predicate
│ │ │ │ -<code class="inline">P(X)</code> is true:</p><pre><code class="makeup erlang" translate="no"><span class="nf">takewhile</span><span class="p" data-group-id="9236021729-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9236021729-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9236021729-2">]</span><span class="p" data-group-id="9236021729-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="9236021729-3">(</span><span class="n">H</span><span class="p" data-group-id="9236021729-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9236021729-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">takewhile</span><span class="p" data-group-id="9236021729-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9236021729-5">)</span><span class="p" data-group-id="9236021729-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9236021729-6">[</span><span class="p" data-group-id="9236021729-6">]</span><span class="w">
│ │ │ │ +<code class="inline">P(X)</code> is true:</p><pre><code class="makeup erlang" translate="no"><span class="nf">takewhile</span><span class="p" data-group-id="4438149784-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4438149784-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4438149784-2">]</span><span class="p" data-group-id="4438149784-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="4438149784-3">(</span><span class="n">H</span><span class="p" data-group-id="4438149784-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4438149784-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">takewhile</span><span class="p" data-group-id="4438149784-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4438149784-5">)</span><span class="p" data-group-id="4438149784-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4438149784-6">[</span><span class="p" data-group-id="4438149784-6">]</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">takewhile</span><span class="p" data-group-id="9236021729-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9236021729-8">[</span><span class="p" data-group-id="9236021729-8">]</span><span class="p" data-group-id="9236021729-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9236021729-9">[</span><span class="p" data-group-id="9236021729-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">takewhile</span><span class="p" data-group-id="9084076490-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9084076490-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9084076490-2">]</span><span class="p" data-group-id="9084076490-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9084076490-3">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="9084076490-3">]</span></code></pre><h3 id="dropwhile" class="section-heading">
│ │ │ │ +</span><span class="nf">takewhile</span><span class="p" data-group-id="4438149784-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4438149784-8">[</span><span class="p" data-group-id="4438149784-8">]</span><span class="p" data-group-id="4438149784-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4438149784-9">[</span><span class="p" data-group-id="4438149784-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">takewhile</span><span class="p" data-group-id="5051479432-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5051479432-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5051479432-2">]</span><span class="p" data-group-id="5051479432-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5051479432-3">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="5051479432-3">]</span></code></pre><h3 id="dropwhile" class="section-heading">
│ │ │ │    <a href="#dropwhile" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">dropwhile</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#dropwhile/2"><code class="inline">lists:dropwhile/2</code></a> is the complement of <code class="inline">takewhile</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">dropwhile</span><span class="p" data-group-id="8607132808-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8607132808-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8607132808-2">]</span><span class="p" data-group-id="8607132808-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="8607132808-3">(</span><span class="n">H</span><span class="p" data-group-id="8607132808-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">dropwhile</span><span class="p" data-group-id="8607132808-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8607132808-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8607132808-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8607132808-5">]</span><span class="w">
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#dropwhile/2"><code class="inline">lists:dropwhile/2</code></a> is the complement of <code class="inline">takewhile</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">dropwhile</span><span class="p" data-group-id="4333374547-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4333374547-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4333374547-2">]</span><span class="p" data-group-id="4333374547-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="4333374547-3">(</span><span class="n">H</span><span class="p" data-group-id="4333374547-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">dropwhile</span><span class="p" data-group-id="4333374547-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4333374547-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4333374547-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4333374547-5">]</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">dropwhile</span><span class="p" data-group-id="8607132808-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8607132808-7">[</span><span class="p" data-group-id="8607132808-7">]</span><span class="p" data-group-id="8607132808-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8607132808-8">[</span><span class="p" data-group-id="8607132808-8">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">dropwhile</span><span class="p" data-group-id="6831226342-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6831226342-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6831226342-2">]</span><span class="p" data-group-id="6831226342-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6831226342-3">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6831226342-3">]</span></code></pre><h3 id="splitwith" class="section-heading">
│ │ │ │ +</span><span class="nf">dropwhile</span><span class="p" data-group-id="4333374547-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4333374547-7">[</span><span class="p" data-group-id="4333374547-7">]</span><span class="p" data-group-id="4333374547-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4333374547-8">[</span><span class="p" data-group-id="4333374547-8">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">dropwhile</span><span class="p" data-group-id="7834153318-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7834153318-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7834153318-2">]</span><span class="p" data-group-id="7834153318-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7834153318-3">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7834153318-3">]</span></code></pre><h3 id="splitwith" class="section-heading">
│ │ │ │    <a href="#splitwith" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">splitwith</span>
│ │ │ │  </h3>
│ │ │ │  <p><a href="../../../lib/stdlib/doc/html/lists.html#splitwith/2"><code class="inline">lists:splitwith/2</code></a> splits the list <code class="inline">L</code> into the two sublists <code class="inline">{L1, L2}</code>, where
│ │ │ │ -<code class="inline">L = takewhile(P, L)</code> and <code class="inline">L2 = dropwhile(P, L)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">splitwith</span><span class="p" data-group-id="4643887674-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4643887674-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">splitwith</span><span class="p" data-group-id="4643887674-2">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4643887674-3">[</span><span class="p" data-group-id="4643887674-3">]</span><span class="p" data-group-id="4643887674-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">L = takewhile(P, L)</code> and <code class="inline">L2 = dropwhile(P, L)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">splitwith</span><span class="p" data-group-id="7278765166-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7278765166-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">splitwith</span><span class="p" data-group-id="7278765166-2">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7278765166-3">[</span><span class="p" data-group-id="7278765166-3">]</span><span class="p" data-group-id="7278765166-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">splitwith</span><span class="p" data-group-id="4643887674-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4643887674-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4643887674-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4643887674-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="4643887674-6">(</span><span class="n">H</span><span class="p" data-group-id="4643887674-6">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">splitwith</span><span class="p" data-group-id="4643887674-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4643887674-8">[</span><span class="n">H</span><span class="p">|</span><span class="n">L</span><span class="p" data-group-id="4643887674-8">]</span><span class="p" data-group-id="4643887674-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4643887674-9">{</span><span class="nf">reverse</span><span class="p" data-group-id="4643887674-10">(</span><span class="n">L</span><span class="p" data-group-id="4643887674-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4643887674-11">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4643887674-11">]</span><span class="p" data-group-id="4643887674-9">}</span><span class="w">
│ │ │ │ +</span><span class="nf">splitwith</span><span class="p" data-group-id="7278765166-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7278765166-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7278765166-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7278765166-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="7278765166-6">(</span><span class="n">H</span><span class="p" data-group-id="7278765166-6">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">splitwith</span><span class="p" data-group-id="7278765166-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7278765166-8">[</span><span class="n">H</span><span class="p">|</span><span class="n">L</span><span class="p" data-group-id="7278765166-8">]</span><span class="p" data-group-id="7278765166-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7278765166-9">{</span><span class="nf">reverse</span><span class="p" data-group-id="7278765166-10">(</span><span class="n">L</span><span class="p" data-group-id="7278765166-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7278765166-11">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7278765166-11">]</span><span class="p" data-group-id="7278765166-9">}</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">splitwith</span><span class="p" data-group-id="4643887674-12">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4643887674-13">[</span><span class="p" data-group-id="4643887674-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4643887674-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4643887674-14">{</span><span class="nf">reverse</span><span class="p" data-group-id="4643887674-15">(</span><span class="n">L</span><span class="p" data-group-id="4643887674-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4643887674-16">[</span><span class="p" data-group-id="4643887674-16">]</span><span class="p" data-group-id="4643887674-14">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">splitwith</span><span class="p" data-group-id="8248445220-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8248445220-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8248445220-2">]</span><span class="p" data-group-id="8248445220-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8248445220-3">{</span><span class="p" data-group-id="8248445220-4">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="8248445220-4">]</span><span class="p">,</span><span class="p" data-group-id="8248445220-5">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8248445220-5">]</span><span class="p" data-group-id="8248445220-3">}</span></code></pre><h2 id="funs-returning-funs" class="section-heading">
│ │ │ │ +</span><span class="nf">splitwith</span><span class="p" data-group-id="7278765166-12">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7278765166-13">[</span><span class="p" data-group-id="7278765166-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7278765166-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7278765166-14">{</span><span class="nf">reverse</span><span class="p" data-group-id="7278765166-15">(</span><span class="n">L</span><span class="p" data-group-id="7278765166-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7278765166-16">[</span><span class="p" data-group-id="7278765166-16">]</span><span class="p" data-group-id="7278765166-14">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">splitwith</span><span class="p" data-group-id="6246934787-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6246934787-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6246934787-2">]</span><span class="p" data-group-id="6246934787-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6246934787-3">{</span><span class="p" data-group-id="6246934787-4">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="6246934787-4">]</span><span class="p">,</span><span class="p" data-group-id="6246934787-5">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6246934787-5">]</span><span class="p" data-group-id="6246934787-3">}</span></code></pre><h2 id="funs-returning-funs" class="section-heading">
│ │ │ │    <a href="#funs-returning-funs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Funs Returning Funs</span>
│ │ │ │  </h2>
│ │ │ │  <p>So far, only functions that take funs as arguments have been described. More
│ │ │ │  powerful functions, that themselves return funs, can also be written. The
│ │ │ │  following examples illustrate these type of functions.</p><h3 id="simple-higher-order-functions" class="section-heading">
│ │ │ │    <a href="#simple-higher-order-functions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Simple Higher Order Functions</span>
│ │ │ │  </h3>
│ │ │ │  <p><code class="inline">Adder(X)</code> is a function that given <code class="inline">X</code>, returns a new function <code class="inline">G</code> such that
│ │ │ │ -<code class="inline">G(K)</code> returns <code class="inline">K + X</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Adder</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0008302937-1">(</span><span class="n">X</span><span class="p" data-group-id="0008302937-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0008302937-2">(</span><span class="n">Y</span><span class="p" data-group-id="0008302937-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">G(K)</code> returns <code class="inline">K + X</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Adder</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0977379140-1">(</span><span class="n">X</span><span class="p" data-group-id="0977379140-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0977379140-2">(</span><span class="n">Y</span><span class="p" data-group-id="0977379140-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="n">Add6</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Adder</span><span class="p" data-group-id="0008302937-3">(</span><span class="mi">6</span><span class="p" data-group-id="0008302937-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&gt; </span><span class="n">Add6</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Adder</span><span class="p" data-group-id="0977379140-3">(</span><span class="mi">6</span><span class="p" data-group-id="0977379140-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="n">Add6</span><span class="p" data-group-id="0008302937-4">(</span><span class="mi">10</span><span class="p" data-group-id="0008302937-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&gt; </span><span class="n">Add6</span><span class="p" data-group-id="0977379140-4">(</span><span class="mi">10</span><span class="p" data-group-id="0977379140-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">16</span></code></pre><h3 id="infinite-lists" class="section-heading">
│ │ │ │    <a href="#infinite-lists" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Infinite Lists</span>
│ │ │ │  </h3>
│ │ │ │ -<p>The idea is to write something like:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5573297450-1">(</span><span class="ss">lazy</span><span class="p" data-group-id="5573297450-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5573297450-2">(</span><span class="p" data-group-id="5573297450-3">[</span><span class="ss">ints_from</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5573297450-3">]</span><span class="p" data-group-id="5573297450-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">ints_from</span><span class="p" data-group-id="5573297450-4">(</span><span class="n">N</span><span class="p" data-group-id="5573297450-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">fun</span><span class="p" data-group-id="5573297450-5">(</span><span class="p" data-group-id="5573297450-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="5573297450-6">[</span><span class="n">N</span><span class="p">|</span><span class="nf">ints_from</span><span class="p" data-group-id="5573297450-7">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="5573297450-7">)</span><span class="p" data-group-id="5573297450-6">]</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Then proceed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lazy</span><span class="p">:</span><span class="nf">ints_from</span><span class="p" data-group-id="1030208636-1">(</span><span class="mi">1</span><span class="p" data-group-id="1030208636-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>The idea is to write something like:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8617653451-1">(</span><span class="ss">lazy</span><span class="p" data-group-id="8617653451-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8617653451-2">(</span><span class="p" data-group-id="8617653451-3">[</span><span class="ss">ints_from</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8617653451-3">]</span><span class="p" data-group-id="8617653451-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">ints_from</span><span class="p" data-group-id="8617653451-4">(</span><span class="n">N</span><span class="p" data-group-id="8617653451-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">fun</span><span class="p" data-group-id="8617653451-5">(</span><span class="p" data-group-id="8617653451-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="8617653451-6">[</span><span class="n">N</span><span class="p">|</span><span class="nf">ints_from</span><span class="p" data-group-id="8617653451-7">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="8617653451-7">)</span><span class="p" data-group-id="8617653451-6">]</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Then proceed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lazy</span><span class="p">:</span><span class="nf">ints_from</span><span class="p" data-group-id="5721463947-1">(</span><span class="mi">1</span><span class="p" data-group-id="5721463947-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="n">XX</span><span class="p" data-group-id="1030208636-2">(</span><span class="p" data-group-id="1030208636-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1030208636-3">[</span><span class="mi">1</span><span class="p">|</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="p" data-group-id="1030208636-3">]</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nf">hd</span><span class="p" data-group-id="1030208636-4">(</span><span class="n">XX</span><span class="p" data-group-id="1030208636-5">(</span><span class="p" data-group-id="1030208636-5">)</span><span class="p" data-group-id="1030208636-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&gt; </span><span class="n">XX</span><span class="p" data-group-id="5721463947-2">(</span><span class="p" data-group-id="5721463947-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5721463947-3">[</span><span class="mi">1</span><span class="p">|</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="p" data-group-id="5721463947-3">]</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="nf">hd</span><span class="p" data-group-id="5721463947-4">(</span><span class="n">XX</span><span class="p" data-group-id="5721463947-5">(</span><span class="p" data-group-id="5721463947-5">)</span><span class="p" data-group-id="5721463947-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tl</span><span class="p" data-group-id="1030208636-6">(</span><span class="n">XX</span><span class="p" data-group-id="1030208636-7">(</span><span class="p" data-group-id="1030208636-7">)</span><span class="p" data-group-id="1030208636-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&gt; </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tl</span><span class="p" data-group-id="5721463947-6">(</span><span class="n">XX</span><span class="p" data-group-id="5721463947-7">(</span><span class="p" data-group-id="5721463947-7">)</span><span class="p" data-group-id="5721463947-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nf">hd</span><span class="p" data-group-id="1030208636-8">(</span><span class="n">Y</span><span class="p" data-group-id="1030208636-9">(</span><span class="p" data-group-id="1030208636-9">)</span><span class="p" data-group-id="1030208636-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&gt; </span><span class="nf">hd</span><span class="p" data-group-id="5721463947-8">(</span><span class="n">Y</span><span class="p" data-group-id="5721463947-9">(</span><span class="p" data-group-id="5721463947-9">)</span><span class="p" data-group-id="5721463947-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">2</span></code></pre><p>And so on. This is an example of &quot;lazy embedding&quot;.</p><h3 id="parsing" class="section-heading">
│ │ │ │    <a href="#parsing" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Parsing</span>
│ │ │ │  </h3>
│ │ │ │ -<p>The following examples show parsers of the following type:</p><pre><code class="makeup erlang" translate="no"><span class="n">Parser</span><span class="p" data-group-id="8798949387-1">(</span><span class="n">Toks</span><span class="p" data-group-id="8798949387-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8798949387-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tree</span><span class="p">,</span><span class="w"> </span><span class="n">Toks1</span><span class="p" data-group-id="8798949387-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">fail</span></code></pre><p><code class="inline">Toks</code> is the list of tokens to be parsed. A successful parse returns
│ │ │ │ +<p>The following examples show parsers of the following type:</p><pre><code class="makeup erlang" translate="no"><span class="n">Parser</span><span class="p" data-group-id="5908636437-1">(</span><span class="n">Toks</span><span class="p" data-group-id="5908636437-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5908636437-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tree</span><span class="p">,</span><span class="w"> </span><span class="n">Toks1</span><span class="p" data-group-id="5908636437-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">fail</span></code></pre><p><code class="inline">Toks</code> is the list of tokens to be parsed. A successful parse returns
│ │ │ │  <code class="inline">{ok, Tree, Toks1}</code>.</p><ul><li><code class="inline">Tree</code> is a parse tree.</li><li><code class="inline">Toks1</code> is a tail of <code class="inline">Tree</code> that contains symbols encountered after the
│ │ │ │  structure that was correctly parsed.</li></ul><p>An unsuccessful parse returns <code class="inline">fail</code>.</p><p>The following example illustrates a simple, functional parser that parses the
│ │ │ │  grammar:</p><pre><code class="text">(a | b) &amp; (c | d)</code></pre><p>The following code defines a function <code class="inline">pconst(X)</code> in the module <code class="inline">funparse</code>,
│ │ │ │ -which returns a fun that parses a list of tokens:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pconst</span><span class="p" data-group-id="7463950502-1">(</span><span class="n">X</span><span class="p" data-group-id="7463950502-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7463950502-2">(</span><span class="n">T</span><span class="p" data-group-id="7463950502-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +which returns a fun that parses a list of tokens:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pconst</span><span class="p" data-group-id="3976067163-1">(</span><span class="n">X</span><span class="p" data-group-id="3976067163-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3976067163-2">(</span><span class="n">T</span><span class="p" data-group-id="3976067163-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │         </span><span class="k">case</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -           </span><span class="p" data-group-id="7463950502-3">[</span><span class="n">X</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="7463950502-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7463950502-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7463950502-5">{</span><span class="ss">const</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7463950502-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="7463950502-4">}</span><span class="p">;</span><span class="w">
│ │ │ │ +           </span><span class="p" data-group-id="3976067163-3">[</span><span class="n">X</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="3976067163-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3976067163-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3976067163-5">{</span><span class="ss">const</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3976067163-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="3976067163-4">}</span><span class="p">;</span><span class="w">
│ │ │ │             </span><span class="p">_</span><span class="w">      </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">fail</span><span class="w">
│ │ │ │         </span><span class="k">end</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>This function can be used as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">pconst</span><span class="p" data-group-id="7297889941-1">(</span><span class="ss">a</span><span class="p" data-group-id="7297889941-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>This function can be used as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">pconst</span><span class="p" data-group-id="3946565869-1">(</span><span class="ss">a</span><span class="p" data-group-id="3946565869-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">funparse</span><span class="p">.</span><span class="mf">0.22674075</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="n">P1</span><span class="p" data-group-id="7297889941-2">(</span><span class="p" data-group-id="7297889941-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7297889941-3">]</span><span class="p" data-group-id="7297889941-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7297889941-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="7297889941-5">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7297889941-5">}</span><span class="p">,</span><span class="p" data-group-id="7297889941-6">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7297889941-6">]</span><span class="p" data-group-id="7297889941-4">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="n">P1</span><span class="p" data-group-id="7297889941-7">(</span><span class="p" data-group-id="7297889941-8">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="7297889941-8">]</span><span class="p" data-group-id="7297889941-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&gt; </span><span class="n">P1</span><span class="p" data-group-id="3946565869-2">(</span><span class="p" data-group-id="3946565869-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3946565869-3">]</span><span class="p" data-group-id="3946565869-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3946565869-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="3946565869-5">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="3946565869-5">}</span><span class="p">,</span><span class="p" data-group-id="3946565869-6">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3946565869-6">]</span><span class="p" data-group-id="3946565869-4">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="n">P1</span><span class="p" data-group-id="3946565869-7">(</span><span class="p" data-group-id="3946565869-8">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="3946565869-8">]</span><span class="p" data-group-id="3946565869-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">fail</span></code></pre><p>Next, the two higher order functions <code class="inline">pand</code> and <code class="inline">por</code> are defined. They combine
│ │ │ │ -primitive parsers to produce more complex parsers.</p><p>First <code class="inline">pand</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pand</span><span class="p" data-group-id="4514280855-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="4514280855-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4514280855-2">(</span><span class="n">T</span><span class="p" data-group-id="4514280855-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="4514280855-3">(</span><span class="n">T</span><span class="p" data-group-id="4514280855-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="4514280855-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4514280855-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="4514280855-5">(</span><span class="n">T1</span><span class="p" data-group-id="4514280855-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="4514280855-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="4514280855-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                        </span><span class="p" data-group-id="4514280855-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4514280855-8">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="4514280855-8">}</span><span class="p" data-group-id="4514280855-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +primitive parsers to produce more complex parsers.</p><p>First <code class="inline">pand</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pand</span><span class="p" data-group-id="1605642814-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="1605642814-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1605642814-2">(</span><span class="n">T</span><span class="p" data-group-id="1605642814-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="1605642814-3">(</span><span class="n">T</span><span class="p" data-group-id="1605642814-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="1605642814-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="1605642814-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="1605642814-5">(</span><span class="n">T1</span><span class="p" data-group-id="1605642814-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="1605642814-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="1605642814-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                        </span><span class="p" data-group-id="1605642814-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1605642814-8">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="1605642814-8">}</span><span class="p" data-group-id="1605642814-7">}</span><span class="p">;</span><span class="w">
│ │ │ │                      </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                          </span><span class="ss">fail</span><span class="w">
│ │ │ │                  </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="ss">fail</span><span class="w">
│ │ │ │          </span><span class="k">end</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Given a parser <code class="inline">P1</code> for grammar <code class="inline">G1</code>, and a parser <code class="inline">P2</code> for grammar <code class="inline">G2</code>,
│ │ │ │  <code class="inline">pand(P1, P2)</code> returns a parser for the grammar, which consists of sequences of
│ │ │ │  tokens that satisfy <code class="inline">G1</code>, followed by sequences of tokens that satisfy <code class="inline">G2</code>.</p><p><code class="inline">por(P1, P2)</code> returns a parser for the language described by the grammar <code class="inline">G1</code> or
│ │ │ │ -<code class="inline">G2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">por</span><span class="p" data-group-id="9860674027-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="9860674027-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="9860674027-2">(</span><span class="n">T</span><span class="p" data-group-id="9860674027-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="9860674027-3">(</span><span class="n">T</span><span class="p" data-group-id="9860674027-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9860674027-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="9860674027-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="9860674027-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9860674027-6">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="n">R</span><span class="p" data-group-id="9860674027-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="9860674027-5">}</span><span class="p">;</span><span class="w">
│ │ │ │ +<code class="inline">G2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">por</span><span class="p" data-group-id="1726425189-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="1726425189-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1726425189-2">(</span><span class="n">T</span><span class="p" data-group-id="1726425189-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="1726425189-3">(</span><span class="n">T</span><span class="p" data-group-id="1726425189-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="1726425189-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="1726425189-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="1726425189-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1726425189-6">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="n">R</span><span class="p" data-group-id="1726425189-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="1726425189-5">}</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="9860674027-7">(</span><span class="n">T</span><span class="p" data-group-id="9860674027-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="9860674027-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="9860674027-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                        </span><span class="p" data-group-id="9860674027-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9860674027-10">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="n">R1</span><span class="p" data-group-id="9860674027-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="9860674027-9">}</span><span class="p">;</span><span class="w">
│ │ │ │ +                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="1726425189-7">(</span><span class="n">T</span><span class="p" data-group-id="1726425189-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="1726425189-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="1726425189-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                        </span><span class="p" data-group-id="1726425189-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1726425189-10">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="n">R1</span><span class="p" data-group-id="1726425189-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="1726425189-9">}</span><span class="p">;</span><span class="w">
│ │ │ │                      </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                          </span><span class="ss">fail</span><span class="w">
│ │ │ │                  </span><span class="k">end</span><span class="w">
│ │ │ │          </span><span class="k">end</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The original problem was to parse the grammar <code class="inline">(a | b) &amp; (c | d)</code>. The following
│ │ │ │ -code addresses this problem:</p><pre><code class="makeup erlang" translate="no"><span class="nf">grammar</span><span class="p" data-group-id="3450009665-1">(</span><span class="p" data-group-id="3450009665-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">pand</span><span class="p" data-group-id="3450009665-2">(</span><span class="w">
│ │ │ │ -         </span><span class="nf">por</span><span class="p" data-group-id="3450009665-3">(</span><span class="nf">pconst</span><span class="p" data-group-id="3450009665-4">(</span><span class="ss">a</span><span class="p" data-group-id="3450009665-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="3450009665-5">(</span><span class="ss">b</span><span class="p" data-group-id="3450009665-5">)</span><span class="p" data-group-id="3450009665-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="nf">por</span><span class="p" data-group-id="3450009665-6">(</span><span class="nf">pconst</span><span class="p" data-group-id="3450009665-7">(</span><span class="ss">c</span><span class="p" data-group-id="3450009665-7">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="3450009665-8">(</span><span class="ss">d</span><span class="p" data-group-id="3450009665-8">)</span><span class="p" data-group-id="3450009665-6">)</span><span class="p" data-group-id="3450009665-2">)</span><span class="p">.</span></code></pre><p>The following code adds a parser interface to the grammar:</p><pre><code class="makeup erlang" translate="no"><span class="nf">parse</span><span class="p" data-group-id="2026416110-1">(</span><span class="n">List</span><span class="p" data-group-id="2026416110-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2026416110-2">(</span><span class="nf">grammar</span><span class="p" data-group-id="2026416110-3">(</span><span class="p" data-group-id="2026416110-3">)</span><span class="p" data-group-id="2026416110-2">)</span><span class="p" data-group-id="2026416110-4">(</span><span class="n">List</span><span class="p" data-group-id="2026416110-4">)</span><span class="p">.</span></code></pre><p>The parser can be tested as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="6071264945-1">(</span><span class="p" data-group-id="6071264945-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6071264945-2">]</span><span class="p" data-group-id="6071264945-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6071264945-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="6071264945-4">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="6071264945-5">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="6071264945-6">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="6071264945-6">}</span><span class="p" data-group-id="6071264945-5">}</span><span class="p">,</span><span class="p" data-group-id="6071264945-7">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="6071264945-8">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6071264945-8">}</span><span class="p" data-group-id="6071264945-7">}</span><span class="p" data-group-id="6071264945-4">}</span><span class="p" data-group-id="6071264945-3">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="6071264945-9">(</span><span class="p" data-group-id="6071264945-10">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="6071264945-10">]</span><span class="p" data-group-id="6071264945-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6071264945-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="6071264945-12">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="6071264945-13">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="6071264945-14">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="6071264945-14">}</span><span class="p" data-group-id="6071264945-13">}</span><span class="p">,</span><span class="p" data-group-id="6071264945-15">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="6071264945-16">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="6071264945-16">}</span><span class="p" data-group-id="6071264945-15">}</span><span class="p" data-group-id="6071264945-12">}</span><span class="p" data-group-id="6071264945-11">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="6071264945-17">(</span><span class="p" data-group-id="6071264945-18">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6071264945-18">]</span><span class="p" data-group-id="6071264945-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6071264945-19">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="6071264945-20">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="6071264945-21">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="6071264945-22">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6071264945-22">}</span><span class="p" data-group-id="6071264945-21">}</span><span class="p">,</span><span class="p" data-group-id="6071264945-23">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="6071264945-24">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6071264945-24">}</span><span class="p" data-group-id="6071264945-23">}</span><span class="p" data-group-id="6071264945-20">}</span><span class="p" data-group-id="6071264945-19">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="6071264945-25">(</span><span class="p" data-group-id="6071264945-26">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="6071264945-26">]</span><span class="p" data-group-id="6071264945-25">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6071264945-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="6071264945-28">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="6071264945-29">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="6071264945-30">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6071264945-30">}</span><span class="p" data-group-id="6071264945-29">}</span><span class="p">,</span><span class="p" data-group-id="6071264945-31">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="6071264945-32">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="6071264945-32">}</span><span class="p" data-group-id="6071264945-31">}</span><span class="p" data-group-id="6071264945-28">}</span><span class="p" data-group-id="6071264945-27">}</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="6071264945-33">(</span><span class="p" data-group-id="6071264945-34">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6071264945-34">]</span><span class="p" data-group-id="6071264945-33">)</span><span class="p">.</span><span class="w">
│ │ │ │ +code addresses this problem:</p><pre><code class="makeup erlang" translate="no"><span class="nf">grammar</span><span class="p" data-group-id="1219409191-1">(</span><span class="p" data-group-id="1219409191-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">pand</span><span class="p" data-group-id="1219409191-2">(</span><span class="w">
│ │ │ │ +         </span><span class="nf">por</span><span class="p" data-group-id="1219409191-3">(</span><span class="nf">pconst</span><span class="p" data-group-id="1219409191-4">(</span><span class="ss">a</span><span class="p" data-group-id="1219409191-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="1219409191-5">(</span><span class="ss">b</span><span class="p" data-group-id="1219409191-5">)</span><span class="p" data-group-id="1219409191-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="nf">por</span><span class="p" data-group-id="1219409191-6">(</span><span class="nf">pconst</span><span class="p" data-group-id="1219409191-7">(</span><span class="ss">c</span><span class="p" data-group-id="1219409191-7">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="1219409191-8">(</span><span class="ss">d</span><span class="p" data-group-id="1219409191-8">)</span><span class="p" data-group-id="1219409191-6">)</span><span class="p" data-group-id="1219409191-2">)</span><span class="p">.</span></code></pre><p>The following code adds a parser interface to the grammar:</p><pre><code class="makeup erlang" translate="no"><span class="nf">parse</span><span class="p" data-group-id="1228559336-1">(</span><span class="n">List</span><span class="p" data-group-id="1228559336-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1228559336-2">(</span><span class="nf">grammar</span><span class="p" data-group-id="1228559336-3">(</span><span class="p" data-group-id="1228559336-3">)</span><span class="p" data-group-id="1228559336-2">)</span><span class="p" data-group-id="1228559336-4">(</span><span class="n">List</span><span class="p" data-group-id="1228559336-4">)</span><span class="p">.</span></code></pre><p>The parser can be tested as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="8095074455-1">(</span><span class="p" data-group-id="8095074455-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8095074455-2">]</span><span class="p" data-group-id="8095074455-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8095074455-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="8095074455-4">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="8095074455-5">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="8095074455-6">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="8095074455-6">}</span><span class="p" data-group-id="8095074455-5">}</span><span class="p">,</span><span class="p" data-group-id="8095074455-7">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="8095074455-8">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8095074455-8">}</span><span class="p" data-group-id="8095074455-7">}</span><span class="p" data-group-id="8095074455-4">}</span><span class="p" data-group-id="8095074455-3">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="8095074455-9">(</span><span class="p" data-group-id="8095074455-10">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="8095074455-10">]</span><span class="p" data-group-id="8095074455-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8095074455-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="8095074455-12">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="8095074455-13">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="8095074455-14">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="8095074455-14">}</span><span class="p" data-group-id="8095074455-13">}</span><span class="p">,</span><span class="p" data-group-id="8095074455-15">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="8095074455-16">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="8095074455-16">}</span><span class="p" data-group-id="8095074455-15">}</span><span class="p" data-group-id="8095074455-12">}</span><span class="p" data-group-id="8095074455-11">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="8095074455-17">(</span><span class="p" data-group-id="8095074455-18">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8095074455-18">]</span><span class="p" data-group-id="8095074455-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8095074455-19">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="8095074455-20">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="8095074455-21">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="8095074455-22">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8095074455-22">}</span><span class="p" data-group-id="8095074455-21">}</span><span class="p">,</span><span class="p" data-group-id="8095074455-23">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="8095074455-24">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8095074455-24">}</span><span class="p" data-group-id="8095074455-23">}</span><span class="p" data-group-id="8095074455-20">}</span><span class="p" data-group-id="8095074455-19">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="8095074455-25">(</span><span class="p" data-group-id="8095074455-26">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="8095074455-26">]</span><span class="p" data-group-id="8095074455-25">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8095074455-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="8095074455-28">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="8095074455-29">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="8095074455-30">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8095074455-30">}</span><span class="p" data-group-id="8095074455-29">}</span><span class="p">,</span><span class="p" data-group-id="8095074455-31">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="8095074455-32">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="8095074455-32">}</span><span class="p" data-group-id="8095074455-31">}</span><span class="p" data-group-id="8095074455-28">}</span><span class="p" data-group-id="8095074455-27">}</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="8095074455-33">(</span><span class="p" data-group-id="8095074455-34">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8095074455-34">]</span><span class="p" data-group-id="8095074455-33">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">fail</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/expressions.xhtml
│ │ │ │ @@ -56,81 +56,81 @@
│ │ │ │  </span><span class="n">Phone_number</span><span class="w">
│ │ │ │  </span><span class="p">_</span><span class="w">
│ │ │ │  </span><span class="p">_</span><span class="n">Height</span><span class="w">
│ │ │ │  </span><span class="ss">name@node</span></code></pre><p>Variables are bound to values using <a href="patterns.xhtml">pattern matching</a>. Erlang uses
│ │ │ │  <em>single assignment</em>, that is, a variable can only be bound once.</p><p>The <em>anonymous variable</em> is denoted by underscore (_) and can be used when a
│ │ │ │  variable is required but its value can be ignored.</p><p><em>Example:</em></p><pre><code class="text">[H|_] = [1,2,3]</code></pre><p>Variables starting with underscore (<code class="inline">_</code>), for example, <code class="inline">_Height</code>, are normal
│ │ │ │  variables, not anonymous. However, they are ignored by the compiler in the sense
│ │ │ │ -that they do not generate warnings.</p><p><em>Example:</em></p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="6890850477-1">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6890850477-2">[</span><span class="p" data-group-id="6890850477-2">]</span><span class="p" data-group-id="6890850477-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6890850477-3">[</span><span class="p" data-group-id="6890850477-3">]</span><span class="p">.</span></code></pre><p>can be rewritten to be more readable:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="4470207378-1">(</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4470207378-2">[</span><span class="p" data-group-id="4470207378-2">]</span><span class="p" data-group-id="4470207378-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4470207378-3">[</span><span class="p" data-group-id="4470207378-3">]</span><span class="p">.</span></code></pre><p>This causes a warning for an unused variable, <code class="inline">Elem</code>. To avoid the warning,
│ │ │ │ -the code can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="5262195445-1">(</span><span class="p">_</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5262195445-2">[</span><span class="p" data-group-id="5262195445-2">]</span><span class="p" data-group-id="5262195445-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5262195445-3">[</span><span class="p" data-group-id="5262195445-3">]</span><span class="p">.</span></code></pre><p>Notice that since variables starting with an underscore are not anonymous, the
│ │ │ │ -following example matches:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0828505887-1">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0828505887-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0828505887-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0828505887-2">}</span></code></pre><p>But this example fails:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3372130034-1">{</span><span class="p">_</span><span class="n">N</span><span class="p">,</span><span class="p">_</span><span class="n">N</span><span class="p" data-group-id="3372130034-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3372130034-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3372130034-2">}</span></code></pre><p>The scope for a variable is its function clause. Variables bound in a branch of
│ │ │ │ +that they do not generate warnings.</p><p><em>Example:</em></p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="9937847943-1">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9937847943-2">[</span><span class="p" data-group-id="9937847943-2">]</span><span class="p" data-group-id="9937847943-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9937847943-3">[</span><span class="p" data-group-id="9937847943-3">]</span><span class="p">.</span></code></pre><p>can be rewritten to be more readable:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="7132877332-1">(</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7132877332-2">[</span><span class="p" data-group-id="7132877332-2">]</span><span class="p" data-group-id="7132877332-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7132877332-3">[</span><span class="p" data-group-id="7132877332-3">]</span><span class="p">.</span></code></pre><p>This causes a warning for an unused variable, <code class="inline">Elem</code>. To avoid the warning,
│ │ │ │ +the code can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="3998986688-1">(</span><span class="p">_</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3998986688-2">[</span><span class="p" data-group-id="3998986688-2">]</span><span class="p" data-group-id="3998986688-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3998986688-3">[</span><span class="p" data-group-id="3998986688-3">]</span><span class="p">.</span></code></pre><p>Notice that since variables starting with an underscore are not anonymous, the
│ │ │ │ +following example matches:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8865071329-1">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8865071329-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8865071329-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8865071329-2">}</span></code></pre><p>But this example fails:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3073836569-1">{</span><span class="p">_</span><span class="n">N</span><span class="p">,</span><span class="p">_</span><span class="n">N</span><span class="p" data-group-id="3073836569-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3073836569-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3073836569-2">}</span></code></pre><p>The scope for a variable is its function clause. Variables bound in a branch of
│ │ │ │  an <code class="inline">if</code>, <code class="inline">case</code>, or <code class="inline">receive</code> expression must be bound in all branches to have a
│ │ │ │  value outside the expression. Otherwise they are regarded as unsafe outside
│ │ │ │  the expression.</p><p>For the <code class="inline">try</code> expression variable scoping is limited so that variables bound in
│ │ │ │  the expression are always unsafe outside the expression.</p><h2 id="patterns" class="section-heading">
│ │ │ │    <a href="#patterns" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Patterns</span>
│ │ │ │  </h2>
│ │ │ │  <p>A pattern has the same structure as a term but can contain unbound variables.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">Name1</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9781959797-1">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9781959797-1">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9781959797-2">{</span><span class="ss">error</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="9781959797-2">}</span></code></pre><p>Patterns are allowed in clause heads, <a href="expressions.xhtml#case">case expressions</a>,
│ │ │ │ +</span><span class="p" data-group-id="9888164533-1">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9888164533-1">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9888164533-2">{</span><span class="ss">error</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="9888164533-2">}</span></code></pre><p>Patterns are allowed in clause heads, <a href="expressions.xhtml#case">case expressions</a>,
│ │ │ │  <a href="expressions.xhtml#receive">receive expressions</a>, and
│ │ │ │  <a href="expressions.xhtml#the-match-operator">match expressions</a>.</p><h3 id="the-compound-pattern-operator" class="section-heading">
│ │ │ │    <a href="#the-compound-pattern-operator" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">The Compound Pattern Operator</span>
│ │ │ │  </h3>
│ │ │ │  <p>If <code class="inline">Pattern1</code> and <code class="inline">Pattern2</code> are valid patterns, the following is also a valid
│ │ │ │  pattern:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Pattern2</span></code></pre><p>When matched against a term, both <code class="inline">Pattern1</code> and <code class="inline">Pattern2</code> are matched against
│ │ │ │ -the term. The idea behind this feature is to avoid reconstruction of terms.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="9127935063-1">(</span><span class="p" data-group-id="9127935063-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="9127935063-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="9127935063-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Signal</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9127935063-3">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="9127935063-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +the term. The idea behind this feature is to avoid reconstruction of terms.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="7125425936-1">(</span><span class="p" data-group-id="7125425936-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="7125425936-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="7125425936-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Signal</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7125425936-3">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="7125425936-3">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="9127935063-4">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="9127935063-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>can instead be written as</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="6274706891-1">(</span><span class="p" data-group-id="6274706891-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6274706891-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="6274706891-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="7125425936-4">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="7125425936-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>can instead be written as</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0804912132-1">(</span><span class="p" data-group-id="0804912132-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0804912132-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="0804912132-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="6274706891-3">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="6274706891-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="0804912132-3">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="0804912132-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>The compound pattern operator does not imply that its operands are matched in
│ │ │ │  any particular order. That means that it is not legal to bind a variable in
│ │ │ │  <code class="inline">Pattern1</code> and use it in <code class="inline">Pattern2</code>, or vice versa.</p><h3 id="string-prefix-in-patterns" class="section-heading">
│ │ │ │    <a href="#string-prefix-in-patterns" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">String Prefix in Patterns</span>
│ │ │ │  </h3>
│ │ │ │ -<p>When matching strings, the following is a valid pattern:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="6042110854-1">(</span><span class="s">&quot;prefix&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="6042110854-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This is syntactic sugar for the equivalent, but harder to read:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="2452647246-1">(</span><span class="p" data-group-id="2452647246-2">[</span><span class="sc">$p</span><span class="p">,</span><span class="sc">$r</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$f</span><span class="p">,</span><span class="sc">$i</span><span class="p">,</span><span class="sc">$x</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="2452647246-2">]</span><span class="p" data-group-id="2452647246-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h3 id="expressions-in-patterns" class="section-heading">
│ │ │ │ +<p>When matching strings, the following is a valid pattern:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="2608919342-1">(</span><span class="s">&quot;prefix&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="2608919342-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This is syntactic sugar for the equivalent, but harder to read:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="1320350541-1">(</span><span class="p" data-group-id="1320350541-2">[</span><span class="sc">$p</span><span class="p">,</span><span class="sc">$r</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$f</span><span class="p">,</span><span class="sc">$i</span><span class="p">,</span><span class="sc">$x</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="1320350541-2">]</span><span class="p" data-group-id="1320350541-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h3 id="expressions-in-patterns" class="section-heading">
│ │ │ │    <a href="#expressions-in-patterns" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Expressions in Patterns</span>
│ │ │ │  </h3>
│ │ │ │  <p>An arithmetic expression can be used within a pattern if it meets both of the
│ │ │ │ -following two conditions:</p><ul><li>It uses only numeric or bitwise operators.</li><li>Its value can be evaluated to a constant when complied.</li></ul><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="p" data-group-id="2949314229-1">{</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2949314229-1">}</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2949314229-2">{</span><span class="o">?</span><span class="n">THRESHOLD</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="2949314229-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="the-match-operator" class="section-heading">
│ │ │ │ +following two conditions:</p><ul><li>It uses only numeric or bitwise operators.</li><li>Its value can be evaluated to a constant when complied.</li></ul><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="p" data-group-id="6080366522-1">{</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6080366522-1">}</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6080366522-2">{</span><span class="o">?</span><span class="n">THRESHOLD</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="6080366522-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="the-match-operator" class="section-heading">
│ │ │ │    <a href="#the-match-operator" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">The Match Operator</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following matches <code class="inline">Pattern</code> against <code class="inline">Expr</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>If the matching succeeds, any unbound variable in the pattern becomes bound and
│ │ │ │  the value of <code class="inline">Expr</code> is returned.</p><p>If multiple match operators are applied in sequence, they will be evaluated from
│ │ │ │ -right to left.</p><p>If the matching fails, a <code class="inline">badmatch</code> run-time error occurs.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7935443591-1">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="7935443591-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7935443591-2">{</span><span class="ss">answer</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="7935443591-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7935443591-3">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7935443591-3">}</span><span class="gp unselectable">
│ │ │ │ +right to left.</p><p>If the matching fails, a <code class="inline">badmatch</code> run-time error occurs.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9898367550-1">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9898367550-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9898367550-2">{</span><span class="ss">answer</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="9898367550-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9898367550-3">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="9898367550-3">}</span><span class="gp unselectable">
│ │ │ │  2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">answer</span><span class="gp unselectable">
│ │ │ │  3&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span><span class="gp unselectable">
│ │ │ │  4&gt; </span><span class="n">T</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7935443591-4">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7935443591-4">}</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="p" data-group-id="7935443591-5">{</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="7935443591-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7935443591-6">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7935443591-6">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9898367550-4">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="9898367550-4">}</span><span class="gp unselectable">
│ │ │ │ +5&gt; </span><span class="p" data-group-id="9898367550-5">{</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9898367550-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9898367550-6">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9898367550-6">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right-hand side value [1,2]</span></code></pre><p>Because multiple match operators are evaluated from right to left, it means
│ │ │ │  that:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Pattern2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PatternN</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expression</span></code></pre><p>is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="n">Temporary</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expression</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="n">PatternN</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Temporary</span><span class="p">,</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="n">Pattern2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Temporary</span><span class="p">,</span><span class="w">
│ │ │ │ @@ -144,30 +144,30 @@
│ │ │ │  can safely be skipped on a first reading.</p></section><p>The <code class="inline">=</code> character is used to denote two similar but distinct operators: the
│ │ │ │  match operator and the compound pattern operator. Which one is meant is
│ │ │ │  determined by context.</p><p>The <em>compound pattern operator</em> is used to construct a compound pattern from two
│ │ │ │  patterns. Compound patterns are accepted everywhere a pattern is accepted. A
│ │ │ │  compound pattern matches if all of its constituent patterns match. It is not
│ │ │ │  legal for a pattern that is part of a compound pattern to use variables (as keys
│ │ │ │  in map patterns or sizes in binary patterns) bound in other sub patterns of the
│ │ │ │ -same compound pattern.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">fun</span><span class="p" data-group-id="3814742417-1">(</span><span class="p" data-group-id="3814742417-2">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="3814742417-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3814742417-3">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="3814742417-3">}</span><span class="p" data-group-id="3814742417-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +same compound pattern.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">fun</span><span class="p" data-group-id="9169092866-1">(</span><span class="p" data-group-id="9169092866-2">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="9169092866-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9169092866-3">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9169092866-3">}</span><span class="p" data-group-id="9169092866-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">* 1:7: variable &#39;Key&#39; is unbound</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3814742417-4">(</span><span class="p" data-group-id="3814742417-5">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="3814742417-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">E</span><span class="p" data-group-id="3814742417-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3814742417-6">{</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="3814742417-6">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="3814742417-7">(</span><span class="p" data-group-id="3814742417-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3814742417-8">}</span><span class="p" data-group-id="3814742417-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3814742417-9">{</span><span class="p" data-group-id="3814742417-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3814742417-10">}</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3814742417-9">}</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="n">G</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3814742417-11">(</span><span class="p" data-group-id="3814742417-12">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">B</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="3814742417-12">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3814742417-13">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="3814742417-13">&gt;&gt;</span><span class="p" data-group-id="3814742417-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3814742417-14">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="3814742417-14">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">G</span><span class="p" data-group-id="3814742417-15">(</span><span class="p" data-group-id="3814742417-16">&lt;&lt;</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p" data-group-id="3814742417-16">&gt;&gt;</span><span class="p" data-group-id="3814742417-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3814742417-17">{</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p">,</span><span class="mi">10795</span><span class="p" data-group-id="3814742417-17">}</span></code></pre><p>The <em>match operator</em> is allowed everywhere an expression is allowed. It is used
│ │ │ │ +2&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9169092866-4">(</span><span class="p" data-group-id="9169092866-5">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9169092866-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">E</span><span class="p" data-group-id="9169092866-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9169092866-6">{</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9169092866-6">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="9169092866-7">(</span><span class="p" data-group-id="9169092866-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9169092866-8">}</span><span class="p" data-group-id="9169092866-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9169092866-9">{</span><span class="p" data-group-id="9169092866-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9169092866-10">}</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9169092866-9">}</span><span class="gp unselectable">
│ │ │ │ +3&gt; </span><span class="n">G</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9169092866-11">(</span><span class="p" data-group-id="9169092866-12">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">B</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="9169092866-12">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9169092866-13">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="9169092866-13">&gt;&gt;</span><span class="p" data-group-id="9169092866-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9169092866-14">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="9169092866-14">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">G</span><span class="p" data-group-id="9169092866-15">(</span><span class="p" data-group-id="9169092866-16">&lt;&lt;</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p" data-group-id="9169092866-16">&gt;&gt;</span><span class="p" data-group-id="9169092866-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9169092866-17">{</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p">,</span><span class="mi">10795</span><span class="p" data-group-id="9169092866-17">}</span></code></pre><p>The <em>match operator</em> is allowed everywhere an expression is allowed. It is used
│ │ │ │  to match the value of an expression to a pattern. If multiple match operators
│ │ │ │ -are applied in sequence, they will be evaluated from right to left.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8537977267-1">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="8537977267-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8537977267-2">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="8537977267-2">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nf">f</span><span class="p" data-group-id="8537977267-3">(</span><span class="n">Key</span><span class="p" data-group-id="8537977267-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8537977267-4">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="8537977267-4">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8537977267-5">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="8537977267-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │ +are applied in sequence, they will be evaluated from right to left.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1034978146-1">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="1034978146-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1034978146-2">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="1034978146-2">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="nf">f</span><span class="p" data-group-id="1034978146-3">(</span><span class="n">Key</span><span class="p" data-group-id="1034978146-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1034978146-4">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="1034978146-4">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1034978146-5">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="1034978146-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">value</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nf">f</span><span class="p" data-group-id="8537977267-6">(</span><span class="n">Key</span><span class="p" data-group-id="8537977267-6">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8537977267-7">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="8537977267-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8537977267-8">(</span><span class="p" data-group-id="8537977267-9">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="8537977267-9">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p" data-group-id="8537977267-8">)</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nf">f</span><span class="p" data-group-id="1034978146-6">(</span><span class="n">Key</span><span class="p" data-group-id="1034978146-6">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1034978146-7">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="1034978146-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1034978146-8">(</span><span class="p" data-group-id="1034978146-9">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="1034978146-9">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p" data-group-id="1034978146-8">)</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">value</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nf">f</span><span class="p" data-group-id="8537977267-10">(</span><span class="n">Key</span><span class="p" data-group-id="8537977267-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8537977267-11">(</span><span class="p" data-group-id="8537977267-12">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="8537977267-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8537977267-13">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="8537977267-13">}</span><span class="p" data-group-id="8537977267-11">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nf">f</span><span class="p" data-group-id="1034978146-10">(</span><span class="n">Key</span><span class="p" data-group-id="1034978146-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1034978146-11">(</span><span class="p" data-group-id="1034978146-12">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="1034978146-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1034978146-13">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="1034978146-13">}</span><span class="p" data-group-id="1034978146-11">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">* 1:12: variable &#39;Key&#39; is unbound</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="p" data-group-id="8537977267-14">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">Y</span><span class="p" data-group-id="8537977267-14">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">begin</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8537977267-15">&lt;&lt;</span><span class="mi">42</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="8537977267-15">&gt;&gt;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="p" data-group-id="1034978146-14">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">Y</span><span class="p" data-group-id="1034978146-14">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">begin</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1034978146-15">&lt;&lt;</span><span class="mi">42</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="1034978146-15">&gt;&gt;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span></code></pre><p>The expression at prompt <code class="inline">2&gt;</code> first matches the value of variable <code class="inline">M</code> against
│ │ │ │  pattern <code class="inline">#{key := Key}</code>, binding variable <code class="inline">Key</code>. It then matches the value of
│ │ │ │  <code class="inline">M</code> against pattern <code class="inline">#{Key := Value}</code> using variable <code class="inline">Key</code> as the key, binding
│ │ │ │  variable <code class="inline">Value</code>.</p><p>The expression at prompt <code class="inline">3&gt;</code> matches expression <code class="inline">(#{key := Key} = M)</code> against
│ │ │ │  pattern <code class="inline">#{Key := Value}</code>. The expression inside the parentheses is evaluated
│ │ │ │  first. That is, <code class="inline">M</code> is matched against <code class="inline">#{key := Key}</code>, and then the value of
│ │ │ │  <code class="inline">M</code> is matched against pattern <code class="inline">#{Key := Value}</code>. That is the same evaluation
│ │ │ │ @@ -181,30 +181,30 @@
│ │ │ │  binding variable <code class="inline">Y</code> and creating a binary. The binary is then matched against
│ │ │ │  pattern <code class="inline">&lt;&lt;X:Y&gt;&gt;</code> using the value of <code class="inline">Y</code> as the size of the segment.</p><h2 id="function-calls" class="section-heading">
│ │ │ │    <a href="#function-calls" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Function Calls</span>
│ │ │ │  </h2>
│ │ │ │ -<pre><code class="makeup erlang" translate="no"><span class="n">ExprF</span><span class="p" data-group-id="3207602002-1">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="3207602002-1">)</span><span class="w">
│ │ │ │ -</span><span class="n">ExprM</span><span class="p">:</span><span class="n">ExprF</span><span class="p" data-group-id="3207602002-2">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="3207602002-2">)</span></code></pre><p>In the first form of function calls, <code class="inline">ExprM:ExprF(Expr1,...,ExprN)</code>, each of
│ │ │ │ +<pre><code class="makeup erlang" translate="no"><span class="n">ExprF</span><span class="p" data-group-id="2421549412-1">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="2421549412-1">)</span><span class="w">
│ │ │ │ +</span><span class="n">ExprM</span><span class="p">:</span><span class="n">ExprF</span><span class="p" data-group-id="2421549412-2">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="2421549412-2">)</span></code></pre><p>In the first form of function calls, <code class="inline">ExprM:ExprF(Expr1,...,ExprN)</code>, each of
│ │ │ │  <code class="inline">ExprM</code> and <code class="inline">ExprF</code> must be an atom or an expression that evaluates to an atom.
│ │ │ │  The function is said to be called by using the <em>fully qualified function name</em>.
│ │ │ │ -This is often referred to as a <em>remote</em> or <em>external function call</em>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="3319950588-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3319950588-1">)</span></code></pre><p>In the second form of function calls, <code class="inline">ExprF(Expr1,...,ExprN)</code>, <code class="inline">ExprF</code> must be
│ │ │ │ +This is often referred to as a <em>remote</em> or <em>external function call</em>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="5942596395-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="5942596395-1">)</span></code></pre><p>In the second form of function calls, <code class="inline">ExprF(Expr1,...,ExprN)</code>, <code class="inline">ExprF</code> must be
│ │ │ │  an atom or evaluate to a fun.</p><p>If <code class="inline">ExprF</code> is an atom, the function is said to be called by using the
│ │ │ │  <em>implicitly qualified function name</em>. If the function <code class="inline">ExprF</code> is locally
│ │ │ │  defined, it is called. Alternatively, if <code class="inline">ExprF</code> is explicitly imported from the
│ │ │ │  <code class="inline">M</code> module, <code class="inline">M:ExprF(Expr1,...,ExprN)</code> is called. If <code class="inline">ExprF</code> is neither declared
│ │ │ │  locally nor explicitly imported, <code class="inline">ExprF</code> must be the name of an automatically
│ │ │ │ -imported BIF.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="2513844694-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="2513844694-1">)</span><span class="w">
│ │ │ │ -</span><span class="nf">spawn</span><span class="p" data-group-id="2513844694-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2513844694-3">[</span><span class="p" data-group-id="2513844694-3">]</span><span class="p" data-group-id="2513844694-2">)</span></code></pre><p><em>Examples</em> where <code class="inline">ExprF</code> is a fun:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3081117756-1">(</span><span class="n">X</span><span class="p" data-group-id="3081117756-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Fun1</span><span class="p" data-group-id="3081117756-2">(</span><span class="mi">3</span><span class="p" data-group-id="3081117756-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +imported BIF.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="1303233423-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1303233423-1">)</span><span class="w">
│ │ │ │ +</span><span class="nf">spawn</span><span class="p" data-group-id="1303233423-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1303233423-3">[</span><span class="p" data-group-id="1303233423-3">]</span><span class="p" data-group-id="1303233423-2">)</span></code></pre><p><em>Examples</em> where <code class="inline">ExprF</code> is a fun:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0703664857-1">(</span><span class="n">X</span><span class="p" data-group-id="0703664857-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Fun1</span><span class="p" data-group-id="0703664857-2">(</span><span class="mi">3</span><span class="p" data-group-id="0703664857-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="k">fun</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="ss">append</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3081117756-3">(</span><span class="p" data-group-id="3081117756-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3081117756-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3081117756-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3081117756-5">]</span><span class="p" data-group-id="3081117756-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3081117756-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3081117756-6">]</span><span class="w">
│ │ │ │ +2&gt; </span><span class="k">fun</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="ss">append</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0703664857-3">(</span><span class="p" data-group-id="0703664857-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0703664857-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0703664857-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0703664857-5">]</span><span class="p" data-group-id="0703664857-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0703664857-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0703664857-6">]</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="o">&gt;</span></code></pre><p>Notice that when calling a local function, there is a difference between using
│ │ │ │  the implicitly or fully qualified function name. The latter always refers to the
│ │ │ │  latest version of the module. See
│ │ │ │  <a href="code_loading.xhtml">Compilation and Code Loading </a>and
│ │ │ │  <a href="ref_man_functions.xhtml#eval">Function Evaluation</a>.</p><h3 id="local-function-names-clashing-with-auto-imported-bifs" class="section-heading">
│ │ │ │    <a href="#local-function-names-clashing-with-auto-imported-bifs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -221,40 +221,40 @@
│ │ │ │  called instead. This is to avoid that future additions to the set of
│ │ │ │  auto-imported BIFs do not silently change the behavior of old code.</p></section><p>However, to avoid that old (pre R14) code changed its behavior when compiled
│ │ │ │  with Erlang/OTP version R14A or later, the following restriction applies: If you
│ │ │ │  override the name of a BIF that was auto-imported in OTP versions prior to R14A
│ │ │ │  (ERTS version 5.8) and have an implicitly qualified call to that function in
│ │ │ │  your code, you either need to explicitly remove the auto-import using a compiler
│ │ │ │  directive, or replace the call with a fully qualified function call. Otherwise
│ │ │ │ -you get a compilation error. See the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2044331698-1">(</span><span class="p" data-group-id="2044331698-2">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2044331698-2">]</span><span class="p" data-group-id="2044331698-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +you get a compilation error. See the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3281753862-1">(</span><span class="p" data-group-id="3281753862-2">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3281753862-2">]</span><span class="p" data-group-id="3281753862-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="2044331698-3">(</span><span class="p" data-group-id="2044331698-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="2044331698-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2044331698-5">]</span><span class="p" data-group-id="2044331698-4">}</span><span class="p" data-group-id="2044331698-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="3281753862-3">(</span><span class="p" data-group-id="3281753862-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="3281753862-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3281753862-5">]</span><span class="p" data-group-id="3281753862-4">}</span><span class="p" data-group-id="3281753862-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">length</span><span class="p" data-group-id="2044331698-6">(</span><span class="p" data-group-id="2044331698-7">[</span><span class="p" data-group-id="2044331698-7">]</span><span class="p" data-group-id="2044331698-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">length</span><span class="p" data-group-id="3281753862-6">(</span><span class="p" data-group-id="3281753862-7">[</span><span class="p" data-group-id="3281753862-7">]</span><span class="p" data-group-id="3281753862-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">length</span><span class="p" data-group-id="2044331698-8">(</span><span class="p" data-group-id="2044331698-9">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2044331698-9">]</span><span class="p" data-group-id="2044331698-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="2044331698-10">(</span><span class="n">T</span><span class="p" data-group-id="2044331698-10">)</span><span class="p">.</span><span class="w"> </span><span class="c1">%% Calls the local function length/1</span><span class="w">
│ │ │ │ +</span><span class="nf">length</span><span class="p" data-group-id="3281753862-8">(</span><span class="p" data-group-id="3281753862-9">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3281753862-9">]</span><span class="p" data-group-id="3281753862-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="3281753862-10">(</span><span class="n">T</span><span class="p" data-group-id="3281753862-10">)</span><span class="p">.</span><span class="w"> </span><span class="c1">%% Calls the local function length/1</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="2044331698-11">(</span><span class="n">X</span><span class="p" data-group-id="2044331698-11">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="2044331698-12">(</span><span class="n">X</span><span class="p" data-group-id="2044331698-12">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="3281753862-11">(</span><span class="n">X</span><span class="p" data-group-id="3281753862-11">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="3281753862-12">(</span><span class="n">X</span><span class="p" data-group-id="3281753862-12">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ │                                    </span><span class="c1">%% which is allowed in guards</span><span class="w">
│ │ │ │      </span><span class="ss">long</span><span class="p">.</span></code></pre><p>The same logic applies to explicitly imported functions from other modules, as
│ │ │ │  to locally defined functions. It is not allowed to both import a function from
│ │ │ │ -another module and have the function declared in the module at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6617817641-1">(</span><span class="p" data-group-id="6617817641-2">[</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6617817641-2">]</span><span class="p" data-group-id="6617817641-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +another module and have the function declared in the module at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2723750877-1">(</span><span class="p" data-group-id="2723750877-2">[</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2723750877-2">]</span><span class="p" data-group-id="2723750877-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="6617817641-3">(</span><span class="p" data-group-id="6617817641-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="6617817641-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6617817641-5">]</span><span class="p" data-group-id="6617817641-4">}</span><span class="p" data-group-id="6617817641-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="2723750877-3">(</span><span class="p" data-group-id="2723750877-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="2723750877-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2723750877-5">]</span><span class="p" data-group-id="2723750877-4">}</span><span class="p" data-group-id="2723750877-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="6617817641-6">(</span><span class="ss">mod</span><span class="p">,</span><span class="p" data-group-id="6617817641-7">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6617817641-7">]</span><span class="p" data-group-id="6617817641-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="2723750877-6">(</span><span class="ss">mod</span><span class="p">,</span><span class="p" data-group-id="2723750877-7">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2723750877-7">]</span><span class="p" data-group-id="2723750877-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="6617817641-8">(</span><span class="n">X</span><span class="p" data-group-id="6617817641-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="6617817641-9">(</span><span class="n">X</span><span class="p" data-group-id="6617817641-9">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">33</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="2723750877-8">(</span><span class="n">X</span><span class="p" data-group-id="2723750877-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="2723750877-9">(</span><span class="n">X</span><span class="p" data-group-id="2723750877-9">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">33</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ │                                     </span><span class="c1">%% which is allowed in guards</span><span class="w">
│ │ │ │  
│ │ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="6617817641-10">(</span><span class="n">X</span><span class="p" data-group-id="6617817641-10">)</span><span class="p">;</span><span class="w">              </span><span class="c1">%% Explicit call to erlang:length in body</span><span class="w">
│ │ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="2723750877-10">(</span><span class="n">X</span><span class="p" data-group-id="2723750877-10">)</span><span class="p">;</span><span class="w">              </span><span class="c1">%% Explicit call to erlang:length in body</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="6617817641-11">(</span><span class="n">X</span><span class="p" data-group-id="6617817641-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">length</span><span class="p" data-group-id="6617817641-12">(</span><span class="n">X</span><span class="p" data-group-id="6617817641-12">)</span><span class="p">.</span><span class="w">                     </span><span class="c1">%% mod:length/1 is called</span></code></pre><p>For auto-imported BIFs added in Erlang/OTP R14A and thereafter, overriding the
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="2723750877-11">(</span><span class="n">X</span><span class="p" data-group-id="2723750877-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">length</span><span class="p" data-group-id="2723750877-12">(</span><span class="n">X</span><span class="p" data-group-id="2723750877-12">)</span><span class="p">.</span><span class="w">                     </span><span class="c1">%% mod:length/1 is called</span></code></pre><p>For auto-imported BIFs added in Erlang/OTP R14A and thereafter, overriding the
│ │ │ │  name with a local function or explicit import is always allowed. However, if the
│ │ │ │  <code class="inline">-compile({no_auto_import,[F/A])</code> directive is not used, the compiler issues a
│ │ │ │  warning whenever the function is called in the module using the implicitly
│ │ │ │  qualified function name.</p><h2 id="if" class="section-heading">
│ │ │ │    <a href="#if" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -266,40 +266,40 @@
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="n">GuardSeqN</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>The branches of an <code class="inline">if</code>-expression are scanned sequentially until a guard
│ │ │ │  sequence <code class="inline">GuardSeq</code> that evaluates to true is found. Then the corresponding
│ │ │ │  <code class="inline">Body</code> (a sequence of expressions separated by <code class="inline">,</code>) is evaluated.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">if</code> expression.</p><p>If no guard sequence is evaluated as true, an <code class="inline">if_clause</code> run-time error occurs.
│ │ │ │  If necessary, the guard expression <code class="inline">true</code> can be used in the last branch, as
│ │ │ │ -that guard sequence is always true.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_greater_than</span><span class="p" data-group-id="2949345143-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2949345143-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +that guard sequence is always true.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_greater_than</span><span class="p" data-group-id="5034370725-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5034370725-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% works as an &#39;else&#39; branch</span><span class="w">
│ │ │ │              </span><span class="ss">false</span><span class="w">
│ │ │ │      </span><span class="k">end</span></code></pre><h2 id="case" class="section-heading">
│ │ │ │    <a href="#case" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Case</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">Expr</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="7703529590-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="7703529590-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="3524254739-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="3524254739-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="7703529590-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="7703529590-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="3524254739-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="3524254739-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>The expression <code class="inline">Expr</code> is evaluated and the patterns <code class="inline">Pattern</code> are sequentially
│ │ │ │  matched against the result. If a match succeeds and the optional guard sequence
│ │ │ │  <code class="inline">GuardSeq</code> is true, the corresponding <code class="inline">Body</code> is evaluated.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">case</code> expression.</p><p>If there is no matching pattern with a true guard sequence, a <code class="inline">case_clause</code>
│ │ │ │ -run-time error occurs.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_valid_signal</span><span class="p" data-group-id="1111699358-1">(</span><span class="n">Signal</span><span class="p" data-group-id="1111699358-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +run-time error occurs.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_valid_signal</span><span class="p" data-group-id="9727478302-1">(</span><span class="n">Signal</span><span class="p" data-group-id="9727478302-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Signal</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1111699358-2">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="1111699358-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9727478302-2">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="9727478302-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1111699358-3">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="1111699358-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9727478302-3">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="9727478302-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">_</span><span class="n">Else</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">false</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="maybe" class="section-heading">
│ │ │ │    <a href="#maybe" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -317,57 +317,57 @@
│ │ │ │  the top-level of a <code class="inline">maybe</code> block. It matches the pattern <code class="inline">Expr1</code> against
│ │ │ │  <code class="inline">Expr2</code>. If the matching succeeds, any unbound variable in the pattern becomes
│ │ │ │  bound. If the expression is the last expression in the <code class="inline">maybe</code> block, it also
│ │ │ │  returns the value of <code class="inline">Expr2</code>. If the matching is unsuccessful, the rest of the
│ │ │ │  expressions in the <code class="inline">maybe</code> block are skipped and the return value of the <code class="inline">maybe</code>
│ │ │ │  block is <code class="inline">Expr2</code>.</p><p>None of the variables bound in a <code class="inline">maybe</code> block must be used in the code that
│ │ │ │  follows the block.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8786181507-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="8786181507-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="8786181507-2">(</span><span class="p" data-group-id="8786181507-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4388248555-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="4388248555-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="4388248555-2">(</span><span class="p" data-group-id="4388248555-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8786181507-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="8786181507-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="8786181507-4">(</span><span class="p" data-group-id="8786181507-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4388248555-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4388248555-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="4388248555-4">(</span><span class="p" data-group-id="4388248555-4">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>Let us first assume that <code class="inline">a()</code> returns <code class="inline">{ok,42}</code> and <code class="inline">b()</code> returns <code class="inline">{ok,58}</code>.
│ │ │ │  With those return values, all of the match operators will succeed, and the
│ │ │ │  return value of the <code class="inline">maybe</code> block is <code class="inline">A + B</code>, which is equal to <code class="inline">42 + 58 = 100</code>.</p><p>Now let us assume that <code class="inline">a()</code> returns <code class="inline">error</code>. The conditional match operator in
│ │ │ │  <code class="inline">{ok, A} ?= a()</code> fails to match, and the return value of the <code class="inline">maybe</code> block is
│ │ │ │  the value of the expression that failed to match, namely <code class="inline">error</code>. Similarly, if
│ │ │ │  <code class="inline">b()</code> returns <code class="inline">wrong</code>, the return value of the <code class="inline">maybe</code> block is <code class="inline">wrong</code>.</p><p>Finally, let us assume that <code class="inline">a()</code> returns <code class="inline">{ok,-1}</code>. Because <code class="inline">true = A &gt;= 0</code> uses
│ │ │ │  the match operator <code class="inline">=</code>, a <code class="inline">{badmatch,false}</code> run-time error occurs when the
│ │ │ │ -expression fails to match the pattern.</p><p>The example can be written in a less succient way using nested case expressions:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="7711062023-1">(</span><span class="p" data-group-id="7711062023-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7711062023-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="7711062023-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +expression fails to match the pattern.</p><p>The example can be written in a less succient way using nested case expressions:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="6382687347-1">(</span><span class="p" data-group-id="6382687347-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6382687347-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="6382687347-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="7711062023-3">(</span><span class="p" data-group-id="7711062023-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="7711062023-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="7711062023-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="6382687347-3">(</span><span class="p" data-group-id="6382687347-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="6382687347-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="6382687347-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="n">Other1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Other1</span><span class="w">
│ │ │ │          </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="n">Other2</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Other2</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">maybe</code> block can be augmented with <code class="inline">else</code> clauses:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │ │      </span><span class="n">Expr1</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">ExprN</span><span class="w">
│ │ │ │  </span><span class="k">else</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="4914851413-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="4914851413-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="5991105369-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="5991105369-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="4914851413-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="4914851413-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="5991105369-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="5991105369-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>If a conditional match operator fails, the failed expression is matched against
│ │ │ │  the patterns in all clauses between the <code class="inline">else</code> and <code class="inline">end</code> keywords. If a match
│ │ │ │  succeeds and the optional guard sequence <code class="inline">GuardSeq</code> is true, the corresponding
│ │ │ │  <code class="inline">Body</code> is evaluated. The value returned from the body is the return value of the
│ │ │ │  <code class="inline">maybe</code> block.</p><p>If there is no matching pattern with a true guard sequence, an <code class="inline">else_clause</code>
│ │ │ │  run-time error occurs.</p><p>None of the variables bound in a <code class="inline">maybe</code> block must be used in the <code class="inline">else</code>
│ │ │ │  clauses. None of the variables bound in the <code class="inline">else</code> clauses must be used in the
│ │ │ │  code that follows the <code class="inline">maybe</code> block.</p><p>Here is the previous example augmented with <code class="inline">else</code> clauses:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4405062676-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="4405062676-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="4405062676-2">(</span><span class="p" data-group-id="4405062676-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9311142657-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="9311142657-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="9311142657-2">(</span><span class="p" data-group-id="9311142657-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4405062676-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4405062676-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="4405062676-4">(</span><span class="p" data-group-id="4405062676-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9311142657-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9311142657-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="9311142657-4">(</span><span class="p" data-group-id="9311142657-4">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="w">
│ │ │ │  </span><span class="k">else</span><span class="w">
│ │ │ │      </span><span class="ss">error</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="ss">wrong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">else</code> clauses translate the failing value from the conditional match
│ │ │ │  operators to the value <code class="inline">error</code>. If the failing value is not one of the
│ │ │ │  recognized values, a <code class="inline">else_clause</code> run-time error occurs.</p><h2 id="send" class="section-heading">
│ │ │ │ @@ -386,75 +386,75 @@
│ │ │ │  <code class="inline">{Name,Node}</code> (or a pid located at another node), also never fails.</li></ul><h2 id="receive" class="section-heading">
│ │ │ │    <a href="#receive" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Receive</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="9634893136-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9634893136-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="2228485963-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="2228485963-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="9634893136-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="9634893136-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="2228485963-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="2228485963-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>Fetches a received message present in the message queue of the process. The
│ │ │ │  first message in the message queue is matched sequentially against the patterns
│ │ │ │  from top to bottom. If no match was found, the matching sequence is repeated for
│ │ │ │  the second message in the queue, and so on. Messages are queued in the
│ │ │ │  <a href="ref_man_processes.xhtml#message-queue-order">order they were received</a>. If a match
│ │ │ │  succeeds, that is, if the <code class="inline">Pattern</code> matches and the optional guard sequence
│ │ │ │  <code class="inline">GuardSeq</code> is true, then the message is removed from the message queue and the
│ │ │ │  corresponding <code class="inline">Body</code> is evaluated. All other messages in the message queue
│ │ │ │  remain unchanged.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">receive</code> expression.</p><p><code class="inline">receive</code> never fails. The execution is suspended, possibly indefinitely, until
│ │ │ │  a message arrives that matches one of the patterns and with a true guard
│ │ │ │ -sequence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="4060891245-1">(</span><span class="p" data-group-id="4060891245-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +sequence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="9425134694-1">(</span><span class="p" data-group-id="9425134694-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">onhook</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="4060891245-2">(</span><span class="p" data-group-id="4060891245-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">idle</span><span class="p" data-group-id="4060891245-3">(</span><span class="p" data-group-id="4060891245-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4060891245-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4060891245-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4060891245-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4060891245-6">(</span><span class="p" data-group-id="4060891245-6">)</span><span class="p" data-group-id="4060891245-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="4060891245-7">(</span><span class="p" data-group-id="4060891245-7">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="9425134694-2">(</span><span class="p" data-group-id="9425134694-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">idle</span><span class="p" data-group-id="9425134694-3">(</span><span class="p" data-group-id="9425134694-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9425134694-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9425134694-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9425134694-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9425134694-6">(</span><span class="p" data-group-id="9425134694-6">)</span><span class="p" data-group-id="9425134694-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="9425134694-7">(</span><span class="p" data-group-id="9425134694-7">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">receive</code> expression can be augmented with a timeout:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="4270608193-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="4270608193-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="7309628888-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="7309628888-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="4270608193-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="4270608193-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="7309628888-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="7309628888-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">after</span><span class="w">
│ │ │ │      </span><span class="n">ExprT</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyT</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p><code class="inline">receive...after</code> works exactly as <code class="inline">receive</code>, except that if no matching message
│ │ │ │  has arrived within <code class="inline">ExprT</code> milliseconds, then <code class="inline">BodyT</code> is evaluated instead. The
│ │ │ │  return value of <code class="inline">BodyT</code> then becomes the return value of the <code class="inline">receive...after</code>
│ │ │ │  expression. <code class="inline">ExprT</code> is to evaluate to an integer, or the atom <code class="inline">infinity</code>. The
│ │ │ │  allowed integer range is from 0 to 4294967295, that is, the longest possible
│ │ │ │  timeout is almost 50 days. With a zero value the timeout occurs immediately if
│ │ │ │  there is no matching message in the message queue.</p><p>The atom <code class="inline">infinity</code> will make the process wait indefinitely for a matching
│ │ │ │  message. This is the same as not using a timeout. It can be useful for timeout
│ │ │ │ -values that are calculated at runtime.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="2016602068-1">(</span><span class="p" data-group-id="2016602068-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +values that are calculated at runtime.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="9616452737-1">(</span><span class="p" data-group-id="9616452737-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">onhook</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="2016602068-2">(</span><span class="p" data-group-id="2016602068-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">idle</span><span class="p" data-group-id="2016602068-3">(</span><span class="p" data-group-id="2016602068-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2016602068-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2016602068-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2016602068-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2016602068-6">(</span><span class="p" data-group-id="2016602068-6">)</span><span class="p" data-group-id="2016602068-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="2016602068-7">(</span><span class="p" data-group-id="2016602068-7">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="9616452737-2">(</span><span class="p" data-group-id="9616452737-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">idle</span><span class="p" data-group-id="9616452737-3">(</span><span class="p" data-group-id="9616452737-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9616452737-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9616452737-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9616452737-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9616452737-6">(</span><span class="p" data-group-id="9616452737-6">)</span><span class="p" data-group-id="9616452737-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="9616452737-7">(</span><span class="p" data-group-id="9616452737-7">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w">
│ │ │ │          </span><span class="mi">60000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="2016602068-8">(</span><span class="p" data-group-id="2016602068-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">error</span><span class="p" data-group-id="2016602068-9">(</span><span class="p" data-group-id="2016602068-9">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="9616452737-8">(</span><span class="p" data-group-id="9616452737-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">error</span><span class="p" data-group-id="9616452737-9">(</span><span class="p" data-group-id="9616452737-9">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>It is legal to use a <code class="inline">receive...after</code> expression with no branches:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │  </span><span class="k">after</span><span class="w">
│ │ │ │      </span><span class="n">ExprT</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyT</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>This construction does not consume any messages, only suspends execution in the
│ │ │ │ -process for <code class="inline">ExprT</code> milliseconds. This can be used to implement simple timers.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">timer</span><span class="p" data-group-id="7218237479-1">(</span><span class="p" data-group-id="7218237479-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="7218237479-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7218237479-3">[</span><span class="nf">self</span><span class="p" data-group-id="7218237479-4">(</span><span class="p" data-group-id="7218237479-4">)</span><span class="p" data-group-id="7218237479-3">]</span><span class="p" data-group-id="7218237479-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +process for <code class="inline">ExprT</code> milliseconds. This can be used to implement simple timers.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">timer</span><span class="p" data-group-id="4827452227-1">(</span><span class="p" data-group-id="4827452227-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="4827452227-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4827452227-3">[</span><span class="nf">self</span><span class="p" data-group-id="4827452227-4">(</span><span class="p" data-group-id="4827452227-4">)</span><span class="p" data-group-id="4827452227-3">]</span><span class="p" data-group-id="4827452227-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">timer</span><span class="p" data-group-id="7218237479-5">(</span><span class="n">Pid</span><span class="p" data-group-id="7218237479-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">timer</span><span class="p" data-group-id="4827452227-5">(</span><span class="n">Pid</span><span class="p" data-group-id="4827452227-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w">
│ │ │ │          </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">timeout</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>For more information on timers in Erlang in general, see the
│ │ │ │  <a href="../../../lib/../erts/doc/html/time_correction.xhtml#timers"><em>Timers</em></a> section of the
│ │ │ │  <a href="../../../lib/../erts/doc/html/time_correction.xhtml"><em>Time and Time Correction in Erlang</em></a>
│ │ │ │ @@ -496,21 +496,21 @@
│ │ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ │  4&gt; </span><span class="mf">0.0</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">-</span><span class="mf">0.0</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ │  5&gt; </span><span class="mf">0.0</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">+</span><span class="mf">0.0</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │  6&gt; </span><span class="mi">1</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ │ -7&gt; </span><span class="p" data-group-id="2730346640-1">#{</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2730346640-1">}</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="2730346640-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2730346640-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +7&gt; </span><span class="p" data-group-id="8745105370-1">#{</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8745105370-1">}</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="8745105370-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8745105370-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ │ -8&gt; </span><span class="p" data-group-id="2730346640-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2730346640-3">}</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="p" data-group-id="2730346640-4">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">2.0</span><span class="p" data-group-id="2730346640-4">}</span><span class="p">.</span><span class="w">
│ │ │ │ +8&gt; </span><span class="p" data-group-id="8745105370-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8745105370-3">}</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="p" data-group-id="8745105370-4">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">2.0</span><span class="p" data-group-id="8745105370-4">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -9&gt; </span><span class="p" data-group-id="2730346640-5">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="2730346640-5">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="2730346640-6">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="2730346640-6">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +9&gt; </span><span class="p" data-group-id="8745105370-5">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="8745105370-5">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="8745105370-6">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="8745105370-6">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -10&gt; </span><span class="p" data-group-id="2730346640-7">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="2730346640-7">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="2730346640-8">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="2730346640-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +10&gt; </span><span class="p" data-group-id="8745105370-7">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="8745105370-7">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="8745105370-8">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="8745105370-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Prior to OTP 27, the term equivalence operators considered <code class="inline">0.0</code>
│ │ │ │  and <code class="inline">-0.0</code> to be the same term.</p><p>This was changed in OTP 27 but legacy code may have expected them to be
│ │ │ │  considered the same. To help users catch errors that may arise from an
│ │ │ │  upgrade, the compiler raises a warning when <code class="inline">0.0</code> is pattern-matched or used
│ │ │ │  in a term equivalence test.</p><p>If you need to match <code class="inline">0.0</code> specifically, the warning can be silenced by
│ │ │ │  writing <code class="inline">+0.0</code> instead, which produces the same term but makes the compiler
│ │ │ │  interpret the match as being done on purpose.</p></section><h2 id="arithmetic-expressions" class="section-heading">
│ │ │ │ @@ -536,15 +536,15 @@
│ │ │ │  </span><span class="mi">0</span><span class="gp unselectable">
│ │ │ │  8&gt; </span><span class="mi">2#10</span><span class="w"> </span><span class="ow">bor</span><span class="w"> </span><span class="mi">2#01</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ │  9&gt; </span><span class="ss">a</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">10</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: an error occurred when evaluating an arithmetic expression
│ │ │ │       in operator  +/2
│ │ │ │          called as a + 10</span><span class="gp unselectable">
│ │ │ │ -10&gt; </span><span class="mi">1</span><span class="w"> </span><span class="nf">bsl</span><span class="w"> </span><span class="p" data-group-id="7728523993-1">(</span><span class="mi">1</span><span class="w"> </span><span class="ow">bsl</span><span class="w"> </span><span class="mi">64</span><span class="p" data-group-id="7728523993-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +10&gt; </span><span class="mi">1</span><span class="w"> </span><span class="nf">bsl</span><span class="w"> </span><span class="p" data-group-id="9368962795-1">(</span><span class="mi">1</span><span class="w"> </span><span class="ow">bsl</span><span class="w"> </span><span class="mi">64</span><span class="p" data-group-id="9368962795-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: a system limit has been reached
│ │ │ │       in operator  bsl/2
│ │ │ │          called as 1 bsl 18446744073709551616</span></code></pre><h2 id="boolean-expressions" class="section-heading">
│ │ │ │    <a href="#boolean-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Boolean Expressions</span>
│ │ │ │ @@ -563,136 +563,136 @@
│ │ │ │    <a href="#short-circuit-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Short-Circuit Expressions</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="n">Expr1</span><span class="w"> </span><span class="ow">orelse</span><span class="w"> </span><span class="n">Expr2</span><span class="w">
│ │ │ │  </span><span class="n">Expr1</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">Expr2</span></code></pre><p><code class="inline">Expr2</code> is evaluated only if necessary. That is, <code class="inline">Expr2</code> is evaluated only if:</p><ul><li><code class="inline">Expr1</code> evaluates to <code class="inline">false</code> in an <code class="inline">orelse</code> expression.</li></ul><p>or</p><ul><li><code class="inline">Expr1</code> evaluates to <code class="inline">true</code> in an <code class="inline">andalso</code> expression.</li></ul><p>Returns either the value of <code class="inline">Expr1</code> (that is, <code class="inline">true</code> or <code class="inline">false</code>) or the value of
│ │ │ │ -<code class="inline">Expr2</code> (if <code class="inline">Expr2</code> is evaluated).</p><p><em>Example 1:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="o">-</span><span class="mf">1.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nc">math</span><span class="p">:</span><span class="nf">sqrt</span><span class="p" data-group-id="1423390515-1">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="1423390515-1">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span></code></pre><p>This works even if <code class="inline">A</code> is less than <code class="inline">-1.0</code>, since in that case, <a href="../../../lib/stdlib/doc/html/math.html#sqrt/1"><code class="inline">math:sqrt/1</code></a> is
│ │ │ │ -never evaluated.</p><p><em>Example 2:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">OnlyOne</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">is_atom</span><span class="p" data-group-id="9932890855-1">(</span><span class="n">L</span><span class="p" data-group-id="9932890855-1">)</span><span class="w"> </span><span class="nf">orelse</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="9932890855-2">(</span><span class="nf">is_list</span><span class="p" data-group-id="9932890855-3">(</span><span class="n">L</span><span class="p" data-group-id="9932890855-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9932890855-4">(</span><span class="n">L</span><span class="p" data-group-id="9932890855-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9932890855-2">)</span><span class="p">,</span></code></pre><p><code class="inline">Expr2</code> is not required to evaluate to a Boolean value. Because of that,
│ │ │ │ -<code class="inline">andalso</code> and <code class="inline">orelse</code> are tail-recursive.</p><p><em>Example 3 (tail-recursive function):</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="9130046024-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9130046024-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="9130046024-2">]</span><span class="p" data-group-id="9130046024-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Pred</span><span class="p" data-group-id="9130046024-3">(</span><span class="n">Hd</span><span class="p" data-group-id="9130046024-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">all</span><span class="p" data-group-id="9130046024-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="9130046024-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">all</span><span class="p" data-group-id="9130046024-5">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9130046024-6">[</span><span class="p" data-group-id="9130046024-6">]</span><span class="p" data-group-id="9130046024-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +<code class="inline">Expr2</code> (if <code class="inline">Expr2</code> is evaluated).</p><p><em>Example 1:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="o">-</span><span class="mf">1.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nc">math</span><span class="p">:</span><span class="nf">sqrt</span><span class="p" data-group-id="1310086619-1">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="1310086619-1">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span></code></pre><p>This works even if <code class="inline">A</code> is less than <code class="inline">-1.0</code>, since in that case, <a href="../../../lib/stdlib/doc/html/math.html#sqrt/1"><code class="inline">math:sqrt/1</code></a> is
│ │ │ │ +never evaluated.</p><p><em>Example 2:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">OnlyOne</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">is_atom</span><span class="p" data-group-id="7053063163-1">(</span><span class="n">L</span><span class="p" data-group-id="7053063163-1">)</span><span class="w"> </span><span class="nf">orelse</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="7053063163-2">(</span><span class="nf">is_list</span><span class="p" data-group-id="7053063163-3">(</span><span class="n">L</span><span class="p" data-group-id="7053063163-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7053063163-4">(</span><span class="n">L</span><span class="p" data-group-id="7053063163-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7053063163-2">)</span><span class="p">,</span></code></pre><p><code class="inline">Expr2</code> is not required to evaluate to a Boolean value. Because of that,
│ │ │ │ +<code class="inline">andalso</code> and <code class="inline">orelse</code> are tail-recursive.</p><p><em>Example 3 (tail-recursive function):</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="1782740061-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1782740061-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="1782740061-2">]</span><span class="p" data-group-id="1782740061-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pred</span><span class="p" data-group-id="1782740061-3">(</span><span class="n">Hd</span><span class="p" data-group-id="1782740061-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">all</span><span class="p" data-group-id="1782740061-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1782740061-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">all</span><span class="p" data-group-id="1782740061-5">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1782740061-6">[</span><span class="p" data-group-id="1782740061-6">]</span><span class="p" data-group-id="1782740061-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">true</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R13A, <code class="inline">Expr2</code> was required to evaluate to a Boolean value,
│ │ │ │  and as consequence, <code class="inline">andalso</code> and <code class="inline">orelse</code> were <strong>not</strong> tail-recursive.</p></section><h2 id="list-operations" class="section-heading">
│ │ │ │    <a href="#list-operations" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">List Operations</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="n">Expr1</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Expr2</span><span class="w">
│ │ │ │  </span><span class="n">Expr1</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="n">Expr2</span></code></pre><p>The list concatenation operator <code class="inline">++</code> appends its second argument to its first
│ │ │ │  and returns the resulting list.</p><p>The list subtraction operator <code class="inline">--</code> produces a list that is a copy of the first
│ │ │ │  argument. The procedure is as follows: for each element in the second argument,
│ │ │ │ -the first occurrence of this element (if any) is removed.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2839665094-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2839665094-1">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2839665094-2">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2839665094-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2839665094-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2839665094-3">]</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="2839665094-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2839665094-4">]</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="p" data-group-id="2839665094-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2839665094-5">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2839665094-6">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2839665094-6">]</span></code></pre><h2 id="map-expressions" class="section-heading">
│ │ │ │ +the first occurrence of this element (if any) is removed.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2658048627-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2658048627-1">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2658048627-2">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2658048627-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2658048627-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2658048627-3">]</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="2658048627-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2658048627-4">]</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="p" data-group-id="2658048627-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2658048627-5">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2658048627-6">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2658048627-6">]</span></code></pre><h2 id="map-expressions" class="section-heading">
│ │ │ │    <a href="#map-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Map Expressions</span>
│ │ │ │  </h2>
│ │ │ │  <h3 id="creating-maps" class="section-heading">
│ │ │ │    <a href="#creating-maps" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating Maps</span>
│ │ │ │  </h3>
│ │ │ │  <p>Constructing a new map is done by letting an expression <code class="inline">K</code> be associated with
│ │ │ │ -another expression <code class="inline">V</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6396012883-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="6396012883-1">}</span></code></pre><p>New maps can include multiple associations at construction by listing every
│ │ │ │ -association:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1266881156-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="1266881156-1">}</span></code></pre><p>An empty map is constructed by not associating any terms with each other:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6316430680-1">#{</span><span class="p" data-group-id="6316430680-1">}</span></code></pre><p>All keys and values in the map are terms. Any expression is first evaluated and
│ │ │ │ +another expression <code class="inline">V</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2424987362-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="2424987362-1">}</span></code></pre><p>New maps can include multiple associations at construction by listing every
│ │ │ │ +association:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0077729831-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="0077729831-1">}</span></code></pre><p>An empty map is constructed by not associating any terms with each other:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3127666991-1">#{</span><span class="p" data-group-id="3127666991-1">}</span></code></pre><p>All keys and values in the map are terms. Any expression is first evaluated and
│ │ │ │  then the resulting terms are used as <em>key</em> and <em>value</em> respectively.</p><p>Keys and values are separated by the <code class="inline">=&gt;</code> arrow and associations are separated
│ │ │ │ -by a comma (<code class="inline">,</code>).</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7439976298-1">#{</span><span class="p" data-group-id="7439976298-1">}</span><span class="p">,</span><span class="w">                 </span><span class="c1">% empty map</span><span class="w">
│ │ │ │ -</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7439976298-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7439976298-3">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7439976298-3">&gt;&gt;</span><span class="p" data-group-id="7439976298-2">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% single association with literals</span><span class="w">
│ │ │ │ -</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7439976298-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7439976298-4">}</span><span class="p">,</span><span class="w">   </span><span class="c1">% multiple associations with literals</span><span class="w">
│ │ │ │ -</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7439976298-5">#{</span><span class="ss">k</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7439976298-6">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="7439976298-6">}</span><span class="p" data-group-id="7439976298-5">}</span><span class="p">,</span><span class="w">       </span><span class="c1">% single association with variables</span><span class="w">
│ │ │ │ -</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7439976298-7">#{</span><span class="p" data-group-id="7439976298-8">{</span><span class="s">&quot;w&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7439976298-8">}</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="7439976298-9">(</span><span class="p" data-group-id="7439976298-9">)</span><span class="p" data-group-id="7439976298-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% compound key associated with an evaluated expression</span></code></pre><p>Here, <code class="inline">A</code> and <code class="inline">B</code> are any expressions and <code class="inline">M0</code> through <code class="inline">M4</code> are the resulting
│ │ │ │ -map terms.</p><p>If two matching keys are declared, the latter key takes precedence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8454001744-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="8454001744-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8454001744-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p" data-group-id="8454001744-2">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="8454001744-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="8454001744-3">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8454001744-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="8454001744-4">}</span></code></pre><p>The order in which the expressions constructing the keys (and their associated
│ │ │ │ +by a comma (<code class="inline">,</code>).</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5290212500-1">#{</span><span class="p" data-group-id="5290212500-1">}</span><span class="p">,</span><span class="w">                 </span><span class="c1">% empty map</span><span class="w">
│ │ │ │ +</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5290212500-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5290212500-3">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5290212500-3">&gt;&gt;</span><span class="p" data-group-id="5290212500-2">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% single association with literals</span><span class="w">
│ │ │ │ +</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5290212500-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="5290212500-4">}</span><span class="p">,</span><span class="w">   </span><span class="c1">% multiple associations with literals</span><span class="w">
│ │ │ │ +</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5290212500-5">#{</span><span class="ss">k</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5290212500-6">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="5290212500-6">}</span><span class="p" data-group-id="5290212500-5">}</span><span class="p">,</span><span class="w">       </span><span class="c1">% single association with variables</span><span class="w">
│ │ │ │ +</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5290212500-7">#{</span><span class="p" data-group-id="5290212500-8">{</span><span class="s">&quot;w&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5290212500-8">}</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="5290212500-9">(</span><span class="p" data-group-id="5290212500-9">)</span><span class="p" data-group-id="5290212500-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% compound key associated with an evaluated expression</span></code></pre><p>Here, <code class="inline">A</code> and <code class="inline">B</code> are any expressions and <code class="inline">M0</code> through <code class="inline">M4</code> are the resulting
│ │ │ │ +map terms.</p><p>If two matching keys are declared, the latter key takes precedence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5450926955-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="5450926955-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5450926955-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p" data-group-id="5450926955-2">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="5450926955-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="5450926955-3">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5450926955-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="5450926955-4">}</span></code></pre><p>The order in which the expressions constructing the keys (and their associated
│ │ │ │  values) are evaluated is not defined. The syntactic order of the key-value pairs
│ │ │ │  in the construction is of no relevance, except in the recently mentioned case of
│ │ │ │  two matching keys.</p><h3 id="updating-maps" class="section-heading">
│ │ │ │    <a href="#updating-maps" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Updating Maps</span>
│ │ │ │  </h3>
│ │ │ │  <p>Updating a map has a similar syntax as constructing it.</p><p>An expression defining the map to be updated is put in front of the expression
│ │ │ │ -defining the keys to be updated and their respective values:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="7351408809-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="7351408809-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map and <code class="inline">K</code> and <code class="inline">V</code> are any expression.</p><p>If key <code class="inline">K</code> does not match any existing key in the map, a new association is
│ │ │ │ +defining the keys to be updated and their respective values:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="2962230864-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="2962230864-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map and <code class="inline">K</code> and <code class="inline">V</code> are any expression.</p><p>If key <code class="inline">K</code> does not match any existing key in the map, a new association is
│ │ │ │  created from key <code class="inline">K</code> to value <code class="inline">V</code>.</p><p>If key <code class="inline">K</code> matches an existing key in map <code class="inline">M</code>, its associated value is replaced
│ │ │ │  by the new value <code class="inline">V</code>. In both cases, the evaluated map expression returns a new
│ │ │ │ -map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p>To only update an existing value, the following syntax is used:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="4964005259-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="4964005259-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map, <code class="inline">V</code> is an expression and <code class="inline">K</code> is an expression
│ │ │ │ +map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p>To only update an existing value, the following syntax is used:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="2312274847-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="2312274847-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map, <code class="inline">V</code> is an expression and <code class="inline">K</code> is an expression
│ │ │ │  that evaluates to an existing key in <code class="inline">M</code>.</p><p>If key <code class="inline">K</code> does not match any existing keys in map <code class="inline">M</code>, an exception of type
│ │ │ │  <code class="inline">badkey</code> is raised at runtime. If a matching key <code class="inline">K</code> is present in map <code class="inline">M</code>,
│ │ │ │  its associated value is replaced by the new value <code class="inline">V</code>, and the evaluated map
│ │ │ │ -expression returns a new map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1021363816-1">#{</span><span class="p" data-group-id="1021363816-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M0</span><span class="p" data-group-id="1021363816-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1021363816-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="1021363816-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1021363816-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M2</span><span class="p" data-group-id="1021363816-4">#{</span><span class="s">&quot;function&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1021363816-5">(</span><span class="p" data-group-id="1021363816-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="1021363816-6">(</span><span class="p" data-group-id="1021363816-6">)</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="1021363816-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M3</span><span class="p" data-group-id="1021363816-7">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1021363816-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% &#39;a&#39; and &#39;b&#39; was added in `M1` and `M2`.</span></code></pre><p>Here <code class="inline">M0</code> is any map. It follows that <code class="inline">M1</code> through <code class="inline">M4</code> are maps as well.</p><p><em>More examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7544357267-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="7544357267-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7544357267-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="p" data-group-id="7544357267-2">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="n">M</span><span class="p" data-group-id="7544357267-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7544357267-3">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7544357267-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7544357267-4">}</span><span class="p">.</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="n">M</span><span class="p" data-group-id="7544357267-5">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7544357267-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7544357267-6">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7544357267-6">}</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="n">M</span><span class="p" data-group-id="7544357267-7">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7544357267-7">}</span><span class="p">.</span><span class="w">
│ │ │ │ +expression returns a new map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8297216536-1">#{</span><span class="p" data-group-id="8297216536-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M0</span><span class="p" data-group-id="8297216536-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8297216536-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="8297216536-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8297216536-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M2</span><span class="p" data-group-id="8297216536-4">#{</span><span class="s">&quot;function&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="8297216536-5">(</span><span class="p" data-group-id="8297216536-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="8297216536-6">(</span><span class="p" data-group-id="8297216536-6">)</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="8297216536-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M3</span><span class="p" data-group-id="8297216536-7">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8297216536-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% &#39;a&#39; and &#39;b&#39; was added in `M1` and `M2`.</span></code></pre><p>Here <code class="inline">M0</code> is any map. It follows that <code class="inline">M1</code> through <code class="inline">M4</code> are maps as well.</p><p><em>More examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1742363323-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="1742363323-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1742363323-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="p" data-group-id="1742363323-2">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="n">M</span><span class="p" data-group-id="1742363323-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1742363323-3">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1742363323-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1742363323-4">}</span><span class="p">.</span><span class="gp unselectable">
│ │ │ │ +3&gt; </span><span class="n">M</span><span class="p" data-group-id="1742363323-5">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1742363323-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1742363323-6">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1742363323-6">}</span><span class="gp unselectable">
│ │ │ │ +4&gt; </span><span class="n">M</span><span class="p" data-group-id="1742363323-7">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1742363323-7">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: bad argument</span></code></pre><p>As in construction, the order in which the key and value expressions are
│ │ │ │  evaluated is not defined. The syntactic order of the key-value pairs in the
│ │ │ │  update is of no relevance, except in the case where two keys match. In that
│ │ │ │  case, the latter value is used.</p><h3 id="maps-in-patterns" class="section-heading">
│ │ │ │    <a href="#maps-in-patterns" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Maps in Patterns</span>
│ │ │ │  </h3>
│ │ │ │ -<p>Matching of key-value associations from maps is done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1657822299-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="1657822299-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here <code class="inline">M</code> is any map. The key <code class="inline">K</code> must be a
│ │ │ │ +<p>Matching of key-value associations from maps is done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3217279561-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="3217279561-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here <code class="inline">M</code> is any map. The key <code class="inline">K</code> must be a
│ │ │ │  <a href="expressions.xhtml#guard-expressions">guard expression</a>, with all variables already
│ │ │ │  bound. <code class="inline">V</code> can be any pattern with either bound or unbound variables.</p><p>If the variable <code class="inline">V</code> is unbound, it becomes bound to the value associated with
│ │ │ │  the key <code class="inline">K</code>, which must exist in the map <code class="inline">M</code>. If the variable <code class="inline">V</code> is bound, it
│ │ │ │  must match the value associated with <code class="inline">K</code> in <code class="inline">M</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 23, the expression defining the key <code class="inline">K</code> was restricted to be
│ │ │ │ -either a single variable or a literal.</p></section><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7499447108-1">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7499447108-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7499447108-2">}</span><span class="p" data-group-id="7499447108-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7499447108-3">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7499447108-4">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7499447108-4">}</span><span class="p" data-group-id="7499447108-3">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="7499447108-5">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="7499447108-6">{</span><span class="mi">1</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="7499447108-6">}</span><span class="p" data-group-id="7499447108-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7499447108-7">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7499447108-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7499447108-8">}</span><span class="p" data-group-id="7499447108-7">}</span><span class="gp unselectable">
│ │ │ │ +either a single variable or a literal.</p></section><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0598546750-1">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0598546750-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0598546750-2">}</span><span class="p" data-group-id="0598546750-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0598546750-3">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0598546750-4">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0598546750-4">}</span><span class="p" data-group-id="0598546750-3">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="0598546750-5">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="0598546750-6">{</span><span class="mi">1</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="0598546750-6">}</span><span class="p" data-group-id="0598546750-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0598546750-7">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0598546750-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0598546750-8">}</span><span class="p" data-group-id="0598546750-7">}</span><span class="gp unselectable">
│ │ │ │  3&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="mi">2</span><span class="p">.</span></code></pre><p>This binds variable <code class="inline">B</code> to integer <code class="inline">2</code>.</p><p>Similarly, multiple values from the map can be matched:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1837969725-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="1837969725-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here keys <code class="inline">K1</code> through <code class="inline">Kn</code> are any expressions with literals or bound
│ │ │ │ +</span><span class="mi">2</span><span class="p">.</span></code></pre><p>This binds variable <code class="inline">B</code> to integer <code class="inline">2</code>.</p><p>Similarly, multiple values from the map can be matched:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9901539662-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="9901539662-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here keys <code class="inline">K1</code> through <code class="inline">Kn</code> are any expressions with literals or bound
│ │ │ │  variables. If all key expressions evaluate successfully and all keys
│ │ │ │  exist in map <code class="inline">M</code>, all variables in <code class="inline">V1 .. Vn</code> is matched to the
│ │ │ │  associated values of their respective keys.</p><p>If the matching conditions are not met the match fails.</p><p>Note that when matching a map, only the <code class="inline">:=</code> operator (not the <code class="inline">=&gt;</code>) is allowed
│ │ │ │  as a delimiter for the associations.</p><p>The order in which keys are declared in matching has no relevance.</p><p>Duplicate keys are allowed in matching and match each pattern associated to the
│ │ │ │ -keys:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6292537479-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V2</span><span class="p" data-group-id="6292537479-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>The empty map literal (<code class="inline">#{}</code>) matches any map when used as a pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7416849251-1">#{</span><span class="p" data-group-id="7416849251-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>This expression matches if the expression <code class="inline">Expr</code> is of type map, otherwise it
│ │ │ │ -fails with an exception <code class="inline">badmatch</code>.</p><p>Here the key to be retrieved is constructed from an expression:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6884221674-1">#{</span><span class="p" data-group-id="6884221674-2">{</span><span class="ss">tag</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="6884221674-3">(</span><span class="n">List</span><span class="p" data-group-id="6884221674-3">)</span><span class="p" data-group-id="6884221674-2">}</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="6884221674-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map</span></code></pre><p><code class="inline">List</code> must be an already bound variable.</p><h4>Matching Syntax</h4><p>Matching of literals as keys are allowed in function heads:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% only start if not_started</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="9434527572-1">(</span><span class="ss">start</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9434527572-2">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">not_started</span><span class="p" data-group-id="9434527572-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="9434527572-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +keys:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0475540150-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V2</span><span class="p" data-group-id="0475540150-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>The empty map literal (<code class="inline">#{}</code>) matches any map when used as a pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5126029527-1">#{</span><span class="p" data-group-id="5126029527-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>This expression matches if the expression <code class="inline">Expr</code> is of type map, otherwise it
│ │ │ │ +fails with an exception <code class="inline">badmatch</code>.</p><p>Here the key to be retrieved is constructed from an expression:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2363260976-1">#{</span><span class="p" data-group-id="2363260976-2">{</span><span class="ss">tag</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="2363260976-3">(</span><span class="n">List</span><span class="p" data-group-id="2363260976-3">)</span><span class="p" data-group-id="2363260976-2">}</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="2363260976-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map</span></code></pre><p><code class="inline">List</code> must be an already bound variable.</p><h4>Matching Syntax</h4><p>Matching of literals as keys are allowed in function heads:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% only start if not_started</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="8473504955-1">(</span><span class="ss">start</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8473504955-2">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">not_started</span><span class="p" data-group-id="8473504955-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="8473504955-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9434527572-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="9434527572-4">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="9434527572-4">}</span><span class="p" data-group-id="9434527572-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8473504955-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="8473504955-4">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="8473504955-4">}</span><span class="p" data-group-id="8473504955-3">}</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% only change if started</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="9434527572-5">(</span><span class="ss">change</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9434527572-6">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="9434527572-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="9434527572-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="8473504955-5">(</span><span class="ss">change</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8473504955-6">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="8473504955-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="8473504955-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9434527572-7">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="9434527572-8">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">changed</span><span class="p" data-group-id="9434527572-8">}</span><span class="p" data-group-id="9434527572-7">}</span><span class="p">;</span></code></pre><h3 id="maps-in-guards" class="section-heading">
│ │ │ │ +    </span><span class="p" data-group-id="8473504955-7">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="8473504955-8">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">changed</span><span class="p" data-group-id="8473504955-8">}</span><span class="p" data-group-id="8473504955-7">}</span><span class="p">;</span></code></pre><h3 id="maps-in-guards" class="section-heading">
│ │ │ │    <a href="#maps-in-guards" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Maps in Guards</span>
│ │ │ │  </h3>
│ │ │ │  <p>Maps are allowed in guards as long as all subexpressions are valid guard
│ │ │ │  expressions.</p><p>The following guard BIFs handle maps:</p><ul><li><a href="../../../lib/../erts/doc/html/erlang.html#is_map/1">is_map/1</a> in the <code class="inline">erlang</code> module</li><li><a href="../../../lib/../erts/doc/html/erlang.html#is_map_key/2">is_map_key/2</a> in the <code class="inline">erlang</code> module</li><li><a href="../../../lib/../erts/doc/html/erlang.html#map_get/2">map_get/2</a> in the <code class="inline">erlang</code> module</li><li><a href="../../../lib/../erts/doc/html/erlang.html#map_size/1">map_size/1</a> in the <code class="inline">erlang</code> module</li></ul><h2 id="bit-syntax-expressions" class="section-heading">
│ │ │ │    <a href="#bit-syntax-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Bit Syntax Expressions</span>
│ │ │ │  </h2>
│ │ │ │  <p>The bit syntax operates on <em>bit strings</em>. A bit string is a sequence of bits
│ │ │ │ -ordered from the most significant bit to the least significant bit.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3452614096-1">&lt;&lt;</span><span class="p" data-group-id="3452614096-1">&gt;&gt;</span><span class="w">  </span><span class="c1">% The empty bit string, zero length</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3452614096-2">&lt;&lt;</span><span class="n">E1</span><span class="p" data-group-id="3452614096-2">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3452614096-3">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">En</span><span class="p" data-group-id="3452614096-3">&gt;&gt;</span></code></pre><p>Each element <code class="inline">Ei</code> specifies a <em>segment</em> of the bit string. The segments are
│ │ │ │ +ordered from the most significant bit to the least significant bit.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7893884299-1">&lt;&lt;</span><span class="p" data-group-id="7893884299-1">&gt;&gt;</span><span class="w">  </span><span class="c1">% The empty bit string, zero length</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7893884299-2">&lt;&lt;</span><span class="n">E1</span><span class="p" data-group-id="7893884299-2">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7893884299-3">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">En</span><span class="p" data-group-id="7893884299-3">&gt;&gt;</span></code></pre><p>Each element <code class="inline">Ei</code> specifies a <em>segment</em> of the bit string. The segments are
│ │ │ │  ordered left to right from the most significant bit to the least significant bit
│ │ │ │  of the bit string.</p><p>Each segment specification <code class="inline">Ei</code> is a value, whose default type is <code class="inline">integer</code>,
│ │ │ │  followed by an optional <em>size expression</em> and an optional <em>type specifier list</em>.</p><pre><code class="makeup erlang" translate="no"><span class="n">Ei</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │ │       </span><span class="n">Value</span><span class="p">:</span><span class="n">Size</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │ │       </span><span class="n">Value</span><span class="o">/</span><span class="n">TypeSpecifierList</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │ │       </span><span class="n">Value</span><span class="p">:</span><span class="n">Size</span><span class="o">/</span><span class="n">TypeSpecifierList</span></code></pre><p>When used in a bit string construction, <code class="inline">Value</code> is an expression that is to
│ │ │ │  evaluate to an integer, float, or bit string. If the expression is not a single
│ │ │ │ @@ -703,34 +703,34 @@
│ │ │ │  <a href="expressions.xhtml#guard-expressions">guard expression</a> that evaluates to an
│ │ │ │  integer. All variables in the guard expression must be already bound.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable
│ │ │ │  bound to an integer.</p></section><p>The value of <code class="inline">Size</code> specifies the size of the segment in units (see below). The
│ │ │ │  default value depends on the type (see below):</p><ul><li>For <code class="inline">integer</code> it is 8.</li><li>For <code class="inline">float</code> it is 64.</li><li>For <code class="inline">binary</code> and <code class="inline">bitstring</code> it is the whole binary or bit string.</li></ul><p>In matching, the default value for a binary or bit string segment is only valid
│ │ │ │  for the last element. All other bit string or binary elements in the matching
│ │ │ │  must have a size specification.</p><p><a href="" id="binaries"></a></p><p><strong>Binaries</strong></p><p>A bit string with a length that is a multiple of 8 bits is known as a <em>binary</em>,
│ │ │ │  which is the most common and useful type of bit string.</p><p>A binary has a canonical representation in memory. Here follows a sequence of
│ │ │ │ -bytes where each byte's value is its sequence number:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8488241870-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p" data-group-id="8488241870-1">&gt;&gt;</span></code></pre><p>Bit strings are a later generalization of binaries, so many texts and much
│ │ │ │ -information about binaries apply just as well for bit strings.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6594852949-1">&lt;&lt;</span><span class="n">A</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6594852949-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6594852949-2">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="6594852949-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +bytes where each byte's value is its sequence number:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6037726417-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p" data-group-id="6037726417-1">&gt;&gt;</span></code></pre><p>Bit strings are a later generalization of binaries, so many texts and much
│ │ │ │ +information about binaries apply just as well for bit strings.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1039325828-1">&lt;&lt;</span><span class="n">A</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1039325828-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1039325828-2">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="1039325828-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">* 1:3: a binary field without size is only allowed at the end of a binary pattern</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="6594852949-3">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">3</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6594852949-3">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6594852949-4">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="6594852949-4">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6594852949-5">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="6594852949-5">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="1039325828-3">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">3</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1039325828-3">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1039325828-4">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="1039325828-4">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1039325828-5">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="1039325828-5">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │  3&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6594852949-6">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6594852949-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +</span><span class="p" data-group-id="1039325828-6">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="1039325828-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │  4&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6594852949-7">&lt;&lt;</span><span class="s">&quot;de&quot;</span><span class="p" data-group-id="6594852949-7">&gt;&gt;</span></code></pre><p>For the <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code> types, <code class="inline">Size</code> must not be given. The size
│ │ │ │ +</span><span class="p" data-group-id="1039325828-7">&lt;&lt;</span><span class="s">&quot;de&quot;</span><span class="p" data-group-id="1039325828-7">&gt;&gt;</span></code></pre><p>For the <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code> types, <code class="inline">Size</code> must not be given. The size
│ │ │ │  of the segment is implicitly determined by the type and value itself.</p><p><code class="inline">TypeSpecifierList</code> is a list of type specifiers, in any order, separated by
│ │ │ │  hyphens (-). Default values are used for any omitted type specifiers.</p><ul><li><p><strong><code class="inline">Type</code>= <code class="inline">integer</code> | <code class="inline">float</code> | <code class="inline">binary</code> | <code class="inline">bytes</code> | <code class="inline">bitstring</code> | <code class="inline">bits</code> |
│ │ │ │  <code class="inline">utf8</code> | <code class="inline">utf16</code> | <code class="inline">utf32</code></strong> - The default is <code class="inline">integer</code>. <code class="inline">bytes</code> is a
│ │ │ │  shorthand for <code class="inline">binary</code> and <code class="inline">bits</code> is a shorthand for <code class="inline">bitstring</code>. See below
│ │ │ │  for more information about the <code class="inline">utf</code> types.</p></li><li><p><strong><code class="inline">Signedness</code>= <code class="inline">signed</code> | <code class="inline">unsigned</code></strong> - Only matters for matching and when
│ │ │ │  the type is <code class="inline">integer</code>. The default is <code class="inline">unsigned</code>.</p></li><li><p><strong><code class="inline">Endianness</code>= <code class="inline">big</code> | <code class="inline">little</code> | <code class="inline">native</code></strong> - Specifies byte level (octet
│ │ │ │  level) endianness (byte order). Native-endian means that the endianness is
│ │ │ │  resolved at load time to be either big-endian or little-endian, depending on
│ │ │ │  what is native for the CPU that the Erlang machine is run on. Endianness only
│ │ │ │  matters when the <strong>Type</strong> is either <code class="inline">integer</code>, <code class="inline">utf16</code>, <code class="inline">utf32</code>, or <code class="inline">float</code>. The
│ │ │ │ -default is <code class="inline">big</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5098662767-1">&lt;&lt;</span><span class="mi">16#1234</span><span class="p">:</span><span class="mi">16</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="5098662767-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5098662767-2">&lt;&lt;</span><span class="mi">16#3412</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5098662767-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5098662767-3">&lt;&lt;</span><span class="mi">16#34</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">16#12</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="5098662767-3">&gt;&gt;</span></code></pre></li><li><p><strong><code class="inline">Unit</code>= <code class="inline">unit:IntegerLiteral</code></strong> - The allowed range is 1 through 256.
│ │ │ │ +default is <code class="inline">big</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7754361643-1">&lt;&lt;</span><span class="mi">16#1234</span><span class="p">:</span><span class="mi">16</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="7754361643-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7754361643-2">&lt;&lt;</span><span class="mi">16#3412</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7754361643-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7754361643-3">&lt;&lt;</span><span class="mi">16#34</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">16#12</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="7754361643-3">&gt;&gt;</span></code></pre></li><li><p><strong><code class="inline">Unit</code>= <code class="inline">unit:IntegerLiteral</code></strong> - The allowed range is 1 through 256.
│ │ │ │  Defaults to 1 for <code class="inline">integer</code>, <code class="inline">float</code>, and <code class="inline">bitstring</code>, and to 8 for <code class="inline">binary</code>.
│ │ │ │  For types <code class="inline">bitstring</code>, <code class="inline">bits</code>, and <code class="inline">bytes</code>, it is not allowed to specify a
│ │ │ │  unit value different from the default value. No unit specifier must be given
│ │ │ │  for the types <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code>.</p></li></ul><h3 id="integer-segments" class="section-heading">
│ │ │ │    <a href="#integer-segments" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -755,41 +755,41 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Binary segments</span>
│ │ │ │  </h3>
│ │ │ │  <p>In this section, the phrase &quot;binary segment&quot; refers to any one of the segment
│ │ │ │  types <code class="inline">binary</code>, <code class="inline">bitstring</code>, <code class="inline">bytes</code>, and <code class="inline">bits</code>.</p><p>See also the paragraphs about <a href="expressions.xhtml#binaries">Binaries</a>.</p><p>When constructing binaries and no size is specified for a binary segment, the
│ │ │ │  entire binary value is interpolated into the binary being constructed. However,
│ │ │ │  the size in bits of the binary being interpolated must be evenly divisible by
│ │ │ │ -the unit value for the segment; otherwise an exception is raised.</p><p>For example, the following examples all succeed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6408275937-1">&lt;&lt;</span><span class="p" data-group-id="6408275937-2">(</span><span class="p" data-group-id="6408275937-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6408275937-3">&gt;&gt;</span><span class="p" data-group-id="6408275937-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="6408275937-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6408275937-4">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6408275937-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="6408275937-5">&lt;&lt;</span><span class="p" data-group-id="6408275937-6">(</span><span class="p" data-group-id="6408275937-7">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6408275937-7">&gt;&gt;</span><span class="p" data-group-id="6408275937-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6408275937-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6408275937-8">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6408275937-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="p" data-group-id="6408275937-9">&lt;&lt;</span><span class="p" data-group-id="6408275937-10">(</span><span class="p" data-group-id="6408275937-11">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6408275937-11">&gt;&gt;</span><span class="p" data-group-id="6408275937-10">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6408275937-9">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6408275937-12">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6408275937-12">&gt;&gt;</span></code></pre><p>The first two examples have a unit value of 1 for the segment, while the third
│ │ │ │ +the unit value for the segment; otherwise an exception is raised.</p><p>For example, the following examples all succeed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0064004263-1">&lt;&lt;</span><span class="p" data-group-id="0064004263-2">(</span><span class="p" data-group-id="0064004263-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0064004263-3">&gt;&gt;</span><span class="p" data-group-id="0064004263-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="0064004263-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0064004263-4">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0064004263-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="0064004263-5">&lt;&lt;</span><span class="p" data-group-id="0064004263-6">(</span><span class="p" data-group-id="0064004263-7">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0064004263-7">&gt;&gt;</span><span class="p" data-group-id="0064004263-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0064004263-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0064004263-8">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0064004263-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +3&gt; </span><span class="p" data-group-id="0064004263-9">&lt;&lt;</span><span class="p" data-group-id="0064004263-10">(</span><span class="p" data-group-id="0064004263-11">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0064004263-11">&gt;&gt;</span><span class="p" data-group-id="0064004263-10">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0064004263-9">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0064004263-12">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0064004263-12">&gt;&gt;</span></code></pre><p>The first two examples have a unit value of 1 for the segment, while the third
│ │ │ │  segment has a unit value of 8.</p><p>Attempting to interpolate a bit string of size 1 into a binary segment with unit
│ │ │ │ -8 (the default unit for <code class="inline">binary</code>) fails as shown in this example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7156532720-1">&lt;&lt;</span><span class="p" data-group-id="7156532720-2">(</span><span class="p" data-group-id="7156532720-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="7156532720-3">&gt;&gt;</span><span class="p" data-group-id="7156532720-2">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7156532720-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="gt">** exception error: bad argument</span></code></pre><p>For the construction to succeed, the unit value of the segment must be 1:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4386120703-1">&lt;&lt;</span><span class="p" data-group-id="4386120703-2">(</span><span class="p" data-group-id="4386120703-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4386120703-3">&gt;&gt;</span><span class="p" data-group-id="4386120703-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="4386120703-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4386120703-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4386120703-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="p" data-group-id="4386120703-5">&lt;&lt;</span><span class="p" data-group-id="4386120703-6">(</span><span class="p" data-group-id="4386120703-7">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4386120703-7">&gt;&gt;</span><span class="p" data-group-id="4386120703-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4386120703-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4386120703-8">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4386120703-8">&gt;&gt;</span></code></pre><p>Similarly, when matching a binary segment with no size specified, the match
│ │ │ │ +8 (the default unit for <code class="inline">binary</code>) fails as shown in this example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1286526590-1">&lt;&lt;</span><span class="p" data-group-id="1286526590-2">(</span><span class="p" data-group-id="1286526590-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="1286526590-3">&gt;&gt;</span><span class="p" data-group-id="1286526590-2">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1286526590-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gt">** exception error: bad argument</span></code></pre><p>For the construction to succeed, the unit value of the segment must be 1:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="5259058041-1">&lt;&lt;</span><span class="p" data-group-id="5259058041-2">(</span><span class="p" data-group-id="5259058041-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5259058041-3">&gt;&gt;</span><span class="p" data-group-id="5259058041-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="5259058041-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5259058041-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5259058041-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +3&gt; </span><span class="p" data-group-id="5259058041-5">&lt;&lt;</span><span class="p" data-group-id="5259058041-6">(</span><span class="p" data-group-id="5259058041-7">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5259058041-7">&gt;&gt;</span><span class="p" data-group-id="5259058041-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5259058041-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5259058041-8">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5259058041-8">&gt;&gt;</span></code></pre><p>Similarly, when matching a binary segment with no size specified, the match
│ │ │ │  succeeds if and only if the size in bits of the rest of the binary is evenly
│ │ │ │ -divisible by the unit value:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7155173437-1">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7155173437-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7155173437-2">&lt;&lt;</span><span class="s">&quot;&quot;</span><span class="p" data-group-id="7155173437-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7155173437-3">&lt;&lt;</span><span class="p" data-group-id="7155173437-3">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="7155173437-4">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7155173437-4">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7155173437-5">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="7155173437-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +divisible by the unit value:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1115603846-1">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1115603846-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1115603846-2">&lt;&lt;</span><span class="s">&quot;&quot;</span><span class="p" data-group-id="1115603846-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1115603846-3">&lt;&lt;</span><span class="p" data-group-id="1115603846-3">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="1115603846-4">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1115603846-4">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1115603846-5">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="1115603846-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value &lt;&lt;&quot;a&quot;&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="p" data-group-id="7155173437-6">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7155173437-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7155173437-7">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="7155173437-7">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7155173437-8">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="7155173437-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="p" data-group-id="7155173437-9">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7155173437-9">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7155173437-10">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="7155173437-10">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="p" data-group-id="1115603846-6">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1115603846-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1115603846-7">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="1115603846-7">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1115603846-8">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="1115603846-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +4&gt; </span><span class="p" data-group-id="1115603846-9">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1115603846-9">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1115603846-10">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="1115603846-10">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value &lt;&lt;&quot;abc&quot;&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="p" data-group-id="7155173437-11">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7155173437-11">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7155173437-12">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="7155173437-12">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7155173437-13">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="7155173437-13">&gt;&gt;</span></code></pre><p>When a size is explicitly specified for a binary segment, the segment size in
│ │ │ │ +5&gt; </span><span class="p" data-group-id="1115603846-11">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1115603846-11">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1115603846-12">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="1115603846-12">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1115603846-13">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="1115603846-13">&gt;&gt;</span></code></pre><p>When a size is explicitly specified for a binary segment, the segment size in
│ │ │ │  bits is the value of <code class="inline">Size</code> multiplied by the default or explicit unit value.</p><p>When constructing binaries, the size of the binary being interpolated into the
│ │ │ │ -constructed binary must be at least as large as the size of the binary segment.</p><p><strong>Examples:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9035284245-1">&lt;&lt;</span><span class="p" data-group-id="9035284245-2">(</span><span class="p" data-group-id="9035284245-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9035284245-3">&gt;&gt;</span><span class="p" data-group-id="9035284245-2">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9035284245-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9035284245-4">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="9035284245-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="9035284245-5">&lt;&lt;</span><span class="p" data-group-id="9035284245-6">(</span><span class="p" data-group-id="9035284245-7">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="9035284245-7">&gt;&gt;</span><span class="p" data-group-id="9035284245-6">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9035284245-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +constructed binary must be at least as large as the size of the binary segment.</p><p><strong>Examples:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3298048046-1">&lt;&lt;</span><span class="p" data-group-id="3298048046-2">(</span><span class="p" data-group-id="3298048046-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="3298048046-3">&gt;&gt;</span><span class="p" data-group-id="3298048046-2">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3298048046-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3298048046-4">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="3298048046-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="3298048046-5">&lt;&lt;</span><span class="p" data-group-id="3298048046-6">(</span><span class="p" data-group-id="3298048046-7">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="3298048046-7">&gt;&gt;</span><span class="p" data-group-id="3298048046-6">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3298048046-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: construction of binary failed
│ │ │ │          *** segment 1 of type &#39;binary&#39;: the value &lt;&lt;&quot;a&quot;&gt;&gt; is shorter than the size of the segment</span></code></pre><h3 id="unicode-segments" class="section-heading">
│ │ │ │    <a href="#unicode-segments" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Unicode segments</span>
│ │ │ │  </h3>
│ │ │ │ @@ -805,78 +805,78 @@
│ │ │ │  range <code class="inline">0</code> through <code class="inline">16#D7FF</code> or <code class="inline">16#E000</code> through <code class="inline">16#10FFFF</code>. The match fails if the
│ │ │ │  returned value falls outside those ranges.</p><p>A segment of type <code class="inline">utf8</code> matches 1-4 bytes in the bit string, if the bit string
│ │ │ │  at the match position contains a valid UTF-8 sequence. (See RFC-3629 or the
│ │ │ │  Unicode standard.)</p><p>A segment of type <code class="inline">utf16</code> can match 2 or 4 bytes in the bit string. The match
│ │ │ │  fails if the bit string at the match position does not contain a legal UTF-16
│ │ │ │  encoding of a Unicode code point. (See RFC-2781 or the Unicode standard.)</p><p>A segment of type <code class="inline">utf32</code> can match 4 bytes in the bit string in the same way as
│ │ │ │  an <code class="inline">integer</code> segment matches 32 bits. The match fails if the resulting integer
│ │ │ │ -is outside the legal ranges previously mentioned.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5084412251-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5084412251-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5084412251-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5084412251-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="5084412251-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-4">&lt;&lt;</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="5084412251-4">&gt;&gt;</span><span class="w">
│ │ │ │ +is outside the legal ranges previously mentioned.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5322834088-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5322834088-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5322834088-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5322834088-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="5322834088-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-4">&lt;&lt;</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="5322834088-4">&gt;&gt;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5084412251-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5084412251-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-6">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5084412251-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="p" data-group-id="5084412251-7">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5084412251-7">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5084412251-8">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5084412251-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-9">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5084412251-9">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5322834088-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5322834088-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-6">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5322834088-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +4&gt; </span><span class="p" data-group-id="5322834088-7">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5322834088-7">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5322834088-8">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5322834088-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-9">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5322834088-9">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │  5&gt; </span><span class="n">C</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="p" data-group-id="5084412251-10">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="n">E</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="5084412251-10">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5084412251-11">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5084412251-11">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-12">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5084412251-12">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +6&gt; </span><span class="p" data-group-id="5322834088-10">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="n">E</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="5322834088-10">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5322834088-11">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5322834088-11">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-12">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5322834088-12">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │  7&gt; </span><span class="n">D</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">273</span><span class="gp unselectable">
│ │ │ │  8&gt; </span><span class="n">F</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span><span class="gp unselectable">
│ │ │ │ -9&gt; </span><span class="p" data-group-id="5084412251-13">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">H</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5084412251-13">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5084412251-14">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5084412251-14">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-15">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5084412251-15">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +9&gt; </span><span class="p" data-group-id="5322834088-13">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">H</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5322834088-13">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5322834088-14">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5322834088-14">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-15">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5322834088-15">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │  10&gt; </span><span class="n">H</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-16">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5084412251-16">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -11&gt; </span><span class="p" data-group-id="5084412251-17">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">J</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="5084412251-17">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5084412251-18">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="5084412251-18">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-19">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5084412251-19">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-16">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5322834088-16">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +11&gt; </span><span class="p" data-group-id="5322834088-17">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">J</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="5322834088-17">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5322834088-18">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="5322834088-18">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-19">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5322834088-19">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │  12&gt; </span><span class="n">J</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-20">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5084412251-20">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-20">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5322834088-20">&gt;&gt;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">13</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="5084412251-21">&lt;&lt;</span><span class="mi">1024</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="5084412251-21">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-22">&lt;&lt;</span><span class="mi">208</span><span class="p">,</span><span class="mi">128</span><span class="p" data-group-id="5084412251-22">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="mi">13</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="5322834088-21">&lt;&lt;</span><span class="mi">1024</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="5322834088-21">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-22">&lt;&lt;</span><span class="mi">208</span><span class="p">,</span><span class="mi">128</span><span class="p" data-group-id="5322834088-22">&gt;&gt;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">14</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="5084412251-23">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">:</span><span class="mi">7</span><span class="p" data-group-id="5084412251-23">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-24">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="5084412251-24">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -15&gt; </span><span class="p" data-group-id="5084412251-25">&lt;&lt;</span><span class="mi">16#123</span><span class="p">:</span><span class="mi">12</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="5084412251-25">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5084412251-26">&lt;&lt;</span><span class="mi">16#231</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="5084412251-26">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5084412251-27">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5084412251-27">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5084412251-28">&lt;&lt;</span><span class="mi">35</span><span class="p">,</span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5084412251-28">&gt;&gt;</span></code></pre><p>Notice that bit string patterns cannot be nested.</p><p>Notice also that &quot;<code class="inline">B=&lt;&lt;1&gt;&gt;</code>&quot; is interpreted as &quot;<code class="inline">B =&lt; &lt;1&gt;&gt;</code>&quot; which is a syntax
│ │ │ │ +</span><span class="mi">14</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="5322834088-23">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">:</span><span class="mi">7</span><span class="p" data-group-id="5322834088-23">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-24">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="5322834088-24">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +15&gt; </span><span class="p" data-group-id="5322834088-25">&lt;&lt;</span><span class="mi">16#123</span><span class="p">:</span><span class="mi">12</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="5322834088-25">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5322834088-26">&lt;&lt;</span><span class="mi">16#231</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="5322834088-26">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5322834088-27">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5322834088-27">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5322834088-28">&lt;&lt;</span><span class="mi">35</span><span class="p">,</span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5322834088-28">&gt;&gt;</span></code></pre><p>Notice that bit string patterns cannot be nested.</p><p>Notice also that &quot;<code class="inline">B=&lt;&lt;1&gt;&gt;</code>&quot; is interpreted as &quot;<code class="inline">B =&lt; &lt;1&gt;&gt;</code>&quot; which is a syntax
│ │ │ │  error. The correct way is to write a space after <code class="inline">=</code>: &quot;<code class="inline">B = &lt;&lt;1&gt;&gt;</code>.</p><p>More examples are provided in <a href="../../../lib/../system/doc/html/bit_syntax.xhtml">Programming Examples</a>.</p><h2 id="fun-expressions" class="section-heading">
│ │ │ │    <a href="#fun-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Fun Expressions</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">fun</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1820260874-1">[</span><span class="n">Name</span><span class="p" data-group-id="1820260874-1">]</span><span class="p" data-group-id="1820260874-2">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="1820260874-2">)</span><span class="w"> </span><span class="p" data-group-id="1820260874-3">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="1820260874-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2274169122-1">[</span><span class="n">Name</span><span class="p" data-group-id="2274169122-1">]</span><span class="p" data-group-id="2274169122-2">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="2274169122-2">)</span><span class="w"> </span><span class="p" data-group-id="2274169122-3">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="2274169122-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1820260874-4">[</span><span class="n">Name</span><span class="p" data-group-id="1820260874-4">]</span><span class="p" data-group-id="1820260874-5">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="1820260874-5">)</span><span class="w"> </span><span class="p" data-group-id="1820260874-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="1820260874-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2274169122-4">[</span><span class="n">Name</span><span class="p" data-group-id="2274169122-4">]</span><span class="p" data-group-id="2274169122-5">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="2274169122-5">)</span><span class="w"> </span><span class="p" data-group-id="2274169122-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="2274169122-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                </span><span class="n">BodyK</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>A fun expression begins with the keyword <code class="inline">fun</code> and ends with the keyword <code class="inline">end</code>.
│ │ │ │  Between them is to be a function declaration, similar to a
│ │ │ │  <a href="ref_man_functions.xhtml#function-declaration-syntax">regular function declaration</a>,
│ │ │ │  except that the function name is optional and is to be a variable, if any.</p><p>Variables in a fun head shadow the function name and both shadow variables in
│ │ │ │  the function clause surrounding the fun expression. Variables bound in a fun
│ │ │ │ -body are local to the fun body.</p><p>The return value of the expression is the resulting fun.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7973976309-1">(</span><span class="n">X</span><span class="p" data-group-id="7973976309-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +body are local to the fun body.</p><p>The return value of the expression is the resulting fun.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2601145814-1">(</span><span class="n">X</span><span class="p" data-group-id="2601145814-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="7973976309-2">(</span><span class="mi">2</span><span class="p" data-group-id="7973976309-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="2601145814-2">(</span><span class="mi">2</span><span class="p" data-group-id="2601145814-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="n">Fun2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7973976309-3">(</span><span class="n">X</span><span class="p" data-group-id="7973976309-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="o">&gt;=</span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">gt</span><span class="p">;</span><span class="w"> </span><span class="p" data-group-id="7973976309-4">(</span><span class="n">X</span><span class="p" data-group-id="7973976309-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">lt</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="n">Fun2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2601145814-3">(</span><span class="n">X</span><span class="p" data-group-id="2601145814-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="o">&gt;=</span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">gt</span><span class="p">;</span><span class="w"> </span><span class="p" data-group-id="2601145814-4">(</span><span class="n">X</span><span class="p" data-group-id="2601145814-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">lt</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="n">Fun2</span><span class="p" data-group-id="7973976309-5">(</span><span class="mi">7</span><span class="p" data-group-id="7973976309-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="n">Fun2</span><span class="p" data-group-id="2601145814-5">(</span><span class="mi">7</span><span class="p" data-group-id="2601145814-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">gt</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="n">Fun3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="7973976309-6">(</span><span class="mi">1</span><span class="p" data-group-id="7973976309-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="7973976309-7">(</span><span class="n">X</span><span class="p" data-group-id="7973976309-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="7973976309-8">(</span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7973976309-8">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="n">Fun3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="2601145814-6">(</span><span class="mi">1</span><span class="p" data-group-id="2601145814-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="2601145814-7">(</span><span class="n">X</span><span class="p" data-group-id="2601145814-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="2601145814-8">(</span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2601145814-8">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="n">Fun3</span><span class="p" data-group-id="7973976309-9">(</span><span class="mi">4</span><span class="p" data-group-id="7973976309-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +6&gt; </span><span class="n">Fun3</span><span class="p" data-group-id="2601145814-9">(</span><span class="mi">4</span><span class="p" data-group-id="2601145814-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">24</span></code></pre><p>The following fun expressions are also allowed:</p><pre><code class="makeup erlang" translate="no"><span class="k">fun</span><span class="w"> </span><span class="n">Name</span><span class="o">/</span><span class="n">Arity</span><span class="w">
│ │ │ │  </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">Name</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In <code class="inline">Name/Arity</code>, <code class="inline">Name</code> is an atom and <code class="inline">Arity</code> is an integer. <code class="inline">Name/Arity</code> must
│ │ │ │ -specify an existing local function. The expression is syntactic sugar for:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4254910854-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="4254910854-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4254910854-2">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="4254910854-2">)</span><span class="w"> </span><span class="k">end</span></code></pre><p>In <code class="inline">Module:Name/Arity</code>, <code class="inline">Module</code>, and <code class="inline">Name</code> are atoms and <code class="inline">Arity</code> is an
│ │ │ │ +specify an existing local function. The expression is syntactic sugar for:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1387185081-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="1387185081-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="1387185081-2">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="1387185081-2">)</span><span class="w"> </span><span class="k">end</span></code></pre><p>In <code class="inline">Module:Name/Arity</code>, <code class="inline">Module</code>, and <code class="inline">Name</code> are atoms and <code class="inline">Arity</code> is an
│ │ │ │  integer. <code class="inline">Module</code>, <code class="inline">Name</code>, and <code class="inline">Arity</code> can also be variables. A fun defined in
│ │ │ │  this way refers to the function <code class="inline">Name</code> with arity <code class="inline">Arity</code> in the <em>latest</em>
│ │ │ │  version of module <code class="inline">Module</code>. A fun defined in this way is not dependent on the
│ │ │ │  code for the module in which it is defined.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R15, <code class="inline">Module</code>, <code class="inline">Name</code>, and <code class="inline">Arity</code> were not allowed to be
│ │ │ │  variables.</p></section><p>More examples are provided in <a href="../../../lib/../system/doc/html/funs.xhtml">Programming Examples</a>.</p><h2 id="catch-and-throw" class="section-heading">
│ │ │ │    <a href="#catch-and-throw" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -886,35 +886,35 @@
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">catch</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>Returns the value of <code class="inline">Expr</code> unless an exception is raised during the evaluation. In
│ │ │ │  that case, the exception is caught. The return value depends on the class of the
│ │ │ │  exception:</p><ul><li><p><strong><code class="inline">error</code></strong> (a run-time error or the code called <a href="../../../lib/../erts/doc/html/erlang.html#error/1"><code class="inline">error(Term)</code></a>) -
│ │ │ │  <code class="inline">{'EXIT',{Reason,Stack}}</code> is returned.</p></li><li><p><strong><code class="inline">exit</code></strong> (the code called <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit(Term)</code></a>) - <code class="inline">{'EXIT',Term}</code> is returned.</p></li><li><p><strong><code class="inline">throw</code></strong> (the code called <a href="../../../lib/../erts/doc/html/erlang.html#throw/1"><code class="inline">throw(Term)</code></a>): <code class="inline">Term</code> is returned.</p></li></ul><p><code class="inline">Reason</code> depends on the type of error that occurred, and <code class="inline">Stack</code> is the stack of
│ │ │ │  recent function calls, see <a href="errors.xhtml#exit_reasons">Exit Reasons</a>.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="k">catch</span><span class="w"> </span><span class="mi">1</span><span class="o">+</span><span class="mi">2</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ │  2&gt; </span><span class="k">catch</span><span class="w"> </span><span class="mi">1</span><span class="o">+</span><span class="ss">a</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3050494821-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="3050494821-2">{</span><span class="ss">badarith</span><span class="p">,</span><span class="p" data-group-id="3050494821-3">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3050494821-3">]</span><span class="p" data-group-id="3050494821-2">}</span><span class="p" data-group-id="3050494821-1">}</span></code></pre><p>The BIF <a href="../../../lib/../erts/doc/html/erlang.html#throw/1"><code class="inline">throw(Any)</code></a> can be used for non-local return from a
│ │ │ │ -function. It must be evaluated within a <code class="inline">catch</code>, which returns the value <code class="inline">Any</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="8399389419-1">(</span><span class="ss">hello</span><span class="p" data-group-id="8399389419-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5393509520-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="5393509520-2">{</span><span class="ss">badarith</span><span class="p">,</span><span class="p" data-group-id="5393509520-3">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5393509520-3">]</span><span class="p" data-group-id="5393509520-2">}</span><span class="p" data-group-id="5393509520-1">}</span></code></pre><p>The BIF <a href="../../../lib/../erts/doc/html/erlang.html#throw/1"><code class="inline">throw(Any)</code></a> can be used for non-local return from a
│ │ │ │ +function. It must be evaluated within a <code class="inline">catch</code>, which returns the value <code class="inline">Any</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="9284411183-1">(</span><span class="ss">hello</span><span class="p" data-group-id="9284411183-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span></code></pre><p>If <a href="../../../lib/../erts/doc/html/erlang.html#throw/1"><code class="inline">throw/1</code></a> is not evaluated within a catch, a <code class="inline">nocatch</code> run-time
│ │ │ │  error occurs.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 24, the <code class="inline">catch</code> operator had the lowest precedence, making
│ │ │ │ -it necessary to add parentheses when combining it with the <code class="inline">match</code> operator:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7436540184-1">(</span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="7436540184-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +it necessary to add parentheses when combining it with the <code class="inline">match</code> operator:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0845268922-1">(</span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="0845268922-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span><span class="gp unselectable">
│ │ │ │  2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span></code></pre><p>Starting from Erlang/OTP 24, the parentheses can be omitted:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span><span class="gp unselectable">
│ │ │ │  2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span></code></pre></section><h2 id="try" class="section-heading">
│ │ │ │    <a href="#try" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Try</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w">
│ │ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="0526174905-1">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="0526174905-1">]</span><span class="w"> </span><span class="p" data-group-id="0526174905-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="0526174905-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="2545806802-1">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="2545806802-1">]</span><span class="w"> </span><span class="p" data-group-id="2545806802-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="2545806802-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="0526174905-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="0526174905-3">]</span><span class="w"> </span><span class="p" data-group-id="0526174905-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="0526174905-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="2545806802-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="2545806802-3">]</span><span class="w"> </span><span class="p" data-group-id="2545806802-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="2545806802-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>This is an enhancement of <a href="expressions.xhtml#catch-and-throw">catch</a>. It gives the
│ │ │ │  possibility to:</p><ul><li>Distinguish between different exception classes.</li><li>Choose to handle only the desired ones.</li><li>Passing the others on to an enclosing <code class="inline">try</code> or <code class="inline">catch</code>, or to default error
│ │ │ │  handling.</li></ul><p>Notice that although the keyword <code class="inline">catch</code> is used in the <code class="inline">try</code> expression, there
│ │ │ │  is not a <code class="inline">catch</code> expression within the <code class="inline">try</code> expression.</p><p>It returns the value of <code class="inline">Exprs</code> (a sequence of expressions <code class="inline">Expr1, ..., ExprN</code>)
│ │ │ │  unless an exception occurs during the evaluation. In that case the exception is
│ │ │ │  caught and the patterns <code class="inline">ExceptionPattern</code> with the right exception class
│ │ │ │ @@ -924,47 +924,47 @@
│ │ │ │  stack trace is bound to the variable when the corresponding <code class="inline">ExceptionPattern</code>
│ │ │ │  matches.</p><p>If an exception occurs during evaluation of <code class="inline">Exprs</code> but there is no matching
│ │ │ │  <code class="inline">ExceptionPattern</code> of the right <code class="inline">Class</code> with a true guard sequence, the
│ │ │ │  exception is passed on as if <code class="inline">Exprs</code> had not been enclosed in a <code class="inline">try</code>
│ │ │ │  expression.</p><p>If an exception occurs during evaluation of <code class="inline">ExceptionBody</code>, it is not caught.</p><p>It is allowed to omit <code class="inline">Class</code> and <code class="inline">Stacktrace</code>. An omitted <code class="inline">Class</code> is shorthand
│ │ │ │  for <code class="inline">throw</code>:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w">
│ │ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ │ -    </span><span class="n">ExceptionPattern1</span><span class="w"> </span><span class="p" data-group-id="9801438921-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="9801438921-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">ExceptionPattern1</span><span class="w"> </span><span class="p" data-group-id="5456138999-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="5456138999-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">ExceptionPatternN</span><span class="w"> </span><span class="p" data-group-id="9801438921-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="9801438921-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">ExceptionPatternN</span><span class="w"> </span><span class="p" data-group-id="5456138999-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="5456138999-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">try</code> expression can have an <code class="inline">of</code> section:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="2901479607-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="2901479607-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="6716369903-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="6716369903-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="2901479607-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="2901479607-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="6716369903-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="6716369903-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="2901479607-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="2901479607-3">]</span><span class="w"> </span><span class="p" data-group-id="2901479607-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="2901479607-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="6716369903-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="6716369903-3">]</span><span class="w"> </span><span class="p" data-group-id="6716369903-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="6716369903-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="2901479607-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="2901479607-5">]</span><span class="w"> </span><span class="p" data-group-id="2901479607-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="2901479607-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="6716369903-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="6716369903-5">]</span><span class="w"> </span><span class="p" data-group-id="6716369903-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="6716369903-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>If the evaluation of <code class="inline">Exprs</code> succeeds without an exception, the patterns
│ │ │ │  <code class="inline">Pattern</code> are sequentially matched against the result in the same way as for a
│ │ │ │  <a href="expressions.xhtml#case">case</a> expression, except that if the matching fails, a
│ │ │ │  <code class="inline">try_clause</code> run-time error occurs instead of a <code class="inline">case_clause</code>.</p><p>Only exceptions occurring during the evaluation of <code class="inline">Exprs</code> can be caught by the
│ │ │ │  <code class="inline">catch</code> section. Exceptions occurring in a <code class="inline">Body</code> or due to a failed match are
│ │ │ │  not caught.</p><p>The <code class="inline">try</code> expression can also be augmented with an <code class="inline">after</code> section, intended to
│ │ │ │  be used for cleanup with side effects:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="3920947195-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="3920947195-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="2562461469-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="2562461469-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="3920947195-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="3920947195-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="2562461469-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="2562461469-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="3920947195-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="3920947195-3">]</span><span class="w"> </span><span class="p" data-group-id="3920947195-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="3920947195-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="2562461469-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="2562461469-3">]</span><span class="w"> </span><span class="p" data-group-id="2562461469-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="2562461469-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="3920947195-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="3920947195-5">]</span><span class="w"> </span><span class="p" data-group-id="3920947195-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="3920947195-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="2562461469-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="2562461469-5">]</span><span class="w"> </span><span class="p" data-group-id="2562461469-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="2562461469-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │ │  </span><span class="k">after</span><span class="w">
│ │ │ │      </span><span class="n">AfterBody</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p><code class="inline">AfterBody</code> is evaluated after either <code class="inline">Body</code> or <code class="inline">ExceptionBody</code>, no matter which
│ │ │ │  one. The evaluated value of <code class="inline">AfterBody</code> is lost; the return value of the <code class="inline">try</code>
│ │ │ │  expression is the same with an <code class="inline">after</code> section as without.</p><p>Even if an exception occurs during evaluation of <code class="inline">Body</code> or <code class="inline">ExceptionBody</code>,
│ │ │ │  <code class="inline">AfterBody</code> is evaluated. In this case the exception is passed on after
│ │ │ │ @@ -987,40 +987,40 @@
│ │ │ │          </span><span class="n">ExpressionBody</span><span class="w">
│ │ │ │  </span><span class="k">after</span><span class="w">
│ │ │ │      </span><span class="n">AfterBody</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="n">AfterBody</span><span class="w"> </span><span class="k">end</span></code></pre><p>Next is an example of using <code class="inline">after</code>. This closes the file, even in the event of
│ │ │ │  exceptions in <a href="../../../lib/kernel/doc/html/file.html#read/2"><code class="inline">file:read/2</code></a> or in <a href="../../../lib/../erts/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a>. The
│ │ │ │ -exceptions are the same as without the <code class="inline">try</code>...<code class="inline">after</code>...<code class="inline">end</code> expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">termize_file</span><span class="p" data-group-id="1275728512-1">(</span><span class="n">Name</span><span class="p" data-group-id="1275728512-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1275728512-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="1275728512-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="1275728512-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1275728512-4">[</span><span class="ss">read</span><span class="p">,</span><span class="ss">binary</span><span class="p" data-group-id="1275728512-4">]</span><span class="p" data-group-id="1275728512-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +exceptions are the same as without the <code class="inline">try</code>...<code class="inline">after</code>...<code class="inline">end</code> expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">termize_file</span><span class="p" data-group-id="8962444273-1">(</span><span class="n">Name</span><span class="p" data-group-id="8962444273-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8962444273-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="8962444273-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="8962444273-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8962444273-4">[</span><span class="ss">read</span><span class="p">,</span><span class="ss">binary</span><span class="p" data-group-id="8962444273-4">]</span><span class="p" data-group-id="8962444273-3">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">try</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1275728512-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">Bin</span><span class="p" data-group-id="1275728512-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="1275728512-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="p" data-group-id="1275728512-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="nf">binary_to_term</span><span class="p" data-group-id="1275728512-7">(</span><span class="n">Bin</span><span class="p" data-group-id="1275728512-7">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8962444273-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">Bin</span><span class="p" data-group-id="8962444273-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="8962444273-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="p" data-group-id="8962444273-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="nf">binary_to_term</span><span class="p" data-group-id="8962444273-7">(</span><span class="n">Bin</span><span class="p" data-group-id="8962444273-7">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w">
│ │ │ │ -        </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="1275728512-8">(</span><span class="n">F</span><span class="p" data-group-id="1275728512-8">)</span><span class="w">
│ │ │ │ +        </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="8962444273-8">(</span><span class="n">F</span><span class="p" data-group-id="8962444273-8">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Next is an example of using <code class="inline">try</code> to emulate <code class="inline">catch Expr</code>:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Expr</span><span class="w">
│ │ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ │      </span><span class="nc">throw</span><span class="p">:</span><span class="n">Term</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Term</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="nc">exit</span><span class="p">:</span><span class="n">Reason</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3853753830-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="3853753830-1">}</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="nc">error</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stk</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3853753830-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="3853753830-3">{</span><span class="n">Reason</span><span class="p">,</span><span class="n">Stk</span><span class="p" data-group-id="3853753830-3">}</span><span class="p" data-group-id="3853753830-2">}</span><span class="w">
│ │ │ │ +    </span><span class="nc">exit</span><span class="p">:</span><span class="n">Reason</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3936383044-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="3936383044-1">}</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nc">error</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stk</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3936383044-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="3936383044-3">{</span><span class="n">Reason</span><span class="p">,</span><span class="n">Stk</span><span class="p" data-group-id="3936383044-3">}</span><span class="p" data-group-id="3936383044-2">}</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>Variables bound in the various parts of these expressions have different scopes.
│ │ │ │  Variables bound just after the <code class="inline">try</code> keyword are:</p><ul><li>bound in the <code class="inline">of</code> section</li><li>unsafe in both the <code class="inline">catch</code> and <code class="inline">after</code> sections, as well as after the whole
│ │ │ │  construct</li></ul><p>Variables bound in <code class="inline">of</code> section are:</p><ul><li>unbound in the <code class="inline">catch</code> section</li><li>unsafe in both the <code class="inline">after</code> section, as well as after the whole construct</li></ul><p>Variables bound in the <code class="inline">catch</code> section are unsafe in the <code class="inline">after</code> section, as
│ │ │ │  well as after the whole construct.</p><p>Variables bound in the <code class="inline">after</code> section are unsafe after the whole construct.</p><h2 id="parenthesized-expressions" class="section-heading">
│ │ │ │    <a href="#parenthesized-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Parenthesized Expressions</span>
│ │ │ │  </h2>
│ │ │ │ -<pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4772975289-1">(</span><span class="n">Expr</span><span class="p" data-group-id="4772975289-1">)</span></code></pre><p>Parenthesized expressions are useful to override
│ │ │ │ +<pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6718591454-1">(</span><span class="n">Expr</span><span class="p" data-group-id="6718591454-1">)</span></code></pre><p>Parenthesized expressions are useful to override
│ │ │ │  <a href="expressions.xhtml#prec">operator precedences</a>, for example, in arithmetic
│ │ │ │  expressions:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">7</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="8227958634-1">(</span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8227958634-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="6957240504-1">(</span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6957240504-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">9</span></code></pre><h2 id="block-expressions" class="section-heading">
│ │ │ │    <a href="#block-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Block Expressions</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">begin</span><span class="w">
│ │ │ │ @@ -1032,71 +1032,71 @@
│ │ │ │    <a href="#comprehensions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Comprehensions</span>
│ │ │ │  </h2>
│ │ │ │  <p>Comprehensions provide a succinct notation for iterating over one or more terms
│ │ │ │  and constructing a new term. Comprehensions come in three different flavors,
│ │ │ │ -depending on the type of term they build.</p><p>List comprehensions construct lists. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9633534191-1">[</span><span class="n">Expr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="9633534191-1">]</span></code></pre><p>Here, <code class="inline">Expr</code> is an arbitrary expression, and each <code class="inline">Qualifier</code> is either a
│ │ │ │ +depending on the type of term they build.</p><p>List comprehensions construct lists. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1712571308-1">[</span><span class="n">Expr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="1712571308-1">]</span></code></pre><p>Here, <code class="inline">Expr</code> is an arbitrary expression, and each <code class="inline">Qualifier</code> is either a
│ │ │ │  <strong>generator</strong> or a <strong>filter</strong>.</p><p>Bit string comprehensions construct bit strings or binaries. They have the
│ │ │ │ -following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6134490792-1">&lt;&lt;</span><span class="w"> </span><span class="n">BitStringExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="w"> </span><span class="p" data-group-id="6134490792-1">&gt;&gt;</span></code></pre><p><code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string. If
│ │ │ │ +following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9751686252-1">&lt;&lt;</span><span class="w"> </span><span class="n">BitStringExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="w"> </span><span class="p" data-group-id="9751686252-1">&gt;&gt;</span></code></pre><p><code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string. If
│ │ │ │  <code class="inline">BitStringExpr</code> is a function call, it must be enclosed in parentheses. Each
│ │ │ │ -<code class="inline">Qualifier</code> is either a <strong>generator</strong> or a <strong>filter</strong>.</p><p>Map comprehensions construct maps. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6840171607-1">#{</span><span class="n">KeyExpr</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="6840171607-1">}</span></code></pre><p>Here, <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> are arbitrary expressions, and each <code class="inline">Qualifier</code>
│ │ │ │ +<code class="inline">Qualifier</code> is either a <strong>generator</strong> or a <strong>filter</strong>.</p><p>Map comprehensions construct maps. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7000503481-1">#{</span><span class="n">KeyExpr</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="7000503481-1">}</span></code></pre><p>Here, <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> are arbitrary expressions, and each <code class="inline">Qualifier</code>
│ │ │ │  is either a <strong>generator</strong> or a <strong>filter</strong>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Map comprehensions and map generators were introduced in Erlang/OTP 26.</p></section><p>There are three kinds of generators.</p><p>A <em>list generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">ListExpr</span></code></pre><p>where <code class="inline">ListExpr</code> is an expression that evaluates to a list of terms.</p><p>A <em>bit string generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">BitstringPattern</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="n">BitStringExpr</span></code></pre><p>where <code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string.</p><p>A <em>map generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">KeyPattern</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">ValuePattern</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">MapExpression</span></code></pre><p>where <code class="inline">MapExpr</code> is an expression that evaluates to a map, or a map iterator
│ │ │ │  obtained by calling <a href="../../../lib/stdlib/doc/html/maps.html#iterator/1"><code class="inline">maps:iterator/1</code></a> or <a href="../../../lib/stdlib/doc/html/maps.html#iterator/2"><code class="inline">maps:iterator/2</code></a>.</p><p>A <em>filter</em> is an expression that evaluates to <code class="inline">true</code> or <code class="inline">false</code>.</p><p>The variables in the generator patterns shadow previously bound variables,
│ │ │ │  including variables bound in a previous generator pattern.</p><p>Variables bound in a generator expression are not visible outside the
│ │ │ │ -expression:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3440664637-1">[</span><span class="p" data-group-id="3440664637-2">{</span><span class="n">E</span><span class="p">,</span><span class="n">L</span><span class="p" data-group-id="3440664637-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="o">=</span><span class="p" data-group-id="3440664637-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3440664637-3">]</span><span class="p" data-group-id="3440664637-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +expression:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6939227951-1">[</span><span class="p" data-group-id="6939227951-2">{</span><span class="n">E</span><span class="p">,</span><span class="n">L</span><span class="p" data-group-id="6939227951-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="o">=</span><span class="p" data-group-id="6939227951-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6939227951-3">]</span><span class="p" data-group-id="6939227951-1">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">* 1:5: variable &#39;L&#39; is unbound</span></code></pre><p>A <strong>list comprehension</strong> returns a list, where the list elements are the result
│ │ │ │  of evaluating <code class="inline">Expr</code> for each combination of generator elements for which all
│ │ │ │  filters are true.</p><p>A <strong>bit string comprehension</strong> returns a bit string, which is created by
│ │ │ │  concatenating the results of evaluating <code class="inline">BitStringExpr</code> for each combination of
│ │ │ │  bit string generator elements for which all filters are true.</p><p>A <strong>map comprehension</strong> returns a map, where the map elements are the result of
│ │ │ │  evaluating <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> for each combination of generator elements
│ │ │ │  for which all filters are true. If the key expressions are not unique, the last
│ │ │ │ -occurrence is stored in the map.</p><p><strong>Examples:</strong></p><p>Multiplying each element in a list by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0160322859-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0160322859-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0160322859-2">]</span><span class="p" data-group-id="0160322859-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0160322859-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="0160322859-3">]</span></code></pre><p>Multiplying each byte in a binary by two, returning a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7294833992-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="7294833992-2">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="7294833992-2">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="7294833992-3">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7294833992-3">&gt;&gt;</span><span class="p" data-group-id="7294833992-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7294833992-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7294833992-4">]</span></code></pre><p>Multiplying each byte in a binary by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5592016459-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="5592016459-2">&lt;&lt;</span><span class="p" data-group-id="5592016459-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="5592016459-3">)</span><span class="p" data-group-id="5592016459-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="5592016459-4">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="5592016459-4">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="5592016459-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5592016459-5">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="5592016459-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5592016459-6">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5592016459-6">&gt;&gt;</span></code></pre><p>Multiplying each element in a list by two, returning a binary:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0980222552-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="0980222552-2">&lt;&lt;</span><span class="p" data-group-id="0980222552-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="0980222552-3">)</span><span class="p" data-group-id="0980222552-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0980222552-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0980222552-4">]</span><span class="w"> </span><span class="p" data-group-id="0980222552-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0980222552-5">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="0980222552-5">&gt;&gt;</span></code></pre><p>Creating a mapping from an integer to its square:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9375920727-1">#{</span><span class="n">X</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9375920727-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9375920727-2">]</span><span class="p" data-group-id="9375920727-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9375920727-3">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="9375920727-3">}</span></code></pre><p>Multiplying the value of each element in a map by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3347851902-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">V</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="3347851902-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3347851902-2">}</span><span class="p" data-group-id="3347851902-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3347851902-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="3347851902-3">}</span></code></pre><p>Filtering a list, keeping odd numbers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9198217985-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9198217985-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9198217985-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9198217985-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9198217985-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9198217985-3">]</span></code></pre><p>Filtering a list, keeping only elements that match:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0170756630-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="0170756630-2">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0170756630-2">}</span><span class="o">=</span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0170756630-3">[</span><span class="p" data-group-id="0170756630-4">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="0170756630-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0170756630-5">[</span><span class="ss">a</span><span class="p" data-group-id="0170756630-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0170756630-6">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="0170756630-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0170756630-7">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0170756630-7">}</span><span class="p" data-group-id="0170756630-3">]</span><span class="p" data-group-id="0170756630-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0170756630-8">[</span><span class="p" data-group-id="0170756630-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="0170756630-9">}</span><span class="p">,</span><span class="p" data-group-id="0170756630-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0170756630-10">}</span><span class="p" data-group-id="0170756630-8">]</span></code></pre><p>Combining elements from two list generators:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0410286799-1">[</span><span class="p" data-group-id="0410286799-2">{</span><span class="n">P</span><span class="p">,</span><span class="n">Q</span><span class="p" data-group-id="0410286799-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0410286799-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0410286799-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0410286799-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0410286799-4">]</span><span class="p" data-group-id="0410286799-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0410286799-5">[</span><span class="p" data-group-id="0410286799-6">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0410286799-6">}</span><span class="p">,</span><span class="p" data-group-id="0410286799-7">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0410286799-7">}</span><span class="p">,</span><span class="p" data-group-id="0410286799-8">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0410286799-8">}</span><span class="p">,</span><span class="p" data-group-id="0410286799-9">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0410286799-9">}</span><span class="p">,</span><span class="p" data-group-id="0410286799-10">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0410286799-10">}</span><span class="p">,</span><span class="p" data-group-id="0410286799-11">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0410286799-11">}</span><span class="p" data-group-id="0410286799-5">]</span></code></pre><p>More examples are provided in
│ │ │ │ +occurrence is stored in the map.</p><p><strong>Examples:</strong></p><p>Multiplying each element in a list by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3041640839-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="3041640839-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3041640839-2">]</span><span class="p" data-group-id="3041640839-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3041640839-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="3041640839-3">]</span></code></pre><p>Multiplying each byte in a binary by two, returning a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7704096157-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="7704096157-2">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="7704096157-2">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="7704096157-3">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7704096157-3">&gt;&gt;</span><span class="p" data-group-id="7704096157-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7704096157-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7704096157-4">]</span></code></pre><p>Multiplying each byte in a binary by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2069918964-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="2069918964-2">&lt;&lt;</span><span class="p" data-group-id="2069918964-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="2069918964-3">)</span><span class="p" data-group-id="2069918964-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="2069918964-4">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="2069918964-4">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="2069918964-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2069918964-5">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="2069918964-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2069918964-6">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2069918964-6">&gt;&gt;</span></code></pre><p>Multiplying each element in a list by two, returning a binary:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8954952346-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="8954952346-2">&lt;&lt;</span><span class="p" data-group-id="8954952346-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="8954952346-3">)</span><span class="p" data-group-id="8954952346-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="8954952346-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8954952346-4">]</span><span class="w"> </span><span class="p" data-group-id="8954952346-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8954952346-5">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8954952346-5">&gt;&gt;</span></code></pre><p>Creating a mapping from an integer to its square:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5554947615-1">#{</span><span class="n">X</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="5554947615-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5554947615-2">]</span><span class="p" data-group-id="5554947615-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5554947615-3">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="5554947615-3">}</span></code></pre><p>Multiplying the value of each element in a map by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4722404271-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">V</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4722404271-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4722404271-2">}</span><span class="p" data-group-id="4722404271-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4722404271-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="4722404271-3">}</span></code></pre><p>Filtering a list, keeping odd numbers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3254064455-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="3254064455-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3254064455-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3254064455-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3254064455-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3254064455-3">]</span></code></pre><p>Filtering a list, keeping only elements that match:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4496581065-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="4496581065-2">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4496581065-2">}</span><span class="o">=</span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4496581065-3">[</span><span class="p" data-group-id="4496581065-4">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4496581065-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4496581065-5">[</span><span class="ss">a</span><span class="p" data-group-id="4496581065-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4496581065-6">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="4496581065-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4496581065-7">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4496581065-7">}</span><span class="p" data-group-id="4496581065-3">]</span><span class="p" data-group-id="4496581065-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4496581065-8">[</span><span class="p" data-group-id="4496581065-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4496581065-9">}</span><span class="p">,</span><span class="p" data-group-id="4496581065-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4496581065-10">}</span><span class="p" data-group-id="4496581065-8">]</span></code></pre><p>Combining elements from two list generators:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5097878701-1">[</span><span class="p" data-group-id="5097878701-2">{</span><span class="n">P</span><span class="p">,</span><span class="n">Q</span><span class="p" data-group-id="5097878701-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="5097878701-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5097878701-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="5097878701-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5097878701-4">]</span><span class="p" data-group-id="5097878701-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5097878701-5">[</span><span class="p" data-group-id="5097878701-6">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5097878701-6">}</span><span class="p">,</span><span class="p" data-group-id="5097878701-7">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5097878701-7">}</span><span class="p">,</span><span class="p" data-group-id="5097878701-8">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5097878701-8">}</span><span class="p">,</span><span class="p" data-group-id="5097878701-9">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5097878701-9">}</span><span class="p">,</span><span class="p" data-group-id="5097878701-10">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5097878701-10">}</span><span class="p">,</span><span class="p" data-group-id="5097878701-11">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5097878701-11">}</span><span class="p" data-group-id="5097878701-5">]</span></code></pre><p>More examples are provided in
│ │ │ │  <a href="../../../lib/../system/doc/html/list_comprehensions.xhtml">Programming Examples.</a></p><p>When there are no generators, a comprehension returns either a term constructed
│ │ │ │  from a single element (the result of evaluating <code class="inline">Expr</code>) if all filters are true,
│ │ │ │  or a term constructed from no elements (that is, <code class="inline">[]</code> for list comprehension,
│ │ │ │ -<code class="inline">&lt;&lt;&gt;&gt;</code> for a bit string comprehension, and <code class="inline">#{}</code> for a map comprehension).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5739337557-1">[</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="5739337557-2">(</span><span class="mi">2</span><span class="p" data-group-id="5739337557-2">)</span><span class="p" data-group-id="5739337557-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5739337557-3">[</span><span class="mi">2</span><span class="p" data-group-id="5739337557-3">]</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="5739337557-4">[</span><span class="ss">x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="5739337557-5">(</span><span class="ss">x</span><span class="p" data-group-id="5739337557-5">)</span><span class="p" data-group-id="5739337557-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5739337557-6">[</span><span class="p" data-group-id="5739337557-6">]</span></code></pre><p>What happens when the filter expression does not evaluate to a boolean value
│ │ │ │ +<code class="inline">&lt;&lt;&gt;&gt;</code> for a bit string comprehension, and <code class="inline">#{}</code> for a map comprehension).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6720373745-1">[</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="6720373745-2">(</span><span class="mi">2</span><span class="p" data-group-id="6720373745-2">)</span><span class="p" data-group-id="6720373745-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6720373745-3">[</span><span class="mi">2</span><span class="p" data-group-id="6720373745-3">]</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="6720373745-4">[</span><span class="ss">x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="6720373745-5">(</span><span class="ss">x</span><span class="p" data-group-id="6720373745-5">)</span><span class="p" data-group-id="6720373745-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6720373745-6">[</span><span class="p" data-group-id="6720373745-6">]</span></code></pre><p>What happens when the filter expression does not evaluate to a boolean value
│ │ │ │  depends on the expression:</p><ul><li>If the expression is a <a href="expressions.xhtml#guard-expressions">guard expression</a>,
│ │ │ │  failure to evaluate or evaluating to a non-boolean value is equivalent to
│ │ │ │  evaluating to <code class="inline">false</code>.</li><li>If the expression is not a guard expression and evaluates to a non-Boolean
│ │ │ │  value <code class="inline">Val</code>, an exception <code class="inline">{bad_filter, Val}</code> is triggered at runtime. If the
│ │ │ │  evaluation of the expression raises an exception, it is not caught by the
│ │ │ │ -comprehension.</li></ul><p><strong>Examples</strong> (using a guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8789985717-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8789985717-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8789985717-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8789985717-2">]</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="8789985717-3">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8789985717-3">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8789985717-4">[</span><span class="p" data-group-id="8789985717-4">]</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="p" data-group-id="8789985717-5">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8789985717-5">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8789985717-6">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8789985717-6">]</span></code></pre><p><strong>Examples</strong> (using a non-guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5583367331-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5583367331-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5583367331-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5583367331-2">]</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="n">FaultyIsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5583367331-3">(</span><span class="n">E</span><span class="p" data-group-id="5583367331-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +comprehension.</li></ul><p><strong>Examples</strong> (using a guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2674023042-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2674023042-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2674023042-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2674023042-2">]</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="2674023042-3">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2674023042-3">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2674023042-4">[</span><span class="p" data-group-id="2674023042-4">]</span><span class="gp unselectable">
│ │ │ │ +3&gt; </span><span class="p" data-group-id="2674023042-5">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2674023042-5">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2674023042-6">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2674023042-6">]</span></code></pre><p><strong>Examples</strong> (using a non-guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9812072056-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="9812072056-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9812072056-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="9812072056-2">]</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="n">FaultyIsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9812072056-3">(</span><span class="n">E</span><span class="p" data-group-id="9812072056-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">42.17316486</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="p" data-group-id="5583367331-4">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">FaultyIsEven</span><span class="p" data-group-id="5583367331-5">(</span><span class="n">E</span><span class="p" data-group-id="5583367331-5">)</span><span class="p" data-group-id="5583367331-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="p" data-group-id="9812072056-4">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">FaultyIsEven</span><span class="p" data-group-id="9812072056-5">(</span><span class="n">E</span><span class="p" data-group-id="9812072056-5">)</span><span class="p" data-group-id="9812072056-4">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: bad filter 1</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="n">IsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5583367331-6">(</span><span class="n">E</span><span class="p" data-group-id="5583367331-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="n">IsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9812072056-6">(</span><span class="n">E</span><span class="p" data-group-id="9812072056-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">42.17316486</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="p" data-group-id="5583367331-7">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="5583367331-8">(</span><span class="n">E</span><span class="p" data-group-id="5583367331-8">)</span><span class="p" data-group-id="5583367331-7">]</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="p" data-group-id="9812072056-7">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="9812072056-8">(</span><span class="n">E</span><span class="p" data-group-id="9812072056-8">)</span><span class="p" data-group-id="9812072056-7">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: an error occurred when evaluating an arithmetic expression
│ │ │ │       in operator  rem/2
│ │ │ │          called as a rem 2</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="p" data-group-id="5583367331-9">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="5583367331-10">(</span><span class="n">E</span><span class="p" data-group-id="5583367331-10">)</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="5583367331-11">(</span><span class="n">E</span><span class="p" data-group-id="5583367331-11">)</span><span class="p" data-group-id="5583367331-9">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5583367331-12">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5583367331-12">]</span></code></pre><p><a href="" id="guards"></a></p><h2 id="guard-sequences" class="section-heading">
│ │ │ │ +6&gt; </span><span class="p" data-group-id="9812072056-9">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="9812072056-10">(</span><span class="n">E</span><span class="p" data-group-id="9812072056-10">)</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="9812072056-11">(</span><span class="n">E</span><span class="p" data-group-id="9812072056-11">)</span><span class="p" data-group-id="9812072056-9">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9812072056-12">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="9812072056-12">]</span></code></pre><p><a href="" id="guards"></a></p><h2 id="guard-sequences" class="section-heading">
│ │ │ │    <a href="#guard-sequences" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Guard Sequences</span>
│ │ │ │  </h2>
│ │ │ │  <p>A <em>guard sequence</em> is a sequence of guards, separated by semicolon (<code class="inline">;</code>). The
│ │ │ │  guard sequence is true if at least one of the guards is true. (The remaining
│ │ │ ├── OEBPS/example.xhtml
│ │ │ │ @@ -36,14 +36,14 @@
│ │ │ │  
│ │ │ │  int bar(int y) {
│ │ │ │    return y*2;
│ │ │ │  }</code></pre><p>The functions are deliberately kept as simple as possible, for readability
│ │ │ │  reasons.</p><p>From an Erlang perspective, it is preferable to be able to call <code class="inline">foo</code> and <code class="inline">bar</code>
│ │ │ │  without having to bother about that they are C functions:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% Erlang code</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="n">Res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">complex</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="4261809694-1">(</span><span class="n">X</span><span class="p" data-group-id="4261809694-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">complex</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="6681599869-1">(</span><span class="n">X</span><span class="p" data-group-id="6681599869-1">)</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Here, the communication with C is hidden in the implementation of <code class="inline">complex.erl</code>.
│ │ │ │  In the following sections, it is shown how this module can be implemented using
│ │ │ │  the different interoperability mechanisms.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/events.xhtml
│ │ │ │ @@ -40,43 +40,43 @@
│ │ │ │  event handler.</p><h2 id="example" class="section-heading">
│ │ │ │    <a href="#example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example</span>
│ │ │ │  </h2>
│ │ │ │  <p>The callback module for the event handler writing error messages to the terminal
│ │ │ │ -can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3979024926-1">(</span><span class="ss">terminal_logger</span><span class="p" data-group-id="3979024926-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3979024926-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="3979024926-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4771226164-1">(</span><span class="ss">terminal_logger</span><span class="p" data-group-id="4771226164-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4771226164-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="4771226164-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3979024926-3">(</span><span class="p" data-group-id="3979024926-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3979024926-4">]</span><span class="p" data-group-id="3979024926-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4771226164-3">(</span><span class="p" data-group-id="4771226164-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4771226164-4">]</span><span class="p" data-group-id="4771226164-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="3979024926-5">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="3979024926-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3979024926-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3979024926-7">[</span><span class="p" data-group-id="3979024926-7">]</span><span class="p" data-group-id="3979024926-6">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="4771226164-5">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="4771226164-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4771226164-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4771226164-7">[</span><span class="p" data-group-id="4771226164-7">]</span><span class="p" data-group-id="4771226164-6">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="3979024926-8">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3979024926-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3979024926-9">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3979024926-10">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="3979024926-10">]</span><span class="p" data-group-id="3979024926-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3979024926-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3979024926-11">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="4771226164-8">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4771226164-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4771226164-9">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4771226164-10">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="4771226164-10">]</span><span class="p" data-group-id="4771226164-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4771226164-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4771226164-11">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="3979024926-12">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="3979024926-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="4771226164-12">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="4771226164-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The callback module for the event handler writing error messages to a file can
│ │ │ │ -look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5533062873-1">(</span><span class="ss">file_logger</span><span class="p" data-group-id="5533062873-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5533062873-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="5533062873-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8242388363-1">(</span><span class="ss">file_logger</span><span class="p" data-group-id="8242388363-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8242388363-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="8242388363-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5533062873-3">(</span><span class="p" data-group-id="5533062873-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5533062873-4">]</span><span class="p" data-group-id="5533062873-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8242388363-3">(</span><span class="p" data-group-id="8242388363-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8242388363-4">]</span><span class="p" data-group-id="8242388363-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="5533062873-5">(</span><span class="n">File</span><span class="p" data-group-id="5533062873-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5533062873-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5533062873-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="5533062873-7">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="5533062873-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5533062873-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5533062873-8">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5533062873-9">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5533062873-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5533062873-10">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5533062873-11">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="5533062873-11">]</span><span class="p" data-group-id="5533062873-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5533062873-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5533062873-12">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8242388363-5">(</span><span class="n">File</span><span class="p" data-group-id="8242388363-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8242388363-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8242388363-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="8242388363-7">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="8242388363-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8242388363-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8242388363-8">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="8242388363-9">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8242388363-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8242388363-10">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8242388363-11">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="8242388363-11">]</span><span class="p" data-group-id="8242388363-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8242388363-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8242388363-12">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="5533062873-13">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5533062873-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="5533062873-14">(</span><span class="n">Fd</span><span class="p" data-group-id="5533062873-14">)</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><p><a href="" id="mgr"></a></p><h2 id="starting-an-event-manager" class="section-heading">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="8242388363-13">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8242388363-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="8242388363-14">(</span><span class="n">Fd</span><span class="p" data-group-id="8242388363-14">)</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><p><a href="" id="mgr"></a></p><h2 id="starting-an-event-manager" class="section-heading">
│ │ │ │    <a href="#starting-an-event-manager" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting an Event Manager</span>
│ │ │ │  </h2>
│ │ │ │  <p>To start an event manager for handling errors, as described in the previous
│ │ │ │  example, call the following function:</p><pre><code class="text">gen_event:start_link({local, error_man})</code></pre><p><a href="../../../lib/stdlib/doc/html/gen_event.html#start_link/1"><code class="inline">gen_event:start_link/1</code></a> spawns and links to a new event manager process.</p><p>The argument, <code class="inline">{local, error_man}</code>, specifies the name under which the
│ │ │ │ @@ -89,57 +89,57 @@
│ │ │ │  manager that is not part of a supervision tree.</p><h2 id="adding-an-event-handler" class="section-heading">
│ │ │ │    <a href="#adding-an-event-handler" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Adding an Event Handler</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following example shows how to start an event manager and add an event
│ │ │ │ -handler to it by using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="2858716966-1">(</span><span class="p" data-group-id="2858716966-2">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="2858716966-2">}</span><span class="p" data-group-id="2858716966-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2858716966-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.31</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2858716966-3">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">add_handler</span><span class="p" data-group-id="2858716966-4">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2858716966-5">[</span><span class="p" data-group-id="2858716966-5">]</span><span class="p" data-group-id="2858716966-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +handler to it by using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="2140186960-1">(</span><span class="p" data-group-id="2140186960-2">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="2140186960-2">}</span><span class="p" data-group-id="2140186960-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2140186960-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.31</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2140186960-3">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">add_handler</span><span class="p" data-group-id="2140186960-4">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2140186960-5">[</span><span class="p" data-group-id="2140186960-5">]</span><span class="p" data-group-id="2140186960-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>This function sends a message to the event manager registered as <code class="inline">error_man</code>,
│ │ │ │  telling it to add the event handler <code class="inline">terminal_logger</code>. The event manager calls
│ │ │ │  the callback function <code class="inline">terminal_logger:init([])</code>, where the argument <code class="inline">[]</code> is the
│ │ │ │  third argument to <code class="inline">add_handler</code>. <code class="inline">init/1</code> is expected to return <code class="inline">{ok, State}</code>,
│ │ │ │ -where <code class="inline">State</code> is the internal state of the event handler.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8834582331-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="8834582331-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8834582331-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8834582331-3">[</span><span class="p" data-group-id="8834582331-3">]</span><span class="p" data-group-id="8834582331-2">}</span><span class="p">.</span></code></pre><p>Here, <code class="inline">init/1</code> does not need any input data and ignores its argument. For
│ │ │ │ +where <code class="inline">State</code> is the internal state of the event handler.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6201064338-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6201064338-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6201064338-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6201064338-3">[</span><span class="p" data-group-id="6201064338-3">]</span><span class="p" data-group-id="6201064338-2">}</span><span class="p">.</span></code></pre><p>Here, <code class="inline">init/1</code> does not need any input data and ignores its argument. For
│ │ │ │  <code class="inline">terminal_logger</code>, the internal state is not used. For <code class="inline">file_logger</code>, the
│ │ │ │ -internal state is used to save the open file descriptor.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5584007448-1">(</span><span class="n">File</span><span class="p" data-group-id="5584007448-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5584007448-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5584007448-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="5584007448-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="5584007448-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5584007448-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5584007448-4">}</span><span class="p">.</span></code></pre><h2 id="notifying-about-events" class="section-heading">
│ │ │ │ +internal state is used to save the open file descriptor.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9003003354-1">(</span><span class="n">File</span><span class="p" data-group-id="9003003354-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9003003354-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="9003003354-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="9003003354-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="9003003354-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9003003354-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="9003003354-4">}</span><span class="p">.</span></code></pre><h2 id="notifying-about-events" class="section-heading">
│ │ │ │    <a href="#notifying-about-events" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Notifying about Events</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="text">3&gt; gen_event:notify(error_man, no_reply).
│ │ │ │  ***Error*** no_reply
│ │ │ │  ok</code></pre><p><code class="inline">error_man</code> is the name of the event manager and <code class="inline">no_reply</code> is the event.</p><p>The event is made into a message and sent to the event manager. When the event
│ │ │ │  is received, the event manager calls <code class="inline">handle_event(Event, State)</code> for each
│ │ │ │  installed event handler, in the same order as they were added. The function is
│ │ │ │  expected to return a tuple <code class="inline">{ok,State1}</code>, where <code class="inline">State1</code> is a new value for the
│ │ │ │ -state of the event handler.</p><p>In <code class="inline">terminal_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="6895050857-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6895050857-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6895050857-2">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6895050857-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="6895050857-3">]</span><span class="p" data-group-id="6895050857-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6895050857-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6895050857-4">}</span><span class="p">.</span></code></pre><p>In <code class="inline">file_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="7986171482-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="7986171482-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7986171482-2">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7986171482-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="7986171482-3">]</span><span class="p" data-group-id="7986171482-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7986171482-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="7986171482-4">}</span><span class="p">.</span></code></pre><h2 id="deleting-an-event-handler" class="section-heading">
│ │ │ │ +state of the event handler.</p><p>In <code class="inline">terminal_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="3919277331-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3919277331-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3919277331-2">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3919277331-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="3919277331-3">]</span><span class="p" data-group-id="3919277331-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3919277331-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3919277331-4">}</span><span class="p">.</span></code></pre><p>In <code class="inline">file_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="8298746379-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8298746379-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8298746379-2">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298746379-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="8298746379-3">]</span><span class="p" data-group-id="8298746379-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8298746379-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8298746379-4">}</span><span class="p">.</span></code></pre><h2 id="deleting-an-event-handler" class="section-heading">
│ │ │ │    <a href="#deleting-an-event-handler" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Deleting an Event Handler</span>
│ │ │ │  </h2>
│ │ │ │ -<pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">delete_handler</span><span class="p" data-group-id="1543214948-1">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1543214948-2">[</span><span class="p" data-group-id="1543214948-2">]</span><span class="p" data-group-id="1543214948-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">delete_handler</span><span class="p" data-group-id="1035541757-1">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1035541757-2">[</span><span class="p" data-group-id="1035541757-2">]</span><span class="p" data-group-id="1035541757-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>This function sends a message to the event manager registered as <code class="inline">error_man</code>,
│ │ │ │  telling it to delete the event handler <code class="inline">terminal_logger</code>. The event manager
│ │ │ │  calls the callback function <code class="inline">terminal_logger:terminate([], State)</code>, where the
│ │ │ │  argument <code class="inline">[]</code> is the third argument to <code class="inline">delete_handler</code>. <code class="inline">terminate/2</code> is to be
│ │ │ │  the opposite of <code class="inline">init/1</code> and do any necessary cleaning up. Its return value is
│ │ │ │ -ignored.</p><p>For <code class="inline">terminal_logger</code>, no cleaning up is necessary:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="8788684068-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="8788684068-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>For <code class="inline">file_logger</code>, the file descriptor opened in <code class="inline">init</code> must be closed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="2011540478-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2011540478-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2011540478-2">(</span><span class="n">Fd</span><span class="p" data-group-id="2011540478-2">)</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │ │ +ignored.</p><p>For <code class="inline">terminal_logger</code>, no cleaning up is necessary:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="9488324451-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="9488324451-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>For <code class="inline">file_logger</code>, the file descriptor opened in <code class="inline">init</code> must be closed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="3902403636-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="3902403636-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="3902403636-2">(</span><span class="n">Fd</span><span class="p" data-group-id="3902403636-2">)</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │ │    <a href="#stopping" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Stopping</span>
│ │ │ │  </h2>
│ │ │ │  <p>When an event manager is stopped, it gives each of the installed event handlers
│ │ │ │  the chance to clean up by calling <code class="inline">terminate/2</code>, the same way as when deleting a
│ │ │ │ @@ -154,29 +154,29 @@
│ │ │ │  this is done is defined by a <a href="sup_princ.xhtml#shutdown">shutdown strategy</a> set in
│ │ │ │  the supervisor.</p><h3 id="standalone-event-managers" class="section-heading">
│ │ │ │    <a href="#standalone-event-managers" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Standalone Event Managers</span>
│ │ │ │  </h3>
│ │ │ │ -<p>An event manager can also be stopped by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="6058552736-1">(</span><span class="ss">error_man</span><span class="p" data-group-id="6058552736-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>An event manager can also be stopped by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="4691270859-1">(</span><span class="ss">error_man</span><span class="p" data-group-id="4691270859-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><h2 id="handling-other-messages" class="section-heading">
│ │ │ │    <a href="#handling-other-messages" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Handling Other Messages</span>
│ │ │ │  </h2>
│ │ │ │  <p>If the <code class="inline">gen_event</code> process is to be able to receive other messages
│ │ │ │  than events, the callback function <code class="inline">handle_info(Info, State)</code> must be
│ │ │ │  implemented to handle them. Examples of other messages are exit
│ │ │ │  messages if the event manager is linked to other processes than the
│ │ │ │  supervisor (for example via <a href="../../../lib/stdlib/doc/html/gen_event.html#add_sup_handler/3"><code class="inline">gen_event:add_sup_handler/3</code></a>) and is
│ │ │ │ -trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="8558266628-1">(</span><span class="p" data-group-id="8558266628-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="8558266628-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8558266628-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="6306562923-1">(</span><span class="p" data-group-id="6306562923-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="6306562923-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6306562923-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Code to handle exits here.</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8558266628-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="8558266628-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="9105539679-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="9105539679-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6306562923-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="6306562923-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="5606682693-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="5606682693-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Code to convert state (and more) during code change.</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9105539679-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="9105539679-2">}</span><span class="p">.</span></code></pre>
│ │ │ │ +    </span><span class="p" data-group-id="5606682693-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="5606682693-2">}</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/errors.xhtml
│ │ │ │ @@ -56,22 +56,22 @@
│ │ │ │  classes, with different origins. The <a href="expressions.xhtml#try">try</a> expression can
│ │ │ │  distinguish between the different classes, whereas the
│ │ │ │  <a href="expressions.xhtml#catch-and-throw">catch</a> expression cannot. <code class="inline">try</code> and <code class="inline">catch</code> are described
│ │ │ │  in <a href="expressions.xhtml">Expressions</a>.</p><table><thead><tr><th style="text-align: left;"><em>Class</em></th><th style="text-align: left;"><em>Origin</em></th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">error</code></td><td style="text-align: left;">Run-time error, for example, <code class="inline">1+a</code>, or the process called <a href="../../../lib/../erts/doc/html/erlang.html#error/1"><code class="inline">error/1</code></a></td></tr><tr><td style="text-align: left;"><code class="inline">exit</code></td><td style="text-align: left;">The process called <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a></td></tr><tr><td style="text-align: left;"><code class="inline">throw</code></td><td style="text-align: left;">The process called <a href="../../../lib/../erts/doc/html/erlang.html#throw/1"><code class="inline">throw/1</code></a></td></tr></tbody></table><p><em>Table: Exception Classes.</em></p><p>All of the above exceptions can also be generated by calling <a href="../../../lib/../erts/doc/html/erlang.html#raise/3"><code class="inline">erlang:raise/3</code></a>.</p><p>An exception consists of its class, an exit reason (see
│ │ │ │  <a href="errors.xhtml#exit_reasons">Exit Reason</a>), and a stack trace (which aids in finding
│ │ │ │  the code location of the exception).</p><p>The stack trace can be bound to a variable from within a <code class="inline">try</code> expression for
│ │ │ │  any exception class, or as part of the exit reason when a run-time error is
│ │ │ │ -caught by a <code class="inline">catch</code>. Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="2749998157-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="2749998157-2">{</span><span class="ss">test</span><span class="p">,</span><span class="n">Stacktrace</span><span class="p" data-group-id="2749998157-2">}</span><span class="p" data-group-id="2749998157-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2749998157-3">(</span><span class="k">catch</span><span class="w"> </span><span class="nf">error</span><span class="p" data-group-id="2749998157-4">(</span><span class="ss">test</span><span class="p" data-group-id="2749998157-4">)</span><span class="p" data-group-id="2749998157-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Stacktrace</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2749998157-5">[</span><span class="p" data-group-id="2749998157-6">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="2749998157-7">[</span><span class="p" data-group-id="2749998157-7">]</span><span class="p" data-group-id="2749998157-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2749998157-8">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="2749998157-9">[</span><span class="p" data-group-id="2749998157-9">]</span><span class="p" data-group-id="2749998157-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2749998157-5">]</span><span class="gp unselectable">
│ │ │ │ -&gt; </span><span class="k">try</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="2749998157-10">(</span><span class="ss">test</span><span class="p" data-group-id="2749998157-10">)</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="n">Class</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stacktrace</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Stacktrace</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2749998157-11">[</span><span class="p" data-group-id="2749998157-12">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="2749998157-13">[</span><span class="p" data-group-id="2749998157-13">]</span><span class="p" data-group-id="2749998157-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2749998157-14">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="2749998157-15">[</span><span class="p" data-group-id="2749998157-15">]</span><span class="p" data-group-id="2749998157-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2749998157-11">]</span></code></pre><p><a href="" id="stacktrace"></a></p><h3 id="the-call-stack-back-trace-stacktrace" class="section-heading">
│ │ │ │ +caught by a <code class="inline">catch</code>. Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="0106813545-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="0106813545-2">{</span><span class="ss">test</span><span class="p">,</span><span class="n">Stacktrace</span><span class="p" data-group-id="0106813545-2">}</span><span class="p" data-group-id="0106813545-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0106813545-3">(</span><span class="k">catch</span><span class="w"> </span><span class="nf">error</span><span class="p" data-group-id="0106813545-4">(</span><span class="ss">test</span><span class="p" data-group-id="0106813545-4">)</span><span class="p" data-group-id="0106813545-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Stacktrace</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0106813545-5">[</span><span class="p" data-group-id="0106813545-6">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="0106813545-7">[</span><span class="p" data-group-id="0106813545-7">]</span><span class="p" data-group-id="0106813545-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0106813545-8">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="0106813545-9">[</span><span class="p" data-group-id="0106813545-9">]</span><span class="p" data-group-id="0106813545-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0106813545-5">]</span><span class="gp unselectable">
│ │ │ │ +&gt; </span><span class="k">try</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="0106813545-10">(</span><span class="ss">test</span><span class="p" data-group-id="0106813545-10">)</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="n">Class</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stacktrace</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Stacktrace</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0106813545-11">[</span><span class="p" data-group-id="0106813545-12">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="0106813545-13">[</span><span class="p" data-group-id="0106813545-13">]</span><span class="p" data-group-id="0106813545-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0106813545-14">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="0106813545-15">[</span><span class="p" data-group-id="0106813545-15">]</span><span class="p" data-group-id="0106813545-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0106813545-11">]</span></code></pre><p><a href="" id="stacktrace"></a></p><h3 id="the-call-stack-back-trace-stacktrace" class="section-heading">
│ │ │ │    <a href="#the-call-stack-back-trace-stacktrace" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">The call-stack back trace (stacktrace)</span>
│ │ │ │  </h3>
│ │ │ │  <p>The stack back-trace (<a href="../../../lib/../erts/doc/html/erlang.html#t:stacktrace/0"><em>stacktrace</em></a>) is a list that
│ │ │ │  contains <code class="inline">{Module, Function, Arity, ExtraInfo}</code> and/or <code class="inline">{Fun, Arity, ExtraInfo}</code>
│ │ │ ├── OEBPS/error_logging.xhtml
│ │ │ │ @@ -48,36 +48,36 @@
│ │ │ │  reports and other error and information reports are by default logged through
│ │ │ │  the log handler which is set up when the Kernel application is started.</p><p>Prior to Erlang/OTP 21.0, supervisor, crash, and progress reports were only
│ │ │ │  logged when the SASL application was running. This behaviour can, for backwards
│ │ │ │  compatibility, be enabled by setting the Kernel configuration parameter
│ │ │ │  <a href="../../../lib/kernel/doc/html/kernel_app.xhtml#logger_sasl_compatible"><code class="inline">logger_sasl_compatible</code></a> to
│ │ │ │  <code class="inline">true</code>. For more information, see
│ │ │ │  <a href="../../../lib/sasl/doc/html/error_logging.xhtml">SASL Error Logging</a> in the SASL User's Guide.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -kernel logger_level info</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">21</span><span class="w"> </span><span class="p" data-group-id="9269084183-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">10.0</span><span class="p" data-group-id="9269084183-1">]</span><span class="w"> </span><span class="p" data-group-id="9269084183-2">[</span><span class="ss">source</span><span class="o">-</span><span class="mi">13</span><span class="ss">c50db</span><span class="p" data-group-id="9269084183-2">]</span><span class="w"> </span><span class="p" data-group-id="9269084183-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="9269084183-3">]</span><span class="w"> </span><span class="p" data-group-id="9269084183-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="9269084183-4">]</span><span class="w"> </span><span class="p" data-group-id="9269084183-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="9269084183-5">]</span><span class="w"> </span><span class="p" data-group-id="9269084183-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="9269084183-6">]</span><span class="w"> </span><span class="p" data-group-id="9269084183-7">[</span><span class="ss">hipe</span><span class="p" data-group-id="9269084183-7">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">21</span><span class="w"> </span><span class="p" data-group-id="3755163177-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">10.0</span><span class="p" data-group-id="3755163177-1">]</span><span class="w"> </span><span class="p" data-group-id="3755163177-2">[</span><span class="ss">source</span><span class="o">-</span><span class="mi">13</span><span class="ss">c50db</span><span class="p" data-group-id="3755163177-2">]</span><span class="w"> </span><span class="p" data-group-id="3755163177-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="3755163177-3">]</span><span class="w"> </span><span class="p" data-group-id="3755163177-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="3755163177-4">]</span><span class="w"> </span><span class="p" data-group-id="3755163177-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="3755163177-5">]</span><span class="w"> </span><span class="p" data-group-id="3755163177-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="3755163177-6">]</span><span class="w"> </span><span class="p" data-group-id="3755163177-7">[</span><span class="ss">hipe</span><span class="p" data-group-id="3755163177-7">]</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.916404</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ │      </span><span class="nc">application</span><span class="p">:</span><span class="w"> </span><span class="ss">kernel</span><span class="w">
│ │ │ │      </span><span class="nc">started_at</span><span class="p">:</span><span class="w"> </span><span class="ss">nonode@nohost</span><span class="w">
│ │ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.922908</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ │      </span><span class="nc">application</span><span class="p">:</span><span class="w"> </span><span class="ss">stdlib</span><span class="w">
│ │ │ │      </span><span class="nc">started_at</span><span class="p">:</span><span class="w"> </span><span class="ss">nonode@nohost</span><span class="w">
│ │ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.925755</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="9269084183-8">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="9269084183-8">}</span><span class="w">
│ │ │ │ -    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="9269084183-9">[</span><span class="p" data-group-id="9269084183-10">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.74</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="9269084183-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="9269084183-11">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_sup</span><span class="p" data-group-id="9269084183-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="9269084183-12">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="9269084183-13">{</span><span class="ss">disk_log_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="9269084183-14">[</span><span class="p" data-group-id="9269084183-14">]</span><span class="p" data-group-id="9269084183-13">}</span><span class="p" data-group-id="9269084183-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="9269084183-15">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="9269084183-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="9269084183-16">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">1000</span><span class="p" data-group-id="9269084183-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="9269084183-17">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">supervisor</span><span class="p" data-group-id="9269084183-17">}</span><span class="p" data-group-id="9269084183-9">]</span><span class="w">
│ │ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="3755163177-8">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="3755163177-8">}</span><span class="w">
│ │ │ │ +    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="3755163177-9">[</span><span class="p" data-group-id="3755163177-10">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.74</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="3755163177-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3755163177-11">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_sup</span><span class="p" data-group-id="3755163177-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3755163177-12">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="3755163177-13">{</span><span class="ss">disk_log_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="3755163177-14">[</span><span class="p" data-group-id="3755163177-14">]</span><span class="p" data-group-id="3755163177-13">}</span><span class="p" data-group-id="3755163177-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3755163177-15">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="3755163177-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3755163177-16">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">1000</span><span class="p" data-group-id="3755163177-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3755163177-17">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">supervisor</span><span class="p" data-group-id="3755163177-17">}</span><span class="p" data-group-id="3755163177-9">]</span><span class="w">
│ │ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.926056</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="9269084183-18">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="9269084183-18">}</span><span class="w">
│ │ │ │ -    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="9269084183-19">[</span><span class="p" data-group-id="9269084183-20">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.75</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="9269084183-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="9269084183-21">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_server</span><span class="p" data-group-id="9269084183-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="9269084183-22">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="9269084183-23">{</span><span class="ss">disk_log_server</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="9269084183-24">[</span><span class="p" data-group-id="9269084183-24">]</span><span class="p" data-group-id="9269084183-23">}</span><span class="p" data-group-id="9269084183-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="9269084183-25">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="9269084183-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="9269084183-26">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">2000</span><span class="p" data-group-id="9269084183-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="9269084183-27">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">worker</span><span class="p" data-group-id="9269084183-27">}</span><span class="p" data-group-id="9269084183-19">]</span><span class="w">
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V10</span><span class="p">.</span><span class="mi">0</span><span class="w">  </span><span class="p" data-group-id="9269084183-28">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="9269084183-28">)</span><span class="w">
│ │ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="3755163177-18">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="3755163177-18">}</span><span class="w">
│ │ │ │ +    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="3755163177-19">[</span><span class="p" data-group-id="3755163177-20">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.75</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="3755163177-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3755163177-21">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_server</span><span class="p" data-group-id="3755163177-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3755163177-22">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="3755163177-23">{</span><span class="ss">disk_log_server</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="3755163177-24">[</span><span class="p" data-group-id="3755163177-24">]</span><span class="p" data-group-id="3755163177-23">}</span><span class="p" data-group-id="3755163177-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3755163177-25">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="3755163177-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3755163177-26">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">2000</span><span class="p" data-group-id="3755163177-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3755163177-27">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">worker</span><span class="p" data-group-id="3755163177-27">}</span><span class="p" data-group-id="3755163177-19">]</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V10</span><span class="p">.</span><span class="mi">0</span><span class="w">  </span><span class="p" data-group-id="3755163177-28">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="3755163177-28">)</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="o">&gt;</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/erl_interface.xhtml
│ │ │ │ @@ -25,119 +25,119 @@
│ │ │ │  to read the port example in <a href="c_port.xhtml">Ports</a> before reading this section.</p><h2 id="erlang-program" class="section-heading">
│ │ │ │    <a href="#erlang-program" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Erlang Program</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following example shows an Erlang program communicating with a C program
│ │ │ │ -over a plain port with home made encoding:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7536189049-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="7536189049-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7536189049-2">(</span><span class="p" data-group-id="7536189049-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7536189049-3">]</span><span class="p" data-group-id="7536189049-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7536189049-4">(</span><span class="p" data-group-id="7536189049-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7536189049-5">]</span><span class="p" data-group-id="7536189049-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="7536189049-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="7536189049-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="7536189049-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7536189049-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="7536189049-8">]</span><span class="p" data-group-id="7536189049-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="7536189049-9">(</span><span class="p" data-group-id="7536189049-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +over a plain port with home made encoding:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2305821051-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="2305821051-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2305821051-2">(</span><span class="p" data-group-id="2305821051-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2305821051-3">]</span><span class="p" data-group-id="2305821051-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2305821051-4">(</span><span class="p" data-group-id="2305821051-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2305821051-5">]</span><span class="p" data-group-id="2305821051-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="2305821051-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="2305821051-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="2305821051-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2305821051-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="2305821051-8">]</span><span class="p" data-group-id="2305821051-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="2305821051-9">(</span><span class="p" data-group-id="2305821051-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="7536189049-10">(</span><span class="n">X</span><span class="p" data-group-id="7536189049-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="7536189049-11">(</span><span class="p" data-group-id="7536189049-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7536189049-12">}</span><span class="p" data-group-id="7536189049-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="7536189049-13">(</span><span class="n">Y</span><span class="p" data-group-id="7536189049-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="7536189049-14">(</span><span class="p" data-group-id="7536189049-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7536189049-15">}</span><span class="p" data-group-id="7536189049-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="2305821051-10">(</span><span class="n">X</span><span class="p" data-group-id="2305821051-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="2305821051-11">(</span><span class="p" data-group-id="2305821051-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2305821051-12">}</span><span class="p" data-group-id="2305821051-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="2305821051-13">(</span><span class="n">Y</span><span class="p" data-group-id="2305821051-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="2305821051-14">(</span><span class="p" data-group-id="2305821051-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2305821051-15">}</span><span class="p" data-group-id="2305821051-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="7536189049-16">(</span><span class="n">Msg</span><span class="p" data-group-id="7536189049-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7536189049-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7536189049-18">(</span><span class="p" data-group-id="7536189049-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7536189049-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="2305821051-16">(</span><span class="n">Msg</span><span class="p" data-group-id="2305821051-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2305821051-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2305821051-18">(</span><span class="p" data-group-id="2305821051-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="2305821051-17">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="7536189049-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7536189049-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="2305821051-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2305821051-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="7536189049-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="7536189049-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="7536189049-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7536189049-22">(</span><span class="p" data-group-id="7536189049-22">)</span><span class="p" data-group-id="7536189049-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="7536189049-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7536189049-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="7536189049-24">(</span><span class="p" data-group-id="7536189049-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="7536189049-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7536189049-26">[</span><span class="p" data-group-id="7536189049-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7536189049-27">}</span><span class="p" data-group-id="7536189049-26">]</span><span class="p" data-group-id="7536189049-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="7536189049-28">(</span><span class="n">Port</span><span class="p" data-group-id="7536189049-28">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="2305821051-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="2305821051-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="2305821051-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2305821051-22">(</span><span class="p" data-group-id="2305821051-22">)</span><span class="p" data-group-id="2305821051-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="2305821051-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2305821051-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="2305821051-24">(</span><span class="p" data-group-id="2305821051-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="2305821051-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2305821051-26">[</span><span class="p" data-group-id="2305821051-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2305821051-27">}</span><span class="p" data-group-id="2305821051-26">]</span><span class="p" data-group-id="2305821051-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="2305821051-28">(</span><span class="n">Port</span><span class="p" data-group-id="2305821051-28">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="7536189049-29">(</span><span class="n">Port</span><span class="p" data-group-id="7536189049-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="2305821051-29">(</span><span class="n">Port</span><span class="p" data-group-id="2305821051-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="7536189049-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7536189049-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7536189049-31">{</span><span class="nf">self</span><span class="p" data-group-id="7536189049-32">(</span><span class="p" data-group-id="7536189049-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7536189049-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="7536189049-34">(</span><span class="n">Msg</span><span class="p" data-group-id="7536189049-34">)</span><span class="p" data-group-id="7536189049-33">}</span><span class="p" data-group-id="7536189049-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="2305821051-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="2305821051-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2305821051-31">{</span><span class="nf">self</span><span class="p" data-group-id="2305821051-32">(</span><span class="p" data-group-id="2305821051-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2305821051-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="2305821051-34">(</span><span class="n">Msg</span><span class="p" data-group-id="2305821051-34">)</span><span class="p" data-group-id="2305821051-33">}</span><span class="p" data-group-id="2305821051-31">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="7536189049-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7536189049-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7536189049-36">}</span><span class="p" data-group-id="7536189049-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7536189049-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="7536189049-38">(</span><span class="n">Data</span><span class="p" data-group-id="7536189049-38">)</span><span class="p" data-group-id="7536189049-37">}</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="2305821051-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2305821051-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2305821051-36">}</span><span class="p" data-group-id="2305821051-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2305821051-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="2305821051-38">(</span><span class="n">Data</span><span class="p" data-group-id="2305821051-38">)</span><span class="p" data-group-id="2305821051-37">}</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="7536189049-39">(</span><span class="n">Port</span><span class="p" data-group-id="7536189049-39">)</span><span class="p">;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="2305821051-39">(</span><span class="n">Port</span><span class="p" data-group-id="2305821051-39">)</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7536189049-40">{</span><span class="nf">self</span><span class="p" data-group-id="7536189049-41">(</span><span class="p" data-group-id="7536189049-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="7536189049-40">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2305821051-40">{</span><span class="nf">self</span><span class="p" data-group-id="2305821051-41">(</span><span class="p" data-group-id="2305821051-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="2305821051-40">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="7536189049-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="7536189049-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="7536189049-43">(</span><span class="ss">normal</span><span class="p" data-group-id="7536189049-43">)</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="2305821051-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="2305821051-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="2305821051-43">(</span><span class="ss">normal</span><span class="p" data-group-id="2305821051-43">)</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="7536189049-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="7536189049-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="7536189049-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="7536189049-45">)</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="2305821051-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="2305821051-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="2305821051-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="2305821051-45">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="7536189049-46">(</span><span class="p" data-group-id="7536189049-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7536189049-47">}</span><span class="p" data-group-id="7536189049-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7536189049-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7536189049-48">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="7536189049-49">(</span><span class="p" data-group-id="7536189049-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7536189049-50">}</span><span class="p" data-group-id="7536189049-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7536189049-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7536189049-51">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="2305821051-46">(</span><span class="p" data-group-id="2305821051-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2305821051-47">}</span><span class="p" data-group-id="2305821051-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2305821051-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2305821051-48">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="2305821051-49">(</span><span class="p" data-group-id="2305821051-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2305821051-50">}</span><span class="p" data-group-id="2305821051-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2305821051-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2305821051-51">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="7536189049-52">(</span><span class="p" data-group-id="7536189049-53">[</span><span class="n">Int</span><span class="p" data-group-id="7536189049-53">]</span><span class="p" data-group-id="7536189049-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>There are two differences when using Erl_Interface on the C side compared to the
│ │ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="2305821051-52">(</span><span class="p" data-group-id="2305821051-53">[</span><span class="n">Int</span><span class="p" data-group-id="2305821051-53">]</span><span class="p" data-group-id="2305821051-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>There are two differences when using Erl_Interface on the C side compared to the
│ │ │ │  example in <a href="c_port.xhtml">Ports</a>, using only the plain port:</p><ul><li>As Erl_Interface operates on the Erlang external term format, the port must be
│ │ │ │  set to use binaries.</li><li>Instead of inventing an encoding/decoding scheme, the
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#term_to_binary/1"><code class="inline">term_to_binary/1</code></a> and
│ │ │ │ -<a href="../../../lib/../erts/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a> BIFs are to be used.</li></ul><p>That is:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="0887544716-1">(</span><span class="p" data-group-id="0887544716-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="0887544716-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0887544716-3">[</span><span class="p" data-group-id="0887544716-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0887544716-4">}</span><span class="p" data-group-id="0887544716-3">]</span><span class="p" data-group-id="0887544716-1">)</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="4153285576-1">(</span><span class="p" data-group-id="4153285576-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="4153285576-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4153285576-3">[</span><span class="p" data-group-id="4153285576-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4153285576-4">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="4153285576-3">]</span><span class="p" data-group-id="4153285576-1">)</span></code></pre><p>And:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0677577771-1">{</span><span class="nf">self</span><span class="p" data-group-id="0677577771-2">(</span><span class="p" data-group-id="0677577771-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0677577771-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="0677577771-4">(</span><span class="n">Msg</span><span class="p" data-group-id="0677577771-4">)</span><span class="p" data-group-id="0677577771-3">}</span><span class="p" data-group-id="0677577771-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +<a href="../../../lib/../erts/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a> BIFs are to be used.</li></ul><p>That is:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="0469962281-1">(</span><span class="p" data-group-id="0469962281-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="0469962281-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0469962281-3">[</span><span class="p" data-group-id="0469962281-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0469962281-4">}</span><span class="p" data-group-id="0469962281-3">]</span><span class="p" data-group-id="0469962281-1">)</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="6172318497-1">(</span><span class="p" data-group-id="6172318497-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="6172318497-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6172318497-3">[</span><span class="p" data-group-id="6172318497-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6172318497-4">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="6172318497-3">]</span><span class="p" data-group-id="6172318497-1">)</span></code></pre><p>And:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5511281411-1">{</span><span class="nf">self</span><span class="p" data-group-id="5511281411-2">(</span><span class="p" data-group-id="5511281411-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5511281411-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="5511281411-4">(</span><span class="n">Msg</span><span class="p" data-group-id="5511281411-4">)</span><span class="p" data-group-id="5511281411-3">}</span><span class="p" data-group-id="5511281411-1">}</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0677577771-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0677577771-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0677577771-6">}</span><span class="p" data-group-id="0677577771-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0677577771-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="0677577771-8">(</span><span class="n">Data</span><span class="p" data-group-id="0677577771-8">)</span><span class="p" data-group-id="0677577771-7">}</span><span class="w">
│ │ │ │ -</span><span class="k">end</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9073899930-1">{</span><span class="nf">self</span><span class="p" data-group-id="9073899930-2">(</span><span class="p" data-group-id="9073899930-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9073899930-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="9073899930-4">(</span><span class="n">Msg</span><span class="p" data-group-id="9073899930-4">)</span><span class="p" data-group-id="9073899930-3">}</span><span class="p" data-group-id="9073899930-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5511281411-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5511281411-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5511281411-6">}</span><span class="p" data-group-id="5511281411-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5511281411-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="5511281411-8">(</span><span class="n">Data</span><span class="p" data-group-id="5511281411-8">)</span><span class="p" data-group-id="5511281411-7">}</span><span class="w">
│ │ │ │ +</span><span class="k">end</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3541373018-1">{</span><span class="nf">self</span><span class="p" data-group-id="3541373018-2">(</span><span class="p" data-group-id="3541373018-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3541373018-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="3541373018-4">(</span><span class="n">Msg</span><span class="p" data-group-id="3541373018-4">)</span><span class="p" data-group-id="3541373018-3">}</span><span class="p" data-group-id="3541373018-1">}</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9073899930-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9073899930-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9073899930-6">}</span><span class="p" data-group-id="9073899930-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9073899930-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="9073899930-8">(</span><span class="n">Data</span><span class="p" data-group-id="9073899930-8">)</span><span class="p" data-group-id="9073899930-7">}</span><span class="w">
│ │ │ │ -</span><span class="k">end</span></code></pre><p>The resulting Erlang program is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6941612315-1">(</span><span class="ss">complex2</span><span class="p" data-group-id="6941612315-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6941612315-2">(</span><span class="p" data-group-id="6941612315-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6941612315-3">]</span><span class="p" data-group-id="6941612315-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6941612315-4">(</span><span class="p" data-group-id="6941612315-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6941612315-5">]</span><span class="p" data-group-id="6941612315-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="6941612315-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="6941612315-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="6941612315-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6941612315-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="6941612315-8">]</span><span class="p" data-group-id="6941612315-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="6941612315-9">(</span><span class="p" data-group-id="6941612315-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3541373018-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3541373018-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3541373018-6">}</span><span class="p" data-group-id="3541373018-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3541373018-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="3541373018-8">(</span><span class="n">Data</span><span class="p" data-group-id="3541373018-8">)</span><span class="p" data-group-id="3541373018-7">}</span><span class="w">
│ │ │ │ +</span><span class="k">end</span></code></pre><p>The resulting Erlang program is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7334589465-1">(</span><span class="ss">complex2</span><span class="p" data-group-id="7334589465-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7334589465-2">(</span><span class="p" data-group-id="7334589465-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7334589465-3">]</span><span class="p" data-group-id="7334589465-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7334589465-4">(</span><span class="p" data-group-id="7334589465-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7334589465-5">]</span><span class="p" data-group-id="7334589465-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="7334589465-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="7334589465-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="7334589465-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7334589465-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="7334589465-8">]</span><span class="p" data-group-id="7334589465-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="7334589465-9">(</span><span class="p" data-group-id="7334589465-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="6941612315-10">(</span><span class="n">X</span><span class="p" data-group-id="6941612315-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="6941612315-11">(</span><span class="p" data-group-id="6941612315-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6941612315-12">}</span><span class="p" data-group-id="6941612315-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="6941612315-13">(</span><span class="n">Y</span><span class="p" data-group-id="6941612315-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="6941612315-14">(</span><span class="p" data-group-id="6941612315-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6941612315-15">}</span><span class="p" data-group-id="6941612315-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="7334589465-10">(</span><span class="n">X</span><span class="p" data-group-id="7334589465-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="7334589465-11">(</span><span class="p" data-group-id="7334589465-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7334589465-12">}</span><span class="p" data-group-id="7334589465-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="7334589465-13">(</span><span class="n">Y</span><span class="p" data-group-id="7334589465-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="7334589465-14">(</span><span class="p" data-group-id="7334589465-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7334589465-15">}</span><span class="p" data-group-id="7334589465-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="6941612315-16">(</span><span class="n">Msg</span><span class="p" data-group-id="6941612315-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6941612315-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6941612315-18">(</span><span class="p" data-group-id="6941612315-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6941612315-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="7334589465-16">(</span><span class="n">Msg</span><span class="p" data-group-id="7334589465-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7334589465-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7334589465-18">(</span><span class="p" data-group-id="7334589465-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7334589465-17">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="6941612315-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6941612315-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="7334589465-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7334589465-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6941612315-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="6941612315-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="6941612315-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6941612315-22">(</span><span class="p" data-group-id="6941612315-22">)</span><span class="p" data-group-id="6941612315-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="6941612315-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6941612315-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="6941612315-24">(</span><span class="p" data-group-id="6941612315-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="6941612315-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6941612315-26">[</span><span class="p" data-group-id="6941612315-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6941612315-27">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="6941612315-26">]</span><span class="p" data-group-id="6941612315-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="6941612315-28">(</span><span class="n">Port</span><span class="p" data-group-id="6941612315-28">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="7334589465-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="7334589465-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="7334589465-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7334589465-22">(</span><span class="p" data-group-id="7334589465-22">)</span><span class="p" data-group-id="7334589465-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="7334589465-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7334589465-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="7334589465-24">(</span><span class="p" data-group-id="7334589465-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="7334589465-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7334589465-26">[</span><span class="p" data-group-id="7334589465-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7334589465-27">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="7334589465-26">]</span><span class="p" data-group-id="7334589465-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="7334589465-28">(</span><span class="n">Port</span><span class="p" data-group-id="7334589465-28">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="6941612315-29">(</span><span class="n">Port</span><span class="p" data-group-id="6941612315-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="7334589465-29">(</span><span class="n">Port</span><span class="p" data-group-id="7334589465-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="6941612315-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6941612315-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6941612315-31">{</span><span class="nf">self</span><span class="p" data-group-id="6941612315-32">(</span><span class="p" data-group-id="6941612315-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6941612315-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="6941612315-34">(</span><span class="n">Msg</span><span class="p" data-group-id="6941612315-34">)</span><span class="p" data-group-id="6941612315-33">}</span><span class="p" data-group-id="6941612315-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="7334589465-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7334589465-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7334589465-31">{</span><span class="nf">self</span><span class="p" data-group-id="7334589465-32">(</span><span class="p" data-group-id="7334589465-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7334589465-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="7334589465-34">(</span><span class="n">Msg</span><span class="p" data-group-id="7334589465-34">)</span><span class="p" data-group-id="7334589465-33">}</span><span class="p" data-group-id="7334589465-31">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="6941612315-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6941612315-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6941612315-36">}</span><span class="p" data-group-id="6941612315-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6941612315-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="6941612315-38">(</span><span class="n">Data</span><span class="p" data-group-id="6941612315-38">)</span><span class="p" data-group-id="6941612315-37">}</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="7334589465-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7334589465-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7334589465-36">}</span><span class="p" data-group-id="7334589465-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7334589465-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="7334589465-38">(</span><span class="n">Data</span><span class="p" data-group-id="7334589465-38">)</span><span class="p" data-group-id="7334589465-37">}</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="6941612315-39">(</span><span class="n">Port</span><span class="p" data-group-id="6941612315-39">)</span><span class="p">;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="7334589465-39">(</span><span class="n">Port</span><span class="p" data-group-id="7334589465-39">)</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6941612315-40">{</span><span class="nf">self</span><span class="p" data-group-id="6941612315-41">(</span><span class="p" data-group-id="6941612315-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="6941612315-40">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7334589465-40">{</span><span class="nf">self</span><span class="p" data-group-id="7334589465-41">(</span><span class="p" data-group-id="7334589465-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="7334589465-40">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="6941612315-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="6941612315-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="6941612315-43">(</span><span class="ss">normal</span><span class="p" data-group-id="6941612315-43">)</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="7334589465-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="7334589465-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="7334589465-43">(</span><span class="ss">normal</span><span class="p" data-group-id="7334589465-43">)</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="6941612315-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="6941612315-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="6941612315-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="6941612315-45">)</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="7334589465-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="7334589465-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="7334589465-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="7334589465-45">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Notice that calling <code class="inline">complex2:foo/1</code> and <code class="inline">complex2:bar/1</code> results in the tuple
│ │ │ │  <code class="inline">{foo,X}</code> or <code class="inline">{bar,Y}</code> being sent to the <code class="inline">complex</code> process, which codes them as
│ │ │ │  binaries and sends them to the port. This means that the C program must be able
│ │ │ │  to handle these two tuples.</p><h2 id="c-program" class="section-heading">
│ │ │ │    <a href="#c-program" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -267,24 +267,24 @@
│ │ │ │      -L/usr/local/otp/lib/erl_interface-3.9.2/lib \
│ │ │ │      complex.c erl_comm.c ei.c -lei -lpthread</code></pre><p>In Erlang/OTP R5B and later versions of OTP, the <code class="inline">include</code> and <code class="inline">lib</code> directories
│ │ │ │  are situated under <code class="inline">$OTPROOT/lib/erl_interface-VSN</code>, where <code class="inline">$OTPROOT</code> is the
│ │ │ │  root directory of the OTP installation (<code class="inline">/usr/local/otp</code> in the recent example)
│ │ │ │  and <code class="inline">VSN</code> is the version of the Erl_interface application (3.2.1 in the recent
│ │ │ │  example).</p><p>In R4B and earlier versions of OTP, <code class="inline">include</code> and <code class="inline">lib</code> are situated under
│ │ │ │  <code class="inline">$OTPROOT/usr</code>.</p><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$ </span><span class="ss">erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="2296929340-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="2296929340-1">]</span><span class="w"> </span><span class="p" data-group-id="2296929340-2">[</span><span class="ss">source</span><span class="p" data-group-id="2296929340-2">]</span><span class="w"> </span><span class="p" data-group-id="2296929340-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="2296929340-3">]</span><span class="w"> </span><span class="p" data-group-id="2296929340-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="2296929340-4">]</span><span class="w"> </span><span class="p" data-group-id="2296929340-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="2296929340-5">]</span><span class="w"> </span><span class="p" data-group-id="2296929340-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2296929340-6">]</span><span class="w"> </span><span class="p" data-group-id="2296929340-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="2296929340-7">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="7049614415-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="7049614415-1">]</span><span class="w"> </span><span class="p" data-group-id="7049614415-2">[</span><span class="ss">source</span><span class="p" data-group-id="7049614415-2">]</span><span class="w"> </span><span class="p" data-group-id="7049614415-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="7049614415-3">]</span><span class="w"> </span><span class="p" data-group-id="7049614415-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="7049614415-4">]</span><span class="w"> </span><span class="p" data-group-id="7049614415-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="7049614415-5">]</span><span class="w"> </span><span class="p" data-group-id="7049614415-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="7049614415-6">]</span><span class="w"> </span><span class="p" data-group-id="7049614415-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="7049614415-7">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="2296929340-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="2296929340-9">(</span><span class="p" data-group-id="2296929340-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="2296929340-8">)</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="nf">c</span><span class="p" data-group-id="2296929340-10">(</span><span class="ss">complex2</span><span class="p" data-group-id="2296929340-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2296929340-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex2</span><span class="p" data-group-id="2296929340-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9736699016-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="9736699016-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="7049614415-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="7049614415-9">(</span><span class="p" data-group-id="7049614415-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="7049614415-8">)</span><span class="gp unselectable">
│ │ │ │ +1&gt; </span><span class="nf">c</span><span class="p" data-group-id="7049614415-10">(</span><span class="ss">complex2</span><span class="p" data-group-id="7049614415-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7049614415-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex2</span><span class="p" data-group-id="7049614415-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9294634031-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="9294634031-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="9736699016-2">(</span><span class="mi">3</span><span class="p" data-group-id="9736699016-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="9294634031-2">(</span><span class="mi">3</span><span class="p" data-group-id="9294634031-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="9736699016-3">(</span><span class="mi">5</span><span class="p" data-group-id="9736699016-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="9294634031-3">(</span><span class="mi">5</span><span class="p" data-group-id="9294634031-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">10</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="9736699016-4">(</span><span class="mi">352</span><span class="p" data-group-id="9736699016-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="9294634031-4">(</span><span class="mi">352</span><span class="p" data-group-id="9294634031-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">704</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="9736699016-5">(</span><span class="p" data-group-id="9736699016-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +6&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="9294634031-5">(</span><span class="p" data-group-id="9294634031-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/eff_guide_processes.xhtml
│ │ │ │ @@ -24,45 +24,45 @@
│ │ │ │    <a href="#creating-an-erlang-process" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating an Erlang Process</span>
│ │ │ │  </h2>
│ │ │ │  <p>An Erlang process is lightweight compared to threads and processes in operating
│ │ │ │  systems.</p><p>A newly spawned Erlang process uses 327 words of memory. The size can be found
│ │ │ │ -as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="2689541684-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p">.</span><span class="mi">3</span><span class="p" data-group-id="2689541684-1">]</span><span class="w"> </span><span class="p" data-group-id="2689541684-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="2689541684-2">]</span><span class="w"> </span><span class="p" data-group-id="2689541684-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="2689541684-3">]</span><span class="w"> </span><span class="p" data-group-id="2689541684-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="2689541684-4">]</span><span class="w"> </span><span class="p" data-group-id="2689541684-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2689541684-5">]</span><span class="w"> </span><span class="p" data-group-id="2689541684-6">[</span><span class="ss">jit</span><span class="p" data-group-id="2689541684-6">]</span><span class="w">
│ │ │ │ +as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="4201565815-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p">.</span><span class="mi">3</span><span class="p" data-group-id="4201565815-1">]</span><span class="w"> </span><span class="p" data-group-id="4201565815-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4201565815-2">]</span><span class="w"> </span><span class="p" data-group-id="4201565815-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4201565815-3">]</span><span class="w"> </span><span class="p" data-group-id="4201565815-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4201565815-4">]</span><span class="w"> </span><span class="p" data-group-id="4201565815-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4201565815-5">]</span><span class="w"> </span><span class="p" data-group-id="4201565815-6">[</span><span class="ss">jit</span><span class="p" data-group-id="4201565815-6">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mf">2.3</span><span class="w"> </span><span class="p" data-group-id="2689541684-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="2689541684-8">(</span><span class="p" data-group-id="2689541684-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="2689541684-7">)</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="2689541684-9">(</span><span class="p" data-group-id="2689541684-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="ss">infinity</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mf">2.3</span><span class="w"> </span><span class="p" data-group-id="4201565815-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="4201565815-8">(</span><span class="p" data-group-id="4201565815-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="4201565815-7">)</span><span class="gp unselectable">
│ │ │ │ +1&gt; </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4201565815-9">(</span><span class="p" data-group-id="4201565815-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="ss">infinity</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">43.39164016</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="2689541684-10">{</span><span class="p">_</span><span class="p">,</span><span class="n">Bytes</span><span class="p" data-group-id="2689541684-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">process_info</span><span class="p" data-group-id="2689541684-11">(</span><span class="nf">spawn</span><span class="p" data-group-id="2689541684-12">(</span><span class="n">Fun</span><span class="p" data-group-id="2689541684-12">)</span><span class="p">,</span><span class="w"> </span><span class="nb">memory</span><span class="p" data-group-id="2689541684-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2689541684-13">{</span><span class="nb">memory</span><span class="p">,</span><span class="mi">2616</span><span class="p" data-group-id="2689541684-13">}</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="n">Bytes</span><span class="w"> </span><span class="ow">div</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="2689541684-14">(</span><span class="ss">wordsize</span><span class="p" data-group-id="2689541684-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="4201565815-10">{</span><span class="p">_</span><span class="p">,</span><span class="n">Bytes</span><span class="p" data-group-id="4201565815-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">process_info</span><span class="p" data-group-id="4201565815-11">(</span><span class="nf">spawn</span><span class="p" data-group-id="4201565815-12">(</span><span class="n">Fun</span><span class="p" data-group-id="4201565815-12">)</span><span class="p">,</span><span class="w"> </span><span class="nb">memory</span><span class="p" data-group-id="4201565815-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4201565815-13">{</span><span class="nb">memory</span><span class="p">,</span><span class="mi">2616</span><span class="p" data-group-id="4201565815-13">}</span><span class="gp unselectable">
│ │ │ │ +3&gt; </span><span class="n">Bytes</span><span class="w"> </span><span class="ow">div</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="4201565815-14">(</span><span class="ss">wordsize</span><span class="p" data-group-id="4201565815-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">327</span></code></pre><p>The size includes 233 words for the heap area (which includes the stack). The
│ │ │ │  garbage collector increases the heap as needed.</p><p>The main (outer) loop for a process <em>must</em> be tail-recursive. Otherwise, the
│ │ │ │ -stack grows until the process terminates.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="4697430805-1">(</span><span class="p" data-group-id="4697430805-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +stack grows until the process terminates.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="8707733966-1">(</span><span class="p" data-group-id="8707733966-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="4697430805-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4697430805-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="4697430805-3">(</span><span class="n">Msg</span><span class="p" data-group-id="4697430805-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="4697430805-4">(</span><span class="p" data-group-id="4697430805-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="4697430805-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4697430805-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -          </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="4697430805-6">(</span><span class="n">Msg</span><span class="p" data-group-id="4697430805-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="8707733966-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8707733966-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="8707733966-3">(</span><span class="n">Msg</span><span class="p" data-group-id="8707733966-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="8707733966-4">(</span><span class="p" data-group-id="8707733966-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="8707733966-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8707733966-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +          </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8707733966-6">(</span><span class="n">Msg</span><span class="p" data-group-id="8707733966-6">)</span><span class="p">,</span><span class="w">
│ │ │ │            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Reply</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="nf">loop</span><span class="p" data-group-id="4697430805-7">(</span><span class="p" data-group-id="4697430805-7">)</span><span class="w">
│ │ │ │ +          </span><span class="nf">loop</span><span class="p" data-group-id="8707733966-7">(</span><span class="p" data-group-id="8707733966-7">)</span><span class="w">
│ │ │ │    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4697430805-8">(</span><span class="s">&quot;Message is processed</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4697430805-9">[</span><span class="p" data-group-id="4697430805-9">]</span><span class="p" data-group-id="4697430805-8">)</span><span class="p">.</span></code></pre><p>The call to <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> will never be executed, but a return address will
│ │ │ │ +  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8707733966-8">(</span><span class="s">&quot;Message is processed</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8707733966-9">[</span><span class="p" data-group-id="8707733966-9">]</span><span class="p" data-group-id="8707733966-8">)</span><span class="p">.</span></code></pre><p>The call to <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> will never be executed, but a return address will
│ │ │ │  still be pushed to the stack each time <code class="inline">loop/0</code> is called recursively. The
│ │ │ │ -correct tail-recursive version of the function looks as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="6264279832-1">(</span><span class="p" data-group-id="6264279832-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +correct tail-recursive version of the function looks as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="1439453604-1">(</span><span class="p" data-group-id="1439453604-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │     </span><span class="k">receive</span><span class="w">
│ │ │ │ -      </span><span class="p" data-group-id="6264279832-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6264279832-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="6264279832-3">(</span><span class="n">Msg</span><span class="p" data-group-id="6264279832-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="6264279832-4">(</span><span class="p" data-group-id="6264279832-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -      </span><span class="p" data-group-id="6264279832-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6264279832-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -         </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="6264279832-6">(</span><span class="n">Msg</span><span class="p" data-group-id="6264279832-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +      </span><span class="p" data-group-id="1439453604-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1439453604-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="1439453604-3">(</span><span class="n">Msg</span><span class="p" data-group-id="1439453604-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="1439453604-4">(</span><span class="p" data-group-id="1439453604-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +      </span><span class="p" data-group-id="1439453604-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1439453604-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +         </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="1439453604-6">(</span><span class="n">Msg</span><span class="p" data-group-id="1439453604-6">)</span><span class="p">,</span><span class="w">
│ │ │ │           </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Reply</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="6264279832-7">(</span><span class="p" data-group-id="6264279832-7">)</span><span class="w">
│ │ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="1439453604-7">(</span><span class="p" data-group-id="1439453604-7">)</span><span class="w">
│ │ │ │   </span><span class="k">end</span><span class="p">.</span></code></pre><h3 id="initial-heap-size" class="section-heading">
│ │ │ │    <a href="#initial-heap-size" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Initial Heap Size</span>
│ │ │ │  </h3>
│ │ │ │  <p>The default initial heap size of 233 words is quite conservative to support
│ │ │ │ @@ -94,30 +94,30 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Receiving messages</span>
│ │ │ │  </h2>
│ │ │ │  <p>The cost of receiving messages depends on how complicated the <code class="inline">receive</code>
│ │ │ │  expression is. A simple expression that matches any message is very cheap
│ │ │ │  because it retrieves the first message in the message queue:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="3067906516-1">(</span><span class="n">Message</span><span class="p" data-group-id="3067906516-1">)</span><span class="w">
│ │ │ │ +    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="0579396042-1">(</span><span class="n">Message</span><span class="p" data-group-id="0579396042-1">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>However, this is not always convenient: we can receive a message that we do not
│ │ │ │  know how to handle at this point, so it is common to only match the messages we
│ │ │ │  expect:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3268440033-1">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3268440033-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="3268440033-2">(</span><span class="n">Message</span><span class="p" data-group-id="3268440033-2">)</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8388544443-1">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8388544443-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8388544443-2">(</span><span class="n">Message</span><span class="p" data-group-id="8388544443-2">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>While this is convenient it means that the entire message queue must be searched
│ │ │ │  until it finds a matching message. This is very expensive for processes with
│ │ │ │  long message queues, so there is an optimization for the common case of
│ │ │ │ -sending a request and waiting for a response shortly after:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="1907830010-1">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="1907830010-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1907830010-2">{</span><span class="nf">self</span><span class="p" data-group-id="1907830010-3">(</span><span class="p" data-group-id="1907830010-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="1907830010-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +sending a request and waiting for a response shortly after:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="5987909373-1">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="5987909373-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5987909373-2">{</span><span class="nf">self</span><span class="p" data-group-id="5987909373-3">(</span><span class="p" data-group-id="5987909373-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="5987909373-2">}</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1907830010-4">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="1907830010-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="1907830010-5">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1907830010-6">[</span><span class="ss">flush</span><span class="p" data-group-id="1907830010-6">]</span><span class="p" data-group-id="1907830010-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="nf">handle_reply</span><span class="p" data-group-id="1907830010-7">(</span><span class="n">Reply</span><span class="p" data-group-id="1907830010-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1907830010-8">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1907830010-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nf">handle_error</span><span class="p" data-group-id="1907830010-9">(</span><span class="n">Reason</span><span class="p" data-group-id="1907830010-9">)</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5987909373-4">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="5987909373-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="5987909373-5">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5987909373-6">[</span><span class="ss">flush</span><span class="p" data-group-id="5987909373-6">]</span><span class="p" data-group-id="5987909373-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="nf">handle_reply</span><span class="p" data-group-id="5987909373-7">(</span><span class="n">Reply</span><span class="p" data-group-id="5987909373-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5987909373-8">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5987909373-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nf">handle_error</span><span class="p" data-group-id="5987909373-9">(</span><span class="n">Reason</span><span class="p" data-group-id="5987909373-9">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>Since the compiler knows that the reference created by
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#monitor/2"><code class="inline">monitor/2</code></a> cannot exist before the call (since it is a globally
│ │ │ │  unique identifier), and that the <code class="inline">receive</code> only matches messages that contain
│ │ │ │  said reference, it will tell the emulator to search only the messages that
│ │ │ │  arrived after the call to <a href="../../../lib/../erts/doc/html/erlang.html#monitor/2"><code class="inline">monitor/2</code></a>.</p><p>The above is a simple example where one is but guaranteed that the optimization
│ │ │ │  will take, but what about more complicated code?</p><p><a href="" id="recv_opt_info"></a></p><h3 id="option-recv_opt_info" class="section-heading">
│ │ │ │    <a href="#option-recv_opt_info" class="hover-link">
│ │ │ │ @@ -133,101 +133,101 @@
│ │ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">200</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">NOT</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">do</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">suitable</span><span class="w"> </span><span class="ss">reference</span><span class="w">
│ │ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">206</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">used</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">mark</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">message</span><span class="w"> </span><span class="ss">queue</span><span class="w"> </span><span class="ss">position</span><span class="w">
│ │ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">208</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">created</span><span class="w"> </span><span class="ss">by</span><span class="w"> </span><span class="nb">monitor</span><span class="p">/</span><span class="mi">2</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">206</span><span class="w">
│ │ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">219</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">INFO</span><span class="p">:</span><span class="w"> </span><span class="ss">passing</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">created</span><span class="w"> </span><span class="ss">by</span><span class="w"> </span><span class="ss">make_ref</span><span class="p">/</span><span class="mi">0</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">218</span><span class="w">
│ │ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">222</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">function</span><span class="w"> </span><span class="ss">parameter</span><span class="w"> </span><span class="mi">1</span></code></pre><p>To make it clearer exactly what code the warnings refer to, the warnings in the
│ │ │ │  following examples are inserted as comments after the clause they refer to, for
│ │ │ │  example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% DO</span><span class="w">
│ │ │ │ -</span><span class="nf">simple_receive</span><span class="p" data-group-id="6470724105-1">(</span><span class="p" data-group-id="6470724105-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">simple_receive</span><span class="p" data-group-id="8661935369-1">(</span><span class="p" data-group-id="8661935369-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="c1">%% efficiency_guide.erl:194: Warning: INFO: not a selective receive, this is always fast</span><span class="w">
│ │ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="6470724105-2">(</span><span class="n">Message</span><span class="p" data-group-id="6470724105-2">)</span><span class="w">
│ │ │ │ +    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8661935369-2">(</span><span class="n">Message</span><span class="p" data-group-id="8661935369-2">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% DO NOT, unless Tag is known to be a suitable reference: see</span><span class="w">
│ │ │ │  </span><span class="c1">%% cross_function_receive/0 further down.</span><span class="w">
│ │ │ │ -</span><span class="nf">selective_receive</span><span class="p" data-group-id="6470724105-3">(</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6470724105-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">selective_receive</span><span class="p" data-group-id="8661935369-3">(</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8661935369-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="c1">%% efficiency_guide.erl:200: Warning: NOT OPTIMIZED: all clauses do not match a suitable reference</span><span class="w">
│ │ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6470724105-4">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6470724105-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="6470724105-5">(</span><span class="n">Message</span><span class="p" data-group-id="6470724105-5">)</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8661935369-4">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8661935369-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8661935369-5">(</span><span class="n">Message</span><span class="p" data-group-id="8661935369-5">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% DO</span><span class="w">
│ │ │ │ -</span><span class="nf">optimized_receive</span><span class="p" data-group-id="6470724105-6">(</span><span class="n">Process</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="6470724105-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">optimized_receive</span><span class="p" data-group-id="8661935369-6">(</span><span class="n">Process</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="8661935369-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="c1">%% efficiency_guide.erl:206: Warning: OPTIMIZED: reference used to mark a message queue position</span><span class="w">
│ │ │ │ -    </span><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="6470724105-7">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="6470724105-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6470724105-8">{</span><span class="nf">self</span><span class="p" data-group-id="6470724105-9">(</span><span class="p" data-group-id="6470724105-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="6470724105-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="8661935369-7">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="8661935369-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8661935369-8">{</span><span class="nf">self</span><span class="p" data-group-id="8661935369-9">(</span><span class="p" data-group-id="8661935369-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="8661935369-8">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="c1">%% efficiency_guide.erl:208: Warning: OPTIMIZED: matches reference created by monitor/2 at efficiency_guide.erl:206</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6470724105-10">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="6470724105-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="6470724105-11">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6470724105-12">[</span><span class="ss">flush</span><span class="p" data-group-id="6470724105-12">]</span><span class="p" data-group-id="6470724105-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="nf">handle_reply</span><span class="p" data-group-id="6470724105-13">(</span><span class="n">Reply</span><span class="p" data-group-id="6470724105-13">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6470724105-14">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="6470724105-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">handle_error</span><span class="p" data-group-id="6470724105-15">(</span><span class="n">Reason</span><span class="p" data-group-id="6470724105-15">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8661935369-10">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="8661935369-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="8661935369-11">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8661935369-12">[</span><span class="ss">flush</span><span class="p" data-group-id="8661935369-12">]</span><span class="p" data-group-id="8661935369-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="nf">handle_reply</span><span class="p" data-group-id="8661935369-13">(</span><span class="n">Reply</span><span class="p" data-group-id="8661935369-13">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8661935369-14">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="8661935369-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">handle_error</span><span class="p" data-group-id="8661935369-15">(</span><span class="n">Reason</span><span class="p" data-group-id="8661935369-15">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% DO</span><span class="w">
│ │ │ │ -</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="6470724105-16">(</span><span class="p" data-group-id="6470724105-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="8661935369-16">(</span><span class="p" data-group-id="8661935369-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% efficiency_guide.erl:218: Warning: OPTIMIZED: reference used to mark a message queue position</span><span class="w">
│ │ │ │ -    </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="6470724105-17">(</span><span class="p" data-group-id="6470724105-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="8661935369-17">(</span><span class="p" data-group-id="8661935369-17">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="c1">%% efficiency_guide.erl:219: Warning: INFO: passing reference created by make_ref/0 at efficiency_guide.erl:218</span><span class="w">
│ │ │ │ -    </span><span class="nf">cross_function_receive</span><span class="p" data-group-id="6470724105-18">(</span><span class="n">Ref</span><span class="p" data-group-id="6470724105-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">cross_function_receive</span><span class="p" data-group-id="8661935369-18">(</span><span class="n">Ref</span><span class="p" data-group-id="8661935369-18">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="6470724105-19">(</span><span class="n">Ref</span><span class="p" data-group-id="6470724105-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="8661935369-19">(</span><span class="n">Ref</span><span class="p" data-group-id="8661935369-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% efficiency_guide.erl:222: Warning: OPTIMIZED: all clauses match reference in function parameter 1</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6470724105-20">{</span><span class="n">Ref</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6470724105-20">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="6470724105-21">(</span><span class="n">Message</span><span class="p" data-group-id="6470724105-21">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8661935369-20">{</span><span class="n">Ref</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8661935369-20">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8661935369-21">(</span><span class="n">Message</span><span class="p" data-group-id="8661935369-21">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="literal-pool" class="section-heading">
│ │ │ │    <a href="#literal-pool" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Literal Pool</span>
│ │ │ │  </h2>
│ │ │ │  <p>Constant Erlang terms (hereafter called <em>literals</em>) are kept in <em>literal pools</em>;
│ │ │ │  each loaded module has its own pool. The following function does not build the
│ │ │ │  tuple every time it is called (only to have it discarded the next time the
│ │ │ │  garbage collector was run), but the tuple is located in the module's literal
│ │ │ │ -pool:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">days_in_month</span><span class="p" data-group-id="1586101775-1">(</span><span class="n">M</span><span class="p" data-group-id="1586101775-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">element</span><span class="p" data-group-id="1586101775-2">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1586101775-3">{</span><span class="mi">31</span><span class="p">,</span><span class="mi">28</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p" data-group-id="1586101775-3">}</span><span class="p" data-group-id="1586101775-2">)</span><span class="p">.</span></code></pre><p>If a literal, or a term that contains a literal, is inserted into an Ets table,
│ │ │ │ +pool:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">days_in_month</span><span class="p" data-group-id="4692758609-1">(</span><span class="n">M</span><span class="p" data-group-id="4692758609-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">element</span><span class="p" data-group-id="4692758609-2">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4692758609-3">{</span><span class="mi">31</span><span class="p">,</span><span class="mi">28</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p" data-group-id="4692758609-3">}</span><span class="p" data-group-id="4692758609-2">)</span><span class="p">.</span></code></pre><p>If a literal, or a term that contains a literal, is inserted into an Ets table,
│ │ │ │  it is <em>copied</em>. The reason is that the module containing the literal can be
│ │ │ │  unloaded in the future.</p><p>When a literal is sent to another process, it is <em>not</em> copied. When a module
│ │ │ │  holding a literal is unloaded, the literal will be copied to the heap of all
│ │ │ │  processes that hold references to that literal.</p><p>There also exists a global literal pool that is managed by the
│ │ │ │  <a href="../../../lib/../erts/doc/html/persistent_term.html"><code class="inline">persistent_term</code></a> module.</p><p>By default, 1 GB of virtual address space is reserved for all literal pools (in
│ │ │ │  BEAM code and persistent terms). The amount of virtual address space reserved
│ │ │ │  for literals can be changed by using the
│ │ │ │  <a href="../../../lib/../erts/doc/html/erts_alloc.xhtml#MIscs"><code class="inline">+MIscs option</code></a> when starting the emulator.</p><p>Here is an example how the reserved virtual address space for literals can be
│ │ │ │  raised to 2 GB (2048 MB):</p><pre><code class="text">erl +MIscs 2048</code></pre><h2 id="loss-of-sharing" class="section-heading">
│ │ │ │    <a href="#loss-of-sharing" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Loss of Sharing</span>
│ │ │ │  </h2>
│ │ │ │ -<p>An Erlang term can have shared subterms. Here is a simple example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2350649465-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="2350649465-1">}</span></code></pre><p>Shared subterms are <em>not</em> preserved in the following cases:</p><ul><li>When a term is sent to another process</li><li>When a term is passed as the initial process arguments in the <code class="inline">spawn</code> call</li><li>When a term is stored in an Ets table</li></ul><p>That is an optimization. Most applications do not send messages with shared
│ │ │ │ -subterms.</p><p>The following example shows how a shared subterm can be created:</p><pre><code class="makeup erlang" translate="no"><span class="nf">kilo_byte</span><span class="p" data-group-id="3563481658-1">(</span><span class="p" data-group-id="3563481658-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="3563481658-2">(</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3563481658-3">[</span><span class="mi">42</span><span class="p" data-group-id="3563481658-3">]</span><span class="p" data-group-id="3563481658-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>An Erlang term can have shared subterms. Here is a simple example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3820817983-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="3820817983-1">}</span></code></pre><p>Shared subterms are <em>not</em> preserved in the following cases:</p><ul><li>When a term is sent to another process</li><li>When a term is passed as the initial process arguments in the <code class="inline">spawn</code> call</li><li>When a term is stored in an Ets table</li></ul><p>That is an optimization. Most applications do not send messages with shared
│ │ │ │ +subterms.</p><p>The following example shows how a shared subterm can be created:</p><pre><code class="makeup erlang" translate="no"><span class="nf">kilo_byte</span><span class="p" data-group-id="7916814880-1">(</span><span class="p" data-group-id="7916814880-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="7916814880-2">(</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7916814880-3">[</span><span class="mi">42</span><span class="p" data-group-id="7916814880-3">]</span><span class="p" data-group-id="7916814880-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">kilo_byte</span><span class="p" data-group-id="3563481658-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3563481658-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">kilo_byte</span><span class="p" data-group-id="7916814880-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7916814880-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">kilo_byte</span><span class="p" data-group-id="3563481658-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3563481658-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="3563481658-6">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3563481658-7">[</span><span class="n">Acc</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="3563481658-7">]</span><span class="p" data-group-id="3563481658-6">)</span><span class="p">.</span></code></pre><p><code class="inline">kilo_byte/1</code> creates a deep list. If <a href="../../../lib/../erts/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a>
│ │ │ │ +</span><span class="nf">kilo_byte</span><span class="p" data-group-id="7916814880-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7916814880-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="7916814880-6">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7916814880-7">[</span><span class="n">Acc</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="7916814880-7">]</span><span class="p" data-group-id="7916814880-6">)</span><span class="p">.</span></code></pre><p><code class="inline">kilo_byte/1</code> creates a deep list. If <a href="../../../lib/../erts/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a>
│ │ │ │  is called, the deep list can be converted to a binary of 1024 bytes:</p><pre><code class="text">1&gt; byte_size(list_to_binary(efficiency_guide:kilo_byte())).
│ │ │ │  1024</code></pre><p>Using the <code class="inline">erts_debug:size/1</code> BIF, it can be seen that the deep list only
│ │ │ │ -requires 22 words of heap space:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="1481199934-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="1481199934-2">(</span><span class="p" data-group-id="1481199934-2">)</span><span class="p" data-group-id="1481199934-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +requires 22 words of heap space:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="0434464654-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="0434464654-2">(</span><span class="p" data-group-id="0434464654-2">)</span><span class="p" data-group-id="0434464654-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">22</span></code></pre><p>Using the <code class="inline">erts_debug:flat_size/1</code> BIF, the size of the deep list can be
│ │ │ │  calculated if sharing is ignored. It becomes the size of the list when it has
│ │ │ │ -been sent to another process or stored in an Ets table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="1671198426-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="1671198426-2">(</span><span class="p" data-group-id="1671198426-2">)</span><span class="p" data-group-id="1671198426-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +been sent to another process or stored in an Ets table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="1745674525-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="1745674525-2">(</span><span class="p" data-group-id="1745674525-2">)</span><span class="p" data-group-id="1745674525-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4094</span></code></pre><p>It can be verified that sharing will be lost if the data is inserted into an Ets
│ │ │ │ -table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="8567762840-1">(</span><span class="ss">tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8567762840-2">[</span><span class="p" data-group-id="8567762840-2">]</span><span class="p" data-group-id="8567762840-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="7234977005-1">(</span><span class="ss">tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7234977005-2">[</span><span class="p" data-group-id="7234977005-2">]</span><span class="p" data-group-id="7234977005-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Ref</span><span class="o">&lt;</span><span class="mf">0.1662103692</span><span class="p">.</span><span class="mf">2407923716.214181</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nc">ets</span><span class="p">:</span><span class="nf">insert</span><span class="p" data-group-id="8567762840-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8567762840-4">{</span><span class="ss">key</span><span class="p">,</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="8567762840-5">(</span><span class="p" data-group-id="8567762840-5">)</span><span class="p" data-group-id="8567762840-4">}</span><span class="p" data-group-id="8567762840-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="nc">ets</span><span class="p">:</span><span class="nf">insert</span><span class="p" data-group-id="7234977005-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7234977005-4">{</span><span class="ss">key</span><span class="p">,</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="7234977005-5">(</span><span class="p" data-group-id="7234977005-5">)</span><span class="p" data-group-id="7234977005-4">}</span><span class="p" data-group-id="7234977005-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="8567762840-6">(</span><span class="nf">element</span><span class="p" data-group-id="8567762840-7">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="8567762840-8">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="8567762840-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="8567762840-9">)</span><span class="p" data-group-id="8567762840-8">)</span><span class="p" data-group-id="8567762840-7">)</span><span class="p" data-group-id="8567762840-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +6&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="7234977005-6">(</span><span class="nf">element</span><span class="p" data-group-id="7234977005-7">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="7234977005-8">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7234977005-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="7234977005-9">)</span><span class="p" data-group-id="7234977005-8">)</span><span class="p" data-group-id="7234977005-7">)</span><span class="p" data-group-id="7234977005-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4094</span><span class="gp unselectable">
│ │ │ │ -7&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="8567762840-10">(</span><span class="nf">element</span><span class="p" data-group-id="8567762840-11">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="8567762840-12">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="8567762840-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="8567762840-13">)</span><span class="p" data-group-id="8567762840-12">)</span><span class="p" data-group-id="8567762840-11">)</span><span class="p" data-group-id="8567762840-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +7&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="7234977005-10">(</span><span class="nf">element</span><span class="p" data-group-id="7234977005-11">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="7234977005-12">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7234977005-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="7234977005-13">)</span><span class="p" data-group-id="7234977005-12">)</span><span class="p" data-group-id="7234977005-11">)</span><span class="p" data-group-id="7234977005-10">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4094</span></code></pre><p>When the data has passed through an Ets table, <code class="inline">erts_debug:size/1</code> and
│ │ │ │  <code class="inline">erts_debug:flat_size/1</code> return the same value. Sharing has been lost.</p><p>It is possible to build an <em>experimental</em> variant of the runtime system that
│ │ │ │  will preserve sharing when copying terms by giving the
│ │ │ │  <code class="inline">--enable-sharing-preserving</code> option to the <code class="inline">configure</code> script.</p><h2 id="smp-run-time-system" class="section-heading">
│ │ │ │    <a href="#smp-run-time-system" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ ├── OEBPS/eff_guide_functions.xhtml
│ │ │ │ @@ -27,67 +27,67 @@
│ │ │ │    <span class="text">Pattern Matching</span>
│ │ │ │  </h2>
│ │ │ │  <p>Pattern matching in function head as well as in <code class="inline">case</code> and <code class="inline">receive</code> clauses are
│ │ │ │  optimized by the compiler. With a few exceptions, there is nothing to gain by
│ │ │ │  rearranging clauses.</p><p>One exception is pattern matching of binaries. The compiler does not rearrange
│ │ │ │  clauses that match binaries. Placing the clause that matches against the empty
│ │ │ │  binary <em>last</em> is usually slightly faster than placing it <em>first</em>.</p><p>The following is a rather unnatural example to show another exception where
│ │ │ │ -rearranging clauses is beneficial:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map1</span><span class="p" data-group-id="9359653421-1">(</span><span class="ss">one</span><span class="p" data-group-id="9359653421-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="9359653421-2">(</span><span class="ss">two</span><span class="p" data-group-id="9359653421-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="9359653421-3">(</span><span class="ss">three</span><span class="p" data-group-id="9359653421-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="9359653421-4">(</span><span class="n">Int</span><span class="p" data-group-id="9359653421-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="9359653421-5">(</span><span class="n">Int</span><span class="p" data-group-id="9359653421-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="9359653421-6">(</span><span class="ss">four</span><span class="p" data-group-id="9359653421-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="9359653421-7">(</span><span class="ss">five</span><span class="p" data-group-id="9359653421-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="9359653421-8">(</span><span class="ss">six</span><span class="p" data-group-id="9359653421-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>The problem is the clause with the variable <code class="inline">Int</code>. As a variable can match
│ │ │ │ +rearranging clauses is beneficial:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map1</span><span class="p" data-group-id="4189847680-1">(</span><span class="ss">one</span><span class="p" data-group-id="4189847680-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="4189847680-2">(</span><span class="ss">two</span><span class="p" data-group-id="4189847680-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="4189847680-3">(</span><span class="ss">three</span><span class="p" data-group-id="4189847680-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="4189847680-4">(</span><span class="n">Int</span><span class="p" data-group-id="4189847680-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="4189847680-5">(</span><span class="n">Int</span><span class="p" data-group-id="4189847680-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="4189847680-6">(</span><span class="ss">four</span><span class="p" data-group-id="4189847680-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="4189847680-7">(</span><span class="ss">five</span><span class="p" data-group-id="4189847680-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="4189847680-8">(</span><span class="ss">six</span><span class="p" data-group-id="4189847680-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>The problem is the clause with the variable <code class="inline">Int</code>. As a variable can match
│ │ │ │  anything, including the atoms <code class="inline">four</code>, <code class="inline">five</code>, and <code class="inline">six</code>, which the following
│ │ │ │  clauses also match, the compiler must generate suboptimal code that executes as
│ │ │ │  follows:</p><ul><li>First, the input value is compared to <code class="inline">one</code>, <code class="inline">two</code>, and <code class="inline">three</code> (using a
│ │ │ │  single instruction that does a binary search; thus, quite efficient even if
│ │ │ │  there are many values) to select which one of the first three clauses to
│ │ │ │  execute (if any).</li><li>If none of the first three clauses match, the fourth clause match as a
│ │ │ │  variable always matches.</li><li>If the guard test <a href="../../../lib/../erts/doc/html/erlang.html#is_integer/1"><code class="inline">is_integer(Int)</code></a> succeeds, the fourth
│ │ │ │  clause is executed.</li><li>If the guard test fails, the input value is compared to <code class="inline">four</code>, <code class="inline">five</code>, and
│ │ │ │  <code class="inline">six</code>, and the appropriate clause is selected. (There is a <code class="inline">function_clause</code>
│ │ │ │ -exception if none of the values matched.)</li></ul><p>Rewriting to either:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map2</span><span class="p" data-group-id="9940505854-1">(</span><span class="ss">one</span><span class="p" data-group-id="9940505854-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="9940505854-2">(</span><span class="ss">two</span><span class="p" data-group-id="9940505854-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="9940505854-3">(</span><span class="ss">three</span><span class="p" data-group-id="9940505854-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="9940505854-4">(</span><span class="ss">four</span><span class="p" data-group-id="9940505854-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="9940505854-5">(</span><span class="ss">five</span><span class="p" data-group-id="9940505854-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="9940505854-6">(</span><span class="ss">six</span><span class="p" data-group-id="9940505854-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="9940505854-7">(</span><span class="n">Int</span><span class="p" data-group-id="9940505854-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="9940505854-8">(</span><span class="n">Int</span><span class="p" data-group-id="9940505854-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>or:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map3</span><span class="p" data-group-id="3209412016-1">(</span><span class="n">Int</span><span class="p" data-group-id="3209412016-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="3209412016-2">(</span><span class="n">Int</span><span class="p" data-group-id="3209412016-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="3209412016-3">(</span><span class="ss">one</span><span class="p" data-group-id="3209412016-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="3209412016-4">(</span><span class="ss">two</span><span class="p" data-group-id="3209412016-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="3209412016-5">(</span><span class="ss">three</span><span class="p" data-group-id="3209412016-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="3209412016-6">(</span><span class="ss">four</span><span class="p" data-group-id="3209412016-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="3209412016-7">(</span><span class="ss">five</span><span class="p" data-group-id="3209412016-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="3209412016-8">(</span><span class="ss">six</span><span class="p" data-group-id="3209412016-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>gives slightly more efficient matching code.</p><p>Another example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs1</span><span class="p" data-group-id="0198981434-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0198981434-2">[</span><span class="p" data-group-id="0198981434-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="0198981434-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +exception if none of the values matched.)</li></ul><p>Rewriting to either:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map2</span><span class="p" data-group-id="5131023389-1">(</span><span class="ss">one</span><span class="p" data-group-id="5131023389-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="5131023389-2">(</span><span class="ss">two</span><span class="p" data-group-id="5131023389-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="5131023389-3">(</span><span class="ss">three</span><span class="p" data-group-id="5131023389-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="5131023389-4">(</span><span class="ss">four</span><span class="p" data-group-id="5131023389-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="5131023389-5">(</span><span class="ss">five</span><span class="p" data-group-id="5131023389-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="5131023389-6">(</span><span class="ss">six</span><span class="p" data-group-id="5131023389-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="5131023389-7">(</span><span class="n">Int</span><span class="p" data-group-id="5131023389-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="5131023389-8">(</span><span class="n">Int</span><span class="p" data-group-id="5131023389-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>or:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map3</span><span class="p" data-group-id="3557919237-1">(</span><span class="n">Int</span><span class="p" data-group-id="3557919237-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="3557919237-2">(</span><span class="n">Int</span><span class="p" data-group-id="3557919237-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="3557919237-3">(</span><span class="ss">one</span><span class="p" data-group-id="3557919237-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="3557919237-4">(</span><span class="ss">two</span><span class="p" data-group-id="3557919237-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="3557919237-5">(</span><span class="ss">three</span><span class="p" data-group-id="3557919237-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="3557919237-6">(</span><span class="ss">four</span><span class="p" data-group-id="3557919237-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="3557919237-7">(</span><span class="ss">five</span><span class="p" data-group-id="3557919237-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="3557919237-8">(</span><span class="ss">six</span><span class="p" data-group-id="3557919237-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>gives slightly more efficient matching code.</p><p>Another example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs1</span><span class="p" data-group-id="5201282103-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5201282103-2">[</span><span class="p" data-group-id="5201282103-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="5201282103-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Ys</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map_pairs1</span><span class="p" data-group-id="0198981434-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0198981434-4">[</span><span class="p" data-group-id="0198981434-4">]</span><span class="p" data-group-id="0198981434-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">map_pairs1</span><span class="p" data-group-id="5201282103-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5201282103-4">[</span><span class="p" data-group-id="5201282103-4">]</span><span class="p" data-group-id="5201282103-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Xs</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map_pairs1</span><span class="p" data-group-id="0198981434-5">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0198981434-6">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="0198981434-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0198981434-7">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="0198981434-7">]</span><span class="p" data-group-id="0198981434-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0198981434-8">[</span><span class="n">Map</span><span class="p" data-group-id="0198981434-9">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0198981434-9">)</span><span class="p">|</span><span class="nf">map_pairs1</span><span class="p" data-group-id="0198981434-10">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="0198981434-10">)</span><span class="p" data-group-id="0198981434-8">]</span><span class="p">.</span></code></pre><p>The first argument is <em>not</em> a problem. It is variable, but it is a variable in
│ │ │ │ +</span><span class="nf">map_pairs1</span><span class="p" data-group-id="5201282103-5">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5201282103-6">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="5201282103-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5201282103-7">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="5201282103-7">]</span><span class="p" data-group-id="5201282103-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5201282103-8">[</span><span class="n">Map</span><span class="p" data-group-id="5201282103-9">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5201282103-9">)</span><span class="p">|</span><span class="nf">map_pairs1</span><span class="p" data-group-id="5201282103-10">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="5201282103-10">)</span><span class="p" data-group-id="5201282103-8">]</span><span class="p">.</span></code></pre><p>The first argument is <em>not</em> a problem. It is variable, but it is a variable in
│ │ │ │  all clauses. The problem is the variable in the second argument, <code class="inline">Xs</code>, in the
│ │ │ │  middle clause. Because the variable can match anything, the compiler is not
│ │ │ │  allowed to rearrange the clauses, but must generate code that matches them in
│ │ │ │  the order written.</p><p>If the function is rewritten as follows, the compiler is free to rearrange the
│ │ │ │ -clauses:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs2</span><span class="p" data-group-id="5599713445-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5599713445-2">[</span><span class="p" data-group-id="5599713445-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="5599713445-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +clauses:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs2</span><span class="p" data-group-id="1228895965-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1228895965-2">[</span><span class="p" data-group-id="1228895965-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="1228895965-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Ys</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map_pairs2</span><span class="p" data-group-id="5599713445-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5599713445-4">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="5599713445-4">]</span><span class="o">=</span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5599713445-5">[</span><span class="p" data-group-id="5599713445-5">]</span><span class="w"> </span><span class="p" data-group-id="5599713445-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">map_pairs2</span><span class="p" data-group-id="1228895965-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1228895965-4">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="1228895965-4">]</span><span class="o">=</span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1228895965-5">[</span><span class="p" data-group-id="1228895965-5">]</span><span class="w"> </span><span class="p" data-group-id="1228895965-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Xs</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map_pairs2</span><span class="p" data-group-id="5599713445-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5599713445-7">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="5599713445-7">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5599713445-8">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="5599713445-8">]</span><span class="p" data-group-id="5599713445-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5599713445-9">[</span><span class="n">Map</span><span class="p" data-group-id="5599713445-10">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5599713445-10">)</span><span class="p">|</span><span class="nf">map_pairs2</span><span class="p" data-group-id="5599713445-11">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="5599713445-11">)</span><span class="p" data-group-id="5599713445-9">]</span><span class="p">.</span></code></pre><p>The compiler will generate code similar to this:</p><p><strong>DO NOT (already done by the compiler)</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="1416209042-1">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs0</span><span class="p">,</span><span class="w"> </span><span class="n">Ys0</span><span class="p" data-group-id="1416209042-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">map_pairs2</span><span class="p" data-group-id="1228895965-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1228895965-7">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="1228895965-7">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1228895965-8">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="1228895965-8">]</span><span class="p" data-group-id="1228895965-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1228895965-9">[</span><span class="n">Map</span><span class="p" data-group-id="1228895965-10">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1228895965-10">)</span><span class="p">|</span><span class="nf">map_pairs2</span><span class="p" data-group-id="1228895965-11">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="1228895965-11">)</span><span class="p" data-group-id="1228895965-9">]</span><span class="p">.</span></code></pre><p>The compiler will generate code similar to this:</p><p><strong>DO NOT (already done by the compiler)</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="3392306707-1">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs0</span><span class="p">,</span><span class="w"> </span><span class="n">Ys0</span><span class="p" data-group-id="3392306707-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Xs0</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="1416209042-2">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="1416209042-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="3392306707-2">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="3392306707-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="k">case</span><span class="w"> </span><span class="n">Ys0</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="1416209042-3">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="1416209042-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="p" data-group-id="1416209042-4">[</span><span class="n">Map</span><span class="p" data-group-id="1416209042-5">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1416209042-5">)</span><span class="p">|</span><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="1416209042-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="1416209042-6">)</span><span class="p" data-group-id="1416209042-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="1416209042-7">[</span><span class="p" data-group-id="1416209042-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="3392306707-3">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="3392306707-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="p" data-group-id="3392306707-4">[</span><span class="n">Map</span><span class="p" data-group-id="3392306707-5">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3392306707-5">)</span><span class="p">|</span><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="3392306707-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="3392306707-6">)</span><span class="p" data-group-id="3392306707-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="3392306707-7">[</span><span class="p" data-group-id="3392306707-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  		    </span><span class="n">Xs0</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="1416209042-8">[</span><span class="p" data-group-id="1416209042-8">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="3392306707-8">[</span><span class="p" data-group-id="3392306707-8">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">Ys0</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>This is slightly faster for probably the most common case that the input lists
│ │ │ │  are not empty or very short. (Another advantage is that Dialyzer can deduce a
│ │ │ │  better type for the <code class="inline">Xs</code> variable.)</p><h2 id="function-calls" class="section-heading">
│ │ │ │    <a href="#function-calls" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ ├── OEBPS/drivers.xhtml
│ │ │ │ @@ -27,23 +27,23 @@
│ │ │ │    <span class="text">Drivers and Concurrency</span>
│ │ │ │  </h2>
│ │ │ │  <p>The runtime system always takes a lock before running any code in a driver.</p><p>By default, that lock is at the driver level, that is, if several ports have
│ │ │ │  been opened to the same driver, only code for one port at the same time can be
│ │ │ │  running.</p><p>A driver can be configured to have one lock for each port instead.</p><p>If a driver is used in a functional way (that is, holds no state, but only does
│ │ │ │  some heavy calculation and returns a result), several ports with registered
│ │ │ │  names can be opened beforehand, and the port to be used can be chosen based on
│ │ │ │ -the scheduler ID as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6292179092-1">(</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="6292179092-2">(</span><span class="p" data-group-id="6292179092-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="6292179092-3">{</span><span class="ss">some_driver_01</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_02</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_03</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_04</span><span class="p">,</span><span class="w">
│ │ │ │ +the scheduler ID as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6117143971-1">(</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="6117143971-2">(</span><span class="p" data-group-id="6117143971-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="6117143971-3">{</span><span class="ss">some_driver_01</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_02</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_03</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_04</span><span class="p">,</span><span class="w">
│ │ │ │  	 </span><span class="ss">some_driver_05</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_06</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_07</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_08</span><span class="p">,</span><span class="w">
│ │ │ │  	 </span><span class="ss">some_driver_09</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_10</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_11</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_12</span><span class="p">,</span><span class="w">
│ │ │ │ -	 </span><span class="ss">some_driver_13</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_14</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_15</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_16</span><span class="p" data-group-id="6292179092-3">}</span><span class="p" data-group-id="6292179092-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +	 </span><span class="ss">some_driver_13</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_14</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_15</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_16</span><span class="p" data-group-id="6117143971-3">}</span><span class="p" data-group-id="6117143971-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">client_port</span><span class="p" data-group-id="6292179092-4">(</span><span class="p" data-group-id="6292179092-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">element</span><span class="p" data-group-id="6292179092-5">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="6292179092-6">(</span><span class="ss">scheduler_id</span><span class="p" data-group-id="6292179092-6">)</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="6292179092-7">(</span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="6292179092-8">(</span><span class="p" data-group-id="6292179092-8">)</span><span class="p" data-group-id="6292179092-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="6292179092-9">(</span><span class="p" data-group-id="6292179092-9">)</span><span class="p" data-group-id="6292179092-5">)</span><span class="p">.</span></code></pre><p>As long as there are no more than 16 schedulers, there will never be any lock
│ │ │ │ +</span><span class="nf">client_port</span><span class="p" data-group-id="6117143971-4">(</span><span class="p" data-group-id="6117143971-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">element</span><span class="p" data-group-id="6117143971-5">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="6117143971-6">(</span><span class="ss">scheduler_id</span><span class="p" data-group-id="6117143971-6">)</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="6117143971-7">(</span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="6117143971-8">(</span><span class="p" data-group-id="6117143971-8">)</span><span class="p" data-group-id="6117143971-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="6117143971-9">(</span><span class="p" data-group-id="6117143971-9">)</span><span class="p" data-group-id="6117143971-5">)</span><span class="p">.</span></code></pre><p>As long as there are no more than 16 schedulers, there will never be any lock
│ │ │ │  contention on the port lock for the driver.</p><h2 id="avoiding-copying-binaries-when-calling-a-driver" class="section-heading">
│ │ │ │    <a href="#avoiding-copying-binaries-when-calling-a-driver" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Avoiding Copying Binaries When Calling a Driver</span>
│ │ │ │  </h2>
│ │ │ │  <p>There are basically two ways to avoid copying a binary that is sent to a driver:</p><ul><li><p>If the <code class="inline">Data</code> argument for <a href="../../../lib/../erts/doc/html/erlang.html#port_control/3"><code class="inline">port_control/3</code></a> is a
│ │ │ ├── OEBPS/documentation.xhtml
│ │ │ │ @@ -17,23 +17,23 @@
│ │ │ │    </head>
│ │ │ │    <body class="content-inner">
│ │ │ │  
│ │ │ │      <h1 id="content">
│ │ │ │  Documentation
│ │ │ │      </h1>
│ │ │ │  <p>Documentation in Erlang is done through the <code class="inline">-moduledoc</code> and <code class="inline">-doc</code>
│ │ │ │ -<a href="modules.xhtml#module-attributes">attributes</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6229476014-1">(</span><span class="ss">arith</span><span class="p" data-group-id="6229476014-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<a href="modules.xhtml#module-attributes">attributes</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8852127514-1">(</span><span class="ss">arith</span><span class="p" data-group-id="8852127514-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │ │  A module for basic arithmetic.
│ │ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6229476014-2">(</span><span class="p" data-group-id="6229476014-3">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6229476014-3">]</span><span class="p" data-group-id="6229476014-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8852127514-2">(</span><span class="p" data-group-id="8852127514-3">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8852127514-3">]</span><span class="p" data-group-id="8852127514-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="6229476014-4">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="6229476014-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The <code class="inline">-moduledoc</code> attribute has to be located before the first <code class="inline">-doc</code> attribute
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="8852127514-4">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="8852127514-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The <code class="inline">-moduledoc</code> attribute has to be located before the first <code class="inline">-doc</code> attribute
│ │ │ │  or function declaration. It documents the overall purpose of the module.</p><p>The <code class="inline">-doc</code> attribute always precedes the <a href="ref_man_functions.xhtml">function</a> or
│ │ │ │  <a href="modules.xhtml#module-attributes">attribute</a> it documents. The
│ │ │ │  attributes that can be documented are
│ │ │ │  <a href="typespec.xhtml#type-declarations-of-user-defined-types">user-defined types</a>
│ │ │ │  (<code class="inline">-type</code> and <code class="inline">-opaque</code>) and
│ │ │ │  <a href="modules.xhtml#behaviour-module-attribute">behaviour module attributes</a>
│ │ │ │  (<code class="inline">-callback</code>).</p><p>By default the format used for documentation attributes is
│ │ │ │ @@ -45,55 +45,55 @@
│ │ │ │  <a href="modules.xhtml#documentation-attributes">Documentation Attributes</a>.</p><p><code class="inline">-doc</code> attributes have been available since Erlang/OTP 27.</p><h2 id="documentation-metadata" class="section-heading">
│ │ │ │    <a href="#documentation-metadata" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Documentation metadata</span>
│ │ │ │  </h2>
│ │ │ │  <p>It is possible to add metadata to the documentation entry. You do this by adding
│ │ │ │ -a <code class="inline">-moduledoc</code> or <code class="inline">-doc</code> attribute with a map as argument. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5940262713-1">(</span><span class="ss">arith</span><span class="p" data-group-id="5940262713-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +a <code class="inline">-moduledoc</code> or <code class="inline">-doc</code> attribute with a map as argument. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6005585259-1">(</span><span class="ss">arith</span><span class="p" data-group-id="6005585259-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │ │  A module for basic arithmetic.
│ │ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="5940262713-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="5940262713-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="6005585259-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="6005585259-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5940262713-3">(</span><span class="p" data-group-id="5940262713-4">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5940262713-4">]</span><span class="p" data-group-id="5940262713-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6005585259-3">(</span><span class="p" data-group-id="6005585259-4">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6005585259-4">]</span><span class="p" data-group-id="6005585259-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="5940262713-5">(</span><span class="p" data-group-id="5940262713-6">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="5940262713-6">}</span><span class="p" data-group-id="5940262713-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="5940262713-7">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5940262713-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The metadata is used by documentation tools to provide extra information to the
│ │ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="6005585259-5">(</span><span class="p" data-group-id="6005585259-6">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="6005585259-6">}</span><span class="p" data-group-id="6005585259-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="6005585259-7">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="6005585259-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The metadata is used by documentation tools to provide extra information to the
│ │ │ │  user. There can be multiple metadata documentation entries, in which case the
│ │ │ │  maps will be merged with the latest taking precedence if there are duplicate
│ │ │ │  keys. Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="0062070956-1">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">author</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p" data-group-id="0062070956-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="0062070956-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="0062070956-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="0062070956-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="0062070956-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>This will result in a metadata entry of <code class="inline">#{since =&gt; &quot;2.0&quot;, author =&gt; &quot;Joe&quot;}</code>.</p><p>The keys and values in the metadata map can be any type, but it is recommended
│ │ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="4716533029-1">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">author</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p" data-group-id="4716533029-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="4716533029-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="4716533029-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="4716533029-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4716533029-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>This will result in a metadata entry of <code class="inline">#{since =&gt; &quot;2.0&quot;, author =&gt; &quot;Joe&quot;}</code>.</p><p>The keys and values in the metadata map can be any type, but it is recommended
│ │ │ │  that only <a href="data_types.xhtml#atom">atoms</a> are used for keys and
│ │ │ │  <a href="data_types.xhtml#string">strings</a> for the values.</p><h2 id="external-documentation-files" class="section-heading">
│ │ │ │    <a href="#external-documentation-files" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">External documentation files</span>
│ │ │ │  </h2>
│ │ │ │  <p>The <code class="inline">-moduledoc</code> and <code class="inline">-doc</code> can also be placed in external files. To do so use
│ │ │ │  <code class="inline">-doc {file, &quot;path/to/doc.md&quot;}</code> to point to the documentation. The path used is
│ │ │ │  relative to the file where the <code class="inline">-doc</code> attribute is located. For example:</p><pre><code class="markdown">%% doc/add.md
│ │ │ │  Adds two numbers.</code></pre><p>and</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% src/arith.erl</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7691881206-1">(</span><span class="p" data-group-id="7691881206-2">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/add.md&quot;</span><span class="p" data-group-id="7691881206-2">}</span><span class="p" data-group-id="7691881206-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="7691881206-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="7691881206-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><h2 id="documenting-a-module" class="section-heading">
│ │ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7551625131-1">(</span><span class="p" data-group-id="7551625131-2">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/add.md&quot;</span><span class="p" data-group-id="7551625131-2">}</span><span class="p" data-group-id="7551625131-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="7551625131-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="7551625131-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><h2 id="documenting-a-module" class="section-heading">
│ │ │ │    <a href="#documenting-a-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Documenting a module</span>
│ │ │ │  </h2>
│ │ │ │  <p>The module description should include details on how to use the API and examples
│ │ │ │  of the different functions working together. Here is a good place to use images
│ │ │ │  and other diagrams to better show the usage of the module. Instead of writing a
│ │ │ │  long text in the <code class="inline">moduledoc</code> attribute, it could be better to break it out into
│ │ │ │  an external page.</p><p>The <code class="inline">moduledoc</code> attribute should start with a short paragraph describing the
│ │ │ │ -module and then go into greater details. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5895584257-1">(</span><span class="ss">arith</span><span class="p" data-group-id="5895584257-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +module and then go into greater details. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5219108708-1">(</span><span class="ss">arith</span><span class="p" data-group-id="5219108708-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="s">&quot;
│ │ │ │     A module for basic arithmetic.
│ │ │ │  
│ │ │ │     This module can be used to add and subtract values. For example:
│ │ │ │  
│ │ │ │     ```erlang
│ │ │ │     1&gt; arith:substract(arith:add(2, 3), 1).
│ │ │ │ @@ -108,94 +108,94 @@
│ │ │ │  <p>There are three reserved metadata keys for <code class="inline">-moduledoc</code>:</p><ul><li><code class="inline">since</code> - Shows in which version of the application the module was added.
│ │ │ │  If this is added, all functions, types, and callbacks within will also receive
│ │ │ │  the same <code class="inline">since</code> value unless specified in the metadata of the function, type
│ │ │ │  or callback.</li><li><code class="inline">deprecated</code> - Shows a text in the documentation explaining that it is
│ │ │ │  deprecated and what to use instead.</li><li><code class="inline">format</code> - The format to use for all documentation in this module. The
│ │ │ │  default is <code class="inline">text/markdown</code>. It should be written using the
│ │ │ │  <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types">mime type</a>
│ │ │ │ -of the format.</li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="4993617479-1">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/arith.asciidoc&quot;</span><span class="p" data-group-id="4993617479-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="4993617479-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;0.1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">format</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;text/asciidoc&quot;</span><span class="p" data-group-id="4993617479-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="4993617479-3">#{</span><span class="ss">deprecated</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Use the Erlang arithmetic operators instead.&quot;</span><span class="p" data-group-id="4993617479-3">}</span><span class="p">.</span></code></pre><h2 id="documenting-functions-user-defined-types-and-callbacks" class="section-heading">
│ │ │ │ +of the format.</li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="0366026924-1">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/arith.asciidoc&quot;</span><span class="p" data-group-id="0366026924-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="0366026924-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;0.1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">format</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;text/asciidoc&quot;</span><span class="p" data-group-id="0366026924-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="0366026924-3">#{</span><span class="ss">deprecated</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Use the Erlang arithmetic operators instead.&quot;</span><span class="p" data-group-id="0366026924-3">}</span><span class="p">.</span></code></pre><h2 id="documenting-functions-user-defined-types-and-callbacks" class="section-heading">
│ │ │ │    <a href="#documenting-functions-user-defined-types-and-callbacks" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Documenting functions, user-defined types, and callbacks</span>
│ │ │ │  </h2>
│ │ │ │  <p>Functions, types, and callbacks can be documented using the <code class="inline">-doc</code> attribute.
│ │ │ │  Each entry should start with a short paragraph describing the purpose of entity,
│ │ │ │  and then go into greater detail in needed.</p><p>It is not recommended to include images or diagrams in this documentation as it
│ │ │ │  is used by IDEs and <a href="../../../lib/stdlib/doc/html/c.html#h/1"><code class="inline">c:h/1</code></a> to show the documentation to the user.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │ │  A number that can be used by the arith module.
│ │ │ │  
│ │ │ │  We use a special number here so that we know
│ │ │ │  that this number comes from this module.
│ │ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4215654573-1">(</span><span class="p" data-group-id="4215654573-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4215654573-2">{</span><span class="ss">arith</span><span class="p">,</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">number</span><span class="p" data-group-id="4215654573-3">(</span><span class="p" data-group-id="4215654573-3">)</span><span class="p" data-group-id="4215654573-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="6353828463-1">(</span><span class="p" data-group-id="6353828463-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6353828463-2">{</span><span class="ss">arith</span><span class="p">,</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">number</span><span class="p" data-group-id="6353828463-3">(</span><span class="p" data-group-id="6353828463-3">)</span><span class="p" data-group-id="6353828463-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │ │  Adds two numbers.
│ │ │ │  
│ │ │ │  ### Example:
│ │ │ │  
│ │ │ │  ```
│ │ │ │  1&gt; arith:add(arith:number(1), arith:number(2)). {number, 3}
│ │ │ │  ```
│ │ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="4215654573-4">(</span><span class="nf">number</span><span class="p" data-group-id="4215654573-5">(</span><span class="p" data-group-id="4215654573-5">)</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4215654573-6">(</span><span class="p" data-group-id="4215654573-6">)</span><span class="p" data-group-id="4215654573-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4215654573-7">(</span><span class="p" data-group-id="4215654573-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="4215654573-8">(</span><span class="p" data-group-id="4215654573-9">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="p" data-group-id="4215654573-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4215654573-10">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4215654573-10">}</span><span class="p" data-group-id="4215654573-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4215654573-11">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4215654573-11">}</span><span class="p">.</span></code></pre><h3 id="doc-metadata" class="section-heading">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="6353828463-4">(</span><span class="nf">number</span><span class="p" data-group-id="6353828463-5">(</span><span class="p" data-group-id="6353828463-5">)</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="6353828463-6">(</span><span class="p" data-group-id="6353828463-6">)</span><span class="p" data-group-id="6353828463-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="6353828463-7">(</span><span class="p" data-group-id="6353828463-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="6353828463-8">(</span><span class="p" data-group-id="6353828463-9">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="p" data-group-id="6353828463-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6353828463-10">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="6353828463-10">}</span><span class="p" data-group-id="6353828463-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6353828463-11">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="6353828463-11">}</span><span class="p">.</span></code></pre><h3 id="doc-metadata" class="section-heading">
│ │ │ │    <a href="#doc-metadata" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Doc metadata</span>
│ │ │ │  </h3>
│ │ │ │  <p>There are four reserved metadata keys for <code class="inline">-doc</code>:</p><ul><li><p><code class="inline">since =&gt; unicode:chardata()</code> - Shows which version of the application the
│ │ │ │  module was added.</p></li><li><p><code class="inline">deprecated =&gt; unicode:chardata()</code> - Shows a text in the documentation
│ │ │ │  explaining that it is deprecated and what to use instead. The compiler will
│ │ │ │  automatically insert this key if there is a <code class="inline">-deprecated</code> attribute marking a
│ │ │ │  function as deprecated.</p></li><li><p><code class="inline">equiv =&gt; unicode:chardata() | F/A | F(...)</code> - Notes that this function is equivalent to
│ │ │ │  another function in this module. The equivalence can be described using either
│ │ │ │ -<code class="inline">Func/Arity</code>, <code class="inline">Func(Args)</code> or a <a href="../../../lib/stdlib/doc/html/unicode.html#t:chardata/0">unicode string</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="2573499042-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">add</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="2573499042-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="2573499042-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="2573499042-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="2573499042-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2573499042-4">[</span><span class="p" data-group-id="2573499042-4">]</span><span class="p" data-group-id="2573499042-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="2573499042-5">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="2573499042-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>or</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="9729442155-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="9729442155-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9729442155-3">[</span><span class="p" data-group-id="9729442155-3">]</span><span class="p" data-group-id="9729442155-2">)</span><span class="p" data-group-id="9729442155-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="9729442155-4">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="9729442155-5">(</span><span class="p" data-group-id="9729442155-5">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="9729442155-6">(</span><span class="p" data-group-id="9729442155-6">)</span><span class="p" data-group-id="9729442155-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="9729442155-7">(</span><span class="p" data-group-id="9729442155-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="9729442155-8">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="9729442155-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="9729442155-9">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9729442155-10">[</span><span class="p" data-group-id="9729442155-10">]</span><span class="p" data-group-id="9729442155-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="9729442155-11">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="9729442155-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The entry into the <a href="../../../lib/kernel/doc/html/eep48_chapter.xhtml">EEP-48</a> doc chunk metadata is
│ │ │ │ +<code class="inline">Func/Arity</code>, <code class="inline">Func(Args)</code> or a <a href="../../../lib/stdlib/doc/html/unicode.html#t:chardata/0">unicode string</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="6036354229-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">add</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="6036354229-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="6036354229-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="6036354229-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="6036354229-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6036354229-4">[</span><span class="p" data-group-id="6036354229-4">]</span><span class="p" data-group-id="6036354229-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="6036354229-5">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="6036354229-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>or</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="4800910214-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="4800910214-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4800910214-3">[</span><span class="p" data-group-id="4800910214-3">]</span><span class="p" data-group-id="4800910214-2">)</span><span class="p" data-group-id="4800910214-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="4800910214-4">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4800910214-5">(</span><span class="p" data-group-id="4800910214-5">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4800910214-6">(</span><span class="p" data-group-id="4800910214-6">)</span><span class="p" data-group-id="4800910214-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4800910214-7">(</span><span class="p" data-group-id="4800910214-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="4800910214-8">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4800910214-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="4800910214-9">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4800910214-10">[</span><span class="p" data-group-id="4800910214-10">]</span><span class="p" data-group-id="4800910214-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="4800910214-11">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="4800910214-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The entry into the <a href="../../../lib/kernel/doc/html/eep48_chapter.xhtml">EEP-48</a> doc chunk metadata is
│ │ │ │  the value converted to a string.</p></li><li><p><code class="inline">exported =&gt; boolean()</code> - A <a href="../../../lib/../erts/doc/html/erlang.html#t:boolean/0"><code class="inline">boolean/0</code></a> signifying if the entry is <code class="inline">exported</code>
│ │ │ │  or not. This value is automatically set by the compiler and should not be set
│ │ │ │  by the user.</p></li></ul><h3 id="doc-signatures" class="section-heading">
│ │ │ │    <a href="#doc-signatures" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Doc signatures</span>
│ │ │ │  </h3>
│ │ │ │  <p>The doc signature is a short text shown to describe the function and its arguments.
│ │ │ │  By default it is determined by looking at the names of the arguments in the
│ │ │ │ -<code class="inline">-spec</code> or function. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add</span><span class="p" data-group-id="7631029957-1">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="7631029957-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">-spec</code> or function. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add</span><span class="p" data-group-id="9867452129-1">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="9867452129-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">sub</span><span class="p" data-group-id="7631029957-2">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="7631029957-3">(</span><span class="p" data-group-id="7631029957-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="7631029957-4">(</span><span class="p" data-group-id="7631029957-4">)</span><span class="p" data-group-id="7631029957-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="7631029957-5">(</span><span class="p" data-group-id="7631029957-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">sub</span><span class="p" data-group-id="7631029957-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7631029957-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>will have a signature of <code class="inline">add(One, Two)</code> and <code class="inline">sub(One, Two)</code>.</p><p>For types or callbacks, the signature is derived from the type or callback
│ │ │ │ -specification. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="1619132890-1">(</span><span class="n">Value</span><span class="p" data-group-id="1619132890-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1619132890-2">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="1619132890-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">sub</span><span class="p" data-group-id="9867452129-2">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="9867452129-3">(</span><span class="p" data-group-id="9867452129-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="9867452129-4">(</span><span class="p" data-group-id="9867452129-4">)</span><span class="p" data-group-id="9867452129-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="9867452129-5">(</span><span class="p" data-group-id="9867452129-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">sub</span><span class="p" data-group-id="9867452129-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9867452129-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>will have a signature of <code class="inline">add(One, Two)</code> and <code class="inline">sub(One, Two)</code>.</p><p>For types or callbacks, the signature is derived from the type or callback
│ │ │ │ +specification. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0154069169-1">(</span><span class="n">Value</span><span class="p" data-group-id="0154069169-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0154069169-2">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="0154069169-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% signature will be `number(Value)`</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="1619132890-3">(</span><span class="p" data-group-id="1619132890-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1619132890-4">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="1619132890-5">(</span><span class="p" data-group-id="1619132890-5">)</span><span class="p" data-group-id="1619132890-4">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0154069169-3">(</span><span class="p" data-group-id="0154069169-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0154069169-4">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0154069169-5">(</span><span class="p" data-group-id="0154069169-5">)</span><span class="p" data-group-id="0154069169-4">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% signature will be `number()`</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="1619132890-6">(</span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="1619132890-7">(</span><span class="p" data-group-id="1619132890-7">)</span><span class="p" data-group-id="1619132890-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="0154069169-6">(</span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0154069169-7">(</span><span class="p" data-group-id="0154069169-7">)</span><span class="p" data-group-id="0154069169-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% signature will be `increment(In)`</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="1619132890-8">(</span><span class="n">In</span><span class="p" data-group-id="1619132890-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="1619132890-9">(</span><span class="p" data-group-id="1619132890-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="0154069169-8">(</span><span class="n">In</span><span class="p" data-group-id="0154069169-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0154069169-9">(</span><span class="p" data-group-id="0154069169-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% signature will be `increment(In)`</span></code></pre><p>If it is not possible to &quot;easily&quot; figure out a nice signature from the code, the
│ │ │ │  MFA syntax is used instead. For example: <code class="inline">add/2</code>, <code class="inline">number/1</code>, <code class="inline">increment/1</code></p><p>It is possible to supply a custom signature by placing it as the first line of the
│ │ │ │  <code class="inline">-doc</code> attribute. The provided signature must be in the form of a function
│ │ │ │  declaration up until the <code class="inline">-&gt;</code>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │ │  add(One, Two)
│ │ │ │  
│ │ │ │  Adds two numbers.
│ │ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="6046859051-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="6046859051-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">.</span></code></pre><p>Will create the signature <code class="inline">add(One, Two)</code>. The signature will be removed from the
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="1453181711-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="1453181711-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">.</span></code></pre><p>Will create the signature <code class="inline">add(One, Two)</code>. The signature will be removed from the
│ │ │ │  documentation string, so in the example above only the text <code class="inline">&quot;Adds two numbers&quot;</code>
│ │ │ │  will be part of the documentation. This works for functions, types, and
│ │ │ │  callbacks.</p><h2 id="links-in-markdown" class="section-heading">
│ │ │ │    <a href="#links-in-markdown" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Links in Markdown</span>
│ │ │ │ @@ -233,28 +233,28 @@
│ │ │ │  modules. That is, modules that should be used by other applications and modules
│ │ │ │  that should not. By default all modules in an application are visible, but by
│ │ │ │  setting <code class="inline">-moduledoc false.</code> specific modules can be hidden from being listed as
│ │ │ │  part of the available API.</p><p>An Erlang <a href="modules.xhtml">module</a> consists of public and private functions and type
│ │ │ │  attributes. By default, all exported functions, exported types and callbacks are
│ │ │ │  considered visible and part of the modules public API. In addition, any
│ │ │ │  non-exported type that is referred to by any other visible type attribute is
│ │ │ │ -also visible, but not considered to be part of the public API. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6616125223-1">(</span><span class="p" data-group-id="6616125223-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6616125223-2">]</span><span class="p" data-group-id="6616125223-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +also visible, but not considered to be part of the public API. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8260549742-1">(</span><span class="p" data-group-id="8260549742-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8260549742-2">]</span><span class="p" data-group-id="8260549742-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="6616125223-3">(</span><span class="p" data-group-id="6616125223-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="6616125223-4">(</span><span class="p" data-group-id="6616125223-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="6616125223-5">(</span><span class="p" data-group-id="6616125223-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="6616125223-6">(</span><span class="p" data-group-id="6616125223-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>in the above code, the function <code class="inline">example/0</code> is exported and it referenced the
│ │ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="8260549742-3">(</span><span class="p" data-group-id="8260549742-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="8260549742-4">(</span><span class="p" data-group-id="8260549742-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="8260549742-5">(</span><span class="p" data-group-id="8260549742-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="8260549742-6">(</span><span class="p" data-group-id="8260549742-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>in the above code, the function <code class="inline">example/0</code> is exported and it referenced the
│ │ │ │  un-exported type <code class="inline">private/0</code>. Therefore both <code class="inline">example/0</code> and <code class="inline">private/0</code> will be
│ │ │ │  marked as visible. The <code class="inline">private/0</code> type will have the metadata field <code class="inline">exported</code>
│ │ │ │  set to <code class="inline">false</code> to show that it is not part of the public API.</p><p>If you want to make a visible entity hidden you need to set the <code class="inline">-doc</code> attribute
│ │ │ │ -to <code class="inline">false</code>. Let us revisit our previous example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4548353364-1">(</span><span class="p" data-group-id="4548353364-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4548353364-2">]</span><span class="p" data-group-id="4548353364-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +to <code class="inline">false</code>. Let us revisit our previous example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1391458436-1">(</span><span class="p" data-group-id="1391458436-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1391458436-2">]</span><span class="p" data-group-id="1391458436-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="4548353364-3">(</span><span class="p" data-group-id="4548353364-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="4548353364-4">(</span><span class="p" data-group-id="4548353364-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="4548353364-5">(</span><span class="p" data-group-id="4548353364-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="1391458436-3">(</span><span class="p" data-group-id="1391458436-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="1391458436-4">(</span><span class="p" data-group-id="1391458436-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="1391458436-5">(</span><span class="p" data-group-id="1391458436-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="ss">false</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="4548353364-6">(</span><span class="p" data-group-id="4548353364-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>The function <code class="inline">example/0</code> is exported but explicitly marked as hidden; therefore
│ │ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="1391458436-6">(</span><span class="p" data-group-id="1391458436-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>The function <code class="inline">example/0</code> is exported but explicitly marked as hidden; therefore
│ │ │ │  both <code class="inline">example/0</code> and <code class="inline">private/0</code> will be hidden.</p><p>Any documentation added to an automatically hidden entity (non-exported function
│ │ │ │  or type) is ignored and will generate a warning. Such functions can be
│ │ │ │  documented using comments.</p><h2 id="compiling-and-getting-documentation" class="section-heading">
│ │ │ │    <a href="#compiling-and-getting-documentation" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Compiling and getting documentation</span>
│ │ │ │ @@ -280,21 +280,21 @@
│ │ │ │    <span class="text">Using ExDoc to generate HTML/ePub documentation</span>
│ │ │ │  </h2>
│ │ │ │  <p><a href="https://hexdocs.pm/ex_doc/">ExDoc</a> has built-in support to generate
│ │ │ │  documentation from Markdown. The simplest way is by using the
│ │ │ │  <a href="https://hexdocs.pm/rebar3_ex_doc">rebar3_ex_doc</a> plugin. To set up a
│ │ │ │  rebar3 project to use <a href="https://hexdocs.pm/ex_doc/">ExDoc</a> to generate
│ │ │ │  documentation add the following to your <code class="inline">rebar3.config</code>.</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Enable the plugin</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9718131473-1">{</span><span class="ss">plugins</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9718131473-2">[</span><span class="ss">rebar3_ex_doc</span><span class="p" data-group-id="9718131473-2">]</span><span class="p" data-group-id="9718131473-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5866158109-1">{</span><span class="ss">plugins</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5866158109-2">[</span><span class="ss">rebar3_ex_doc</span><span class="p" data-group-id="5866158109-2">]</span><span class="p" data-group-id="5866158109-1">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p" data-group-id="9718131473-3">{</span><span class="ss">ex_doc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9718131473-4">[</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9718131473-5">{</span><span class="ss">extras</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9718131473-6">[</span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="9718131473-6">]</span><span class="p" data-group-id="9718131473-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9718131473-7">{</span><span class="ss">main</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="9718131473-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9718131473-8">{</span><span class="ss">source_url</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;https://github.com/namespace/your_app&quot;</span><span class="p" data-group-id="9718131473-8">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9718131473-4">]</span><span class="p" data-group-id="9718131473-3">}</span><span class="p">.</span></code></pre><p>When configured you can run <code class="inline">rebar3 ex_doc</code> to generate the
│ │ │ │ +</span><span class="p" data-group-id="5866158109-3">{</span><span class="ss">ex_doc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5866158109-4">[</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5866158109-5">{</span><span class="ss">extras</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5866158109-6">[</span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="5866158109-6">]</span><span class="p" data-group-id="5866158109-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5866158109-7">{</span><span class="ss">main</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="5866158109-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5866158109-8">{</span><span class="ss">source_url</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;https://github.com/namespace/your_app&quot;</span><span class="p" data-group-id="5866158109-8">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5866158109-4">]</span><span class="p" data-group-id="5866158109-3">}</span><span class="p">.</span></code></pre><p>When configured you can run <code class="inline">rebar3 ex_doc</code> to generate the
│ │ │ │  documentation to <code class="inline">doc/index.html</code>. For more details and options see
│ │ │ │  the <a href="https://hexdocs.pm/rebar3_ex_doc">rebar3_ex_doc</a> documentation.</p><p>You can also download the
│ │ │ │  <a href="https://github.com/elixir/ex_doc/releases/latest">release escript bundle</a> from
│ │ │ │  github and run it from the command line. The documentation for using the escript
│ │ │ │  is found by running <code class="inline">ex_doc --help</code>.</p><p>If you are writing documentation that will be using
│ │ │ │  <a href="https://hexdocs.pm/ex_doc/">ExDoc</a> to generate HTML/ePub it is highly
│ │ │ │  recommended to read its documentation.</p>
│ │ │ ├── OEBPS/distributed_applications.xhtml
│ │ │ │ @@ -55,36 +55,36 @@
│ │ │ │  (within the time-out specified by <code class="inline">sync_nodes_timeout</code>).</li><li><p><code class="inline">sync_nodes_timeout = integer() | infinity</code> - Specifies how many milliseconds
│ │ │ │  to wait for the other nodes to start.</p></li></ul><p>When started, the node waits for all nodes specified by <code class="inline">sync_nodes_mandatory</code>
│ │ │ │  and <code class="inline">sync_nodes_optional</code> to come up. When all nodes are up, or when all
│ │ │ │  mandatory nodes are up and the time specified by <code class="inline">sync_nodes_timeout</code> has
│ │ │ │  elapsed, all applications start. If not all mandatory nodes are up, the node
│ │ │ │  terminates.</p><p><em>Example:</em></p><p>An application <code class="inline">myapp</code> is to run at the node <code class="inline">cp1@cave</code>. If this node goes down,
│ │ │ │  <code class="inline">myapp</code> is to be restarted at <code class="inline">cp2@cave</code> or <code class="inline">cp3@cave</code>. A system configuration
│ │ │ │ -file <code class="inline">cp1.config</code> for <code class="inline">cp1@cave</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9753816764-1">[</span><span class="p" data-group-id="9753816764-2">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9753816764-3">[</span><span class="p" data-group-id="9753816764-4">{</span><span class="ss">distributed</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9753816764-5">[</span><span class="p" data-group-id="9753816764-6">{</span><span class="ss">myapp</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9753816764-7">[</span><span class="ss">cp1@cave</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9753816764-8">{</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="9753816764-8">}</span><span class="p" data-group-id="9753816764-7">]</span><span class="p" data-group-id="9753816764-6">}</span><span class="p" data-group-id="9753816764-5">]</span><span class="p" data-group-id="9753816764-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="9753816764-9">{</span><span class="ss">sync_nodes_mandatory</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9753816764-10">[</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="9753816764-10">]</span><span class="p" data-group-id="9753816764-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="9753816764-11">{</span><span class="ss">sync_nodes_timeout</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p" data-group-id="9753816764-11">}</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9753816764-3">]</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9753816764-2">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9753816764-1">]</span><span class="p">.</span></code></pre><p>The system configuration files for <code class="inline">cp2@cave</code> and <code class="inline">cp3@cave</code> are identical,
│ │ │ │ +file <code class="inline">cp1.config</code> for <code class="inline">cp1@cave</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2897061490-1">[</span><span class="p" data-group-id="2897061490-2">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="2897061490-3">[</span><span class="p" data-group-id="2897061490-4">{</span><span class="ss">distributed</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2897061490-5">[</span><span class="p" data-group-id="2897061490-6">{</span><span class="ss">myapp</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2897061490-7">[</span><span class="ss">cp1@cave</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2897061490-8">{</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="2897061490-8">}</span><span class="p" data-group-id="2897061490-7">]</span><span class="p" data-group-id="2897061490-6">}</span><span class="p" data-group-id="2897061490-5">]</span><span class="p" data-group-id="2897061490-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="2897061490-9">{</span><span class="ss">sync_nodes_mandatory</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2897061490-10">[</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="2897061490-10">]</span><span class="p" data-group-id="2897061490-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="2897061490-11">{</span><span class="ss">sync_nodes_timeout</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p" data-group-id="2897061490-11">}</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="2897061490-3">]</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2897061490-2">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2897061490-1">]</span><span class="p">.</span></code></pre><p>The system configuration files for <code class="inline">cp2@cave</code> and <code class="inline">cp3@cave</code> are identical,
│ │ │ │  except for the list of mandatory nodes, which is to be <code class="inline">[cp1@cave, cp3@cave]</code>
│ │ │ │  for <code class="inline">cp2@cave</code> and <code class="inline">[cp1@cave, cp2@cave]</code> for <code class="inline">cp3@cave</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>All involved nodes must have the same value for <code class="inline">distributed</code> and
│ │ │ │  <code class="inline">sync_nodes_timeout</code>. Otherwise the system behavior is undefined.</p></section><h2 id="starting-and-stopping-distributed-applications" class="section-heading">
│ │ │ │    <a href="#starting-and-stopping-distributed-applications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting and Stopping Distributed Applications</span>
│ │ │ │  </h2>
│ │ │ │  <p>When all involved (mandatory) nodes have been started, the distributed
│ │ │ │  application can be started by calling <code class="inline">application:start(Application)</code> at <em>all
│ │ │ │  of these nodes.</em></p><p>A boot script (see <a href="release_structure.xhtml">Releases</a>) can be used that
│ │ │ │  automatically starts the application.</p><p>The application is started at the first operational node that is listed in the
│ │ │ │  list of nodes in the <code class="inline">distributed</code> configuration parameter. The application is
│ │ │ │  started as usual. That is, an application master is created and calls the
│ │ │ │ -application callback function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5539627096-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="5539627096-1">)</span></code></pre><p>Example:</p><p>Continuing the example from the previous section, the three nodes are started,
│ │ │ │ +application callback function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8634984964-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="8634984964-1">)</span></code></pre><p>Example:</p><p>Continuing the example from the previous section, the three nodes are started,
│ │ │ │  specifying the system configuration file:</p><pre><code class="text">&gt; erl -sname cp1 -config cp1
│ │ │ │  &gt; erl -sname cp2 -config cp2
│ │ │ │  &gt; erl -sname cp3 -config cp3</code></pre><p>When all nodes are operational, <code class="inline">myapp</code> can be started. This is achieved by
│ │ │ │  calling <code class="inline">application:start(myapp)</code> at all three nodes. It is then started at
│ │ │ │  <code class="inline">cp1</code>, as shown in the following figure:</p><p><a href="" id="dist1"></a></p><p><img src="assets/dist1.gif" alt="Application myapp - Situation 1" title="Application myapp - Situation 1"/></p><p>Similarly, the application must be stopped by calling
│ │ │ │  <code class="inline">application:stop(Application)</code> at all involved nodes.</p><h2 id="failover" class="section-heading">
│ │ │ │    <a href="#failover" class="hover-link">
│ │ │ │ @@ -92,30 +92,30 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Failover</span>
│ │ │ │  </h2>
│ │ │ │  <p>If the node where the application is running goes down, the application is
│ │ │ │  restarted (after the specified time-out) at the first operational node that is
│ │ │ │  listed in the list of nodes in the <code class="inline">distributed</code> configuration parameter. This
│ │ │ │  is called a <em>failover</em>.</p><p>The application is started the normal way at the new node, that is, by the
│ │ │ │ -application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9494113435-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="9494113435-1">)</span></code></pre><p>An exception is if the application has the <code class="inline">start_phases</code> key defined (see
│ │ │ │ +application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6021277264-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="6021277264-1">)</span></code></pre><p>An exception is if the application has the <code class="inline">start_phases</code> key defined (see
│ │ │ │  <a href="included_applications.xhtml">Included Applications</a>). The application is then
│ │ │ │ -instead started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="2919132616-1">(</span><span class="p" data-group-id="2919132616-2">{</span><span class="ss">failover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="2919132616-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="2919132616-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the terminated node.</p><p><em>Example:</em></p><p>If <code class="inline">cp1</code> goes down, the system checks which one of the other nodes, <code class="inline">cp2</code> or
│ │ │ │ +instead started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="2596551623-1">(</span><span class="p" data-group-id="2596551623-2">{</span><span class="ss">failover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="2596551623-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="2596551623-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the terminated node.</p><p><em>Example:</em></p><p>If <code class="inline">cp1</code> goes down, the system checks which one of the other nodes, <code class="inline">cp2</code> or
│ │ │ │  <code class="inline">cp3</code>, has the least number of running applications, but waits for 5 seconds for
│ │ │ │  <code class="inline">cp1</code> to restart. If <code class="inline">cp1</code> does not restart and <code class="inline">cp2</code> runs fewer applications
│ │ │ │  than <code class="inline">cp3</code>, <code class="inline">myapp</code> is restarted on <code class="inline">cp2</code>.</p><p><a href="" id="dist2"></a></p><p><img src="assets/dist2.gif" alt="Application myapp - Situation 2" title="Application myapp - Situation 2"/></p><p>Suppose now that <code class="inline">cp2</code> goes also down and does not restart within 5 seconds.
│ │ │ │  <code class="inline">myapp</code> is now restarted on <code class="inline">cp3</code>.</p><p><a href="" id="dist3"></a></p><p><img src="assets/dist3.gif" alt="Application myapp - Situation 3" title="Application myapp - Situation 3"/></p><h2 id="takeover" class="section-heading">
│ │ │ │    <a href="#takeover" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Takeover</span>
│ │ │ │  </h2>
│ │ │ │  <p>If a node is started, which has higher priority according to <code class="inline">distributed</code> than
│ │ │ │  the node where a distributed application is running, the application is
│ │ │ │  restarted at the new node and stopped at the old node. This is called a
│ │ │ │ -<em>takeover</em>.</p><p>The application is started by the application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="2886957861-1">(</span><span class="p" data-group-id="2886957861-2">{</span><span class="ss">takeover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="2886957861-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="2886957861-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the old node.</p><p><em>Example:</em></p><p>If <code class="inline">myapp</code> is running at <code class="inline">cp3</code>, and if <code class="inline">cp2</code> now restarts, it does not restart
│ │ │ │ +<em>takeover</em>.</p><p>The application is started by the application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7265992494-1">(</span><span class="p" data-group-id="7265992494-2">{</span><span class="ss">takeover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="7265992494-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="7265992494-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the old node.</p><p><em>Example:</em></p><p>If <code class="inline">myapp</code> is running at <code class="inline">cp3</code>, and if <code class="inline">cp2</code> now restarts, it does not restart
│ │ │ │  <code class="inline">myapp</code>, as the order between the <code class="inline">cp2</code> and <code class="inline">cp3</code> nodes is undefined.</p><p><a href="" id="dist4"></a></p><p><img src="assets/dist4.gif" alt="Application myapp - Situation 4" title="Application myapp - Situation 4"/></p><p>However, if <code class="inline">cp1</code> also restarts, the function <a href="../../../lib/kernel/doc/html/application.html#takeover/2"><code class="inline">application:takeover/2</code></a> moves
│ │ │ │  <code class="inline">myapp</code> to <code class="inline">cp1</code>, as <code class="inline">cp1</code> has a higher priority than <code class="inline">cp3</code> for this
│ │ │ │  application. In this case, <code class="inline">Module:start({takeover, cp3@cave}, StartArgs)</code> is
│ │ │ │  executed at <code class="inline">cp1</code> to start the application.</p><p><a href="" id="dist5"></a></p><p><img src="assets/dist5.gif" alt="Application myapp - Situation 5" title="Application myapp - Situation 5"/></p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/distributed.xhtml
│ │ │ │ @@ -47,25 +47,25 @@
│ │ │ │  </h2>
│ │ │ │  <p>A <em>node</em> is an executing Erlang runtime system that has been given a name, using
│ │ │ │  the command-line flag <a href="../../../lib/../erts/doc/html/erl_cmd.xhtml#name"><code class="inline">-name</code></a> (long names) or
│ │ │ │  <a href="../../../lib/../erts/doc/html/erl_cmd.xhtml#sname"><code class="inline">-sname</code></a> (short names).</p><p>The format of the node name is an atom <code class="inline">name@host</code>. <code class="inline">name</code> is the name given by
│ │ │ │  the user. <code class="inline">host</code> is the full host name if long names are used, or the first part
│ │ │ │  of the host name if short names are used. Function <a href="../../../lib/../erts/doc/html/erlang.html#node/0"><code class="inline">node()</code></a>
│ │ │ │  returns the name of the node.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -name dilbert</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4967649492-1">(</span><span class="ss">dilbert@uab</span><span class="p">.</span><span class="ss">ericsson</span><span class="p">.</span><span class="ss">se</span><span class="p" data-group-id="4967649492-1">)</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="4967649492-2">(</span><span class="p" data-group-id="4967649492-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5440082812-1">(</span><span class="ss">dilbert@uab</span><span class="p">.</span><span class="ss">ericsson</span><span class="p">.</span><span class="ss">se</span><span class="p" data-group-id="5440082812-1">)</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="5440082812-2">(</span><span class="p" data-group-id="5440082812-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">&#39;dilbert@uab.ericsson.se&#39;</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">% erl -sname dilbert</span><span class="gp unselectable">
│ │ │ │ -(dilbert@uab)1&gt; </span><span class="nf">node</span><span class="p" data-group-id="4967649492-3">(</span><span class="p" data-group-id="4967649492-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +(dilbert@uab)1&gt; </span><span class="nf">node</span><span class="p" data-group-id="5440082812-3">(</span><span class="p" data-group-id="5440082812-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">dilbert@uab</span></code></pre><p>The node name can also be given in runtime by calling <a href="../../../lib/kernel/doc/html/net_kernel.html#start/1"><code class="inline">net_kernel:start/1</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="nf">node</span><span class="p" data-group-id="7039404296-1">(</span><span class="p" data-group-id="7039404296-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +1&gt; </span><span class="nf">node</span><span class="p" data-group-id="9233304719-1">(</span><span class="p" data-group-id="9233304719-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">nonode@nohost</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">net_kernel</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7039404296-2">(</span><span class="p" data-group-id="7039404296-3">[</span><span class="ss">dilbert</span><span class="p">,</span><span class="ss">shortnames</span><span class="p" data-group-id="7039404296-3">]</span><span class="p" data-group-id="7039404296-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7039404296-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.102</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7039404296-4">}</span><span class="gp unselectable">
│ │ │ │ -(dilbert@uab)3&gt; </span><span class="nf">node</span><span class="p" data-group-id="7039404296-5">(</span><span class="p" data-group-id="7039404296-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="nc">net_kernel</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9233304719-2">(</span><span class="p" data-group-id="9233304719-3">[</span><span class="ss">dilbert</span><span class="p">,</span><span class="ss">shortnames</span><span class="p" data-group-id="9233304719-3">]</span><span class="p" data-group-id="9233304719-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9233304719-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.102</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="9233304719-4">}</span><span class="gp unselectable">
│ │ │ │ +(dilbert@uab)3&gt; </span><span class="nf">node</span><span class="p" data-group-id="9233304719-5">(</span><span class="p" data-group-id="9233304719-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">dilbert@uab</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>A node with a long node name cannot communicate with a node with a short node
│ │ │ │  name.</p></section><h2 id="node-connections" class="section-heading">
│ │ │ │    <a href="#node-connections" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Node Connections</span>
│ │ │ │  </h2>
│ │ │ ├── OEBPS/design_principles.xhtml
│ │ │ │ @@ -57,135 +57,135 @@
│ │ │ │  the code for a process in a generic part (a behaviour module) and a specific
│ │ │ │  part (a <em>callback module</em>).</p><p>The behaviour module is part of Erlang/OTP. To implement a process such as a
│ │ │ │  supervisor, the user only needs to implement the callback module, which is to
│ │ │ │  export a pre-defined set of functions, the <em>callback functions</em>.</p><p>The following example illustrate how code can be divided into a generic and a
│ │ │ │  specific part. Consider the following code (written in plain Erlang) for a
│ │ │ │  simple server, which keeps track of a number of &quot;channels&quot;. Other processes can
│ │ │ │  allocate and free the channels by calling the functions <code class="inline">alloc/0</code> and <code class="inline">free/1</code>,
│ │ │ │ -respectively.</p><p><a href="" id="ch1"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9933087551-1">(</span><span class="ss">ch1</span><span class="p" data-group-id="9933087551-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9933087551-2">(</span><span class="p" data-group-id="9933087551-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9933087551-3">]</span><span class="p" data-group-id="9933087551-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9933087551-4">(</span><span class="p" data-group-id="9933087551-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9933087551-5">]</span><span class="p" data-group-id="9933087551-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9933087551-6">(</span><span class="p" data-group-id="9933087551-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9933087551-7">]</span><span class="p" data-group-id="9933087551-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +respectively.</p><p><a href="" id="ch1"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6609916916-1">(</span><span class="ss">ch1</span><span class="p" data-group-id="6609916916-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6609916916-2">(</span><span class="p" data-group-id="6609916916-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6609916916-3">]</span><span class="p" data-group-id="6609916916-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6609916916-4">(</span><span class="p" data-group-id="6609916916-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6609916916-5">]</span><span class="p" data-group-id="6609916916-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6609916916-6">(</span><span class="p" data-group-id="6609916916-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6609916916-7">]</span><span class="p" data-group-id="6609916916-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="9933087551-8">(</span><span class="p" data-group-id="9933087551-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9933087551-9">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9933087551-10">[</span><span class="p" data-group-id="9933087551-10">]</span><span class="p" data-group-id="9933087551-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="6609916916-8">(</span><span class="p" data-group-id="6609916916-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="6609916916-9">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6609916916-10">[</span><span class="p" data-group-id="6609916916-10">]</span><span class="p" data-group-id="6609916916-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="9933087551-11">(</span><span class="p" data-group-id="9933087551-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9933087551-12">{</span><span class="nf">self</span><span class="p" data-group-id="9933087551-13">(</span><span class="p" data-group-id="9933087551-13">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="9933087551-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="6609916916-11">(</span><span class="p" data-group-id="6609916916-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6609916916-12">{</span><span class="nf">self</span><span class="p" data-group-id="6609916916-13">(</span><span class="p" data-group-id="6609916916-13">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="6609916916-12">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9933087551-14">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="9933087551-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6609916916-14">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="6609916916-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">Res</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="9933087551-15">(</span><span class="n">Ch</span><span class="p" data-group-id="9933087551-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9933087551-16">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9933087551-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="6609916916-15">(</span><span class="n">Ch</span><span class="p" data-group-id="6609916916-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6609916916-16">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6609916916-16">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="9933087551-17">(</span><span class="p" data-group-id="9933087551-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9933087551-18">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9933087551-19">(</span><span class="p" data-group-id="9933087551-19">)</span><span class="p" data-group-id="9933087551-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="9933087551-20">(</span><span class="p" data-group-id="9933087551-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="9933087551-21">(</span><span class="n">Chs</span><span class="p" data-group-id="9933087551-21">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="6609916916-17">(</span><span class="p" data-group-id="6609916916-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="6609916916-18">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6609916916-19">(</span><span class="p" data-group-id="6609916916-19">)</span><span class="p" data-group-id="6609916916-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="6609916916-20">(</span><span class="p" data-group-id="6609916916-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="6609916916-21">(</span><span class="n">Chs</span><span class="p" data-group-id="6609916916-21">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="9933087551-22">(</span><span class="n">Chs</span><span class="p" data-group-id="9933087551-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="6609916916-22">(</span><span class="n">Chs</span><span class="p" data-group-id="6609916916-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9933087551-23">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="9933087551-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9933087551-24">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="9933087551-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="9933087551-25">(</span><span class="n">Chs</span><span class="p" data-group-id="9933087551-25">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9933087551-26">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9933087551-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="9933087551-27">(</span><span class="n">Chs2</span><span class="p" data-group-id="9933087551-27">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9933087551-28">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9933087551-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="9933087551-29">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="9933087551-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="9933087551-30">(</span><span class="n">Chs2</span><span class="p" data-group-id="9933087551-30">)</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The code for the server can be rewritten into a generic part <code class="inline">server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1218485196-1">(</span><span class="ss">server</span><span class="p" data-group-id="1218485196-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1218485196-2">(</span><span class="p" data-group-id="1218485196-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1218485196-3">]</span><span class="p" data-group-id="1218485196-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1218485196-4">(</span><span class="p" data-group-id="1218485196-5">[</span><span class="ss">call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1218485196-5">]</span><span class="p" data-group-id="1218485196-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1218485196-6">(</span><span class="p" data-group-id="1218485196-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1218485196-7">]</span><span class="p" data-group-id="1218485196-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6609916916-23">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="6609916916-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="6609916916-24">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6609916916-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="6609916916-25">(</span><span class="n">Chs</span><span class="p" data-group-id="6609916916-25">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6609916916-26">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6609916916-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="6609916916-27">(</span><span class="n">Chs2</span><span class="p" data-group-id="6609916916-27">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6609916916-28">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6609916916-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="6609916916-29">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6609916916-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="6609916916-30">(</span><span class="n">Chs2</span><span class="p" data-group-id="6609916916-30">)</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The code for the server can be rewritten into a generic part <code class="inline">server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4726366569-1">(</span><span class="ss">server</span><span class="p" data-group-id="4726366569-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4726366569-2">(</span><span class="p" data-group-id="4726366569-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4726366569-3">]</span><span class="p" data-group-id="4726366569-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4726366569-4">(</span><span class="p" data-group-id="4726366569-5">[</span><span class="ss">call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4726366569-5">]</span><span class="p" data-group-id="4726366569-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4726366569-6">(</span><span class="p" data-group-id="4726366569-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4726366569-7">]</span><span class="p" data-group-id="4726366569-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="1218485196-8">(</span><span class="n">Mod</span><span class="p" data-group-id="1218485196-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1218485196-9">(</span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1218485196-10">[</span><span class="n">Mod</span><span class="p" data-group-id="1218485196-10">]</span><span class="p" data-group-id="1218485196-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="4726366569-8">(</span><span class="n">Mod</span><span class="p" data-group-id="4726366569-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="4726366569-9">(</span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4726366569-10">[</span><span class="n">Mod</span><span class="p" data-group-id="4726366569-10">]</span><span class="p" data-group-id="4726366569-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call</span><span class="p" data-group-id="1218485196-11">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="1218485196-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1218485196-12">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1218485196-13">(</span><span class="p" data-group-id="1218485196-13">)</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="1218485196-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call</span><span class="p" data-group-id="4726366569-11">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="4726366569-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4726366569-12">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4726366569-13">(</span><span class="p" data-group-id="4726366569-13">)</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="4726366569-12">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1218485196-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="1218485196-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4726366569-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="4726366569-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">Res</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">cast</span><span class="p" data-group-id="1218485196-15">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="1218485196-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1218485196-16">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="1218485196-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">cast</span><span class="p" data-group-id="4726366569-15">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="4726366569-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4726366569-16">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="4726366569-16">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1218485196-17">(</span><span class="n">Mod</span><span class="p" data-group-id="1218485196-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="1218485196-18">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1218485196-19">(</span><span class="p" data-group-id="1218485196-19">)</span><span class="p" data-group-id="1218485196-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">init</span><span class="p" data-group-id="1218485196-20">(</span><span class="p" data-group-id="1218485196-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="1218485196-21">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1218485196-21">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="4726366569-17">(</span><span class="n">Mod</span><span class="p" data-group-id="4726366569-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="4726366569-18">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4726366569-19">(</span><span class="p" data-group-id="4726366569-19">)</span><span class="p" data-group-id="4726366569-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">init</span><span class="p" data-group-id="4726366569-20">(</span><span class="p" data-group-id="4726366569-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="4726366569-21">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4726366569-21">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="1218485196-22">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1218485196-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="4726366569-22">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4726366569-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1218485196-23">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="1218485196-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="1218485196-24">{</span><span class="n">Res</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="1218485196-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_call</span><span class="p" data-group-id="1218485196-25">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1218485196-25">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1218485196-26">{</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="1218485196-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="1218485196-27">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="1218485196-27">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1218485196-28">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="1218485196-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">State2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_cast</span><span class="p" data-group-id="1218485196-29">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1218485196-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="1218485196-30">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="1218485196-30">)</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>And a callback module <code class="inline">ch2.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8818432376-1">(</span><span class="ss">ch2</span><span class="p" data-group-id="8818432376-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8818432376-2">(</span><span class="p" data-group-id="8818432376-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8818432376-3">]</span><span class="p" data-group-id="8818432376-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8818432376-4">(</span><span class="p" data-group-id="8818432376-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8818432376-5">]</span><span class="p" data-group-id="8818432376-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8818432376-6">(</span><span class="p" data-group-id="8818432376-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8818432376-7">]</span><span class="p" data-group-id="8818432376-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="8818432376-8">(</span><span class="p" data-group-id="8818432376-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8818432376-9">(</span><span class="ss">ch2</span><span class="p" data-group-id="8818432376-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="8818432376-10">(</span><span class="p" data-group-id="8818432376-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="8818432376-11">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="8818432376-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="8818432376-12">(</span><span class="n">Ch</span><span class="p" data-group-id="8818432376-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8818432376-13">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8818432376-14">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8818432376-14">}</span><span class="p" data-group-id="8818432376-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4726366569-23">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="4726366569-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="4726366569-24">{</span><span class="n">Res</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="4726366569-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_call</span><span class="p" data-group-id="4726366569-25">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4726366569-25">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4726366569-26">{</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="4726366569-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="4726366569-27">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="4726366569-27">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4726366569-28">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="4726366569-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">State2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_cast</span><span class="p" data-group-id="4726366569-29">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4726366569-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="4726366569-30">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="4726366569-30">)</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>And a callback module <code class="inline">ch2.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8334653857-1">(</span><span class="ss">ch2</span><span class="p" data-group-id="8334653857-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8334653857-2">(</span><span class="p" data-group-id="8334653857-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8334653857-3">]</span><span class="p" data-group-id="8334653857-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8334653857-4">(</span><span class="p" data-group-id="8334653857-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8334653857-5">]</span><span class="p" data-group-id="8334653857-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8334653857-6">(</span><span class="p" data-group-id="8334653857-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8334653857-7">]</span><span class="p" data-group-id="8334653857-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8334653857-8">(</span><span class="p" data-group-id="8334653857-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8334653857-9">(</span><span class="ss">ch2</span><span class="p" data-group-id="8334653857-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="8334653857-10">(</span><span class="p" data-group-id="8334653857-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="8334653857-11">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="8334653857-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="8334653857-12">(</span><span class="n">Ch</span><span class="p" data-group-id="8334653857-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8334653857-13">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8334653857-14">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8334653857-14">}</span><span class="p" data-group-id="8334653857-13">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8818432376-15">(</span><span class="p" data-group-id="8818432376-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">channels</span><span class="p" data-group-id="8818432376-16">(</span><span class="p" data-group-id="8818432376-16">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8334653857-15">(</span><span class="p" data-group-id="8334653857-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">channels</span><span class="p" data-group-id="8334653857-16">(</span><span class="p" data-group-id="8334653857-16">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="8818432376-17">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8818432376-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">alloc</span><span class="p" data-group-id="8818432376-18">(</span><span class="n">Chs</span><span class="p" data-group-id="8818432376-18">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; {Ch,Chs2}</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="8334653857-17">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8334653857-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">alloc</span><span class="p" data-group-id="8334653857-18">(</span><span class="n">Chs</span><span class="p" data-group-id="8334653857-18">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; {Ch,Chs2}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="8818432376-19">(</span><span class="p" data-group-id="8818432376-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8818432376-20">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8818432376-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">free</span><span class="p" data-group-id="8818432376-21">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8818432376-21">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; Chs2</span></code></pre><p>Notice the following:</p><ul><li>The code in <code class="inline">server</code> can be reused to build many different servers.</li><li>The server name, in this example the atom <code class="inline">ch2</code>, is hidden from the users of
│ │ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="8334653857-19">(</span><span class="p" data-group-id="8334653857-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8334653857-20">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8334653857-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">free</span><span class="p" data-group-id="8334653857-21">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8334653857-21">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; Chs2</span></code></pre><p>Notice the following:</p><ul><li>The code in <code class="inline">server</code> can be reused to build many different servers.</li><li>The server name, in this example the atom <code class="inline">ch2</code>, is hidden from the users of
│ │ │ │  the client functions. This means that the name can be changed without
│ │ │ │  affecting them.</li><li>The protocol (messages sent to and received from the server) is also hidden.
│ │ │ │  This is good programming practice and allows one to change the protocol
│ │ │ │  without changing the code using the interface functions.</li><li>The functionality of <code class="inline">server</code> can be extended without having to change <code class="inline">ch2</code>
│ │ │ │  or any other callback module.</li></ul><p>In <code class="inline">ch1.erl</code> and <code class="inline">ch2.erl</code> above, the implementation of <code class="inline">channels/0</code>, <code class="inline">alloc/1</code>,
│ │ │ │  and <code class="inline">free/2</code> has been intentionally left out, as it is not relevant to the
│ │ │ │  example. For completeness, one way to write these functions is given below. This
│ │ │ │  is an example only, a realistic implementation must be able to handle situations
│ │ │ │ -like running out of channels to allocate, and so on.</p><p><a href="" id="channels-implementation"></a></p><pre><code class="makeup erlang" translate="no"><span class="nf">channels</span><span class="p" data-group-id="7881805561-1">(</span><span class="p" data-group-id="7881805561-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="7881805561-2">{</span><span class="p">_</span><span class="n">Allocated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7881805561-3">[</span><span class="p" data-group-id="7881805561-3">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="7881805561-4">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="7881805561-4">)</span><span class="p" data-group-id="7881805561-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +like running out of channels to allocate, and so on.</p><p><a href="" id="channels-implementation"></a></p><pre><code class="makeup erlang" translate="no"><span class="nf">channels</span><span class="p" data-group-id="9259185097-1">(</span><span class="p" data-group-id="9259185097-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="9259185097-2">{</span><span class="p">_</span><span class="n">Allocated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9259185097-3">[</span><span class="p" data-group-id="9259185097-3">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="9259185097-4">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="9259185097-4">)</span><span class="p" data-group-id="9259185097-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="7881805561-5">(</span><span class="p" data-group-id="7881805561-6">{</span><span class="n">Allocated</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7881805561-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7881805561-7">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="p" data-group-id="7881805561-6">}</span><span class="p" data-group-id="7881805561-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="7881805561-8">{</span><span class="n">H</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7881805561-9">{</span><span class="p" data-group-id="7881805561-10">[</span><span class="n">H</span><span class="p">|</span><span class="n">Allocated</span><span class="p" data-group-id="7881805561-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="7881805561-9">}</span><span class="p" data-group-id="7881805561-8">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="9259185097-5">(</span><span class="p" data-group-id="9259185097-6">{</span><span class="n">Allocated</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9259185097-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9259185097-7">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="p" data-group-id="9259185097-6">}</span><span class="p" data-group-id="9259185097-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="9259185097-8">{</span><span class="n">H</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9259185097-9">{</span><span class="p" data-group-id="9259185097-10">[</span><span class="n">H</span><span class="p">|</span><span class="n">Allocated</span><span class="p" data-group-id="9259185097-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9259185097-9">}</span><span class="p" data-group-id="9259185097-8">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="7881805561-11">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7881805561-12">{</span><span class="n">Alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Free</span><span class="p" data-group-id="7881805561-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Channels</span><span class="p" data-group-id="7881805561-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="7881805561-13">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="7881805561-13">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="9259185097-11">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9259185097-12">{</span><span class="n">Alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Free</span><span class="p" data-group-id="9259185097-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Channels</span><span class="p" data-group-id="9259185097-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="9259185097-13">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="9259185097-13">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │        </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="7881805561-14">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="7881805561-15">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="7881805561-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7881805561-16">[</span><span class="n">Ch</span><span class="p">|</span><span class="n">Free</span><span class="p" data-group-id="7881805561-16">]</span><span class="p" data-group-id="7881805561-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="9259185097-14">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="9259185097-15">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="9259185097-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9259185097-16">[</span><span class="n">Ch</span><span class="p">|</span><span class="n">Free</span><span class="p" data-group-id="9259185097-16">]</span><span class="p" data-group-id="9259185097-14">}</span><span class="p">;</span><span class="w">
│ │ │ │        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │           </span><span class="n">Channels</span><span class="w">
│ │ │ │     </span><span class="k">end</span><span class="p">.</span></code></pre><p>Code written without using behaviours can be more efficient, but the increased
│ │ │ │  efficiency is at the expense of generality. The ability to manage all
│ │ │ │  applications in the system in a consistent manner is important.</p><p>Using behaviours also makes it easier to read and understand code written by
│ │ │ │  other programmers. Improvised programming structures, while possibly more
│ │ │ │  efficient, are always more difficult to understand.</p><p>The <code class="inline">server</code> module corresponds, greatly simplified, to the Erlang/OTP behaviour
│ │ │ │  <code class="inline">gen_server</code>.</p><p>The standard Erlang/OTP behaviours are:</p><ul><li><p><a href="gen_server_concepts.xhtml">gen_server</a></p><p>For implementing the server of a client-server relation</p></li><li><p><a href="statem.xhtml">gen_statem</a></p><p>For implementing state machines</p></li><li><p><a href="events.xhtml">gen_event</a></p><p>For implementing event handling functionality</p></li><li><p><a href="sup_princ.xhtml">supervisor</a></p><p>For implementing a supervisor in a supervision tree</p></li></ul><p>The compiler understands the module attribute <code class="inline">-behaviour(Behaviour)</code> and issues
│ │ │ │ -warnings about missing callback functions, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3165575091-1">(</span><span class="ss">chs3</span><span class="p" data-group-id="3165575091-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3165575091-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="3165575091-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +warnings about missing callback functions, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8859834162-1">(</span><span class="ss">chs3</span><span class="p" data-group-id="8859834162-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8859834162-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="8859834162-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="3165575091-3">(</span><span class="ss">chs3</span><span class="p" data-group-id="3165575091-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="8859834162-3">(</span><span class="ss">chs3</span><span class="p" data-group-id="8859834162-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="o">/</span><span class="ss">chs3</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">10</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="ss">undefined</span><span class="w"> </span><span class="ss">call</span><span class="o">-</span><span class="ss">back</span><span class="w"> </span><span class="ss">function</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3165575091-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">chs3</span><span class="p" data-group-id="3165575091-4">}</span></code></pre><h2 id="applications" class="section-heading">
│ │ │ │ +</span><span class="p" data-group-id="8859834162-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">chs3</span><span class="p" data-group-id="8859834162-4">}</span></code></pre><h2 id="applications" class="section-heading">
│ │ │ │    <a href="#applications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Applications</span>
│ │ │ │  </h2>
│ │ │ │  <p>Erlang/OTP comes with a number of components, each implementing some specific
│ │ │ │  functionality. Components are with Erlang/OTP terminology called <em>applications</em>.
│ │ │ ├── OEBPS/data_types.xhtml
│ │ │ │ @@ -97,18 +97,18 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Representation of Floating Point Numbers</span>
│ │ │ │  </h3>
│ │ │ │  <p>When working with floats you may not see what you expect when printing or doing
│ │ │ │  arithmetic operations. This is because floats are represented by a fixed number
│ │ │ │  of bits in a base-2 system while printed floats are represented with a base-10
│ │ │ │  system. Erlang uses 64-bit floats. Here are examples of this phenomenon:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="mf">0.30000000000000004</span></code></pre><p>The real numbers <code class="inline">0.1</code> and <code class="inline">0.2</code> cannot be represented exactly as floats.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6401922843-1">{</span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963968</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="mf">36028797018963970.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963970</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963970.0</span><span class="p" data-group-id="6401922843-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6401922843-2">{</span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="6401922843-2">}</span><span class="p">.</span></code></pre><p>The value <code class="inline">36028797018963968</code> can be represented exactly as a float value but
│ │ │ │ +</span><span class="mf">0.30000000000000004</span></code></pre><p>The real numbers <code class="inline">0.1</code> and <code class="inline">0.2</code> cannot be represented exactly as floats.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1838634842-1">{</span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963968</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="mf">36028797018963970.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963970</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963970.0</span><span class="p" data-group-id="1838634842-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1838634842-2">{</span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="1838634842-2">}</span><span class="p">.</span></code></pre><p>The value <code class="inline">36028797018963968</code> can be represented exactly as a float value but
│ │ │ │  Erlang's pretty printer rounds <code class="inline">36028797018963968.0</code> to <code class="inline">3.602879701896397e16</code>
│ │ │ │  (<code class="inline">=36028797018963970.0</code>) as all values in the range
│ │ │ │  <code class="inline">[36028797018963966.0, 36028797018963972.0]</code> are represented by
│ │ │ │  <code class="inline">36028797018963968.0</code>.</p><p>For more information about floats and issues with them see:</p><ul><li><a href="https://floating-point-gui.de/">What Every Programmer Should Know About Floating-Point Arithmetic</a></li><li><a href="https://0.30000000000000004.com/">0.30000000000000004.com/</a></li><li><a href="https://docs.python.org/3/tutorial/floatingpoint.html">Floating Point Arithmetic: Issues and Limitations</a></li></ul><p>If you need to work with exact decimal fractions, for instance to represent
│ │ │ │  money, it is recommended to use a library that handles that, or work in
│ │ │ │  cents instead of dollars or euros so that decimal fractions are not needed.</p><p>Also note that Erlang's floats do not exactly match IEEE 754 floats,
│ │ │ │  in that neither <em>Inf</em> nor <em>NaN</em> are supported in Erlang. Any
│ │ │ │ @@ -142,52 +142,52 @@
│ │ │ │  by eight are called <em>binaries</em>.</p><p><em>Examples:</em></p><pre><code class="text">1&gt; &lt;&lt;10,20&gt;&gt;.
│ │ │ │  &lt;&lt;10,20&gt;&gt;
│ │ │ │  2&gt; &lt;&lt;&quot;ABC&quot;&gt;&gt;.
│ │ │ │  &lt;&lt;&quot;ABC&quot;&gt;&gt;
│ │ │ │  3&gt; &lt;&lt;1:1,0:1&gt;&gt;.
│ │ │ │  &lt;&lt;2:2&gt;&gt;</code></pre><p>The <a href="../../../lib/../erts/doc/html/erlang.html#is_bitstring/1"><code class="inline">is_bitstring/1</code></a> BIF tests whether a
│ │ │ │  term is a bit string, and the <a href="../../../lib/../erts/doc/html/erlang.html#is_binary/1"><code class="inline">is_binary/1</code></a>
│ │ │ │ -BIF tests whether a term is a binary.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">is_bitstring</span><span class="p" data-group-id="2207510984-1">(</span><span class="p" data-group-id="2207510984-2">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2207510984-2">&gt;&gt;</span><span class="p" data-group-id="2207510984-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +BIF tests whether a term is a binary.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">is_bitstring</span><span class="p" data-group-id="2881721509-1">(</span><span class="p" data-group-id="2881721509-2">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2881721509-2">&gt;&gt;</span><span class="p" data-group-id="2881721509-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="2207510984-3">(</span><span class="p" data-group-id="2207510984-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2207510984-4">&gt;&gt;</span><span class="p" data-group-id="2207510984-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="2881721509-3">(</span><span class="p" data-group-id="2881721509-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2881721509-4">&gt;&gt;</span><span class="p" data-group-id="2881721509-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="2207510984-5">(</span><span class="p" data-group-id="2207510984-6">&lt;&lt;</span><span class="mi">42</span><span class="p" data-group-id="2207510984-6">&gt;&gt;</span><span class="p" data-group-id="2207510984-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="2881721509-5">(</span><span class="p" data-group-id="2881721509-6">&lt;&lt;</span><span class="mi">42</span><span class="p" data-group-id="2881721509-6">&gt;&gt;</span><span class="p" data-group-id="2881721509-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │  </span></code></pre><p>For more examples, see <a href="../../../lib/../system/doc/html/bit_syntax.xhtml">Programming Examples</a>.</p><h2 id="reference" class="section-heading">
│ │ │ │    <a href="#reference" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Reference</span>
│ │ │ │  </h2>
│ │ │ │  <p>A term that is <a href="../../../lib/../system/doc/html/system_limits.xhtml#unique_references">unique</a>
│ │ │ │  among connected nodes. A reference is created by calling the
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#make_ref/0"><code class="inline">make_ref/0</code></a> BIF. The
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#is_reference/1"><code class="inline">is_reference/1</code></a> BIF tests whether a term
│ │ │ │ -is a reference.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="2069856668-1">(</span><span class="p" data-group-id="2069856668-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +is a reference.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="7723422792-1">(</span><span class="p" data-group-id="7723422792-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Ref</span><span class="o">&lt;</span><span class="mf">0.76482849</span><span class="p">.</span><span class="mf">3801088007.198204</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nf">is_reference</span><span class="p" data-group-id="2069856668-2">(</span><span class="n">Ref</span><span class="p" data-group-id="2069856668-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="nf">is_reference</span><span class="p" data-group-id="7723422792-2">(</span><span class="n">Ref</span><span class="p" data-group-id="7723422792-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span></code></pre><h2 id="fun" class="section-heading">
│ │ │ │    <a href="#fun" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Fun</span>
│ │ │ │  </h2>
│ │ │ │  <p>A fun is a functional object. Funs make it possible to create an anonymous
│ │ │ │  function and pass the function itself — not its name — as argument to other
│ │ │ │ -functions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7503633978-1">(</span><span class="n">X</span><span class="p" data-group-id="7503633978-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +functions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8926748255-1">(</span><span class="n">X</span><span class="p" data-group-id="8926748255-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="7503633978-2">(</span><span class="mi">2</span><span class="p" data-group-id="7503633978-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="8926748255-2">(</span><span class="mi">2</span><span class="p" data-group-id="8926748255-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span></code></pre><p>The <a href="../../../lib/../erts/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> and <a href="../../../lib/../erts/doc/html/erlang.html#is_function/2"><code class="inline">is_function/2</code></a>
│ │ │ │ -BIFs tests whether a term is a fun.</p><p><em>Examples</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="7239410525-1">(</span><span class="p" data-group-id="7239410525-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +BIFs tests whether a term is a fun.</p><p><em>Examples</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="7805657175-1">(</span><span class="p" data-group-id="7805657175-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">43.105768164</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="7239410525-2">(</span><span class="n">F</span><span class="p" data-group-id="7239410525-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="7805657175-2">(</span><span class="n">F</span><span class="p" data-group-id="7805657175-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="7239410525-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7239410525-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="7805657175-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7805657175-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="7239410525-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7239410525-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="7805657175-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7805657175-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span></code></pre><p>Read more about funs in <a href="expressions.xhtml#fun-expressions">Fun Expressions</a>. For more
│ │ │ │  examples, see <a href="../../../lib/../system/doc/html/funs.xhtml">Programming Examples</a>.</p><h2 id="port-identifier" class="section-heading">
│ │ │ │    <a href="#port-identifier" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Port Identifier</span>
│ │ │ │  </h2>
│ │ │ │ @@ -205,94 +205,94 @@
│ │ │ │  for a new process after a while.</p><p>The BIF <a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the Pid of the calling process. When
│ │ │ │  <a href="ref_man_processes.xhtml#process-creation">creating a new process</a>, the parent
│ │ │ │  process will be able to get the Pid of the child process either via the return
│ │ │ │  value, as is the case when calling the <a href="../../../lib/../erts/doc/html/erlang.html#spawn/3"><code class="inline">spawn/3</code></a> BIF, or via
│ │ │ │  a message, which is the case when calling the
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#spawn_request/5"><code class="inline">spawn_request/5</code></a> BIF. A Pid is typically used when
│ │ │ │  when sending a process a <a href="ref_man_processes.xhtml#signals">signal</a>. The
│ │ │ │ -<a href="../../../lib/../erts/doc/html/erlang.html#is_pid/1"><code class="inline">is_pid/1</code></a> BIF tests whether a term is a Pid.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0710941620-1">(</span><span class="ss">m</span><span class="p" data-group-id="0710941620-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0710941620-2">(</span><span class="p" data-group-id="0710941620-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0710941620-3">]</span><span class="p" data-group-id="0710941620-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<a href="../../../lib/../erts/doc/html/erlang.html#is_pid/1"><code class="inline">is_pid/1</code></a> BIF tests whether a term is a Pid.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6134919601-1">(</span><span class="ss">m</span><span class="p" data-group-id="6134919601-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6134919601-2">(</span><span class="p" data-group-id="6134919601-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6134919601-3">]</span><span class="p" data-group-id="6134919601-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="0710941620-4">(</span><span class="p" data-group-id="0710941620-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="6134919601-4">(</span><span class="p" data-group-id="6134919601-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">who_are_you</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0710941620-5">(</span><span class="s">&quot;I am </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0710941620-6">[</span><span class="nf">self</span><span class="p" data-group-id="0710941620-7">(</span><span class="p" data-group-id="0710941620-7">)</span><span class="p" data-group-id="0710941620-6">]</span><span class="p" data-group-id="0710941620-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="0710941620-8">(</span><span class="p" data-group-id="0710941620-8">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6134919601-5">(</span><span class="s">&quot;I am </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6134919601-6">[</span><span class="nf">self</span><span class="p" data-group-id="6134919601-7">(</span><span class="p" data-group-id="6134919601-7">)</span><span class="p" data-group-id="6134919601-6">]</span><span class="p" data-group-id="6134919601-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="6134919601-8">(</span><span class="p" data-group-id="6134919601-8">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0710941620-9">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">loop</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0710941620-10">[</span><span class="p" data-group-id="0710941620-10">]</span><span class="p" data-group-id="0710941620-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="6134919601-9">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">loop</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6134919601-10">[</span><span class="p" data-group-id="6134919601-10">]</span><span class="p" data-group-id="6134919601-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.58</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │  2&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">who_are_you</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">I</span><span class="w"> </span><span class="ss">am</span><span class="w"> </span><span class="o">&lt;</span><span class="mf">0.58</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="ss">who_are_you</span></code></pre><p>Read more about processes in <a href="ref_man_processes.xhtml">Processes</a>.</p><h2 id="tuple" class="section-heading">
│ │ │ │    <a href="#tuple" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Tuple</span>
│ │ │ │  </h2>
│ │ │ │  <p>A tuple is a compound data type with a fixed number of terms:</p><pre><code class="text">{Term1,...,TermN}</code></pre><p>Each term <code class="inline">Term</code> in the tuple is called an <em>element</em>. The number of elements is
│ │ │ │ -said to be the <em>size</em> of the tuple.</p><p>There exists a number of BIFs to manipulate tuples.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1409824123-1">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="1409824123-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="1409824123-2">}</span><span class="p" data-group-id="1409824123-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1409824123-3">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="1409824123-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="1409824123-4">}</span><span class="p" data-group-id="1409824123-3">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nf">element</span><span class="p" data-group-id="1409824123-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="1409824123-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +said to be the <em>size</em> of the tuple.</p><p>There exists a number of BIFs to manipulate tuples.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8724862954-1">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="8724862954-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8724862954-2">}</span><span class="p" data-group-id="8724862954-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8724862954-3">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="8724862954-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8724862954-4">}</span><span class="p" data-group-id="8724862954-3">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="nf">element</span><span class="p" data-group-id="8724862954-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="8724862954-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">adam</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nf">element</span><span class="p" data-group-id="1409824123-6">(</span><span class="mi">3</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="1409824123-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1409824123-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="1409824123-7">}</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="1409824123-8">(</span><span class="mi">2</span><span class="p">,</span><span class="n">P</span><span class="p">,</span><span class="mi">25</span><span class="p" data-group-id="1409824123-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1409824123-9">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">25</span><span class="p">,</span><span class="p" data-group-id="1409824123-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="1409824123-10">}</span><span class="p" data-group-id="1409824123-9">}</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="1409824123-11">(</span><span class="n">P</span><span class="p" data-group-id="1409824123-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nf">element</span><span class="p" data-group-id="8724862954-6">(</span><span class="mi">3</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="8724862954-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8724862954-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8724862954-7">}</span><span class="gp unselectable">
│ │ │ │ +4&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="8724862954-8">(</span><span class="mi">2</span><span class="p">,</span><span class="n">P</span><span class="p">,</span><span class="mi">25</span><span class="p" data-group-id="8724862954-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8724862954-9">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">25</span><span class="p">,</span><span class="p" data-group-id="8724862954-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8724862954-10">}</span><span class="p" data-group-id="8724862954-9">}</span><span class="gp unselectable">
│ │ │ │ +5&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="8724862954-11">(</span><span class="n">P</span><span class="p" data-group-id="8724862954-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="1409824123-12">(</span><span class="p" data-group-id="1409824123-13">{</span><span class="p" data-group-id="1409824123-13">}</span><span class="p" data-group-id="1409824123-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +6&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="8724862954-12">(</span><span class="p" data-group-id="8724862954-13">{</span><span class="p" data-group-id="8724862954-13">}</span><span class="p" data-group-id="8724862954-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">0</span><span class="gp unselectable">
│ │ │ │ -7&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="1409824123-14">(</span><span class="p" data-group-id="1409824123-15">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1409824123-15">}</span><span class="p" data-group-id="1409824123-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +7&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="8724862954-14">(</span><span class="p" data-group-id="8724862954-15">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8724862954-15">}</span><span class="p" data-group-id="8724862954-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span></code></pre><h2 id="map" class="section-heading">
│ │ │ │    <a href="#map" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Map</span>
│ │ │ │  </h2>
│ │ │ │  <p>A map is a compound data type with a variable number of key-value associations:</p><pre><code class="text">#{Key1 =&gt; Value1, ..., KeyN =&gt; ValueN}</code></pre><p>Each key-value association in the map is called an <em>association pair</em>. The key
│ │ │ │  and value parts of the pair are called <em>elements</em>. The number of association
│ │ │ │ -pairs is said to be the <em>size</em> of the map.</p><p>There exists a number of BIFs to manipulate maps.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8276290173-1">#{</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="w"> </span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8276290173-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8276290173-2">}</span><span class="p" data-group-id="8276290173-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8276290173-3">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8276290173-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8276290173-4">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="8276290173-3">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="8276290173-5">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="8276290173-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +pairs is said to be the <em>size</em> of the map.</p><p>There exists a number of BIFs to manipulate maps.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2896872365-1">#{</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="w"> </span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2896872365-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2896872365-2">}</span><span class="p" data-group-id="2896872365-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2896872365-3">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2896872365-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2896872365-4">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="2896872365-3">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="2896872365-5">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="2896872365-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">adam</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="8276290173-6">(</span><span class="ss">date</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="8276290173-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8276290173-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8276290173-7">}</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="8276290173-8">(</span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="8276290173-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8276290173-9">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8276290173-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8276290173-10">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="8276290173-9">}</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="8276290173-11">(</span><span class="n">M</span><span class="p" data-group-id="8276290173-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="2896872365-6">(</span><span class="ss">date</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="2896872365-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2896872365-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2896872365-7">}</span><span class="gp unselectable">
│ │ │ │ +4&gt; </span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="2896872365-8">(</span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="2896872365-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2896872365-9">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2896872365-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2896872365-10">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="2896872365-9">}</span><span class="gp unselectable">
│ │ │ │ +5&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="2896872365-11">(</span><span class="n">M</span><span class="p" data-group-id="2896872365-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="8276290173-12">(</span><span class="p" data-group-id="8276290173-13">#{</span><span class="p" data-group-id="8276290173-13">}</span><span class="p" data-group-id="8276290173-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +6&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="2896872365-12">(</span><span class="p" data-group-id="2896872365-13">#{</span><span class="p" data-group-id="2896872365-13">}</span><span class="p" data-group-id="2896872365-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">0</span></code></pre><p>A collection of maps processing functions are found in module <a href="../../../lib/stdlib/doc/html/maps.html"><code class="inline">maps</code></a>
│ │ │ │  in STDLIB.</p><p>Read more about maps in <a href="expressions.xhtml#map-expressions">Map Expressions</a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Maps were introduced as an experimental feature in Erlang/OTP R17. Their
│ │ │ │  functionality was extended and became fully supported in Erlang/OTP 18.</p></section><h2 id="list" class="section-heading">
│ │ │ │    <a href="#list" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">List</span>
│ │ │ │  </h2>
│ │ │ │  <p>A list is a compound data type with a variable number of terms.</p><pre><code class="text">[Term1,...,TermN]</code></pre><p>Each term <code class="inline">Term</code> in the list is called an <em>element</em>. The number of elements is
│ │ │ │  said to be the <em>length</em> of the list.</p><p>Formally, a list is either the empty list <code class="inline">[]</code> or consists of a <em>head</em> (first
│ │ │ │  element) and a <em>tail</em> (remainder of the list). The <em>tail</em> is also a list. The
│ │ │ │  latter can be expressed as <code class="inline">[H|T]</code>. The notation <code class="inline">[Term1,...,TermN]</code> above is
│ │ │ │  equivalent with the list <code class="inline">[Term1|[...|[TermN|[]]]]</code>.</p><p><em>Example:</em></p><p><code class="inline">[]</code> is a list, thus<br/><code class="inline">[c|[]]</code> is a list, thus<br/><code class="inline">[b|[c|[]]]</code> is a list, thus<br/><code class="inline">[a|[b|[c|[]]]]</code> is a list, or in short <code class="inline">[a,b,c]</code></p><p>A list where the tail is a list is sometimes called a <em>proper list</em>. It is
│ │ │ │  allowed to have a list where the tail is not a list, for example, <code class="inline">[a|b]</code>.
│ │ │ │ -However, this type of list is of little practical use.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5412695706-1">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5412695706-2">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5412695706-2">}</span><span class="p" data-group-id="5412695706-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5412695706-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5412695706-4">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5412695706-4">}</span><span class="p" data-group-id="5412695706-3">]</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="p" data-group-id="5412695706-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5412695706-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5412695706-6">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5412695706-7">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5412695706-7">}</span><span class="p" data-group-id="5412695706-6">]</span><span class="gp unselectable">
│ │ │ │ +However, this type of list is of little practical use.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5801664017-1">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5801664017-2">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5801664017-2">}</span><span class="p" data-group-id="5801664017-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5801664017-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5801664017-4">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5801664017-4">}</span><span class="p" data-group-id="5801664017-3">]</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="p" data-group-id="5801664017-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5801664017-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5801664017-6">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5801664017-7">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5801664017-7">}</span><span class="p" data-group-id="5801664017-6">]</span><span class="gp unselectable">
│ │ │ │  3&gt; </span><span class="n">H</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">a</span><span class="gp unselectable">
│ │ │ │  4&gt; </span><span class="n">T</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5412695706-8">[</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5412695706-9">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5412695706-9">}</span><span class="p" data-group-id="5412695706-8">]</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="n">L2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5412695706-10">[</span><span class="ss">d</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5412695706-10">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5412695706-11">[</span><span class="ss">d</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5412695706-12">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5412695706-12">}</span><span class="p" data-group-id="5412695706-11">]</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nf">length</span><span class="p" data-group-id="5412695706-13">(</span><span class="n">L1</span><span class="p" data-group-id="5412695706-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5801664017-8">[</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5801664017-9">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5801664017-9">}</span><span class="p" data-group-id="5801664017-8">]</span><span class="gp unselectable">
│ │ │ │ +5&gt; </span><span class="n">L2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5801664017-10">[</span><span class="ss">d</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5801664017-10">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5801664017-11">[</span><span class="ss">d</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5801664017-12">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5801664017-12">}</span><span class="p" data-group-id="5801664017-11">]</span><span class="gp unselectable">
│ │ │ │ +6&gt; </span><span class="nf">length</span><span class="p" data-group-id="5801664017-13">(</span><span class="n">L1</span><span class="p" data-group-id="5801664017-13">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ │ -7&gt; </span><span class="nf">length</span><span class="p" data-group-id="5412695706-14">(</span><span class="p" data-group-id="5412695706-15">[</span><span class="p" data-group-id="5412695706-15">]</span><span class="p" data-group-id="5412695706-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +7&gt; </span><span class="nf">length</span><span class="p" data-group-id="5801664017-14">(</span><span class="p" data-group-id="5801664017-15">[</span><span class="p" data-group-id="5801664017-15">]</span><span class="p" data-group-id="5801664017-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">0</span></code></pre><p>A collection of list processing functions are found in module
│ │ │ │  <a href="../../../lib/stdlib/doc/html/lists.html"><code class="inline">lists</code></a> in STDLIB.</p><h2 id="string" class="section-heading">
│ │ │ │    <a href="#string" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">String</span>
│ │ │ │  </h2>
│ │ │ │ @@ -412,41 +412,41 @@
│ │ │ │    <span class="text">Record</span>
│ │ │ │  </h2>
│ │ │ │  <p>A record is a data structure for storing a fixed number of elements. It has
│ │ │ │  named fields and is similar to a struct in C. However, a record is not a true
│ │ │ │  data type. Instead, record expressions are translated to tuple expressions
│ │ │ │  during compilation. Therefore, record expressions are not understood by the
│ │ │ │  shell unless special actions are taken. For details, see module <a href="../../../lib/stdlib/doc/html/shell.html"><code class="inline">shell</code></a>
│ │ │ │ -in STDLIB.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8987026336-1">(</span><span class="ss">person</span><span class="p" data-group-id="8987026336-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8987026336-2">(</span><span class="p" data-group-id="8987026336-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8987026336-3">]</span><span class="p" data-group-id="8987026336-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +in STDLIB.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8741113130-1">(</span><span class="ss">person</span><span class="p" data-group-id="8741113130-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8741113130-2">(</span><span class="p" data-group-id="8741113130-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8741113130-3">]</span><span class="p" data-group-id="8741113130-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8987026336-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8987026336-5">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="8987026336-5">}</span><span class="p" data-group-id="8987026336-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8741113130-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8741113130-5">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="8741113130-5">}</span><span class="p" data-group-id="8741113130-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">new</span><span class="p" data-group-id="8987026336-6">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="8987026336-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8987026336-7">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="o">=</span><span class="n">Age</span><span class="p" data-group-id="8987026336-7">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">new</span><span class="p" data-group-id="8741113130-6">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="8741113130-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8741113130-7">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="o">=</span><span class="n">Age</span><span class="p" data-group-id="8741113130-7">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">person</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="8987026336-8">(</span><span class="ss">ernie</span><span class="p">,</span><span class="w"> </span><span class="mi">44</span><span class="p" data-group-id="8987026336-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8987026336-9">{</span><span class="ss">person</span><span class="p">,</span><span class="ss">ernie</span><span class="p">,</span><span class="mi">44</span><span class="p" data-group-id="8987026336-9">}</span></code></pre><p>Read more about records in <a href="ref_man_records.xhtml">Records</a>. More examples are
│ │ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">person</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="8741113130-8">(</span><span class="ss">ernie</span><span class="p">,</span><span class="w"> </span><span class="mi">44</span><span class="p" data-group-id="8741113130-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8741113130-9">{</span><span class="ss">person</span><span class="p">,</span><span class="ss">ernie</span><span class="p">,</span><span class="mi">44</span><span class="p" data-group-id="8741113130-9">}</span></code></pre><p>Read more about records in <a href="ref_man_records.xhtml">Records</a>. More examples are
│ │ │ │  found in <a href="../../../lib/../system/doc/html/prog_ex_records.xhtml">Programming Examples</a>.</p><h2 id="boolean" class="section-heading">
│ │ │ │    <a href="#boolean" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Boolean</span>
│ │ │ │  </h2>
│ │ │ │  <p>There is no Boolean data type in Erlang. Instead the atoms <code class="inline">true</code> and <code class="inline">false</code>
│ │ │ │  are used to denote Boolean values. The <a href="../../../lib/../erts/doc/html/erlang.html#is_boolean/1"><code class="inline">is_boolean/1</code></a>
│ │ │ │  BIF tests whether a term is a boolean.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mi">2</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │  2&gt; </span><span class="ss">true</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="ss">false</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="4421971391-1">(</span><span class="ss">true</span><span class="p" data-group-id="4421971391-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="7360266886-1">(</span><span class="ss">true</span><span class="p" data-group-id="7360266886-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="4421971391-2">(</span><span class="ss">false</span><span class="p" data-group-id="4421971391-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="7360266886-2">(</span><span class="ss">false</span><span class="p" data-group-id="7360266886-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="4421971391-3">(</span><span class="ss">ok</span><span class="p" data-group-id="4421971391-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="7360266886-3">(</span><span class="ss">ok</span><span class="p" data-group-id="7360266886-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span></code></pre><h2 id="escape-sequences" class="section-heading">
│ │ │ │    <a href="#escape-sequences" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Escape Sequences</span>
│ │ │ │  </h2>
│ │ │ │  <p>Within strings (<code class="inline">&quot;</code>-delimited), quoted atoms, and the content of
│ │ │ │ @@ -464,44 +464,44 @@
│ │ │ │  <a href="data_types.xhtml#sigil"><code class="inline">~b</code> or <code class="inline">~s</code> sigils </a>the escape sequences for normal
│ │ │ │  strings, above, are used.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Triple-quoted strings and sigils were introduced in Erlang/OTP 27.</p></section><h2 id="type-conversions" class="section-heading">
│ │ │ │    <a href="#type-conversions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Type Conversions</span>
│ │ │ │  </h2>
│ │ │ │ -<p>There are a number of BIFs for type conversions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="5220175546-1">(</span><span class="ss">hello</span><span class="p" data-group-id="5220175546-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>There are a number of BIFs for type conversions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="4041686059-1">(</span><span class="ss">hello</span><span class="p" data-group-id="4041686059-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;hello&quot;</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="5220175546-2">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5220175546-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +2&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="4041686059-2">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4041686059-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="5220175546-3">(</span><span class="p" data-group-id="5220175546-4">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5220175546-4">&gt;&gt;</span><span class="p" data-group-id="5220175546-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="4041686059-3">(</span><span class="p" data-group-id="4041686059-4">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4041686059-4">&gt;&gt;</span><span class="p" data-group-id="4041686059-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;hello&quot;</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="5220175546-5">(</span><span class="p" data-group-id="5220175546-6">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="5220175546-6">&gt;&gt;</span><span class="p" data-group-id="5220175546-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="4041686059-5">(</span><span class="p" data-group-id="4041686059-6">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="4041686059-6">&gt;&gt;</span><span class="p" data-group-id="4041686059-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;hello&quot;</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nf">list_to_binary</span><span class="p" data-group-id="5220175546-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5220175546-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5220175546-8">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="5220175546-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="5220175546-9">(</span><span class="mf">7.0</span><span class="p" data-group-id="5220175546-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="nf">list_to_binary</span><span class="p" data-group-id="4041686059-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4041686059-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4041686059-8">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="4041686059-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +6&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4041686059-9">(</span><span class="mf">7.0</span><span class="p" data-group-id="4041686059-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="gp unselectable">
│ │ │ │ -7&gt; </span><span class="nf">list_to_float</span><span class="p" data-group-id="5220175546-10">(</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="5220175546-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +7&gt; </span><span class="nf">list_to_float</span><span class="p" data-group-id="4041686059-10">(</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="4041686059-10">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">7.0</span><span class="gp unselectable">
│ │ │ │ -8&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="5220175546-11">(</span><span class="mi">77</span><span class="p" data-group-id="5220175546-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +8&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="4041686059-11">(</span><span class="mi">77</span><span class="p" data-group-id="4041686059-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;77&quot;</span><span class="gp unselectable">
│ │ │ │ -9&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="5220175546-12">(</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="5220175546-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +9&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="4041686059-12">(</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="4041686059-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">77</span><span class="gp unselectable">
│ │ │ │ -10&gt; </span><span class="nf">tuple_to_list</span><span class="p" data-group-id="5220175546-13">(</span><span class="p" data-group-id="5220175546-14">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5220175546-14">}</span><span class="p" data-group-id="5220175546-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5220175546-15">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5220175546-15">]</span><span class="gp unselectable">
│ │ │ │ -11&gt; </span><span class="nf">list_to_tuple</span><span class="p" data-group-id="5220175546-16">(</span><span class="p" data-group-id="5220175546-17">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5220175546-17">]</span><span class="p" data-group-id="5220175546-16">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5220175546-18">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5220175546-18">}</span><span class="gp unselectable">
│ │ │ │ -12&gt; </span><span class="nf">term_to_binary</span><span class="p" data-group-id="5220175546-19">(</span><span class="p" data-group-id="5220175546-20">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5220175546-20">}</span><span class="p" data-group-id="5220175546-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5220175546-21">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="5220175546-21">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -13&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="5220175546-22">(</span><span class="p" data-group-id="5220175546-23">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="5220175546-23">&gt;&gt;</span><span class="p" data-group-id="5220175546-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5220175546-24">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5220175546-24">}</span><span class="gp unselectable">
│ │ │ │ -14&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="5220175546-25">(</span><span class="p" data-group-id="5220175546-26">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="5220175546-26">&gt;&gt;</span><span class="p" data-group-id="5220175546-25">)</span><span class="p">.</span><span class="w">
│ │ │ │ +10&gt; </span><span class="nf">tuple_to_list</span><span class="p" data-group-id="4041686059-13">(</span><span class="p" data-group-id="4041686059-14">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4041686059-14">}</span><span class="p" data-group-id="4041686059-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4041686059-15">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4041686059-15">]</span><span class="gp unselectable">
│ │ │ │ +11&gt; </span><span class="nf">list_to_tuple</span><span class="p" data-group-id="4041686059-16">(</span><span class="p" data-group-id="4041686059-17">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4041686059-17">]</span><span class="p" data-group-id="4041686059-16">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4041686059-18">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4041686059-18">}</span><span class="gp unselectable">
│ │ │ │ +12&gt; </span><span class="nf">term_to_binary</span><span class="p" data-group-id="4041686059-19">(</span><span class="p" data-group-id="4041686059-20">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4041686059-20">}</span><span class="p" data-group-id="4041686059-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4041686059-21">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="4041686059-21">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +13&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="4041686059-22">(</span><span class="p" data-group-id="4041686059-23">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="4041686059-23">&gt;&gt;</span><span class="p" data-group-id="4041686059-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4041686059-24">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4041686059-24">}</span><span class="gp unselectable">
│ │ │ │ +14&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="4041686059-25">(</span><span class="p" data-group-id="4041686059-26">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="4041686059-26">&gt;&gt;</span><span class="p" data-group-id="4041686059-25">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">77</span><span class="gp unselectable">
│ │ │ │ -15&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="5220175546-27">(</span><span class="mi">77</span><span class="p" data-group-id="5220175546-27">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5220175546-28">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="5220175546-28">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -16&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="5220175546-29">(</span><span class="mf">7.0</span><span class="p" data-group-id="5220175546-29">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5220175546-30">&lt;&lt;</span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="p" data-group-id="5220175546-30">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ -17&gt; </span><span class="nf">binary_to_float</span><span class="p" data-group-id="5220175546-31">(</span><span class="p" data-group-id="5220175546-32">&lt;&lt;</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="5220175546-32">&gt;&gt;</span><span class="p" data-group-id="5220175546-31">)</span><span class="p">.</span><span class="w">
│ │ │ │ +15&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="4041686059-27">(</span><span class="mi">77</span><span class="p" data-group-id="4041686059-27">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4041686059-28">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="4041686059-28">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +16&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="4041686059-29">(</span><span class="mf">7.0</span><span class="p" data-group-id="4041686059-29">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4041686059-30">&lt;&lt;</span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="p" data-group-id="4041686059-30">&gt;&gt;</span><span class="gp unselectable">
│ │ │ │ +17&gt; </span><span class="nf">binary_to_float</span><span class="p" data-group-id="4041686059-31">(</span><span class="p" data-group-id="4041686059-32">&lt;&lt;</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="4041686059-32">&gt;&gt;</span><span class="p" data-group-id="4041686059-31">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">7.0</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/create_target.xhtml
│ │ │ │ @@ -43,21 +43,21 @@
│ │ │ │    <span class="text">Creating a Target System</span>
│ │ │ │  </h2>
│ │ │ │  <p>It is assumed that you have a working Erlang/OTP system structured according to
│ │ │ │  the OTP design principles.</p><p><em>Step 1.</em> Create a <code class="inline">.rel</code> file (see the <a href="../../../lib/sasl/doc/html/rel.xhtml">rel(4)</a> manual page in
│ │ │ │  SASL), which specifies the ERTS version and lists all applications that are to
│ │ │ │  be included in the new basic target system. An example is the following
│ │ │ │  <code class="inline">mysystem.rel</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% mysystem.rel</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0841427469-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0841427469-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;FIRST&quot;</span><span class="p" data-group-id="0841427469-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0841427469-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.10.4&quot;</span><span class="p" data-group-id="0841427469-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0841427469-4">[</span><span class="p" data-group-id="0841427469-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.16.4&quot;</span><span class="p" data-group-id="0841427469-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0841427469-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.19.4&quot;</span><span class="p" data-group-id="0841427469-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0841427469-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.3.4&quot;</span><span class="p" data-group-id="0841427469-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0841427469-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="0841427469-8">}</span><span class="p" data-group-id="0841427469-4">]</span><span class="p" data-group-id="0841427469-1">}</span><span class="p">.</span></code></pre><p>The listed applications are not only original Erlang/OTP applications but
│ │ │ │ +</span><span class="p" data-group-id="7154623998-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7154623998-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;FIRST&quot;</span><span class="p" data-group-id="7154623998-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7154623998-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.10.4&quot;</span><span class="p" data-group-id="7154623998-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7154623998-4">[</span><span class="p" data-group-id="7154623998-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.16.4&quot;</span><span class="p" data-group-id="7154623998-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7154623998-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.19.4&quot;</span><span class="p" data-group-id="7154623998-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7154623998-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.3.4&quot;</span><span class="p" data-group-id="7154623998-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7154623998-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="7154623998-8">}</span><span class="p" data-group-id="7154623998-4">]</span><span class="p" data-group-id="7154623998-1">}</span><span class="p">.</span></code></pre><p>The listed applications are not only original Erlang/OTP applications but
│ │ │ │  possibly also new applications that you have written (here exemplified by the
│ │ │ │  application Pea (<code class="inline">pea</code>)).</p><p><em>Step 2.</em> Start Erlang/OTP from the directory where the <code class="inline">mysystem.rel</code> file
│ │ │ │  resides:</p><pre><code class="text">% erl -pa /home/user/target_system/myapps/pea-1.0/ebin</code></pre><p>The <code class="inline">-pa</code> argument prepends the path to the <code class="inline">ebin</code> directory for
│ │ │ │  the Pea application to the code path.</p><p><em>Step 3.</em> Create the target system:</p><pre><code class="text">1&gt; target_system:create(&quot;mysystem&quot;).</code></pre><p>The function <code class="inline">target_system:create/1</code> performs the following:</p><ol><li><p>Reads the file <code class="inline">mysystem.rel</code> and creates a new file <code class="inline">plain.rel</code>.
│ │ │ │  The new file is identical to the original, except that it only
│ │ │ │  lists the Kernel and STDLIB applications.</p></li><li><p>From the files <code class="inline">mysystem.rel</code> and <code class="inline">plain.rel</code> creates the files
│ │ │ │  <code class="inline">mysystem.script</code>, <code class="inline">mysystem.boot</code>, <code class="inline">plain.script</code>, and <code class="inline">plain.boot</code>
│ │ │ │ @@ -147,25 +147,25 @@
│ │ │ │    <a href="#creating-the-next-version" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating the Next Version</span>
│ │ │ │  </h2>
│ │ │ │  <p>In this example the Pea application has been changed, and so are the
│ │ │ │  applications ERTS, Kernel, STDLIB and SASL.</p><p><em>Step 1.</em> Create the file <code class="inline">.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% mysystem2.rel</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9181938861-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9181938861-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;SECOND&quot;</span><span class="p" data-group-id="9181938861-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9181938861-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;6.0&quot;</span><span class="p" data-group-id="9181938861-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9181938861-4">[</span><span class="p" data-group-id="9181938861-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;3.0&quot;</span><span class="p" data-group-id="9181938861-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9181938861-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="9181938861-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9181938861-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.4&quot;</span><span class="p" data-group-id="9181938861-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9181938861-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="9181938861-8">}</span><span class="p" data-group-id="9181938861-4">]</span><span class="p" data-group-id="9181938861-1">}</span><span class="p">.</span></code></pre><p><em>Step 2.</em> Create the application upgrade file (see
│ │ │ │ +</span><span class="p" data-group-id="0906762358-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0906762358-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;SECOND&quot;</span><span class="p" data-group-id="0906762358-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0906762358-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;6.0&quot;</span><span class="p" data-group-id="0906762358-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0906762358-4">[</span><span class="p" data-group-id="0906762358-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;3.0&quot;</span><span class="p" data-group-id="0906762358-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0906762358-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="0906762358-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0906762358-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.4&quot;</span><span class="p" data-group-id="0906762358-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0906762358-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="0906762358-8">}</span><span class="p" data-group-id="0906762358-4">]</span><span class="p" data-group-id="0906762358-1">}</span><span class="p">.</span></code></pre><p><em>Step 2.</em> Create the application upgrade file (see
│ │ │ │  <a href="../../../lib/sasl/doc/html/appup.xhtml">appup</a> in SASL) for Pea, for example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% pea.appup</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6977663217-1">{</span><span class="s">&quot;2.0&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6977663217-2">[</span><span class="p" data-group-id="6977663217-3">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="6977663217-4">[</span><span class="p" data-group-id="6977663217-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="6977663217-5">}</span><span class="p" data-group-id="6977663217-4">]</span><span class="p" data-group-id="6977663217-3">}</span><span class="p" data-group-id="6977663217-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6977663217-6">[</span><span class="p" data-group-id="6977663217-7">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="6977663217-8">[</span><span class="p" data-group-id="6977663217-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="6977663217-9">}</span><span class="p" data-group-id="6977663217-8">]</span><span class="p" data-group-id="6977663217-7">}</span><span class="p" data-group-id="6977663217-6">]</span><span class="p" data-group-id="6977663217-1">}</span><span class="p">.</span></code></pre><p><em>Step 3.</em> From the directory where the file <code class="inline">mysystem2.rel</code> resides, start the
│ │ │ │ +</span><span class="p" data-group-id="0649665288-1">{</span><span class="s">&quot;2.0&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0649665288-2">[</span><span class="p" data-group-id="0649665288-3">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="0649665288-4">[</span><span class="p" data-group-id="0649665288-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="0649665288-5">}</span><span class="p" data-group-id="0649665288-4">]</span><span class="p" data-group-id="0649665288-3">}</span><span class="p" data-group-id="0649665288-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0649665288-6">[</span><span class="p" data-group-id="0649665288-7">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="0649665288-8">[</span><span class="p" data-group-id="0649665288-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="0649665288-9">}</span><span class="p" data-group-id="0649665288-8">]</span><span class="p" data-group-id="0649665288-7">}</span><span class="p" data-group-id="0649665288-6">]</span><span class="p" data-group-id="0649665288-1">}</span><span class="p">.</span></code></pre><p><em>Step 3.</em> From the directory where the file <code class="inline">mysystem2.rel</code> resides, start the
│ │ │ │  Erlang/OTP system, giving the path to the new version of Pea:</p><pre><code class="text">% erl -pa /home/user/target_system/myapps/pea-2.0/ebin</code></pre><p><em>Step 4.</em> Create the release upgrade file (see <a href="../../../lib/sasl/doc/html/relup.xhtml">relup</a>
│ │ │ │  in SASL):</p><pre><code class="text">1&gt; systools:make_relup(&quot;mysystem2&quot;,[&quot;mysystem&quot;],[&quot;mysystem&quot;],
│ │ │ │      [{path,[&quot;/home/user/target_system/myapps/pea-1.0/ebin&quot;,
│ │ │ │      &quot;/my/old/erlang/lib/*/ebin&quot;]}]).</code></pre><p>Here <code class="inline">&quot;mysystem&quot;</code> is the base release and <code class="inline">&quot;mysystem2&quot;</code> is the release to
│ │ │ │  upgrade to.</p><p>The <code class="inline">path</code> option is used for pointing out the old version of all applications.
│ │ │ │  (The new versions are already in the code path - assuming of course that the
│ │ │ │  Erlang node on which this is executed is running the correct version of
│ │ │ │ @@ -197,21 +197,21 @@
│ │ │ │  {continue_after_restart,&quot;FIRST&quot;,[]}
│ │ │ │  heart: Tue Apr  1 12:15:10 2014: Erlang has closed.
│ │ │ │  heart: Tue Apr  1 12:15:11 2014: Executed &quot;/usr/local/erl-target/bin/start /usr/local/erl-target/releases/new_start_erl.data&quot; -&gt; 0. Terminating.
│ │ │ │  [End]</code></pre><p>The above return value and output after the call to
│ │ │ │  <a href="../../../lib/sasl/doc/html/release_handler.html#install_release/1"><code class="inline">release_handler:install_release/1</code></a> means that the <code class="inline">release_handler</code> has
│ │ │ │  restarted the node by using <code class="inline">heart</code>. This is always done when the upgrade
│ │ │ │  involves a change of the applications ERTS, Kernel, STDLIB, or SASL. For more
│ │ │ │ -information, see <a href="upgrade.xhtml">Upgrade when Erlang/OTP has Changed</a>.</p><p>The node is accessible through a new pipe:</p><pre><code class="text">% /usr/local/erl-target/bin/to_erl /tmp/erlang.pipe.2</code></pre><p>List the available releases in the system:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">which_releases</span><span class="p" data-group-id="2767483108-1">(</span><span class="p" data-group-id="2767483108-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2767483108-2">[</span><span class="p" data-group-id="2767483108-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2767483108-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="2767483108-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">current</span><span class="p" data-group-id="2767483108-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2767483108-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2767483108-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="2767483108-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">permanent</span><span class="p" data-group-id="2767483108-5">}</span><span class="p" data-group-id="2767483108-2">]</span></code></pre><p>Our new release, &quot;SECOND&quot;, is now the current release, but we can also see that
│ │ │ │ +information, see <a href="upgrade.xhtml">Upgrade when Erlang/OTP has Changed</a>.</p><p>The node is accessible through a new pipe:</p><pre><code class="text">% /usr/local/erl-target/bin/to_erl /tmp/erlang.pipe.2</code></pre><p>List the available releases in the system:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">which_releases</span><span class="p" data-group-id="1606153346-1">(</span><span class="p" data-group-id="1606153346-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1606153346-2">[</span><span class="p" data-group-id="1606153346-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="1606153346-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="1606153346-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">current</span><span class="p" data-group-id="1606153346-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1606153346-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="1606153346-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="1606153346-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">permanent</span><span class="p" data-group-id="1606153346-5">}</span><span class="p" data-group-id="1606153346-2">]</span></code></pre><p>Our new release, &quot;SECOND&quot;, is now the current release, but we can also see that
│ │ │ │  our &quot;FIRST&quot; release is still permanent. This means that if the node would be
│ │ │ │  restarted now, it would come up running the &quot;FIRST&quot; release again.</p><p><em>Step 3.</em> Make the new release permanent:</p><pre><code class="text">2&gt; release_handler:make_permanent(&quot;SECOND&quot;).</code></pre><p>Check the releases again:</p><pre><code class="c">3&gt; release_handler:which_releases().
│ │ │ │  [{&quot;MYSYSTEM&quot;,&quot;SECOND&quot;,
│ │ │ │    [&quot;kernel-3.0&quot;,&quot;stdlib-2.0&quot;,&quot;sasl-2.4&quot;,&quot;pea-2.0&quot;],
│ │ │ │    permanent},
│ │ │ │   {&quot;MYSYSTEM&quot;,&quot;FIRST&quot;,
│ │ │ │    [&quot;kernel-2.16.4&quot;,&quot;stdlib-1.19.4&quot;,&quot;sasl-2.3.4&quot;,&quot;pea-1.0&quot;],
│ │ │ │ @@ -220,264 +220,264 @@
│ │ │ │    <a href="#listing-of-target_system-erl" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Listing of target_system.erl</span>
│ │ │ │  </h2>
│ │ │ │  <p>This module can also be found in the <code class="inline">examples</code> directory of the SASL
│ │ │ │  application.</p><pre><code class="makeup erlang" translate="no"><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1447096874-1">(</span><span class="ss">target_system</span><span class="p" data-group-id="1447096874-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1447096874-2">(</span><span class="p" data-group-id="1447096874-3">[</span><span class="ss">create</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">create</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">install</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1447096874-3">]</span><span class="p" data-group-id="1447096874-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9979816171-1">(</span><span class="ss">target_system</span><span class="p" data-group-id="9979816171-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9979816171-2">(</span><span class="p" data-group-id="9979816171-3">[</span><span class="ss">create</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">create</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">install</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9979816171-3">]</span><span class="p" data-group-id="9979816171-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% Note: RelFileName below is the *stem* without trailing .rel,</span><span class="w">
│ │ │ │  </span><span class="c1">%% .script etc.</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% create(RelFileName)</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">create</span><span class="p" data-group-id="1447096874-4">(</span><span class="n">RelFileName</span><span class="p" data-group-id="1447096874-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">create</span><span class="p" data-group-id="1447096874-5">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="p" data-group-id="1447096874-6">[</span><span class="p" data-group-id="1447096874-6">]</span><span class="p" data-group-id="1447096874-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">create</span><span class="p" data-group-id="9979816171-4">(</span><span class="n">RelFileName</span><span class="p" data-group-id="9979816171-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">create</span><span class="p" data-group-id="9979816171-5">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="p" data-group-id="9979816171-6">[</span><span class="p" data-group-id="9979816171-6">]</span><span class="p" data-group-id="9979816171-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">create</span><span class="p" data-group-id="1447096874-7">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="1447096874-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">create</span><span class="p" data-group-id="9979816171-7">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="9979816171-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">RelFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="1447096874-8">(</span><span class="n">RelFileName</span><span class="p" data-group-id="1447096874-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-9">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;plain&quot;</span><span class="p" data-group-id="1447096874-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="9979816171-8">(</span><span class="n">RelFileName</span><span class="p" data-group-id="9979816171-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-9">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;plain&quot;</span><span class="p" data-group-id="9979816171-9">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">PlainRelFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-10">(</span><span class="s">&quot;Reading file: ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-11">[</span><span class="n">RelFile</span><span class="p" data-group-id="1447096874-11">]</span><span class="p" data-group-id="1447096874-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-13">[</span><span class="n">RelSpec</span><span class="p" data-group-id="1447096874-13">]</span><span class="p" data-group-id="1447096874-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">consult</span><span class="p" data-group-id="1447096874-14">(</span><span class="n">RelFile</span><span class="p" data-group-id="1447096874-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-15">(</span><span class="s">&quot;Creating file: ~ts from ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="1447096874-16">[</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="n">RelFile</span><span class="p" data-group-id="1447096874-16">]</span><span class="p" data-group-id="1447096874-15">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-17">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="1447096874-18">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="1447096874-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="1447096874-19">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="1447096874-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="n">AppVsns</span><span class="p" data-group-id="1447096874-17">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelSpec</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">PlainRelSpec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1447096874-20">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="1447096874-21">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="1447096874-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="1447096874-22">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="1447096874-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="1447096874-23">(</span><span class="nf">fun</span><span class="p" data-group-id="1447096874-24">(</span><span class="p" data-group-id="1447096874-25">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1447096874-25">}</span><span class="p" data-group-id="1447096874-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-10">(</span><span class="s">&quot;Reading file: ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-11">[</span><span class="n">RelFile</span><span class="p" data-group-id="9979816171-11">]</span><span class="p" data-group-id="9979816171-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-13">[</span><span class="n">RelSpec</span><span class="p" data-group-id="9979816171-13">]</span><span class="p" data-group-id="9979816171-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">consult</span><span class="p" data-group-id="9979816171-14">(</span><span class="n">RelFile</span><span class="p" data-group-id="9979816171-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-15">(</span><span class="s">&quot;Creating file: ~ts from ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="9979816171-16">[</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="n">RelFile</span><span class="p" data-group-id="9979816171-16">]</span><span class="p" data-group-id="9979816171-15">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-17">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="9979816171-18">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="9979816171-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="9979816171-19">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="9979816171-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="n">AppVsns</span><span class="p" data-group-id="9979816171-17">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelSpec</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">PlainRelSpec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9979816171-20">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="9979816171-21">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="9979816171-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="9979816171-22">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="9979816171-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="9979816171-23">(</span><span class="nf">fun</span><span class="p" data-group-id="9979816171-24">(</span><span class="p" data-group-id="9979816171-25">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9979816171-25">}</span><span class="p" data-group-id="9979816171-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                                           </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │ -                                    </span><span class="p" data-group-id="1447096874-26">(</span><span class="p" data-group-id="1447096874-27">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1447096874-27">}</span><span class="p" data-group-id="1447096874-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                                    </span><span class="p" data-group-id="9979816171-26">(</span><span class="p" data-group-id="9979816171-27">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9979816171-27">}</span><span class="p" data-group-id="9979816171-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                                           </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │ -                                    </span><span class="p" data-group-id="1447096874-28">(</span><span class="p">_</span><span class="p" data-group-id="1447096874-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                                    </span><span class="p" data-group-id="9979816171-28">(</span><span class="p">_</span><span class="p" data-group-id="9979816171-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                                           </span><span class="ss">false</span><span class="w">
│ │ │ │ -                                 </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsns</span><span class="p" data-group-id="1447096874-23">)</span><span class="w">
│ │ │ │ -                   </span><span class="p" data-group-id="1447096874-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="1447096874-29">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="1447096874-30">(</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-31">[</span><span class="ss">write</span><span class="p" data-group-id="1447096874-31">]</span><span class="p" data-group-id="1447096874-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-32">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-33">[</span><span class="n">PlainRelSpec</span><span class="p" data-group-id="1447096874-33">]</span><span class="p" data-group-id="1447096874-32">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="1447096874-34">(</span><span class="n">Fd</span><span class="p" data-group-id="1447096874-34">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-35">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -	      </span><span class="p" data-group-id="1447096874-36">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">PlainRelFileName</span><span class="p" data-group-id="1447096874-36">]</span><span class="p" data-group-id="1447096874-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">make_script</span><span class="p" data-group-id="1447096874-37">(</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="1447096874-37">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-38">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="1447096874-39">[</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="1447096874-39">]</span><span class="p" data-group-id="1447096874-38">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">make_script</span><span class="p" data-group-id="1447096874-40">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="1447096874-40">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                                 </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsns</span><span class="p" data-group-id="9979816171-23">)</span><span class="w">
│ │ │ │ +                   </span><span class="p" data-group-id="9979816171-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="9979816171-29">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="9979816171-30">(</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-31">[</span><span class="ss">write</span><span class="p" data-group-id="9979816171-31">]</span><span class="p" data-group-id="9979816171-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-32">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-33">[</span><span class="n">PlainRelSpec</span><span class="p" data-group-id="9979816171-33">]</span><span class="p" data-group-id="9979816171-32">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="9979816171-34">(</span><span class="n">Fd</span><span class="p" data-group-id="9979816171-34">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-35">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +	      </span><span class="p" data-group-id="9979816171-36">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">PlainRelFileName</span><span class="p" data-group-id="9979816171-36">]</span><span class="p" data-group-id="9979816171-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">make_script</span><span class="p" data-group-id="9979816171-37">(</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="9979816171-37">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-38">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="9979816171-39">[</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="9979816171-39">]</span><span class="p" data-group-id="9979816171-38">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">make_script</span><span class="p" data-group-id="9979816171-40">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="9979816171-40">)</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │      </span><span class="n">TarFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.tar.gz&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-41">(</span><span class="s">&quot;Creating tar file ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-42">[</span><span class="n">TarFileName</span><span class="p" data-group-id="1447096874-42">]</span><span class="p" data-group-id="1447096874-41">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">make_tar</span><span class="p" data-group-id="1447096874-43">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="1447096874-43">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-41">(</span><span class="s">&quot;Creating tar file ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-42">[</span><span class="n">TarFileName</span><span class="p" data-group-id="9979816171-42">]</span><span class="p" data-group-id="9979816171-41">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">make_tar</span><span class="p" data-group-id="9979816171-43">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="9979816171-43">)</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │ -    </span><span class="n">TmpDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-44">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;tmp&quot;</span><span class="p" data-group-id="1447096874-44">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-45">(</span><span class="s">&quot;Creating directory ~tp ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="1447096874-46">[</span><span class="n">TmpDir</span><span class="p" data-group-id="1447096874-46">]</span><span class="p" data-group-id="1447096874-45">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="1447096874-47">(</span><span class="n">TmpDir</span><span class="p" data-group-id="1447096874-47">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-48">(</span><span class="s">&quot;Extracting ~ts into directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-49">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="1447096874-49">]</span><span class="p" data-group-id="1447096874-48">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">extract_tar</span><span class="p" data-group-id="1447096874-50">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="n">TmpDir</span><span class="p" data-group-id="1447096874-50">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="n">TmpBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-51">(</span><span class="p" data-group-id="1447096874-52">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="1447096874-52">]</span><span class="p" data-group-id="1447096874-51">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-53">(</span><span class="p" data-group-id="1447096874-54">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="1447096874-54">]</span><span class="p" data-group-id="1447096874-53">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-55">(</span><span class="s">&quot;Deleting \&quot;erl\&quot; and \&quot;start\&quot; in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="1447096874-56">[</span><span class="n">ErtsBinDir</span><span class="p" data-group-id="1447096874-56">]</span><span class="p" data-group-id="1447096874-55">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="1447096874-57">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-58">(</span><span class="p" data-group-id="1447096874-59">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erl&quot;</span><span class="p" data-group-id="1447096874-59">]</span><span class="p" data-group-id="1447096874-58">)</span><span class="p" data-group-id="1447096874-57">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="1447096874-60">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-61">(</span><span class="p" data-group-id="1447096874-62">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="1447096874-62">]</span><span class="p" data-group-id="1447096874-61">)</span><span class="p" data-group-id="1447096874-60">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-63">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-64">[</span><span class="n">TmpBinDir</span><span class="p" data-group-id="1447096874-64">]</span><span class="p" data-group-id="1447096874-63">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="1447096874-65">(</span><span class="n">TmpBinDir</span><span class="p" data-group-id="1447096874-65">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-66">(</span><span class="s">&quot;Copying file \&quot;~ts.boot\&quot; to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="1447096874-67">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-68">(</span><span class="p" data-group-id="1447096874-69">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="1447096874-69">]</span><span class="p" data-group-id="1447096874-68">)</span><span class="p" data-group-id="1447096874-67">]</span><span class="p" data-group-id="1447096874-66">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="1447096874-70">(</span><span class="n">PlainRelFileName</span><span class="o">++</span><span class="s">&quot;.boot&quot;</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-71">(</span><span class="p" data-group-id="1447096874-72">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="1447096874-72">]</span><span class="p" data-group-id="1447096874-71">)</span><span class="p" data-group-id="1447096874-70">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">TmpDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-44">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;tmp&quot;</span><span class="p" data-group-id="9979816171-44">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-45">(</span><span class="s">&quot;Creating directory ~tp ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="9979816171-46">[</span><span class="n">TmpDir</span><span class="p" data-group-id="9979816171-46">]</span><span class="p" data-group-id="9979816171-45">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="9979816171-47">(</span><span class="n">TmpDir</span><span class="p" data-group-id="9979816171-47">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-48">(</span><span class="s">&quot;Extracting ~ts into directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-49">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="9979816171-49">]</span><span class="p" data-group-id="9979816171-48">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">extract_tar</span><span class="p" data-group-id="9979816171-50">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="n">TmpDir</span><span class="p" data-group-id="9979816171-50">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="n">TmpBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-51">(</span><span class="p" data-group-id="9979816171-52">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="9979816171-52">]</span><span class="p" data-group-id="9979816171-51">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-53">(</span><span class="p" data-group-id="9979816171-54">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="9979816171-54">]</span><span class="p" data-group-id="9979816171-53">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-55">(</span><span class="s">&quot;Deleting \&quot;erl\&quot; and \&quot;start\&quot; in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="9979816171-56">[</span><span class="n">ErtsBinDir</span><span class="p" data-group-id="9979816171-56">]</span><span class="p" data-group-id="9979816171-55">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="9979816171-57">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-58">(</span><span class="p" data-group-id="9979816171-59">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erl&quot;</span><span class="p" data-group-id="9979816171-59">]</span><span class="p" data-group-id="9979816171-58">)</span><span class="p" data-group-id="9979816171-57">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="9979816171-60">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-61">(</span><span class="p" data-group-id="9979816171-62">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="9979816171-62">]</span><span class="p" data-group-id="9979816171-61">)</span><span class="p" data-group-id="9979816171-60">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-63">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-64">[</span><span class="n">TmpBinDir</span><span class="p" data-group-id="9979816171-64">]</span><span class="p" data-group-id="9979816171-63">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="9979816171-65">(</span><span class="n">TmpBinDir</span><span class="p" data-group-id="9979816171-65">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-66">(</span><span class="s">&quot;Copying file \&quot;~ts.boot\&quot; to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="9979816171-67">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-68">(</span><span class="p" data-group-id="9979816171-69">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="9979816171-69">]</span><span class="p" data-group-id="9979816171-68">)</span><span class="p" data-group-id="9979816171-67">]</span><span class="p" data-group-id="9979816171-66">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="9979816171-70">(</span><span class="n">PlainRelFileName</span><span class="o">++</span><span class="s">&quot;.boot&quot;</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-71">(</span><span class="p" data-group-id="9979816171-72">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="9979816171-72">]</span><span class="p" data-group-id="9979816171-71">)</span><span class="p" data-group-id="9979816171-70">)</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-73">(</span><span class="s">&quot;Copying files \&quot;epmd\&quot;, \&quot;run_erl\&quot; and \&quot;to_erl\&quot; from \n&quot;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-73">(</span><span class="s">&quot;Copying files \&quot;epmd\&quot;, \&quot;run_erl\&quot; and \&quot;to_erl\&quot; from \n&quot;</span><span class="w">
│ │ │ │                </span><span class="s">&quot;~ts to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="1447096874-74">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">TmpBinDir</span><span class="p" data-group-id="1447096874-74">]</span><span class="p" data-group-id="1447096874-73">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="1447096874-75">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-76">(</span><span class="p" data-group-id="1447096874-77">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="1447096874-77">]</span><span class="p" data-group-id="1447096874-76">)</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-78">(</span><span class="p" data-group-id="1447096874-79">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="1447096874-79">]</span><span class="p" data-group-id="1447096874-78">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-80">[</span><span class="ss">preserve</span><span class="p" data-group-id="1447096874-80">]</span><span class="p" data-group-id="1447096874-75">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="1447096874-81">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-82">(</span><span class="p" data-group-id="1447096874-83">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="1447096874-83">]</span><span class="p" data-group-id="1447096874-82">)</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-84">(</span><span class="p" data-group-id="1447096874-85">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="1447096874-85">]</span><span class="p" data-group-id="1447096874-84">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-86">[</span><span class="ss">preserve</span><span class="p" data-group-id="1447096874-86">]</span><span class="p" data-group-id="1447096874-81">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="1447096874-87">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-88">(</span><span class="p" data-group-id="1447096874-89">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="1447096874-89">]</span><span class="p" data-group-id="1447096874-88">)</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-90">(</span><span class="p" data-group-id="1447096874-91">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="1447096874-91">]</span><span class="p" data-group-id="1447096874-90">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-92">[</span><span class="ss">preserve</span><span class="p" data-group-id="1447096874-92">]</span><span class="p" data-group-id="1447096874-87">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="9979816171-74">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">TmpBinDir</span><span class="p" data-group-id="9979816171-74">]</span><span class="p" data-group-id="9979816171-73">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="9979816171-75">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-76">(</span><span class="p" data-group-id="9979816171-77">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="9979816171-77">]</span><span class="p" data-group-id="9979816171-76">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-78">(</span><span class="p" data-group-id="9979816171-79">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="9979816171-79">]</span><span class="p" data-group-id="9979816171-78">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-80">[</span><span class="ss">preserve</span><span class="p" data-group-id="9979816171-80">]</span><span class="p" data-group-id="9979816171-75">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="9979816171-81">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-82">(</span><span class="p" data-group-id="9979816171-83">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="9979816171-83">]</span><span class="p" data-group-id="9979816171-82">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-84">(</span><span class="p" data-group-id="9979816171-85">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="9979816171-85">]</span><span class="p" data-group-id="9979816171-84">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-86">[</span><span class="ss">preserve</span><span class="p" data-group-id="9979816171-86">]</span><span class="p" data-group-id="9979816171-81">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="9979816171-87">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-88">(</span><span class="p" data-group-id="9979816171-89">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="9979816171-89">]</span><span class="p" data-group-id="9979816171-88">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-90">(</span><span class="p" data-group-id="9979816171-91">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="9979816171-91">]</span><span class="p" data-group-id="9979816171-90">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-92">[</span><span class="ss">preserve</span><span class="p" data-group-id="9979816171-92">]</span><span class="p" data-group-id="9979816171-87">)</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │      </span><span class="c1">%% This is needed if &#39;start&#39; script created from &#39;start.src&#39; shall</span><span class="w">
│ │ │ │      </span><span class="c1">%% be used as it points out this directory as log dir for &#39;run_erl&#39;</span><span class="w">
│ │ │ │ -    </span><span class="n">TmpLogDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-93">(</span><span class="p" data-group-id="1447096874-94">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="1447096874-94">]</span><span class="p" data-group-id="1447096874-93">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-95">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-96">[</span><span class="n">TmpLogDir</span><span class="p" data-group-id="1447096874-96">]</span><span class="p" data-group-id="1447096874-95">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="1447096874-97">(</span><span class="n">TmpLogDir</span><span class="p" data-group-id="1447096874-97">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-98">(</span><span class="p" data-group-id="1447096874-99">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="1447096874-99">]</span><span class="p" data-group-id="1447096874-98">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-100">(</span><span class="s">&quot;Creating ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-101">[</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="1447096874-101">]</span><span class="p" data-group-id="1447096874-100">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">StartErlData</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">io_lib</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-102">(</span><span class="s">&quot;</span><span class="si">~s</span><span class="s"> </span><span class="si">~s</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-103">[</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="1447096874-103">]</span><span class="p" data-group-id="1447096874-102">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">write_file</span><span class="p" data-group-id="1447096874-104">(</span><span class="n">StartErlDataFile</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="1447096874-104">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-105">(</span><span class="s">&quot;Recreating tar file ~ts from contents in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -	      </span><span class="p" data-group-id="1447096874-106">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="1447096874-106">]</span><span class="p" data-group-id="1447096874-105">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-107">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tar</span><span class="p" data-group-id="1447096874-107">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="1447096874-108">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-109">[</span><span class="ss">write</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="1447096874-109">]</span><span class="p" data-group-id="1447096874-108">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">TmpLogDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-93">(</span><span class="p" data-group-id="9979816171-94">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="9979816171-94">]</span><span class="p" data-group-id="9979816171-93">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-95">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-96">[</span><span class="n">TmpLogDir</span><span class="p" data-group-id="9979816171-96">]</span><span class="p" data-group-id="9979816171-95">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="9979816171-97">(</span><span class="n">TmpLogDir</span><span class="p" data-group-id="9979816171-97">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-98">(</span><span class="p" data-group-id="9979816171-99">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="9979816171-99">]</span><span class="p" data-group-id="9979816171-98">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-100">(</span><span class="s">&quot;Creating ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-101">[</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="9979816171-101">]</span><span class="p" data-group-id="9979816171-100">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">StartErlData</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">io_lib</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-102">(</span><span class="s">&quot;</span><span class="si">~s</span><span class="s"> </span><span class="si">~s</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-103">[</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="9979816171-103">]</span><span class="p" data-group-id="9979816171-102">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">write_file</span><span class="p" data-group-id="9979816171-104">(</span><span class="n">StartErlDataFile</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="9979816171-104">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-105">(</span><span class="s">&quot;Recreating tar file ~ts from contents in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +	      </span><span class="p" data-group-id="9979816171-106">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="9979816171-106">]</span><span class="p" data-group-id="9979816171-105">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-107">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tar</span><span class="p" data-group-id="9979816171-107">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="9979816171-108">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-109">[</span><span class="ss">write</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="9979816171-109">]</span><span class="p" data-group-id="9979816171-108">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="c1">%% {ok, Cwd} = file:get_cwd(),</span><span class="w">
│ │ │ │      </span><span class="c1">%% file:set_cwd(&quot;tmp&quot;),</span><span class="w">
│ │ │ │      </span><span class="n">ErtsDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="o">++</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="1447096874-110">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-111">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="1447096874-111">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-112">[</span><span class="p" data-group-id="1447096874-112">]</span><span class="p" data-group-id="1447096874-110">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="1447096874-113">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-114">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="n">ErtsDir</span><span class="p" data-group-id="1447096874-114">)</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsDir</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-115">[</span><span class="p" data-group-id="1447096874-115">]</span><span class="p" data-group-id="1447096874-113">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="1447096874-116">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-117">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;releases&quot;</span><span class="p" data-group-id="1447096874-117">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-118">[</span><span class="p" data-group-id="1447096874-118">]</span><span class="p" data-group-id="1447096874-116">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="1447096874-119">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-120">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;lib&quot;</span><span class="p" data-group-id="1447096874-120">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;lib&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-121">[</span><span class="p" data-group-id="1447096874-121">]</span><span class="p" data-group-id="1447096874-119">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="1447096874-122">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-123">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="1447096874-123">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-124">[</span><span class="p" data-group-id="1447096874-124">]</span><span class="p" data-group-id="1447096874-122">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="1447096874-125">(</span><span class="n">Tar</span><span class="p" data-group-id="1447096874-125">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="9979816171-110">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-111">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="9979816171-111">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-112">[</span><span class="p" data-group-id="9979816171-112">]</span><span class="p" data-group-id="9979816171-110">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="9979816171-113">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-114">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="n">ErtsDir</span><span class="p" data-group-id="9979816171-114">)</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsDir</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-115">[</span><span class="p" data-group-id="9979816171-115">]</span><span class="p" data-group-id="9979816171-113">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="9979816171-116">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-117">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;releases&quot;</span><span class="p" data-group-id="9979816171-117">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-118">[</span><span class="p" data-group-id="9979816171-118">]</span><span class="p" data-group-id="9979816171-116">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="9979816171-119">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-120">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;lib&quot;</span><span class="p" data-group-id="9979816171-120">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;lib&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-121">[</span><span class="p" data-group-id="9979816171-121">]</span><span class="p" data-group-id="9979816171-119">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="9979816171-122">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-123">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="9979816171-123">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-124">[</span><span class="p" data-group-id="9979816171-124">]</span><span class="p" data-group-id="9979816171-122">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="9979816171-125">(</span><span class="n">Tar</span><span class="p" data-group-id="9979816171-125">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="c1">%% file:set_cwd(Cwd),</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-126">(</span><span class="s">&quot;Removing directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="1447096874-127">[</span><span class="n">TmpDir</span><span class="p" data-group-id="1447096874-127">]</span><span class="p" data-group-id="1447096874-126">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="1447096874-128">(</span><span class="n">TmpDir</span><span class="p" data-group-id="1447096874-128">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-126">(</span><span class="s">&quot;Removing directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="9979816171-127">[</span><span class="n">TmpDir</span><span class="p" data-group-id="9979816171-127">]</span><span class="p" data-group-id="9979816171-126">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="9979816171-128">(</span><span class="n">TmpDir</span><span class="p" data-group-id="9979816171-128">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │ -</span><span class="nf">install</span><span class="p" data-group-id="1447096874-129">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="1447096874-129">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">install</span><span class="p" data-group-id="9979816171-129">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="9979816171-129">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">TarFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.tar.gz&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-130">(</span><span class="s">&quot;Extracting ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-131">[</span><span class="n">TarFile</span><span class="p" data-group-id="1447096874-131">]</span><span class="p" data-group-id="1447096874-130">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">extract_tar</span><span class="p" data-group-id="1447096874-132">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="1447096874-132">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-133">(</span><span class="p" data-group-id="1447096874-134">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="1447096874-134">]</span><span class="p" data-group-id="1447096874-133">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-135">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="1447096874-135">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="1447096874-136">(</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="1447096874-136">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-137">[</span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">RelVsn</span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1447096874-137">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">string</span><span class="p">:</span><span class="nf">tokens</span><span class="p" data-group-id="1447096874-138">(</span><span class="n">StartErlData</span><span class="p">,</span><span class="w"> </span><span class="s">&quot; \n&quot;</span><span class="p" data-group-id="1447096874-138">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-139">(</span><span class="p" data-group-id="1447096874-140">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="1447096874-140">]</span><span class="p" data-group-id="1447096874-139">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">BinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-141">(</span><span class="p" data-group-id="1447096874-142">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="1447096874-142">]</span><span class="p" data-group-id="1447096874-141">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-143">(</span><span class="s">&quot;Substituting in erl.src, start.src and start_erl.src to &quot;</span><span class="w">
│ │ │ │ -              </span><span class="s">&quot;form erl, start and start_erl ...\n&quot;</span><span class="p" data-group-id="1447096874-143">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="1447096874-144">(</span><span class="p" data-group-id="1447096874-145">[</span><span class="s">&quot;erl&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="1447096874-145">]</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">BinDir</span><span class="p">,</span><span class="w">
│ │ │ │ -                      </span><span class="p" data-group-id="1447096874-146">[</span><span class="p" data-group-id="1447096874-147">{</span><span class="s">&quot;FINAL_ROOTDIR&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="1447096874-147">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-148">{</span><span class="s">&quot;EMU&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;beam&quot;</span><span class="p" data-group-id="1447096874-148">}</span><span class="p" data-group-id="1447096874-146">]</span><span class="p">,</span><span class="w">
│ │ │ │ -                      </span><span class="p" data-group-id="1447096874-149">[</span><span class="ss">preserve</span><span class="p" data-group-id="1447096874-149">]</span><span class="p" data-group-id="1447096874-144">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-130">(</span><span class="s">&quot;Extracting ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-131">[</span><span class="n">TarFile</span><span class="p" data-group-id="9979816171-131">]</span><span class="p" data-group-id="9979816171-130">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">extract_tar</span><span class="p" data-group-id="9979816171-132">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="9979816171-132">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-133">(</span><span class="p" data-group-id="9979816171-134">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="9979816171-134">]</span><span class="p" data-group-id="9979816171-133">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-135">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="9979816171-135">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="9979816171-136">(</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="9979816171-136">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-137">[</span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">RelVsn</span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9979816171-137">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">string</span><span class="p">:</span><span class="nf">tokens</span><span class="p" data-group-id="9979816171-138">(</span><span class="n">StartErlData</span><span class="p">,</span><span class="w"> </span><span class="s">&quot; \n&quot;</span><span class="p" data-group-id="9979816171-138">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-139">(</span><span class="p" data-group-id="9979816171-140">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="9979816171-140">]</span><span class="p" data-group-id="9979816171-139">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">BinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-141">(</span><span class="p" data-group-id="9979816171-142">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="9979816171-142">]</span><span class="p" data-group-id="9979816171-141">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-143">(</span><span class="s">&quot;Substituting in erl.src, start.src and start_erl.src to &quot;</span><span class="w">
│ │ │ │ +              </span><span class="s">&quot;form erl, start and start_erl ...\n&quot;</span><span class="p" data-group-id="9979816171-143">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="9979816171-144">(</span><span class="p" data-group-id="9979816171-145">[</span><span class="s">&quot;erl&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="9979816171-145">]</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">BinDir</span><span class="p">,</span><span class="w">
│ │ │ │ +                      </span><span class="p" data-group-id="9979816171-146">[</span><span class="p" data-group-id="9979816171-147">{</span><span class="s">&quot;FINAL_ROOTDIR&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="9979816171-147">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-148">{</span><span class="s">&quot;EMU&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;beam&quot;</span><span class="p" data-group-id="9979816171-148">}</span><span class="p" data-group-id="9979816171-146">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                      </span><span class="p" data-group-id="9979816171-149">[</span><span class="ss">preserve</span><span class="p" data-group-id="9979816171-149">]</span><span class="p" data-group-id="9979816171-144">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="c1">%%! Workaround for pre OTP 17.0: start.src and start_erl.src did</span><span class="w">
│ │ │ │      </span><span class="c1">%%! not have correct permissions, so the above &#39;preserve&#39; option did not help</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="1447096874-150">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-151">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="1447096874-151">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="1447096874-150">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="1447096874-152">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-153">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="1447096874-153">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="1447096874-152">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="9979816171-150">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-151">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="9979816171-151">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="9979816171-150">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="9979816171-152">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-153">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="9979816171-153">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="9979816171-152">)</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="1447096874-154">(</span><span class="s">&quot;Creating the RELEASES file ...\n&quot;</span><span class="p" data-group-id="1447096874-154">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">create_RELEASES</span><span class="p" data-group-id="1447096874-155">(</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-156">(</span><span class="p" data-group-id="1447096874-157">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -					    </span><span class="nc">filename</span><span class="p">:</span><span class="nf">basename</span><span class="p" data-group-id="1447096874-158">(</span><span class="n">RelFileName</span><span class="p" data-group-id="1447096874-158">)</span><span class="p" data-group-id="1447096874-157">]</span><span class="p" data-group-id="1447096874-156">)</span><span class="p" data-group-id="1447096874-155">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="9979816171-154">(</span><span class="s">&quot;Creating the RELEASES file ...\n&quot;</span><span class="p" data-group-id="9979816171-154">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">create_RELEASES</span><span class="p" data-group-id="9979816171-155">(</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-156">(</span><span class="p" data-group-id="9979816171-157">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +					    </span><span class="nc">filename</span><span class="p">:</span><span class="nf">basename</span><span class="p" data-group-id="9979816171-158">(</span><span class="n">RelFileName</span><span class="p" data-group-id="9979816171-158">)</span><span class="p" data-group-id="9979816171-157">]</span><span class="p" data-group-id="9979816171-156">)</span><span class="p" data-group-id="9979816171-155">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% LOCALS</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% make_script(RelFileName,Opts)</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">make_script</span><span class="p" data-group-id="1447096874-159">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="1447096874-159">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="1447096874-160">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-161">[</span><span class="ss">no_module_tests</span><span class="p">,</span><span class="w">
│ │ │ │ -				       </span><span class="p" data-group-id="1447096874-162">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="1447096874-163">(</span><span class="n">RelFileName</span><span class="p" data-group-id="1447096874-163">)</span><span class="p" data-group-id="1447096874-162">}</span><span class="w">
│ │ │ │ -				       </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="1447096874-161">]</span><span class="p" data-group-id="1447096874-160">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">make_script</span><span class="p" data-group-id="9979816171-159">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="9979816171-159">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="9979816171-160">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-161">[</span><span class="ss">no_module_tests</span><span class="p">,</span><span class="w">
│ │ │ │ +				       </span><span class="p" data-group-id="9979816171-162">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="9979816171-163">(</span><span class="n">RelFileName</span><span class="p" data-group-id="9979816171-163">)</span><span class="p" data-group-id="9979816171-162">}</span><span class="w">
│ │ │ │ +				       </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="9979816171-161">]</span><span class="p" data-group-id="9979816171-160">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% make_tar(RelFileName,Opts)</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">make_tar</span><span class="p" data-group-id="1447096874-164">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="1447096874-164">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">RootDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">code</span><span class="p">:</span><span class="nf">root_dir</span><span class="p" data-group-id="1447096874-165">(</span><span class="p" data-group-id="1447096874-165">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="1447096874-166">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-167">[</span><span class="p" data-group-id="1447096874-168">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="1447096874-168">}</span><span class="p">,</span><span class="w">
│ │ │ │ -				    </span><span class="p" data-group-id="1447096874-169">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="1447096874-170">(</span><span class="n">RelFileName</span><span class="p" data-group-id="1447096874-170">)</span><span class="p" data-group-id="1447096874-169">}</span><span class="w">
│ │ │ │ -				    </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="1447096874-167">]</span><span class="p" data-group-id="1447096874-166">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">make_tar</span><span class="p" data-group-id="9979816171-164">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="9979816171-164">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">RootDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">code</span><span class="p">:</span><span class="nf">root_dir</span><span class="p" data-group-id="9979816171-165">(</span><span class="p" data-group-id="9979816171-165">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="9979816171-166">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-167">[</span><span class="p" data-group-id="9979816171-168">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="9979816171-168">}</span><span class="p">,</span><span class="w">
│ │ │ │ +				    </span><span class="p" data-group-id="9979816171-169">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="9979816171-170">(</span><span class="n">RelFileName</span><span class="p" data-group-id="9979816171-170">)</span><span class="p" data-group-id="9979816171-169">}</span><span class="w">
│ │ │ │ +				    </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="9979816171-167">]</span><span class="p" data-group-id="9979816171-166">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% extract_tar(TarFile, DestDir)</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">extract_tar</span><span class="p" data-group-id="1447096874-171">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="1447096874-171">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">extract</span><span class="p" data-group-id="1447096874-172">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-173">[</span><span class="p" data-group-id="1447096874-174">{</span><span class="ss">cwd</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="1447096874-174">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="1447096874-173">]</span><span class="p" data-group-id="1447096874-172">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">extract_tar</span><span class="p" data-group-id="9979816171-171">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="9979816171-171">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">extract</span><span class="p" data-group-id="9979816171-172">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-173">[</span><span class="p" data-group-id="9979816171-174">{</span><span class="ss">cwd</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="9979816171-174">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="9979816171-173">]</span><span class="p" data-group-id="9979816171-172">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="1447096874-175">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="1447096874-175">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="1447096874-176">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p" data-group-id="1447096874-176">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="9979816171-175">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="9979816171-175">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="9979816171-176">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p" data-group-id="9979816171-176">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="1447096874-177">(</span><span class="n">Scripts</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="1447096874-177">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="1447096874-178">(</span><span class="nf">fun</span><span class="p" data-group-id="1447096874-179">(</span><span class="n">Script</span><span class="p" data-group-id="1447096874-179">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                          </span><span class="nf">subst_src_script</span><span class="p" data-group-id="1447096874-180">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w">
│ │ │ │ -                                           </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="1447096874-180">)</span><span class="w">
│ │ │ │ -                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Scripts</span><span class="p" data-group-id="1447096874-178">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">subst_src_script</span><span class="p" data-group-id="1447096874-181">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="1447096874-181">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_file</span><span class="p" data-group-id="1447096874-182">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-183">(</span><span class="p" data-group-id="1447096874-184">[</span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.src&quot;</span><span class="p" data-group-id="1447096874-184">]</span><span class="p" data-group-id="1447096874-183">)</span><span class="p">,</span><span class="w">
│ │ │ │ -               </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-185">(</span><span class="p" data-group-id="1447096874-186">[</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="p" data-group-id="1447096874-186">]</span><span class="p" data-group-id="1447096874-185">)</span><span class="p">,</span><span class="w">
│ │ │ │ -               </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="1447096874-182">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">subst_file</span><span class="p" data-group-id="1447096874-187">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="1447096874-187">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-188">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="1447096874-188">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="1447096874-189">(</span><span class="n">Src</span><span class="p" data-group-id="1447096874-189">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">NConts</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">subst</span><span class="p" data-group-id="1447096874-190">(</span><span class="n">Conts</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="1447096874-190">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">write_file</span><span class="p" data-group-id="1447096874-191">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">NConts</span><span class="p" data-group-id="1447096874-191">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="1447096874-192">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="1447096874-192">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="9979816171-177">(</span><span class="n">Scripts</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="9979816171-177">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="9979816171-178">(</span><span class="nf">fun</span><span class="p" data-group-id="9979816171-179">(</span><span class="n">Script</span><span class="p" data-group-id="9979816171-179">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                          </span><span class="nf">subst_src_script</span><span class="p" data-group-id="9979816171-180">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w">
│ │ │ │ +                                           </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="9979816171-180">)</span><span class="w">
│ │ │ │ +                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Scripts</span><span class="p" data-group-id="9979816171-178">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">subst_src_script</span><span class="p" data-group-id="9979816171-181">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="9979816171-181">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_file</span><span class="p" data-group-id="9979816171-182">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-183">(</span><span class="p" data-group-id="9979816171-184">[</span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.src&quot;</span><span class="p" data-group-id="9979816171-184">]</span><span class="p" data-group-id="9979816171-183">)</span><span class="p">,</span><span class="w">
│ │ │ │ +               </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-185">(</span><span class="p" data-group-id="9979816171-186">[</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="p" data-group-id="9979816171-186">]</span><span class="p" data-group-id="9979816171-185">)</span><span class="p">,</span><span class="w">
│ │ │ │ +               </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="9979816171-182">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">subst_file</span><span class="p" data-group-id="9979816171-187">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="9979816171-187">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-188">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="9979816171-188">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="9979816171-189">(</span><span class="n">Src</span><span class="p" data-group-id="9979816171-189">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">NConts</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">subst</span><span class="p" data-group-id="9979816171-190">(</span><span class="n">Conts</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="9979816171-190">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">write_file</span><span class="p" data-group-id="9979816171-191">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">NConts</span><span class="p" data-group-id="9979816171-191">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="9979816171-192">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="9979816171-192">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="1447096874-193">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="1447096874-193">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="1447096874-194">(</span><span class="n">Src</span><span class="p" data-group-id="1447096874-194">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="1447096874-195">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="1447096874-195">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9979816171-193">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="9979816171-193">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="9979816171-194">(</span><span class="n">Src</span><span class="p" data-group-id="9979816171-194">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="9979816171-195">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="9979816171-195">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">ok</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% subst(Str, Vars)</span><span class="w">
│ │ │ │  </span><span class="c1">%% Vars = [{Var, Val}]</span><span class="w">
│ │ │ │  </span><span class="c1">%% Var = Val = string()</span><span class="w">
│ │ │ │  </span><span class="c1">%% Substitute all occurrences of %Var% for Val in Str, using the list</span><span class="w">
│ │ │ │  </span><span class="c1">%% of variables in Vars.</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="1447096874-196">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="1447096874-196">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="1447096874-197">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-198">[</span><span class="p" data-group-id="1447096874-198">]</span><span class="p" data-group-id="1447096874-197">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="9979816171-196">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="9979816171-196">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="9979816171-197">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-198">[</span><span class="p" data-group-id="9979816171-198">]</span><span class="p" data-group-id="9979816171-197">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="1447096874-199">(</span><span class="p" data-group-id="1447096874-200">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1447096874-200">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1447096874-199">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$Z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="1447096874-201">(</span><span class="p" data-group-id="1447096874-202">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1447096874-202">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-203">[</span><span class="p" data-group-id="1447096874-203">]</span><span class="p" data-group-id="1447096874-201">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="1447096874-204">(</span><span class="p" data-group-id="1447096874-205">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1447096874-205">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1447096874-204">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="1447096874-206">(</span><span class="p" data-group-id="1447096874-207">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1447096874-207">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-208">[</span><span class="p" data-group-id="1447096874-208">]</span><span class="p" data-group-id="1447096874-206">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="1447096874-209">(</span><span class="p" data-group-id="1447096874-210">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1447096874-210">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1447096874-209">)</span><span class="w"> </span><span class="k">when</span><span class="w">  </span><span class="n">C</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">$_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="1447096874-211">(</span><span class="p" data-group-id="1447096874-212">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1447096874-212">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-213">[</span><span class="p" data-group-id="1447096874-213">]</span><span class="p" data-group-id="1447096874-211">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="1447096874-214">(</span><span class="p" data-group-id="1447096874-215">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1447096874-215">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1447096874-214">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="1447096874-216">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-217">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1447096874-217">]</span><span class="p" data-group-id="1447096874-216">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="1447096874-218">(</span><span class="p" data-group-id="1447096874-219">[</span><span class="p" data-group-id="1447096874-219">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1447096874-218">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="1447096874-220">(</span><span class="n">Result</span><span class="p" data-group-id="1447096874-220">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="1447096874-221">(</span><span class="p" data-group-id="1447096874-222">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1447096874-222">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="1447096874-221">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Key</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="1447096874-223">(</span><span class="n">VarAcc</span><span class="p" data-group-id="1447096874-223">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="1447096874-224">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="1447096874-224">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1447096874-225">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-226">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="1447096874-226">}</span><span class="p" data-group-id="1447096874-225">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">subst</span><span class="p" data-group-id="1447096874-227">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="1447096874-228">(</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1447096874-228">)</span><span class="p" data-group-id="1447096874-227">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="9979816171-199">(</span><span class="p" data-group-id="9979816171-200">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9979816171-200">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9979816171-199">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$Z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="9979816171-201">(</span><span class="p" data-group-id="9979816171-202">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9979816171-202">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-203">[</span><span class="p" data-group-id="9979816171-203">]</span><span class="p" data-group-id="9979816171-201">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="9979816171-204">(</span><span class="p" data-group-id="9979816171-205">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9979816171-205">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9979816171-204">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="9979816171-206">(</span><span class="p" data-group-id="9979816171-207">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9979816171-207">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-208">[</span><span class="p" data-group-id="9979816171-208">]</span><span class="p" data-group-id="9979816171-206">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="9979816171-209">(</span><span class="p" data-group-id="9979816171-210">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9979816171-210">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9979816171-209">)</span><span class="w"> </span><span class="k">when</span><span class="w">  </span><span class="n">C</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">$_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="9979816171-211">(</span><span class="p" data-group-id="9979816171-212">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9979816171-212">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-213">[</span><span class="p" data-group-id="9979816171-213">]</span><span class="p" data-group-id="9979816171-211">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="9979816171-214">(</span><span class="p" data-group-id="9979816171-215">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9979816171-215">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9979816171-214">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="9979816171-216">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-217">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9979816171-217">]</span><span class="p" data-group-id="9979816171-216">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="9979816171-218">(</span><span class="p" data-group-id="9979816171-219">[</span><span class="p" data-group-id="9979816171-219">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9979816171-218">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="9979816171-220">(</span><span class="n">Result</span><span class="p" data-group-id="9979816171-220">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="9979816171-221">(</span><span class="p" data-group-id="9979816171-222">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9979816171-222">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="9979816171-221">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Key</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="9979816171-223">(</span><span class="n">VarAcc</span><span class="p" data-group-id="9979816171-223">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9979816171-224">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="9979816171-224">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9979816171-225">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-226">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="9979816171-226">}</span><span class="p" data-group-id="9979816171-225">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">subst</span><span class="p" data-group-id="9979816171-227">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="9979816171-228">(</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9979816171-228">)</span><span class="p" data-group-id="9979816171-227">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">subst</span><span class="p" data-group-id="1447096874-229">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-230">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1447096874-231">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1447096874-231">]</span><span class="p" data-group-id="1447096874-230">]</span><span class="p" data-group-id="1447096874-229">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">subst</span><span class="p" data-group-id="9979816171-229">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-230">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9979816171-231">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9979816171-231">]</span><span class="p" data-group-id="9979816171-230">]</span><span class="p" data-group-id="9979816171-229">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="1447096874-232">(</span><span class="p" data-group-id="1447096874-233">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1447096874-233">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="1447096874-232">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="1447096874-234">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-235">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="1447096874-235">]</span><span class="p" data-group-id="1447096874-234">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="1447096874-236">(</span><span class="p" data-group-id="1447096874-237">[</span><span class="p" data-group-id="1447096874-237">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="1447096874-236">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="1447096874-238">(</span><span class="p" data-group-id="1447096874-239">[</span><span class="p" data-group-id="1447096874-239">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-240">[</span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1447096874-241">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1447096874-241">]</span><span class="p" data-group-id="1447096874-240">]</span><span class="p" data-group-id="1447096874-238">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">copy_file</span><span class="p" data-group-id="1447096874-242">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="1447096874-242">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="1447096874-243">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-244">[</span><span class="p" data-group-id="1447096874-244">]</span><span class="p" data-group-id="1447096874-243">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">copy_file</span><span class="p" data-group-id="1447096874-245">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="1447096874-245">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-246">{</span><span class="ss">ok</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1447096874-246">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">copy</span><span class="p" data-group-id="1447096874-247">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="1447096874-247">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="1447096874-248">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="1447096874-248">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="9979816171-232">(</span><span class="p" data-group-id="9979816171-233">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9979816171-233">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="9979816171-232">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="9979816171-234">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-235">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="9979816171-235">]</span><span class="p" data-group-id="9979816171-234">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="9979816171-236">(</span><span class="p" data-group-id="9979816171-237">[</span><span class="p" data-group-id="9979816171-237">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="9979816171-236">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="9979816171-238">(</span><span class="p" data-group-id="9979816171-239">[</span><span class="p" data-group-id="9979816171-239">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-240">[</span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9979816171-241">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9979816171-241">]</span><span class="p" data-group-id="9979816171-240">]</span><span class="p" data-group-id="9979816171-238">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">copy_file</span><span class="p" data-group-id="9979816171-242">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="9979816171-242">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="9979816171-243">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-244">[</span><span class="p" data-group-id="9979816171-244">]</span><span class="p" data-group-id="9979816171-243">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">copy_file</span><span class="p" data-group-id="9979816171-245">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="9979816171-245">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-246">{</span><span class="ss">ok</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9979816171-246">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">copy</span><span class="p" data-group-id="9979816171-247">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="9979816171-247">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="9979816171-248">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="9979816171-248">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="1447096874-249">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="1447096874-249">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="1447096874-250">(</span><span class="n">Src</span><span class="p" data-group-id="1447096874-250">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="1447096874-251">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="1447096874-251">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9979816171-249">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="9979816171-249">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="9979816171-250">(</span><span class="n">Src</span><span class="p" data-group-id="9979816171-250">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="9979816171-251">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="9979816171-251">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">ok</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">write_file</span><span class="p" data-group-id="1447096874-252">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="1447096874-252">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Enc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">native_name_encoding</span><span class="p" data-group-id="1447096874-253">(</span><span class="p" data-group-id="1447096874-253">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-254">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="1447096874-254">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="1447096874-255">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-256">[</span><span class="ss">write</span><span class="p" data-group-id="1447096874-256">]</span><span class="p" data-group-id="1447096874-255">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">write</span><span class="p" data-group-id="1447096874-257">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="nc">unicode</span><span class="p">:</span><span class="nf">characters_to_binary</span><span class="p" data-group-id="1447096874-258">(</span><span class="n">Conts</span><span class="p">,</span><span class="n">Enc</span><span class="p">,</span><span class="n">Enc</span><span class="p" data-group-id="1447096874-258">)</span><span class="p" data-group-id="1447096874-257">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="1447096874-259">(</span><span class="n">Fd</span><span class="p" data-group-id="1447096874-259">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">read_txt_file</span><span class="p" data-group-id="1447096874-260">(</span><span class="n">File</span><span class="p" data-group-id="1447096874-260">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-261">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="1447096874-261">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file</span><span class="p" data-group-id="1447096874-262">(</span><span class="n">File</span><span class="p" data-group-id="1447096874-262">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1447096874-263">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_list</span><span class="p" data-group-id="1447096874-264">(</span><span class="n">Bin</span><span class="p" data-group-id="1447096874-264">)</span><span class="p" data-group-id="1447096874-263">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="1447096874-265">(</span><span class="n">Dir</span><span class="p" data-group-id="1447096874-265">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">remove_all_files</span><span class="p" data-group-id="1447096874-266">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1447096874-267">[</span><span class="n">Dir</span><span class="p" data-group-id="1447096874-267">]</span><span class="p" data-group-id="1447096874-266">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">remove_all_files</span><span class="p" data-group-id="1447096874-268">(</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="1447096874-268">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="1447096874-269">(</span><span class="nf">fun</span><span class="p" data-group-id="1447096874-270">(</span><span class="n">File</span><span class="p" data-group-id="1447096874-270">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                          </span><span class="n">FilePath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1447096874-271">(</span><span class="p" data-group-id="1447096874-272">[</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">File</span><span class="p" data-group-id="1447096874-272">]</span><span class="p" data-group-id="1447096874-271">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="k">case</span><span class="w"> </span><span class="nc">filelib</span><span class="p">:</span><span class="nf">is_dir</span><span class="p" data-group-id="1447096874-273">(</span><span class="n">FilePath</span><span class="p" data-group-id="1447096874-273">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">write_file</span><span class="p" data-group-id="9979816171-252">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="9979816171-252">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Enc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">native_name_encoding</span><span class="p" data-group-id="9979816171-253">(</span><span class="p" data-group-id="9979816171-253">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-254">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="9979816171-254">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="9979816171-255">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-256">[</span><span class="ss">write</span><span class="p" data-group-id="9979816171-256">]</span><span class="p" data-group-id="9979816171-255">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">write</span><span class="p" data-group-id="9979816171-257">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="nc">unicode</span><span class="p">:</span><span class="nf">characters_to_binary</span><span class="p" data-group-id="9979816171-258">(</span><span class="n">Conts</span><span class="p">,</span><span class="n">Enc</span><span class="p">,</span><span class="n">Enc</span><span class="p" data-group-id="9979816171-258">)</span><span class="p" data-group-id="9979816171-257">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="9979816171-259">(</span><span class="n">Fd</span><span class="p" data-group-id="9979816171-259">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">read_txt_file</span><span class="p" data-group-id="9979816171-260">(</span><span class="n">File</span><span class="p" data-group-id="9979816171-260">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-261">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="9979816171-261">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file</span><span class="p" data-group-id="9979816171-262">(</span><span class="n">File</span><span class="p" data-group-id="9979816171-262">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9979816171-263">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_list</span><span class="p" data-group-id="9979816171-264">(</span><span class="n">Bin</span><span class="p" data-group-id="9979816171-264">)</span><span class="p" data-group-id="9979816171-263">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="9979816171-265">(</span><span class="n">Dir</span><span class="p" data-group-id="9979816171-265">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">remove_all_files</span><span class="p" data-group-id="9979816171-266">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9979816171-267">[</span><span class="n">Dir</span><span class="p" data-group-id="9979816171-267">]</span><span class="p" data-group-id="9979816171-266">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">remove_all_files</span><span class="p" data-group-id="9979816171-268">(</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="9979816171-268">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="9979816171-269">(</span><span class="nf">fun</span><span class="p" data-group-id="9979816171-270">(</span><span class="n">File</span><span class="p" data-group-id="9979816171-270">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                          </span><span class="n">FilePath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9979816171-271">(</span><span class="p" data-group-id="9979816171-272">[</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">File</span><span class="p" data-group-id="9979816171-272">]</span><span class="p" data-group-id="9979816171-271">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="k">case</span><span class="w"> </span><span class="nc">filelib</span><span class="p">:</span><span class="nf">is_dir</span><span class="p" data-group-id="9979816171-273">(</span><span class="n">FilePath</span><span class="p" data-group-id="9979816171-273">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │                                </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                                  </span><span class="p" data-group-id="1447096874-274">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="1447096874-274">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">list_dir</span><span class="p" data-group-id="1447096874-275">(</span><span class="n">FilePath</span><span class="p" data-group-id="1447096874-275">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                                  </span><span class="nf">remove_all_files</span><span class="p" data-group-id="1447096874-276">(</span><span class="n">FilePath</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="1447096874-276">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">del_dir</span><span class="p" data-group-id="1447096874-277">(</span><span class="n">FilePath</span><span class="p" data-group-id="1447096874-277">)</span><span class="p">;</span><span class="w">
│ │ │ │ +                                  </span><span class="p" data-group-id="9979816171-274">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="9979816171-274">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">list_dir</span><span class="p" data-group-id="9979816171-275">(</span><span class="n">FilePath</span><span class="p" data-group-id="9979816171-275">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                                  </span><span class="nf">remove_all_files</span><span class="p" data-group-id="9979816171-276">(</span><span class="n">FilePath</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="9979816171-276">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">del_dir</span><span class="p" data-group-id="9979816171-277">(</span><span class="n">FilePath</span><span class="p" data-group-id="9979816171-277">)</span><span class="p">;</span><span class="w">
│ │ │ │                                </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="1447096874-278">(</span><span class="n">FilePath</span><span class="p" data-group-id="1447096874-278">)</span><span class="w">
│ │ │ │ +                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="9979816171-278">(</span><span class="n">FilePath</span><span class="p" data-group-id="9979816171-278">)</span><span class="w">
│ │ │ │                            </span><span class="k">end</span><span class="w">
│ │ │ │ -                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="1447096874-269">)</span><span class="p">.</span></code></pre>
│ │ │ │ +                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="9979816171-269">)</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/content.opf
│ │ │ │ ├── OEBPS/content.opf
│ │ │ │ │ @@ -1,14 +1,14 @@
│ │ │ │ │  <?xml version="1.0" encoding="utf-8"?>
│ │ │ │ │  <package xmlns="http://www.idpf.org/2007/opf" unique-identifier="project-Erlang System Documentation" version="3.0">
│ │ │ │ │    <metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
│ │ │ │ │      <dc:title>Erlang System Documentation - 27.3.4.1</dc:title>
│ │ │ │ │ -    <dc:identifier id="project-Erlang System Documentation">urn:uuid:0afb0830-b2de-2fb7-c2e5-cdfb4c0e115d</dc:identifier>
│ │ │ │ │ +    <dc:identifier id="project-Erlang System Documentation">urn:uuid:b246ea87-8e62-c130-762d-b003dff91d16</dc:identifier>
│ │ │ │ │      <dc:language>en</dc:language>
│ │ │ │ │ -    <meta property="dcterms:modified">2025-07-08T08:11:07Z</meta>
│ │ │ │ │ +    <meta property="dcterms:modified">2025-08-22T21:52:09Z</meta>
│ │ │ │ │    </metadata>
│ │ │ │ │    <manifest>
│ │ │ │ │      <item id="nav" href="nav.xhtml" media-type="application/xhtml+xml" properties="nav scripted"/>
│ │ │ │ │      <item id="cover" href="title.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="readme" href="readme.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="installation_guide" href="installation_guide.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="install" href="install.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │ @@ -82,21 +82,21 @@
│ │ │ │ │      <item id="c_portdriver" href="c_portdriver.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="cnode" href="cnode.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="nif" href="nif.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="debugging" href="debugging.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="embedded" href="embedded.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="epub-lsjciytm-js" href="dist/epub-LSJCIYTM.js" media-type="text/javascript"/>
│ │ │ │ │      <item id="epub-erlang-espt6bqv-css" href="dist/epub-erlang-ESPT6BQV.css" media-type="text/css"/>
│ │ │ │ │ -    <item id="erlang-logo-png" href="assets/erlang-logo.png" media-type="image/png"/>
│ │ │ │ │ -    <item id="dist1-gif" href="assets/dist1.gif" media-type="image/gif"/>
│ │ │ │ │      <item id="dist2-gif" href="assets/dist2.gif" media-type="image/gif"/>
│ │ │ │ │ -    <item id="dist3-gif" href="assets/dist3.gif" media-type="image/gif"/>
│ │ │ │ │ -    <item id="dist4-gif" href="assets/dist4.gif" media-type="image/gif"/>
│ │ │ │ │      <item id="dist5-gif" href="assets/dist5.gif" media-type="image/gif"/>
│ │ │ │ │ +    <item id="dist4-gif" href="assets/dist4.gif" media-type="image/gif"/>
│ │ │ │ │ +    <item id="dist3-gif" href="assets/dist3.gif" media-type="image/gif"/>
│ │ │ │ │ +    <item id="dist1-gif" href="assets/dist1.gif" media-type="image/gif"/>
│ │ │ │ │      <item id="ballpoint-pen-svg" href="assets/ballpoint-pen.svg" media-type="image/svg+xml"/>
│ │ │ │ │ +    <item id="erlang-logo-png" href="assets/erlang-logo.png" media-type="image/png"/>
│ │ │ │ │      <item id="logo" href="assets/logo.png" media-type="image/png"/>
│ │ │ │ │    </manifest>
│ │ │ │ │    <spine>
│ │ │ │ │      <itemref idref="cover"/>
│ │ │ │ │      <itemref idref="nav"/>
│ │ │ │ │      <itemref idref="readme"/>
│ │ │ │ │      <itemref idref="installation_guide"/>
│ │ │ ├── OEBPS/conc_prog.xhtml
│ │ │ │ @@ -37,107 +37,107 @@
│ │ │ │  threads of execution in an Erlang program and to allow these threads to
│ │ │ │  communicate with each other. In Erlang, each thread of execution is called a
│ │ │ │  <em>process</em>.</p><p>(Aside: the term &quot;process&quot; is usually used when the threads of execution share
│ │ │ │  no data with each other and the term &quot;thread&quot; when they share data in some way.
│ │ │ │  Threads of execution in Erlang share no data, that is why they are called
│ │ │ │  processes).</p><p>The Erlang BIF <code class="inline">spawn</code> is used to create a new process:
│ │ │ │  <code class="inline">spawn(Module, Exported_Function, List of Arguments)</code>. Consider the following
│ │ │ │ -module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7213903561-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="7213903561-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5799899135-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="5799899135-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7213903561-2">(</span><span class="p" data-group-id="7213903561-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7213903561-3">]</span><span class="p" data-group-id="7213903561-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5799899135-2">(</span><span class="p" data-group-id="5799899135-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5799899135-3">]</span><span class="p" data-group-id="5799899135-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">say_something</span><span class="p" data-group-id="7213903561-4">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7213903561-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">say_something</span><span class="p" data-group-id="5799899135-4">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5799899135-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">done</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">say_something</span><span class="p" data-group-id="7213903561-5">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="p" data-group-id="7213903561-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7213903561-6">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7213903561-7">[</span><span class="n">What</span><span class="p" data-group-id="7213903561-7">]</span><span class="p" data-group-id="7213903561-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">say_something</span><span class="p" data-group-id="7213903561-8">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7213903561-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="7213903561-9">(</span><span class="p" data-group-id="7213903561-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="7213903561-10">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7213903561-11">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7213903561-11">]</span><span class="p" data-group-id="7213903561-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="7213903561-12">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7213903561-13">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7213903561-13">]</span><span class="p" data-group-id="7213903561-12">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="6344488674-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="6344488674-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6344488674-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut14</span><span class="p" data-group-id="6344488674-2">}</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">say_something</span><span class="p" data-group-id="6344488674-3">(</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6344488674-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">say_something</span><span class="p" data-group-id="5799899135-5">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="p" data-group-id="5799899135-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5799899135-6">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5799899135-7">[</span><span class="n">What</span><span class="p" data-group-id="5799899135-7">]</span><span class="p" data-group-id="5799899135-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">say_something</span><span class="p" data-group-id="5799899135-8">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5799899135-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="5799899135-9">(</span><span class="p" data-group-id="5799899135-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="5799899135-10">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5799899135-11">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5799899135-11">]</span><span class="p" data-group-id="5799899135-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="5799899135-12">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5799899135-13">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5799899135-13">]</span><span class="p" data-group-id="5799899135-12">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="5260501257-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="5260501257-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5260501257-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut14</span><span class="p" data-group-id="5260501257-2">}</span><span class="gp unselectable">
│ │ │ │ +6&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">say_something</span><span class="p" data-group-id="5260501257-3">(</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5260501257-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">done</span></code></pre><p>As shown, the function <code class="inline">say_something</code> writes its first argument the number of
│ │ │ │  times specified by second argument. The function <code class="inline">start</code> starts two Erlang
│ │ │ │  processes, one that writes &quot;hello&quot; three times and one that writes &quot;goodbye&quot;
│ │ │ │  three times. Both processes use the function <code class="inline">say_something</code>. Notice that a
│ │ │ │  function used in this way by <code class="inline">spawn</code>, to start a process, must be exported from
│ │ │ │ -the module (that is, in the <code class="inline">-export</code> at the start of the module).</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1247946099-1">(</span><span class="p" data-group-id="1247946099-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the module (that is, in the <code class="inline">-export</code> at the start of the module).</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5467058269-1">(</span><span class="p" data-group-id="5467058269-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">goodbye</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.63</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">goodbye</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">goodbye</span></code></pre><p>Notice that it did not write &quot;hello&quot; three times and then &quot;goodbye&quot; three times.
│ │ │ │  Instead, the first process wrote a &quot;hello&quot;, the second a &quot;goodbye&quot;, the first
│ │ │ │  another &quot;hello&quot; and so forth. But where did the <code class="inline">&lt;0.63.0&gt;</code> come from? The return
│ │ │ │  value of a function is the return value of the last &quot;thing&quot; in the function. The
│ │ │ │ -last thing in the function <code class="inline">start</code> is</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="7836198218-1">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7836198218-2">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7836198218-2">]</span><span class="p" data-group-id="7836198218-1">)</span><span class="p">.</span></code></pre><p><code class="inline">spawn</code> returns a <em>process identifier</em>, or <em>pid</em>, which uniquely identifies the
│ │ │ │ +last thing in the function <code class="inline">start</code> is</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="2201245567-1">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2201245567-2">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2201245567-2">]</span><span class="p" data-group-id="2201245567-1">)</span><span class="p">.</span></code></pre><p><code class="inline">spawn</code> returns a <em>process identifier</em>, or <em>pid</em>, which uniquely identifies the
│ │ │ │  process. So <code class="inline">&lt;0.63.0&gt;</code> is the pid of the <code class="inline">spawn</code> function call above. The next
│ │ │ │  example shows how to use pids.</p><p>Notice also that ~p is used instead of ~w in <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a>. To quote <a href="../../../lib/stdlib/doc/html/io.html#tilde_p">the manual</a>:</p><blockquote><p>~p Writes the data with standard syntax in the same way as ~w, but breaks terms
│ │ │ │  whose printed representation is longer than one line into many lines and indents
│ │ │ │  each line sensibly. It also tries to detect flat lists of printable characters and
│ │ │ │  to output these as strings</p></blockquote><h2 id="message-passing" class="section-heading">
│ │ │ │    <a href="#message-passing" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Message Passing</span>
│ │ │ │  </h2>
│ │ │ │  <p>In the following example two processes are created and they send messages to
│ │ │ │ -each other a number of times.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9763090977-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="9763090977-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +each other a number of times.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1675886442-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="1675886442-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9763090977-2">(</span><span class="p" data-group-id="9763090977-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9763090977-3">]</span><span class="p" data-group-id="9763090977-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1675886442-2">(</span><span class="p" data-group-id="1675886442-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1675886442-3">]</span><span class="p" data-group-id="1675886442-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="9763090977-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="9763090977-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="1675886442-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="1675886442-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9763090977-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9763090977-6">[</span><span class="p" data-group-id="9763090977-6">]</span><span class="p" data-group-id="9763090977-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1675886442-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1675886442-6">[</span><span class="p" data-group-id="1675886442-6">]</span><span class="p" data-group-id="1675886442-5">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="9763090977-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="9763090977-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9763090977-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9763090977-9">(</span><span class="p" data-group-id="9763090977-9">)</span><span class="p" data-group-id="9763090977-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="1675886442-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="1675886442-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1675886442-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1675886442-9">(</span><span class="p" data-group-id="1675886442-9">)</span><span class="p" data-group-id="1675886442-8">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9763090977-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9763090977-11">[</span><span class="p" data-group-id="9763090977-11">]</span><span class="p" data-group-id="9763090977-10">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1675886442-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1675886442-11">[</span><span class="p" data-group-id="1675886442-11">]</span><span class="p" data-group-id="1675886442-10">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="9763090977-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="9763090977-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="1675886442-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="1675886442-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="9763090977-13">(</span><span class="p" data-group-id="9763090977-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="1675886442-13">(</span><span class="p" data-group-id="1675886442-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9763090977-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9763090977-15">[</span><span class="p" data-group-id="9763090977-15">]</span><span class="p" data-group-id="9763090977-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9763090977-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9763090977-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9763090977-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9763090977-18">[</span><span class="p" data-group-id="9763090977-18">]</span><span class="p" data-group-id="9763090977-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1675886442-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1675886442-15">[</span><span class="p" data-group-id="1675886442-15">]</span><span class="p" data-group-id="1675886442-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="1675886442-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="1675886442-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1675886442-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1675886442-18">[</span><span class="p" data-group-id="1675886442-18">]</span><span class="p" data-group-id="1675886442-17">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="9763090977-19">(</span><span class="p" data-group-id="9763090977-19">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="1675886442-19">(</span><span class="p" data-group-id="1675886442-19">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="9763090977-20">(</span><span class="p" data-group-id="9763090977-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9763090977-21">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9763090977-22">[</span><span class="p" data-group-id="9763090977-22">]</span><span class="p" data-group-id="9763090977-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9763090977-23">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9763090977-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="9763090977-24">]</span><span class="p" data-group-id="9763090977-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="6487803965-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="6487803965-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6487803965-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut15</span><span class="p" data-group-id="6487803965-2">}</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">tut15</span><span class="p">:</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="6487803965-3">(</span><span class="p" data-group-id="6487803965-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="1675886442-20">(</span><span class="p" data-group-id="1675886442-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1675886442-21">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1675886442-22">[</span><span class="p" data-group-id="1675886442-22">]</span><span class="p" data-group-id="1675886442-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="1675886442-23">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1675886442-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="1675886442-24">]</span><span class="p" data-group-id="1675886442-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="8515675733-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="8515675733-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8515675733-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut15</span><span class="p" data-group-id="8515675733-2">}</span><span class="gp unselectable">
│ │ │ │ +2&gt; </span><span class="nc">tut15</span><span class="p">:</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="8515675733-3">(</span><span class="p" data-group-id="8515675733-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.36</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span><span class="w">
│ │ │ │ -</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>The function <code class="inline">start</code> first creates a process, let us call it &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="4113586179-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4113586179-2">[</span><span class="p" data-group-id="4113586179-2">]</span><span class="p" data-group-id="4113586179-1">)</span></code></pre><p>This process executes <code class="inline">tut15:pong()</code>. <code class="inline">Pong_PID</code> is the process identity of the
│ │ │ │ -&quot;pong&quot; process. The function <code class="inline">start</code> now creates another process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="0970018025-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0970018025-2">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0970018025-2">]</span><span class="p" data-group-id="0970018025-1">)</span><span class="p">,</span></code></pre><p>This process executes:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="5635649810-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="5635649810-1">)</span></code></pre><p><code class="inline">&lt;0.36.0&gt;</code> is the return value from the <code class="inline">start</code> function.</p><p>The process &quot;pong&quot; now does:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │ +</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>The function <code class="inline">start</code> first creates a process, let us call it &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9283241317-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9283241317-2">[</span><span class="p" data-group-id="9283241317-2">]</span><span class="p" data-group-id="9283241317-1">)</span></code></pre><p>This process executes <code class="inline">tut15:pong()</code>. <code class="inline">Pong_PID</code> is the process identity of the
│ │ │ │ +&quot;pong&quot; process. The function <code class="inline">start</code> now creates another process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="7260614162-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7260614162-2">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="7260614162-2">]</span><span class="p" data-group-id="7260614162-1">)</span><span class="p">,</span></code></pre><p>This process executes:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="8983767958-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="8983767958-1">)</span></code></pre><p><code class="inline">&lt;0.36.0&gt;</code> is the return value from the <code class="inline">start</code> function.</p><p>The process &quot;pong&quot; now does:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │      </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9811994243-1">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9811994243-2">[</span><span class="p" data-group-id="9811994243-2">]</span><span class="p" data-group-id="9811994243-1">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9811994243-3">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9811994243-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9811994243-4">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9811994243-5">[</span><span class="p" data-group-id="9811994243-5">]</span><span class="p" data-group-id="9811994243-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9142874464-1">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9142874464-2">[</span><span class="p" data-group-id="9142874464-2">]</span><span class="p" data-group-id="9142874464-1">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9142874464-3">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9142874464-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9142874464-4">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9142874464-5">[</span><span class="p" data-group-id="9142874464-5">]</span><span class="p" data-group-id="9142874464-4">)</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="nf">pong</span><span class="p" data-group-id="9811994243-6">(</span><span class="p" data-group-id="9811994243-6">)</span><span class="w">
│ │ │ │ +        </span><span class="nf">pong</span><span class="p" data-group-id="9142874464-6">(</span><span class="p" data-group-id="9142874464-6">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">receive</code> construct is used to allow processes to wait for messages from
│ │ │ │  other processes. It has the following format:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │     </span><span class="ss">pattern1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │         </span><span class="ss">actions1</span><span class="p">;</span><span class="w">
│ │ │ │     </span><span class="ss">pattern2</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │         </span><span class="ss">actions2</span><span class="p">;</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ @@ -158,84 +158,84 @@
│ │ │ │  queue (keeping the first message and any other messages in the queue). If the
│ │ │ │  second message does not match, the third message is tried, and so on, until the
│ │ │ │  end of the queue is reached. If the end of the queue is reached, the process
│ │ │ │  blocks (stops execution) and waits until a new message is received and this
│ │ │ │  procedure is repeated.</p><p>The Erlang implementation is &quot;clever&quot; and minimizes the number of times each
│ │ │ │  message is tested against the patterns in each <code class="inline">receive</code>.</p><p>Now back to the ping pong example.</p><p>&quot;Pong&quot; is waiting for messages. If the atom <code class="inline">finished</code> is received, &quot;pong&quot;
│ │ │ │  writes &quot;Pong finished&quot; to the output and, as it has nothing more to do,
│ │ │ │ -terminates. If it receives a message with the format:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9562381039-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9562381039-1">}</span></code></pre><p>it writes &quot;Pong received ping&quot; to the output and sends the atom <code class="inline">pong</code> to the
│ │ │ │ +terminates. If it receives a message with the format:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3631005490-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="3631005490-1">}</span></code></pre><p>it writes &quot;Pong received ping&quot; to the output and sends the atom <code class="inline">pong</code> to the
│ │ │ │  process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span></code></pre><p>Notice how the operator &quot;!&quot; is used to send messages. The syntax of &quot;!&quot; is:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Message</span></code></pre><p>That is, <code class="inline">Message</code> (any Erlang term) is sent to the process with identity <code class="inline">Pid</code>.</p><p>After sending the message <code class="inline">pong</code> to the process &quot;ping&quot;, &quot;pong&quot; calls the <code class="inline">pong</code>
│ │ │ │  function again, which causes it to get back to the <code class="inline">receive</code> again and wait for
│ │ │ │ -another message.</p><p>Now let us look at the process &quot;ping&quot;. Recall that it was started by executing:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="2215663377-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="2215663377-1">)</span></code></pre><p>Looking at the function <code class="inline">ping/2</code>, the second clause of <code class="inline">ping/2</code> is executed
│ │ │ │ +another message.</p><p>Now let us look at the process &quot;ping&quot;. Recall that it was started by executing:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="0319129814-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0319129814-1">)</span></code></pre><p>Looking at the function <code class="inline">ping/2</code>, the second clause of <code class="inline">ping/2</code> is executed
│ │ │ │  since the value of the first argument is 3 (not 0) (first clause head is
│ │ │ │ -<code class="inline">ping(0,Pong_PID)</code>, second clause head is <code class="inline">ping(N,Pong_PID)</code>, so <code class="inline">N</code> becomes 3).</p><p>The second clause sends a message to &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6876894988-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6876894988-2">(</span><span class="p" data-group-id="6876894988-2">)</span><span class="p" data-group-id="6876894988-1">}</span><span class="p">,</span></code></pre><p><a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the pid of the process that executes <a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a>, in this case the
│ │ │ │ +<code class="inline">ping(0,Pong_PID)</code>, second clause head is <code class="inline">ping(N,Pong_PID)</code>, so <code class="inline">N</code> becomes 3).</p><p>The second clause sends a message to &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5593627387-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5593627387-2">(</span><span class="p" data-group-id="5593627387-2">)</span><span class="p" data-group-id="5593627387-1">}</span><span class="p">,</span></code></pre><p><a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the pid of the process that executes <a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a>, in this case the
│ │ │ │  pid of &quot;ping&quot;. (Recall the code for &quot;pong&quot;, this lands up in the variable
│ │ │ │  <code class="inline">Ping_PID</code> in the <code class="inline">receive</code> previously explained.)</p><p>&quot;Ping&quot; now waits for a reply from &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │      </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1057448267-1">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1057448267-2">[</span><span class="p" data-group-id="1057448267-2">]</span><span class="p" data-group-id="1057448267-1">)</span><span class="w">
│ │ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1042273792-1">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1042273792-2">[</span><span class="p" data-group-id="1042273792-2">]</span><span class="p" data-group-id="1042273792-1">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre><p>It writes &quot;Ping received pong&quot; when this reply arrives, after which &quot;ping&quot; calls
│ │ │ │ -the <code class="inline">ping</code> function again.</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="2582399312-1">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="2582399312-1">)</span></code></pre><p><code class="inline">N-1</code> causes the first argument to be decremented until it becomes 0. When this
│ │ │ │ -occurs, the first clause of <code class="inline">ping/2</code> is executed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="0204926211-1">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0204926211-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +the <code class="inline">ping</code> function again.</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="6000664787-1">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="6000664787-1">)</span></code></pre><p><code class="inline">N-1</code> causes the first argument to be decremented until it becomes 0. When this
│ │ │ │ +occurs, the first clause of <code class="inline">ping/2</code> is executed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="4003995529-1">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="4003995529-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0204926211-2">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0204926211-3">[</span><span class="p" data-group-id="0204926211-3">]</span><span class="p" data-group-id="0204926211-2">)</span><span class="p">;</span></code></pre><p>The atom <code class="inline">finished</code> is sent to &quot;pong&quot; (causing it to terminate as described
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4003995529-2">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4003995529-3">[</span><span class="p" data-group-id="4003995529-3">]</span><span class="p" data-group-id="4003995529-2">)</span><span class="p">;</span></code></pre><p>The atom <code class="inline">finished</code> is sent to &quot;pong&quot; (causing it to terminate as described
│ │ │ │  above) and &quot;ping finished&quot; is written to the output. &quot;Ping&quot; then terminates as
│ │ │ │  it has nothing left to do.</p><h2 id="registered-process-names" class="section-heading">
│ │ │ │    <a href="#registered-process-names" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Registered Process Names</span>
│ │ │ │  </h2>
│ │ │ │  <p>In the above example, &quot;pong&quot; was first created to be able to give the identity
│ │ │ │  of &quot;pong&quot; when &quot;ping&quot; was started. That is, in some way &quot;ping&quot; must be able to
│ │ │ │  know the identity of &quot;pong&quot; to be able to send a message to it. Sometimes
│ │ │ │  processes which need to know each other's identities are started independently
│ │ │ │  of each other. Erlang thus provides a mechanism for processes to be given names
│ │ │ │  so that these names can be used as identities instead of pids. This is done by
│ │ │ │ -using the <code class="inline">register</code> BIF:</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="0309880342-1">(</span><span class="ss">some_atom</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="0309880342-1">)</span></code></pre><p>Let us now rewrite the ping pong example using this and give the name <code class="inline">pong</code> to
│ │ │ │ -the &quot;pong&quot; process:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8595499684-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="8595499684-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +using the <code class="inline">register</code> BIF:</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="0817676045-1">(</span><span class="ss">some_atom</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="0817676045-1">)</span></code></pre><p>Let us now rewrite the ping pong example using this and give the name <code class="inline">pong</code> to
│ │ │ │ +the &quot;pong&quot; process:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2686045681-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="2686045681-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8595499684-2">(</span><span class="p" data-group-id="8595499684-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8595499684-3">]</span><span class="p" data-group-id="8595499684-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2686045681-2">(</span><span class="p" data-group-id="2686045681-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2686045681-3">]</span><span class="p" data-group-id="2686045681-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="8595499684-4">(</span><span class="mi">0</span><span class="p" data-group-id="8595499684-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="2686045681-4">(</span><span class="mi">0</span><span class="p" data-group-id="2686045681-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8595499684-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8595499684-6">[</span><span class="p" data-group-id="8595499684-6">]</span><span class="p" data-group-id="8595499684-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2686045681-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2686045681-6">[</span><span class="p" data-group-id="2686045681-6">]</span><span class="p" data-group-id="2686045681-5">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="8595499684-7">(</span><span class="n">N</span><span class="p" data-group-id="8595499684-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8595499684-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8595499684-9">(</span><span class="p" data-group-id="8595499684-9">)</span><span class="p" data-group-id="8595499684-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="2686045681-7">(</span><span class="n">N</span><span class="p" data-group-id="2686045681-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2686045681-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2686045681-9">(</span><span class="p" data-group-id="2686045681-9">)</span><span class="p" data-group-id="2686045681-8">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8595499684-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8595499684-11">[</span><span class="p" data-group-id="8595499684-11">]</span><span class="p" data-group-id="8595499684-10">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2686045681-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2686045681-11">[</span><span class="p" data-group-id="2686045681-11">]</span><span class="p" data-group-id="2686045681-10">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="8595499684-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8595499684-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="2686045681-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2686045681-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="8595499684-13">(</span><span class="p" data-group-id="8595499684-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="2686045681-13">(</span><span class="p" data-group-id="2686045681-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8595499684-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8595499684-15">[</span><span class="p" data-group-id="8595499684-15">]</span><span class="p" data-group-id="8595499684-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8595499684-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="8595499684-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8595499684-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8595499684-18">[</span><span class="p" data-group-id="8595499684-18">]</span><span class="p" data-group-id="8595499684-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2686045681-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2686045681-15">[</span><span class="p" data-group-id="2686045681-15">]</span><span class="p" data-group-id="2686045681-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2686045681-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2686045681-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2686045681-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2686045681-18">[</span><span class="p" data-group-id="2686045681-18">]</span><span class="p" data-group-id="2686045681-17">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="8595499684-19">(</span><span class="p" data-group-id="8595499684-19">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="2686045681-19">(</span><span class="p" data-group-id="2686045681-19">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="8595499684-20">(</span><span class="p" data-group-id="8595499684-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="8595499684-21">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="8595499684-22">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8595499684-23">[</span><span class="p" data-group-id="8595499684-23">]</span><span class="p" data-group-id="8595499684-22">)</span><span class="p" data-group-id="8595499684-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="8595499684-24">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8595499684-25">[</span><span class="mi">3</span><span class="p" data-group-id="8595499684-25">]</span><span class="p" data-group-id="8595499684-24">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nf">c</span><span class="p" data-group-id="1882382299-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="1882382299-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1882382299-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut16</span><span class="p" data-group-id="1882382299-2">}</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nc">tut16</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1882382299-3">(</span><span class="p" data-group-id="1882382299-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="2686045681-20">(</span><span class="p" data-group-id="2686045681-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="2686045681-21">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2686045681-22">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2686045681-23">[</span><span class="p" data-group-id="2686045681-23">]</span><span class="p" data-group-id="2686045681-22">)</span><span class="p" data-group-id="2686045681-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="2686045681-24">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2686045681-25">[</span><span class="mi">3</span><span class="p" data-group-id="2686045681-25">]</span><span class="p" data-group-id="2686045681-24">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nf">c</span><span class="p" data-group-id="9860003776-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="9860003776-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9860003776-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut16</span><span class="p" data-group-id="9860003776-2">}</span><span class="gp unselectable">
│ │ │ │ +3&gt; </span><span class="nc">tut16</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9860003776-3">(</span><span class="p" data-group-id="9860003776-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.38</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span><span class="w">
│ │ │ │ -</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>Here the <code class="inline">start/0</code> function,</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="0326985796-1">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0326985796-2">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0326985796-3">[</span><span class="p" data-group-id="0326985796-3">]</span><span class="p" data-group-id="0326985796-2">)</span><span class="p" data-group-id="0326985796-1">)</span><span class="p">,</span></code></pre><p>both spawns the &quot;pong&quot; process and gives it the name <code class="inline">pong</code>. In the &quot;ping&quot;
│ │ │ │ -process, messages can be sent to <code class="inline">pong</code> by:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6214877014-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6214877014-2">(</span><span class="p" data-group-id="6214877014-2">)</span><span class="p" data-group-id="6214877014-1">}</span><span class="p">,</span></code></pre><p><code class="inline">ping/2</code> now becomes <code class="inline">ping/1</code> as the argument <code class="inline">Pong_PID</code> is not needed.</p><h2 id="distributed-programming" class="section-heading">
│ │ │ │ +</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>Here the <code class="inline">start/0</code> function,</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="5625737533-1">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="5625737533-2">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5625737533-3">[</span><span class="p" data-group-id="5625737533-3">]</span><span class="p" data-group-id="5625737533-2">)</span><span class="p" data-group-id="5625737533-1">)</span><span class="p">,</span></code></pre><p>both spawns the &quot;pong&quot; process and gives it the name <code class="inline">pong</code>. In the &quot;ping&quot;
│ │ │ │ +process, messages can be sent to <code class="inline">pong</code> by:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0204179596-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0204179596-2">(</span><span class="p" data-group-id="0204179596-2">)</span><span class="p" data-group-id="0204179596-1">}</span><span class="p">,</span></code></pre><p><code class="inline">ping/2</code> now becomes <code class="inline">ping/1</code> as the argument <code class="inline">Pong_PID</code> is not needed.</p><h2 id="distributed-programming" class="section-heading">
│ │ │ │    <a href="#distributed-programming" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Distributed Programming</span>
│ │ │ │  </h2>
│ │ │ │  <p>Let us rewrite the ping pong program with &quot;ping&quot; and &quot;pong&quot; on different
│ │ │ │  computers. First a few things are needed to set up to get this to work. The
│ │ │ │ @@ -255,106 +255,106 @@
│ │ │ │  of the file. This is a requirement.</p><p>When you start an Erlang system that is going to talk to other Erlang systems,
│ │ │ │  you must give it a name, for example:</p><pre><code class="text">$ erl -sname my_name</code></pre><p>We will see more details of this later. If you want to experiment with
│ │ │ │  distributed Erlang, but you only have one computer to work on, you can start two
│ │ │ │  separate Erlang systems on the same computer but give them different names. Each
│ │ │ │  Erlang system running on a computer is called an <em>Erlang node</em>.</p><p>(Note: <code class="inline">erl -sname</code> assumes that all nodes are in the same IP domain and we can
│ │ │ │  use only the first component of the IP address, if we want to use nodes in
│ │ │ │  different domains we use <code class="inline">-name</code> instead, but then all IP address must be given
│ │ │ │ -in full.)</p><p>Here is the ping pong example modified to run on two separate nodes:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0275841130-1">(</span><span class="ss">tut17</span><span class="p" data-group-id="0275841130-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +in full.)</p><p>Here is the ping pong example modified to run on two separate nodes:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9031390658-1">(</span><span class="ss">tut17</span><span class="p" data-group-id="9031390658-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0275841130-2">(</span><span class="p" data-group-id="0275841130-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0275841130-3">]</span><span class="p" data-group-id="0275841130-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9031390658-2">(</span><span class="p" data-group-id="9031390658-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9031390658-3">]</span><span class="p" data-group-id="9031390658-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="0275841130-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0275841130-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0275841130-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0275841130-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0275841130-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0275841130-7">[</span><span class="p" data-group-id="0275841130-7">]</span><span class="p" data-group-id="0275841130-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="9031390658-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9031390658-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9031390658-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9031390658-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9031390658-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9031390658-7">[</span><span class="p" data-group-id="9031390658-7">]</span><span class="p" data-group-id="9031390658-6">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="0275841130-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0275841130-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0275841130-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0275841130-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0275841130-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0275841130-11">(</span><span class="p" data-group-id="0275841130-11">)</span><span class="p" data-group-id="0275841130-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="9031390658-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9031390658-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9031390658-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9031390658-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9031390658-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9031390658-11">(</span><span class="p" data-group-id="9031390658-11">)</span><span class="p" data-group-id="9031390658-10">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0275841130-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0275841130-13">[</span><span class="p" data-group-id="0275841130-13">]</span><span class="p" data-group-id="0275841130-12">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9031390658-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9031390658-13">[</span><span class="p" data-group-id="9031390658-13">]</span><span class="p" data-group-id="9031390658-12">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="0275841130-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0275841130-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="9031390658-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9031390658-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="0275841130-15">(</span><span class="p" data-group-id="0275841130-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="9031390658-15">(</span><span class="p" data-group-id="9031390658-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0275841130-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0275841130-17">[</span><span class="p" data-group-id="0275841130-17">]</span><span class="p" data-group-id="0275841130-16">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0275841130-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="0275841130-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0275841130-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0275841130-20">[</span><span class="p" data-group-id="0275841130-20">]</span><span class="p" data-group-id="0275841130-19">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9031390658-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9031390658-17">[</span><span class="p" data-group-id="9031390658-17">]</span><span class="p" data-group-id="9031390658-16">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9031390658-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9031390658-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9031390658-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9031390658-20">[</span><span class="p" data-group-id="9031390658-20">]</span><span class="p" data-group-id="9031390658-19">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="0275841130-21">(</span><span class="p" data-group-id="0275841130-21">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="9031390658-21">(</span><span class="p" data-group-id="9031390658-21">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_pong</span><span class="p" data-group-id="0275841130-22">(</span><span class="p" data-group-id="0275841130-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="0275841130-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0275841130-24">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0275841130-25">[</span><span class="p" data-group-id="0275841130-25">]</span><span class="p" data-group-id="0275841130-24">)</span><span class="p" data-group-id="0275841130-23">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_pong</span><span class="p" data-group-id="9031390658-22">(</span><span class="p" data-group-id="9031390658-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="9031390658-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9031390658-24">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9031390658-25">[</span><span class="p" data-group-id="9031390658-25">]</span><span class="p" data-group-id="9031390658-24">)</span><span class="p" data-group-id="9031390658-23">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_ping</span><span class="p" data-group-id="0275841130-26">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="0275841130-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="0275841130-27">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0275841130-28">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0275841130-28">]</span><span class="p" data-group-id="0275841130-27">)</span><span class="p">.</span></code></pre><p>Let us assume there are two computers called gollum and kosken. First a node is
│ │ │ │ +</span><span class="nf">start_ping</span><span class="p" data-group-id="9031390658-26">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="9031390658-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9031390658-27">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9031390658-28">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9031390658-28">]</span><span class="p" data-group-id="9031390658-27">)</span><span class="p">.</span></code></pre><p>Let us assume there are two computers called gollum and kosken. First a node is
│ │ │ │  started on kosken, called ping, and then a node on gollum, called pong.</p><p>On kosken (on a Linux/UNIX system):</p><pre><code class="text">kosken&gt; erl -sname ping
│ │ │ │  Erlang (BEAM) emulator version 5.2.3.7 [hipe] [threads:0]
│ │ │ │  
│ │ │ │  Eshell V5.2.3.7  (abort with ^G)
│ │ │ │  (ping@kosken)1&gt;</code></pre><p>On gollum:</p><pre><code class="text">gollum&gt; erl -sname pong
│ │ │ │  Erlang (BEAM) emulator version 5.2.3.7 [hipe] [threads:0]
│ │ │ │  
│ │ │ │  Eshell V5.2.3.7  (abort with ^G)
│ │ │ │ -(pong@gollum)1&gt;</code></pre><p>Now the &quot;pong&quot; process on gollum is started:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_pong</span><span class="p" data-group-id="9894021232-1">(</span><span class="p" data-group-id="9894021232-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +(pong@gollum)1&gt;</code></pre><p>Now the &quot;pong&quot; process on gollum is started:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_pong</span><span class="p" data-group-id="9904874959-1">(</span><span class="p" data-group-id="9904874959-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span></code></pre><p>And the &quot;ping&quot; process on kosken is started (from the code above you can see
│ │ │ │  that a parameter of the <code class="inline">start_ping</code> function is the node name of the Erlang
│ │ │ │ -system where &quot;pong&quot; is running):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(ping@kosken)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_ping</span><span class="p" data-group-id="9333739703-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="9333739703-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +system where &quot;pong&quot; is running):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(ping@kosken)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_ping</span><span class="p" data-group-id="7555887320-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="7555887320-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.37</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>As shown, the ping pong program has run. On the &quot;pong&quot; side:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)2&gt; </span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="nf">finished</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4779458557-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="4779458557-1">)</span><span class="mi">2</span><span class="o">&gt;</span><span class="w"> </span></code></pre><p>Looking at the <code class="inline">tut17</code> code, you see that the <code class="inline">pong</code> function itself is
│ │ │ │ +</span><span class="p" data-group-id="3577410892-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="3577410892-1">)</span><span class="mi">2</span><span class="o">&gt;</span><span class="w"> </span></code></pre><p>Looking at the <code class="inline">tut17</code> code, you see that the <code class="inline">pong</code> function itself is
│ │ │ │  unchanged, the following lines work in the same way irrespective of on which
│ │ │ │ -node the &quot;ping&quot; process is executes:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9706863839-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9706863839-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9706863839-2">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9706863839-3">[</span><span class="p" data-group-id="9706863839-3">]</span><span class="p" data-group-id="9706863839-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +node the &quot;ping&quot; process is executes:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8992721039-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="8992721039-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8992721039-2">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8992721039-3">[</span><span class="p" data-group-id="8992721039-3">]</span><span class="p" data-group-id="8992721039-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span></code></pre><p>Thus, Erlang pids contain information about where the process executes. So if
│ │ │ │  you know the pid of a process, the <code class="inline">!</code> operator can be used to send it a
│ │ │ │ -message disregarding if the process is on the same node or on a different node.</p><p>A difference is how messages are sent to a registered process on another node:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1478616113-1">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1478616113-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1478616113-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1478616113-3">(</span><span class="p" data-group-id="1478616113-3">)</span><span class="p" data-group-id="1478616113-2">}</span><span class="p">,</span></code></pre><p>A tuple <code class="inline">{registered_name,node_name}</code> is used instead of just the
│ │ │ │ +message disregarding if the process is on the same node or on a different node.</p><p>A difference is how messages are sent to a registered process on another node:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8613731424-1">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8613731424-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8613731424-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8613731424-3">(</span><span class="p" data-group-id="8613731424-3">)</span><span class="p" data-group-id="8613731424-2">}</span><span class="p">,</span></code></pre><p>A tuple <code class="inline">{registered_name,node_name}</code> is used instead of just the
│ │ │ │  <code class="inline">registered_name</code>.</p><p>In the previous example, &quot;ping&quot; and &quot;pong&quot; were started from the shells of two
│ │ │ │  separate Erlang nodes. <code class="inline">spawn</code> can also be used to start processes in other
│ │ │ │  nodes.</p><p>The next example is the ping pong program, yet again, but this time &quot;ping&quot; is
│ │ │ │ -started in another node:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1811473469-1">(</span><span class="ss">tut18</span><span class="p" data-group-id="1811473469-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +started in another node:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8655657656-1">(</span><span class="ss">tut18</span><span class="p" data-group-id="8655657656-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1811473469-2">(</span><span class="p" data-group-id="1811473469-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1811473469-3">]</span><span class="p" data-group-id="1811473469-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8655657656-2">(</span><span class="p" data-group-id="8655657656-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8655657656-3">]</span><span class="p" data-group-id="8655657656-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="1811473469-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1811473469-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1811473469-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1811473469-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1811473469-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1811473469-7">[</span><span class="p" data-group-id="1811473469-7">]</span><span class="p" data-group-id="1811473469-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="8655657656-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8655657656-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8655657656-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8655657656-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8655657656-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8655657656-7">[</span><span class="p" data-group-id="8655657656-7">]</span><span class="p" data-group-id="8655657656-6">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="1811473469-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1811473469-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1811473469-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1811473469-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1811473469-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1811473469-11">(</span><span class="p" data-group-id="1811473469-11">)</span><span class="p" data-group-id="1811473469-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="8655657656-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8655657656-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8655657656-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8655657656-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8655657656-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8655657656-11">(</span><span class="p" data-group-id="8655657656-11">)</span><span class="p" data-group-id="8655657656-10">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1811473469-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1811473469-13">[</span><span class="p" data-group-id="1811473469-13">]</span><span class="p" data-group-id="1811473469-12">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8655657656-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8655657656-13">[</span><span class="p" data-group-id="8655657656-13">]</span><span class="p" data-group-id="8655657656-12">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="1811473469-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1811473469-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="8655657656-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8655657656-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="1811473469-15">(</span><span class="p" data-group-id="1811473469-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="8655657656-15">(</span><span class="p" data-group-id="8655657656-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1811473469-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1811473469-17">[</span><span class="p" data-group-id="1811473469-17">]</span><span class="p" data-group-id="1811473469-16">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1811473469-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="1811473469-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1811473469-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1811473469-20">[</span><span class="p" data-group-id="1811473469-20">]</span><span class="p" data-group-id="1811473469-19">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8655657656-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8655657656-17">[</span><span class="p" data-group-id="8655657656-17">]</span><span class="p" data-group-id="8655657656-16">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8655657656-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="8655657656-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8655657656-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8655657656-20">[</span><span class="p" data-group-id="8655657656-20">]</span><span class="p" data-group-id="8655657656-19">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="1811473469-21">(</span><span class="p" data-group-id="1811473469-21">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="8655657656-21">(</span><span class="p" data-group-id="8655657656-21">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="1811473469-22">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="1811473469-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="1811473469-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1811473469-24">(</span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1811473469-25">[</span><span class="p" data-group-id="1811473469-25">]</span><span class="p" data-group-id="1811473469-24">)</span><span class="p" data-group-id="1811473469-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1811473469-26">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1811473469-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="1811473469-28">(</span><span class="p" data-group-id="1811473469-28">)</span><span class="p" data-group-id="1811473469-27">]</span><span class="p" data-group-id="1811473469-26">)</span><span class="p">.</span></code></pre><p>Assuming an Erlang system called ping (but not the &quot;ping&quot; process) has already
│ │ │ │ -been started on kosken, then on gollum this is done:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut18</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3671062647-1">(</span><span class="ss">ping@kosken</span><span class="p" data-group-id="3671062647-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8655657656-22">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="8655657656-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="8655657656-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="8655657656-24">(</span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8655657656-25">[</span><span class="p" data-group-id="8655657656-25">]</span><span class="p" data-group-id="8655657656-24">)</span><span class="p" data-group-id="8655657656-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="8655657656-26">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8655657656-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="8655657656-28">(</span><span class="p" data-group-id="8655657656-28">)</span><span class="p" data-group-id="8655657656-27">]</span><span class="p" data-group-id="8655657656-26">)</span><span class="p">.</span></code></pre><p>Assuming an Erlang system called ping (but not the &quot;ping&quot; process) has already
│ │ │ │ +been started on kosken, then on gollum this is done:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut18</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8674096842-1">(</span><span class="ss">ping@kosken</span><span class="p" data-group-id="8674096842-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">3934.39</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │ @@ -421,184 +421,184 @@
│ │ │ │  </span><span class="c1">%%% Started: messenger:client(Server_Node, Name)</span><span class="w">
│ │ │ │  </span><span class="c1">%%% To client: logoff</span><span class="w">
│ │ │ │  </span><span class="c1">%%% To client: {message_to, ToName, Message}</span><span class="w">
│ │ │ │  </span><span class="c1">%%%</span><span class="w">
│ │ │ │  </span><span class="c1">%%% Configuration: change the server_node() function to return the</span><span class="w">
│ │ │ │  </span><span class="c1">%%% name of the node where the messenger server runs</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6352318446-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="6352318446-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6352318446-2">(</span><span class="p" data-group-id="6352318446-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6352318446-3">]</span><span class="p" data-group-id="6352318446-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7262954866-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="7262954866-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7262954866-2">(</span><span class="p" data-group-id="7262954866-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7262954866-3">]</span><span class="p" data-group-id="7262954866-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Change the function below to return the name of the node where the</span><span class="w">
│ │ │ │  </span><span class="c1">%%% messenger server runs</span><span class="w">
│ │ │ │ -</span><span class="nf">server_node</span><span class="p" data-group-id="6352318446-4">(</span><span class="p" data-group-id="6352318446-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_node</span><span class="p" data-group-id="7262954866-4">(</span><span class="p" data-group-id="7262954866-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">messenger@super</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% This is the server process for the &quot;messenger&quot;</span><span class="w">
│ │ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="6352318446-5">(</span><span class="n">User_List</span><span class="p" data-group-id="6352318446-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="7262954866-5">(</span><span class="n">User_List</span><span class="p" data-group-id="7262954866-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6352318446-6">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6352318446-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="6352318446-7">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="6352318446-8">(</span><span class="n">New_User_List</span><span class="p" data-group-id="6352318446-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6352318446-9">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="6352318446-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="6352318446-10">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="6352318446-11">(</span><span class="n">New_User_List</span><span class="p" data-group-id="6352318446-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6352318446-12">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6352318446-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="6352318446-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6352318446-14">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6352318446-15">[</span><span class="n">User_List</span><span class="p" data-group-id="6352318446-15">]</span><span class="p" data-group-id="6352318446-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="6352318446-16">(</span><span class="n">User_List</span><span class="p" data-group-id="6352318446-16">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7262954866-6">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7262954866-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="7262954866-7">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="7262954866-8">(</span><span class="n">New_User_List</span><span class="p" data-group-id="7262954866-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7262954866-9">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="7262954866-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="7262954866-10">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="7262954866-11">(</span><span class="n">New_User_List</span><span class="p" data-group-id="7262954866-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7262954866-12">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7262954866-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="7262954866-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7262954866-14">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7262954866-15">[</span><span class="n">User_List</span><span class="p" data-group-id="7262954866-15">]</span><span class="p" data-group-id="7262954866-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="7262954866-16">(</span><span class="n">User_List</span><span class="p" data-group-id="7262954866-16">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="6352318446-17">(</span><span class="p" data-group-id="6352318446-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="6352318446-18">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="6352318446-19">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6352318446-20">[</span><span class="p" data-group-id="6352318446-21">[</span><span class="p" data-group-id="6352318446-21">]</span><span class="p" data-group-id="6352318446-20">]</span><span class="p" data-group-id="6352318446-19">)</span><span class="p" data-group-id="6352318446-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="7262954866-17">(</span><span class="p" data-group-id="7262954866-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="7262954866-18">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7262954866-19">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7262954866-20">[</span><span class="p" data-group-id="7262954866-21">[</span><span class="p" data-group-id="7262954866-21">]</span><span class="p" data-group-id="7262954866-20">]</span><span class="p" data-group-id="7262954866-19">)</span><span class="p" data-group-id="7262954866-18">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="6352318446-22">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="7262954866-22">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="6352318446-23">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-23">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="7262954866-23">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-23">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6352318446-24">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="6352318446-24">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7262954866-24">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="7262954866-24">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6352318446-25">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="6352318446-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="6352318446-26">[</span><span class="p" data-group-id="6352318446-27">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6352318446-27">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-26">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7262954866-25">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="7262954866-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="7262954866-26">[</span><span class="p" data-group-id="7262954866-27">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7262954866-27">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-26">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="6352318446-28">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="6352318446-29">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-29">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="7262954866-28">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="7262954866-29">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-29">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="6352318446-30">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="7262954866-30">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="6352318446-31">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-31">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="7262954866-31">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-31">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6352318446-32">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="6352318446-32">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6352318446-33">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6352318446-34">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6352318446-34">}</span><span class="p" data-group-id="6352318446-33">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="6352318446-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-35">)</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7262954866-32">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="7262954866-32">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7262954866-33">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7262954866-34">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7262954866-34">}</span><span class="p" data-group-id="7262954866-33">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="7262954866-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-35">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="6352318446-36">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="7262954866-36">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="6352318446-37">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6352318446-37">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="7262954866-37">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7262954866-37">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6352318446-38">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="6352318446-38">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6352318446-39">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6352318446-40">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="6352318446-40">}</span><span class="p" data-group-id="6352318446-39">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6352318446-41">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6352318446-41">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6352318446-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="6352318446-42">}</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7262954866-38">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="7262954866-38">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7262954866-39">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7262954866-40">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="7262954866-40">}</span><span class="p" data-group-id="7262954866-39">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7262954866-41">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7262954866-41">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7262954866-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="7262954866-42">}</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% User Commands</span><span class="w">
│ │ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="6352318446-43">(</span><span class="n">Name</span><span class="p" data-group-id="6352318446-43">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="6352318446-44">(</span><span class="ss">mess_client</span><span class="p" data-group-id="6352318446-44">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="7262954866-43">(</span><span class="n">Name</span><span class="p" data-group-id="7262954866-43">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="7262954866-44">(</span><span class="ss">mess_client</span><span class="p" data-group-id="7262954866-44">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="6352318446-45">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="6352318446-46">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6352318446-47">[</span><span class="nf">server_node</span><span class="p" data-group-id="6352318446-48">(</span><span class="p" data-group-id="6352318446-48">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6352318446-47">]</span><span class="p" data-group-id="6352318446-46">)</span><span class="p" data-group-id="6352318446-45">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="7262954866-45">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="7262954866-46">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7262954866-47">[</span><span class="nf">server_node</span><span class="p" data-group-id="7262954866-48">(</span><span class="p" data-group-id="7262954866-48">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7262954866-47">]</span><span class="p" data-group-id="7262954866-46">)</span><span class="p" data-group-id="7262954866-45">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="6352318446-49">(</span><span class="p" data-group-id="6352318446-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="7262954866-49">(</span><span class="p" data-group-id="7262954866-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="6352318446-50">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6352318446-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="6352318446-51">(</span><span class="ss">mess_client</span><span class="p" data-group-id="6352318446-51">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="7262954866-50">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7262954866-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="7262954866-51">(</span><span class="ss">mess_client</span><span class="p" data-group-id="7262954866-51">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6352318446-52">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6352318446-52">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7262954866-52">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7262954866-52">}</span><span class="p">,</span><span class="w">
│ │ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% The client process which runs on each server node</span><span class="w">
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="6352318446-53">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6352318446-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6352318446-54">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="6352318446-54">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6352318446-55">{</span><span class="nf">self</span><span class="p" data-group-id="6352318446-56">(</span><span class="p" data-group-id="6352318446-56">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6352318446-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="6352318446-57">(</span><span class="p" data-group-id="6352318446-57">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="6352318446-58">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6352318446-58">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="7262954866-53">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7262954866-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7262954866-54">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="7262954866-54">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7262954866-55">{</span><span class="nf">self</span><span class="p" data-group-id="7262954866-56">(</span><span class="p" data-group-id="7262954866-56">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7262954866-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="7262954866-57">(</span><span class="p" data-group-id="7262954866-57">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="7262954866-58">(</span><span class="n">Server_Node</span><span class="p" data-group-id="7262954866-58">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="6352318446-59">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6352318446-59">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="7262954866-59">(</span><span class="n">Server_Node</span><span class="p" data-group-id="7262954866-59">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="6352318446-60">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="6352318446-60">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6352318446-61">{</span><span class="nf">self</span><span class="p" data-group-id="6352318446-62">(</span><span class="p" data-group-id="6352318446-62">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="6352318446-61">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="6352318446-63">(</span><span class="ss">normal</span><span class="p" data-group-id="6352318446-63">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6352318446-64">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6352318446-64">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="6352318446-65">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="6352318446-65">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6352318446-66">{</span><span class="nf">self</span><span class="p" data-group-id="6352318446-67">(</span><span class="p" data-group-id="6352318446-67">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6352318446-66">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="6352318446-68">(</span><span class="p" data-group-id="6352318446-68">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6352318446-69">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6352318446-69">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6352318446-70">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6352318446-71">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6352318446-71">]</span><span class="p" data-group-id="6352318446-70">)</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="7262954866-60">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="7262954866-60">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7262954866-61">{</span><span class="nf">self</span><span class="p" data-group-id="7262954866-62">(</span><span class="p" data-group-id="7262954866-62">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="7262954866-61">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="7262954866-63">(</span><span class="ss">normal</span><span class="p" data-group-id="7262954866-63">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7262954866-64">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7262954866-64">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="7262954866-65">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="7262954866-65">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7262954866-66">{</span><span class="nf">self</span><span class="p" data-group-id="7262954866-67">(</span><span class="p" data-group-id="7262954866-67">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7262954866-66">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="7262954866-68">(</span><span class="p" data-group-id="7262954866-68">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7262954866-69">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7262954866-69">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7262954866-70">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7262954866-71">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7262954866-71">]</span><span class="p" data-group-id="7262954866-70">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="6352318446-72">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6352318446-72">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="7262954866-72">(</span><span class="n">Server_Node</span><span class="p" data-group-id="7262954866-72">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="6352318446-73">(</span><span class="p" data-group-id="6352318446-73">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="7262954866-73">(</span><span class="p" data-group-id="7262954866-73">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6352318446-74">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="6352318446-74">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6352318446-75">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6352318446-76">[</span><span class="n">Why</span><span class="p" data-group-id="6352318446-76">]</span><span class="p" data-group-id="6352318446-75">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="6352318446-77">(</span><span class="ss">normal</span><span class="p" data-group-id="6352318446-77">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6352318446-78">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="6352318446-78">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6352318446-79">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6352318446-80">[</span><span class="n">What</span><span class="p" data-group-id="6352318446-80">]</span><span class="p" data-group-id="6352318446-79">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7262954866-74">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="7262954866-74">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7262954866-75">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7262954866-76">[</span><span class="n">Why</span><span class="p" data-group-id="7262954866-76">]</span><span class="p" data-group-id="7262954866-75">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="7262954866-77">(</span><span class="ss">normal</span><span class="p" data-group-id="7262954866-77">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7262954866-78">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="7262954866-78">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7262954866-79">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7262954866-80">[</span><span class="n">What</span><span class="p" data-group-id="7262954866-80">]</span><span class="p" data-group-id="7262954866-79">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>To use this program, you need to:</p><ul><li>Configure the <code class="inline">server_node()</code> function.</li><li>Copy the compiled code (<code class="inline">messenger.beam</code>) to the directory on each computer
│ │ │ │  where you start Erlang.</li></ul><p>In the following example using this program, nodes are started on four different
│ │ │ │  computers. If you do not have that many machines available on your network, you
│ │ │ │  can start several nodes on the same machine.</p><p>Four Erlang nodes are started up: messenger@super, c1@bilbo, c2@kosken,
│ │ │ │ -c3@gollum.</p><p>First the server at messenger@super is started up:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(messenger@super)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">start_server</span><span class="p" data-group-id="5466948176-1">(</span><span class="p" data-group-id="5466948176-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">true</span></code></pre><p>Now Peter logs on at c1@bilbo:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="4267181706-1">(</span><span class="ss">peter</span><span class="p" data-group-id="4267181706-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +c3@gollum.</p><p>First the server at messenger@super is started up:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(messenger@super)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">start_server</span><span class="p" data-group-id="6960400936-1">(</span><span class="p" data-group-id="6960400936-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">true</span></code></pre><p>Now Peter logs on at c1@bilbo:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="5794046372-1">(</span><span class="ss">peter</span><span class="p" data-group-id="5794046372-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="ss">logged_on</span></code></pre><p>James logs on at c2@kosken:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="2566644749-1">(</span><span class="ss">james</span><span class="p" data-group-id="2566644749-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">logged_on</span></code></pre><p>James logs on at c2@kosken:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="5510257282-1">(</span><span class="ss">james</span><span class="p" data-group-id="5510257282-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="ss">logged_on</span></code></pre><p>And Fred logs on at c3@gollum:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c3@gollum)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="7112304892-1">(</span><span class="ss">fred</span><span class="p" data-group-id="7112304892-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">logged_on</span></code></pre><p>And Fred logs on at c3@gollum:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c3@gollum)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="9329122906-1">(</span><span class="ss">fred</span><span class="p" data-group-id="9329122906-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="ss">logged_on</span></code></pre><p>Now Peter sends Fred a message:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="9865437557-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="9865437557-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">logged_on</span></code></pre><p>Now Peter sends Fred a message:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="0139342186-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0139342186-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="ss">sent</span></code></pre><p>Fred receives the message and sends a message to Peter and logs off:</p><pre><code class="makeup erlang" translate="no"><span class="n">Message</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="nc">peter</span><span class="p">:</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="gp unselectable">
│ │ │ │ -(c3@gollum)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="5862390914-1">(</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;go away, I&#39;m busy&quot;</span><span class="p" data-group-id="5862390914-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +(c3@gollum)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="2591064130-1">(</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;go away, I&#39;m busy&quot;</span><span class="p" data-group-id="2591064130-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="nf">sent</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5862390914-2">(</span><span class="ss">c3@gollum</span><span class="p" data-group-id="5862390914-2">)</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logoff</span><span class="p" data-group-id="5862390914-3">(</span><span class="p" data-group-id="5862390914-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">logoff</span></code></pre><p>James now tries to send a message to Fred:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="1464915246-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;peter doesn&#39;t like you&quot;</span><span class="p" data-group-id="1464915246-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2591064130-2">(</span><span class="ss">c3@gollum</span><span class="p" data-group-id="2591064130-2">)</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logoff</span><span class="p" data-group-id="2591064130-3">(</span><span class="p" data-group-id="2591064130-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">logoff</span></code></pre><p>James now tries to send a message to Fred:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="4188618430-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;peter doesn&#39;t like you&quot;</span><span class="p" data-group-id="4188618430-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="ss">receiver_not_found</span></code></pre><p>But this fails as Fred has already logged off.</p><p>First let us look at some of the new concepts that have been introduced.</p><p>There are two versions of the <code class="inline">server_transfer</code> function: one with four
│ │ │ │  arguments (<code class="inline">server_transfer/4</code>) and one with five (<code class="inline">server_transfer/5</code>). These
│ │ │ │  are regarded by Erlang as two separate functions.</p><p>Notice how to write the <code class="inline">server</code> function so that it calls itself, through
│ │ │ │  <code class="inline">server(User_List)</code>, and thus creates a loop. The Erlang compiler is &quot;clever&quot;
│ │ │ │  and optimizes the code so that this really is a sort of loop and not a proper
│ │ │ │  function call. But this only works if there is no code after the call.
│ │ │ │  Otherwise, the compiler expects the call to return and make a proper function
│ │ │ │  call. This would result in the process getting bigger and bigger for every loop.</p><p>Functions in the <code class="inline">lists</code> module are used. This is a very useful module and a
│ │ │ │  study of the manual page is recommended (<code class="inline">erl -man lists</code>).
│ │ │ │  <code class="inline">lists:keymember(Key,Position,Lists)</code> looks through a list of tuples and looks
│ │ │ │  at <code class="inline">Position</code> in each tuple to see if it is the same as <code class="inline">Key</code>. The first element
│ │ │ │  is position 1. If it finds a tuple where the element at <code class="inline">Position</code> is the same
│ │ │ │ -as <code class="inline">Key</code>, it returns <code class="inline">true</code>, otherwise <code class="inline">false</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="7523309191-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7523309191-2">[</span><span class="p" data-group-id="7523309191-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="7523309191-3">}</span><span class="p">,</span><span class="p" data-group-id="7523309191-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7523309191-4">}</span><span class="p">,</span><span class="p" data-group-id="7523309191-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7523309191-5">}</span><span class="p">,</span><span class="p" data-group-id="7523309191-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="7523309191-6">}</span><span class="p" data-group-id="7523309191-2">]</span><span class="p" data-group-id="7523309191-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +as <code class="inline">Key</code>, it returns <code class="inline">true</code>, otherwise <code class="inline">false</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="4514092444-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4514092444-2">[</span><span class="p" data-group-id="4514092444-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="4514092444-3">}</span><span class="p">,</span><span class="p" data-group-id="4514092444-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4514092444-4">}</span><span class="p">,</span><span class="p" data-group-id="4514092444-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4514092444-5">}</span><span class="p">,</span><span class="p" data-group-id="4514092444-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="4514092444-6">}</span><span class="p" data-group-id="4514092444-2">]</span><span class="p" data-group-id="4514092444-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="7523309191-7">(</span><span class="ss">p</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7523309191-8">[</span><span class="p" data-group-id="7523309191-9">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="7523309191-9">}</span><span class="p">,</span><span class="p" data-group-id="7523309191-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7523309191-10">}</span><span class="p">,</span><span class="p" data-group-id="7523309191-11">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7523309191-11">}</span><span class="p">,</span><span class="p" data-group-id="7523309191-12">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="7523309191-12">}</span><span class="p" data-group-id="7523309191-8">]</span><span class="p" data-group-id="7523309191-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="4514092444-7">(</span><span class="ss">p</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4514092444-8">[</span><span class="p" data-group-id="4514092444-9">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="4514092444-9">}</span><span class="p">,</span><span class="p" data-group-id="4514092444-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4514092444-10">}</span><span class="p">,</span><span class="p" data-group-id="4514092444-11">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4514092444-11">}</span><span class="p">,</span><span class="p" data-group-id="4514092444-12">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="4514092444-12">}</span><span class="p" data-group-id="4514092444-8">]</span><span class="p" data-group-id="4514092444-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span></code></pre><p><code class="inline">lists:keydelete</code> works in the same way but deletes the first tuple found (if
│ │ │ │ -any) and returns the remaining list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="2425675537-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2425675537-2">[</span><span class="p" data-group-id="2425675537-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="2425675537-3">}</span><span class="p">,</span><span class="p" data-group-id="2425675537-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2425675537-4">}</span><span class="p">,</span><span class="p" data-group-id="2425675537-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="2425675537-5">}</span><span class="p">,</span><span class="p" data-group-id="2425675537-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="2425675537-6">}</span><span class="p" data-group-id="2425675537-2">]</span><span class="p" data-group-id="2425675537-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2425675537-7">[</span><span class="p" data-group-id="2425675537-8">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="2425675537-8">}</span><span class="p">,</span><span class="p" data-group-id="2425675537-9">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2425675537-9">}</span><span class="p">,</span><span class="p" data-group-id="2425675537-10">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="2425675537-10">}</span><span class="p" data-group-id="2425675537-7">]</span></code></pre><p><code class="inline">lists:keysearch</code> is like <code class="inline">lists:keymember</code>, but it returns
│ │ │ │ +any) and returns the remaining list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="3663539661-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3663539661-2">[</span><span class="p" data-group-id="3663539661-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="3663539661-3">}</span><span class="p">,</span><span class="p" data-group-id="3663539661-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3663539661-4">}</span><span class="p">,</span><span class="p" data-group-id="3663539661-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3663539661-5">}</span><span class="p">,</span><span class="p" data-group-id="3663539661-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="3663539661-6">}</span><span class="p" data-group-id="3663539661-2">]</span><span class="p" data-group-id="3663539661-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3663539661-7">[</span><span class="p" data-group-id="3663539661-8">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="3663539661-8">}</span><span class="p">,</span><span class="p" data-group-id="3663539661-9">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3663539661-9">}</span><span class="p">,</span><span class="p" data-group-id="3663539661-10">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="3663539661-10">}</span><span class="p" data-group-id="3663539661-7">]</span></code></pre><p><code class="inline">lists:keysearch</code> is like <code class="inline">lists:keymember</code>, but it returns
│ │ │ │  <code class="inline">{value,Tuple_Found}</code> or the atom <code class="inline">false</code>.</p><p>There are many very useful functions in the <code class="inline">lists</code> module.</p><p>An Erlang process (conceptually) runs until it does a <code class="inline">receive</code> and there is no
│ │ │ │  message which it wants to receive in the message queue. &quot;conceptually&quot; is used
│ │ │ │  here because the Erlang system shares the CPU time between the active processes
│ │ │ │  in the system.</p><p>A process terminates when there is nothing more for it to do, that is, the last
│ │ │ │  function it calls simply returns and does not call another function. Another way
│ │ │ │  for a process to terminate is for it to call <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a>. The argument
│ │ │ │  to <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a> has a special meaning, which is discussed later. In this
│ │ │ │  example, <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a> is done, which has the same effect as a
│ │ │ │  process running out of functions to call.</p><p>The BIF <a href="../../../lib/../erts/doc/html/erlang.html#whereis/1"><code class="inline">whereis(RegisteredName)</code></a> checks if a registered process
│ │ │ │  of name <code class="inline">RegisteredName</code> exists. If it exists, the pid of that process is
│ │ │ │  returned. If it does not exist, the atom <code class="inline">undefined</code> is returned.</p><p>You should by now be able to understand most of the code in the
│ │ │ │  messenger-module. Let us study one case in detail: a message is sent from one
│ │ │ │ -user to another.</p><p>The first user &quot;sends&quot; the message in the example above by:</p><pre><code class="makeup erlang" translate="no"><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="7673345795-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7673345795-1">)</span></code></pre><p>After testing that the client process exists:</p><pre><code class="makeup erlang" translate="no"><span class="nf">whereis</span><span class="p" data-group-id="3384985854-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="3384985854-1">)</span></code></pre><p>And a message is sent to <code class="inline">mess_client</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2618971500-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="2618971500-1">}</span></code></pre><p>The client sends the message to the server by:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1988729728-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="1988729728-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1988729728-2">{</span><span class="nf">self</span><span class="p" data-group-id="1988729728-3">(</span><span class="p" data-group-id="1988729728-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="1988729728-2">}</span><span class="p">,</span></code></pre><p>And waits for a reply from the server.</p><p>The server receives this message and calls:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="1477568189-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="1477568189-1">)</span><span class="p">,</span></code></pre><p>This checks that the pid <code class="inline">From</code> is in the <code class="inline">User_List</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="8262756042-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8262756042-1">)</span></code></pre><p>If <code class="inline">keysearch</code> returns the atom <code class="inline">false</code>, some error has occurred and the server
│ │ │ │ -sends back the message:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6737891365-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="6737891365-1">}</span></code></pre><p>This is received by the client, which in turn does <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a>
│ │ │ │ +user to another.</p><p>The first user &quot;sends&quot; the message in the example above by:</p><pre><code class="makeup erlang" translate="no"><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="0410213752-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0410213752-1">)</span></code></pre><p>After testing that the client process exists:</p><pre><code class="makeup erlang" translate="no"><span class="nf">whereis</span><span class="p" data-group-id="3606587044-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="3606587044-1">)</span></code></pre><p>And a message is sent to <code class="inline">mess_client</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8951985598-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8951985598-1">}</span></code></pre><p>The client sends the message to the server by:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7468638405-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="7468638405-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7468638405-2">{</span><span class="nf">self</span><span class="p" data-group-id="7468638405-3">(</span><span class="p" data-group-id="7468638405-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7468638405-2">}</span><span class="p">,</span></code></pre><p>And waits for a reply from the server.</p><p>The server receives this message and calls:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="4890526475-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4890526475-1">)</span><span class="p">,</span></code></pre><p>This checks that the pid <code class="inline">From</code> is in the <code class="inline">User_List</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3888303973-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3888303973-1">)</span></code></pre><p>If <code class="inline">keysearch</code> returns the atom <code class="inline">false</code>, some error has occurred and the server
│ │ │ │ +sends back the message:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3708618678-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="3708618678-1">}</span></code></pre><p>This is received by the client, which in turn does <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a>
│ │ │ │  and terminates. If <code class="inline">keysearch</code> returns <code class="inline">{value,{From,Name}}</code> it is certain that
│ │ │ │ -the user is logged on and that his name (peter) is in variable <code class="inline">Name</code>.</p><p>Let us now call:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="2242400910-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2242400910-1">)</span></code></pre><p>Notice that as this is <code class="inline">server_transfer/5</code>, it is not the same as the previous
│ │ │ │ +the user is logged on and that his name (peter) is in variable <code class="inline">Name</code>.</p><p>Let us now call:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="1974174604-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="1974174604-1">)</span></code></pre><p>Notice that as this is <code class="inline">server_transfer/5</code>, it is not the same as the previous
│ │ │ │  function <code class="inline">server_transfer/4</code>. Another <code class="inline">keysearch</code> is done on <code class="inline">User_List</code> to find
│ │ │ │ -the pid of the client corresponding to fred:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="6216254552-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6216254552-1">)</span></code></pre><p>This time argument 2 is used, which is the second element in the tuple. If this
│ │ │ │ +the pid of the client corresponding to fred:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="7546742215-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7546742215-1">)</span></code></pre><p>This time argument 2 is used, which is the second element in the tuple. If this
│ │ │ │  returns the atom <code class="inline">false</code>, fred is not logged on and the following message is
│ │ │ │ -sent:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9804386421-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="9804386421-1">}</span><span class="p">;</span></code></pre><p>This is received by the client.</p><p>If <code class="inline">keysearch</code> returns:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1983463290-1">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1983463290-2">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p" data-group-id="1983463290-2">}</span><span class="p" data-group-id="1983463290-1">}</span></code></pre><p>The following message is sent to fred's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8010744309-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8010744309-1">}</span><span class="p">,</span></code></pre><p>The following message is sent to peter's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2259949089-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="2259949089-1">}</span></code></pre><p>Fred's client receives the message and prints it:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6639403345-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6639403345-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6639403345-2">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6639403345-3">[</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6639403345-3">]</span><span class="p" data-group-id="6639403345-2">)</span></code></pre><p>Peter's client receives the message in the <code class="inline">await_result</code> function.</p>
│ │ │ │ +sent:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5151132294-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="5151132294-1">}</span><span class="p">;</span></code></pre><p>This is received by the client.</p><p>If <code class="inline">keysearch</code> returns:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1316146574-1">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1316146574-2">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p" data-group-id="1316146574-2">}</span><span class="p" data-group-id="1316146574-1">}</span></code></pre><p>The following message is sent to fred's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9185927128-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="9185927128-1">}</span><span class="p">,</span></code></pre><p>The following message is sent to peter's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0961048327-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="0961048327-1">}</span></code></pre><p>Fred's client receives the message and prints it:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5938379621-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5938379621-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5938379621-2">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5938379621-3">[</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5938379621-3">]</span><span class="p" data-group-id="5938379621-2">)</span></code></pre><p>Peter's client receives the message in the <code class="inline">await_result</code> function.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/commoncaveats.xhtml
│ │ │ │ @@ -23,31 +23,31 @@
│ │ │ │  <p>This section lists a few constructs to watch out for.</p><h2 id="operator" class="section-heading">
│ │ │ │    <a href="#operator" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Operator <code class="inline">++</code></span>
│ │ │ │  </h2>
│ │ │ │  <p>The <code class="inline">++</code> operator copies its left-hand side operand. That is clearly
│ │ │ │ -seen if we do our own implementation in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_plus_plus</span><span class="p" data-group-id="0398780163-1">(</span><span class="p" data-group-id="0398780163-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0398780163-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="0398780163-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0398780163-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="0398780163-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="0398780163-4">)</span><span class="p" data-group-id="0398780163-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="0398780163-5">(</span><span class="p" data-group-id="0398780163-6">[</span><span class="p" data-group-id="0398780163-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="0398780163-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>We must be careful how we use <code class="inline">++</code> in a loop. First is how not to use it:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_reverse</span><span class="p" data-group-id="5886551604-1">(</span><span class="p" data-group-id="5886551604-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5886551604-2">]</span><span class="p" data-group-id="5886551604-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">naive_reverse</span><span class="p" data-group-id="5886551604-3">(</span><span class="n">T</span><span class="p" data-group-id="5886551604-3">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="5886551604-4">[</span><span class="n">H</span><span class="p" data-group-id="5886551604-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">naive_reverse</span><span class="p" data-group-id="5886551604-5">(</span><span class="p" data-group-id="5886551604-6">[</span><span class="p" data-group-id="5886551604-6">]</span><span class="p" data-group-id="5886551604-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5886551604-7">[</span><span class="p" data-group-id="5886551604-7">]</span><span class="p">.</span></code></pre><p>As the <code class="inline">++</code> operator copies its left-hand side operand, the growing
│ │ │ │ -result is copied repeatedly, leading to quadratic complexity.</p><p>On the other hand, using <code class="inline">++</code> in loop like this is perfectly fine:</p><p><strong>OK</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="4378991249-1">(</span><span class="n">List</span><span class="p" data-group-id="4378991249-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="4378991249-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4378991249-3">[</span><span class="p" data-group-id="4378991249-3">]</span><span class="p" data-group-id="4378991249-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +seen if we do our own implementation in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_plus_plus</span><span class="p" data-group-id="8922739944-1">(</span><span class="p" data-group-id="8922739944-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8922739944-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="8922739944-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8922739944-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="8922739944-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="8922739944-4">)</span><span class="p" data-group-id="8922739944-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="8922739944-5">(</span><span class="p" data-group-id="8922739944-6">[</span><span class="p" data-group-id="8922739944-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="8922739944-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>We must be careful how we use <code class="inline">++</code> in a loop. First is how not to use it:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_reverse</span><span class="p" data-group-id="6914286565-1">(</span><span class="p" data-group-id="6914286565-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6914286565-2">]</span><span class="p" data-group-id="6914286565-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">naive_reverse</span><span class="p" data-group-id="6914286565-3">(</span><span class="n">T</span><span class="p" data-group-id="6914286565-3">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6914286565-4">[</span><span class="n">H</span><span class="p" data-group-id="6914286565-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">naive_reverse</span><span class="p" data-group-id="6914286565-5">(</span><span class="p" data-group-id="6914286565-6">[</span><span class="p" data-group-id="6914286565-6">]</span><span class="p" data-group-id="6914286565-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6914286565-7">[</span><span class="p" data-group-id="6914286565-7">]</span><span class="p">.</span></code></pre><p>As the <code class="inline">++</code> operator copies its left-hand side operand, the growing
│ │ │ │ +result is copied repeatedly, leading to quadratic complexity.</p><p>On the other hand, using <code class="inline">++</code> in loop like this is perfectly fine:</p><p><strong>OK</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8537462387-1">(</span><span class="n">List</span><span class="p" data-group-id="8537462387-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8537462387-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8537462387-3">[</span><span class="p" data-group-id="8537462387-3">]</span><span class="p" data-group-id="8537462387-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="4378991249-4">(</span><span class="p" data-group-id="4378991249-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4378991249-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4378991249-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="4378991249-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4378991249-7">[</span><span class="n">H</span><span class="p" data-group-id="4378991249-7">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4378991249-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="4378991249-8">(</span><span class="p" data-group-id="4378991249-9">[</span><span class="p" data-group-id="4378991249-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4378991249-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8537462387-4">(</span><span class="p" data-group-id="8537462387-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8537462387-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8537462387-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8537462387-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8537462387-7">[</span><span class="n">H</span><span class="p" data-group-id="8537462387-7">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8537462387-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8537462387-8">(</span><span class="p" data-group-id="8537462387-9">[</span><span class="p" data-group-id="8537462387-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8537462387-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Each list element is copied only once. The growing result <code class="inline">Acc</code> is the right-hand
│ │ │ │ -side operand, which it is <em>not</em> copied.</p><p>Experienced Erlang programmers would probably write as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">vanilla_reverse</span><span class="p" data-group-id="7063648395-1">(</span><span class="p" data-group-id="7063648395-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7063648395-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7063648395-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="7063648395-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7063648395-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="7063648395-4">]</span><span class="p" data-group-id="7063648395-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="7063648395-5">(</span><span class="p" data-group-id="7063648395-6">[</span><span class="p" data-group-id="7063648395-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7063648395-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +side operand, which it is <em>not</em> copied.</p><p>Experienced Erlang programmers would probably write as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">vanilla_reverse</span><span class="p" data-group-id="7779420768-1">(</span><span class="p" data-group-id="7779420768-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7779420768-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7779420768-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="7779420768-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7779420768-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="7779420768-4">]</span><span class="p" data-group-id="7779420768-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="7779420768-5">(</span><span class="p" data-group-id="7779420768-6">[</span><span class="p" data-group-id="7779420768-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7779420768-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>In principle, this is slightly more efficient because the list element <code class="inline">[H]</code>
│ │ │ │  is not built before being copied and discarded. In practice, the compiler
│ │ │ │  rewrites <code class="inline">[H] ++ Acc</code> to <code class="inline">[H|Acc]</code>.</p><h2 id="timer-module" class="section-heading">
│ │ │ │    <a href="#timer-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Timer Module</span>
│ │ │ │ @@ -65,77 +65,77 @@
│ │ │ │  therefore harmless.</p><h2 id="accidental-copying-and-loss-of-sharing" class="section-heading">
│ │ │ │    <a href="#accidental-copying-and-loss-of-sharing" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Accidental Copying and Loss of Sharing</span>
│ │ │ │  </h2>
│ │ │ │  <p>When spawning a new process using a fun, one can accidentally copy more data to
│ │ │ │ -the process than intended. For example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental1</span><span class="p" data-group-id="5373244963-1">(</span><span class="n">State</span><span class="p" data-group-id="5373244963-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="5373244963-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5373244963-3">(</span><span class="p" data-group-id="5373244963-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5373244963-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5373244963-5">[</span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p" data-group-id="5373244963-5">]</span><span class="p" data-group-id="5373244963-4">)</span><span class="w">
│ │ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="5373244963-2">)</span><span class="p">.</span></code></pre><p>The code in the fun will extract one element from the record and print it. The
│ │ │ │ +the process than intended. For example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental1</span><span class="p" data-group-id="0677420447-1">(</span><span class="n">State</span><span class="p" data-group-id="0677420447-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="0677420447-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0677420447-3">(</span><span class="p" data-group-id="0677420447-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0677420447-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0677420447-5">[</span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p" data-group-id="0677420447-5">]</span><span class="p" data-group-id="0677420447-4">)</span><span class="w">
│ │ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="0677420447-2">)</span><span class="p">.</span></code></pre><p>The code in the fun will extract one element from the record and print it. The
│ │ │ │  rest of the <code class="inline">state</code> record is not used. However, when the <a href="../../../lib/../erts/doc/html/erlang.html#spawn/1"><code class="inline">spawn/1</code></a>
│ │ │ │ -function is executed, the entire record is copied to the newly created process.</p><p>The same kind of problem can happen with a map:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental2</span><span class="p" data-group-id="5095375366-1">(</span><span class="n">State</span><span class="p" data-group-id="5095375366-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="5095375366-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5095375366-3">(</span><span class="p" data-group-id="5095375366-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5095375366-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5095375366-5">[</span><span class="nf">map_get</span><span class="p" data-group-id="5095375366-6">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5095375366-6">)</span><span class="p" data-group-id="5095375366-5">]</span><span class="p" data-group-id="5095375366-4">)</span><span class="w">
│ │ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="5095375366-2">)</span><span class="p">.</span></code></pre><p>In the following example (part of a module implementing the <a href="../../../lib/stdlib/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │ │ -behavior) the created fun is sent to another process:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="3936193891-1">(</span><span class="ss">give_me_a_fun</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3936193891-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3936193891-2">(</span><span class="p" data-group-id="3936193891-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="nb">size</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3936193891-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3936193891-3">}</span><span class="p">.</span></code></pre><p>How bad that unnecessary copy is depends on the contents of the record or the
│ │ │ │ -map.</p><p>For example, if the <code class="inline">state</code> record is initialized like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init1</span><span class="p" data-group-id="9068422824-1">(</span><span class="p" data-group-id="9068422824-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="9068422824-2">{</span><span class="ss">data</span><span class="o">=</span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="9068422824-3">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">10000</span><span class="p" data-group-id="9068422824-3">)</span><span class="p" data-group-id="9068422824-2">}</span><span class="p">.</span></code></pre><p>a list with 10000 elements (or about 20000 heap words) will be copied to the
│ │ │ │ +function is executed, the entire record is copied to the newly created process.</p><p>The same kind of problem can happen with a map:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental2</span><span class="p" data-group-id="2852370228-1">(</span><span class="n">State</span><span class="p" data-group-id="2852370228-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="2852370228-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2852370228-3">(</span><span class="p" data-group-id="2852370228-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2852370228-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2852370228-5">[</span><span class="nf">map_get</span><span class="p" data-group-id="2852370228-6">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="2852370228-6">)</span><span class="p" data-group-id="2852370228-5">]</span><span class="p" data-group-id="2852370228-4">)</span><span class="w">
│ │ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="2852370228-2">)</span><span class="p">.</span></code></pre><p>In the following example (part of a module implementing the <a href="../../../lib/stdlib/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │ │ +behavior) the created fun is sent to another process:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="6927726637-1">(</span><span class="ss">give_me_a_fun</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6927726637-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6927726637-2">(</span><span class="p" data-group-id="6927726637-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="nb">size</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6927726637-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6927726637-3">}</span><span class="p">.</span></code></pre><p>How bad that unnecessary copy is depends on the contents of the record or the
│ │ │ │ +map.</p><p>For example, if the <code class="inline">state</code> record is initialized like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init1</span><span class="p" data-group-id="7973260812-1">(</span><span class="p" data-group-id="7973260812-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="7973260812-2">{</span><span class="ss">data</span><span class="o">=</span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="7973260812-3">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">10000</span><span class="p" data-group-id="7973260812-3">)</span><span class="p" data-group-id="7973260812-2">}</span><span class="p">.</span></code></pre><p>a list with 10000 elements (or about 20000 heap words) will be copied to the
│ │ │ │  newly created process.</p><p>An unnecessary copy of 10000 element list can be bad enough, but it can get even
│ │ │ │  worse if the <code class="inline">state</code> record contains <em>shared subterms</em>. Here is a simple example
│ │ │ │ -of a term with a shared subterm:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2711632252-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="2711632252-1">}</span></code></pre><p>When a term is copied to another process, sharing of subterms will be lost and
│ │ │ │ -the copied term can be many times larger than the original term. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init2</span><span class="p" data-group-id="2076352558-1">(</span><span class="p" data-group-id="2076352558-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SharedSubTerms</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="2076352558-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2076352558-3">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2076352558-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2076352558-4">[</span><span class="n">A</span><span class="p">|</span><span class="n">A</span><span class="p" data-group-id="2076352558-4">]</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2076352558-5">[</span><span class="mi">0</span><span class="p" data-group-id="2076352558-5">]</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2076352558-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">15</span><span class="p" data-group-id="2076352558-6">)</span><span class="p" data-group-id="2076352558-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="2076352558-7">{</span><span class="ss">data</span><span class="o">=</span><span class="n">Shared</span><span class="p" data-group-id="2076352558-7">}</span><span class="p">.</span></code></pre><p>In the process that calls <code class="inline">init2/0</code>, the size of the <code class="inline">data</code> field in the <code class="inline">state</code>
│ │ │ │ +of a term with a shared subterm:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8733117462-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="8733117462-1">}</span></code></pre><p>When a term is copied to another process, sharing of subterms will be lost and
│ │ │ │ +the copied term can be many times larger than the original term. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init2</span><span class="p" data-group-id="2088144812-1">(</span><span class="p" data-group-id="2088144812-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SharedSubTerms</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="2088144812-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2088144812-3">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2088144812-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2088144812-4">[</span><span class="n">A</span><span class="p">|</span><span class="n">A</span><span class="p" data-group-id="2088144812-4">]</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2088144812-5">[</span><span class="mi">0</span><span class="p" data-group-id="2088144812-5">]</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2088144812-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">15</span><span class="p" data-group-id="2088144812-6">)</span><span class="p" data-group-id="2088144812-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="2088144812-7">{</span><span class="ss">data</span><span class="o">=</span><span class="n">Shared</span><span class="p" data-group-id="2088144812-7">}</span><span class="p">.</span></code></pre><p>In the process that calls <code class="inline">init2/0</code>, the size of the <code class="inline">data</code> field in the <code class="inline">state</code>
│ │ │ │  record will be 32 heap words. When the record is copied to the newly created
│ │ │ │  process, sharing will be lost and the size of the copied <code class="inline">data</code> field will be
│ │ │ │  131070 heap words. More details about
│ │ │ │  <a href="eff_guide_processes.xhtml#loss-of-sharing">loss off sharing</a> are found in a later
│ │ │ │  section.</p><p>To avoid the problem, outside of the fun extract only the fields of the record
│ │ │ │ -that are actually used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental1</span><span class="p" data-group-id="3833489247-1">(</span><span class="n">State</span><span class="p" data-group-id="3833489247-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +that are actually used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental1</span><span class="p" data-group-id="9468295375-1">(</span><span class="n">State</span><span class="p" data-group-id="9468295375-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="3833489247-2">(</span><span class="nf">fun</span><span class="p" data-group-id="3833489247-3">(</span><span class="p" data-group-id="3833489247-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3833489247-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3833489247-5">[</span><span class="n">Info</span><span class="p" data-group-id="3833489247-5">]</span><span class="p" data-group-id="3833489247-4">)</span><span class="w">
│ │ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="3833489247-2">)</span><span class="p">.</span></code></pre><p>Similarly, outside of the fun extract only the map elements that are actually
│ │ │ │ -used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental2</span><span class="p" data-group-id="5789633545-1">(</span><span class="n">State</span><span class="p" data-group-id="5789633545-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">map_get</span><span class="p" data-group-id="5789633545-2">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5789633545-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="5789633545-3">(</span><span class="nf">fun</span><span class="p" data-group-id="5789633545-4">(</span><span class="p" data-group-id="5789633545-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5789633545-5">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5789633545-6">[</span><span class="n">Info</span><span class="p" data-group-id="5789633545-6">]</span><span class="p" data-group-id="5789633545-5">)</span><span class="w">
│ │ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="5789633545-3">)</span><span class="p">.</span></code></pre><h2 id="list_to_atom-1" class="section-heading">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9468295375-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9468295375-3">(</span><span class="p" data-group-id="9468295375-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9468295375-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9468295375-5">[</span><span class="n">Info</span><span class="p" data-group-id="9468295375-5">]</span><span class="p" data-group-id="9468295375-4">)</span><span class="w">
│ │ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="9468295375-2">)</span><span class="p">.</span></code></pre><p>Similarly, outside of the fun extract only the map elements that are actually
│ │ │ │ +used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental2</span><span class="p" data-group-id="3237109437-1">(</span><span class="n">State</span><span class="p" data-group-id="3237109437-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">map_get</span><span class="p" data-group-id="3237109437-2">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3237109437-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="3237109437-3">(</span><span class="nf">fun</span><span class="p" data-group-id="3237109437-4">(</span><span class="p" data-group-id="3237109437-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3237109437-5">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3237109437-6">[</span><span class="n">Info</span><span class="p" data-group-id="3237109437-6">]</span><span class="p" data-group-id="3237109437-5">)</span><span class="w">
│ │ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="3237109437-3">)</span><span class="p">.</span></code></pre><h2 id="list_to_atom-1" class="section-heading">
│ │ │ │    <a href="#list_to_atom-1" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">list_to_atom/1</span>
│ │ │ │  </h2>
│ │ │ │  <p>Atoms are not garbage-collected. Once an atom is created, it is never removed.
│ │ │ │  The emulator terminates if the limit for the number of atoms (1,048,576 by
│ │ │ │  default) is reached.</p><p>Therefore, converting arbitrary input strings to atoms can be dangerous in a
│ │ │ │  system that runs continuously. If only certain well-defined atoms are allowed as
│ │ │ │  input, <a href="../../../lib/../erts/doc/html/erlang.html#list_to_existing_atom/1"><code class="inline">list_to_existing_atom/1</code></a> or
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#binary_to_existing_atom/1"><code class="inline">binary_to_existing_atom/1</code></a> can be used
│ │ │ │  to guard against a denial-of-service attack. (All atoms that are allowed must
│ │ │ │  have been created earlier, for example, by using all of them in a module
│ │ │ │  and loading that module.)</p><p>Using <a href="../../../lib/../erts/doc/html/erlang.html#list_to_atom/1"><code class="inline">list_to_atom/1</code></a> to construct an atom that
│ │ │ │ -is passed to <a href="../../../lib/../erts/doc/html/erlang.html#apply/3"><code class="inline">apply/3</code></a> is quite expensive.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">apply</span><span class="p" data-group-id="1053962018-1">(</span><span class="nf">list_to_atom</span><span class="p" data-group-id="1053962018-2">(</span><span class="s">&quot;some_prefix&quot;</span><span class="o">++</span><span class="n">Var</span><span class="p" data-group-id="1053962018-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="1053962018-1">)</span></code></pre><h2 id="length-1" class="section-heading">
│ │ │ │ +is passed to <a href="../../../lib/../erts/doc/html/erlang.html#apply/3"><code class="inline">apply/3</code></a> is quite expensive.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">apply</span><span class="p" data-group-id="1504857563-1">(</span><span class="nf">list_to_atom</span><span class="p" data-group-id="1504857563-2">(</span><span class="s">&quot;some_prefix&quot;</span><span class="o">++</span><span class="n">Var</span><span class="p" data-group-id="1504857563-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="1504857563-1">)</span></code></pre><h2 id="length-1" class="section-heading">
│ │ │ │    <a href="#length-1" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">length/1</span>
│ │ │ │  </h2>
│ │ │ │  <p>The time for calculating the length of a list is proportional to the length of
│ │ │ │  the list, as opposed to <a href="../../../lib/../erts/doc/html/erlang.html#tuple_size/1"><code class="inline">tuple_size/1</code></a>,
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#byte_size/1"><code class="inline">byte_size/1</code></a>, and <a href="../../../lib/../erts/doc/html/erlang.html#bit_size/1"><code class="inline">bit_size/1</code></a>, which all
│ │ │ │  execute in constant time.</p><p>Normally, there is no need to worry about the speed of <a href="../../../lib/../erts/doc/html/erlang.html#length/1"><code class="inline">length/1</code></a>,
│ │ │ │  because it is efficiently implemented in C. In time-critical code, you might
│ │ │ │  want to avoid it if the input list could potentially be very long.</p><p>Some uses of <a href="../../../lib/../erts/doc/html/erlang.html#length/1"><code class="inline">length/1</code></a> can be replaced by matching. For example,
│ │ │ │ -the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="9293914392-1">(</span><span class="n">L</span><span class="p" data-group-id="9293914392-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9293914392-2">(</span><span class="n">L</span><span class="p" data-group-id="9293914392-2">)</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="7769410829-1">(</span><span class="p" data-group-id="7769410829-2">[</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="7769410829-2">]</span><span class="o">=</span><span class="n">L</span><span class="p" data-group-id="7769410829-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="2261791866-1">(</span><span class="n">L</span><span class="p" data-group-id="2261791866-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="2261791866-2">(</span><span class="n">L</span><span class="p" data-group-id="2261791866-2">)</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="5097821188-1">(</span><span class="p" data-group-id="5097821188-2">[</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="5097821188-2">]</span><span class="o">=</span><span class="n">L</span><span class="p" data-group-id="5097821188-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>One slight difference is that <a href="../../../lib/../erts/doc/html/erlang.html#length/1"><code class="inline">length(L)</code></a> fails if <code class="inline">L</code> is an
│ │ │ │  improper list, while the pattern in the second code fragment accepts an improper
│ │ │ │  list.</p><h2 id="setelement-3" class="section-heading">
│ │ │ │    <a href="#setelement-3" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">setelement/3</span>
│ │ │ │ @@ -143,18 +143,18 @@
│ │ │ │  <p><a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> copies the tuple it modifies. Therefore,
│ │ │ │  updating a tuple in a loop using <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> creates a new
│ │ │ │  copy of the tuple every time.</p><p>There is one exception to the rule that the tuple is copied. If the compiler
│ │ │ │  clearly can see that destructively updating the tuple would give the same result
│ │ │ │  as if the tuple was copied, the call to <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> is
│ │ │ │  replaced with a special destructive <code class="inline">setelement</code> instruction. In the following
│ │ │ │  code sequence, the first <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> call copies the tuple
│ │ │ │ -and modifies the ninth element:</p><pre><code class="makeup erlang" translate="no"><span class="nf">multiple_setelement</span><span class="p" data-group-id="7894574596-1">(</span><span class="n">T0</span><span class="p" data-group-id="7894574596-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="7894574596-2">(</span><span class="n">T0</span><span class="p" data-group-id="7894574596-2">)</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">T1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="7894574596-3">(</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p" data-group-id="7894574596-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">T2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="7894574596-4">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="ss">foobar</span><span class="p" data-group-id="7894574596-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">setelement</span><span class="p" data-group-id="7894574596-5">(</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p">,</span><span class="w"> </span><span class="ss">new_value</span><span class="p" data-group-id="7894574596-5">)</span><span class="p">.</span></code></pre><p>The two following <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> calls modify the tuple in
│ │ │ │ +and modifies the ninth element:</p><pre><code class="makeup erlang" translate="no"><span class="nf">multiple_setelement</span><span class="p" data-group-id="2512214237-1">(</span><span class="n">T0</span><span class="p" data-group-id="2512214237-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="2512214237-2">(</span><span class="n">T0</span><span class="p" data-group-id="2512214237-2">)</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">T1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="2512214237-3">(</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p" data-group-id="2512214237-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">T2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="2512214237-4">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="ss">foobar</span><span class="p" data-group-id="2512214237-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">setelement</span><span class="p" data-group-id="2512214237-5">(</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p">,</span><span class="w"> </span><span class="ss">new_value</span><span class="p" data-group-id="2512214237-5">)</span><span class="p">.</span></code></pre><p>The two following <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> calls modify the tuple in
│ │ │ │  place.</p><p>For the optimization to be applied, <em>all</em> the following conditions must be true:</p><ul><li>The tuple argument must be known to be a tuple of a known size.</li><li>The indices must be integer literals, not variables or expressions.</li><li>The indices must be given in descending order.</li><li>There must be no calls to another function in between the calls to
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a>.</li><li>The tuple returned from one <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> call must only be
│ │ │ │  used in the subsequent call to <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a>.</li></ul><p>If the code cannot be structured as in the <code class="inline">multiple_setelement/1</code> example, the
│ │ │ │  best way to modify multiple elements in a large tuple is to convert the tuple to
│ │ │ │  a list, modify the list, and convert it back to a tuple.</p><h2 id="size-1" class="section-heading">
│ │ │ │    <a href="#size-1" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ ├── OEBPS/code_loading.xhtml
│ │ │ │ @@ -27,16 +27,16 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Compilation</span>
│ │ │ │  </h2>
│ │ │ │  <p>Erlang programs must be <em>compiled</em> to object code. The compiler can generate a
│ │ │ │  new file that contains the object code. The current abstract machine, which runs
│ │ │ │  the object code, is called BEAM, therefore the object files get the suffix
│ │ │ │ -<code class="inline">.beam</code>. The compiler can also generate a binary which can be loaded directly.</p><p>The compiler is located in the module <a href="../../../lib/compiler/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><pre><code class="makeup erlang" translate="no"><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="1306201750-1">(</span><span class="n">Module</span><span class="p" data-group-id="1306201750-1">)</span><span class="w">
│ │ │ │ -</span><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="1306201750-2">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="1306201750-2">)</span></code></pre><p>The Erlang shell understands the command <code class="inline">c(Module)</code>, which both compiles and
│ │ │ │ +<code class="inline">.beam</code>. The compiler can also generate a binary which can be loaded directly.</p><p>The compiler is located in the module <a href="../../../lib/compiler/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><pre><code class="makeup erlang" translate="no"><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="3083302047-1">(</span><span class="n">Module</span><span class="p" data-group-id="3083302047-1">)</span><span class="w">
│ │ │ │ +</span><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="3083302047-2">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="3083302047-2">)</span></code></pre><p>The Erlang shell understands the command <code class="inline">c(Module)</code>, which both compiles and
│ │ │ │  loads <code class="inline">Module</code>.</p><p>There is also a module <code class="inline">make</code>, which provides a set of functions similar to the
│ │ │ │  UNIX type Make functions, see module <a href="../../../lib/tools/doc/html/make.html"><code class="inline">make</code></a> in Tools.</p><p>The compiler can also be accessed from the OS prompt using the
│ │ │ │  <a href="../../../lib/../erts/doc/html/erl_cmd.xhtml">erl</a> executable in ERTS.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -compile Module1...ModuleN</span><span class="w">
│ │ │ │  </span><span class="c1">% erl -make</span></code></pre><p>The <code class="inline">erlc</code> program provides way to compile modules from the OS
│ │ │ │  shell, see the <a href="../../../lib/../erts/doc/html/erlc_cmd.xhtml">erlc</a> executable in ERTS. It
│ │ │ │  understands a number of flags that can be used to define macros, add search
│ │ │ │  paths for include files, and more.</p><pre><code class="text">% erlc &lt;flags&gt; File1.erl...FileN.erl</code></pre><p><a href="" id="loading"></a></p><h2 id="code-loading" class="section-heading">
│ │ │ │ @@ -61,51 +61,51 @@
│ │ │ │  When a module is loaded into the system for the first time, the code becomes
│ │ │ │  'current'. If then a new instance of the module is loaded, the code of the
│ │ │ │  previous instance becomes 'old' and the new instance becomes 'current'.</p><p>Both old and current code is valid, and can be evaluated concurrently. Fully
│ │ │ │  qualified function calls always refer to current code. Old code can still be
│ │ │ │  evaluated because of processes lingering in the old code.</p><p>If a third instance of the module is loaded, the code server removes (purges)
│ │ │ │  the old code and any processes lingering in it is terminated. Then the third
│ │ │ │  instance becomes 'current' and the previously current code becomes 'old'.</p><p>To change from old code to current code, a process must make a fully qualified
│ │ │ │ -function call.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1558253738-1">(</span><span class="ss">m</span><span class="p" data-group-id="1558253738-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1558253738-2">(</span><span class="p" data-group-id="1558253738-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1558253738-3">]</span><span class="p" data-group-id="1558253738-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +function call.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2666407018-1">(</span><span class="ss">m</span><span class="p" data-group-id="2666407018-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2666407018-2">(</span><span class="p" data-group-id="2666407018-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2666407018-3">]</span><span class="p" data-group-id="2666407018-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="1558253738-4">(</span><span class="p" data-group-id="1558253738-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="2666407018-4">(</span><span class="p" data-group-id="2666407018-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">code_switch</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">m</span><span class="p">:</span><span class="nf">loop</span><span class="p" data-group-id="1558253738-5">(</span><span class="p" data-group-id="1558253738-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="nc">m</span><span class="p">:</span><span class="nf">loop</span><span class="p" data-group-id="2666407018-5">(</span><span class="p" data-group-id="2666407018-5">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="n">Msg</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="1558253738-6">(</span><span class="p" data-group-id="1558253738-6">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="2666407018-6">(</span><span class="p" data-group-id="2666407018-6">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>To make the process change code, send the message <code class="inline">code_switch</code> to it. The
│ │ │ │  process then makes a fully qualified call to <code class="inline">m:loop()</code> and changes to current
│ │ │ │  code. Notice that <code class="inline">m:loop/0</code> must be exported.</p><p>For code replacement of funs to work, use the syntax
│ │ │ │  <code class="inline">fun Module:FunctionName/Arity</code>.</p><p><a href="" id="on_load"></a></p><h2 id="running-a-function-when-a-module-is-loaded" class="section-heading">
│ │ │ │    <a href="#running-a-function-when-a-module-is-loaded" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Running a Function When a Module is Loaded</span>
│ │ │ │  </h2>
│ │ │ │  <p>The <code class="inline">-on_load()</code> directive names a function that is to be run automatically when
│ │ │ │ -a module is loaded.</p><p>Its syntax is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="9403823917-1">(</span><span class="n">Name</span><span class="o">/</span><span class="mi">0</span><span class="p" data-group-id="9403823917-1">)</span><span class="p">.</span></code></pre><p>It is not necessary to export the function. It is called in a freshly spawned
│ │ │ │ +a module is loaded.</p><p>Its syntax is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="1281808519-1">(</span><span class="n">Name</span><span class="o">/</span><span class="mi">0</span><span class="p" data-group-id="1281808519-1">)</span><span class="p">.</span></code></pre><p>It is not necessary to export the function. It is called in a freshly spawned
│ │ │ │  process (which terminates as soon as the function returns).</p><p>The function must return <code class="inline">ok</code> if the module is to become the new current code
│ │ │ │  for the module and become callable.</p><p>Returning any other value or generating an exception causes the new code to be
│ │ │ │  unloaded. If the return value is not an atom, a warning error report is sent to
│ │ │ │  the error logger.</p><p>If there already is current code for the module, that code will remain current
│ │ │ │  and can be called until the <code class="inline">on_load</code> function has returned. If the <code class="inline">on_load</code>
│ │ │ │  function fails, the current code (if any) will remain current. If there is no
│ │ │ │  current code for a module, any process that makes an external call to the module
│ │ │ │  before the <code class="inline">on_load</code> function has finished will be suspended until the <code class="inline">on_load</code>
│ │ │ │  function have finished.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 19, if the <code class="inline">on_load</code> function failed, any previously current
│ │ │ │  code would become old, essentially leaving the system without any working and
│ │ │ │  reachable instance of the module.</p></section><p>In embedded mode, first all modules are loaded. Then all <code class="inline">on_load</code> functions are
│ │ │ │  called. The system is terminated unless all of the <code class="inline">on_load</code> functions return
│ │ │ │ -<code class="inline">ok</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0279177211-1">(</span><span class="ss">m</span><span class="p" data-group-id="0279177211-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="0279177211-2">(</span><span class="ss">load_my_nifs</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0279177211-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">ok</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3832558499-1">(</span><span class="ss">m</span><span class="p" data-group-id="3832558499-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="3832558499-2">(</span><span class="ss">load_my_nifs</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3832558499-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">load_my_nifs</span><span class="p" data-group-id="0279177211-3">(</span><span class="p" data-group-id="0279177211-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">load_my_nifs</span><span class="p" data-group-id="3832558499-3">(</span><span class="p" data-group-id="3832558499-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NifPath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">    </span><span class="c1">%Set up the path to the NIF library.</span><span class="w">
│ │ │ │      </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">       </span><span class="c1">%Initialize the Info term</span><span class="w">
│ │ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="0279177211-4">(</span><span class="n">NifPath</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="0279177211-4">)</span><span class="p">.</span></code></pre><p>If the call to <a href="../../../lib/../erts/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a> fails, the module is unloaded and a warning
│ │ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="3832558499-4">(</span><span class="n">NifPath</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="3832558499-4">)</span><span class="p">.</span></code></pre><p>If the call to <a href="../../../lib/../erts/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a> fails, the module is unloaded and a warning
│ │ │ │  report is sent to the error loader.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/c_portdriver.xhtml
│ │ │ │ @@ -56,112 +56,112 @@
│ │ │ │  <p>Like a port program, the port communicates with an Erlang process. All
│ │ │ │  communication goes through one Erlang process that is the <em>connected process</em> of
│ │ │ │  the port driver. Terminating this process closes the port driver.</p><p>Before the port is created, the driver must be loaded. This is done with the
│ │ │ │  function <a href="../../../lib/kernel/doc/html/erl_ddll.html#load_driver/2"><code class="inline">erl_ddll:load_driver/2</code></a>, with the name of the shared library as
│ │ │ │  argument.</p><p>The port is then created using the BIF <a href="../../../lib/../erts/doc/html/erlang.html#open_port/2"><code class="inline">open_port/2</code></a>, with the
│ │ │ │  tuple <code class="inline">{spawn, DriverName}</code> as the first argument. The string <code class="inline">SharedLib</code> is the
│ │ │ │  name of the port driver. The second argument is a list of options, none in this
│ │ │ │ -case:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0615340870-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="0615340870-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0615340870-2">(</span><span class="p" data-group-id="0615340870-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0615340870-3">]</span><span class="p" data-group-id="0615340870-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +case:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7124801893-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="7124801893-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7124801893-2">(</span><span class="p" data-group-id="7124801893-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7124801893-3">]</span><span class="p" data-group-id="7124801893-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="0615340870-4">(</span><span class="n">SharedLib</span><span class="p" data-group-id="0615340870-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="0615340870-5">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="0615340870-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="7124801893-4">(</span><span class="n">SharedLib</span><span class="p" data-group-id="7124801893-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="7124801893-5">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="7124801893-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0615340870-6">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="0615340870-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="0615340870-7">(</span><span class="p" data-group-id="0615340870-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="0615340870-8">}</span><span class="p" data-group-id="0615340870-7">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7124801893-6">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="7124801893-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="7124801893-7">(</span><span class="p" data-group-id="7124801893-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="7124801893-8">}</span><span class="p" data-group-id="7124801893-7">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="0615340870-9">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0615340870-10">[</span><span class="n">SharedLib</span><span class="p" data-group-id="0615340870-10">]</span><span class="p" data-group-id="0615340870-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="7124801893-9">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7124801893-10">[</span><span class="n">SharedLib</span><span class="p" data-group-id="7124801893-10">]</span><span class="p" data-group-id="7124801893-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="0615340870-11">(</span><span class="n">SharedLib</span><span class="p" data-group-id="0615340870-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nf">register</span><span class="p" data-group-id="0615340870-12">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0615340870-13">(</span><span class="p" data-group-id="0615340870-13">)</span><span class="p" data-group-id="0615340870-12">)</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="0615340870-14">(</span><span class="p" data-group-id="0615340870-15">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="0615340870-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0615340870-16">[</span><span class="p" data-group-id="0615340870-16">]</span><span class="p" data-group-id="0615340870-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="nf">loop</span><span class="p" data-group-id="0615340870-17">(</span><span class="n">Port</span><span class="p" data-group-id="0615340870-17">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex5:foo/1</code> and <code class="inline">complex5:bar/1</code> can be implemented. Both send a
│ │ │ │ -message to the <code class="inline">complex</code> process and receive the following reply:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="0349679056-1">(</span><span class="n">X</span><span class="p" data-group-id="0349679056-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="0349679056-2">(</span><span class="p" data-group-id="0349679056-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0349679056-3">}</span><span class="p" data-group-id="0349679056-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="0349679056-4">(</span><span class="n">Y</span><span class="p" data-group-id="0349679056-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="0349679056-5">(</span><span class="p" data-group-id="0349679056-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0349679056-6">}</span><span class="p" data-group-id="0349679056-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="7124801893-11">(</span><span class="n">SharedLib</span><span class="p" data-group-id="7124801893-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nf">register</span><span class="p" data-group-id="7124801893-12">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7124801893-13">(</span><span class="p" data-group-id="7124801893-13">)</span><span class="p" data-group-id="7124801893-12">)</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="7124801893-14">(</span><span class="p" data-group-id="7124801893-15">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="7124801893-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7124801893-16">[</span><span class="p" data-group-id="7124801893-16">]</span><span class="p" data-group-id="7124801893-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="nf">loop</span><span class="p" data-group-id="7124801893-17">(</span><span class="n">Port</span><span class="p" data-group-id="7124801893-17">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex5:foo/1</code> and <code class="inline">complex5:bar/1</code> can be implemented. Both send a
│ │ │ │ +message to the <code class="inline">complex</code> process and receive the following reply:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="4562491566-1">(</span><span class="n">X</span><span class="p" data-group-id="4562491566-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="4562491566-2">(</span><span class="p" data-group-id="4562491566-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4562491566-3">}</span><span class="p" data-group-id="4562491566-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="4562491566-4">(</span><span class="n">Y</span><span class="p" data-group-id="4562491566-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="4562491566-5">(</span><span class="p" data-group-id="4562491566-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4562491566-6">}</span><span class="p" data-group-id="4562491566-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="0349679056-7">(</span><span class="n">Msg</span><span class="p" data-group-id="0349679056-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0349679056-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0349679056-9">(</span><span class="p" data-group-id="0349679056-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="0349679056-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="4562491566-7">(</span><span class="n">Msg</span><span class="p" data-group-id="4562491566-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4562491566-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4562491566-9">(</span><span class="p" data-group-id="4562491566-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4562491566-8">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0349679056-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0349679056-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4562491566-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="4562491566-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">Result</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process performs the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="9549264636-1">(</span><span class="n">Port</span><span class="p" data-group-id="9549264636-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process performs the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="3997957988-1">(</span><span class="n">Port</span><span class="p" data-group-id="3997957988-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9549264636-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9549264636-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9549264636-3">{</span><span class="nf">self</span><span class="p" data-group-id="9549264636-4">(</span><span class="p" data-group-id="9549264636-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9549264636-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="9549264636-6">(</span><span class="n">Msg</span><span class="p" data-group-id="9549264636-6">)</span><span class="p" data-group-id="9549264636-5">}</span><span class="p" data-group-id="9549264636-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3997957988-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3997957988-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3997957988-3">{</span><span class="nf">self</span><span class="p" data-group-id="3997957988-4">(</span><span class="p" data-group-id="3997957988-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3997957988-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="3997957988-6">(</span><span class="n">Msg</span><span class="p" data-group-id="3997957988-6">)</span><span class="p" data-group-id="3997957988-5">}</span><span class="p" data-group-id="3997957988-3">}</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="k">receive</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="9549264636-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9549264636-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9549264636-8">}</span><span class="p" data-group-id="9549264636-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9549264636-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="9549264636-10">(</span><span class="n">Data</span><span class="p" data-group-id="9549264636-10">)</span><span class="p" data-group-id="9549264636-9">}</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="3997957988-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3997957988-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3997957988-8">}</span><span class="p" data-group-id="3997957988-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3997957988-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="3997957988-10">(</span><span class="n">Data</span><span class="p" data-group-id="3997957988-10">)</span><span class="p" data-group-id="3997957988-9">}</span><span class="w">
│ │ │ │              </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="9549264636-11">(</span><span class="n">Port</span><span class="p" data-group-id="9549264636-11">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="3997957988-11">(</span><span class="n">Port</span><span class="p" data-group-id="3997957988-11">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Assuming that both the arguments and the results from the C functions are less
│ │ │ │  than 256, a simple encoding/decoding scheme is employed. In this scheme, <code class="inline">foo</code>
│ │ │ │  is represented by byte 1, <code class="inline">bar</code> is represented by 2, and the argument/result is
│ │ │ │ -represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="0106666256-1">(</span><span class="p" data-group-id="0106666256-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0106666256-2">}</span><span class="p" data-group-id="0106666256-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0106666256-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0106666256-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="0106666256-4">(</span><span class="p" data-group-id="0106666256-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0106666256-5">}</span><span class="p" data-group-id="0106666256-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0106666256-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0106666256-6">]</span><span class="p">.</span><span class="w">
│ │ │ │ +represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="3298533763-1">(</span><span class="p" data-group-id="3298533763-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3298533763-2">}</span><span class="p" data-group-id="3298533763-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3298533763-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3298533763-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="3298533763-4">(</span><span class="p" data-group-id="3298533763-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3298533763-5">}</span><span class="p" data-group-id="3298533763-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3298533763-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3298533763-6">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="0106666256-7">(</span><span class="p" data-group-id="0106666256-8">[</span><span class="n">Int</span><span class="p" data-group-id="0106666256-8">]</span><span class="p" data-group-id="0106666256-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functions for stopping the port and
│ │ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="3298533763-7">(</span><span class="p" data-group-id="3298533763-8">[</span><span class="n">Int</span><span class="p" data-group-id="3298533763-8">]</span><span class="p" data-group-id="3298533763-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functions for stopping the port and
│ │ │ │  detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8528260444-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="8528260444-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8528260444-2">(</span><span class="p" data-group-id="8528260444-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8528260444-3">]</span><span class="p" data-group-id="8528260444-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8528260444-4">(</span><span class="p" data-group-id="8528260444-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8528260444-5">]</span><span class="p" data-group-id="8528260444-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6718761887-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="6718761887-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6718761887-2">(</span><span class="p" data-group-id="6718761887-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6718761887-3">]</span><span class="p" data-group-id="6718761887-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6718761887-4">(</span><span class="p" data-group-id="6718761887-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6718761887-5">]</span><span class="p" data-group-id="6718761887-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="8528260444-6">(</span><span class="n">SharedLib</span><span class="p" data-group-id="8528260444-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="8528260444-7">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="8528260444-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="6718761887-6">(</span><span class="n">SharedLib</span><span class="p" data-group-id="6718761887-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="6718761887-7">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="6718761887-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │  	</span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="8528260444-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="8528260444-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="8528260444-9">(</span><span class="p" data-group-id="8528260444-10">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="8528260444-10">}</span><span class="p" data-group-id="8528260444-9">)</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="6718761887-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="6718761887-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ +	</span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="6718761887-9">(</span><span class="p" data-group-id="6718761887-10">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="6718761887-10">}</span><span class="p" data-group-id="6718761887-9">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="8528260444-11">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8528260444-12">[</span><span class="n">SharedLib</span><span class="p" data-group-id="8528260444-12">]</span><span class="p" data-group-id="8528260444-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="6718761887-11">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6718761887-12">[</span><span class="n">SharedLib</span><span class="p" data-group-id="6718761887-12">]</span><span class="p" data-group-id="6718761887-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8528260444-13">(</span><span class="n">SharedLib</span><span class="p" data-group-id="8528260444-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="8528260444-14">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8528260444-15">(</span><span class="p" data-group-id="8528260444-15">)</span><span class="p" data-group-id="8528260444-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="8528260444-16">(</span><span class="p" data-group-id="8528260444-17">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="8528260444-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8528260444-18">[</span><span class="p" data-group-id="8528260444-18">]</span><span class="p" data-group-id="8528260444-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="8528260444-19">(</span><span class="n">Port</span><span class="p" data-group-id="8528260444-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="6718761887-13">(</span><span class="n">SharedLib</span><span class="p" data-group-id="6718761887-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="6718761887-14">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6718761887-15">(</span><span class="p" data-group-id="6718761887-15">)</span><span class="p" data-group-id="6718761887-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="6718761887-16">(</span><span class="p" data-group-id="6718761887-17">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="6718761887-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6718761887-18">[</span><span class="p" data-group-id="6718761887-18">]</span><span class="p" data-group-id="6718761887-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="6718761887-19">(</span><span class="n">Port</span><span class="p" data-group-id="6718761887-19">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="8528260444-20">(</span><span class="p" data-group-id="8528260444-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="6718761887-20">(</span><span class="p" data-group-id="6718761887-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="8528260444-21">(</span><span class="n">X</span><span class="p" data-group-id="8528260444-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="8528260444-22">(</span><span class="p" data-group-id="8528260444-23">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8528260444-23">}</span><span class="p" data-group-id="8528260444-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="8528260444-24">(</span><span class="n">Y</span><span class="p" data-group-id="8528260444-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="8528260444-25">(</span><span class="p" data-group-id="8528260444-26">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8528260444-26">}</span><span class="p" data-group-id="8528260444-25">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="6718761887-21">(</span><span class="n">X</span><span class="p" data-group-id="6718761887-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="6718761887-22">(</span><span class="p" data-group-id="6718761887-23">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6718761887-23">}</span><span class="p" data-group-id="6718761887-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="6718761887-24">(</span><span class="n">Y</span><span class="p" data-group-id="6718761887-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="6718761887-25">(</span><span class="p" data-group-id="6718761887-26">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6718761887-26">}</span><span class="p" data-group-id="6718761887-25">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="8528260444-27">(</span><span class="n">Msg</span><span class="p" data-group-id="8528260444-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8528260444-28">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8528260444-29">(</span><span class="p" data-group-id="8528260444-29">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8528260444-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="6718761887-27">(</span><span class="n">Msg</span><span class="p" data-group-id="6718761887-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6718761887-28">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6718761887-29">(</span><span class="p" data-group-id="6718761887-29">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6718761887-28">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="8528260444-30">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8528260444-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="6718761887-30">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6718761887-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="8528260444-31">(</span><span class="n">Port</span><span class="p" data-group-id="8528260444-31">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="6718761887-31">(</span><span class="n">Port</span><span class="p" data-group-id="6718761887-31">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="8528260444-32">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8528260444-32">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8528260444-33">{</span><span class="nf">self</span><span class="p" data-group-id="8528260444-34">(</span><span class="p" data-group-id="8528260444-34">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8528260444-35">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="8528260444-36">(</span><span class="n">Msg</span><span class="p" data-group-id="8528260444-36">)</span><span class="p" data-group-id="8528260444-35">}</span><span class="p" data-group-id="8528260444-33">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="6718761887-32">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6718761887-32">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6718761887-33">{</span><span class="nf">self</span><span class="p" data-group-id="6718761887-34">(</span><span class="p" data-group-id="6718761887-34">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6718761887-35">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="6718761887-36">(</span><span class="n">Msg</span><span class="p" data-group-id="6718761887-36">)</span><span class="p" data-group-id="6718761887-35">}</span><span class="p" data-group-id="6718761887-33">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="8528260444-37">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8528260444-38">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8528260444-38">}</span><span class="p" data-group-id="8528260444-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8528260444-39">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="8528260444-40">(</span><span class="n">Data</span><span class="p" data-group-id="8528260444-40">)</span><span class="p" data-group-id="8528260444-39">}</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="6718761887-37">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6718761887-38">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6718761887-38">}</span><span class="p" data-group-id="6718761887-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6718761887-39">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="6718761887-40">(</span><span class="n">Data</span><span class="p" data-group-id="6718761887-40">)</span><span class="p" data-group-id="6718761887-39">}</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="8528260444-41">(</span><span class="n">Port</span><span class="p" data-group-id="8528260444-41">)</span><span class="p">;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="6718761887-41">(</span><span class="n">Port</span><span class="p" data-group-id="6718761887-41">)</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8528260444-42">{</span><span class="nf">self</span><span class="p" data-group-id="8528260444-43">(</span><span class="p" data-group-id="8528260444-43">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="8528260444-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6718761887-42">{</span><span class="nf">self</span><span class="p" data-group-id="6718761887-43">(</span><span class="p" data-group-id="6718761887-43">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="6718761887-42">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="8528260444-44">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="8528260444-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="8528260444-45">(</span><span class="ss">normal</span><span class="p" data-group-id="8528260444-45">)</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="6718761887-44">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="6718761887-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="6718761887-45">(</span><span class="ss">normal</span><span class="p" data-group-id="6718761887-45">)</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="8528260444-46">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="8528260444-46">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8528260444-47">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8528260444-48">[</span><span class="n">Reason</span><span class="p" data-group-id="8528260444-48">]</span><span class="p" data-group-id="8528260444-47">)</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="8528260444-49">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="8528260444-49">)</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="6718761887-46">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="6718761887-46">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6718761887-47">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6718761887-48">[</span><span class="n">Reason</span><span class="p" data-group-id="6718761887-48">]</span><span class="p" data-group-id="6718761887-47">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="6718761887-49">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="6718761887-49">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="8528260444-50">(</span><span class="p" data-group-id="8528260444-51">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8528260444-51">}</span><span class="p" data-group-id="8528260444-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8528260444-52">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8528260444-52">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="8528260444-53">(</span><span class="p" data-group-id="8528260444-54">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8528260444-54">}</span><span class="p" data-group-id="8528260444-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8528260444-55">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8528260444-55">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="6718761887-50">(</span><span class="p" data-group-id="6718761887-51">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6718761887-51">}</span><span class="p" data-group-id="6718761887-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6718761887-52">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6718761887-52">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="6718761887-53">(</span><span class="p" data-group-id="6718761887-54">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6718761887-54">}</span><span class="p" data-group-id="6718761887-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6718761887-55">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6718761887-55">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="8528260444-56">(</span><span class="p" data-group-id="8528260444-57">[</span><span class="n">Int</span><span class="p" data-group-id="8528260444-57">]</span><span class="p" data-group-id="8528260444-56">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-driver" class="section-heading">
│ │ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="6718761887-56">(</span><span class="p" data-group-id="6718761887-57">[</span><span class="n">Int</span><span class="p" data-group-id="6718761887-57">]</span><span class="p" data-group-id="6718761887-56">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-driver" class="section-heading">
│ │ │ │    <a href="#c-driver" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">C Driver</span>
│ │ │ │  </h2>
│ │ │ │  <p>The C driver is a module that is compiled and linked into a shared library. It
│ │ │ │  uses a driver structure and includes the header file <code class="inline">erl_driver.h</code>.</p><p>The driver structure is filled with the driver name and function pointers. It is
│ │ │ │ @@ -252,22 +252,22 @@
│ │ │ │    <a href="#running-the-example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Running the Example</span>
│ │ │ │  </h2>
│ │ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">unix&gt; gcc -o example_drv.so -fpic -shared complex.c port_driver.c
│ │ │ │  windows&gt; cl -LD -MD -Fe example_drv.dll complex.c port_driver.c</code></pre><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="ss">erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="6877466630-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="6877466630-1">]</span><span class="w"> </span><span class="p" data-group-id="6877466630-2">[</span><span class="ss">source</span><span class="p" data-group-id="6877466630-2">]</span><span class="w"> </span><span class="p" data-group-id="6877466630-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="6877466630-3">]</span><span class="w"> </span><span class="p" data-group-id="6877466630-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="6877466630-4">]</span><span class="w"> </span><span class="p" data-group-id="6877466630-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="6877466630-5">]</span><span class="w"> </span><span class="p" data-group-id="6877466630-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6877466630-6">]</span><span class="w"> </span><span class="p" data-group-id="6877466630-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="6877466630-7">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="8301259147-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="8301259147-1">]</span><span class="w"> </span><span class="p" data-group-id="8301259147-2">[</span><span class="ss">source</span><span class="p" data-group-id="8301259147-2">]</span><span class="w"> </span><span class="p" data-group-id="8301259147-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="8301259147-3">]</span><span class="w"> </span><span class="p" data-group-id="8301259147-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="8301259147-4">]</span><span class="w"> </span><span class="p" data-group-id="8301259147-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="8301259147-5">]</span><span class="w"> </span><span class="p" data-group-id="8301259147-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8301259147-6">]</span><span class="w"> </span><span class="p" data-group-id="8301259147-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="8301259147-7">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="6877466630-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="6877466630-9">(</span><span class="p" data-group-id="6877466630-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="6877466630-8">)</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="nf">c</span><span class="p" data-group-id="6877466630-10">(</span><span class="ss">complex5</span><span class="p" data-group-id="6877466630-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6877466630-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex5</span><span class="p" data-group-id="6877466630-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0614687562-1">(</span><span class="s">&quot;example_drv&quot;</span><span class="p" data-group-id="0614687562-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="8301259147-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="8301259147-9">(</span><span class="p" data-group-id="8301259147-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="8301259147-8">)</span><span class="gp unselectable">
│ │ │ │ +1&gt; </span><span class="nf">c</span><span class="p" data-group-id="8301259147-10">(</span><span class="ss">complex5</span><span class="p" data-group-id="8301259147-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8301259147-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex5</span><span class="p" data-group-id="8301259147-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1397425959-1">(</span><span class="s">&quot;example_drv&quot;</span><span class="p" data-group-id="1397425959-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="0614687562-2">(</span><span class="mi">3</span><span class="p" data-group-id="0614687562-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="1397425959-2">(</span><span class="mi">3</span><span class="p" data-group-id="1397425959-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="0614687562-3">(</span><span class="mi">5</span><span class="p" data-group-id="0614687562-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="1397425959-3">(</span><span class="mi">5</span><span class="p" data-group-id="1397425959-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">10</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="0614687562-4">(</span><span class="p" data-group-id="0614687562-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="1397425959-4">(</span><span class="p" data-group-id="1397425959-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/c_port.xhtml
│ │ │ │ @@ -53,101 +53,101 @@
│ │ │ │  external program, if it is written properly).</p><p>The port is created using the BIF <a href="../../../lib/../erts/doc/html/erlang.html#open_port/2"><code class="inline">open_port/2</code></a> with
│ │ │ │  <code class="inline">{spawn,ExtPrg}</code> as the first argument. The string <code class="inline">ExtPrg</code> is the name of the
│ │ │ │  external program, including any command line arguments. The second argument is a
│ │ │ │  list of options, in this case only <code class="inline">{packet,2}</code>. This option says that a 2 byte
│ │ │ │  length indicator is to be used to simplify the communication between C and
│ │ │ │  Erlang. The Erlang port automatically adds the length indicator, but this must
│ │ │ │  be done explicitly in the external C program.</p><p>The process is also set to trap exits, which enables detection of failure of the
│ │ │ │ -external program:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0711459628-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="0711459628-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0711459628-2">(</span><span class="p" data-group-id="0711459628-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0711459628-3">]</span><span class="p" data-group-id="0711459628-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +external program:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7357254712-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="7357254712-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7357254712-2">(</span><span class="p" data-group-id="7357254712-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7357254712-3">]</span><span class="p" data-group-id="7357254712-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="0711459628-4">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="0711459628-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nf">spawn</span><span class="p" data-group-id="0711459628-5">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0711459628-6">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="0711459628-6">]</span><span class="p" data-group-id="0711459628-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="7357254712-4">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="7357254712-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nf">spawn</span><span class="p" data-group-id="7357254712-5">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7357254712-6">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="7357254712-6">]</span><span class="p" data-group-id="7357254712-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="0711459628-7">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="0711459628-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nf">register</span><span class="p" data-group-id="0711459628-8">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0711459628-9">(</span><span class="p" data-group-id="0711459628-9">)</span><span class="p" data-group-id="0711459628-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="nf">process_flag</span><span class="p" data-group-id="0711459628-10">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0711459628-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="0711459628-11">(</span><span class="p" data-group-id="0711459628-12">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="0711459628-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0711459628-13">[</span><span class="p" data-group-id="0711459628-14">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0711459628-14">}</span><span class="p" data-group-id="0711459628-13">]</span><span class="p" data-group-id="0711459628-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="nf">loop</span><span class="p" data-group-id="0711459628-15">(</span><span class="n">Port</span><span class="p" data-group-id="0711459628-15">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex1:foo/1</code> and <code class="inline">complex1:bar/1</code> can be implemented. Both send a
│ │ │ │ -message to the <code class="inline">complex</code> process and receive the following replies:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="0370314703-1">(</span><span class="n">X</span><span class="p" data-group-id="0370314703-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nf">call_port</span><span class="p" data-group-id="0370314703-2">(</span><span class="p" data-group-id="0370314703-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0370314703-3">}</span><span class="p" data-group-id="0370314703-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="0370314703-4">(</span><span class="n">Y</span><span class="p" data-group-id="0370314703-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nf">call_port</span><span class="p" data-group-id="0370314703-5">(</span><span class="p" data-group-id="0370314703-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0370314703-6">}</span><span class="p" data-group-id="0370314703-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="7357254712-7">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="7357254712-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nf">register</span><span class="p" data-group-id="7357254712-8">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7357254712-9">(</span><span class="p" data-group-id="7357254712-9">)</span><span class="p" data-group-id="7357254712-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="nf">process_flag</span><span class="p" data-group-id="7357254712-10">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7357254712-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="7357254712-11">(</span><span class="p" data-group-id="7357254712-12">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="7357254712-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7357254712-13">[</span><span class="p" data-group-id="7357254712-14">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7357254712-14">}</span><span class="p" data-group-id="7357254712-13">]</span><span class="p" data-group-id="7357254712-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="nf">loop</span><span class="p" data-group-id="7357254712-15">(</span><span class="n">Port</span><span class="p" data-group-id="7357254712-15">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex1:foo/1</code> and <code class="inline">complex1:bar/1</code> can be implemented. Both send a
│ │ │ │ +message to the <code class="inline">complex</code> process and receive the following replies:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="3424818820-1">(</span><span class="n">X</span><span class="p" data-group-id="3424818820-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nf">call_port</span><span class="p" data-group-id="3424818820-2">(</span><span class="p" data-group-id="3424818820-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3424818820-3">}</span><span class="p" data-group-id="3424818820-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="3424818820-4">(</span><span class="n">Y</span><span class="p" data-group-id="3424818820-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nf">call_port</span><span class="p" data-group-id="3424818820-5">(</span><span class="p" data-group-id="3424818820-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3424818820-6">}</span><span class="p" data-group-id="3424818820-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="0370314703-7">(</span><span class="n">Msg</span><span class="p" data-group-id="0370314703-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0370314703-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0370314703-9">(</span><span class="p" data-group-id="0370314703-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="0370314703-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="3424818820-7">(</span><span class="n">Msg</span><span class="p" data-group-id="3424818820-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3424818820-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3424818820-9">(</span><span class="p" data-group-id="3424818820-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3424818820-8">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0370314703-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0370314703-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3424818820-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="3424818820-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │        </span><span class="n">Result</span><span class="w">
│ │ │ │ -  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process does the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="7624027803-1">(</span><span class="n">Port</span><span class="p" data-group-id="7624027803-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process does the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="1639783058-1">(</span><span class="n">Port</span><span class="p" data-group-id="1639783058-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7624027803-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7624027803-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -      </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7624027803-3">{</span><span class="nf">self</span><span class="p" data-group-id="7624027803-4">(</span><span class="p" data-group-id="7624027803-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7624027803-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="7624027803-6">(</span><span class="n">Msg</span><span class="p" data-group-id="7624027803-6">)</span><span class="p" data-group-id="7624027803-5">}</span><span class="p" data-group-id="7624027803-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1639783058-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1639783058-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +      </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1639783058-3">{</span><span class="nf">self</span><span class="p" data-group-id="1639783058-4">(</span><span class="p" data-group-id="1639783058-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1639783058-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="1639783058-6">(</span><span class="n">Msg</span><span class="p" data-group-id="1639783058-6">)</span><span class="p" data-group-id="1639783058-5">}</span><span class="p" data-group-id="1639783058-3">}</span><span class="p">,</span><span class="w">
│ │ │ │        </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7624027803-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7624027803-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7624027803-8">}</span><span class="p" data-group-id="7624027803-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -          </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7624027803-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="7624027803-10">(</span><span class="n">Data</span><span class="p" data-group-id="7624027803-10">)</span><span class="p" data-group-id="7624027803-9">}</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="1639783058-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1639783058-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1639783058-8">}</span><span class="p" data-group-id="1639783058-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +          </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1639783058-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="1639783058-10">(</span><span class="n">Data</span><span class="p" data-group-id="1639783058-10">)</span><span class="p" data-group-id="1639783058-9">}</span><span class="w">
│ │ │ │        </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -      </span><span class="nf">loop</span><span class="p" data-group-id="7624027803-11">(</span><span class="n">Port</span><span class="p" data-group-id="7624027803-11">)</span><span class="w">
│ │ │ │ +      </span><span class="nf">loop</span><span class="p" data-group-id="1639783058-11">(</span><span class="n">Port</span><span class="p" data-group-id="1639783058-11">)</span><span class="w">
│ │ │ │    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Assuming that both the arguments and the results from the C functions are less
│ │ │ │  than 256, a simple encoding/decoding scheme is employed. In this scheme, <code class="inline">foo</code>
│ │ │ │  is represented by byte 1, <code class="inline">bar</code> is represented by 2, and the argument/result is
│ │ │ │ -represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="3626228198-1">(</span><span class="p" data-group-id="3626228198-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3626228198-2">}</span><span class="p" data-group-id="3626228198-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3626228198-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3626228198-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="3626228198-4">(</span><span class="p" data-group-id="3626228198-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3626228198-5">}</span><span class="p" data-group-id="3626228198-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3626228198-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3626228198-6">]</span><span class="p">.</span><span class="w">
│ │ │ │ +represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="7527048508-1">(</span><span class="p" data-group-id="7527048508-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7527048508-2">}</span><span class="p" data-group-id="7527048508-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7527048508-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7527048508-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="7527048508-4">(</span><span class="p" data-group-id="7527048508-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7527048508-5">}</span><span class="p" data-group-id="7527048508-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7527048508-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7527048508-6">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="3626228198-7">(</span><span class="p" data-group-id="3626228198-8">[</span><span class="n">Int</span><span class="p" data-group-id="3626228198-8">]</span><span class="p" data-group-id="3626228198-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functionality for stopping the port and
│ │ │ │ -detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9767386516-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="9767386516-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9767386516-2">(</span><span class="p" data-group-id="9767386516-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9767386516-3">]</span><span class="p" data-group-id="9767386516-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9767386516-4">(</span><span class="p" data-group-id="9767386516-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9767386516-5">]</span><span class="p" data-group-id="9767386516-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="9767386516-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="9767386516-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9767386516-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9767386516-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="9767386516-8">]</span><span class="p" data-group-id="9767386516-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="9767386516-9">(</span><span class="p" data-group-id="9767386516-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="7527048508-7">(</span><span class="p" data-group-id="7527048508-8">[</span><span class="n">Int</span><span class="p" data-group-id="7527048508-8">]</span><span class="p" data-group-id="7527048508-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functionality for stopping the port and
│ │ │ │ +detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3068752502-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="3068752502-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3068752502-2">(</span><span class="p" data-group-id="3068752502-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3068752502-3">]</span><span class="p" data-group-id="3068752502-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3068752502-4">(</span><span class="p" data-group-id="3068752502-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3068752502-5">]</span><span class="p" data-group-id="3068752502-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="3068752502-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="3068752502-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="3068752502-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3068752502-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="3068752502-8">]</span><span class="p" data-group-id="3068752502-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="3068752502-9">(</span><span class="p" data-group-id="3068752502-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="9767386516-10">(</span><span class="n">X</span><span class="p" data-group-id="9767386516-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="9767386516-11">(</span><span class="p" data-group-id="9767386516-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9767386516-12">}</span><span class="p" data-group-id="9767386516-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="9767386516-13">(</span><span class="n">Y</span><span class="p" data-group-id="9767386516-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="9767386516-14">(</span><span class="p" data-group-id="9767386516-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9767386516-15">}</span><span class="p" data-group-id="9767386516-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="3068752502-10">(</span><span class="n">X</span><span class="p" data-group-id="3068752502-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="3068752502-11">(</span><span class="p" data-group-id="3068752502-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3068752502-12">}</span><span class="p" data-group-id="3068752502-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="3068752502-13">(</span><span class="n">Y</span><span class="p" data-group-id="3068752502-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="3068752502-14">(</span><span class="p" data-group-id="3068752502-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3068752502-15">}</span><span class="p" data-group-id="3068752502-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="9767386516-16">(</span><span class="n">Msg</span><span class="p" data-group-id="9767386516-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9767386516-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9767386516-18">(</span><span class="p" data-group-id="9767386516-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9767386516-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="3068752502-16">(</span><span class="n">Msg</span><span class="p" data-group-id="3068752502-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3068752502-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3068752502-18">(</span><span class="p" data-group-id="3068752502-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3068752502-17">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="9767386516-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9767386516-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="3068752502-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="3068752502-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="9767386516-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="9767386516-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9767386516-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9767386516-22">(</span><span class="p" data-group-id="9767386516-22">)</span><span class="p" data-group-id="9767386516-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9767386516-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9767386516-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="9767386516-24">(</span><span class="p" data-group-id="9767386516-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="9767386516-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9767386516-26">[</span><span class="p" data-group-id="9767386516-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9767386516-27">}</span><span class="p" data-group-id="9767386516-26">]</span><span class="p" data-group-id="9767386516-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="9767386516-28">(</span><span class="n">Port</span><span class="p" data-group-id="9767386516-28">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="3068752502-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="3068752502-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="3068752502-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3068752502-22">(</span><span class="p" data-group-id="3068752502-22">)</span><span class="p" data-group-id="3068752502-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="3068752502-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="3068752502-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="3068752502-24">(</span><span class="p" data-group-id="3068752502-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="3068752502-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3068752502-26">[</span><span class="p" data-group-id="3068752502-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3068752502-27">}</span><span class="p" data-group-id="3068752502-26">]</span><span class="p" data-group-id="3068752502-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="3068752502-28">(</span><span class="n">Port</span><span class="p" data-group-id="3068752502-28">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="9767386516-29">(</span><span class="n">Port</span><span class="p" data-group-id="9767386516-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="3068752502-29">(</span><span class="n">Port</span><span class="p" data-group-id="3068752502-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="9767386516-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9767386516-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9767386516-31">{</span><span class="nf">self</span><span class="p" data-group-id="9767386516-32">(</span><span class="p" data-group-id="9767386516-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9767386516-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="9767386516-34">(</span><span class="n">Msg</span><span class="p" data-group-id="9767386516-34">)</span><span class="p" data-group-id="9767386516-33">}</span><span class="p" data-group-id="9767386516-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="3068752502-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3068752502-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3068752502-31">{</span><span class="nf">self</span><span class="p" data-group-id="3068752502-32">(</span><span class="p" data-group-id="3068752502-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3068752502-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="3068752502-34">(</span><span class="n">Msg</span><span class="p" data-group-id="3068752502-34">)</span><span class="p" data-group-id="3068752502-33">}</span><span class="p" data-group-id="3068752502-31">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="9767386516-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9767386516-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9767386516-36">}</span><span class="p" data-group-id="9767386516-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9767386516-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="9767386516-38">(</span><span class="n">Data</span><span class="p" data-group-id="9767386516-38">)</span><span class="p" data-group-id="9767386516-37">}</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="3068752502-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3068752502-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3068752502-36">}</span><span class="p" data-group-id="3068752502-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3068752502-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="3068752502-38">(</span><span class="n">Data</span><span class="p" data-group-id="3068752502-38">)</span><span class="p" data-group-id="3068752502-37">}</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="9767386516-39">(</span><span class="n">Port</span><span class="p" data-group-id="9767386516-39">)</span><span class="p">;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="3068752502-39">(</span><span class="n">Port</span><span class="p" data-group-id="3068752502-39">)</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9767386516-40">{</span><span class="nf">self</span><span class="p" data-group-id="9767386516-41">(</span><span class="p" data-group-id="9767386516-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="9767386516-40">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3068752502-40">{</span><span class="nf">self</span><span class="p" data-group-id="3068752502-41">(</span><span class="p" data-group-id="3068752502-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="3068752502-40">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="9767386516-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="9767386516-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="9767386516-43">(</span><span class="ss">normal</span><span class="p" data-group-id="9767386516-43">)</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="3068752502-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="3068752502-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="3068752502-43">(</span><span class="ss">normal</span><span class="p" data-group-id="3068752502-43">)</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="9767386516-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="9767386516-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="9767386516-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="9767386516-45">)</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="3068752502-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="3068752502-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="3068752502-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="3068752502-45">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="9767386516-46">(</span><span class="p" data-group-id="9767386516-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9767386516-47">}</span><span class="p" data-group-id="9767386516-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9767386516-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9767386516-48">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="9767386516-49">(</span><span class="p" data-group-id="9767386516-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9767386516-50">}</span><span class="p" data-group-id="9767386516-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9767386516-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9767386516-51">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="3068752502-46">(</span><span class="p" data-group-id="3068752502-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3068752502-47">}</span><span class="p" data-group-id="3068752502-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3068752502-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3068752502-48">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="3068752502-49">(</span><span class="p" data-group-id="3068752502-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3068752502-50">}</span><span class="p" data-group-id="3068752502-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3068752502-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3068752502-51">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="9767386516-52">(</span><span class="p" data-group-id="9767386516-53">[</span><span class="n">Int</span><span class="p" data-group-id="9767386516-53">]</span><span class="p" data-group-id="9767386516-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-program" class="section-heading">
│ │ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="3068752502-52">(</span><span class="p" data-group-id="3068752502-53">[</span><span class="n">Int</span><span class="p" data-group-id="3068752502-53">]</span><span class="p" data-group-id="3068752502-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-program" class="section-heading">
│ │ │ │    <a href="#c-program" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">C Program</span>
│ │ │ │  </h2>
│ │ │ │  <p>On the C side, it is necessary to write functions for receiving and sending data
│ │ │ │  with 2 byte length indicators from/to Erlang. By default, the C program is to
│ │ │ │ @@ -238,22 +238,22 @@
│ │ │ │  and terminates.</p><h2 id="running-the-example" class="section-heading">
│ │ │ │    <a href="#running-the-example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Running the Example</span>
│ │ │ │  </h2>
│ │ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">$ gcc -o extprg complex.c erl_comm.c port.c</code></pre><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$ </span><span class="ss">erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="8613461546-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="8613461546-1">]</span><span class="w"> </span><span class="p" data-group-id="8613461546-2">[</span><span class="ss">source</span><span class="p" data-group-id="8613461546-2">]</span><span class="w"> </span><span class="p" data-group-id="8613461546-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="8613461546-3">]</span><span class="w"> </span><span class="p" data-group-id="8613461546-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="8613461546-4">]</span><span class="w"> </span><span class="p" data-group-id="8613461546-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="8613461546-5">]</span><span class="w"> </span><span class="p" data-group-id="8613461546-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8613461546-6">]</span><span class="w"> </span><span class="p" data-group-id="8613461546-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="8613461546-7">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="3697988355-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="3697988355-1">]</span><span class="w"> </span><span class="p" data-group-id="3697988355-2">[</span><span class="ss">source</span><span class="p" data-group-id="3697988355-2">]</span><span class="w"> </span><span class="p" data-group-id="3697988355-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="3697988355-3">]</span><span class="w"> </span><span class="p" data-group-id="3697988355-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="3697988355-4">]</span><span class="w"> </span><span class="p" data-group-id="3697988355-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="3697988355-5">]</span><span class="w"> </span><span class="p" data-group-id="3697988355-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="3697988355-6">]</span><span class="w"> </span><span class="p" data-group-id="3697988355-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="3697988355-7">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="8613461546-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="8613461546-9">(</span><span class="p" data-group-id="8613461546-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="8613461546-8">)</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="nf">c</span><span class="p" data-group-id="8613461546-10">(</span><span class="ss">complex1</span><span class="p" data-group-id="8613461546-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8613461546-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex1</span><span class="p" data-group-id="8613461546-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6893013243-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="6893013243-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="3697988355-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="3697988355-9">(</span><span class="p" data-group-id="3697988355-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="3697988355-8">)</span><span class="gp unselectable">
│ │ │ │ +1&gt; </span><span class="nf">c</span><span class="p" data-group-id="3697988355-10">(</span><span class="ss">complex1</span><span class="p" data-group-id="3697988355-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3697988355-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex1</span><span class="p" data-group-id="3697988355-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3722638760-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="3722638760-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ │ -3&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="6893013243-2">(</span><span class="mi">3</span><span class="p" data-group-id="6893013243-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +3&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="3722638760-2">(</span><span class="mi">3</span><span class="p" data-group-id="3722638760-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="6893013243-3">(</span><span class="mi">5</span><span class="p" data-group-id="6893013243-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +4&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="3722638760-3">(</span><span class="mi">5</span><span class="p" data-group-id="3722638760-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">10</span><span class="gp unselectable">
│ │ │ │ -5&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="6893013243-4">(</span><span class="p" data-group-id="6893013243-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +5&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="3722638760-4">(</span><span class="p" data-group-id="3722638760-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/bit_syntax.xhtml
│ │ │ │ @@ -24,48 +24,48 @@
│ │ │ │    <a href="#introduction" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Introduction</span>
│ │ │ │  </h2>
│ │ │ │  <p>The complete specification for the bit syntax appears in the
│ │ │ │  <a href="../../../lib/../system/doc/html/expressions.xhtml#bit-syntax-expressions">Reference Manual</a>.</p><p>In Erlang, a Bin is used for constructing binaries and matching binary patterns.
│ │ │ │ -A Bin is written with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5981040026-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="5981040026-1">&gt;&gt;</span></code></pre><p>A Bin is a low-level sequence of bits or bytes. The purpose of a Bin is to
│ │ │ │ -enable construction of binaries:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6946820082-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="6946820082-1">&gt;&gt;</span></code></pre><p>All elements must be bound. Or match a binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6351261838-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="6351261838-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span></code></pre><p>Here, <code class="inline">Bin</code> is bound and the elements are bound or unbound, as in any match.</p><p>A Bin does not need to consist of a whole number of bytes.</p><p>A <em>bitstring</em> is a sequence of zero or more bits, where the number of bits does
│ │ │ │ +A Bin is written with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1331769576-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="1331769576-1">&gt;&gt;</span></code></pre><p>A Bin is a low-level sequence of bits or bytes. The purpose of a Bin is to
│ │ │ │ +enable construction of binaries:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8750267604-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="8750267604-1">&gt;&gt;</span></code></pre><p>All elements must be bound. Or match a binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8799945076-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="8799945076-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span></code></pre><p>Here, <code class="inline">Bin</code> is bound and the elements are bound or unbound, as in any match.</p><p>A Bin does not need to consist of a whole number of bytes.</p><p>A <em>bitstring</em> is a sequence of zero or more bits, where the number of bits does
│ │ │ │  not need to be divisible by 8. If the number of bits is divisible by 8, the
│ │ │ │  bitstring is also a binary.</p><p>Each element specifies a certain <em>segment</em> of the bitstring. A segment is a set
│ │ │ │  of contiguous bits of the binary (not necessarily on a byte boundary). The first
│ │ │ │  element specifies the initial segment, the second element specifies the
│ │ │ │  following segment, and so on.</p><p>The following examples illustrate how binaries are constructed, or matched, and
│ │ │ │  how elements and tails are specified.</p><h3 id="examples" class="section-heading">
│ │ │ │    <a href="#examples" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Examples</span>
│ │ │ │  </h3>
│ │ │ │  <p><em>Example 1:</em> A binary can be constructed from a set of constants or a string
│ │ │ │ -literal:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin11</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0871284050-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="0871284050-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Bin12</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0871284050-2">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0871284050-2">&gt;&gt;</span></code></pre><p>This gives two binaries of size 3, with the following evaluations:</p><ul><li><a href="../../../lib/../erts/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin11)</code></a> evaluates to <code class="inline">[1, 17, 42]</code>.</li><li><a href="../../../lib/../erts/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin12)</code></a> evaluates to <code class="inline">[97, 98, 99]</code>.</li></ul><p><em>Example 2:</em>Similarly, a binary can be constructed from a set of bound
│ │ │ │ +literal:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin11</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4595106013-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="4595106013-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Bin12</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4595106013-2">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="4595106013-2">&gt;&gt;</span></code></pre><p>This gives two binaries of size 3, with the following evaluations:</p><ul><li><a href="../../../lib/../erts/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin11)</code></a> evaluates to <code class="inline">[1, 17, 42]</code>.</li><li><a href="../../../lib/../erts/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin12)</code></a> evaluates to <code class="inline">[97, 98, 99]</code>.</li></ul><p><em>Example 2:</em>Similarly, a binary can be constructed from a set of bound
│ │ │ │  variables:</p><pre><code class="makeup erlang" translate="no"><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8002794089-1">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="8002794089-1">&gt;&gt;</span></code></pre><p>This gives a binary of size 4. Here, a <em>size expression</em> is used for the
│ │ │ │ +</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6144523061-1">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="6144523061-1">&gt;&gt;</span></code></pre><p>This gives a binary of size 4. Here, a <em>size expression</em> is used for the
│ │ │ │  variable <code class="inline">C</code> to specify a 16-bits segment of <code class="inline">Bin2</code>.</p><p><a href="../../../lib/../erts/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin2)</code></a> evaluates to <code class="inline">[1, 17, 00, 42]</code>.</p><p><em>Example 3:</em> A Bin can also be used for matching. <code class="inline">D</code>, <code class="inline">E</code>, and <code class="inline">F</code> are unbound
│ │ │ │ -variables, and <code class="inline">Bin2</code> is bound, as in Example 2:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7052985664-1">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7052985664-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin2</span></code></pre><p>This gives <code class="inline">D = 273</code>, <code class="inline">E = 00</code>, and F binds to a binary of size 1:
│ │ │ │ +variables, and <code class="inline">Bin2</code> is bound, as in Example 2:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9567785592-1">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9567785592-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin2</span></code></pre><p>This gives <code class="inline">D = 273</code>, <code class="inline">E = 00</code>, and F binds to a binary of size 1:
│ │ │ │  <code class="inline">binary_to_list(F) = [42]</code>.</p><p><em>Example 4:</em> The following is a more elaborate example of matching. Here,
│ │ │ │  <code class="inline">Dgram</code> is bound to the consecutive bytes of an IP datagram of IP protocol
│ │ │ │ -version 4. The ambition is to extract the header and the data of the datagram:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0444158251-1">(</span><span class="n">IP_VERSION</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="0444158251-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0444158251-2">(</span><span class="n">IP_MIN_HDR_LEN</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="0444158251-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +version 4. The ambition is to extract the header and the data of the datagram:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8951765469-1">(</span><span class="n">IP_VERSION</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="8951765469-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8951765469-2">(</span><span class="n">IP_MIN_HDR_LEN</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="8951765469-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">DgramSize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="0444158251-3">(</span><span class="n">Dgram</span><span class="p" data-group-id="0444158251-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">DgramSize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="8951765469-3">(</span><span class="n">Dgram</span><span class="p" data-group-id="8951765469-3">)</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="k">case</span><span class="w"> </span><span class="n">Dgram</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0444158251-4">&lt;&lt;</span><span class="o">?</span><span class="n">IP_VERSION</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">HLen</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">SrvcType</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">TotLen</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8951765469-4">&lt;&lt;</span><span class="o">?</span><span class="n">IP_VERSION</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">HLen</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">SrvcType</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">TotLen</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │ │        </span><span class="n">ID</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">Flgs</span><span class="p">:</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">FragOff</span><span class="p">:</span><span class="mi">13</span><span class="p">,</span><span class="w">
│ │ │ │        </span><span class="n">TTL</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">Proto</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">HdrChkSum</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │ │        </span><span class="n">SrcIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w">
│ │ │ │ -      </span><span class="n">DestIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w"> </span><span class="n">RestDgram</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0444158251-4">&gt;&gt;</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">HLen</span><span class="o">&gt;=</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="n">HLen</span><span class="o">=&lt;</span><span class="n">DgramSize</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="n">OptsLen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="p" data-group-id="0444158251-5">(</span><span class="n">HLen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">?</span><span class="n">IP_MIN_HDR_LEN</span><span class="p" data-group-id="0444158251-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0444158251-6">&lt;&lt;</span><span class="n">Opts</span><span class="p">:</span><span class="n">OptsLen</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Data</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0444158251-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RestDgram</span><span class="p">,</span><span class="w">
│ │ │ │ +      </span><span class="n">DestIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w"> </span><span class="n">RestDgram</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8951765469-4">&gt;&gt;</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">HLen</span><span class="o">&gt;=</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="n">HLen</span><span class="o">=&lt;</span><span class="n">DgramSize</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="n">OptsLen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="p" data-group-id="8951765469-5">(</span><span class="n">HLen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">?</span><span class="n">IP_MIN_HDR_LEN</span><span class="p" data-group-id="8951765469-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8951765469-6">&lt;&lt;</span><span class="n">Opts</span><span class="p">:</span><span class="n">OptsLen</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Data</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8951765469-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RestDgram</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>Here, the segment corresponding to the <code class="inline">Opts</code> variable has a <em>type modifier</em>,
│ │ │ │  specifying that <code class="inline">Opts</code> is to bind to a binary. All other variables have the
│ │ │ │  default type equal to unsigned integer.</p><p>An IP datagram header is of variable length. This length is measured in the
│ │ │ │  number of 32-bit words and is given in the segment corresponding to <code class="inline">HLen</code>. The
│ │ │ │  minimum value of <code class="inline">HLen</code> is 5. It is the segment corresponding to <code class="inline">Opts</code> that is
│ │ │ │  variable, so if <code class="inline">HLen</code> is equal to 5, <code class="inline">Opts</code> becomes an empty binary.</p><p>The tail variables <code class="inline">RestDgram</code> and <code class="inline">Data</code> bind to binaries, as all tail
│ │ │ │ @@ -123,77 +123,77 @@
│ │ │ │  <p>This section describes the rules for constructing binaries using the bit syntax.
│ │ │ │  Unlike when constructing lists or tuples, the construction of a binary can fail
│ │ │ │  with a <code class="inline">badarg</code> exception.</p><p>There can be zero or more segments in a binary to be constructed. The expression
│ │ │ │  <code class="inline">&lt;&lt;&gt;&gt;</code> constructs a zero length binary.</p><p>Each segment in a binary can consist of zero or more bits. There are no
│ │ │ │  alignment rules for individual segments of type <code class="inline">integer</code> and <code class="inline">float</code>. For
│ │ │ │  binaries and bitstrings without size, the unit specifies the alignment. Since
│ │ │ │  the default alignment for the <code class="inline">binary</code> type is 8, the size of a binary segment
│ │ │ │ -must be a multiple of 8 bits, that is, only whole bytes.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9773218219-1">&lt;&lt;</span><span class="n">Bin</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Bitstring</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="9773218219-1">&gt;&gt;</span></code></pre><p>The variable <code class="inline">Bin</code> must contain a whole number of bytes, because the <code class="inline">binary</code>
│ │ │ │ +must be a multiple of 8 bits, that is, only whole bytes.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1147806813-1">&lt;&lt;</span><span class="n">Bin</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Bitstring</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="1147806813-1">&gt;&gt;</span></code></pre><p>The variable <code class="inline">Bin</code> must contain a whole number of bytes, because the <code class="inline">binary</code>
│ │ │ │  type defaults to <code class="inline">unit:8</code>. A <code class="inline">badarg</code> exception is generated if <code class="inline">Bin</code> consist
│ │ │ │  of, for example, 17 bits.</p><p>The <code class="inline">Bitstring</code> variable can consist of any number of bits, for example, 0, 1,
│ │ │ │  8, 11, 17, 42, and so on. This is because the default <code class="inline">unit</code> for bitstrings
│ │ │ │  is 1.</p><p>For clarity, it is recommended not to change the unit size for binaries.
│ │ │ │  Instead, use <code class="inline">binary</code> when you need byte alignment and <code class="inline">bitstring</code> when you need
│ │ │ │  bit alignment.</p><p>The following example successfully constructs a bitstring of 7 bits, provided
│ │ │ │ -that all of X and Y are integers:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7429260617-1">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">6</span><span class="p" data-group-id="7429260617-1">&gt;&gt;</span></code></pre><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When constructing binaries, <code class="inline">Value</code> and <code class="inline">Size</code> can be any Erlang expression.
│ │ │ │ +that all of X and Y are integers:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3834019772-1">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">6</span><span class="p" data-group-id="3834019772-1">&gt;&gt;</span></code></pre><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When constructing binaries, <code class="inline">Value</code> and <code class="inline">Size</code> can be any Erlang expression.
│ │ │ │  However, for syntactical reasons, both <code class="inline">Value</code> and <code class="inline">Size</code> must be enclosed in
│ │ │ │  parenthesis if the expression consists of anything more than a single literal or
│ │ │ │ -a variable. The following gives a compiler syntax error:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6680635947-1">&lt;&lt;</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="6680635947-1">&gt;&gt;</span></code></pre><p>This expression must be rewritten into the following, to be accepted by the
│ │ │ │ -compiler:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7119871024-1">&lt;&lt;</span><span class="p" data-group-id="7119871024-2">(</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="7119871024-2">)</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="7119871024-1">&gt;&gt;</span></code></pre><h3 id="including-literal-strings" class="section-heading">
│ │ │ │ +a variable. The following gives a compiler syntax error:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4434870666-1">&lt;&lt;</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4434870666-1">&gt;&gt;</span></code></pre><p>This expression must be rewritten into the following, to be accepted by the
│ │ │ │ +compiler:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7920624795-1">&lt;&lt;</span><span class="p" data-group-id="7920624795-2">(</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="7920624795-2">)</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="7920624795-1">&gt;&gt;</span></code></pre><h3 id="including-literal-strings" class="section-heading">
│ │ │ │    <a href="#including-literal-strings" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Including Literal Strings</span>
│ │ │ │  </h3>
│ │ │ │ -<p>A literal string can be written instead of an element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3074895389-1">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="3074895389-1">&gt;&gt;</span></code></pre><p>This is syntactic sugar for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1801435165-1">&lt;&lt;</span><span class="sc">$h</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$o</span><span class="p" data-group-id="1801435165-1">&gt;&gt;</span></code></pre><h2 id="matching-binaries" class="section-heading">
│ │ │ │ +<p>A literal string can be written instead of an element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8951912811-1">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8951912811-1">&gt;&gt;</span></code></pre><p>This is syntactic sugar for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2039916000-1">&lt;&lt;</span><span class="sc">$h</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$o</span><span class="p" data-group-id="2039916000-1">&gt;&gt;</span></code></pre><h2 id="matching-binaries" class="section-heading">
│ │ │ │    <a href="#matching-binaries" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Matching Binaries</span>
│ │ │ │  </h2>
│ │ │ │  <p>This section describes the rules for matching binaries, using the bit syntax.</p><p>There can be zero or more segments in a binary pattern. A binary pattern can
│ │ │ │  occur wherever patterns are allowed, including inside other patterns. Binary
│ │ │ │  patterns cannot be nested. The pattern <code class="inline">&lt;&lt;&gt;&gt;</code> matches a zero length binary.</p><p>Each segment in a binary can consist of zero or more bits. A segment of type
│ │ │ │  <code class="inline">binary</code> must have a size evenly divisible by 8 (or divisible by the unit size,
│ │ │ │  if the unit size has been changed). A segment of type <code class="inline">bitstring</code> has no
│ │ │ │  restrictions on the size. A segment of type <code class="inline">float</code> must have size 64 or 32.</p><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When matching <code class="inline">Value</code>, value must be either a variable or an integer, or a
│ │ │ │  floating point literal. Expressions are not allowed.</p><p><code class="inline">Size</code> must be a
│ │ │ │  <a href="../../../lib/../system/doc/html/expressions.xhtml#guard-expressions">guard expression</a>, which can use
│ │ │ │ -literals and previously bound variables. The following is not allowed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="2137928124-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2137928124-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2137928124-2">&gt;&gt;</span><span class="p" data-group-id="2137928124-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="2137928124-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="2137928124-3">}</span><span class="p">.</span></code></pre><p>The two occurrences of <code class="inline">N</code> are not related. The compiler will complain that the
│ │ │ │ -<code class="inline">N</code> in the size field is unbound.</p><p>The correct way to write this example is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="5866287688-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="5866287688-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="5866287688-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5866287688-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="5866287688-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="5866287688-3">}</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Before OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable bound to
│ │ │ │ +literals and previously bound variables. The following is not allowed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="3019684115-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3019684115-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3019684115-2">&gt;&gt;</span><span class="p" data-group-id="3019684115-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="3019684115-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="3019684115-3">}</span><span class="p">.</span></code></pre><p>The two occurrences of <code class="inline">N</code> are not related. The compiler will complain that the
│ │ │ │ +<code class="inline">N</code> in the size field is unbound.</p><p>The correct way to write this example is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="9463286837-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="9463286837-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="9463286837-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9463286837-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="9463286837-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="9463286837-3">}</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Before OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable bound to
│ │ │ │  an integer.</p></section><h3 id="binding-and-using-a-size-variable" class="section-heading">
│ │ │ │    <a href="#binding-and-using-a-size-variable" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Binding and Using a Size Variable</span>
│ │ │ │  </h3>
│ │ │ │  <p>There is one exception to the rule that a variable that is used as size must be
│ │ │ │  previously bound. It is possible to match and bind a variable, and use it as a
│ │ │ │ -size within the same binary pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="2459699632-1">(</span><span class="p" data-group-id="2459699632-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="n">Sz</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2459699632-2">&gt;&gt;</span><span class="p" data-group-id="2459699632-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="2459699632-3">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="2459699632-3">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is bound to the value in the first byte of the binary. <code class="inline">Sz</code> is then
│ │ │ │ -used at the number of bytes to match out as a binary.</p><p>Starting in OTP 23, the size can be a guard expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="6417015793-1">(</span><span class="p" data-group-id="6417015793-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="p" data-group-id="6417015793-3">(</span><span class="p" data-group-id="6417015793-4">(</span><span class="n">Sz</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="6417015793-4">)</span><span class="o">*</span><span class="mi">8</span><span class="p" data-group-id="6417015793-3">)</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6417015793-2">&gt;&gt;</span><span class="p" data-group-id="6417015793-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="6417015793-5">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="6417015793-5">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is the combined size of the header and the payload, so we will need to
│ │ │ │ +size within the same binary pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="7602117485-1">(</span><span class="p" data-group-id="7602117485-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="n">Sz</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7602117485-2">&gt;&gt;</span><span class="p" data-group-id="7602117485-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="7602117485-3">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="7602117485-3">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is bound to the value in the first byte of the binary. <code class="inline">Sz</code> is then
│ │ │ │ +used at the number of bytes to match out as a binary.</p><p>Starting in OTP 23, the size can be a guard expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="3340572295-1">(</span><span class="p" data-group-id="3340572295-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="p" data-group-id="3340572295-3">(</span><span class="p" data-group-id="3340572295-4">(</span><span class="n">Sz</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="3340572295-4">)</span><span class="o">*</span><span class="mi">8</span><span class="p" data-group-id="3340572295-3">)</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3340572295-2">&gt;&gt;</span><span class="p" data-group-id="3340572295-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="3340572295-5">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="3340572295-5">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is the combined size of the header and the payload, so we will need to
│ │ │ │  subtract one byte to get the size of the payload.</p><h3 id="getting-the-rest-of-the-binary-or-bitstring" class="section-heading">
│ │ │ │    <a href="#getting-the-rest-of-the-binary-or-bitstring" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Getting the Rest of the Binary or Bitstring</span>
│ │ │ │  </h3>
│ │ │ │ -<p>To match out the rest of a binary, specify a binary field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="9611880439-1">(</span><span class="p" data-group-id="9611880439-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9611880439-2">&gt;&gt;</span><span class="p" data-group-id="9611880439-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>The size of the tail must be evenly divisible by 8.</p><p>To match out the rest of a bitstring, specify a field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="4865437285-1">(</span><span class="p" data-group-id="4865437285-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="4865437285-2">&gt;&gt;</span><span class="p" data-group-id="4865437285-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>There are no restrictions on the number of bits in the tail.</p><h2 id="appending-to-a-binary" class="section-heading">
│ │ │ │ +<p>To match out the rest of a binary, specify a binary field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="8102589409-1">(</span><span class="p" data-group-id="8102589409-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8102589409-2">&gt;&gt;</span><span class="p" data-group-id="8102589409-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>The size of the tail must be evenly divisible by 8.</p><p>To match out the rest of a bitstring, specify a field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="9475533297-1">(</span><span class="p" data-group-id="9475533297-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="9475533297-2">&gt;&gt;</span><span class="p" data-group-id="9475533297-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>There are no restrictions on the number of bits in the tail.</p><h2 id="appending-to-a-binary" class="section-heading">
│ │ │ │    <a href="#appending-to-a-binary" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Appending to a Binary</span>
│ │ │ │  </h2>
│ │ │ │ -<p>Appending to a binary in an efficient way can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">triples_to_bin</span><span class="p" data-group-id="0017487187-1">(</span><span class="n">T</span><span class="p" data-group-id="0017487187-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="0017487187-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0017487187-3">&lt;&lt;</span><span class="p" data-group-id="0017487187-3">&gt;&gt;</span><span class="p" data-group-id="0017487187-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>Appending to a binary in an efficient way can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">triples_to_bin</span><span class="p" data-group-id="6882983825-1">(</span><span class="n">T</span><span class="p" data-group-id="6882983825-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="6882983825-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6882983825-3">&lt;&lt;</span><span class="p" data-group-id="6882983825-3">&gt;&gt;</span><span class="p" data-group-id="6882983825-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="0017487187-4">(</span><span class="p" data-group-id="0017487187-5">[</span><span class="p" data-group-id="0017487187-6">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p" data-group-id="0017487187-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="0017487187-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0017487187-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="0017487187-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0017487187-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">X</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Z</span><span class="p">:</span><span class="mi">32</span><span class="p" data-group-id="0017487187-8">&gt;&gt;</span><span class="p" data-group-id="0017487187-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="0017487187-9">(</span><span class="p" data-group-id="0017487187-10">[</span><span class="p" data-group-id="0017487187-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0017487187-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="6882983825-4">(</span><span class="p" data-group-id="6882983825-5">[</span><span class="p" data-group-id="6882983825-6">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p" data-group-id="6882983825-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6882983825-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6882983825-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="6882983825-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6882983825-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">X</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Z</span><span class="p">:</span><span class="mi">32</span><span class="p" data-group-id="6882983825-8">&gt;&gt;</span><span class="p" data-group-id="6882983825-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="6882983825-9">(</span><span class="p" data-group-id="6882983825-10">[</span><span class="p" data-group-id="6882983825-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6882983825-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/binaryhandling.xhtml
│ │ │ │ @@ -19,43 +19,43 @@
│ │ │ │  
│ │ │ │      <h1 id="content">
│ │ │ │  Constructing and Matching Binaries
│ │ │ │      </h1>
│ │ │ │  <p>This section gives a few examples on how to handle binaries in an efficient way.
│ │ │ │  The sections that follow take an in-depth look at how binaries are implemented
│ │ │ │  and how to best take advantages of the optimizations done by the compiler and
│ │ │ │ -runtime system.</p><p>Binaries can be efficiently <em>built</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_list_to_binary</span><span class="p" data-group-id="6672986628-1">(</span><span class="n">List</span><span class="p" data-group-id="6672986628-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="6672986628-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6672986628-3">&lt;&lt;</span><span class="p" data-group-id="6672986628-3">&gt;&gt;</span><span class="p" data-group-id="6672986628-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +runtime system.</p><p>Binaries can be efficiently <em>built</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_list_to_binary</span><span class="p" data-group-id="4198449692-1">(</span><span class="n">List</span><span class="p" data-group-id="4198449692-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="4198449692-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4198449692-3">&lt;&lt;</span><span class="p" data-group-id="4198449692-3">&gt;&gt;</span><span class="p" data-group-id="4198449692-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="6672986628-4">(</span><span class="p" data-group-id="6672986628-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6672986628-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6672986628-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="6672986628-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6672986628-7">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="6672986628-7">&gt;&gt;</span><span class="p" data-group-id="6672986628-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="6672986628-8">(</span><span class="p" data-group-id="6672986628-9">[</span><span class="p" data-group-id="6672986628-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6672986628-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="4198449692-4">(</span><span class="p" data-group-id="4198449692-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4198449692-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4198449692-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="4198449692-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4198449692-7">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="4198449692-7">&gt;&gt;</span><span class="p" data-group-id="4198449692-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="4198449692-8">(</span><span class="p" data-group-id="4198449692-9">[</span><span class="p" data-group-id="4198449692-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4198449692-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Appending data to a binary as in the example is efficient because it is
│ │ │ │  specially optimized by the runtime system to avoid copying the <code class="inline">Acc</code> binary
│ │ │ │ -every time.</p><p>Prepending data to a binary in a loop is not efficient:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1282886560-1">(</span><span class="n">List</span><span class="p" data-group-id="1282886560-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1282886560-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1282886560-3">&lt;&lt;</span><span class="p" data-group-id="1282886560-3">&gt;&gt;</span><span class="p" data-group-id="1282886560-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +every time.</p><p>Prepending data to a binary in a loop is not efficient:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="3318399371-1">(</span><span class="n">List</span><span class="p" data-group-id="3318399371-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="3318399371-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3318399371-3">&lt;&lt;</span><span class="p" data-group-id="3318399371-3">&gt;&gt;</span><span class="p" data-group-id="3318399371-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1282886560-4">(</span><span class="p" data-group-id="1282886560-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1282886560-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1282886560-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1282886560-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1282886560-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1282886560-7">&gt;&gt;</span><span class="p" data-group-id="1282886560-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1282886560-8">(</span><span class="p" data-group-id="1282886560-9">[</span><span class="p" data-group-id="1282886560-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1282886560-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="3318399371-4">(</span><span class="p" data-group-id="3318399371-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3318399371-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3318399371-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="3318399371-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3318399371-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3318399371-7">&gt;&gt;</span><span class="p" data-group-id="3318399371-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="3318399371-8">(</span><span class="p" data-group-id="3318399371-9">[</span><span class="p" data-group-id="3318399371-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3318399371-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>This is not efficient for long lists because the <code class="inline">Acc</code> binary is copied every
│ │ │ │ -time. One way to make the function more efficient is like this:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5458615151-1">(</span><span class="n">List</span><span class="p" data-group-id="5458615151-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5458615151-2">(</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="5458615151-3">(</span><span class="n">List</span><span class="p" data-group-id="5458615151-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5458615151-4">&lt;&lt;</span><span class="p" data-group-id="5458615151-4">&gt;&gt;</span><span class="p" data-group-id="5458615151-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +time. One way to make the function more efficient is like this:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="3975040489-1">(</span><span class="n">List</span><span class="p" data-group-id="3975040489-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="3975040489-2">(</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="3975040489-3">(</span><span class="n">List</span><span class="p" data-group-id="3975040489-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3975040489-4">&lt;&lt;</span><span class="p" data-group-id="3975040489-4">&gt;&gt;</span><span class="p" data-group-id="3975040489-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5458615151-5">(</span><span class="p" data-group-id="5458615151-6">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5458615151-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5458615151-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5458615151-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5458615151-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="5458615151-8">&gt;&gt;</span><span class="p" data-group-id="5458615151-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5458615151-9">(</span><span class="p" data-group-id="5458615151-10">[</span><span class="p" data-group-id="5458615151-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5458615151-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Another way to avoid copying the binary each time is like this:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="0864177168-1">(</span><span class="p" data-group-id="0864177168-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0864177168-2">]</span><span class="p" data-group-id="0864177168-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">RevTail</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="0864177168-3">(</span><span class="n">T</span><span class="p" data-group-id="0864177168-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0864177168-4">&lt;&lt;</span><span class="n">RevTail</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="0864177168-4">&gt;&gt;</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="0864177168-5">(</span><span class="p" data-group-id="0864177168-6">[</span><span class="p" data-group-id="0864177168-6">]</span><span class="p" data-group-id="0864177168-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0864177168-7">&lt;&lt;</span><span class="p" data-group-id="0864177168-7">&gt;&gt;</span><span class="p">.</span></code></pre><p>Note that in each of the <strong>DO</strong> examples, the binary to be appended to is always
│ │ │ │ -given as the first segment.</p><p>Binaries can be efficiently <em>matched</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="7616235987-1">(</span><span class="p" data-group-id="7616235987-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7616235987-2">&gt;&gt;</span><span class="p" data-group-id="7616235987-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7616235987-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="7616235987-4">(</span><span class="n">T</span><span class="p" data-group-id="7616235987-4">)</span><span class="p" data-group-id="7616235987-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="7616235987-5">(</span><span class="p" data-group-id="7616235987-6">&lt;&lt;</span><span class="p" data-group-id="7616235987-6">&gt;&gt;</span><span class="p" data-group-id="7616235987-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7616235987-7">[</span><span class="p" data-group-id="7616235987-7">]</span><span class="p">.</span></code></pre><h2 id="how-binaries-are-implemented" class="section-heading">
│ │ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="3975040489-5">(</span><span class="p" data-group-id="3975040489-6">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3975040489-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3975040489-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="3975040489-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3975040489-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="3975040489-8">&gt;&gt;</span><span class="p" data-group-id="3975040489-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="3975040489-9">(</span><span class="p" data-group-id="3975040489-10">[</span><span class="p" data-group-id="3975040489-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3975040489-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Another way to avoid copying the binary each time is like this:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1331307300-1">(</span><span class="p" data-group-id="1331307300-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1331307300-2">]</span><span class="p" data-group-id="1331307300-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">RevTail</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1331307300-3">(</span><span class="n">T</span><span class="p" data-group-id="1331307300-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1331307300-4">&lt;&lt;</span><span class="n">RevTail</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="1331307300-4">&gt;&gt;</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1331307300-5">(</span><span class="p" data-group-id="1331307300-6">[</span><span class="p" data-group-id="1331307300-6">]</span><span class="p" data-group-id="1331307300-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1331307300-7">&lt;&lt;</span><span class="p" data-group-id="1331307300-7">&gt;&gt;</span><span class="p">.</span></code></pre><p>Note that in each of the <strong>DO</strong> examples, the binary to be appended to is always
│ │ │ │ +given as the first segment.</p><p>Binaries can be efficiently <em>matched</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="7331086653-1">(</span><span class="p" data-group-id="7331086653-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7331086653-2">&gt;&gt;</span><span class="p" data-group-id="7331086653-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7331086653-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="7331086653-4">(</span><span class="n">T</span><span class="p" data-group-id="7331086653-4">)</span><span class="p" data-group-id="7331086653-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="7331086653-5">(</span><span class="p" data-group-id="7331086653-6">&lt;&lt;</span><span class="p" data-group-id="7331086653-6">&gt;&gt;</span><span class="p" data-group-id="7331086653-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7331086653-7">[</span><span class="p" data-group-id="7331086653-7">]</span><span class="p">.</span></code></pre><h2 id="how-binaries-are-implemented" class="section-heading">
│ │ │ │    <a href="#how-binaries-are-implemented" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">How Binaries are Implemented</span>
│ │ │ │  </h2>
│ │ │ │  <p>Internally, binaries and bitstrings are implemented in the same way. In this
│ │ │ │  section, they are called <em>binaries</em> because that is what they are called in the
│ │ │ │ @@ -110,29 +110,29 @@
│ │ │ │  called referential transparency) of Erlang would break.</p><h2 id="constructing-binaries" class="section-heading">
│ │ │ │    <a href="#constructing-binaries" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Constructing Binaries</span>
│ │ │ │  </h2>
│ │ │ │  <p>Appending to a binary or bitstring in the following way is specially optimized
│ │ │ │ -to avoid copying the binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1251566901-1">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1251566901-1">&gt;&gt;</span><span class="w">
│ │ │ │ +to avoid copying the binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5880892072-1">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5880892072-1">&gt;&gt;</span><span class="w">
│ │ │ │  </span><span class="c1">%% - OR -</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1251566901-2">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">bitstring</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1251566901-2">&gt;&gt;</span></code></pre><p>This optimization is applied by the runtime system in a way that makes it
│ │ │ │ +</span><span class="p" data-group-id="5880892072-2">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">bitstring</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5880892072-2">&gt;&gt;</span></code></pre><p>This optimization is applied by the runtime system in a way that makes it
│ │ │ │  effective in most circumstances (for exceptions, see
│ │ │ │  <a href="binaryhandling.xhtml#forced_copying">Circumstances That Force Copying</a>). The
│ │ │ │  optimization in its basic form does not need any help from the compiler.
│ │ │ │  However, the compiler add hints to the runtime system when it is safe to apply
│ │ │ │  the optimization in a more efficient way.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>The compiler support for making the optimization more efficient was added in
│ │ │ │  Erlang/OTP 26.</p></section><p>To explain how the basic optimization works, let us examine the following code
│ │ │ │ -line by line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7833427571-1">&lt;&lt;</span><span class="mi">0</span><span class="p" data-group-id="7833427571-1">&gt;&gt;</span><span class="p">,</span><span class="w">                    </span><span class="c1">%% 1</span><span class="w">
│ │ │ │ -</span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7833427571-2">&lt;&lt;</span><span class="n">Bin0</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7833427571-2">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 2</span><span class="w">
│ │ │ │ -</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7833427571-3">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7833427571-3">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 3</span><span class="w">
│ │ │ │ -</span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7833427571-4">&lt;&lt;</span><span class="n">Bin2</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p" data-group-id="7833427571-4">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 4</span><span class="w">
│ │ │ │ -</span><span class="n">Bin4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7833427571-5">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="7833427571-5">&gt;&gt;</span><span class="p">,</span><span class="w">       </span><span class="c1">%% 5 !!!</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7833427571-6">{</span><span class="n">Bin4</span><span class="p">,</span><span class="n">Bin3</span><span class="p" data-group-id="7833427571-6">}</span><span class="w">                      </span><span class="c1">%% 6</span></code></pre><ul><li><p>Line 1 (marked with the <code class="inline">%% 1</code> comment), assigns a
│ │ │ │ +line by line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3551077449-1">&lt;&lt;</span><span class="mi">0</span><span class="p" data-group-id="3551077449-1">&gt;&gt;</span><span class="p">,</span><span class="w">                    </span><span class="c1">%% 1</span><span class="w">
│ │ │ │ +</span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3551077449-2">&lt;&lt;</span><span class="n">Bin0</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3551077449-2">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 2</span><span class="w">
│ │ │ │ +</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3551077449-3">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="3551077449-3">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 3</span><span class="w">
│ │ │ │ +</span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3551077449-4">&lt;&lt;</span><span class="n">Bin2</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p" data-group-id="3551077449-4">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 4</span><span class="w">
│ │ │ │ +</span><span class="n">Bin4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3551077449-5">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="3551077449-5">&gt;&gt;</span><span class="p">,</span><span class="w">       </span><span class="c1">%% 5 !!!</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3551077449-6">{</span><span class="n">Bin4</span><span class="p">,</span><span class="n">Bin3</span><span class="p" data-group-id="3551077449-6">}</span><span class="w">                      </span><span class="c1">%% 6</span></code></pre><ul><li><p>Line 1 (marked with the <code class="inline">%% 1</code> comment), assigns a
│ │ │ │  <a href="binaryhandling.xhtml#heap_binary">heap binary</a> to the <code class="inline">Bin0</code> variable.</p></li><li><p>Line 2 is an append operation. As <code class="inline">Bin0</code> has not been involved in an append
│ │ │ │  operation, a new <a href="binaryhandling.xhtml#refc_binary">refc binary</a> is created and
│ │ │ │  the contents of <code class="inline">Bin0</code> is copied into it. The <em>ProcBin</em> part of the refc
│ │ │ │  binary has its size set to the size of the data stored in the binary, while
│ │ │ │  the binary object has extra space allocated. The size of the binary object is
│ │ │ │  either twice the size of <code class="inline">Bin1</code> or 256, whichever is larger. In this case it
│ │ │ │  is 256.</p></li><li><p>Line 3 is more interesting. <code class="inline">Bin1</code> <em>has</em> been used in an append operation, and
│ │ │ │ @@ -158,23 +158,23 @@
│ │ │ │  handle an append operation to a heap binary by copying it to a refc binary (line
│ │ │ │  2), and also handle an append operation to a previous version of the binary by
│ │ │ │  copying it (line 5). The support for doing that does not come for free. For
│ │ │ │  example, to make it possible to know when it is necessary to copy the binary,
│ │ │ │  for every append operation, the runtime system must create a sub binary.</p><p>When the compiler can determine that none of those situations need to be handled
│ │ │ │  and that the append operation cannot possibly fail, the compiler generates code
│ │ │ │  that causes the runtime system to apply a more efficient variant of the
│ │ │ │ -optimization.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8010595213-1">(</span><span class="ss">repack</span><span class="p" data-group-id="8010595213-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8010595213-2">(</span><span class="p" data-group-id="8010595213-3">[</span><span class="ss">repack</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8010595213-3">]</span><span class="p" data-group-id="8010595213-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +optimization.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8076426042-1">(</span><span class="ss">repack</span><span class="p" data-group-id="8076426042-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8076426042-2">(</span><span class="p" data-group-id="8076426042-3">[</span><span class="ss">repack</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8076426042-3">]</span><span class="p" data-group-id="8076426042-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="8010595213-4">(</span><span class="n">Bin</span><span class="p" data-group-id="8010595213-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_binary</span><span class="p" data-group-id="8010595213-5">(</span><span class="n">Bin</span><span class="p" data-group-id="8010595213-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">repack</span><span class="p" data-group-id="8010595213-6">(</span><span class="n">Bin</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8010595213-7">&lt;&lt;</span><span class="p" data-group-id="8010595213-7">&gt;&gt;</span><span class="p" data-group-id="8010595213-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="8076426042-4">(</span><span class="n">Bin</span><span class="p" data-group-id="8076426042-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_binary</span><span class="p" data-group-id="8076426042-5">(</span><span class="n">Bin</span><span class="p" data-group-id="8076426042-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">repack</span><span class="p" data-group-id="8076426042-6">(</span><span class="n">Bin</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8076426042-7">&lt;&lt;</span><span class="p" data-group-id="8076426042-7">&gt;&gt;</span><span class="p" data-group-id="8076426042-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="8010595213-8">(</span><span class="p" data-group-id="8010595213-9">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8010595213-9">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8010595213-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">repack</span><span class="p" data-group-id="8010595213-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8010595213-11">&lt;&lt;</span><span class="n">Result</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="8010595213-11">&gt;&gt;</span><span class="p" data-group-id="8010595213-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="8010595213-12">(</span><span class="p" data-group-id="8010595213-13">&lt;&lt;</span><span class="p" data-group-id="8010595213-13">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8010595213-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="8076426042-8">(</span><span class="p" data-group-id="8076426042-9">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8076426042-9">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8076426042-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">repack</span><span class="p" data-group-id="8076426042-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8076426042-11">&lt;&lt;</span><span class="n">Result</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="8076426042-11">&gt;&gt;</span><span class="p" data-group-id="8076426042-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="8076426042-12">(</span><span class="p" data-group-id="8076426042-13">&lt;&lt;</span><span class="p" data-group-id="8076426042-13">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8076426042-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Result</span><span class="p">.</span></code></pre><p>The <code class="inline">repack/2</code> function only keeps a single version of the binary, so there is
│ │ │ │  never any need to copy the binary. The compiler rewrites the creation of the
│ │ │ │  empty binary in <code class="inline">repack/1</code> to instead create a refc binary with 256 bytes
│ │ │ │  already reserved; thus, the append operation in <code class="inline">repack/2</code> never needs to handle
│ │ │ │  a binary not prepared for appending.</p><p><a href="" id="forced_copying"></a></p><h3 id="circumstances-that-force-copying" class="section-heading">
│ │ │ │    <a href="#circumstances-that-force-copying" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -186,72 +186,72 @@
│ │ │ │  reason is that the binary object can be moved (reallocated) during an append
│ │ │ │  operation, and when that happens, the pointer in the ProcBin must be updated. If
│ │ │ │  there would be more than one ProcBin pointing to the binary object, it would not
│ │ │ │  be possible to find and update all of them.</p><p>Therefore, certain operations on a binary mark it so that any future append
│ │ │ │  operation will be forced to copy the binary. In most cases, the binary object
│ │ │ │  will be shrunk at the same time to reclaim the extra space allocated for
│ │ │ │  growing.</p><p>When appending to a binary as follows, only the binary returned from the latest
│ │ │ │ -append operation will support further cheap append operations:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1184974500-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1184974500-1">&gt;&gt;</span></code></pre><p>In the code fragment in the beginning of this section, appending to <code class="inline">Bin</code> will
│ │ │ │ +append operation will support further cheap append operations:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6650924372-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6650924372-1">&gt;&gt;</span></code></pre><p>In the code fragment in the beginning of this section, appending to <code class="inline">Bin</code> will
│ │ │ │  be cheap, while appending to <code class="inline">Bin0</code> will force the creation of a new binary and
│ │ │ │  copying of the contents of <code class="inline">Bin0</code>.</p><p>If a binary is sent as a message to a process or port, the binary will be shrunk
│ │ │ │  and any further append operation will copy the binary data into a new binary.
│ │ │ │  For example, in the following code fragment <code class="inline">Bin1</code> will be copied in the third
│ │ │ │ -line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3764821789-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3764821789-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3715223954-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3715223954-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="n">PortOrPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3764821789-2">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3764821789-2">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The same happens if you insert a binary into an Ets table, send it to a port
│ │ │ │ +</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3715223954-2">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3715223954-2">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The same happens if you insert a binary into an Ets table, send it to a port
│ │ │ │  using <a href="../../../lib/../erts/doc/html/erlang.html#port_command/2"><code class="inline">erlang:port_command/2</code></a>, or pass it to
│ │ │ │  <a href="../../../lib/../erts/doc/html/erl_nif.xhtml#enif_inspect_binary">enif_inspect_binary</a> in a NIF.</p><p>Matching a binary will also cause it to shrink and the next append operation
│ │ │ │ -will copy the binary data:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8560844973-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8560844973-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8560844973-2">&lt;&lt;</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8560844973-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8560844973-3">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8560844973-3">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The reason is that a <a href="binaryhandling.xhtml#match_context">match context</a> contains a
│ │ │ │ +will copy the binary data:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1210353783-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1210353783-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1210353783-2">&lt;&lt;</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1210353783-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1210353783-3">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1210353783-3">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The reason is that a <a href="binaryhandling.xhtml#match_context">match context</a> contains a
│ │ │ │  direct pointer to the binary data.</p><p>If a process simply keeps binaries (either in &quot;loop data&quot; or in the process
│ │ │ │  dictionary), the garbage collector can eventually shrink the binaries. If only
│ │ │ │  one such binary is kept, it will not be shrunk. If the process later appends to
│ │ │ │  a binary that has been shrunk, the binary object will be reallocated to make
│ │ │ │  place for the data to be appended.</p><h2 id="matching-binaries" class="section-heading">
│ │ │ │    <a href="#matching-binaries" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Matching Binaries</span>
│ │ │ │  </h2>
│ │ │ │ -<p>Let us revisit the example in the beginning of the previous section:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="9474404374-1">(</span><span class="p" data-group-id="9474404374-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9474404374-2">&gt;&gt;</span><span class="p" data-group-id="9474404374-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9474404374-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="9474404374-4">(</span><span class="n">T</span><span class="p" data-group-id="9474404374-4">)</span><span class="p" data-group-id="9474404374-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="9474404374-5">(</span><span class="p" data-group-id="9474404374-6">&lt;&lt;</span><span class="p" data-group-id="9474404374-6">&gt;&gt;</span><span class="p" data-group-id="9474404374-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9474404374-7">[</span><span class="p" data-group-id="9474404374-7">]</span><span class="p">.</span></code></pre><p>The first time <code class="inline">my_binary_to_list/1</code> is called, a
│ │ │ │ +<p>Let us revisit the example in the beginning of the previous section:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="6417391310-1">(</span><span class="p" data-group-id="6417391310-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6417391310-2">&gt;&gt;</span><span class="p" data-group-id="6417391310-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6417391310-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="6417391310-4">(</span><span class="n">T</span><span class="p" data-group-id="6417391310-4">)</span><span class="p" data-group-id="6417391310-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="6417391310-5">(</span><span class="p" data-group-id="6417391310-6">&lt;&lt;</span><span class="p" data-group-id="6417391310-6">&gt;&gt;</span><span class="p" data-group-id="6417391310-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6417391310-7">[</span><span class="p" data-group-id="6417391310-7">]</span><span class="p">.</span></code></pre><p>The first time <code class="inline">my_binary_to_list/1</code> is called, a
│ │ │ │  <a href="binaryhandling.xhtml#match_context">match context</a> is created. The match context
│ │ │ │  points to the first byte of the binary. 1 byte is matched out and the match
│ │ │ │  context is updated to point to the second byte in the binary.</p><p>At this point it would make sense to create a
│ │ │ │  <a href="binaryhandling.xhtml#sub_binary">sub binary</a>, but in this particular example the
│ │ │ │  compiler sees that there will soon be a call to a function (in this case, to
│ │ │ │  <code class="inline">my_binary_to_list/1</code> itself) that immediately will create a new match context
│ │ │ │  and discard the sub binary.</p><p>Therefore <code class="inline">my_binary_to_list/1</code> calls itself with the match context instead of
│ │ │ │  with a sub binary. The instruction that initializes the matching operation
│ │ │ │  basically does nothing when it sees that it was passed a match context instead
│ │ │ │  of a binary.</p><p>When the end of the binary is reached and the second clause matches, the match
│ │ │ │  context will simply be discarded (removed in the next garbage collection, as
│ │ │ │  there is no longer any reference to it).</p><p>To summarize, <code class="inline">my_binary_to_list/1</code> only needs to create <em>one</em> match context and
│ │ │ │  no sub binaries.</p><p>Notice that the match context in <code class="inline">my_binary_to_list/1</code> was discarded when the
│ │ │ │  entire binary had been traversed. What happens if the iteration stops before it
│ │ │ │ -has reached the end of the binary? Will the optimization still work?</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="9149512589-1">(</span><span class="p" data-group-id="9149512589-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9149512589-2">&gt;&gt;</span><span class="p" data-group-id="9149512589-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +has reached the end of the binary? Will the optimization still work?</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="5332581784-1">(</span><span class="p" data-group-id="5332581784-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5332581784-2">&gt;&gt;</span><span class="p" data-group-id="5332581784-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="9149512589-3">(</span><span class="p" data-group-id="9149512589-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9149512589-4">&gt;&gt;</span><span class="p" data-group-id="9149512589-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="9149512589-5">(</span><span class="n">T</span><span class="p" data-group-id="9149512589-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="9149512589-6">(</span><span class="p" data-group-id="9149512589-7">&lt;&lt;</span><span class="p" data-group-id="9149512589-7">&gt;&gt;</span><span class="p" data-group-id="9149512589-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9149512589-8">&lt;&lt;</span><span class="p" data-group-id="9149512589-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>Yes, it will. The compiler will remove the building of the sub binary in the
│ │ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="5332581784-3">(</span><span class="p" data-group-id="5332581784-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5332581784-4">&gt;&gt;</span><span class="p" data-group-id="5332581784-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="5332581784-5">(</span><span class="n">T</span><span class="p" data-group-id="5332581784-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="5332581784-6">(</span><span class="p" data-group-id="5332581784-7">&lt;&lt;</span><span class="p" data-group-id="5332581784-7">&gt;&gt;</span><span class="p" data-group-id="5332581784-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5332581784-8">&lt;&lt;</span><span class="p" data-group-id="5332581784-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>Yes, it will. The compiler will remove the building of the sub binary in the
│ │ │ │  second clause:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="2833464380-1">(</span><span class="p" data-group-id="2833464380-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2833464380-2">&gt;&gt;</span><span class="p" data-group-id="2833464380-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="2833464380-3">(</span><span class="n">T</span><span class="p" data-group-id="2833464380-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>But it will generate code that builds a sub binary in the first clause:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="5537300143-1">(</span><span class="p" data-group-id="5537300143-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5537300143-2">&gt;&gt;</span><span class="p" data-group-id="5537300143-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="8849024463-1">(</span><span class="p" data-group-id="8849024463-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8849024463-2">&gt;&gt;</span><span class="p" data-group-id="8849024463-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="8849024463-3">(</span><span class="n">T</span><span class="p" data-group-id="8849024463-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>But it will generate code that builds a sub binary in the first clause:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="4534504414-1">(</span><span class="p" data-group-id="4534504414-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4534504414-2">&gt;&gt;</span><span class="p" data-group-id="4534504414-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Therefore, <code class="inline">after_zero/1</code> builds one match context and one sub binary (assuming
│ │ │ │ -it is passed a binary that contains a zero byte).</p><p>Code like the following will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="5493130805-1">(</span><span class="n">Buffer</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5493130805-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5493130805-2">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="5493130805-3">(</span><span class="n">Acc</span><span class="p" data-group-id="5493130805-3">)</span><span class="p">,</span><span class="n">Buffer</span><span class="p" data-group-id="5493130805-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="5493130805-4">(</span><span class="p" data-group-id="5493130805-5">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5493130805-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="5493130805-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="5493130805-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5493130805-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="5493130805-7">(</span><span class="p" data-group-id="5493130805-8">&lt;&lt;</span><span class="n">Byte</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5493130805-8">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="5493130805-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="5493130805-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5493130805-10">[</span><span class="n">Byte</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="5493130805-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5493130805-9">)</span><span class="p">.</span></code></pre><p>The compiler removes building of sub binaries in the second and third clauses,
│ │ │ │ +it is passed a binary that contains a zero byte).</p><p>Code like the following will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="5173689879-1">(</span><span class="n">Buffer</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5173689879-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5173689879-2">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="5173689879-3">(</span><span class="n">Acc</span><span class="p" data-group-id="5173689879-3">)</span><span class="p">,</span><span class="n">Buffer</span><span class="p" data-group-id="5173689879-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="5173689879-4">(</span><span class="p" data-group-id="5173689879-5">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5173689879-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="5173689879-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="5173689879-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5173689879-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="5173689879-7">(</span><span class="p" data-group-id="5173689879-8">&lt;&lt;</span><span class="n">Byte</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5173689879-8">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="5173689879-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="5173689879-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5173689879-10">[</span><span class="n">Byte</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="5173689879-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5173689879-9">)</span><span class="p">.</span></code></pre><p>The compiler removes building of sub binaries in the second and third clauses,
│ │ │ │  and it adds an instruction to the first clause that converts <code class="inline">Buffer</code> from a
│ │ │ │  match context to a sub binary (or do nothing if <code class="inline">Buffer</code> is a binary already).</p><p>But in more complicated code, how can one know whether the optimization is
│ │ │ │  applied or not?</p><p><a href="" id="bin_opt_info"></a></p><h3 id="option-bin_opt_info" class="section-heading">
│ │ │ │    <a href="#option-bin_opt_info" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Option bin_opt_info</span>
│ │ │ │ @@ -259,35 +259,35 @@
│ │ │ │  <p>Use the <code class="inline">bin_opt_info</code> option to have the compiler print a lot of information
│ │ │ │  about binary optimizations. It can be given either to the compiler or <code class="inline">erlc</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">erlc</span><span class="w"> </span><span class="o">+</span><span class="ss">bin_opt_info</span><span class="w"> </span><span class="n">Mod</span><span class="p">.</span><span class="ss">erl</span></code></pre><p>or passed through an environment variable:</p><pre><code class="makeup erlang" translate="no"><span class="ss">export</span><span class="w"> </span><span class="n">ERL_COMPILER_OPTIONS</span><span class="o">=</span><span class="ss">bin_opt_info</span></code></pre><p>Notice that the <code class="inline">bin_opt_info</code> is not meant to be a permanent option added to
│ │ │ │  your <code class="inline">Makefile</code>s, because all messages that it generates cannot be eliminated.
│ │ │ │  Therefore, passing the option through the environment is in most cases the most
│ │ │ │  practical approach.</p><p>The warnings look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="o">/</span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">60</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">NOT</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">binary</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">returned</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">function</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="o">/</span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">62</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">context</span><span class="w"> </span><span class="ss">reused</span></code></pre><p>To make it clearer exactly what code the warnings refer to, the warnings in the
│ │ │ │  following examples are inserted as comments after the clause they refer to, for
│ │ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="7149717021-1">(</span><span class="p" data-group-id="7149717021-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7149717021-2">&gt;&gt;</span><span class="p" data-group-id="7149717021-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="1055283589-1">(</span><span class="p" data-group-id="1055283589-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1055283589-2">&gt;&gt;</span><span class="p" data-group-id="1055283589-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │           </span><span class="c1">%% BINARY CREATED: binary is returned from the function</span><span class="w">
│ │ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="7149717021-3">(</span><span class="p" data-group-id="7149717021-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7149717021-4">&gt;&gt;</span><span class="p" data-group-id="7149717021-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="1055283589-3">(</span><span class="p" data-group-id="1055283589-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1055283589-4">&gt;&gt;</span><span class="p" data-group-id="1055283589-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │           </span><span class="c1">%% OPTIMIZED: match context reused</span><span class="w">
│ │ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="7149717021-5">(</span><span class="n">T</span><span class="p" data-group-id="7149717021-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="7149717021-6">(</span><span class="p" data-group-id="7149717021-7">&lt;&lt;</span><span class="p" data-group-id="7149717021-7">&gt;&gt;</span><span class="p" data-group-id="7149717021-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7149717021-8">&lt;&lt;</span><span class="p" data-group-id="7149717021-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>The warning for the first clause says that the creation of a sub binary cannot
│ │ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="1055283589-5">(</span><span class="n">T</span><span class="p" data-group-id="1055283589-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="1055283589-6">(</span><span class="p" data-group-id="1055283589-7">&lt;&lt;</span><span class="p" data-group-id="1055283589-7">&gt;&gt;</span><span class="p" data-group-id="1055283589-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1055283589-8">&lt;&lt;</span><span class="p" data-group-id="1055283589-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>The warning for the first clause says that the creation of a sub binary cannot
│ │ │ │  be delayed, because it will be returned. The warning for the second clause says
│ │ │ │  that a sub binary will not be created (yet).</p><h3 id="unused-variables" class="section-heading">
│ │ │ │    <a href="#unused-variables" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Unused Variables</span>
│ │ │ │  </h3>
│ │ │ │  <p>The compiler figures out if a variable is unused. The same code is generated for
│ │ │ │ -each of the following functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">count1</span><span class="p" data-group-id="9273670279-1">(</span><span class="p" data-group-id="9273670279-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9273670279-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9273670279-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count1</span><span class="p" data-group-id="9273670279-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="9273670279-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">count1</span><span class="p" data-group-id="9273670279-4">(</span><span class="p" data-group-id="9273670279-5">&lt;&lt;</span><span class="p" data-group-id="9273670279-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9273670279-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ │ +each of the following functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">count1</span><span class="p" data-group-id="9000975526-1">(</span><span class="p" data-group-id="9000975526-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9000975526-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9000975526-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count1</span><span class="p" data-group-id="9000975526-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="9000975526-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">count1</span><span class="p" data-group-id="9000975526-4">(</span><span class="p" data-group-id="9000975526-5">&lt;&lt;</span><span class="p" data-group-id="9000975526-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9000975526-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">count2</span><span class="p" data-group-id="9273670279-6">(</span><span class="p" data-group-id="9273670279-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9273670279-7">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9273670279-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count2</span><span class="p" data-group-id="9273670279-8">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="9273670279-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">count2</span><span class="p" data-group-id="9273670279-9">(</span><span class="p" data-group-id="9273670279-10">&lt;&lt;</span><span class="p" data-group-id="9273670279-10">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9273670279-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">count2</span><span class="p" data-group-id="9000975526-6">(</span><span class="p" data-group-id="9000975526-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9000975526-7">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9000975526-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count2</span><span class="p" data-group-id="9000975526-8">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="9000975526-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">count2</span><span class="p" data-group-id="9000975526-9">(</span><span class="p" data-group-id="9000975526-10">&lt;&lt;</span><span class="p" data-group-id="9000975526-10">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9000975526-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">count3</span><span class="p" data-group-id="9273670279-11">(</span><span class="p" data-group-id="9273670279-12">&lt;&lt;</span><span class="p">_</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9273670279-12">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9273670279-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count3</span><span class="p" data-group-id="9273670279-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="9273670279-13">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">count3</span><span class="p" data-group-id="9273670279-14">(</span><span class="p" data-group-id="9273670279-15">&lt;&lt;</span><span class="p" data-group-id="9273670279-15">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9273670279-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span></code></pre><p>In each iteration, the first 8 bits in the binary will be skipped, not matched
│ │ │ │ +</span><span class="nf">count3</span><span class="p" data-group-id="9000975526-11">(</span><span class="p" data-group-id="9000975526-12">&lt;&lt;</span><span class="p">_</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9000975526-12">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9000975526-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count3</span><span class="p" data-group-id="9000975526-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="9000975526-13">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">count3</span><span class="p" data-group-id="9000975526-14">(</span><span class="p" data-group-id="9000975526-15">&lt;&lt;</span><span class="p" data-group-id="9000975526-15">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="9000975526-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span></code></pre><p>In each iteration, the first 8 bits in the binary will be skipped, not matched
│ │ │ │  out.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/benchmarking.xhtml
│ │ │ │ @@ -49,16 +49,16 @@
│ │ │ │  fast as possible, what can we do? One way could be to generate more
│ │ │ │  than two bytes at the time.</p><pre><code class="text">% erlperf 'rand:bytes(100).' 'crypto:strong_rand_bytes(100).'
│ │ │ │  Code                                   ||        QPS       Time   Rel
│ │ │ │  rand:bytes(100).                        1    2124 Ki     470 ns  100%
│ │ │ │  crypto:strong_rand_bytes(100).          1    1915 Ki     522 ns   90%</code></pre><p><a href="../../../lib/stdlib/doc/html/rand.html#bytes/1"><code class="inline">rand:bytes/1</code></a> is still faster when we generate 100 bytes at the time,
│ │ │ │  but the relative difference is smaller.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erlperf &#39;rand:bytes(1000).&#39; &#39;crypto:strong_rand_bytes(1000).&#39;</span><span class="w">
│ │ │ │  </span><span class="n">Code</span><span class="w">                                    </span><span class="p">||</span><span class="w">        </span><span class="n">QPS</span><span class="w">       </span><span class="n">Time</span><span class="w">   </span><span class="n">Rel</span><span class="w">
│ │ │ │ -</span><span class="nc">crypto</span><span class="p">:</span><span class="nf">strong_rand_bytes</span><span class="p" data-group-id="2688501447-1">(</span><span class="mi">1000</span><span class="p" data-group-id="2688501447-1">)</span><span class="p">.</span><span class="w">          </span><span class="mi">1</span><span class="w">    </span><span class="mi">1518</span><span class="w"> </span><span class="n">Ki</span><span class="w">     </span><span class="mi">658</span><span class="w"> </span><span class="ss">ns</span><span class="w">  </span><span class="mi">100</span><span class="c1">%</span><span class="w">
│ │ │ │ -</span><span class="nc">rand</span><span class="p">:</span><span class="nf">bytes</span><span class="p" data-group-id="2688501447-2">(</span><span class="mi">1000</span><span class="p" data-group-id="2688501447-2">)</span><span class="p">.</span><span class="w">                        </span><span class="mi">1</span><span class="w">     </span><span class="mi">284</span><span class="w"> </span><span class="n">Ki</span><span class="w">    </span><span class="mi">3521</span><span class="w"> </span><span class="ss">ns</span><span class="w">   </span><span class="mi">19</span><span class="c1">%</span></code></pre><p>When we generate 1000 bytes at the time, <a href="../../../lib/crypto/doc/html/crypto.html#strong_rand_bytes/1"><code class="inline">crypto:strong_rand_bytes/1</code></a> is
│ │ │ │ +</span><span class="nc">crypto</span><span class="p">:</span><span class="nf">strong_rand_bytes</span><span class="p" data-group-id="5003750092-1">(</span><span class="mi">1000</span><span class="p" data-group-id="5003750092-1">)</span><span class="p">.</span><span class="w">          </span><span class="mi">1</span><span class="w">    </span><span class="mi">1518</span><span class="w"> </span><span class="n">Ki</span><span class="w">     </span><span class="mi">658</span><span class="w"> </span><span class="ss">ns</span><span class="w">  </span><span class="mi">100</span><span class="c1">%</span><span class="w">
│ │ │ │ +</span><span class="nc">rand</span><span class="p">:</span><span class="nf">bytes</span><span class="p" data-group-id="5003750092-2">(</span><span class="mi">1000</span><span class="p" data-group-id="5003750092-2">)</span><span class="p">.</span><span class="w">                        </span><span class="mi">1</span><span class="w">     </span><span class="mi">284</span><span class="w"> </span><span class="n">Ki</span><span class="w">    </span><span class="mi">3521</span><span class="w"> </span><span class="ss">ns</span><span class="w">   </span><span class="mi">19</span><span class="c1">%</span></code></pre><p>When we generate 1000 bytes at the time, <a href="../../../lib/crypto/doc/html/crypto.html#strong_rand_bytes/1"><code class="inline">crypto:strong_rand_bytes/1</code></a> is
│ │ │ │  now the fastest.</p><h2 id="benchmarking-using-erlang-otp-functionality" class="section-heading">
│ │ │ │    <a href="#benchmarking-using-erlang-otp-functionality" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Benchmarking using Erlang/OTP functionality</span>
│ │ │ │  </h2>
│ │ │ │  <p>Benchmarks can measure wall-clock time or CPU time.</p><ul><li><p><a href="../../../lib/stdlib/doc/html/timer.html#tc/3"><code class="inline">timer:tc/3</code></a> measures wall-clock time. The advantage with wall-clock time is
│ │ │ ├── OEBPS/appup_cookbook.xhtml
│ │ │ │ @@ -25,18 +25,18 @@
│ │ │ │    <a href="#changing-a-functional-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing a Functional Module</span>
│ │ │ │  </h2>
│ │ │ │  <p>When a functional module has been changed, for example, if a new function has
│ │ │ │  been added or a bug has been corrected, simple code replacement is sufficient,
│ │ │ │ -for example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5009450712-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5009450712-2">[</span><span class="p" data-group-id="5009450712-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5009450712-4">[</span><span class="p" data-group-id="5009450712-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="5009450712-5">}</span><span class="p" data-group-id="5009450712-4">]</span><span class="p" data-group-id="5009450712-3">}</span><span class="p" data-group-id="5009450712-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5009450712-6">[</span><span class="p" data-group-id="5009450712-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5009450712-8">[</span><span class="p" data-group-id="5009450712-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="5009450712-9">}</span><span class="p" data-group-id="5009450712-8">]</span><span class="p" data-group-id="5009450712-7">}</span><span class="p" data-group-id="5009450712-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5009450712-1">}</span><span class="p">.</span></code></pre><h2 id="changing-a-residence-module" class="section-heading">
│ │ │ │ +for example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7375752501-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7375752501-2">[</span><span class="p" data-group-id="7375752501-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7375752501-4">[</span><span class="p" data-group-id="7375752501-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="7375752501-5">}</span><span class="p" data-group-id="7375752501-4">]</span><span class="p" data-group-id="7375752501-3">}</span><span class="p" data-group-id="7375752501-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7375752501-6">[</span><span class="p" data-group-id="7375752501-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7375752501-8">[</span><span class="p" data-group-id="7375752501-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="7375752501-9">}</span><span class="p" data-group-id="7375752501-8">]</span><span class="p" data-group-id="7375752501-7">}</span><span class="p" data-group-id="7375752501-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7375752501-1">}</span><span class="p">.</span></code></pre><h2 id="changing-a-residence-module" class="section-heading">
│ │ │ │    <a href="#changing-a-residence-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing a Residence Module</span>
│ │ │ │  </h2>
│ │ │ │  <p>In a system implemented according to the OTP design principles, all processes,
│ │ │ │  except system processes and special processes, reside in one of the behaviours
│ │ │ │ @@ -47,46 +47,46 @@
│ │ │ │    <a href="#changing-a-callback-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing a Callback Module</span>
│ │ │ │  </h2>
│ │ │ │  <p>A callback module is a functional module, and for code extensions simple code
│ │ │ │  replacement is sufficient.</p><p><em>Example</em></p><p>When adding a function to <code class="inline">ch3</code>, as described in the example in
│ │ │ │ -<a href="release_handling.xhtml#appup">Release Handling</a>, <code class="inline">ch_app.appup</code> looks as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6401599889-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6401599889-2">[</span><span class="p" data-group-id="6401599889-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6401599889-4">[</span><span class="p" data-group-id="6401599889-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6401599889-5">}</span><span class="p" data-group-id="6401599889-4">]</span><span class="p" data-group-id="6401599889-3">}</span><span class="p" data-group-id="6401599889-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6401599889-6">[</span><span class="p" data-group-id="6401599889-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6401599889-8">[</span><span class="p" data-group-id="6401599889-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6401599889-9">}</span><span class="p" data-group-id="6401599889-8">]</span><span class="p" data-group-id="6401599889-7">}</span><span class="p" data-group-id="6401599889-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6401599889-1">}</span><span class="p">.</span></code></pre><p>OTP also supports changing the internal state of behaviour processes; see
│ │ │ │ +<a href="release_handling.xhtml#appup">Release Handling</a>, <code class="inline">ch_app.appup</code> looks as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8700415290-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8700415290-2">[</span><span class="p" data-group-id="8700415290-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8700415290-4">[</span><span class="p" data-group-id="8700415290-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8700415290-5">}</span><span class="p" data-group-id="8700415290-4">]</span><span class="p" data-group-id="8700415290-3">}</span><span class="p" data-group-id="8700415290-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8700415290-6">[</span><span class="p" data-group-id="8700415290-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8700415290-8">[</span><span class="p" data-group-id="8700415290-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8700415290-9">}</span><span class="p" data-group-id="8700415290-8">]</span><span class="p" data-group-id="8700415290-7">}</span><span class="p" data-group-id="8700415290-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8700415290-1">}</span><span class="p">.</span></code></pre><p>OTP also supports changing the internal state of behaviour processes; see
│ │ │ │  <a href="appup_cookbook.xhtml#int_state">Changing Internal State</a>.</p><p><a href="" id="int_state"></a></p><h2 id="changing-internal-state" class="section-heading">
│ │ │ │    <a href="#changing-internal-state" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing Internal State</span>
│ │ │ │  </h2>
│ │ │ │  <p>In this case, simple code replacement is not sufficient. The process must
│ │ │ │  explicitly transform its state using the callback function <code class="inline">code_change/3</code> before
│ │ │ │  switching to the new version of the callback module. Thus, synchronized code
│ │ │ │  replacement is used.</p><p><em>Example</em></p><p>Consider the <code class="inline">ch3</code> module from
│ │ │ │  <a href="gen_server_concepts.xhtml#ex">gen_server Behaviour</a>. The internal state is a term
│ │ │ │  <code class="inline">Chs</code> representing the available channels. Assume you want to add a counter <code class="inline">N</code>,
│ │ │ │  which keeps track of the number of <code class="inline">alloc</code> requests so far. This means that the
│ │ │ │ -format must be changed to <code class="inline">{Chs,N}</code>.</p><p>The <code class="inline">.appup</code> file can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0665311963-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0665311963-2">[</span><span class="p" data-group-id="0665311963-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0665311963-4">[</span><span class="p" data-group-id="0665311963-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0665311963-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0665311963-7">[</span><span class="p" data-group-id="0665311963-7">]</span><span class="p" data-group-id="0665311963-6">}</span><span class="p" data-group-id="0665311963-5">}</span><span class="p" data-group-id="0665311963-4">]</span><span class="p" data-group-id="0665311963-3">}</span><span class="p" data-group-id="0665311963-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0665311963-8">[</span><span class="p" data-group-id="0665311963-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0665311963-10">[</span><span class="p" data-group-id="0665311963-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0665311963-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0665311963-13">[</span><span class="p" data-group-id="0665311963-13">]</span><span class="p" data-group-id="0665311963-12">}</span><span class="p" data-group-id="0665311963-11">}</span><span class="p" data-group-id="0665311963-10">]</span><span class="p" data-group-id="0665311963-9">}</span><span class="p" data-group-id="0665311963-8">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0665311963-1">}</span><span class="p">.</span></code></pre><p>The third element of the <code class="inline">update</code> instruction is a tuple <code class="inline">{advanced,Extra}</code>,
│ │ │ │ +format must be changed to <code class="inline">{Chs,N}</code>.</p><p>The <code class="inline">.appup</code> file can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1999422030-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1999422030-2">[</span><span class="p" data-group-id="1999422030-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1999422030-4">[</span><span class="p" data-group-id="1999422030-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1999422030-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1999422030-7">[</span><span class="p" data-group-id="1999422030-7">]</span><span class="p" data-group-id="1999422030-6">}</span><span class="p" data-group-id="1999422030-5">}</span><span class="p" data-group-id="1999422030-4">]</span><span class="p" data-group-id="1999422030-3">}</span><span class="p" data-group-id="1999422030-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1999422030-8">[</span><span class="p" data-group-id="1999422030-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1999422030-10">[</span><span class="p" data-group-id="1999422030-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1999422030-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1999422030-13">[</span><span class="p" data-group-id="1999422030-13">]</span><span class="p" data-group-id="1999422030-12">}</span><span class="p" data-group-id="1999422030-11">}</span><span class="p" data-group-id="1999422030-10">]</span><span class="p" data-group-id="1999422030-9">}</span><span class="p" data-group-id="1999422030-8">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1999422030-1">}</span><span class="p">.</span></code></pre><p>The third element of the <code class="inline">update</code> instruction is a tuple <code class="inline">{advanced,Extra}</code>,
│ │ │ │  which says that the affected processes are to do a state transformation before
│ │ │ │  loading the new version of the module. This is done by the processes calling the
│ │ │ │  callback function <code class="inline">code_change/3</code> (see <a href="../../../lib/stdlib/doc/html/gen_server.html"><code class="inline">gen_server</code></a> in STDLIB).
│ │ │ │ -The term <code class="inline">Extra</code>, in this case <code class="inline">[]</code>, is passed as is to the function:</p><p><a href="" id="code_change"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8933223056-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="8933223056-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +The term <code class="inline">Extra</code>, in this case <code class="inline">[]</code>, is passed as is to the function:</p><p><a href="" id="code_change"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4839277250-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="4839277250-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8933223056-2">(</span><span class="p" data-group-id="8933223056-3">[</span><span class="ss">code_change</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="8933223056-3">]</span><span class="p" data-group-id="8933223056-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4839277250-2">(</span><span class="p" data-group-id="4839277250-3">[</span><span class="ss">code_change</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4839277250-3">]</span><span class="p" data-group-id="4839277250-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">code_change</span><span class="p" data-group-id="8933223056-4">(</span><span class="p" data-group-id="8933223056-5">{</span><span class="ss">down</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vsn</span><span class="p" data-group-id="8933223056-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8933223056-6">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="8933223056-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="8933223056-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8933223056-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8933223056-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">code_change</span><span class="p" data-group-id="8933223056-8">(</span><span class="p">_</span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="8933223056-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8933223056-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8933223056-10">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8933223056-10">}</span><span class="p" data-group-id="8933223056-9">}</span><span class="p">.</span></code></pre><p>The first argument is <code class="inline">{down,Vsn}</code> if there is a downgrade, or <code class="inline">Vsn</code> if there is
│ │ │ │ +</span><span class="nf">code_change</span><span class="p" data-group-id="4839277250-4">(</span><span class="p" data-group-id="4839277250-5">{</span><span class="ss">down</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vsn</span><span class="p" data-group-id="4839277250-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4839277250-6">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="4839277250-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="4839277250-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4839277250-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4839277250-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">code_change</span><span class="p" data-group-id="4839277250-8">(</span><span class="p">_</span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="4839277250-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4839277250-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4839277250-10">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4839277250-10">}</span><span class="p" data-group-id="4839277250-9">}</span><span class="p">.</span></code></pre><p>The first argument is <code class="inline">{down,Vsn}</code> if there is a downgrade, or <code class="inline">Vsn</code> if there is
│ │ │ │  a upgrade. The term <code class="inline">Vsn</code> is fetched from the 'original' version of the module,
│ │ │ │  that is, the version you are upgrading from, or downgrading to.</p><p>The version is defined by the module attribute <code class="inline">vsn</code>, if any. There is no such
│ │ │ │  attribute in <code class="inline">ch3</code>, so in this case the version is the checksum (a huge integer)
│ │ │ │  of the beam file, an uninteresting value, which is ignored.</p><p>The other callback functions of <code class="inline">ch3</code> must also be modified and perhaps a new
│ │ │ │  interface function must be added, but this is not shown here.</p><h2 id="module-dependencies" class="section-heading">
│ │ │ │    <a href="#module-dependencies" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -95,67 +95,67 @@
│ │ │ │  </h2>
│ │ │ │  <p>Assume that a module is extended by adding an interface function, as in the
│ │ │ │  example in <a href="release_handling.xhtml#appup">Release Handling</a>, where a function
│ │ │ │  <code class="inline">available/0</code> is added to <code class="inline">ch3</code>.</p><p>If a call is added to this function, say in module <code class="inline">m1</code>, a runtime error could
│ │ │ │  can occur during release upgrade if the new version of <code class="inline">m1</code> is loaded first and
│ │ │ │  calls <code class="inline">ch3:available/0</code> before the new version of <code class="inline">ch3</code> is loaded.</p><p>Thus, <code class="inline">ch3</code> must be loaded before <code class="inline">m1</code>, in the upgrade case, and conversely in
│ │ │ │  the downgrade case. <code class="inline">m1</code> is said to be <em>dependent on</em> <code class="inline">ch3</code>. In a release
│ │ │ │ -handling instruction, this is expressed by the <code class="inline">DepMods</code> element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9567088751-1">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="9567088751-1">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9567088751-2">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9567088751-3">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="9567088751-3">}</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="9567088751-2">}</span></code></pre><p><code class="inline">DepMods</code> is a list of modules, on which <code class="inline">Module</code> is dependent.</p><p><em>Example</em></p><p>The module <code class="inline">m1</code> in application <code class="inline">myapp</code> is dependent on <code class="inline">ch3</code> when
│ │ │ │ +handling instruction, this is expressed by the <code class="inline">DepMods</code> element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8541361944-1">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="8541361944-1">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8541361944-2">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8541361944-3">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="8541361944-3">}</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="8541361944-2">}</span></code></pre><p><code class="inline">DepMods</code> is a list of modules, on which <code class="inline">Module</code> is dependent.</p><p><em>Example</em></p><p>The module <code class="inline">m1</code> in application <code class="inline">myapp</code> is dependent on <code class="inline">ch3</code> when
│ │ │ │  upgrading from &quot;1&quot; to &quot;2&quot;, or downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="ss">myapp</span><span class="p">.</span><span class="nc">appup</span><span class="p">:</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p" data-group-id="2355140769-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2355140769-2">[</span><span class="p" data-group-id="2355140769-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2355140769-4">[</span><span class="p" data-group-id="2355140769-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2355140769-6">[</span><span class="ss">ch3</span><span class="p" data-group-id="2355140769-6">]</span><span class="p" data-group-id="2355140769-5">}</span><span class="p" data-group-id="2355140769-4">]</span><span class="p" data-group-id="2355140769-3">}</span><span class="p" data-group-id="2355140769-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2355140769-7">[</span><span class="p" data-group-id="2355140769-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2355140769-9">[</span><span class="p" data-group-id="2355140769-10">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2355140769-11">[</span><span class="ss">ch3</span><span class="p" data-group-id="2355140769-11">]</span><span class="p" data-group-id="2355140769-10">}</span><span class="p" data-group-id="2355140769-9">]</span><span class="p" data-group-id="2355140769-8">}</span><span class="p" data-group-id="2355140769-7">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2355140769-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0588848301-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0588848301-2">[</span><span class="p" data-group-id="0588848301-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0588848301-4">[</span><span class="p" data-group-id="0588848301-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0588848301-6">[</span><span class="ss">ch3</span><span class="p" data-group-id="0588848301-6">]</span><span class="p" data-group-id="0588848301-5">}</span><span class="p" data-group-id="0588848301-4">]</span><span class="p" data-group-id="0588848301-3">}</span><span class="p" data-group-id="0588848301-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0588848301-7">[</span><span class="p" data-group-id="0588848301-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0588848301-9">[</span><span class="p" data-group-id="0588848301-10">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0588848301-11">[</span><span class="ss">ch3</span><span class="p" data-group-id="0588848301-11">]</span><span class="p" data-group-id="0588848301-10">}</span><span class="p" data-group-id="0588848301-9">]</span><span class="p" data-group-id="0588848301-8">}</span><span class="p" data-group-id="0588848301-7">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0588848301-1">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="ss">ch_app</span><span class="p">.</span><span class="nc">appup</span><span class="p">:</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p" data-group-id="2355140769-12">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2355140769-13">[</span><span class="p" data-group-id="2355140769-14">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2355140769-15">[</span><span class="p" data-group-id="2355140769-16">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2355140769-16">}</span><span class="p" data-group-id="2355140769-15">]</span><span class="p" data-group-id="2355140769-14">}</span><span class="p" data-group-id="2355140769-13">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2355140769-17">[</span><span class="p" data-group-id="2355140769-18">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2355140769-19">[</span><span class="p" data-group-id="2355140769-20">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2355140769-20">}</span><span class="p" data-group-id="2355140769-19">]</span><span class="p" data-group-id="2355140769-18">}</span><span class="p" data-group-id="2355140769-17">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2355140769-12">}</span><span class="p">.</span></code></pre><p>If instead <code class="inline">m1</code> and <code class="inline">ch3</code> belong to the same application, the <code class="inline">.appup</code> file can
│ │ │ │ -look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9434678847-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9434678847-2">[</span><span class="p" data-group-id="9434678847-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="9434678847-4">[</span><span class="p" data-group-id="9434678847-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="9434678847-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9434678847-6">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9434678847-7">[</span><span class="ss">ch3</span><span class="p" data-group-id="9434678847-7">]</span><span class="p" data-group-id="9434678847-6">}</span><span class="p" data-group-id="9434678847-4">]</span><span class="p" data-group-id="9434678847-3">}</span><span class="p" data-group-id="9434678847-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9434678847-8">[</span><span class="p" data-group-id="9434678847-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="9434678847-10">[</span><span class="p" data-group-id="9434678847-11">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="9434678847-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9434678847-12">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9434678847-13">[</span><span class="ss">ch3</span><span class="p" data-group-id="9434678847-13">]</span><span class="p" data-group-id="9434678847-12">}</span><span class="p" data-group-id="9434678847-10">]</span><span class="p" data-group-id="9434678847-9">}</span><span class="p" data-group-id="9434678847-8">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9434678847-1">}</span><span class="p">.</span></code></pre><p><code class="inline">m1</code> is dependent on <code class="inline">ch3</code> also when downgrading. <code class="inline">systools</code> knows the
│ │ │ │ +</span><span class="p" data-group-id="0588848301-12">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0588848301-13">[</span><span class="p" data-group-id="0588848301-14">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0588848301-15">[</span><span class="p" data-group-id="0588848301-16">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0588848301-16">}</span><span class="p" data-group-id="0588848301-15">]</span><span class="p" data-group-id="0588848301-14">}</span><span class="p" data-group-id="0588848301-13">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0588848301-17">[</span><span class="p" data-group-id="0588848301-18">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0588848301-19">[</span><span class="p" data-group-id="0588848301-20">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0588848301-20">}</span><span class="p" data-group-id="0588848301-19">]</span><span class="p" data-group-id="0588848301-18">}</span><span class="p" data-group-id="0588848301-17">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0588848301-12">}</span><span class="p">.</span></code></pre><p>If instead <code class="inline">m1</code> and <code class="inline">ch3</code> belong to the same application, the <code class="inline">.appup</code> file can
│ │ │ │ +look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2049091322-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2049091322-2">[</span><span class="p" data-group-id="2049091322-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="2049091322-4">[</span><span class="p" data-group-id="2049091322-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2049091322-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2049091322-6">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2049091322-7">[</span><span class="ss">ch3</span><span class="p" data-group-id="2049091322-7">]</span><span class="p" data-group-id="2049091322-6">}</span><span class="p" data-group-id="2049091322-4">]</span><span class="p" data-group-id="2049091322-3">}</span><span class="p" data-group-id="2049091322-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2049091322-8">[</span><span class="p" data-group-id="2049091322-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="2049091322-10">[</span><span class="p" data-group-id="2049091322-11">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2049091322-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2049091322-12">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2049091322-13">[</span><span class="ss">ch3</span><span class="p" data-group-id="2049091322-13">]</span><span class="p" data-group-id="2049091322-12">}</span><span class="p" data-group-id="2049091322-10">]</span><span class="p" data-group-id="2049091322-9">}</span><span class="p" data-group-id="2049091322-8">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2049091322-1">}</span><span class="p">.</span></code></pre><p><code class="inline">m1</code> is dependent on <code class="inline">ch3</code> also when downgrading. <code class="inline">systools</code> knows the
│ │ │ │  difference between up- and downgrading and generates a correct <code class="inline">relup</code>, where
│ │ │ │  <code class="inline">ch3</code> is loaded before <code class="inline">m1</code> when upgrading, but <code class="inline">m1</code> is loaded before <code class="inline">ch3</code> when
│ │ │ │  downgrading.</p><p><a href="" id="spec"></a></p><h2 id="changing-code-for-a-special-process" class="section-heading">
│ │ │ │    <a href="#changing-code-for-a-special-process" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing Code for a Special Process</span>
│ │ │ │  </h2>
│ │ │ │  <p>In this case, simple code replacement is not sufficient. When a new version of a
│ │ │ │  residence module for a special process is loaded, the process must make a fully
│ │ │ │  qualified call to its loop function to switch to the new code. Thus,
│ │ │ │  synchronized code replacement must be used.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The name(s) of the user-defined residence module(s) must be listed in the
│ │ │ │  <code class="inline">Modules</code> part of the child specification for the special process. Otherwise
│ │ │ │  the release handler cannot find the process.</p></section><p><em>Example</em></p><p>Consider the example <code class="inline">ch4</code> in <a href="spec_proc.xhtml#ex">sys and proc_lib</a>.
│ │ │ │ -When started by a supervisor, the child specification can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2198418346-1">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2198418346-2">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2198418346-3">[</span><span class="p" data-group-id="2198418346-3">]</span><span class="p" data-group-id="2198418346-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="ss">permanent</span><span class="p">,</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2198418346-4">[</span><span class="ss">ch4</span><span class="p" data-group-id="2198418346-4">]</span><span class="p" data-group-id="2198418346-1">}</span></code></pre><p>If <code class="inline">ch4</code> is part of the application <code class="inline">sp_app</code> and a new version of the module is
│ │ │ │ +When started by a supervisor, the child specification can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5407085022-1">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5407085022-2">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5407085022-3">[</span><span class="p" data-group-id="5407085022-3">]</span><span class="p" data-group-id="5407085022-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="ss">permanent</span><span class="p">,</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5407085022-4">[</span><span class="ss">ch4</span><span class="p" data-group-id="5407085022-4">]</span><span class="p" data-group-id="5407085022-1">}</span></code></pre><p>If <code class="inline">ch4</code> is part of the application <code class="inline">sp_app</code> and a new version of the module is
│ │ │ │  to be loaded when upgrading from version &quot;1&quot; to &quot;2&quot; of this application,
│ │ │ │ -<code class="inline">sp_app.appup</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9304419880-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9304419880-2">[</span><span class="p" data-group-id="9304419880-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9304419880-4">[</span><span class="p" data-group-id="9304419880-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9304419880-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9304419880-7">[</span><span class="p" data-group-id="9304419880-7">]</span><span class="p" data-group-id="9304419880-6">}</span><span class="p" data-group-id="9304419880-5">}</span><span class="p" data-group-id="9304419880-4">]</span><span class="p" data-group-id="9304419880-3">}</span><span class="p" data-group-id="9304419880-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9304419880-8">[</span><span class="p" data-group-id="9304419880-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9304419880-10">[</span><span class="p" data-group-id="9304419880-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9304419880-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9304419880-13">[</span><span class="p" data-group-id="9304419880-13">]</span><span class="p" data-group-id="9304419880-12">}</span><span class="p" data-group-id="9304419880-11">}</span><span class="p" data-group-id="9304419880-10">]</span><span class="p" data-group-id="9304419880-9">}</span><span class="p" data-group-id="9304419880-8">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9304419880-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">update</code> instruction must contain the tuple <code class="inline">{advanced,Extra}</code>. The
│ │ │ │ +<code class="inline">sp_app.appup</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4700693449-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4700693449-2">[</span><span class="p" data-group-id="4700693449-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4700693449-4">[</span><span class="p" data-group-id="4700693449-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4700693449-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4700693449-7">[</span><span class="p" data-group-id="4700693449-7">]</span><span class="p" data-group-id="4700693449-6">}</span><span class="p" data-group-id="4700693449-5">}</span><span class="p" data-group-id="4700693449-4">]</span><span class="p" data-group-id="4700693449-3">}</span><span class="p" data-group-id="4700693449-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4700693449-8">[</span><span class="p" data-group-id="4700693449-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4700693449-10">[</span><span class="p" data-group-id="4700693449-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4700693449-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4700693449-13">[</span><span class="p" data-group-id="4700693449-13">]</span><span class="p" data-group-id="4700693449-12">}</span><span class="p" data-group-id="4700693449-11">}</span><span class="p" data-group-id="4700693449-10">]</span><span class="p" data-group-id="4700693449-9">}</span><span class="p" data-group-id="4700693449-8">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4700693449-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">update</code> instruction must contain the tuple <code class="inline">{advanced,Extra}</code>. The
│ │ │ │  instruction makes the special process call the callback function
│ │ │ │  <code class="inline">system_code_change/4</code>, a function the user must implement. The term <code class="inline">Extra</code>, in
│ │ │ │ -this case <code class="inline">[]</code>, is passed as is to <code class="inline">system_code_change/4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7489846155-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="7489846155-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +this case <code class="inline">[]</code>, is passed as is to <code class="inline">system_code_change/4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0913934013-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="0913934013-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7489846155-2">(</span><span class="p" data-group-id="7489846155-3">[</span><span class="ss">system_code_change</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="7489846155-3">]</span><span class="p" data-group-id="7489846155-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0913934013-2">(</span><span class="p" data-group-id="0913934013-3">[</span><span class="ss">system_code_change</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="0913934013-3">]</span><span class="p" data-group-id="0913934013-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_code_change</span><span class="p" data-group-id="7489846155-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="7489846155-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7489846155-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7489846155-5">}</span><span class="p">.</span></code></pre><ul><li>The first argument is the internal state <code class="inline">State</code>, passed from
│ │ │ │ +</span><span class="nf">system_code_change</span><span class="p" data-group-id="0913934013-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="0913934013-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0913934013-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0913934013-5">}</span><span class="p">.</span></code></pre><ul><li>The first argument is the internal state <code class="inline">State</code>, passed from
│ │ │ │  function <a href="../../../lib/stdlib/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg(Request, From, Parent, Module, Deb, State)</code></a>, and called by the special
│ │ │ │  process when a system message is received. In <code class="inline">ch4</code>, the internal
│ │ │ │  state is the set of available channels <code class="inline">Chs</code>.</li><li>The second argument is the name of the module (<code class="inline">ch4</code>).</li><li>The third argument is <code class="inline">Vsn</code> or <code class="inline">{down,Vsn}</code>, as described for
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_server.html#c:code_change/3"><code class="inline">gen_server:code_change/3</code></a> in
│ │ │ │  <a href="appup_cookbook.xhtml#code_change">Changing Internal State</a>.</li></ul><p>In this case, all arguments but the first are ignored and the function simply
│ │ │ │  returns the internal state again. This is enough if the code only has been
│ │ │ │  extended. If instead the internal state is changed (similar to the example in
│ │ │ │ @@ -176,85 +176,85 @@
│ │ │ │    <span class="text">Changing Properties</span>
│ │ │ │  </h3>
│ │ │ │  <p>Since the supervisor is to change its internal state, synchronized code
│ │ │ │  replacement is required. However, a special <code class="inline">update</code> instruction must be used.</p><p>First, the new version of the callback module must be loaded, both in the case
│ │ │ │  of upgrade and downgrade. Then the new return value of <code class="inline">init/1</code> can be checked
│ │ │ │  and the internal state be changed accordingly.</p><p>The following <code class="inline">upgrade</code> instruction is used for supervisors:</p><pre><code class="text">{update, Module, supervisor}</code></pre><p><em>Example</em></p><p>To change the restart strategy of <code class="inline">ch_sup</code> (from
│ │ │ │  <a href="sup_princ.xhtml#ex">Supervisor Behaviour</a>) from <code class="inline">one_for_one</code> to <code class="inline">one_for_all</code>,
│ │ │ │ -change the callback function <code class="inline">init/1</code> in <code class="inline">ch_sup.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8544414745-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="8544414745-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +change the callback function <code class="inline">init/1</code> in <code class="inline">ch_sup.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2093910890-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="2093910890-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8544414745-2">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="8544414745-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8544414745-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8544414745-4">{</span><span class="p" data-group-id="8544414745-5">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_all</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8544414745-5">}</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8544414745-4">}</span><span class="p" data-group-id="8544414745-3">}</span><span class="p">.</span></code></pre><p>The file <code class="inline">ch_app.appup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7783491763-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7783491763-2">[</span><span class="p" data-group-id="7783491763-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7783491763-4">[</span><span class="p" data-group-id="7783491763-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7783491763-5">}</span><span class="p" data-group-id="7783491763-4">]</span><span class="p" data-group-id="7783491763-3">}</span><span class="p" data-group-id="7783491763-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7783491763-6">[</span><span class="p" data-group-id="7783491763-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7783491763-8">[</span><span class="p" data-group-id="7783491763-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7783491763-9">}</span><span class="p" data-group-id="7783491763-8">]</span><span class="p" data-group-id="7783491763-7">}</span><span class="p" data-group-id="7783491763-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7783491763-1">}</span><span class="p">.</span></code></pre><h3 id="changing-child-specifications" class="section-heading">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="2093910890-2">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="2093910890-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2093910890-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2093910890-4">{</span><span class="p" data-group-id="2093910890-5">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_all</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2093910890-5">}</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2093910890-4">}</span><span class="p" data-group-id="2093910890-3">}</span><span class="p">.</span></code></pre><p>The file <code class="inline">ch_app.appup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3564246410-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3564246410-2">[</span><span class="p" data-group-id="3564246410-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3564246410-4">[</span><span class="p" data-group-id="3564246410-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3564246410-5">}</span><span class="p" data-group-id="3564246410-4">]</span><span class="p" data-group-id="3564246410-3">}</span><span class="p" data-group-id="3564246410-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3564246410-6">[</span><span class="p" data-group-id="3564246410-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3564246410-8">[</span><span class="p" data-group-id="3564246410-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3564246410-9">}</span><span class="p" data-group-id="3564246410-8">]</span><span class="p" data-group-id="3564246410-7">}</span><span class="p" data-group-id="3564246410-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3564246410-1">}</span><span class="p">.</span></code></pre><h3 id="changing-child-specifications" class="section-heading">
│ │ │ │    <a href="#changing-child-specifications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing Child Specifications</span>
│ │ │ │  </h3>
│ │ │ │  <p>The instruction, and thus the <code class="inline">.appup</code> file, when changing an existing child
│ │ │ │ -specification, is the same as when changing properties as described earlier:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3770808576-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3770808576-2">[</span><span class="p" data-group-id="3770808576-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3770808576-4">[</span><span class="p" data-group-id="3770808576-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3770808576-5">}</span><span class="p" data-group-id="3770808576-4">]</span><span class="p" data-group-id="3770808576-3">}</span><span class="p" data-group-id="3770808576-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3770808576-6">[</span><span class="p" data-group-id="3770808576-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3770808576-8">[</span><span class="p" data-group-id="3770808576-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3770808576-9">}</span><span class="p" data-group-id="3770808576-8">]</span><span class="p" data-group-id="3770808576-7">}</span><span class="p" data-group-id="3770808576-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3770808576-1">}</span><span class="p">.</span></code></pre><p>The changes do not affect existing child processes. For example, changing the
│ │ │ │ +specification, is the same as when changing properties as described earlier:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3947469203-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3947469203-2">[</span><span class="p" data-group-id="3947469203-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3947469203-4">[</span><span class="p" data-group-id="3947469203-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3947469203-5">}</span><span class="p" data-group-id="3947469203-4">]</span><span class="p" data-group-id="3947469203-3">}</span><span class="p" data-group-id="3947469203-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3947469203-6">[</span><span class="p" data-group-id="3947469203-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3947469203-8">[</span><span class="p" data-group-id="3947469203-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3947469203-9">}</span><span class="p" data-group-id="3947469203-8">]</span><span class="p" data-group-id="3947469203-7">}</span><span class="p" data-group-id="3947469203-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3947469203-1">}</span><span class="p">.</span></code></pre><p>The changes do not affect existing child processes. For example, changing the
│ │ │ │  start function only specifies how the child process is to be restarted, if
│ │ │ │  needed later on.</p><p>The id of the child specification cannot be changed.</p><p>Changing the <code class="inline">Modules</code> field of the child specification can affect the release
│ │ │ │  handling process itself, as this field is used to identify which processes are
│ │ │ │  affected when doing a synchronized code replacement.</p><p><a href="" id="sup_add"></a></p><h3 id="adding-and-deleting-child-processes" class="section-heading">
│ │ │ │    <a href="#adding-and-deleting-child-processes" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Adding and Deleting Child Processes</span>
│ │ │ │  </h3>
│ │ │ │  <p>As stated earlier, changing child specifications does not affect existing child
│ │ │ │  processes. New child specifications are automatically added, but not deleted.
│ │ │ │  Child processes are not automatically started or terminated, this must be done
│ │ │ │  using <code class="inline">apply</code> instructions.</p><p><em>Example</em></p><p>Assume a new child process <code class="inline">m1</code> is to be added to <code class="inline">ch_sup</code> when
│ │ │ │  upgrading <code class="inline">ch_app</code> from &quot;1&quot; to &quot;2&quot;. This means <code class="inline">m1</code> is to be deleted when
│ │ │ │ -downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7159988803-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7159988803-2">[</span><span class="p" data-group-id="7159988803-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="7159988803-4">[</span><span class="p" data-group-id="7159988803-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7159988803-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7159988803-6">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7159988803-7">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7159988803-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7159988803-8">]</span><span class="p" data-group-id="7159988803-7">}</span><span class="p" data-group-id="7159988803-6">}</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="7159988803-4">]</span><span class="p" data-group-id="7159988803-3">}</span><span class="p" data-group-id="7159988803-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7159988803-9">[</span><span class="p" data-group-id="7159988803-10">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="7159988803-11">[</span><span class="p" data-group-id="7159988803-12">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7159988803-13">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7159988803-14">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7159988803-14">]</span><span class="p" data-group-id="7159988803-13">}</span><span class="p" data-group-id="7159988803-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7159988803-15">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7159988803-16">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7159988803-17">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7159988803-17">]</span><span class="p" data-group-id="7159988803-16">}</span><span class="p" data-group-id="7159988803-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7159988803-18">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7159988803-18">}</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="7159988803-11">]</span><span class="p" data-group-id="7159988803-10">}</span><span class="p" data-group-id="7159988803-9">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7159988803-1">}</span><span class="p">.</span></code></pre><p>The order of the instructions is important.</p><p>The supervisor must be registered as <code class="inline">ch_sup</code> for the script to work. If the
│ │ │ │ +downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2703928775-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2703928775-2">[</span><span class="p" data-group-id="2703928775-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="2703928775-4">[</span><span class="p" data-group-id="2703928775-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="2703928775-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2703928775-6">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2703928775-7">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2703928775-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="2703928775-8">]</span><span class="p" data-group-id="2703928775-7">}</span><span class="p" data-group-id="2703928775-6">}</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="2703928775-4">]</span><span class="p" data-group-id="2703928775-3">}</span><span class="p" data-group-id="2703928775-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2703928775-9">[</span><span class="p" data-group-id="2703928775-10">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="2703928775-11">[</span><span class="p" data-group-id="2703928775-12">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2703928775-13">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2703928775-14">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="2703928775-14">]</span><span class="p" data-group-id="2703928775-13">}</span><span class="p" data-group-id="2703928775-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2703928775-15">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2703928775-16">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2703928775-17">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="2703928775-17">]</span><span class="p" data-group-id="2703928775-16">}</span><span class="p" data-group-id="2703928775-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2703928775-18">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="2703928775-18">}</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="2703928775-11">]</span><span class="p" data-group-id="2703928775-10">}</span><span class="p" data-group-id="2703928775-9">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2703928775-1">}</span><span class="p">.</span></code></pre><p>The order of the instructions is important.</p><p>The supervisor must be registered as <code class="inline">ch_sup</code> for the script to work. If the
│ │ │ │  supervisor is not registered, it cannot be accessed directly from the script.
│ │ │ │  Instead a help function that finds the pid of the supervisor and calls
│ │ │ │  <code class="inline">supervisor:restart_child</code>, and so on, must be written. This function is then to
│ │ │ │  be called from the script using the <code class="inline">apply</code> instruction.</p><p>If the module <code class="inline">m1</code> is introduced in version &quot;2&quot; of <code class="inline">ch_app</code>, it must also be
│ │ │ │ -loaded when upgrading and deleted when downgrading:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3023025375-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3023025375-2">[</span><span class="p" data-group-id="3023025375-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="3023025375-4">[</span><span class="p" data-group-id="3023025375-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="3023025375-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3023025375-6">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3023025375-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3023025375-7">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3023025375-8">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3023025375-9">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="3023025375-9">]</span><span class="p" data-group-id="3023025375-8">}</span><span class="p" data-group-id="3023025375-7">}</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="3023025375-4">]</span><span class="p" data-group-id="3023025375-3">}</span><span class="p" data-group-id="3023025375-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3023025375-10">[</span><span class="p" data-group-id="3023025375-11">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="3023025375-12">[</span><span class="p" data-group-id="3023025375-13">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3023025375-14">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3023025375-15">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="3023025375-15">]</span><span class="p" data-group-id="3023025375-14">}</span><span class="p" data-group-id="3023025375-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3023025375-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3023025375-17">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3023025375-18">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="3023025375-18">]</span><span class="p" data-group-id="3023025375-17">}</span><span class="p" data-group-id="3023025375-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3023025375-19">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3023025375-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3023025375-20">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="3023025375-20">}</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="3023025375-12">]</span><span class="p" data-group-id="3023025375-11">}</span><span class="p" data-group-id="3023025375-10">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3023025375-1">}</span><span class="p">.</span></code></pre><p>As stated earlier, the order of the instructions is important. When upgrading,
│ │ │ │ +loaded when upgrading and deleted when downgrading:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3314735692-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3314735692-2">[</span><span class="p" data-group-id="3314735692-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="3314735692-4">[</span><span class="p" data-group-id="3314735692-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="3314735692-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3314735692-6">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3314735692-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3314735692-7">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314735692-8">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314735692-9">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="3314735692-9">]</span><span class="p" data-group-id="3314735692-8">}</span><span class="p" data-group-id="3314735692-7">}</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="3314735692-4">]</span><span class="p" data-group-id="3314735692-3">}</span><span class="p" data-group-id="3314735692-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3314735692-10">[</span><span class="p" data-group-id="3314735692-11">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="3314735692-12">[</span><span class="p" data-group-id="3314735692-13">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314735692-14">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314735692-15">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="3314735692-15">]</span><span class="p" data-group-id="3314735692-14">}</span><span class="p" data-group-id="3314735692-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3314735692-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314735692-17">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3314735692-18">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="3314735692-18">]</span><span class="p" data-group-id="3314735692-17">}</span><span class="p" data-group-id="3314735692-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3314735692-19">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3314735692-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3314735692-20">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="3314735692-20">}</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="3314735692-12">]</span><span class="p" data-group-id="3314735692-11">}</span><span class="p" data-group-id="3314735692-10">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3314735692-1">}</span><span class="p">.</span></code></pre><p>As stated earlier, the order of the instructions is important. When upgrading,
│ │ │ │  <code class="inline">m1</code> must be loaded, and the supervisor child specification changed, before the
│ │ │ │  new child process can be started. When downgrading, the child process must be
│ │ │ │  terminated before the child specification is changed and the module is deleted.</p><h2 id="adding-or-deleting-a-module" class="section-heading">
│ │ │ │    <a href="#adding-or-deleting-a-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Adding or Deleting a Module</span>
│ │ │ │  </h2>
│ │ │ │ -<p>_Example</p><p>_ A new functional module <code class="inline">m</code> is added to <code class="inline">ch_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6524411579-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6524411579-2">[</span><span class="p" data-group-id="6524411579-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6524411579-4">[</span><span class="p" data-group-id="6524411579-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="6524411579-5">}</span><span class="p" data-group-id="6524411579-4">]</span><span class="p" data-group-id="6524411579-3">}</span><span class="p" data-group-id="6524411579-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6524411579-6">[</span><span class="p" data-group-id="6524411579-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6524411579-8">[</span><span class="p" data-group-id="6524411579-9">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="6524411579-9">}</span><span class="p" data-group-id="6524411579-8">]</span><span class="p" data-group-id="6524411579-7">}</span><span class="p" data-group-id="6524411579-6">]</span></code></pre><h2 id="starting-or-terminating-a-process" class="section-heading">
│ │ │ │ +<p>_Example</p><p>_ A new functional module <code class="inline">m</code> is added to <code class="inline">ch_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0979286499-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0979286499-2">[</span><span class="p" data-group-id="0979286499-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0979286499-4">[</span><span class="p" data-group-id="0979286499-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="0979286499-5">}</span><span class="p" data-group-id="0979286499-4">]</span><span class="p" data-group-id="0979286499-3">}</span><span class="p" data-group-id="0979286499-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0979286499-6">[</span><span class="p" data-group-id="0979286499-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0979286499-8">[</span><span class="p" data-group-id="0979286499-9">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="0979286499-9">}</span><span class="p" data-group-id="0979286499-8">]</span><span class="p" data-group-id="0979286499-7">}</span><span class="p" data-group-id="0979286499-6">]</span></code></pre><h2 id="starting-or-terminating-a-process" class="section-heading">
│ │ │ │    <a href="#starting-or-terminating-a-process" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting or Terminating a Process</span>
│ │ │ │  </h2>
│ │ │ │  <p>In a system structured according to the OTP design principles, any process would
│ │ │ │  be a child process belonging to a supervisor, see
│ │ │ │ @@ -274,29 +274,29 @@
│ │ │ │    <span class="text">Restarting an Application</span>
│ │ │ │  </h2>
│ │ │ │  <p>Restarting an application is useful when a change is too complicated to be made
│ │ │ │  without restarting the processes, for example, if the supervisor hierarchy has
│ │ │ │  been restructured.</p><p><em>Example</em></p><p>When adding a child <code class="inline">m1</code> to <code class="inline">ch_sup</code>, as in
│ │ │ │  <a href="appup_cookbook.xhtml#sup_add">Adding and Deleting Child Processes</a> in Changing a
│ │ │ │  Supervisor, an alternative to updating the supervisor is to restart the entire
│ │ │ │ -application:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8724100171-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8724100171-2">[</span><span class="p" data-group-id="8724100171-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8724100171-4">[</span><span class="p" data-group-id="8724100171-5">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="8724100171-5">}</span><span class="p" data-group-id="8724100171-4">]</span><span class="p" data-group-id="8724100171-3">}</span><span class="p" data-group-id="8724100171-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8724100171-6">[</span><span class="p" data-group-id="8724100171-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8724100171-8">[</span><span class="p" data-group-id="8724100171-9">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="8724100171-9">}</span><span class="p" data-group-id="8724100171-8">]</span><span class="p" data-group-id="8724100171-7">}</span><span class="p" data-group-id="8724100171-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8724100171-1">}</span><span class="p">.</span></code></pre><p><a href="" id="app_spec"></a></p><h2 id="changing-an-application-specification" class="section-heading">
│ │ │ │ +application:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4904459284-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4904459284-2">[</span><span class="p" data-group-id="4904459284-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4904459284-4">[</span><span class="p" data-group-id="4904459284-5">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="4904459284-5">}</span><span class="p" data-group-id="4904459284-4">]</span><span class="p" data-group-id="4904459284-3">}</span><span class="p" data-group-id="4904459284-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4904459284-6">[</span><span class="p" data-group-id="4904459284-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4904459284-8">[</span><span class="p" data-group-id="4904459284-9">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="4904459284-9">}</span><span class="p" data-group-id="4904459284-8">]</span><span class="p" data-group-id="4904459284-7">}</span><span class="p" data-group-id="4904459284-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4904459284-1">}</span><span class="p">.</span></code></pre><p><a href="" id="app_spec"></a></p><h2 id="changing-an-application-specification" class="section-heading">
│ │ │ │    <a href="#changing-an-application-specification" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing an Application Specification</span>
│ │ │ │  </h2>
│ │ │ │  <p>When installing a release, the application specifications are automatically
│ │ │ │  updated before evaluating the <code class="inline">relup</code> script. Thus, no instructions are needed
│ │ │ │ -in the <code class="inline">.appup</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5583452697-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5583452697-2">[</span><span class="p" data-group-id="5583452697-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5583452697-4">[</span><span class="p" data-group-id="5583452697-4">]</span><span class="p" data-group-id="5583452697-3">}</span><span class="p" data-group-id="5583452697-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5583452697-5">[</span><span class="p" data-group-id="5583452697-6">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5583452697-7">[</span><span class="p" data-group-id="5583452697-7">]</span><span class="p" data-group-id="5583452697-6">}</span><span class="p" data-group-id="5583452697-5">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5583452697-1">}</span><span class="p">.</span></code></pre><h2 id="changing-application-configuration" class="section-heading">
│ │ │ │ +in the <code class="inline">.appup</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9199063219-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9199063219-2">[</span><span class="p" data-group-id="9199063219-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9199063219-4">[</span><span class="p" data-group-id="9199063219-4">]</span><span class="p" data-group-id="9199063219-3">}</span><span class="p" data-group-id="9199063219-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9199063219-5">[</span><span class="p" data-group-id="9199063219-6">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9199063219-7">[</span><span class="p" data-group-id="9199063219-7">]</span><span class="p" data-group-id="9199063219-6">}</span><span class="p" data-group-id="9199063219-5">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9199063219-1">}</span><span class="p">.</span></code></pre><h2 id="changing-application-configuration" class="section-heading">
│ │ │ │    <a href="#changing-application-configuration" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing Application Configuration</span>
│ │ │ │  </h2>
│ │ │ │  <p>Changing an application configuration by updating the <code class="inline">env</code> key in the <code class="inline">.app</code>
│ │ │ │  file is an instance of changing an application specification, see the previous
│ │ │ │ @@ -311,26 +311,26 @@
│ │ │ │  applications apply to primary applications only. There are no corresponding
│ │ │ │  instructions for included applications. However, since an included application
│ │ │ │  is really a supervision tree with a topmost supervisor, started as a child
│ │ │ │  process to a supervisor in the including application, a <code class="inline">.relup</code> file can be
│ │ │ │  manually created.</p><p><em>Example</em></p><p>Assume there is a release containing an application <code class="inline">prim_app</code>, which
│ │ │ │  have a supervisor <code class="inline">prim_sup</code> in its supervision tree.</p><p>In a new version of the release, the application <code class="inline">ch_app</code> is to be included in
│ │ │ │  <code class="inline">prim_app</code>. That is, its topmost supervisor <code class="inline">ch_sup</code> is to be started as a child
│ │ │ │ -process to <code class="inline">prim_sup</code>.</p><p>The workflow is as follows:</p><p><em>Step 1)</em> Edit the code for <code class="inline">prim_sup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6283599157-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6283599157-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6283599157-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6283599157-3">{</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="ss">supervisor</span><span class="w"> </span><span class="ss">flags</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="6283599157-4">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -           </span><span class="p" data-group-id="6283599157-5">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6283599157-6">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="6283599157-7">[</span><span class="p" data-group-id="6283599157-7">]</span><span class="p" data-group-id="6283599157-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="ss">permanent</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="ss">supervisor</span><span class="p">,</span><span class="p" data-group-id="6283599157-8">[</span><span class="ss">ch_sup</span><span class="p" data-group-id="6283599157-8">]</span><span class="p" data-group-id="6283599157-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -           </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6283599157-4">]</span><span class="p" data-group-id="6283599157-3">}</span><span class="p" data-group-id="6283599157-2">}</span><span class="p">.</span></code></pre><p><em>Step 2)</em> Edit the <code class="inline">.app</code> file for <code class="inline">prim_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5792249585-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5792249585-2">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5792249585-3">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="5792249585-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +process to <code class="inline">prim_sup</code>.</p><p>The workflow is as follows:</p><p><em>Step 1)</em> Edit the code for <code class="inline">prim_sup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1905755438-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1905755438-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1905755438-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1905755438-3">{</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="ss">supervisor</span><span class="w"> </span><span class="ss">flags</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="1905755438-4">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ +           </span><span class="p" data-group-id="1905755438-5">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1905755438-6">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="1905755438-7">[</span><span class="p" data-group-id="1905755438-7">]</span><span class="p" data-group-id="1905755438-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="ss">permanent</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="ss">supervisor</span><span class="p">,</span><span class="p" data-group-id="1905755438-8">[</span><span class="ss">ch_sup</span><span class="p" data-group-id="1905755438-8">]</span><span class="p" data-group-id="1905755438-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +           </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1905755438-4">]</span><span class="p" data-group-id="1905755438-3">}</span><span class="p" data-group-id="1905755438-2">}</span><span class="p">.</span></code></pre><p><em>Step 2)</em> Edit the <code class="inline">.app</code> file for <code class="inline">prim_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7758448332-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7758448332-2">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7758448332-3">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="7758448332-3">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5792249585-4">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5792249585-5">[</span><span class="ss">ch_app</span><span class="p" data-group-id="5792249585-5">]</span><span class="p" data-group-id="5792249585-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7758448332-4">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7758448332-5">[</span><span class="ss">ch_app</span><span class="p" data-group-id="7758448332-5">]</span><span class="p" data-group-id="7758448332-4">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5792249585-2">]</span><span class="p" data-group-id="5792249585-1">}</span><span class="p">.</span></code></pre><p><em>Step 3)</em> Create a new <code class="inline">.rel</code> file, including <code class="inline">ch_app</code>:</p><pre><code class="text">{release,
│ │ │ │ + </span><span class="p" data-group-id="7758448332-2">]</span><span class="p" data-group-id="7758448332-1">}</span><span class="p">.</span></code></pre><p><em>Step 3)</em> Create a new <code class="inline">.rel</code> file, including <code class="inline">ch_app</code>:</p><pre><code class="text">{release,
│ │ │ │   ...,
│ │ │ │   [...,
│ │ │ │    {prim_app, &quot;2&quot;},
│ │ │ │    {ch_app, &quot;1&quot;}]}.</code></pre><p>The included application can be started in two ways. This is described in the
│ │ │ │  next two sections.</p><h3 id="application-restart" class="section-heading">
│ │ │ │    <a href="#application-restart" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -385,74 +385,74 @@
│ │ │ │  <p><em>Step 4b)</em> Another way to start the included application (or stop it in the case
│ │ │ │  of downgrade) is by combining instructions for adding and removing child
│ │ │ │  processes to/from <code class="inline">prim_sup</code> with instructions for loading/unloading all
│ │ │ │  <code class="inline">ch_app</code> code and its application specification.</p><p>Again, the <code class="inline">.relup</code> file is created manually, either from scratch or by editing a
│ │ │ │  generated version. Load all code for <code class="inline">ch_app</code> first, and also load the
│ │ │ │  application specification, before <code class="inline">prim_sup</code> is updated. When downgrading,
│ │ │ │  <code class="inline">prim_sup</code> is to updated first, before the code for <code class="inline">ch_app</code> and its application
│ │ │ │ -specification are unloaded.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5955471547-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5955471547-2">[</span><span class="p" data-group-id="5955471547-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="5955471547-4">[</span><span class="p" data-group-id="5955471547-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="5955471547-5">[</span><span class="p" data-group-id="5955471547-6">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="5955471547-7">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="5955471547-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="5955471547-8">]</span><span class="p" data-group-id="5955471547-7">}</span><span class="p" data-group-id="5955471547-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-9">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="5955471547-10">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="5955471547-11">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="5955471547-11">]</span><span class="p" data-group-id="5955471547-10">}</span><span class="p" data-group-id="5955471547-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +specification are unloaded.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6379122695-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6379122695-2">[</span><span class="p" data-group-id="6379122695-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="6379122695-4">[</span><span class="p" data-group-id="6379122695-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="6379122695-5">[</span><span class="p" data-group-id="6379122695-6">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="6379122695-7">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="6379122695-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="6379122695-8">]</span><span class="p" data-group-id="6379122695-7">}</span><span class="p" data-group-id="6379122695-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-9">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="6379122695-10">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="6379122695-11">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="6379122695-11">]</span><span class="p" data-group-id="6379122695-10">}</span><span class="p" data-group-id="6379122695-9">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-12">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="5955471547-13">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="5955471547-13">}</span><span class="p" data-group-id="5955471547-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-14">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="5955471547-15">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="5955471547-15">}</span><span class="p" data-group-id="5955471547-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="5955471547-17">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="5955471547-18">[</span><span class="ss">ch_app</span><span class="p" data-group-id="5955471547-18">]</span><span class="p" data-group-id="5955471547-17">}</span><span class="p" data-group-id="5955471547-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-19">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="5955471547-20">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="5955471547-20">]</span><span class="p" data-group-id="5955471547-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-21">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="5955471547-22">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="5955471547-22">}</span><span class="p" data-group-id="5955471547-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-23">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">up</span><span class="p">,</span><span class="p" data-group-id="5955471547-24">[</span><span class="p" data-group-id="5955471547-25">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="5955471547-26">[</span><span class="p" data-group-id="5955471547-26">]</span><span class="p" data-group-id="5955471547-25">}</span><span class="p" data-group-id="5955471547-24">]</span><span class="p" data-group-id="5955471547-23">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-27">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="5955471547-28">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="5955471547-28">]</span><span class="p" data-group-id="5955471547-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-29">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="5955471547-30">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">restart_child</span><span class="p">,</span><span class="p" data-group-id="5955471547-31">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="5955471547-31">]</span><span class="p" data-group-id="5955471547-30">}</span><span class="p" data-group-id="5955471547-29">}</span><span class="p" data-group-id="5955471547-5">]</span><span class="p" data-group-id="5955471547-3">}</span><span class="p" data-group-id="5955471547-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5955471547-32">[</span><span class="p" data-group-id="5955471547-33">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="5955471547-34">[</span><span class="p" data-group-id="5955471547-34">]</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="5955471547-35">[</span><span class="p" data-group-id="5955471547-36">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="5955471547-37">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="5955471547-38">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="5955471547-38">]</span><span class="p" data-group-id="5955471547-37">}</span><span class="p" data-group-id="5955471547-36">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-12">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="6379122695-13">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="6379122695-13">}</span><span class="p" data-group-id="6379122695-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-14">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="6379122695-15">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="6379122695-15">}</span><span class="p" data-group-id="6379122695-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="6379122695-17">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="6379122695-18">[</span><span class="ss">ch_app</span><span class="p" data-group-id="6379122695-18">]</span><span class="p" data-group-id="6379122695-17">}</span><span class="p" data-group-id="6379122695-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-19">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="6379122695-20">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="6379122695-20">]</span><span class="p" data-group-id="6379122695-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-21">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="6379122695-22">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="6379122695-22">}</span><span class="p" data-group-id="6379122695-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-23">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">up</span><span class="p">,</span><span class="p" data-group-id="6379122695-24">[</span><span class="p" data-group-id="6379122695-25">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="6379122695-26">[</span><span class="p" data-group-id="6379122695-26">]</span><span class="p" data-group-id="6379122695-25">}</span><span class="p" data-group-id="6379122695-24">]</span><span class="p" data-group-id="6379122695-23">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-27">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="6379122695-28">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="6379122695-28">]</span><span class="p" data-group-id="6379122695-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-29">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="6379122695-30">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">restart_child</span><span class="p">,</span><span class="p" data-group-id="6379122695-31">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="6379122695-31">]</span><span class="p" data-group-id="6379122695-30">}</span><span class="p" data-group-id="6379122695-29">}</span><span class="p" data-group-id="6379122695-5">]</span><span class="p" data-group-id="6379122695-3">}</span><span class="p" data-group-id="6379122695-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6379122695-32">[</span><span class="p" data-group-id="6379122695-33">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="6379122695-34">[</span><span class="p" data-group-id="6379122695-34">]</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="6379122695-35">[</span><span class="p" data-group-id="6379122695-36">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="6379122695-37">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="6379122695-38">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="6379122695-38">]</span><span class="p" data-group-id="6379122695-37">}</span><span class="p" data-group-id="6379122695-36">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-39">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="5955471547-40">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">terminate_child</span><span class="p">,</span><span class="p" data-group-id="5955471547-41">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="5955471547-41">]</span><span class="p" data-group-id="5955471547-40">}</span><span class="p" data-group-id="5955471547-39">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-42">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="5955471547-43">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">delete_child</span><span class="p">,</span><span class="p" data-group-id="5955471547-44">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="5955471547-44">]</span><span class="p" data-group-id="5955471547-43">}</span><span class="p" data-group-id="5955471547-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-45">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="5955471547-46">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="5955471547-46">]</span><span class="p" data-group-id="5955471547-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-47">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="5955471547-48">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="5955471547-48">}</span><span class="p" data-group-id="5955471547-47">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-49">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">down</span><span class="p">,</span><span class="p" data-group-id="5955471547-50">[</span><span class="p" data-group-id="5955471547-51">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="5955471547-52">[</span><span class="p" data-group-id="5955471547-52">]</span><span class="p" data-group-id="5955471547-51">}</span><span class="p" data-group-id="5955471547-50">]</span><span class="p" data-group-id="5955471547-49">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-53">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="5955471547-54">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="5955471547-54">]</span><span class="p" data-group-id="5955471547-53">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-55">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="5955471547-56">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="5955471547-56">}</span><span class="p" data-group-id="5955471547-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-57">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="5955471547-58">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="5955471547-58">}</span><span class="p" data-group-id="5955471547-57">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-59">{</span><span class="ss">purge</span><span class="p">,</span><span class="p" data-group-id="5955471547-60">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="5955471547-60">]</span><span class="p" data-group-id="5955471547-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5955471547-61">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="5955471547-62">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">unload</span><span class="p">,</span><span class="p" data-group-id="5955471547-63">[</span><span class="ss">ch_app</span><span class="p" data-group-id="5955471547-63">]</span><span class="p" data-group-id="5955471547-62">}</span><span class="p" data-group-id="5955471547-61">}</span><span class="p" data-group-id="5955471547-35">]</span><span class="p" data-group-id="5955471547-33">}</span><span class="p" data-group-id="5955471547-32">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5955471547-1">}</span><span class="p">.</span></code></pre><h2 id="changing-non-erlang-code" class="section-heading">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-39">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="6379122695-40">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">terminate_child</span><span class="p">,</span><span class="p" data-group-id="6379122695-41">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="6379122695-41">]</span><span class="p" data-group-id="6379122695-40">}</span><span class="p" data-group-id="6379122695-39">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-42">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="6379122695-43">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">delete_child</span><span class="p">,</span><span class="p" data-group-id="6379122695-44">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="6379122695-44">]</span><span class="p" data-group-id="6379122695-43">}</span><span class="p" data-group-id="6379122695-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-45">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="6379122695-46">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="6379122695-46">]</span><span class="p" data-group-id="6379122695-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-47">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="6379122695-48">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="6379122695-48">}</span><span class="p" data-group-id="6379122695-47">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-49">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">down</span><span class="p">,</span><span class="p" data-group-id="6379122695-50">[</span><span class="p" data-group-id="6379122695-51">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="6379122695-52">[</span><span class="p" data-group-id="6379122695-52">]</span><span class="p" data-group-id="6379122695-51">}</span><span class="p" data-group-id="6379122695-50">]</span><span class="p" data-group-id="6379122695-49">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-53">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="6379122695-54">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="6379122695-54">]</span><span class="p" data-group-id="6379122695-53">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-55">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="6379122695-56">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="6379122695-56">}</span><span class="p" data-group-id="6379122695-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-57">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="6379122695-58">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="6379122695-58">}</span><span class="p" data-group-id="6379122695-57">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-59">{</span><span class="ss">purge</span><span class="p">,</span><span class="p" data-group-id="6379122695-60">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="6379122695-60">]</span><span class="p" data-group-id="6379122695-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6379122695-61">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="6379122695-62">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">unload</span><span class="p">,</span><span class="p" data-group-id="6379122695-63">[</span><span class="ss">ch_app</span><span class="p" data-group-id="6379122695-63">]</span><span class="p" data-group-id="6379122695-62">}</span><span class="p" data-group-id="6379122695-61">}</span><span class="p" data-group-id="6379122695-35">]</span><span class="p" data-group-id="6379122695-33">}</span><span class="p" data-group-id="6379122695-32">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6379122695-1">}</span><span class="p">.</span></code></pre><h2 id="changing-non-erlang-code" class="section-heading">
│ │ │ │    <a href="#changing-non-erlang-code" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing Non-Erlang Code</span>
│ │ │ │  </h2>
│ │ │ │  <p>Changing code for a program written in another programming language than Erlang,
│ │ │ │  for example, a port program, is application-dependent and OTP provides no
│ │ │ │  special support.</p><p><em>Example</em></p><p>When changing code for a port program, assume that the Erlang process
│ │ │ │  controlling the port is a <code class="inline">gen_server</code> <code class="inline">portc</code> and that the port is opened in
│ │ │ │ -the callback function <code class="inline">init/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6647622111-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6647622111-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +the callback function <code class="inline">init/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7934410033-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7934410033-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6647622111-2">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="6647622111-3">(</span><span class="n">App</span><span class="p" data-group-id="6647622111-3">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="6647622111-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="6647622111-4">(</span><span class="p" data-group-id="6647622111-5">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="6647622111-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6647622111-6">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6647622111-6">]</span><span class="p" data-group-id="6647622111-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7934410033-2">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="7934410033-3">(</span><span class="n">App</span><span class="p" data-group-id="7934410033-3">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="7934410033-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="7934410033-4">(</span><span class="p" data-group-id="7934410033-5">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="7934410033-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7934410033-6">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7934410033-6">]</span><span class="p" data-group-id="7934410033-4">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6647622111-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="6647622111-8">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6647622111-8">}</span><span class="p" data-group-id="6647622111-7">}</span><span class="p">.</span></code></pre><p>If the port program is to be updated, the code for the <code class="inline">gen_server</code> can be
│ │ │ │ +    </span><span class="p" data-group-id="7934410033-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="7934410033-8">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7934410033-8">}</span><span class="p" data-group-id="7934410033-7">}</span><span class="p">.</span></code></pre><p>If the port program is to be updated, the code for the <code class="inline">gen_server</code> can be
│ │ │ │  extended with a <code class="inline">code_change/3</code> function, which closes the old port and opens a
│ │ │ │  new port. (If necessary, the <code class="inline">gen_server</code> can first request data that must be
│ │ │ │ -saved from the port program and pass this data to the new port):</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="5521569391-1">(</span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="ss">port</span><span class="p" data-group-id="5521569391-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +saved from the port program and pass this data to the new port):</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="2074558976-1">(</span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="ss">port</span><span class="p" data-group-id="2074558976-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">close</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="5521569391-2">{</span><span class="n">Port</span><span class="p">,</span><span class="ss">close</span><span class="p" data-group-id="5521569391-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2074558976-2">{</span><span class="n">Port</span><span class="p">,</span><span class="ss">close</span><span class="p" data-group-id="2074558976-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="5521569391-3">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="5521569391-4">(</span><span class="n">App</span><span class="p" data-group-id="5521569391-4">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="5521569391-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="5521569391-5">(</span><span class="p" data-group-id="5521569391-6">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="5521569391-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5521569391-7">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5521569391-7">]</span><span class="p" data-group-id="5521569391-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5521569391-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="5521569391-9">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5521569391-9">}</span><span class="p" data-group-id="5521569391-8">}</span><span class="p">.</span></code></pre><p>Update the application version number in the <code class="inline">.app</code> file and write an <code class="inline">.appup</code>
│ │ │ │ -file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2994391697-1">[</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2994391697-2">[</span><span class="p" data-group-id="2994391697-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2994391697-4">[</span><span class="p" data-group-id="2994391697-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2994391697-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="2994391697-6">}</span><span class="p" data-group-id="2994391697-5">}</span><span class="p" data-group-id="2994391697-4">]</span><span class="p" data-group-id="2994391697-3">}</span><span class="p" data-group-id="2994391697-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2994391697-7">[</span><span class="p" data-group-id="2994391697-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2994391697-9">[</span><span class="p" data-group-id="2994391697-10">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2994391697-11">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="2994391697-11">}</span><span class="p" data-group-id="2994391697-10">}</span><span class="p" data-group-id="2994391697-9">]</span><span class="p" data-group-id="2994391697-8">}</span><span class="p" data-group-id="2994391697-7">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2994391697-1">]</span><span class="p">.</span></code></pre><p>Ensure that the <code class="inline">priv</code> directory, where the C program is located, is included in
│ │ │ │ -the new release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="7814958885-1">(</span><span class="s">&quot;my_release&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7814958885-2">[</span><span class="p" data-group-id="7814958885-3">{</span><span class="ss">dirs</span><span class="p">,</span><span class="p" data-group-id="7814958885-4">[</span><span class="ss">priv</span><span class="p" data-group-id="7814958885-4">]</span><span class="p" data-group-id="7814958885-3">}</span><span class="p" data-group-id="7814958885-2">]</span><span class="p" data-group-id="7814958885-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2074558976-3">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="2074558976-4">(</span><span class="n">App</span><span class="p" data-group-id="2074558976-4">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="2074558976-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="2074558976-5">(</span><span class="p" data-group-id="2074558976-6">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="2074558976-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2074558976-7">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2074558976-7">]</span><span class="p" data-group-id="2074558976-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2074558976-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="2074558976-9">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2074558976-9">}</span><span class="p" data-group-id="2074558976-8">}</span><span class="p">.</span></code></pre><p>Update the application version number in the <code class="inline">.app</code> file and write an <code class="inline">.appup</code>
│ │ │ │ +file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2878383659-1">[</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2878383659-2">[</span><span class="p" data-group-id="2878383659-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2878383659-4">[</span><span class="p" data-group-id="2878383659-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2878383659-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="2878383659-6">}</span><span class="p" data-group-id="2878383659-5">}</span><span class="p" data-group-id="2878383659-4">]</span><span class="p" data-group-id="2878383659-3">}</span><span class="p" data-group-id="2878383659-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2878383659-7">[</span><span class="p" data-group-id="2878383659-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2878383659-9">[</span><span class="p" data-group-id="2878383659-10">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2878383659-11">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="2878383659-11">}</span><span class="p" data-group-id="2878383659-10">}</span><span class="p" data-group-id="2878383659-9">]</span><span class="p" data-group-id="2878383659-8">}</span><span class="p" data-group-id="2878383659-7">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2878383659-1">]</span><span class="p">.</span></code></pre><p>Ensure that the <code class="inline">priv</code> directory, where the C program is located, is included in
│ │ │ │ +the new release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="9148389659-1">(</span><span class="s">&quot;my_release&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9148389659-2">[</span><span class="p" data-group-id="9148389659-3">{</span><span class="ss">dirs</span><span class="p">,</span><span class="p" data-group-id="9148389659-4">[</span><span class="ss">priv</span><span class="p" data-group-id="9148389659-4">]</span><span class="p" data-group-id="9148389659-3">}</span><span class="p" data-group-id="9148389659-2">]</span><span class="p" data-group-id="9148389659-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="runtime-system-restart-and-upgrade" class="section-heading">
│ │ │ │    <a href="#runtime-system-restart-and-upgrade" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Runtime System Restart and Upgrade</span>
│ │ │ │  </h2>
│ │ │ │  <p>Two upgrade instructions restart the runtime system:</p><ul><li><p><code class="inline">restart_new_emulator</code></p><p>Intended when ERTS, Kernel, STDLIB, or SASL is upgraded. It is automatically
│ │ │ │ @@ -460,20 +460,20 @@
│ │ │ │  executed before all other upgrade instructions. For more information about
│ │ │ │  this instruction, see restart_new_emulator (Low-Level) in
│ │ │ │  <a href="release_handling.xhtml#restart_new_emulator_instr">Release Handling Instructions</a>.</p></li><li><p><code class="inline">restart_emulator</code></p><p>Used when a restart of the runtime system is required after all other upgrade
│ │ │ │  instructions are executed. For more information about this instruction, see
│ │ │ │  restart_emulator (Low-Level) in
│ │ │ │  <a href="release_handling.xhtml#restart_emulator_instr">Release Handling Instructions</a>.</p></li></ul><p>If a runtime system restart is necessary and no upgrade instructions are needed,
│ │ │ │  that is, if the restart itself is enough for the upgraded applications to start
│ │ │ │ -running the new versions, a simple <code class="inline">.relup</code> file can be created manually:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5700042729-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5700042729-2">[</span><span class="p" data-group-id="5700042729-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="5700042729-4">[</span><span class="p" data-group-id="5700042729-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="5700042729-5">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="5700042729-5">]</span><span class="p" data-group-id="5700042729-3">}</span><span class="p" data-group-id="5700042729-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5700042729-6">[</span><span class="p" data-group-id="5700042729-7">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="5700042729-8">[</span><span class="p" data-group-id="5700042729-8">]</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="5700042729-9">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="5700042729-9">]</span><span class="p" data-group-id="5700042729-7">}</span><span class="p" data-group-id="5700042729-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5700042729-1">}</span><span class="p">.</span></code></pre><p>In this case, the release handler framework with automatic packing and unpacking
│ │ │ │ +running the new versions, a simple <code class="inline">.relup</code> file can be created manually:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9400949426-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9400949426-2">[</span><span class="p" data-group-id="9400949426-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="9400949426-4">[</span><span class="p" data-group-id="9400949426-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="9400949426-5">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="9400949426-5">]</span><span class="p" data-group-id="9400949426-3">}</span><span class="p" data-group-id="9400949426-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9400949426-6">[</span><span class="p" data-group-id="9400949426-7">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="9400949426-8">[</span><span class="p" data-group-id="9400949426-8">]</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="9400949426-9">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="9400949426-9">]</span><span class="p" data-group-id="9400949426-7">}</span><span class="p" data-group-id="9400949426-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9400949426-1">}</span><span class="p">.</span></code></pre><p>In this case, the release handler framework with automatic packing and unpacking
│ │ │ │  of release packages, automatic path updates, and so on, can be used without
│ │ │ │  having to specify <code class="inline">.appup</code> files.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/applications.xhtml
│ │ │ │ @@ -40,34 +40,34 @@
│ │ │ │  <a href="applications.xhtml#app_dir">directory structure</a>.</p><p><a href="" id="callback_module"></a></p><h2 id="application-callback-module" class="section-heading">
│ │ │ │    <a href="#application-callback-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Application Callback Module</span>
│ │ │ │  </h2>
│ │ │ │  <p>How to start and stop the code for the application, including its supervision
│ │ │ │ -tree, is described by two callback functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start</span><span class="p" data-group-id="7257856397-1">(</span><span class="n">StartType</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="7257856397-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7257856397-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="7257856397-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="7257856397-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7257856397-3">}</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="7257856397-4">(</span><span class="n">State</span><span class="p" data-group-id="7257856397-4">)</span></code></pre><ul><li><code class="inline">start/2</code> is called when starting the application and is to create the
│ │ │ │ +tree, is described by two callback functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start</span><span class="p" data-group-id="6647290461-1">(</span><span class="n">StartType</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="6647290461-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6647290461-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="6647290461-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="6647290461-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6647290461-3">}</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="6647290461-4">(</span><span class="n">State</span><span class="p" data-group-id="6647290461-4">)</span></code></pre><ul><li><code class="inline">start/2</code> is called when starting the application and is to create the
│ │ │ │  supervision tree by starting the top supervisor. It is expected to return the
│ │ │ │  pid of the top supervisor and an optional term, <code class="inline">State</code>, which defaults to
│ │ │ │  <code class="inline">[]</code>. This term is passed as is to <code class="inline">stop/1</code>.</li><li><code class="inline">StartType</code> is usually the atom <code class="inline">normal</code>. It has other values only in the case
│ │ │ │  of a takeover or failover; see
│ │ │ │  <a href="distributed_applications.xhtml">Distributed Applications</a>.</li><li><code class="inline">StartArgs</code> is defined by the key <code class="inline">mod</code> in the
│ │ │ │  <a href="applications.xhtml#appl_res_file">application resource file</a>.</li><li><code class="inline">stop/1</code> is called <em>after</em> the application has been stopped and is to do any
│ │ │ │  necessary cleaning up. The actual stopping of the application, that is,
│ │ │ │  shutting down the supervision tree, is handled automatically as described in
│ │ │ │  <a href="applications.xhtml#stopping">Starting and Stopping Applications</a>.</li></ul><p><a href="" id="ch_app"></a></p><p>Example of an application callback module for packaging the supervision tree
│ │ │ │ -from <a href="sup_princ.xhtml#ex">Supervisor Behaviour</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7577438785-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="7577438785-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="7577438785-2">(</span><span class="ss">application</span><span class="p" data-group-id="7577438785-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +from <a href="sup_princ.xhtml#ex">Supervisor Behaviour</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5328780834-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="5328780834-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5328780834-2">(</span><span class="ss">application</span><span class="p" data-group-id="5328780834-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7577438785-3">(</span><span class="p" data-group-id="7577438785-4">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7577438785-4">]</span><span class="p" data-group-id="7577438785-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5328780834-3">(</span><span class="p" data-group-id="5328780834-4">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5328780834-4">]</span><span class="p" data-group-id="5328780834-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="7577438785-5">(</span><span class="p">_</span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="7577438785-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">ch_sup</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="7577438785-6">(</span><span class="p" data-group-id="7577438785-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="5328780834-5">(</span><span class="p">_</span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5328780834-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">ch_sup</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5328780834-6">(</span><span class="p" data-group-id="5328780834-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="7577438785-7">(</span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="7577438785-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="5328780834-7">(</span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="5328780834-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>A library application that cannot be started or stopped does not need any
│ │ │ │  application callback module.</p><p><a href="" id="appl_res_file"></a></p><h2 id="application-resource-file" class="section-heading">
│ │ │ │    <a href="#application-resource-file" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Application Resource File</span>
│ │ │ │  </h2>
│ │ │ │ @@ -78,22 +78,22 @@
│ │ │ │  keys.</li></ul><p>The contents of a minimal <code class="inline">.app</code> file for a library application <code class="inline">libapp</code> looks
│ │ │ │  as follows:</p><pre><code class="text">{application, libapp, []}.</code></pre><p>The contents of a minimal <code class="inline">.app</code> file <code class="inline">ch_app.app</code> for a supervision tree
│ │ │ │  application like <code class="inline">ch_app</code> looks as follows:</p><pre><code class="text">{application, ch_app,
│ │ │ │   [{mod, {ch_app,[]}}]}.</code></pre><p>The key <code class="inline">mod</code> defines the callback module and start argument of the application,
│ │ │ │  in this case <code class="inline">ch_app</code> and <code class="inline">[]</code>, respectively. This means that the following is
│ │ │ │  called when the application is to be started:</p><pre><code class="text">ch_app:start(normal, [])</code></pre><p>The following is called when the application is stopped:</p><pre><code class="text">ch_app:stop([])</code></pre><p>When using <a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a>, the Erlang/OTP tools for packaging code (see Section
│ │ │ │  <a href="release_structure.xhtml">Releases</a>), the keys <code class="inline">description</code>, <code class="inline">vsn</code>, <code class="inline">modules</code>,
│ │ │ │ -<code class="inline">registered</code>, and <code class="inline">applications</code> are also to be specified:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3466576460-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3466576460-2">[</span><span class="p" data-group-id="3466576460-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="3466576460-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="3466576460-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="3466576460-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="3466576460-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3466576460-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="3466576460-6">]</span><span class="p" data-group-id="3466576460-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="3466576460-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3466576460-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="3466576460-8">]</span><span class="p" data-group-id="3466576460-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="3466576460-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3466576460-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="3466576460-10">]</span><span class="p" data-group-id="3466576460-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="3466576460-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3466576460-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="3466576460-13">[</span><span class="p" data-group-id="3466576460-13">]</span><span class="p" data-group-id="3466576460-12">}</span><span class="p" data-group-id="3466576460-11">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3466576460-2">]</span><span class="p" data-group-id="3466576460-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">description</code> - A short description, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">vsn</code> - Version number, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">modules</code> - All modules <em>introduced</em> by this application. <a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a> uses
│ │ │ │ +<code class="inline">registered</code>, and <code class="inline">applications</code> are also to be specified:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0291104303-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0291104303-2">[</span><span class="p" data-group-id="0291104303-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="0291104303-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0291104303-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="0291104303-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0291104303-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0291104303-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0291104303-6">]</span><span class="p" data-group-id="0291104303-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0291104303-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0291104303-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="0291104303-8">]</span><span class="p" data-group-id="0291104303-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0291104303-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0291104303-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="0291104303-10">]</span><span class="p" data-group-id="0291104303-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0291104303-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0291104303-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="0291104303-13">[</span><span class="p" data-group-id="0291104303-13">]</span><span class="p" data-group-id="0291104303-12">}</span><span class="p" data-group-id="0291104303-11">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0291104303-2">]</span><span class="p" data-group-id="0291104303-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">description</code> - A short description, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">vsn</code> - Version number, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">modules</code> - All modules <em>introduced</em> by this application. <a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a> uses
│ │ │ │  this list when generating boot scripts and tar files. A module must only
│ │ │ │  be included in one application. Defaults to <code class="inline">[]</code>.</li><li><code class="inline">registered</code> - All names of registered processes in the application.
│ │ │ │  <a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a> uses this list to detect name clashes between applications.
│ │ │ │  Defaults to <code class="inline">[]</code>.</li><li><code class="inline">applications</code> - All applications that must be started before this
│ │ │ │  application is started. <a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a> uses this list to generate correct boot
│ │ │ │  scripts. Defaults to <code class="inline">[]</code>. Notice that all applications have dependencies to
│ │ │ │  at least Kernel and STDLIB.</li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>For details about the syntax and contents of the application resource file,
│ │ │ │ @@ -205,38 +205,38 @@
│ │ │ │  stop applications.</p><h2 id="loading-and-unloading-applications" class="section-heading">
│ │ │ │    <a href="#loading-and-unloading-applications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Loading and Unloading Applications</span>
│ │ │ │  </h2>
│ │ │ │  <p>Before an application can be started, it must be <em>loaded</em>. The application
│ │ │ │ -controller reads and stores the information from the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">load</span><span class="p" data-group-id="2754003182-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="2754003182-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +controller reads and stores the information from the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">load</span><span class="p" data-group-id="9981162194-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="9981162194-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="2754003182-2">(</span><span class="p" data-group-id="2754003182-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2754003182-3">[</span><span class="p" data-group-id="2754003182-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="2754003182-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2754003182-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="2754003182-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2754003182-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="2754003182-6">}</span><span class="p" data-group-id="2754003182-3">]</span></code></pre><p>An application that has been stopped, or has never been started, can be
│ │ │ │ +2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="9981162194-2">(</span><span class="p" data-group-id="9981162194-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9981162194-3">[</span><span class="p" data-group-id="9981162194-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="9981162194-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9981162194-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="9981162194-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9981162194-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="9981162194-6">}</span><span class="p" data-group-id="9981162194-3">]</span></code></pre><p>An application that has been stopped, or has never been started, can be
│ │ │ │  unloaded. The information about the application is erased from the internal
│ │ │ │ -database of the application controller.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">unload</span><span class="p" data-group-id="8134846817-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="8134846817-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +database of the application controller.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">unload</span><span class="p" data-group-id="1968710434-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="1968710434-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -4&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="8134846817-2">(</span><span class="p" data-group-id="8134846817-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8134846817-3">[</span><span class="p" data-group-id="8134846817-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="8134846817-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8134846817-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="8134846817-5">}</span><span class="p" data-group-id="8134846817-3">]</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Loading/unloading an application does not load/unload the code used by the
│ │ │ │ +4&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="1968710434-2">(</span><span class="p" data-group-id="1968710434-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1968710434-3">[</span><span class="p" data-group-id="1968710434-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="1968710434-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1968710434-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="1968710434-5">}</span><span class="p" data-group-id="1968710434-3">]</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Loading/unloading an application does not load/unload the code used by the
│ │ │ │  application. Code loading is handled in the usual way by the code server.</p></section><p><a href="" id="stopping"></a></p><h2 id="starting-and-stopping-applications" class="section-heading">
│ │ │ │    <a href="#starting-and-stopping-applications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting and Stopping Applications</span>
│ │ │ │  </h2>
│ │ │ │ -<p>An application is started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8962661694-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="8962661694-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>An application is started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5397999923-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="5397999923-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -6&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">which_applications</span><span class="p" data-group-id="8962661694-2">(</span><span class="p" data-group-id="8962661694-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8962661694-3">[</span><span class="p" data-group-id="8962661694-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="8962661694-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8962661694-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="8962661694-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8962661694-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="8962661694-6">}</span><span class="p" data-group-id="8962661694-3">]</span></code></pre><p>If the application is not already loaded, the application controller first loads
│ │ │ │ +6&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">which_applications</span><span class="p" data-group-id="5397999923-2">(</span><span class="p" data-group-id="5397999923-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5397999923-3">[</span><span class="p" data-group-id="5397999923-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="5397999923-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5397999923-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="5397999923-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5397999923-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="5397999923-6">}</span><span class="p" data-group-id="5397999923-3">]</span></code></pre><p>If the application is not already loaded, the application controller first loads
│ │ │ │  it using <a href="../../../lib/kernel/doc/html/application.html#load/1"><code class="inline">application:load/1</code></a>. It checks the value of the <code class="inline">applications</code> key to
│ │ │ │  ensure that all applications that are to be started before this application are
│ │ │ │  running.</p><p><a href="" id="application_master"></a></p><p>Following that, the application controller creates an <em>application master</em> for
│ │ │ │  the application.</p><p>The application master establishes itself as the <a href="../../../lib/../erts/doc/html/erlang.html#group_leader/0">group
│ │ │ │  leader</a> of all processes in the application
│ │ │ │  and will forward I/O to the previous group leader.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The purpose of the application master being the group leader is to easily
│ │ │ │  keep track of which processes that belong to the application. That is needed
│ │ │ │ @@ -252,55 +252,55 @@
│ │ │ │  defined by the <code class="inline">mod</code> key.</p><h2 id="configuring-an-application" class="section-heading">
│ │ │ │    <a href="#configuring-an-application" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Configuring an Application</span>
│ │ │ │  </h2>
│ │ │ │  <p>An application can be configured using <em>configuration parameters</em>. These are a
│ │ │ │ -list of <code class="inline">{Par,Val}</code> tuples specified by a key <code class="inline">env</code> in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9860843367-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9860843367-2">[</span><span class="p" data-group-id="9860843367-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="9860843367-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9860843367-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="9860843367-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9860843367-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9860843367-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="9860843367-6">]</span><span class="p" data-group-id="9860843367-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9860843367-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9860843367-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="9860843367-8">]</span><span class="p" data-group-id="9860843367-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9860843367-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9860843367-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="9860843367-10">]</span><span class="p" data-group-id="9860843367-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9860843367-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9860843367-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="9860843367-13">[</span><span class="p" data-group-id="9860843367-13">]</span><span class="p" data-group-id="9860843367-12">}</span><span class="p" data-group-id="9860843367-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9860843367-14">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9860843367-15">[</span><span class="p" data-group-id="9860843367-16">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="9860843367-16">}</span><span class="p" data-group-id="9860843367-15">]</span><span class="p" data-group-id="9860843367-14">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9860843367-2">]</span><span class="p" data-group-id="9860843367-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Par</code> is to be an atom. <code class="inline">Val</code> is any term. The application can retrieve the
│ │ │ │ +list of <code class="inline">{Par,Val}</code> tuples specified by a key <code class="inline">env</code> in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8639806224-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8639806224-2">[</span><span class="p" data-group-id="8639806224-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="8639806224-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="8639806224-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="8639806224-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="8639806224-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8639806224-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8639806224-6">]</span><span class="p" data-group-id="8639806224-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="8639806224-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8639806224-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="8639806224-8">]</span><span class="p" data-group-id="8639806224-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="8639806224-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8639806224-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="8639806224-10">]</span><span class="p" data-group-id="8639806224-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="8639806224-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8639806224-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="8639806224-13">[</span><span class="p" data-group-id="8639806224-13">]</span><span class="p" data-group-id="8639806224-12">}</span><span class="p" data-group-id="8639806224-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="8639806224-14">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8639806224-15">[</span><span class="p" data-group-id="8639806224-16">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="8639806224-16">}</span><span class="p" data-group-id="8639806224-15">]</span><span class="p" data-group-id="8639806224-14">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8639806224-2">]</span><span class="p" data-group-id="8639806224-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Par</code> is to be an atom. <code class="inline">Val</code> is any term. The application can retrieve the
│ │ │ │  value of a configuration parameter by calling <code class="inline">application:get_env(App, Par)</code> or
│ │ │ │  a number of similar functions. For more information, see module <a href="../../../lib/kernel/doc/html/application.html"><code class="inline">application</code></a>
│ │ │ │  in Kernel.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="3533016730-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="3533016730-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="3533016730-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="3533016730-2">]</span><span class="w"> </span><span class="p" data-group-id="3533016730-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="3533016730-3">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="3659025944-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="3659025944-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="3659025944-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="3659025944-2">]</span><span class="w"> </span><span class="p" data-group-id="3659025944-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="3659025944-3">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="3533016730-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="3533016730-4">)</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3533016730-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="3533016730-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="3659025944-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="3659025944-4">)</span><span class="gp unselectable">
│ │ │ │ +1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3659025944-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="3659025944-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="3533016730-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="3533016730-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3533016730-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="3533016730-7">}</span></code></pre><p>The values in the <code class="inline">.app</code> file can be overridden by values in a <em>system
│ │ │ │ +2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="3659025944-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="3659025944-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3659025944-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="3659025944-7">}</span></code></pre><p>The values in the <code class="inline">.app</code> file can be overridden by values in a <em>system
│ │ │ │  configuration file</em>. This is a file that contains configuration parameters for
│ │ │ │ -relevant applications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7867580019-1">[</span><span class="p" data-group-id="7867580019-2">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7867580019-3">[</span><span class="p" data-group-id="7867580019-4">{</span><span class="n">Par11</span><span class="p">,</span><span class="n">Val11</span><span class="p" data-group-id="7867580019-4">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7867580019-3">]</span><span class="p" data-group-id="7867580019-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +relevant applications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0635563694-1">[</span><span class="p" data-group-id="0635563694-2">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0635563694-3">[</span><span class="p" data-group-id="0635563694-4">{</span><span class="n">Par11</span><span class="p">,</span><span class="n">Val11</span><span class="p" data-group-id="0635563694-4">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0635563694-3">]</span><span class="p" data-group-id="0635563694-2">}</span><span class="p">,</span><span class="w">
│ │ │ │   </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7867580019-5">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7867580019-6">[</span><span class="p" data-group-id="7867580019-7">{</span><span class="n">ParN1</span><span class="p">,</span><span class="n">ValN1</span><span class="p" data-group-id="7867580019-7">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7867580019-6">]</span><span class="p" data-group-id="7867580019-5">}</span><span class="p" data-group-id="7867580019-1">]</span><span class="p">.</span></code></pre><p>The system configuration is to be called <code class="inline">Name.config</code> and Erlang is to be
│ │ │ │ + </span><span class="p" data-group-id="0635563694-5">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0635563694-6">[</span><span class="p" data-group-id="0635563694-7">{</span><span class="n">ParN1</span><span class="p">,</span><span class="n">ValN1</span><span class="p" data-group-id="0635563694-7">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0635563694-6">]</span><span class="p" data-group-id="0635563694-5">}</span><span class="p" data-group-id="0635563694-1">]</span><span class="p">.</span></code></pre><p>The system configuration is to be called <code class="inline">Name.config</code> and Erlang is to be
│ │ │ │  started with the command-line argument <code class="inline">-config Name</code>. For details, see
│ │ │ │  <a href="../../../lib/kernel/doc/html/config.xhtml"><code class="inline">config</code></a> in Kernel.</p><p><em>Example:</em></p><p>A file <code class="inline">test.config</code> is created with the following contents:</p><pre><code class="text">[{ch_app, [{file, &quot;testlog&quot;}]}].</code></pre><p>The value of <code class="inline">file</code> overrides the value of <code class="inline">file</code> as defined in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -config test</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="6682517096-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="6682517096-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="6682517096-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="6682517096-2">]</span><span class="w"> </span><span class="p" data-group-id="6682517096-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="6682517096-3">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="8696962192-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="8696962192-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="8696962192-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="8696962192-2">]</span><span class="w"> </span><span class="p" data-group-id="8696962192-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="8696962192-3">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="6682517096-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="6682517096-4">)</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6682517096-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="6682517096-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="8696962192-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="8696962192-4">)</span><span class="gp unselectable">
│ │ │ │ +1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8696962192-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="8696962192-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="6682517096-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="6682517096-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6682517096-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="6682517096-7">}</span></code></pre><p>If <a href="release_handling.xhtml#sys">release handling</a> is used, exactly one system
│ │ │ │ +2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="8696962192-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="8696962192-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8696962192-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="8696962192-7">}</span></code></pre><p>If <a href="release_handling.xhtml#sys">release handling</a> is used, exactly one system
│ │ │ │  configuration file is to be used and that file is to be called <code class="inline">sys.config</code>.</p><p>The values in the <code class="inline">.app</code> file and the values in a system configuration file can
│ │ │ │  be overridden directly from the command line:</p><pre><code class="text">% erl -ApplName Par1 Val1 ... ParN ValN</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -ch_app file &#39;&quot;testlog&quot;&#39;</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="1442859343-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="1442859343-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="1442859343-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="1442859343-2">]</span><span class="w"> </span><span class="p" data-group-id="1442859343-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="1442859343-3">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="0110441546-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="0110441546-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="0110441546-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="0110441546-2">]</span><span class="w"> </span><span class="p" data-group-id="0110441546-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="0110441546-3">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="1442859343-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="1442859343-4">)</span><span class="gp unselectable">
│ │ │ │ -1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1442859343-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="1442859343-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="0110441546-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="0110441546-4">)</span><span class="gp unselectable">
│ │ │ │ +1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0110441546-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="0110441546-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ │ -2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="1442859343-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="1442859343-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1442859343-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="1442859343-7">}</span></code></pre><h2 id="application-start-types" class="section-heading">
│ │ │ │ +2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="0110441546-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="0110441546-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0110441546-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="0110441546-7">}</span></code></pre><h2 id="application-start-types" class="section-heading">
│ │ │ │    <a href="#application-start-types" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Application Start Types</span>
│ │ │ │  </h2>
│ │ │ │  <p>A <em>start type</em> is defined when starting the application:</p><pre><code class="text">application:start(Application, Type)</code></pre><p><code class="inline">application:start(Application)</code> is the same as calling
│ │ │ │  <code class="inline">application:start(Application, temporary)</code>. The type can also be <code class="inline">permanent</code> or
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/applications.html
│ │ │ @@ -135,34 +135,34 @@
│ │ │  <a href="applications.html#app_dir">directory structure</a>.</p><p><a href="" id="callback_module"></a></p><h2 id="application-callback-module" class="section-heading">
│ │ │    <a href="#application-callback-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Application Callback Module</span>
│ │ │  </h2>
│ │ │  <p>How to start and stop the code for the application, including its supervision
│ │ │ -tree, is described by two callback functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start</span><span class="p" data-group-id="5860179524-1">(</span><span class="n">StartType</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="5860179524-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5860179524-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="5860179524-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="5860179524-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5860179524-3">}</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="5860179524-4">(</span><span class="n">State</span><span class="p" data-group-id="5860179524-4">)</span></code></pre><ul><li><code class="inline">start/2</code> is called when starting the application and is to create the
│ │ │ +tree, is described by two callback functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start</span><span class="p" data-group-id="0409626721-1">(</span><span class="n">StartType</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="0409626721-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0409626721-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="0409626721-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="0409626721-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="0409626721-3">}</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="0409626721-4">(</span><span class="n">State</span><span class="p" data-group-id="0409626721-4">)</span></code></pre><ul><li><code class="inline">start/2</code> is called when starting the application and is to create the
│ │ │  supervision tree by starting the top supervisor. It is expected to return the
│ │ │  pid of the top supervisor and an optional term, <code class="inline">State</code>, which defaults to
│ │ │  <code class="inline">[]</code>. This term is passed as is to <code class="inline">stop/1</code>.</li><li><code class="inline">StartType</code> is usually the atom <code class="inline">normal</code>. It has other values only in the case
│ │ │  of a takeover or failover; see
│ │ │  <a href="distributed_applications.html">Distributed Applications</a>.</li><li><code class="inline">StartArgs</code> is defined by the key <code class="inline">mod</code> in the
│ │ │  <a href="applications.html#appl_res_file">application resource file</a>.</li><li><code class="inline">stop/1</code> is called <em>after</em> the application has been stopped and is to do any
│ │ │  necessary cleaning up. The actual stopping of the application, that is,
│ │ │  shutting down the supervision tree, is handled automatically as described in
│ │ │  <a href="applications.html#stopping">Starting and Stopping Applications</a>.</li></ul><p><a href="" id="ch_app"></a></p><p>Example of an application callback module for packaging the supervision tree
│ │ │ -from <a href="sup_princ.html#ex">Supervisor Behaviour</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5936919941-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="5936919941-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5936919941-2">(</span><span class="ss">application</span><span class="p" data-group-id="5936919941-2">)</span><span class="p">.</span><span class="w">
│ │ │ +from <a href="sup_princ.html#ex">Supervisor Behaviour</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5544245891-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="5544245891-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5544245891-2">(</span><span class="ss">application</span><span class="p" data-group-id="5544245891-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5936919941-3">(</span><span class="p" data-group-id="5936919941-4">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5936919941-4">]</span><span class="p" data-group-id="5936919941-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5544245891-3">(</span><span class="p" data-group-id="5544245891-4">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5544245891-4">]</span><span class="p" data-group-id="5544245891-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="5936919941-5">(</span><span class="p">_</span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5936919941-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">ch_sup</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5936919941-6">(</span><span class="p" data-group-id="5936919941-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="5544245891-5">(</span><span class="p">_</span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5544245891-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">ch_sup</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5544245891-6">(</span><span class="p" data-group-id="5544245891-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="5936919941-7">(</span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="5936919941-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="5544245891-7">(</span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="5544245891-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>A library application that cannot be started or stopped does not need any
│ │ │  application callback module.</p><p><a href="" id="appl_res_file"></a></p><h2 id="application-resource-file" class="section-heading">
│ │ │    <a href="#application-resource-file" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Application Resource File</span>
│ │ │  </h2>
│ │ │ @@ -173,22 +173,22 @@
│ │ │  keys.</li></ul><p>The contents of a minimal <code class="inline">.app</code> file for a library application <code class="inline">libapp</code> looks
│ │ │  as follows:</p><pre><code class="text">{application, libapp, []}.</code></pre><p>The contents of a minimal <code class="inline">.app</code> file <code class="inline">ch_app.app</code> for a supervision tree
│ │ │  application like <code class="inline">ch_app</code> looks as follows:</p><pre><code class="text">{application, ch_app,
│ │ │   [{mod, {ch_app,[]}}]}.</code></pre><p>The key <code class="inline">mod</code> defines the callback module and start argument of the application,
│ │ │  in this case <code class="inline">ch_app</code> and <code class="inline">[]</code>, respectively. This means that the following is
│ │ │  called when the application is to be started:</p><pre><code class="text">ch_app:start(normal, [])</code></pre><p>The following is called when the application is stopped:</p><pre><code class="text">ch_app:stop([])</code></pre><p>When using <a href="../../lib/sasl-4.2.2/doc/html/systools.html"><code class="inline">systools</code></a>, the Erlang/OTP tools for packaging code (see Section
│ │ │  <a href="release_structure.html">Releases</a>), the keys <code class="inline">description</code>, <code class="inline">vsn</code>, <code class="inline">modules</code>,
│ │ │ -<code class="inline">registered</code>, and <code class="inline">applications</code> are also to be specified:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0995059216-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0995059216-2">[</span><span class="p" data-group-id="0995059216-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="0995059216-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0995059216-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="0995059216-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0995059216-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0995059216-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0995059216-6">]</span><span class="p" data-group-id="0995059216-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0995059216-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0995059216-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="0995059216-8">]</span><span class="p" data-group-id="0995059216-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0995059216-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0995059216-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="0995059216-10">]</span><span class="p" data-group-id="0995059216-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0995059216-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0995059216-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="0995059216-13">[</span><span class="p" data-group-id="0995059216-13">]</span><span class="p" data-group-id="0995059216-12">}</span><span class="p" data-group-id="0995059216-11">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0995059216-2">]</span><span class="p" data-group-id="0995059216-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">description</code> - A short description, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">vsn</code> - Version number, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">modules</code> - All modules <em>introduced</em> by this application. <a href="../../lib/sasl-4.2.2/doc/html/systools.html"><code class="inline">systools</code></a> uses
│ │ │ +<code class="inline">registered</code>, and <code class="inline">applications</code> are also to be specified:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5096555909-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5096555909-2">[</span><span class="p" data-group-id="5096555909-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="5096555909-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5096555909-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="5096555909-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5096555909-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5096555909-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="5096555909-6">]</span><span class="p" data-group-id="5096555909-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5096555909-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5096555909-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="5096555909-8">]</span><span class="p" data-group-id="5096555909-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5096555909-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5096555909-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="5096555909-10">]</span><span class="p" data-group-id="5096555909-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5096555909-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5096555909-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="5096555909-13">[</span><span class="p" data-group-id="5096555909-13">]</span><span class="p" data-group-id="5096555909-12">}</span><span class="p" data-group-id="5096555909-11">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5096555909-2">]</span><span class="p" data-group-id="5096555909-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">description</code> - A short description, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">vsn</code> - Version number, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">modules</code> - All modules <em>introduced</em> by this application. <a href="../../lib/sasl-4.2.2/doc/html/systools.html"><code class="inline">systools</code></a> uses
│ │ │  this list when generating boot scripts and tar files. A module must only
│ │ │  be included in one application. Defaults to <code class="inline">[]</code>.</li><li><code class="inline">registered</code> - All names of registered processes in the application.
│ │ │  <a href="../../lib/sasl-4.2.2/doc/html/systools.html"><code class="inline">systools</code></a> uses this list to detect name clashes between applications.
│ │ │  Defaults to <code class="inline">[]</code>.</li><li><code class="inline">applications</code> - All applications that must be started before this
│ │ │  application is started. <a href="../../lib/sasl-4.2.2/doc/html/systools.html"><code class="inline">systools</code></a> uses this list to generate correct boot
│ │ │  scripts. Defaults to <code class="inline">[]</code>. Notice that all applications have dependencies to
│ │ │  at least Kernel and STDLIB.</li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>For details about the syntax and contents of the application resource file,
│ │ │ @@ -300,38 +300,38 @@
│ │ │  stop applications.</p><h2 id="loading-and-unloading-applications" class="section-heading">
│ │ │    <a href="#loading-and-unloading-applications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Loading and Unloading Applications</span>
│ │ │  </h2>
│ │ │  <p>Before an application can be started, it must be <em>loaded</em>. The application
│ │ │ -controller reads and stores the information from the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">load</span><span class="p" data-group-id="3328671684-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="3328671684-1">)</span><span class="p">.</span><span class="w">
│ │ │ +controller reads and stores the information from the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">load</span><span class="p" data-group-id="3362802473-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="3362802473-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="3328671684-2">(</span><span class="p" data-group-id="3328671684-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3328671684-3">[</span><span class="p" data-group-id="3328671684-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="3328671684-4">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3328671684-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="3328671684-5">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3328671684-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="3328671684-6">}</span><span class="p" data-group-id="3328671684-3">]</span></code></pre><p>An application that has been stopped, or has never been started, can be
│ │ │ +2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="3362802473-2">(</span><span class="p" data-group-id="3362802473-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3362802473-3">[</span><span class="p" data-group-id="3362802473-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="3362802473-4">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3362802473-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="3362802473-5">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3362802473-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="3362802473-6">}</span><span class="p" data-group-id="3362802473-3">]</span></code></pre><p>An application that has been stopped, or has never been started, can be
│ │ │  unloaded. The information about the application is erased from the internal
│ │ │ -database of the application controller.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">unload</span><span class="p" data-group-id="3866590285-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="3866590285-1">)</span><span class="p">.</span><span class="w">
│ │ │ +database of the application controller.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">unload</span><span class="p" data-group-id="3623119021-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="3623119021-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="3866590285-2">(</span><span class="p" data-group-id="3866590285-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3866590285-3">[</span><span class="p" data-group-id="3866590285-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="3866590285-4">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3866590285-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="3866590285-5">}</span><span class="p" data-group-id="3866590285-3">]</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Loading/unloading an application does not load/unload the code used by the
│ │ │ +4&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="3623119021-2">(</span><span class="p" data-group-id="3623119021-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3623119021-3">[</span><span class="p" data-group-id="3623119021-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="3623119021-4">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3623119021-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="3623119021-5">}</span><span class="p" data-group-id="3623119021-3">]</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Loading/unloading an application does not load/unload the code used by the
│ │ │  application. Code loading is handled in the usual way by the code server.</p></section><p><a href="" id="stopping"></a></p><h2 id="starting-and-stopping-applications" class="section-heading">
│ │ │    <a href="#starting-and-stopping-applications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting and Stopping Applications</span>
│ │ │  </h2>
│ │ │ -<p>An application is started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6457826963-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="6457826963-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>An application is started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9711136281-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="9711136281-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">which_applications</span><span class="p" data-group-id="6457826963-2">(</span><span class="p" data-group-id="6457826963-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6457826963-3">[</span><span class="p" data-group-id="6457826963-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="6457826963-4">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6457826963-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="6457826963-5">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6457826963-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6457826963-6">}</span><span class="p" data-group-id="6457826963-3">]</span></code></pre><p>If the application is not already loaded, the application controller first loads
│ │ │ +6&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">which_applications</span><span class="p" data-group-id="9711136281-2">(</span><span class="p" data-group-id="9711136281-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9711136281-3">[</span><span class="p" data-group-id="9711136281-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="9711136281-4">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9711136281-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="9711136281-5">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9711136281-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="9711136281-6">}</span><span class="p" data-group-id="9711136281-3">]</span></code></pre><p>If the application is not already loaded, the application controller first loads
│ │ │  it using <a href="../../lib/kernel-10.2.7.1/doc/html/application.html#load/1"><code class="inline">application:load/1</code></a>. It checks the value of the <code class="inline">applications</code> key to
│ │ │  ensure that all applications that are to be started before this application are
│ │ │  running.</p><p><a href="" id="application_master"></a></p><p>Following that, the application controller creates an <em>application master</em> for
│ │ │  the application.</p><p>The application master establishes itself as the <a href="../../erts-15.2.7/doc/html/erlang.html#group_leader/0">group
│ │ │  leader</a> of all processes in the application
│ │ │  and will forward I/O to the previous group leader.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The purpose of the application master being the group leader is to easily
│ │ │  keep track of which processes that belong to the application. That is needed
│ │ │ @@ -347,55 +347,55 @@
│ │ │  defined by the <code class="inline">mod</code> key.</p><h2 id="configuring-an-application" class="section-heading">
│ │ │    <a href="#configuring-an-application" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Configuring an Application</span>
│ │ │  </h2>
│ │ │  <p>An application can be configured using <em>configuration parameters</em>. These are a
│ │ │ -list of <code class="inline">{Par,Val}</code> tuples specified by a key <code class="inline">env</code> in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8501335369-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8501335369-2">[</span><span class="p" data-group-id="8501335369-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="8501335369-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8501335369-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="8501335369-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8501335369-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8501335369-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8501335369-6">]</span><span class="p" data-group-id="8501335369-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8501335369-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8501335369-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="8501335369-8">]</span><span class="p" data-group-id="8501335369-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8501335369-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8501335369-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="8501335369-10">]</span><span class="p" data-group-id="8501335369-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8501335369-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8501335369-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="8501335369-13">[</span><span class="p" data-group-id="8501335369-13">]</span><span class="p" data-group-id="8501335369-12">}</span><span class="p" data-group-id="8501335369-11">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8501335369-14">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8501335369-15">[</span><span class="p" data-group-id="8501335369-16">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="8501335369-16">}</span><span class="p" data-group-id="8501335369-15">]</span><span class="p" data-group-id="8501335369-14">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8501335369-2">]</span><span class="p" data-group-id="8501335369-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Par</code> is to be an atom. <code class="inline">Val</code> is any term. The application can retrieve the
│ │ │ +list of <code class="inline">{Par,Val}</code> tuples specified by a key <code class="inline">env</code> in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1564702111-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1564702111-2">[</span><span class="p" data-group-id="1564702111-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="1564702111-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1564702111-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="1564702111-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1564702111-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1564702111-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="1564702111-6">]</span><span class="p" data-group-id="1564702111-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1564702111-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1564702111-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="1564702111-8">]</span><span class="p" data-group-id="1564702111-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1564702111-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1564702111-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="1564702111-10">]</span><span class="p" data-group-id="1564702111-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1564702111-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1564702111-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="1564702111-13">[</span><span class="p" data-group-id="1564702111-13">]</span><span class="p" data-group-id="1564702111-12">}</span><span class="p" data-group-id="1564702111-11">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1564702111-14">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1564702111-15">[</span><span class="p" data-group-id="1564702111-16">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="1564702111-16">}</span><span class="p" data-group-id="1564702111-15">]</span><span class="p" data-group-id="1564702111-14">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1564702111-2">]</span><span class="p" data-group-id="1564702111-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Par</code> is to be an atom. <code class="inline">Val</code> is any term. The application can retrieve the
│ │ │  value of a configuration parameter by calling <code class="inline">application:get_env(App, Par)</code> or
│ │ │  a number of similar functions. For more information, see module <a href="../../lib/kernel-10.2.7.1/doc/html/application.html"><code class="inline">application</code></a>
│ │ │  in Kernel.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="4277294441-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="4277294441-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="4277294441-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="4277294441-2">]</span><span class="w"> </span><span class="p" data-group-id="4277294441-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="4277294441-3">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="5080815166-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="5080815166-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="5080815166-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="5080815166-2">]</span><span class="w"> </span><span class="p" data-group-id="5080815166-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="5080815166-3">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="4277294441-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="4277294441-4">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4277294441-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="4277294441-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="5080815166-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="5080815166-4">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5080815166-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="5080815166-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="4277294441-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="4277294441-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4277294441-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="4277294441-7">}</span></code></pre><p>The values in the <code class="inline">.app</code> file can be overridden by values in a <em>system
│ │ │ +2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="5080815166-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="5080815166-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5080815166-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="5080815166-7">}</span></code></pre><p>The values in the <code class="inline">.app</code> file can be overridden by values in a <em>system
│ │ │  configuration file</em>. This is a file that contains configuration parameters for
│ │ │ -relevant applications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7612457406-1">[</span><span class="p" data-group-id="7612457406-2">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7612457406-3">[</span><span class="p" data-group-id="7612457406-4">{</span><span class="n">Par11</span><span class="p">,</span><span class="n">Val11</span><span class="p" data-group-id="7612457406-4">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7612457406-3">]</span><span class="p" data-group-id="7612457406-2">}</span><span class="p">,</span><span class="w">
│ │ │ +relevant applications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4158597197-1">[</span><span class="p" data-group-id="4158597197-2">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4158597197-3">[</span><span class="p" data-group-id="4158597197-4">{</span><span class="n">Par11</span><span class="p">,</span><span class="n">Val11</span><span class="p" data-group-id="4158597197-4">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4158597197-3">]</span><span class="p" data-group-id="4158597197-2">}</span><span class="p">,</span><span class="w">
│ │ │   </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7612457406-5">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7612457406-6">[</span><span class="p" data-group-id="7612457406-7">{</span><span class="n">ParN1</span><span class="p">,</span><span class="n">ValN1</span><span class="p" data-group-id="7612457406-7">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7612457406-6">]</span><span class="p" data-group-id="7612457406-5">}</span><span class="p" data-group-id="7612457406-1">]</span><span class="p">.</span></code></pre><p>The system configuration is to be called <code class="inline">Name.config</code> and Erlang is to be
│ │ │ + </span><span class="p" data-group-id="4158597197-5">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4158597197-6">[</span><span class="p" data-group-id="4158597197-7">{</span><span class="n">ParN1</span><span class="p">,</span><span class="n">ValN1</span><span class="p" data-group-id="4158597197-7">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4158597197-6">]</span><span class="p" data-group-id="4158597197-5">}</span><span class="p" data-group-id="4158597197-1">]</span><span class="p">.</span></code></pre><p>The system configuration is to be called <code class="inline">Name.config</code> and Erlang is to be
│ │ │  started with the command-line argument <code class="inline">-config Name</code>. For details, see
│ │ │  <a href="../../lib/kernel-10.2.7.1/doc/html/config.html"><code class="inline">config</code></a> in Kernel.</p><p><em>Example:</em></p><p>A file <code class="inline">test.config</code> is created with the following contents:</p><pre><code class="text">[{ch_app, [{file, &quot;testlog&quot;}]}].</code></pre><p>The value of <code class="inline">file</code> overrides the value of <code class="inline">file</code> as defined in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -config test</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="0856295691-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="0856295691-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="0856295691-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="0856295691-2">]</span><span class="w"> </span><span class="p" data-group-id="0856295691-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="0856295691-3">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="0751202271-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="0751202271-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="0751202271-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="0751202271-2">]</span><span class="w"> </span><span class="p" data-group-id="0751202271-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="0751202271-3">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="0856295691-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="0856295691-4">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0856295691-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="0856295691-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="0751202271-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="0751202271-4">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0751202271-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="0751202271-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="0856295691-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="0856295691-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0856295691-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="0856295691-7">}</span></code></pre><p>If <a href="release_handling.html#sys">release handling</a> is used, exactly one system
│ │ │ +2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="0751202271-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="0751202271-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0751202271-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="0751202271-7">}</span></code></pre><p>If <a href="release_handling.html#sys">release handling</a> is used, exactly one system
│ │ │  configuration file is to be used and that file is to be called <code class="inline">sys.config</code>.</p><p>The values in the <code class="inline">.app</code> file and the values in a system configuration file can
│ │ │  be overridden directly from the command line:</p><pre><code class="text">% erl -ApplName Par1 Val1 ... ParN ValN</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -ch_app file &#39;&quot;testlog&quot;&#39;</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="7715958306-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="7715958306-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="7715958306-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="7715958306-2">]</span><span class="w"> </span><span class="p" data-group-id="7715958306-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="7715958306-3">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="4132779115-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="4132779115-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="4132779115-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="4132779115-2">]</span><span class="w"> </span><span class="p" data-group-id="4132779115-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="4132779115-3">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="7715958306-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="7715958306-4">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7715958306-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="7715958306-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="4132779115-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="4132779115-4">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4132779115-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="4132779115-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="7715958306-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="7715958306-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7715958306-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="7715958306-7">}</span></code></pre><h2 id="application-start-types" class="section-heading">
│ │ │ +2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="4132779115-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="4132779115-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4132779115-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="4132779115-7">}</span></code></pre><h2 id="application-start-types" class="section-heading">
│ │ │    <a href="#application-start-types" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Application Start Types</span>
│ │ │  </h2>
│ │ │  <p>A <em>start type</em> is defined when starting the application:</p><pre><code class="text">application:start(Application, Type)</code></pre><p><code class="inline">application:start(Application)</code> is the same as calling
│ │ │  <code class="inline">application:start(Application, temporary)</code>. The type can also be <code class="inline">permanent</code> or
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/appup_cookbook.html
│ │ │ @@ -120,18 +120,18 @@
│ │ │    <a href="#changing-a-functional-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing a Functional Module</span>
│ │ │  </h2>
│ │ │  <p>When a functional module has been changed, for example, if a new function has
│ │ │  been added or a bug has been corrected, simple code replacement is sufficient,
│ │ │ -for example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8669128512-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8669128512-2">[</span><span class="p" data-group-id="8669128512-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8669128512-4">[</span><span class="p" data-group-id="8669128512-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="8669128512-5">}</span><span class="p" data-group-id="8669128512-4">]</span><span class="p" data-group-id="8669128512-3">}</span><span class="p" data-group-id="8669128512-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8669128512-6">[</span><span class="p" data-group-id="8669128512-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8669128512-8">[</span><span class="p" data-group-id="8669128512-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="8669128512-9">}</span><span class="p" data-group-id="8669128512-8">]</span><span class="p" data-group-id="8669128512-7">}</span><span class="p" data-group-id="8669128512-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8669128512-1">}</span><span class="p">.</span></code></pre><h2 id="changing-a-residence-module" class="section-heading">
│ │ │ +for example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1609064655-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1609064655-2">[</span><span class="p" data-group-id="1609064655-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1609064655-4">[</span><span class="p" data-group-id="1609064655-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="1609064655-5">}</span><span class="p" data-group-id="1609064655-4">]</span><span class="p" data-group-id="1609064655-3">}</span><span class="p" data-group-id="1609064655-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1609064655-6">[</span><span class="p" data-group-id="1609064655-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1609064655-8">[</span><span class="p" data-group-id="1609064655-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="1609064655-9">}</span><span class="p" data-group-id="1609064655-8">]</span><span class="p" data-group-id="1609064655-7">}</span><span class="p" data-group-id="1609064655-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1609064655-1">}</span><span class="p">.</span></code></pre><h2 id="changing-a-residence-module" class="section-heading">
│ │ │    <a href="#changing-a-residence-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing a Residence Module</span>
│ │ │  </h2>
│ │ │  <p>In a system implemented according to the OTP design principles, all processes,
│ │ │  except system processes and special processes, reside in one of the behaviours
│ │ │ @@ -142,46 +142,46 @@
│ │ │    <a href="#changing-a-callback-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing a Callback Module</span>
│ │ │  </h2>
│ │ │  <p>A callback module is a functional module, and for code extensions simple code
│ │ │  replacement is sufficient.</p><p><em>Example</em></p><p>When adding a function to <code class="inline">ch3</code>, as described in the example in
│ │ │ -<a href="release_handling.html#appup">Release Handling</a>, <code class="inline">ch_app.appup</code> looks as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7803869459-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7803869459-2">[</span><span class="p" data-group-id="7803869459-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7803869459-4">[</span><span class="p" data-group-id="7803869459-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7803869459-5">}</span><span class="p" data-group-id="7803869459-4">]</span><span class="p" data-group-id="7803869459-3">}</span><span class="p" data-group-id="7803869459-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7803869459-6">[</span><span class="p" data-group-id="7803869459-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7803869459-8">[</span><span class="p" data-group-id="7803869459-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7803869459-9">}</span><span class="p" data-group-id="7803869459-8">]</span><span class="p" data-group-id="7803869459-7">}</span><span class="p" data-group-id="7803869459-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7803869459-1">}</span><span class="p">.</span></code></pre><p>OTP also supports changing the internal state of behaviour processes; see
│ │ │ +<a href="release_handling.html#appup">Release Handling</a>, <code class="inline">ch_app.appup</code> looks as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8948128128-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8948128128-2">[</span><span class="p" data-group-id="8948128128-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8948128128-4">[</span><span class="p" data-group-id="8948128128-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8948128128-5">}</span><span class="p" data-group-id="8948128128-4">]</span><span class="p" data-group-id="8948128128-3">}</span><span class="p" data-group-id="8948128128-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8948128128-6">[</span><span class="p" data-group-id="8948128128-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8948128128-8">[</span><span class="p" data-group-id="8948128128-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8948128128-9">}</span><span class="p" data-group-id="8948128128-8">]</span><span class="p" data-group-id="8948128128-7">}</span><span class="p" data-group-id="8948128128-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8948128128-1">}</span><span class="p">.</span></code></pre><p>OTP also supports changing the internal state of behaviour processes; see
│ │ │  <a href="appup_cookbook.html#int_state">Changing Internal State</a>.</p><p><a href="" id="int_state"></a></p><h2 id="changing-internal-state" class="section-heading">
│ │ │    <a href="#changing-internal-state" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing Internal State</span>
│ │ │  </h2>
│ │ │  <p>In this case, simple code replacement is not sufficient. The process must
│ │ │  explicitly transform its state using the callback function <code class="inline">code_change/3</code> before
│ │ │  switching to the new version of the callback module. Thus, synchronized code
│ │ │  replacement is used.</p><p><em>Example</em></p><p>Consider the <code class="inline">ch3</code> module from
│ │ │  <a href="gen_server_concepts.html#ex">gen_server Behaviour</a>. The internal state is a term
│ │ │  <code class="inline">Chs</code> representing the available channels. Assume you want to add a counter <code class="inline">N</code>,
│ │ │  which keeps track of the number of <code class="inline">alloc</code> requests so far. This means that the
│ │ │ -format must be changed to <code class="inline">{Chs,N}</code>.</p><p>The <code class="inline">.appup</code> file can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5051359121-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5051359121-2">[</span><span class="p" data-group-id="5051359121-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5051359121-4">[</span><span class="p" data-group-id="5051359121-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5051359121-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5051359121-7">[</span><span class="p" data-group-id="5051359121-7">]</span><span class="p" data-group-id="5051359121-6">}</span><span class="p" data-group-id="5051359121-5">}</span><span class="p" data-group-id="5051359121-4">]</span><span class="p" data-group-id="5051359121-3">}</span><span class="p" data-group-id="5051359121-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5051359121-8">[</span><span class="p" data-group-id="5051359121-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5051359121-10">[</span><span class="p" data-group-id="5051359121-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5051359121-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5051359121-13">[</span><span class="p" data-group-id="5051359121-13">]</span><span class="p" data-group-id="5051359121-12">}</span><span class="p" data-group-id="5051359121-11">}</span><span class="p" data-group-id="5051359121-10">]</span><span class="p" data-group-id="5051359121-9">}</span><span class="p" data-group-id="5051359121-8">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5051359121-1">}</span><span class="p">.</span></code></pre><p>The third element of the <code class="inline">update</code> instruction is a tuple <code class="inline">{advanced,Extra}</code>,
│ │ │ +format must be changed to <code class="inline">{Chs,N}</code>.</p><p>The <code class="inline">.appup</code> file can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7442060477-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7442060477-2">[</span><span class="p" data-group-id="7442060477-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7442060477-4">[</span><span class="p" data-group-id="7442060477-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7442060477-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7442060477-7">[</span><span class="p" data-group-id="7442060477-7">]</span><span class="p" data-group-id="7442060477-6">}</span><span class="p" data-group-id="7442060477-5">}</span><span class="p" data-group-id="7442060477-4">]</span><span class="p" data-group-id="7442060477-3">}</span><span class="p" data-group-id="7442060477-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7442060477-8">[</span><span class="p" data-group-id="7442060477-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7442060477-10">[</span><span class="p" data-group-id="7442060477-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7442060477-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7442060477-13">[</span><span class="p" data-group-id="7442060477-13">]</span><span class="p" data-group-id="7442060477-12">}</span><span class="p" data-group-id="7442060477-11">}</span><span class="p" data-group-id="7442060477-10">]</span><span class="p" data-group-id="7442060477-9">}</span><span class="p" data-group-id="7442060477-8">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7442060477-1">}</span><span class="p">.</span></code></pre><p>The third element of the <code class="inline">update</code> instruction is a tuple <code class="inline">{advanced,Extra}</code>,
│ │ │  which says that the affected processes are to do a state transformation before
│ │ │  loading the new version of the module. This is done by the processes calling the
│ │ │  callback function <code class="inline">code_change/3</code> (see <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html"><code class="inline">gen_server</code></a> in STDLIB).
│ │ │ -The term <code class="inline">Extra</code>, in this case <code class="inline">[]</code>, is passed as is to the function:</p><p><a href="" id="code_change"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2343402269-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="2343402269-1">)</span><span class="p">.</span><span class="w">
│ │ │ +The term <code class="inline">Extra</code>, in this case <code class="inline">[]</code>, is passed as is to the function:</p><p><a href="" id="code_change"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7627590105-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="7627590105-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2343402269-2">(</span><span class="p" data-group-id="2343402269-3">[</span><span class="ss">code_change</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="2343402269-3">]</span><span class="p" data-group-id="2343402269-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7627590105-2">(</span><span class="p" data-group-id="7627590105-3">[</span><span class="ss">code_change</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="7627590105-3">]</span><span class="p" data-group-id="7627590105-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">code_change</span><span class="p" data-group-id="2343402269-4">(</span><span class="p" data-group-id="2343402269-5">{</span><span class="ss">down</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vsn</span><span class="p" data-group-id="2343402269-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2343402269-6">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="2343402269-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="2343402269-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2343402269-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2343402269-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">code_change</span><span class="p" data-group-id="2343402269-8">(</span><span class="p">_</span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="2343402269-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2343402269-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2343402269-10">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2343402269-10">}</span><span class="p" data-group-id="2343402269-9">}</span><span class="p">.</span></code></pre><p>The first argument is <code class="inline">{down,Vsn}</code> if there is a downgrade, or <code class="inline">Vsn</code> if there is
│ │ │ +</span><span class="nf">code_change</span><span class="p" data-group-id="7627590105-4">(</span><span class="p" data-group-id="7627590105-5">{</span><span class="ss">down</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vsn</span><span class="p" data-group-id="7627590105-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7627590105-6">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="7627590105-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="7627590105-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7627590105-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7627590105-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">code_change</span><span class="p" data-group-id="7627590105-8">(</span><span class="p">_</span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="7627590105-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7627590105-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7627590105-10">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7627590105-10">}</span><span class="p" data-group-id="7627590105-9">}</span><span class="p">.</span></code></pre><p>The first argument is <code class="inline">{down,Vsn}</code> if there is a downgrade, or <code class="inline">Vsn</code> if there is
│ │ │  a upgrade. The term <code class="inline">Vsn</code> is fetched from the 'original' version of the module,
│ │ │  that is, the version you are upgrading from, or downgrading to.</p><p>The version is defined by the module attribute <code class="inline">vsn</code>, if any. There is no such
│ │ │  attribute in <code class="inline">ch3</code>, so in this case the version is the checksum (a huge integer)
│ │ │  of the beam file, an uninteresting value, which is ignored.</p><p>The other callback functions of <code class="inline">ch3</code> must also be modified and perhaps a new
│ │ │  interface function must be added, but this is not shown here.</p><h2 id="module-dependencies" class="section-heading">
│ │ │    <a href="#module-dependencies" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -190,67 +190,67 @@
│ │ │  </h2>
│ │ │  <p>Assume that a module is extended by adding an interface function, as in the
│ │ │  example in <a href="release_handling.html#appup">Release Handling</a>, where a function
│ │ │  <code class="inline">available/0</code> is added to <code class="inline">ch3</code>.</p><p>If a call is added to this function, say in module <code class="inline">m1</code>, a runtime error could
│ │ │  can occur during release upgrade if the new version of <code class="inline">m1</code> is loaded first and
│ │ │  calls <code class="inline">ch3:available/0</code> before the new version of <code class="inline">ch3</code> is loaded.</p><p>Thus, <code class="inline">ch3</code> must be loaded before <code class="inline">m1</code>, in the upgrade case, and conversely in
│ │ │  the downgrade case. <code class="inline">m1</code> is said to be <em>dependent on</em> <code class="inline">ch3</code>. In a release
│ │ │ -handling instruction, this is expressed by the <code class="inline">DepMods</code> element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9818727810-1">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="9818727810-1">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9818727810-2">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9818727810-3">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="9818727810-3">}</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="9818727810-2">}</span></code></pre><p><code class="inline">DepMods</code> is a list of modules, on which <code class="inline">Module</code> is dependent.</p><p><em>Example</em></p><p>The module <code class="inline">m1</code> in application <code class="inline">myapp</code> is dependent on <code class="inline">ch3</code> when
│ │ │ +handling instruction, this is expressed by the <code class="inline">DepMods</code> element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1974340662-1">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="1974340662-1">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1974340662-2">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1974340662-3">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="1974340662-3">}</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="1974340662-2">}</span></code></pre><p><code class="inline">DepMods</code> is a list of modules, on which <code class="inline">Module</code> is dependent.</p><p><em>Example</em></p><p>The module <code class="inline">m1</code> in application <code class="inline">myapp</code> is dependent on <code class="inline">ch3</code> when
│ │ │  upgrading from &quot;1&quot; to &quot;2&quot;, or downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="ss">myapp</span><span class="p">.</span><span class="nc">appup</span><span class="p">:</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="1471092139-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1471092139-2">[</span><span class="p" data-group-id="1471092139-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1471092139-4">[</span><span class="p" data-group-id="1471092139-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1471092139-6">[</span><span class="ss">ch3</span><span class="p" data-group-id="1471092139-6">]</span><span class="p" data-group-id="1471092139-5">}</span><span class="p" data-group-id="1471092139-4">]</span><span class="p" data-group-id="1471092139-3">}</span><span class="p" data-group-id="1471092139-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1471092139-7">[</span><span class="p" data-group-id="1471092139-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1471092139-9">[</span><span class="p" data-group-id="1471092139-10">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1471092139-11">[</span><span class="ss">ch3</span><span class="p" data-group-id="1471092139-11">]</span><span class="p" data-group-id="1471092139-10">}</span><span class="p" data-group-id="1471092139-9">]</span><span class="p" data-group-id="1471092139-8">}</span><span class="p" data-group-id="1471092139-7">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1471092139-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4478603335-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4478603335-2">[</span><span class="p" data-group-id="4478603335-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4478603335-4">[</span><span class="p" data-group-id="4478603335-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4478603335-6">[</span><span class="ss">ch3</span><span class="p" data-group-id="4478603335-6">]</span><span class="p" data-group-id="4478603335-5">}</span><span class="p" data-group-id="4478603335-4">]</span><span class="p" data-group-id="4478603335-3">}</span><span class="p" data-group-id="4478603335-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4478603335-7">[</span><span class="p" data-group-id="4478603335-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4478603335-9">[</span><span class="p" data-group-id="4478603335-10">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4478603335-11">[</span><span class="ss">ch3</span><span class="p" data-group-id="4478603335-11">]</span><span class="p" data-group-id="4478603335-10">}</span><span class="p" data-group-id="4478603335-9">]</span><span class="p" data-group-id="4478603335-8">}</span><span class="p" data-group-id="4478603335-7">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4478603335-1">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="ss">ch_app</span><span class="p">.</span><span class="nc">appup</span><span class="p">:</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="1471092139-12">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1471092139-13">[</span><span class="p" data-group-id="1471092139-14">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1471092139-15">[</span><span class="p" data-group-id="1471092139-16">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="1471092139-16">}</span><span class="p" data-group-id="1471092139-15">]</span><span class="p" data-group-id="1471092139-14">}</span><span class="p" data-group-id="1471092139-13">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1471092139-17">[</span><span class="p" data-group-id="1471092139-18">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1471092139-19">[</span><span class="p" data-group-id="1471092139-20">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="1471092139-20">}</span><span class="p" data-group-id="1471092139-19">]</span><span class="p" data-group-id="1471092139-18">}</span><span class="p" data-group-id="1471092139-17">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1471092139-12">}</span><span class="p">.</span></code></pre><p>If instead <code class="inline">m1</code> and <code class="inline">ch3</code> belong to the same application, the <code class="inline">.appup</code> file can
│ │ │ -look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2734096731-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2734096731-2">[</span><span class="p" data-group-id="2734096731-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="2734096731-4">[</span><span class="p" data-group-id="2734096731-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2734096731-5">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2734096731-6">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2734096731-7">[</span><span class="ss">ch3</span><span class="p" data-group-id="2734096731-7">]</span><span class="p" data-group-id="2734096731-6">}</span><span class="p" data-group-id="2734096731-4">]</span><span class="p" data-group-id="2734096731-3">}</span><span class="p" data-group-id="2734096731-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2734096731-8">[</span><span class="p" data-group-id="2734096731-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="2734096731-10">[</span><span class="p" data-group-id="2734096731-11">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2734096731-11">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2734096731-12">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2734096731-13">[</span><span class="ss">ch3</span><span class="p" data-group-id="2734096731-13">]</span><span class="p" data-group-id="2734096731-12">}</span><span class="p" data-group-id="2734096731-10">]</span><span class="p" data-group-id="2734096731-9">}</span><span class="p" data-group-id="2734096731-8">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2734096731-1">}</span><span class="p">.</span></code></pre><p><code class="inline">m1</code> is dependent on <code class="inline">ch3</code> also when downgrading. <code class="inline">systools</code> knows the
│ │ │ +</span><span class="p" data-group-id="4478603335-12">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4478603335-13">[</span><span class="p" data-group-id="4478603335-14">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4478603335-15">[</span><span class="p" data-group-id="4478603335-16">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="4478603335-16">}</span><span class="p" data-group-id="4478603335-15">]</span><span class="p" data-group-id="4478603335-14">}</span><span class="p" data-group-id="4478603335-13">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4478603335-17">[</span><span class="p" data-group-id="4478603335-18">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4478603335-19">[</span><span class="p" data-group-id="4478603335-20">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="4478603335-20">}</span><span class="p" data-group-id="4478603335-19">]</span><span class="p" data-group-id="4478603335-18">}</span><span class="p" data-group-id="4478603335-17">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4478603335-12">}</span><span class="p">.</span></code></pre><p>If instead <code class="inline">m1</code> and <code class="inline">ch3</code> belong to the same application, the <code class="inline">.appup</code> file can
│ │ │ +look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5378558560-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5378558560-2">[</span><span class="p" data-group-id="5378558560-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="5378558560-4">[</span><span class="p" data-group-id="5378558560-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="5378558560-5">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5378558560-6">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5378558560-7">[</span><span class="ss">ch3</span><span class="p" data-group-id="5378558560-7">]</span><span class="p" data-group-id="5378558560-6">}</span><span class="p" data-group-id="5378558560-4">]</span><span class="p" data-group-id="5378558560-3">}</span><span class="p" data-group-id="5378558560-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5378558560-8">[</span><span class="p" data-group-id="5378558560-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="5378558560-10">[</span><span class="p" data-group-id="5378558560-11">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="5378558560-11">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5378558560-12">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5378558560-13">[</span><span class="ss">ch3</span><span class="p" data-group-id="5378558560-13">]</span><span class="p" data-group-id="5378558560-12">}</span><span class="p" data-group-id="5378558560-10">]</span><span class="p" data-group-id="5378558560-9">}</span><span class="p" data-group-id="5378558560-8">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5378558560-1">}</span><span class="p">.</span></code></pre><p><code class="inline">m1</code> is dependent on <code class="inline">ch3</code> also when downgrading. <code class="inline">systools</code> knows the
│ │ │  difference between up- and downgrading and generates a correct <code class="inline">relup</code>, where
│ │ │  <code class="inline">ch3</code> is loaded before <code class="inline">m1</code> when upgrading, but <code class="inline">m1</code> is loaded before <code class="inline">ch3</code> when
│ │ │  downgrading.</p><p><a href="" id="spec"></a></p><h2 id="changing-code-for-a-special-process" class="section-heading">
│ │ │    <a href="#changing-code-for-a-special-process" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing Code for a Special Process</span>
│ │ │  </h2>
│ │ │  <p>In this case, simple code replacement is not sufficient. When a new version of a
│ │ │  residence module for a special process is loaded, the process must make a fully
│ │ │  qualified call to its loop function to switch to the new code. Thus,
│ │ │  synchronized code replacement must be used.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The name(s) of the user-defined residence module(s) must be listed in the
│ │ │  <code class="inline">Modules</code> part of the child specification for the special process. Otherwise
│ │ │  the release handler cannot find the process.</p></section><p><em>Example</em></p><p>Consider the example <code class="inline">ch4</code> in <a href="spec_proc.html#ex">sys and proc_lib</a>.
│ │ │ -When started by a supervisor, the child specification can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2091816981-1">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2091816981-2">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2091816981-3">[</span><span class="p" data-group-id="2091816981-3">]</span><span class="p" data-group-id="2091816981-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="ss">permanent</span><span class="p">,</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2091816981-4">[</span><span class="ss">ch4</span><span class="p" data-group-id="2091816981-4">]</span><span class="p" data-group-id="2091816981-1">}</span></code></pre><p>If <code class="inline">ch4</code> is part of the application <code class="inline">sp_app</code> and a new version of the module is
│ │ │ +When started by a supervisor, the child specification can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6812491050-1">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6812491050-2">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6812491050-3">[</span><span class="p" data-group-id="6812491050-3">]</span><span class="p" data-group-id="6812491050-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="ss">permanent</span><span class="p">,</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6812491050-4">[</span><span class="ss">ch4</span><span class="p" data-group-id="6812491050-4">]</span><span class="p" data-group-id="6812491050-1">}</span></code></pre><p>If <code class="inline">ch4</code> is part of the application <code class="inline">sp_app</code> and a new version of the module is
│ │ │  to be loaded when upgrading from version &quot;1&quot; to &quot;2&quot; of this application,
│ │ │ -<code class="inline">sp_app.appup</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4526457077-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4526457077-2">[</span><span class="p" data-group-id="4526457077-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4526457077-4">[</span><span class="p" data-group-id="4526457077-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4526457077-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4526457077-7">[</span><span class="p" data-group-id="4526457077-7">]</span><span class="p" data-group-id="4526457077-6">}</span><span class="p" data-group-id="4526457077-5">}</span><span class="p" data-group-id="4526457077-4">]</span><span class="p" data-group-id="4526457077-3">}</span><span class="p" data-group-id="4526457077-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4526457077-8">[</span><span class="p" data-group-id="4526457077-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4526457077-10">[</span><span class="p" data-group-id="4526457077-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4526457077-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4526457077-13">[</span><span class="p" data-group-id="4526457077-13">]</span><span class="p" data-group-id="4526457077-12">}</span><span class="p" data-group-id="4526457077-11">}</span><span class="p" data-group-id="4526457077-10">]</span><span class="p" data-group-id="4526457077-9">}</span><span class="p" data-group-id="4526457077-8">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4526457077-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">update</code> instruction must contain the tuple <code class="inline">{advanced,Extra}</code>. The
│ │ │ +<code class="inline">sp_app.appup</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7722414094-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7722414094-2">[</span><span class="p" data-group-id="7722414094-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7722414094-4">[</span><span class="p" data-group-id="7722414094-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7722414094-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7722414094-7">[</span><span class="p" data-group-id="7722414094-7">]</span><span class="p" data-group-id="7722414094-6">}</span><span class="p" data-group-id="7722414094-5">}</span><span class="p" data-group-id="7722414094-4">]</span><span class="p" data-group-id="7722414094-3">}</span><span class="p" data-group-id="7722414094-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7722414094-8">[</span><span class="p" data-group-id="7722414094-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7722414094-10">[</span><span class="p" data-group-id="7722414094-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7722414094-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7722414094-13">[</span><span class="p" data-group-id="7722414094-13">]</span><span class="p" data-group-id="7722414094-12">}</span><span class="p" data-group-id="7722414094-11">}</span><span class="p" data-group-id="7722414094-10">]</span><span class="p" data-group-id="7722414094-9">}</span><span class="p" data-group-id="7722414094-8">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7722414094-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">update</code> instruction must contain the tuple <code class="inline">{advanced,Extra}</code>. The
│ │ │  instruction makes the special process call the callback function
│ │ │  <code class="inline">system_code_change/4</code>, a function the user must implement. The term <code class="inline">Extra</code>, in
│ │ │ -this case <code class="inline">[]</code>, is passed as is to <code class="inline">system_code_change/4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0486530412-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="0486530412-1">)</span><span class="p">.</span><span class="w">
│ │ │ +this case <code class="inline">[]</code>, is passed as is to <code class="inline">system_code_change/4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8441923639-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="8441923639-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0486530412-2">(</span><span class="p" data-group-id="0486530412-3">[</span><span class="ss">system_code_change</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="0486530412-3">]</span><span class="p" data-group-id="0486530412-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8441923639-2">(</span><span class="p" data-group-id="8441923639-3">[</span><span class="ss">system_code_change</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="8441923639-3">]</span><span class="p" data-group-id="8441923639-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_code_change</span><span class="p" data-group-id="0486530412-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="0486530412-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0486530412-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0486530412-5">}</span><span class="p">.</span></code></pre><ul><li>The first argument is the internal state <code class="inline">State</code>, passed from
│ │ │ +</span><span class="nf">system_code_change</span><span class="p" data-group-id="8441923639-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="8441923639-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8441923639-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8441923639-5">}</span><span class="p">.</span></code></pre><ul><li>The first argument is the internal state <code class="inline">State</code>, passed from
│ │ │  function <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg(Request, From, Parent, Module, Deb, State)</code></a>, and called by the special
│ │ │  process when a system message is received. In <code class="inline">ch4</code>, the internal
│ │ │  state is the set of available channels <code class="inline">Chs</code>.</li><li>The second argument is the name of the module (<code class="inline">ch4</code>).</li><li>The third argument is <code class="inline">Vsn</code> or <code class="inline">{down,Vsn}</code>, as described for
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#c:code_change/3"><code class="inline">gen_server:code_change/3</code></a> in
│ │ │  <a href="appup_cookbook.html#code_change">Changing Internal State</a>.</li></ul><p>In this case, all arguments but the first are ignored and the function simply
│ │ │  returns the internal state again. This is enough if the code only has been
│ │ │  extended. If instead the internal state is changed (similar to the example in
│ │ │ @@ -271,85 +271,85 @@
│ │ │    <span class="text">Changing Properties</span>
│ │ │  </h3>
│ │ │  <p>Since the supervisor is to change its internal state, synchronized code
│ │ │  replacement is required. However, a special <code class="inline">update</code> instruction must be used.</p><p>First, the new version of the callback module must be loaded, both in the case
│ │ │  of upgrade and downgrade. Then the new return value of <code class="inline">init/1</code> can be checked
│ │ │  and the internal state be changed accordingly.</p><p>The following <code class="inline">upgrade</code> instruction is used for supervisors:</p><pre><code class="text">{update, Module, supervisor}</code></pre><p><em>Example</em></p><p>To change the restart strategy of <code class="inline">ch_sup</code> (from
│ │ │  <a href="sup_princ.html#ex">Supervisor Behaviour</a>) from <code class="inline">one_for_one</code> to <code class="inline">one_for_all</code>,
│ │ │ -change the callback function <code class="inline">init/1</code> in <code class="inline">ch_sup.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1941950584-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="1941950584-1">)</span><span class="p">.</span><span class="w">
│ │ │ +change the callback function <code class="inline">init/1</code> in <code class="inline">ch_sup.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3747115938-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="3747115938-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1941950584-2">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="1941950584-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1941950584-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1941950584-4">{</span><span class="p" data-group-id="1941950584-5">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_all</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1941950584-5">}</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1941950584-4">}</span><span class="p" data-group-id="1941950584-3">}</span><span class="p">.</span></code></pre><p>The file <code class="inline">ch_app.appup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7226040572-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7226040572-2">[</span><span class="p" data-group-id="7226040572-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7226040572-4">[</span><span class="p" data-group-id="7226040572-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7226040572-5">}</span><span class="p" data-group-id="7226040572-4">]</span><span class="p" data-group-id="7226040572-3">}</span><span class="p" data-group-id="7226040572-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7226040572-6">[</span><span class="p" data-group-id="7226040572-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7226040572-8">[</span><span class="p" data-group-id="7226040572-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7226040572-9">}</span><span class="p" data-group-id="7226040572-8">]</span><span class="p" data-group-id="7226040572-7">}</span><span class="p" data-group-id="7226040572-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7226040572-1">}</span><span class="p">.</span></code></pre><h3 id="changing-child-specifications" class="section-heading">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="3747115938-2">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="3747115938-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3747115938-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3747115938-4">{</span><span class="p" data-group-id="3747115938-5">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_all</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3747115938-5">}</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3747115938-4">}</span><span class="p" data-group-id="3747115938-3">}</span><span class="p">.</span></code></pre><p>The file <code class="inline">ch_app.appup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8781257357-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8781257357-2">[</span><span class="p" data-group-id="8781257357-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8781257357-4">[</span><span class="p" data-group-id="8781257357-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="8781257357-5">}</span><span class="p" data-group-id="8781257357-4">]</span><span class="p" data-group-id="8781257357-3">}</span><span class="p" data-group-id="8781257357-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8781257357-6">[</span><span class="p" data-group-id="8781257357-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8781257357-8">[</span><span class="p" data-group-id="8781257357-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="8781257357-9">}</span><span class="p" data-group-id="8781257357-8">]</span><span class="p" data-group-id="8781257357-7">}</span><span class="p" data-group-id="8781257357-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8781257357-1">}</span><span class="p">.</span></code></pre><h3 id="changing-child-specifications" class="section-heading">
│ │ │    <a href="#changing-child-specifications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing Child Specifications</span>
│ │ │  </h3>
│ │ │  <p>The instruction, and thus the <code class="inline">.appup</code> file, when changing an existing child
│ │ │ -specification, is the same as when changing properties as described earlier:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9116615178-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9116615178-2">[</span><span class="p" data-group-id="9116615178-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9116615178-4">[</span><span class="p" data-group-id="9116615178-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="9116615178-5">}</span><span class="p" data-group-id="9116615178-4">]</span><span class="p" data-group-id="9116615178-3">}</span><span class="p" data-group-id="9116615178-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9116615178-6">[</span><span class="p" data-group-id="9116615178-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9116615178-8">[</span><span class="p" data-group-id="9116615178-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="9116615178-9">}</span><span class="p" data-group-id="9116615178-8">]</span><span class="p" data-group-id="9116615178-7">}</span><span class="p" data-group-id="9116615178-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9116615178-1">}</span><span class="p">.</span></code></pre><p>The changes do not affect existing child processes. For example, changing the
│ │ │ +specification, is the same as when changing properties as described earlier:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1227045508-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1227045508-2">[</span><span class="p" data-group-id="1227045508-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1227045508-4">[</span><span class="p" data-group-id="1227045508-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="1227045508-5">}</span><span class="p" data-group-id="1227045508-4">]</span><span class="p" data-group-id="1227045508-3">}</span><span class="p" data-group-id="1227045508-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1227045508-6">[</span><span class="p" data-group-id="1227045508-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1227045508-8">[</span><span class="p" data-group-id="1227045508-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="1227045508-9">}</span><span class="p" data-group-id="1227045508-8">]</span><span class="p" data-group-id="1227045508-7">}</span><span class="p" data-group-id="1227045508-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1227045508-1">}</span><span class="p">.</span></code></pre><p>The changes do not affect existing child processes. For example, changing the
│ │ │  start function only specifies how the child process is to be restarted, if
│ │ │  needed later on.</p><p>The id of the child specification cannot be changed.</p><p>Changing the <code class="inline">Modules</code> field of the child specification can affect the release
│ │ │  handling process itself, as this field is used to identify which processes are
│ │ │  affected when doing a synchronized code replacement.</p><p><a href="" id="sup_add"></a></p><h3 id="adding-and-deleting-child-processes" class="section-heading">
│ │ │    <a href="#adding-and-deleting-child-processes" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Adding and Deleting Child Processes</span>
│ │ │  </h3>
│ │ │  <p>As stated earlier, changing child specifications does not affect existing child
│ │ │  processes. New child specifications are automatically added, but not deleted.
│ │ │  Child processes are not automatically started or terminated, this must be done
│ │ │  using <code class="inline">apply</code> instructions.</p><p><em>Example</em></p><p>Assume a new child process <code class="inline">m1</code> is to be added to <code class="inline">ch_sup</code> when
│ │ │  upgrading <code class="inline">ch_app</code> from &quot;1&quot; to &quot;2&quot;. This means <code class="inline">m1</code> is to be deleted when
│ │ │ -downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6859005907-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6859005907-2">[</span><span class="p" data-group-id="6859005907-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6859005907-4">[</span><span class="p" data-group-id="6859005907-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="6859005907-5">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6859005907-6">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6859005907-7">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6859005907-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="6859005907-8">]</span><span class="p" data-group-id="6859005907-7">}</span><span class="p" data-group-id="6859005907-6">}</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6859005907-4">]</span><span class="p" data-group-id="6859005907-3">}</span><span class="p" data-group-id="6859005907-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6859005907-9">[</span><span class="p" data-group-id="6859005907-10">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6859005907-11">[</span><span class="p" data-group-id="6859005907-12">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6859005907-13">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6859005907-14">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="6859005907-14">]</span><span class="p" data-group-id="6859005907-13">}</span><span class="p" data-group-id="6859005907-12">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6859005907-15">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6859005907-16">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6859005907-17">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="6859005907-17">]</span><span class="p" data-group-id="6859005907-16">}</span><span class="p" data-group-id="6859005907-15">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6859005907-18">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="6859005907-18">}</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6859005907-11">]</span><span class="p" data-group-id="6859005907-10">}</span><span class="p" data-group-id="6859005907-9">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6859005907-1">}</span><span class="p">.</span></code></pre><p>The order of the instructions is important.</p><p>The supervisor must be registered as <code class="inline">ch_sup</code> for the script to work. If the
│ │ │ +downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8600355784-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8600355784-2">[</span><span class="p" data-group-id="8600355784-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8600355784-4">[</span><span class="p" data-group-id="8600355784-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="8600355784-5">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8600355784-6">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8600355784-7">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8600355784-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="8600355784-8">]</span><span class="p" data-group-id="8600355784-7">}</span><span class="p" data-group-id="8600355784-6">}</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8600355784-4">]</span><span class="p" data-group-id="8600355784-3">}</span><span class="p" data-group-id="8600355784-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8600355784-9">[</span><span class="p" data-group-id="8600355784-10">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8600355784-11">[</span><span class="p" data-group-id="8600355784-12">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8600355784-13">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8600355784-14">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="8600355784-14">]</span><span class="p" data-group-id="8600355784-13">}</span><span class="p" data-group-id="8600355784-12">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8600355784-15">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8600355784-16">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8600355784-17">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="8600355784-17">]</span><span class="p" data-group-id="8600355784-16">}</span><span class="p" data-group-id="8600355784-15">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8600355784-18">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="8600355784-18">}</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8600355784-11">]</span><span class="p" data-group-id="8600355784-10">}</span><span class="p" data-group-id="8600355784-9">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8600355784-1">}</span><span class="p">.</span></code></pre><p>The order of the instructions is important.</p><p>The supervisor must be registered as <code class="inline">ch_sup</code> for the script to work. If the
│ │ │  supervisor is not registered, it cannot be accessed directly from the script.
│ │ │  Instead a help function that finds the pid of the supervisor and calls
│ │ │  <code class="inline">supervisor:restart_child</code>, and so on, must be written. This function is then to
│ │ │  be called from the script using the <code class="inline">apply</code> instruction.</p><p>If the module <code class="inline">m1</code> is introduced in version &quot;2&quot; of <code class="inline">ch_app</code>, it must also be
│ │ │ -loaded when upgrading and deleted when downgrading:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4840666029-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4840666029-2">[</span><span class="p" data-group-id="4840666029-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="4840666029-4">[</span><span class="p" data-group-id="4840666029-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="4840666029-5">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4840666029-6">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="4840666029-6">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4840666029-7">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4840666029-8">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4840666029-9">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="4840666029-9">]</span><span class="p" data-group-id="4840666029-8">}</span><span class="p" data-group-id="4840666029-7">}</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="4840666029-4">]</span><span class="p" data-group-id="4840666029-3">}</span><span class="p" data-group-id="4840666029-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4840666029-10">[</span><span class="p" data-group-id="4840666029-11">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="4840666029-12">[</span><span class="p" data-group-id="4840666029-13">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4840666029-14">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4840666029-15">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="4840666029-15">]</span><span class="p" data-group-id="4840666029-14">}</span><span class="p" data-group-id="4840666029-13">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4840666029-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4840666029-17">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4840666029-18">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="4840666029-18">]</span><span class="p" data-group-id="4840666029-17">}</span><span class="p" data-group-id="4840666029-16">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4840666029-19">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="4840666029-19">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4840666029-20">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="4840666029-20">}</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="4840666029-12">]</span><span class="p" data-group-id="4840666029-11">}</span><span class="p" data-group-id="4840666029-10">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4840666029-1">}</span><span class="p">.</span></code></pre><p>As stated earlier, the order of the instructions is important. When upgrading,
│ │ │ +loaded when upgrading and deleted when downgrading:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1570823009-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1570823009-2">[</span><span class="p" data-group-id="1570823009-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="1570823009-4">[</span><span class="p" data-group-id="1570823009-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="1570823009-5">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1570823009-6">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="1570823009-6">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1570823009-7">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1570823009-8">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1570823009-9">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="1570823009-9">]</span><span class="p" data-group-id="1570823009-8">}</span><span class="p" data-group-id="1570823009-7">}</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="1570823009-4">]</span><span class="p" data-group-id="1570823009-3">}</span><span class="p" data-group-id="1570823009-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1570823009-10">[</span><span class="p" data-group-id="1570823009-11">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="1570823009-12">[</span><span class="p" data-group-id="1570823009-13">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1570823009-14">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1570823009-15">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="1570823009-15">]</span><span class="p" data-group-id="1570823009-14">}</span><span class="p" data-group-id="1570823009-13">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1570823009-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1570823009-17">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1570823009-18">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="1570823009-18">]</span><span class="p" data-group-id="1570823009-17">}</span><span class="p" data-group-id="1570823009-16">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1570823009-19">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="1570823009-19">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1570823009-20">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="1570823009-20">}</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="1570823009-12">]</span><span class="p" data-group-id="1570823009-11">}</span><span class="p" data-group-id="1570823009-10">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1570823009-1">}</span><span class="p">.</span></code></pre><p>As stated earlier, the order of the instructions is important. When upgrading,
│ │ │  <code class="inline">m1</code> must be loaded, and the supervisor child specification changed, before the
│ │ │  new child process can be started. When downgrading, the child process must be
│ │ │  terminated before the child specification is changed and the module is deleted.</p><h2 id="adding-or-deleting-a-module" class="section-heading">
│ │ │    <a href="#adding-or-deleting-a-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Adding or Deleting a Module</span>
│ │ │  </h2>
│ │ │ -<p>_Example</p><p>_ A new functional module <code class="inline">m</code> is added to <code class="inline">ch_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5663416455-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5663416455-2">[</span><span class="p" data-group-id="5663416455-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5663416455-4">[</span><span class="p" data-group-id="5663416455-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="5663416455-5">}</span><span class="p" data-group-id="5663416455-4">]</span><span class="p" data-group-id="5663416455-3">}</span><span class="p" data-group-id="5663416455-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5663416455-6">[</span><span class="p" data-group-id="5663416455-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5663416455-8">[</span><span class="p" data-group-id="5663416455-9">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="5663416455-9">}</span><span class="p" data-group-id="5663416455-8">]</span><span class="p" data-group-id="5663416455-7">}</span><span class="p" data-group-id="5663416455-6">]</span></code></pre><h2 id="starting-or-terminating-a-process" class="section-heading">
│ │ │ +<p>_Example</p><p>_ A new functional module <code class="inline">m</code> is added to <code class="inline">ch_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0422866053-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0422866053-2">[</span><span class="p" data-group-id="0422866053-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0422866053-4">[</span><span class="p" data-group-id="0422866053-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="0422866053-5">}</span><span class="p" data-group-id="0422866053-4">]</span><span class="p" data-group-id="0422866053-3">}</span><span class="p" data-group-id="0422866053-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0422866053-6">[</span><span class="p" data-group-id="0422866053-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0422866053-8">[</span><span class="p" data-group-id="0422866053-9">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="0422866053-9">}</span><span class="p" data-group-id="0422866053-8">]</span><span class="p" data-group-id="0422866053-7">}</span><span class="p" data-group-id="0422866053-6">]</span></code></pre><h2 id="starting-or-terminating-a-process" class="section-heading">
│ │ │    <a href="#starting-or-terminating-a-process" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting or Terminating a Process</span>
│ │ │  </h2>
│ │ │  <p>In a system structured according to the OTP design principles, any process would
│ │ │  be a child process belonging to a supervisor, see
│ │ │ @@ -369,29 +369,29 @@
│ │ │    <span class="text">Restarting an Application</span>
│ │ │  </h2>
│ │ │  <p>Restarting an application is useful when a change is too complicated to be made
│ │ │  without restarting the processes, for example, if the supervisor hierarchy has
│ │ │  been restructured.</p><p><em>Example</em></p><p>When adding a child <code class="inline">m1</code> to <code class="inline">ch_sup</code>, as in
│ │ │  <a href="appup_cookbook.html#sup_add">Adding and Deleting Child Processes</a> in Changing a
│ │ │  Supervisor, an alternative to updating the supervisor is to restart the entire
│ │ │ -application:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1493649307-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1493649307-2">[</span><span class="p" data-group-id="1493649307-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1493649307-4">[</span><span class="p" data-group-id="1493649307-5">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="1493649307-5">}</span><span class="p" data-group-id="1493649307-4">]</span><span class="p" data-group-id="1493649307-3">}</span><span class="p" data-group-id="1493649307-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1493649307-6">[</span><span class="p" data-group-id="1493649307-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1493649307-8">[</span><span class="p" data-group-id="1493649307-9">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="1493649307-9">}</span><span class="p" data-group-id="1493649307-8">]</span><span class="p" data-group-id="1493649307-7">}</span><span class="p" data-group-id="1493649307-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1493649307-1">}</span><span class="p">.</span></code></pre><p><a href="" id="app_spec"></a></p><h2 id="changing-an-application-specification" class="section-heading">
│ │ │ +application:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1019110137-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1019110137-2">[</span><span class="p" data-group-id="1019110137-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1019110137-4">[</span><span class="p" data-group-id="1019110137-5">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="1019110137-5">}</span><span class="p" data-group-id="1019110137-4">]</span><span class="p" data-group-id="1019110137-3">}</span><span class="p" data-group-id="1019110137-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1019110137-6">[</span><span class="p" data-group-id="1019110137-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1019110137-8">[</span><span class="p" data-group-id="1019110137-9">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="1019110137-9">}</span><span class="p" data-group-id="1019110137-8">]</span><span class="p" data-group-id="1019110137-7">}</span><span class="p" data-group-id="1019110137-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1019110137-1">}</span><span class="p">.</span></code></pre><p><a href="" id="app_spec"></a></p><h2 id="changing-an-application-specification" class="section-heading">
│ │ │    <a href="#changing-an-application-specification" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing an Application Specification</span>
│ │ │  </h2>
│ │ │  <p>When installing a release, the application specifications are automatically
│ │ │  updated before evaluating the <code class="inline">relup</code> script. Thus, no instructions are needed
│ │ │ -in the <code class="inline">.appup</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8889785801-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8889785801-2">[</span><span class="p" data-group-id="8889785801-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8889785801-4">[</span><span class="p" data-group-id="8889785801-4">]</span><span class="p" data-group-id="8889785801-3">}</span><span class="p" data-group-id="8889785801-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8889785801-5">[</span><span class="p" data-group-id="8889785801-6">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8889785801-7">[</span><span class="p" data-group-id="8889785801-7">]</span><span class="p" data-group-id="8889785801-6">}</span><span class="p" data-group-id="8889785801-5">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8889785801-1">}</span><span class="p">.</span></code></pre><h2 id="changing-application-configuration" class="section-heading">
│ │ │ +in the <code class="inline">.appup</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6275035768-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6275035768-2">[</span><span class="p" data-group-id="6275035768-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6275035768-4">[</span><span class="p" data-group-id="6275035768-4">]</span><span class="p" data-group-id="6275035768-3">}</span><span class="p" data-group-id="6275035768-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6275035768-5">[</span><span class="p" data-group-id="6275035768-6">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6275035768-7">[</span><span class="p" data-group-id="6275035768-7">]</span><span class="p" data-group-id="6275035768-6">}</span><span class="p" data-group-id="6275035768-5">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6275035768-1">}</span><span class="p">.</span></code></pre><h2 id="changing-application-configuration" class="section-heading">
│ │ │    <a href="#changing-application-configuration" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing Application Configuration</span>
│ │ │  </h2>
│ │ │  <p>Changing an application configuration by updating the <code class="inline">env</code> key in the <code class="inline">.app</code>
│ │ │  file is an instance of changing an application specification, see the previous
│ │ │ @@ -406,26 +406,26 @@
│ │ │  applications apply to primary applications only. There are no corresponding
│ │ │  instructions for included applications. However, since an included application
│ │ │  is really a supervision tree with a topmost supervisor, started as a child
│ │ │  process to a supervisor in the including application, a <code class="inline">.relup</code> file can be
│ │ │  manually created.</p><p><em>Example</em></p><p>Assume there is a release containing an application <code class="inline">prim_app</code>, which
│ │ │  have a supervisor <code class="inline">prim_sup</code> in its supervision tree.</p><p>In a new version of the release, the application <code class="inline">ch_app</code> is to be included in
│ │ │  <code class="inline">prim_app</code>. That is, its topmost supervisor <code class="inline">ch_sup</code> is to be started as a child
│ │ │ -process to <code class="inline">prim_sup</code>.</p><p>The workflow is as follows:</p><p><em>Step 1)</em> Edit the code for <code class="inline">prim_sup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="3101421546-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3101421546-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3101421546-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3101421546-3">{</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="ss">supervisor</span><span class="w"> </span><span class="ss">flags</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="3101421546-4">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -           </span><span class="p" data-group-id="3101421546-5">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3101421546-6">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="3101421546-7">[</span><span class="p" data-group-id="3101421546-7">]</span><span class="p" data-group-id="3101421546-6">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="ss">permanent</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="ss">supervisor</span><span class="p">,</span><span class="p" data-group-id="3101421546-8">[</span><span class="ss">ch_sup</span><span class="p" data-group-id="3101421546-8">]</span><span class="p" data-group-id="3101421546-5">}</span><span class="p">,</span><span class="w">
│ │ │ -           </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3101421546-4">]</span><span class="p" data-group-id="3101421546-3">}</span><span class="p" data-group-id="3101421546-2">}</span><span class="p">.</span></code></pre><p><em>Step 2)</em> Edit the <code class="inline">.app</code> file for <code class="inline">prim_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5182838340-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5182838340-2">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5182838340-3">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="5182838340-3">}</span><span class="p">,</span><span class="w">
│ │ │ +process to <code class="inline">prim_sup</code>.</p><p>The workflow is as follows:</p><p><em>Step 1)</em> Edit the code for <code class="inline">prim_sup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1882601408-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1882601408-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1882601408-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1882601408-3">{</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="ss">supervisor</span><span class="w"> </span><span class="ss">flags</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="1882601408-4">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ +           </span><span class="p" data-group-id="1882601408-5">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1882601408-6">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="1882601408-7">[</span><span class="p" data-group-id="1882601408-7">]</span><span class="p" data-group-id="1882601408-6">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="ss">permanent</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="ss">supervisor</span><span class="p">,</span><span class="p" data-group-id="1882601408-8">[</span><span class="ss">ch_sup</span><span class="p" data-group-id="1882601408-8">]</span><span class="p" data-group-id="1882601408-5">}</span><span class="p">,</span><span class="w">
│ │ │ +           </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1882601408-4">]</span><span class="p" data-group-id="1882601408-3">}</span><span class="p" data-group-id="1882601408-2">}</span><span class="p">.</span></code></pre><p><em>Step 2)</em> Edit the <code class="inline">.app</code> file for <code class="inline">prim_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0558951752-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0558951752-2">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="0558951752-3">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="0558951752-3">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5182838340-4">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5182838340-5">[</span><span class="ss">ch_app</span><span class="p" data-group-id="5182838340-5">]</span><span class="p" data-group-id="5182838340-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="0558951752-4">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0558951752-5">[</span><span class="ss">ch_app</span><span class="p" data-group-id="0558951752-5">]</span><span class="p" data-group-id="0558951752-4">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5182838340-2">]</span><span class="p" data-group-id="5182838340-1">}</span><span class="p">.</span></code></pre><p><em>Step 3)</em> Create a new <code class="inline">.rel</code> file, including <code class="inline">ch_app</code>:</p><pre><code class="text">{release,
│ │ │ + </span><span class="p" data-group-id="0558951752-2">]</span><span class="p" data-group-id="0558951752-1">}</span><span class="p">.</span></code></pre><p><em>Step 3)</em> Create a new <code class="inline">.rel</code> file, including <code class="inline">ch_app</code>:</p><pre><code class="text">{release,
│ │ │   ...,
│ │ │   [...,
│ │ │    {prim_app, &quot;2&quot;},
│ │ │    {ch_app, &quot;1&quot;}]}.</code></pre><p>The included application can be started in two ways. This is described in the
│ │ │  next two sections.</p><h3 id="application-restart" class="section-heading">
│ │ │    <a href="#application-restart" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -480,74 +480,74 @@
│ │ │  <p><em>Step 4b)</em> Another way to start the included application (or stop it in the case
│ │ │  of downgrade) is by combining instructions for adding and removing child
│ │ │  processes to/from <code class="inline">prim_sup</code> with instructions for loading/unloading all
│ │ │  <code class="inline">ch_app</code> code and its application specification.</p><p>Again, the <code class="inline">.relup</code> file is created manually, either from scratch or by editing a
│ │ │  generated version. Load all code for <code class="inline">ch_app</code> first, and also load the
│ │ │  application specification, before <code class="inline">prim_sup</code> is updated. When downgrading,
│ │ │  <code class="inline">prim_sup</code> is to updated first, before the code for <code class="inline">ch_app</code> and its application
│ │ │ -specification are unloaded.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8578691912-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8578691912-2">[</span><span class="p" data-group-id="8578691912-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8578691912-4">[</span><span class="p" data-group-id="8578691912-4">]</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8578691912-5">[</span><span class="p" data-group-id="8578691912-6">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="8578691912-7">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="8578691912-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="8578691912-8">]</span><span class="p" data-group-id="8578691912-7">}</span><span class="p" data-group-id="8578691912-6">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-9">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="8578691912-10">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="8578691912-11">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8578691912-11">]</span><span class="p" data-group-id="8578691912-10">}</span><span class="p" data-group-id="8578691912-9">}</span><span class="p">,</span><span class="w">
│ │ │ +specification are unloaded.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3062113233-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3062113233-2">[</span><span class="p" data-group-id="3062113233-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="3062113233-4">[</span><span class="p" data-group-id="3062113233-4">]</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="3062113233-5">[</span><span class="p" data-group-id="3062113233-6">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="3062113233-7">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="3062113233-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="3062113233-8">]</span><span class="p" data-group-id="3062113233-7">}</span><span class="p" data-group-id="3062113233-6">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-9">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="3062113233-10">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="3062113233-11">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="3062113233-11">]</span><span class="p" data-group-id="3062113233-10">}</span><span class="p" data-group-id="3062113233-9">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-12">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="8578691912-13">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8578691912-13">}</span><span class="p" data-group-id="8578691912-12">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-14">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="8578691912-15">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8578691912-15">}</span><span class="p" data-group-id="8578691912-14">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="8578691912-17">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="8578691912-18">[</span><span class="ss">ch_app</span><span class="p" data-group-id="8578691912-18">]</span><span class="p" data-group-id="8578691912-17">}</span><span class="p" data-group-id="8578691912-16">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-19">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="8578691912-20">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8578691912-20">]</span><span class="p" data-group-id="8578691912-19">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-21">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="8578691912-22">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8578691912-22">}</span><span class="p" data-group-id="8578691912-21">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-23">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">up</span><span class="p">,</span><span class="p" data-group-id="8578691912-24">[</span><span class="p" data-group-id="8578691912-25">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="8578691912-26">[</span><span class="p" data-group-id="8578691912-26">]</span><span class="p" data-group-id="8578691912-25">}</span><span class="p" data-group-id="8578691912-24">]</span><span class="p" data-group-id="8578691912-23">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-27">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="8578691912-28">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8578691912-28">]</span><span class="p" data-group-id="8578691912-27">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-29">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="8578691912-30">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">restart_child</span><span class="p">,</span><span class="p" data-group-id="8578691912-31">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="8578691912-31">]</span><span class="p" data-group-id="8578691912-30">}</span><span class="p" data-group-id="8578691912-29">}</span><span class="p" data-group-id="8578691912-5">]</span><span class="p" data-group-id="8578691912-3">}</span><span class="p" data-group-id="8578691912-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8578691912-32">[</span><span class="p" data-group-id="8578691912-33">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8578691912-34">[</span><span class="p" data-group-id="8578691912-34">]</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8578691912-35">[</span><span class="p" data-group-id="8578691912-36">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="8578691912-37">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="8578691912-38">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8578691912-38">]</span><span class="p" data-group-id="8578691912-37">}</span><span class="p" data-group-id="8578691912-36">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-12">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="3062113233-13">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="3062113233-13">}</span><span class="p" data-group-id="3062113233-12">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-14">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="3062113233-15">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="3062113233-15">}</span><span class="p" data-group-id="3062113233-14">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="3062113233-17">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="3062113233-18">[</span><span class="ss">ch_app</span><span class="p" data-group-id="3062113233-18">]</span><span class="p" data-group-id="3062113233-17">}</span><span class="p" data-group-id="3062113233-16">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-19">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="3062113233-20">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="3062113233-20">]</span><span class="p" data-group-id="3062113233-19">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-21">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="3062113233-22">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="3062113233-22">}</span><span class="p" data-group-id="3062113233-21">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-23">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">up</span><span class="p">,</span><span class="p" data-group-id="3062113233-24">[</span><span class="p" data-group-id="3062113233-25">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="3062113233-26">[</span><span class="p" data-group-id="3062113233-26">]</span><span class="p" data-group-id="3062113233-25">}</span><span class="p" data-group-id="3062113233-24">]</span><span class="p" data-group-id="3062113233-23">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-27">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="3062113233-28">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="3062113233-28">]</span><span class="p" data-group-id="3062113233-27">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-29">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="3062113233-30">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">restart_child</span><span class="p">,</span><span class="p" data-group-id="3062113233-31">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="3062113233-31">]</span><span class="p" data-group-id="3062113233-30">}</span><span class="p" data-group-id="3062113233-29">}</span><span class="p" data-group-id="3062113233-5">]</span><span class="p" data-group-id="3062113233-3">}</span><span class="p" data-group-id="3062113233-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3062113233-32">[</span><span class="p" data-group-id="3062113233-33">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="3062113233-34">[</span><span class="p" data-group-id="3062113233-34">]</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="3062113233-35">[</span><span class="p" data-group-id="3062113233-36">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="3062113233-37">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="3062113233-38">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="3062113233-38">]</span><span class="p" data-group-id="3062113233-37">}</span><span class="p" data-group-id="3062113233-36">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-39">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="8578691912-40">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">terminate_child</span><span class="p">,</span><span class="p" data-group-id="8578691912-41">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="8578691912-41">]</span><span class="p" data-group-id="8578691912-40">}</span><span class="p" data-group-id="8578691912-39">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-42">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="8578691912-43">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">delete_child</span><span class="p">,</span><span class="p" data-group-id="8578691912-44">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="8578691912-44">]</span><span class="p" data-group-id="8578691912-43">}</span><span class="p" data-group-id="8578691912-42">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-45">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="8578691912-46">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8578691912-46">]</span><span class="p" data-group-id="8578691912-45">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-47">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="8578691912-48">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8578691912-48">}</span><span class="p" data-group-id="8578691912-47">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-49">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">down</span><span class="p">,</span><span class="p" data-group-id="8578691912-50">[</span><span class="p" data-group-id="8578691912-51">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="8578691912-52">[</span><span class="p" data-group-id="8578691912-52">]</span><span class="p" data-group-id="8578691912-51">}</span><span class="p" data-group-id="8578691912-50">]</span><span class="p" data-group-id="8578691912-49">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-53">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="8578691912-54">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8578691912-54">]</span><span class="p" data-group-id="8578691912-53">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-55">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="8578691912-56">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8578691912-56">}</span><span class="p" data-group-id="8578691912-55">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-57">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="8578691912-58">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8578691912-58">}</span><span class="p" data-group-id="8578691912-57">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-59">{</span><span class="ss">purge</span><span class="p">,</span><span class="p" data-group-id="8578691912-60">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="8578691912-60">]</span><span class="p" data-group-id="8578691912-59">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8578691912-61">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="8578691912-62">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">unload</span><span class="p">,</span><span class="p" data-group-id="8578691912-63">[</span><span class="ss">ch_app</span><span class="p" data-group-id="8578691912-63">]</span><span class="p" data-group-id="8578691912-62">}</span><span class="p" data-group-id="8578691912-61">}</span><span class="p" data-group-id="8578691912-35">]</span><span class="p" data-group-id="8578691912-33">}</span><span class="p" data-group-id="8578691912-32">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8578691912-1">}</span><span class="p">.</span></code></pre><h2 id="changing-non-erlang-code" class="section-heading">
│ │ │ +    </span><span class="p" data-group-id="3062113233-39">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="3062113233-40">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">terminate_child</span><span class="p">,</span><span class="p" data-group-id="3062113233-41">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="3062113233-41">]</span><span class="p" data-group-id="3062113233-40">}</span><span class="p" data-group-id="3062113233-39">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-42">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="3062113233-43">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">delete_child</span><span class="p">,</span><span class="p" data-group-id="3062113233-44">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="3062113233-44">]</span><span class="p" data-group-id="3062113233-43">}</span><span class="p" data-group-id="3062113233-42">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-45">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="3062113233-46">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="3062113233-46">]</span><span class="p" data-group-id="3062113233-45">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-47">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="3062113233-48">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="3062113233-48">}</span><span class="p" data-group-id="3062113233-47">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-49">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">down</span><span class="p">,</span><span class="p" data-group-id="3062113233-50">[</span><span class="p" data-group-id="3062113233-51">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="3062113233-52">[</span><span class="p" data-group-id="3062113233-52">]</span><span class="p" data-group-id="3062113233-51">}</span><span class="p" data-group-id="3062113233-50">]</span><span class="p" data-group-id="3062113233-49">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-53">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="3062113233-54">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="3062113233-54">]</span><span class="p" data-group-id="3062113233-53">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-55">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="3062113233-56">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="3062113233-56">}</span><span class="p" data-group-id="3062113233-55">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-57">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="3062113233-58">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="3062113233-58">}</span><span class="p" data-group-id="3062113233-57">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-59">{</span><span class="ss">purge</span><span class="p">,</span><span class="p" data-group-id="3062113233-60">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="3062113233-60">]</span><span class="p" data-group-id="3062113233-59">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3062113233-61">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="3062113233-62">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">unload</span><span class="p">,</span><span class="p" data-group-id="3062113233-63">[</span><span class="ss">ch_app</span><span class="p" data-group-id="3062113233-63">]</span><span class="p" data-group-id="3062113233-62">}</span><span class="p" data-group-id="3062113233-61">}</span><span class="p" data-group-id="3062113233-35">]</span><span class="p" data-group-id="3062113233-33">}</span><span class="p" data-group-id="3062113233-32">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3062113233-1">}</span><span class="p">.</span></code></pre><h2 id="changing-non-erlang-code" class="section-heading">
│ │ │    <a href="#changing-non-erlang-code" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing Non-Erlang Code</span>
│ │ │  </h2>
│ │ │  <p>Changing code for a program written in another programming language than Erlang,
│ │ │  for example, a port program, is application-dependent and OTP provides no
│ │ │  special support.</p><p><em>Example</em></p><p>When changing code for a port program, assume that the Erlang process
│ │ │  controlling the port is a <code class="inline">gen_server</code> <code class="inline">portc</code> and that the port is opened in
│ │ │ -the callback function <code class="inline">init/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4735851350-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4735851350-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +the callback function <code class="inline">init/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4299514740-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4299514740-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="4735851350-2">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="4735851350-3">(</span><span class="n">App</span><span class="p" data-group-id="4735851350-3">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="4735851350-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="4735851350-4">(</span><span class="p" data-group-id="4735851350-5">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="4735851350-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4735851350-6">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4735851350-6">]</span><span class="p" data-group-id="4735851350-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="4299514740-2">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="4299514740-3">(</span><span class="n">App</span><span class="p" data-group-id="4299514740-3">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="4299514740-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="4299514740-4">(</span><span class="p" data-group-id="4299514740-5">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="4299514740-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4299514740-6">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4299514740-6">]</span><span class="p" data-group-id="4299514740-4">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4735851350-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="4735851350-8">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4735851350-8">}</span><span class="p" data-group-id="4735851350-7">}</span><span class="p">.</span></code></pre><p>If the port program is to be updated, the code for the <code class="inline">gen_server</code> can be
│ │ │ +    </span><span class="p" data-group-id="4299514740-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="4299514740-8">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4299514740-8">}</span><span class="p" data-group-id="4299514740-7">}</span><span class="p">.</span></code></pre><p>If the port program is to be updated, the code for the <code class="inline">gen_server</code> can be
│ │ │  extended with a <code class="inline">code_change/3</code> function, which closes the old port and opens a
│ │ │  new port. (If necessary, the <code class="inline">gen_server</code> can first request data that must be
│ │ │ -saved from the port program and pass this data to the new port):</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="8831112005-1">(</span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="ss">port</span><span class="p" data-group-id="8831112005-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +saved from the port program and pass this data to the new port):</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="7218903968-1">(</span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="ss">port</span><span class="p" data-group-id="7218903968-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">close</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8831112005-2">{</span><span class="n">Port</span><span class="p">,</span><span class="ss">close</span><span class="p" data-group-id="8831112005-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7218903968-2">{</span><span class="n">Port</span><span class="p">,</span><span class="ss">close</span><span class="p" data-group-id="7218903968-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="8831112005-3">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="8831112005-4">(</span><span class="n">App</span><span class="p" data-group-id="8831112005-4">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="8831112005-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="8831112005-5">(</span><span class="p" data-group-id="8831112005-6">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="8831112005-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8831112005-7">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8831112005-7">]</span><span class="p" data-group-id="8831112005-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8831112005-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="8831112005-9">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8831112005-9">}</span><span class="p" data-group-id="8831112005-8">}</span><span class="p">.</span></code></pre><p>Update the application version number in the <code class="inline">.app</code> file and write an <code class="inline">.appup</code>
│ │ │ -file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2692905221-1">[</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2692905221-2">[</span><span class="p" data-group-id="2692905221-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2692905221-4">[</span><span class="p" data-group-id="2692905221-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2692905221-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="2692905221-6">}</span><span class="p" data-group-id="2692905221-5">}</span><span class="p" data-group-id="2692905221-4">]</span><span class="p" data-group-id="2692905221-3">}</span><span class="p" data-group-id="2692905221-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2692905221-7">[</span><span class="p" data-group-id="2692905221-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2692905221-9">[</span><span class="p" data-group-id="2692905221-10">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2692905221-11">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="2692905221-11">}</span><span class="p" data-group-id="2692905221-10">}</span><span class="p" data-group-id="2692905221-9">]</span><span class="p" data-group-id="2692905221-8">}</span><span class="p" data-group-id="2692905221-7">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2692905221-1">]</span><span class="p">.</span></code></pre><p>Ensure that the <code class="inline">priv</code> directory, where the C program is located, is included in
│ │ │ -the new release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="5610244475-1">(</span><span class="s">&quot;my_release&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5610244475-2">[</span><span class="p" data-group-id="5610244475-3">{</span><span class="ss">dirs</span><span class="p">,</span><span class="p" data-group-id="5610244475-4">[</span><span class="ss">priv</span><span class="p" data-group-id="5610244475-4">]</span><span class="p" data-group-id="5610244475-3">}</span><span class="p" data-group-id="5610244475-2">]</span><span class="p" data-group-id="5610244475-1">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7218903968-3">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="7218903968-4">(</span><span class="n">App</span><span class="p" data-group-id="7218903968-4">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="7218903968-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="7218903968-5">(</span><span class="p" data-group-id="7218903968-6">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="7218903968-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7218903968-7">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7218903968-7">]</span><span class="p" data-group-id="7218903968-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7218903968-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="7218903968-9">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7218903968-9">}</span><span class="p" data-group-id="7218903968-8">}</span><span class="p">.</span></code></pre><p>Update the application version number in the <code class="inline">.app</code> file and write an <code class="inline">.appup</code>
│ │ │ +file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2778163877-1">[</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2778163877-2">[</span><span class="p" data-group-id="2778163877-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2778163877-4">[</span><span class="p" data-group-id="2778163877-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2778163877-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="2778163877-6">}</span><span class="p" data-group-id="2778163877-5">}</span><span class="p" data-group-id="2778163877-4">]</span><span class="p" data-group-id="2778163877-3">}</span><span class="p" data-group-id="2778163877-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2778163877-7">[</span><span class="p" data-group-id="2778163877-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2778163877-9">[</span><span class="p" data-group-id="2778163877-10">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2778163877-11">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="2778163877-11">}</span><span class="p" data-group-id="2778163877-10">}</span><span class="p" data-group-id="2778163877-9">]</span><span class="p" data-group-id="2778163877-8">}</span><span class="p" data-group-id="2778163877-7">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2778163877-1">]</span><span class="p">.</span></code></pre><p>Ensure that the <code class="inline">priv</code> directory, where the C program is located, is included in
│ │ │ +the new release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="8998419775-1">(</span><span class="s">&quot;my_release&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8998419775-2">[</span><span class="p" data-group-id="8998419775-3">{</span><span class="ss">dirs</span><span class="p">,</span><span class="p" data-group-id="8998419775-4">[</span><span class="ss">priv</span><span class="p" data-group-id="8998419775-4">]</span><span class="p" data-group-id="8998419775-3">}</span><span class="p" data-group-id="8998419775-2">]</span><span class="p" data-group-id="8998419775-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="runtime-system-restart-and-upgrade" class="section-heading">
│ │ │    <a href="#runtime-system-restart-and-upgrade" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Runtime System Restart and Upgrade</span>
│ │ │  </h2>
│ │ │  <p>Two upgrade instructions restart the runtime system:</p><ul><li><p><code class="inline">restart_new_emulator</code></p><p>Intended when ERTS, Kernel, STDLIB, or SASL is upgraded. It is automatically
│ │ │ @@ -555,22 +555,22 @@
│ │ │  executed before all other upgrade instructions. For more information about
│ │ │  this instruction, see restart_new_emulator (Low-Level) in
│ │ │  <a href="release_handling.html#restart_new_emulator_instr">Release Handling Instructions</a>.</p></li><li><p><code class="inline">restart_emulator</code></p><p>Used when a restart of the runtime system is required after all other upgrade
│ │ │  instructions are executed. For more information about this instruction, see
│ │ │  restart_emulator (Low-Level) in
│ │ │  <a href="release_handling.html#restart_emulator_instr">Release Handling Instructions</a>.</p></li></ul><p>If a runtime system restart is necessary and no upgrade instructions are needed,
│ │ │  that is, if the restart itself is enough for the upgraded applications to start
│ │ │ -running the new versions, a simple <code class="inline">.relup</code> file can be created manually:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8253568120-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8253568120-2">[</span><span class="p" data-group-id="8253568120-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8253568120-4">[</span><span class="p" data-group-id="8253568120-4">]</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8253568120-5">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="8253568120-5">]</span><span class="p" data-group-id="8253568120-3">}</span><span class="p" data-group-id="8253568120-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8253568120-6">[</span><span class="p" data-group-id="8253568120-7">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8253568120-8">[</span><span class="p" data-group-id="8253568120-8">]</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8253568120-9">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="8253568120-9">]</span><span class="p" data-group-id="8253568120-7">}</span><span class="p" data-group-id="8253568120-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8253568120-1">}</span><span class="p">.</span></code></pre><p>In this case, the release handler framework with automatic packing and unpacking
│ │ │ +running the new versions, a simple <code class="inline">.relup</code> file can be created manually:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2513900899-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2513900899-2">[</span><span class="p" data-group-id="2513900899-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2513900899-4">[</span><span class="p" data-group-id="2513900899-4">]</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2513900899-5">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="2513900899-5">]</span><span class="p" data-group-id="2513900899-3">}</span><span class="p" data-group-id="2513900899-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2513900899-6">[</span><span class="p" data-group-id="2513900899-7">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2513900899-8">[</span><span class="p" data-group-id="2513900899-8">]</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2513900899-9">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="2513900899-9">]</span><span class="p" data-group-id="2513900899-7">}</span><span class="p" data-group-id="2513900899-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2513900899-1">}</span><span class="p">.</span></code></pre><p>In this case, the release handler framework with automatic packing and unpacking
│ │ │  of release packages, automatic path updates, and so on, can be used without
│ │ │  having to specify <code class="inline">.appup</code> files.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/benchmarking.html
│ │ │ @@ -144,16 +144,16 @@
│ │ │  fast as possible, what can we do? One way could be to generate more
│ │ │  than two bytes at the time.</p><pre><code class="text">% erlperf 'rand:bytes(100).' 'crypto:strong_rand_bytes(100).'
│ │ │  Code                                   ||        QPS       Time   Rel
│ │ │  rand:bytes(100).                        1    2124 Ki     470 ns  100%
│ │ │  crypto:strong_rand_bytes(100).          1    1915 Ki     522 ns   90%</code></pre><p><a href="../../lib/stdlib-6.2.2.1/doc/html/rand.html#bytes/1"><code class="inline">rand:bytes/1</code></a> is still faster when we generate 100 bytes at the time,
│ │ │  but the relative difference is smaller.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erlperf &#39;rand:bytes(1000).&#39; &#39;crypto:strong_rand_bytes(1000).&#39;</span><span class="w">
│ │ │  </span><span class="n">Code</span><span class="w">                                    </span><span class="p">||</span><span class="w">        </span><span class="n">QPS</span><span class="w">       </span><span class="n">Time</span><span class="w">   </span><span class="n">Rel</span><span class="w">
│ │ │ -</span><span class="nc">crypto</span><span class="p">:</span><span class="nf">strong_rand_bytes</span><span class="p" data-group-id="5278165687-1">(</span><span class="mi">1000</span><span class="p" data-group-id="5278165687-1">)</span><span class="p">.</span><span class="w">          </span><span class="mi">1</span><span class="w">    </span><span class="mi">1518</span><span class="w"> </span><span class="n">Ki</span><span class="w">     </span><span class="mi">658</span><span class="w"> </span><span class="ss">ns</span><span class="w">  </span><span class="mi">100</span><span class="c1">%</span><span class="w">
│ │ │ -</span><span class="nc">rand</span><span class="p">:</span><span class="nf">bytes</span><span class="p" data-group-id="5278165687-2">(</span><span class="mi">1000</span><span class="p" data-group-id="5278165687-2">)</span><span class="p">.</span><span class="w">                        </span><span class="mi">1</span><span class="w">     </span><span class="mi">284</span><span class="w"> </span><span class="n">Ki</span><span class="w">    </span><span class="mi">3521</span><span class="w"> </span><span class="ss">ns</span><span class="w">   </span><span class="mi">19</span><span class="c1">%</span></code></pre><p>When we generate 1000 bytes at the time, <a href="../../lib/crypto-5.5.3/doc/html/crypto.html#strong_rand_bytes/1"><code class="inline">crypto:strong_rand_bytes/1</code></a> is
│ │ │ +</span><span class="nc">crypto</span><span class="p">:</span><span class="nf">strong_rand_bytes</span><span class="p" data-group-id="5532690455-1">(</span><span class="mi">1000</span><span class="p" data-group-id="5532690455-1">)</span><span class="p">.</span><span class="w">          </span><span class="mi">1</span><span class="w">    </span><span class="mi">1518</span><span class="w"> </span><span class="n">Ki</span><span class="w">     </span><span class="mi">658</span><span class="w"> </span><span class="ss">ns</span><span class="w">  </span><span class="mi">100</span><span class="c1">%</span><span class="w">
│ │ │ +</span><span class="nc">rand</span><span class="p">:</span><span class="nf">bytes</span><span class="p" data-group-id="5532690455-2">(</span><span class="mi">1000</span><span class="p" data-group-id="5532690455-2">)</span><span class="p">.</span><span class="w">                        </span><span class="mi">1</span><span class="w">     </span><span class="mi">284</span><span class="w"> </span><span class="n">Ki</span><span class="w">    </span><span class="mi">3521</span><span class="w"> </span><span class="ss">ns</span><span class="w">   </span><span class="mi">19</span><span class="c1">%</span></code></pre><p>When we generate 1000 bytes at the time, <a href="../../lib/crypto-5.5.3/doc/html/crypto.html#strong_rand_bytes/1"><code class="inline">crypto:strong_rand_bytes/1</code></a> is
│ │ │  now the fastest.</p><h2 id="benchmarking-using-erlang-otp-functionality" class="section-heading">
│ │ │    <a href="#benchmarking-using-erlang-otp-functionality" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Benchmarking using Erlang/OTP functionality</span>
│ │ │  </h2>
│ │ │  <p>Benchmarks can measure wall-clock time or CPU time.</p><ul><li><p><a href="../../lib/stdlib-6.2.2.1/doc/html/timer.html#tc/3"><code class="inline">timer:tc/3</code></a> measures wall-clock time. The advantage with wall-clock time is
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/binaryhandling.html
│ │ │ @@ -114,43 +114,43 @@
│ │ │  
│ │ │      <span>Constructing and Matching Binaries</span>
│ │ │    </h1>
│ │ │  
│ │ │  <p>This section gives a few examples on how to handle binaries in an efficient way.
│ │ │  The sections that follow take an in-depth look at how binaries are implemented
│ │ │  and how to best take advantages of the optimizations done by the compiler and
│ │ │ -runtime system.</p><p>Binaries can be efficiently <em>built</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_list_to_binary</span><span class="p" data-group-id="4805131308-1">(</span><span class="n">List</span><span class="p" data-group-id="4805131308-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="4805131308-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4805131308-3">&lt;&lt;</span><span class="p" data-group-id="4805131308-3">&gt;&gt;</span><span class="p" data-group-id="4805131308-2">)</span><span class="p">.</span><span class="w">
│ │ │ +runtime system.</p><p>Binaries can be efficiently <em>built</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_list_to_binary</span><span class="p" data-group-id="8933740408-1">(</span><span class="n">List</span><span class="p" data-group-id="8933740408-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="8933740408-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8933740408-3">&lt;&lt;</span><span class="p" data-group-id="8933740408-3">&gt;&gt;</span><span class="p" data-group-id="8933740408-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="4805131308-4">(</span><span class="p" data-group-id="4805131308-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4805131308-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4805131308-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="4805131308-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4805131308-7">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="4805131308-7">&gt;&gt;</span><span class="p" data-group-id="4805131308-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="4805131308-8">(</span><span class="p" data-group-id="4805131308-9">[</span><span class="p" data-group-id="4805131308-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4805131308-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="8933740408-4">(</span><span class="p" data-group-id="8933740408-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8933740408-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8933740408-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="8933740408-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8933740408-7">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="8933740408-7">&gt;&gt;</span><span class="p" data-group-id="8933740408-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="8933740408-8">(</span><span class="p" data-group-id="8933740408-9">[</span><span class="p" data-group-id="8933740408-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8933740408-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Appending data to a binary as in the example is efficient because it is
│ │ │  specially optimized by the runtime system to avoid copying the <code class="inline">Acc</code> binary
│ │ │ -every time.</p><p>Prepending data to a binary in a loop is not efficient:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="2748835385-1">(</span><span class="n">List</span><span class="p" data-group-id="2748835385-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="2748835385-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2748835385-3">&lt;&lt;</span><span class="p" data-group-id="2748835385-3">&gt;&gt;</span><span class="p" data-group-id="2748835385-2">)</span><span class="p">.</span><span class="w">
│ │ │ +every time.</p><p>Prepending data to a binary in a loop is not efficient:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4241560489-1">(</span><span class="n">List</span><span class="p" data-group-id="4241560489-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4241560489-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4241560489-3">&lt;&lt;</span><span class="p" data-group-id="4241560489-3">&gt;&gt;</span><span class="p" data-group-id="4241560489-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="2748835385-4">(</span><span class="p" data-group-id="2748835385-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2748835385-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2748835385-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="2748835385-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2748835385-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2748835385-7">&gt;&gt;</span><span class="p" data-group-id="2748835385-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="2748835385-8">(</span><span class="p" data-group-id="2748835385-9">[</span><span class="p" data-group-id="2748835385-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2748835385-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4241560489-4">(</span><span class="p" data-group-id="4241560489-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4241560489-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4241560489-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4241560489-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4241560489-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4241560489-7">&gt;&gt;</span><span class="p" data-group-id="4241560489-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4241560489-8">(</span><span class="p" data-group-id="4241560489-9">[</span><span class="p" data-group-id="4241560489-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4241560489-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>This is not efficient for long lists because the <code class="inline">Acc</code> binary is copied every
│ │ │ -time. One way to make the function more efficient is like this:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5176571032-1">(</span><span class="n">List</span><span class="p" data-group-id="5176571032-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5176571032-2">(</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="5176571032-3">(</span><span class="n">List</span><span class="p" data-group-id="5176571032-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5176571032-4">&lt;&lt;</span><span class="p" data-group-id="5176571032-4">&gt;&gt;</span><span class="p" data-group-id="5176571032-2">)</span><span class="p">.</span><span class="w">
│ │ │ +time. One way to make the function more efficient is like this:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9991072778-1">(</span><span class="n">List</span><span class="p" data-group-id="9991072778-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9991072778-2">(</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="9991072778-3">(</span><span class="n">List</span><span class="p" data-group-id="9991072778-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9991072778-4">&lt;&lt;</span><span class="p" data-group-id="9991072778-4">&gt;&gt;</span><span class="p" data-group-id="9991072778-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5176571032-5">(</span><span class="p" data-group-id="5176571032-6">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5176571032-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5176571032-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5176571032-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5176571032-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="5176571032-8">&gt;&gt;</span><span class="p" data-group-id="5176571032-7">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5176571032-9">(</span><span class="p" data-group-id="5176571032-10">[</span><span class="p" data-group-id="5176571032-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5176571032-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Another way to avoid copying the binary each time is like this:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="7588122010-1">(</span><span class="p" data-group-id="7588122010-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7588122010-2">]</span><span class="p" data-group-id="7588122010-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">RevTail</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="7588122010-3">(</span><span class="n">T</span><span class="p" data-group-id="7588122010-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7588122010-4">&lt;&lt;</span><span class="n">RevTail</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="7588122010-4">&gt;&gt;</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="7588122010-5">(</span><span class="p" data-group-id="7588122010-6">[</span><span class="p" data-group-id="7588122010-6">]</span><span class="p" data-group-id="7588122010-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7588122010-7">&lt;&lt;</span><span class="p" data-group-id="7588122010-7">&gt;&gt;</span><span class="p">.</span></code></pre><p>Note that in each of the <strong>DO</strong> examples, the binary to be appended to is always
│ │ │ -given as the first segment.</p><p>Binaries can be efficiently <em>matched</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="9031915575-1">(</span><span class="p" data-group-id="9031915575-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9031915575-2">&gt;&gt;</span><span class="p" data-group-id="9031915575-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9031915575-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="9031915575-4">(</span><span class="n">T</span><span class="p" data-group-id="9031915575-4">)</span><span class="p" data-group-id="9031915575-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="9031915575-5">(</span><span class="p" data-group-id="9031915575-6">&lt;&lt;</span><span class="p" data-group-id="9031915575-6">&gt;&gt;</span><span class="p" data-group-id="9031915575-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9031915575-7">[</span><span class="p" data-group-id="9031915575-7">]</span><span class="p">.</span></code></pre><h2 id="how-binaries-are-implemented" class="section-heading">
│ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9991072778-5">(</span><span class="p" data-group-id="9991072778-6">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9991072778-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9991072778-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9991072778-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9991072778-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="9991072778-8">&gt;&gt;</span><span class="p" data-group-id="9991072778-7">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9991072778-9">(</span><span class="p" data-group-id="9991072778-10">[</span><span class="p" data-group-id="9991072778-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9991072778-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Another way to avoid copying the binary each time is like this:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5244894938-1">(</span><span class="p" data-group-id="5244894938-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5244894938-2">]</span><span class="p" data-group-id="5244894938-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">RevTail</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5244894938-3">(</span><span class="n">T</span><span class="p" data-group-id="5244894938-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5244894938-4">&lt;&lt;</span><span class="n">RevTail</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="5244894938-4">&gt;&gt;</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5244894938-5">(</span><span class="p" data-group-id="5244894938-6">[</span><span class="p" data-group-id="5244894938-6">]</span><span class="p" data-group-id="5244894938-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5244894938-7">&lt;&lt;</span><span class="p" data-group-id="5244894938-7">&gt;&gt;</span><span class="p">.</span></code></pre><p>Note that in each of the <strong>DO</strong> examples, the binary to be appended to is always
│ │ │ +given as the first segment.</p><p>Binaries can be efficiently <em>matched</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="7082820678-1">(</span><span class="p" data-group-id="7082820678-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7082820678-2">&gt;&gt;</span><span class="p" data-group-id="7082820678-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7082820678-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="7082820678-4">(</span><span class="n">T</span><span class="p" data-group-id="7082820678-4">)</span><span class="p" data-group-id="7082820678-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="7082820678-5">(</span><span class="p" data-group-id="7082820678-6">&lt;&lt;</span><span class="p" data-group-id="7082820678-6">&gt;&gt;</span><span class="p" data-group-id="7082820678-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7082820678-7">[</span><span class="p" data-group-id="7082820678-7">]</span><span class="p">.</span></code></pre><h2 id="how-binaries-are-implemented" class="section-heading">
│ │ │    <a href="#how-binaries-are-implemented" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">How Binaries are Implemented</span>
│ │ │  </h2>
│ │ │  <p>Internally, binaries and bitstrings are implemented in the same way. In this
│ │ │  section, they are called <em>binaries</em> because that is what they are called in the
│ │ │ @@ -205,29 +205,29 @@
│ │ │  called referential transparency) of Erlang would break.</p><h2 id="constructing-binaries" class="section-heading">
│ │ │    <a href="#constructing-binaries" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Constructing Binaries</span>
│ │ │  </h2>
│ │ │  <p>Appending to a binary or bitstring in the following way is specially optimized
│ │ │ -to avoid copying the binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1920253660-1">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1920253660-1">&gt;&gt;</span><span class="w">
│ │ │ +to avoid copying the binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4250253367-1">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4250253367-1">&gt;&gt;</span><span class="w">
│ │ │  </span><span class="c1">%% - OR -</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1920253660-2">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">bitstring</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1920253660-2">&gt;&gt;</span></code></pre><p>This optimization is applied by the runtime system in a way that makes it
│ │ │ +</span><span class="p" data-group-id="4250253367-2">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">bitstring</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4250253367-2">&gt;&gt;</span></code></pre><p>This optimization is applied by the runtime system in a way that makes it
│ │ │  effective in most circumstances (for exceptions, see
│ │ │  <a href="binaryhandling.html#forced_copying">Circumstances That Force Copying</a>). The
│ │ │  optimization in its basic form does not need any help from the compiler.
│ │ │  However, the compiler add hints to the runtime system when it is safe to apply
│ │ │  the optimization in a more efficient way.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>The compiler support for making the optimization more efficient was added in
│ │ │  Erlang/OTP 26.</p></section><p>To explain how the basic optimization works, let us examine the following code
│ │ │ -line by line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1258657350-1">&lt;&lt;</span><span class="mi">0</span><span class="p" data-group-id="1258657350-1">&gt;&gt;</span><span class="p">,</span><span class="w">                    </span><span class="c1">%% 1</span><span class="w">
│ │ │ -</span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1258657350-2">&lt;&lt;</span><span class="n">Bin0</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1258657350-2">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 2</span><span class="w">
│ │ │ -</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1258657350-3">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1258657350-3">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 3</span><span class="w">
│ │ │ -</span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1258657350-4">&lt;&lt;</span><span class="n">Bin2</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p" data-group-id="1258657350-4">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 4</span><span class="w">
│ │ │ -</span><span class="n">Bin4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1258657350-5">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="1258657350-5">&gt;&gt;</span><span class="p">,</span><span class="w">       </span><span class="c1">%% 5 !!!</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1258657350-6">{</span><span class="n">Bin4</span><span class="p">,</span><span class="n">Bin3</span><span class="p" data-group-id="1258657350-6">}</span><span class="w">                      </span><span class="c1">%% 6</span></code></pre><ul><li><p>Line 1 (marked with the <code class="inline">%% 1</code> comment), assigns a
│ │ │ +line by line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2926485562-1">&lt;&lt;</span><span class="mi">0</span><span class="p" data-group-id="2926485562-1">&gt;&gt;</span><span class="p">,</span><span class="w">                    </span><span class="c1">%% 1</span><span class="w">
│ │ │ +</span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2926485562-2">&lt;&lt;</span><span class="n">Bin0</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2926485562-2">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 2</span><span class="w">
│ │ │ +</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2926485562-3">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2926485562-3">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 3</span><span class="w">
│ │ │ +</span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2926485562-4">&lt;&lt;</span><span class="n">Bin2</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p" data-group-id="2926485562-4">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 4</span><span class="w">
│ │ │ +</span><span class="n">Bin4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2926485562-5">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="2926485562-5">&gt;&gt;</span><span class="p">,</span><span class="w">       </span><span class="c1">%% 5 !!!</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2926485562-6">{</span><span class="n">Bin4</span><span class="p">,</span><span class="n">Bin3</span><span class="p" data-group-id="2926485562-6">}</span><span class="w">                      </span><span class="c1">%% 6</span></code></pre><ul><li><p>Line 1 (marked with the <code class="inline">%% 1</code> comment), assigns a
│ │ │  <a href="binaryhandling.html#heap_binary">heap binary</a> to the <code class="inline">Bin0</code> variable.</p></li><li><p>Line 2 is an append operation. As <code class="inline">Bin0</code> has not been involved in an append
│ │ │  operation, a new <a href="binaryhandling.html#refc_binary">refc binary</a> is created and
│ │ │  the contents of <code class="inline">Bin0</code> is copied into it. The <em>ProcBin</em> part of the refc
│ │ │  binary has its size set to the size of the data stored in the binary, while
│ │ │  the binary object has extra space allocated. The size of the binary object is
│ │ │  either twice the size of <code class="inline">Bin1</code> or 256, whichever is larger. In this case it
│ │ │  is 256.</p></li><li><p>Line 3 is more interesting. <code class="inline">Bin1</code> <em>has</em> been used in an append operation, and
│ │ │ @@ -253,23 +253,23 @@
│ │ │  handle an append operation to a heap binary by copying it to a refc binary (line
│ │ │  2), and also handle an append operation to a previous version of the binary by
│ │ │  copying it (line 5). The support for doing that does not come for free. For
│ │ │  example, to make it possible to know when it is necessary to copy the binary,
│ │ │  for every append operation, the runtime system must create a sub binary.</p><p>When the compiler can determine that none of those situations need to be handled
│ │ │  and that the append operation cannot possibly fail, the compiler generates code
│ │ │  that causes the runtime system to apply a more efficient variant of the
│ │ │ -optimization.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2631467852-1">(</span><span class="ss">repack</span><span class="p" data-group-id="2631467852-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2631467852-2">(</span><span class="p" data-group-id="2631467852-3">[</span><span class="ss">repack</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2631467852-3">]</span><span class="p" data-group-id="2631467852-2">)</span><span class="p">.</span><span class="w">
│ │ │ +optimization.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0220107895-1">(</span><span class="ss">repack</span><span class="p" data-group-id="0220107895-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0220107895-2">(</span><span class="p" data-group-id="0220107895-3">[</span><span class="ss">repack</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0220107895-3">]</span><span class="p" data-group-id="0220107895-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="2631467852-4">(</span><span class="n">Bin</span><span class="p" data-group-id="2631467852-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_binary</span><span class="p" data-group-id="2631467852-5">(</span><span class="n">Bin</span><span class="p" data-group-id="2631467852-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">repack</span><span class="p" data-group-id="2631467852-6">(</span><span class="n">Bin</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2631467852-7">&lt;&lt;</span><span class="p" data-group-id="2631467852-7">&gt;&gt;</span><span class="p" data-group-id="2631467852-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="0220107895-4">(</span><span class="n">Bin</span><span class="p" data-group-id="0220107895-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_binary</span><span class="p" data-group-id="0220107895-5">(</span><span class="n">Bin</span><span class="p" data-group-id="0220107895-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">repack</span><span class="p" data-group-id="0220107895-6">(</span><span class="n">Bin</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0220107895-7">&lt;&lt;</span><span class="p" data-group-id="0220107895-7">&gt;&gt;</span><span class="p" data-group-id="0220107895-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="2631467852-8">(</span><span class="p" data-group-id="2631467852-9">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2631467852-9">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2631467852-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">repack</span><span class="p" data-group-id="2631467852-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2631467852-11">&lt;&lt;</span><span class="n">Result</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="2631467852-11">&gt;&gt;</span><span class="p" data-group-id="2631467852-10">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="2631467852-12">(</span><span class="p" data-group-id="2631467852-13">&lt;&lt;</span><span class="p" data-group-id="2631467852-13">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2631467852-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="0220107895-8">(</span><span class="p" data-group-id="0220107895-9">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0220107895-9">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0220107895-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">repack</span><span class="p" data-group-id="0220107895-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0220107895-11">&lt;&lt;</span><span class="n">Result</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0220107895-11">&gt;&gt;</span><span class="p" data-group-id="0220107895-10">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="0220107895-12">(</span><span class="p" data-group-id="0220107895-13">&lt;&lt;</span><span class="p" data-group-id="0220107895-13">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0220107895-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Result</span><span class="p">.</span></code></pre><p>The <code class="inline">repack/2</code> function only keeps a single version of the binary, so there is
│ │ │  never any need to copy the binary. The compiler rewrites the creation of the
│ │ │  empty binary in <code class="inline">repack/1</code> to instead create a refc binary with 256 bytes
│ │ │  already reserved; thus, the append operation in <code class="inline">repack/2</code> never needs to handle
│ │ │  a binary not prepared for appending.</p><p><a href="" id="forced_copying"></a></p><h3 id="circumstances-that-force-copying" class="section-heading">
│ │ │    <a href="#circumstances-that-force-copying" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -281,72 +281,72 @@
│ │ │  reason is that the binary object can be moved (reallocated) during an append
│ │ │  operation, and when that happens, the pointer in the ProcBin must be updated. If
│ │ │  there would be more than one ProcBin pointing to the binary object, it would not
│ │ │  be possible to find and update all of them.</p><p>Therefore, certain operations on a binary mark it so that any future append
│ │ │  operation will be forced to copy the binary. In most cases, the binary object
│ │ │  will be shrunk at the same time to reclaim the extra space allocated for
│ │ │  growing.</p><p>When appending to a binary as follows, only the binary returned from the latest
│ │ │ -append operation will support further cheap append operations:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6071025632-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6071025632-1">&gt;&gt;</span></code></pre><p>In the code fragment in the beginning of this section, appending to <code class="inline">Bin</code> will
│ │ │ +append operation will support further cheap append operations:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9296536490-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9296536490-1">&gt;&gt;</span></code></pre><p>In the code fragment in the beginning of this section, appending to <code class="inline">Bin</code> will
│ │ │  be cheap, while appending to <code class="inline">Bin0</code> will force the creation of a new binary and
│ │ │  copying of the contents of <code class="inline">Bin0</code>.</p><p>If a binary is sent as a message to a process or port, the binary will be shrunk
│ │ │  and any further append operation will copy the binary data into a new binary.
│ │ │  For example, in the following code fragment <code class="inline">Bin1</code> will be copied in the third
│ │ │ -line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9937780620-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9937780620-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ +line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7982120050-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7982120050-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="n">PortOrPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9937780620-2">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9937780620-2">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The same happens if you insert a binary into an Ets table, send it to a port
│ │ │ +</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7982120050-2">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7982120050-2">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The same happens if you insert a binary into an Ets table, send it to a port
│ │ │  using <a href="../../erts-15.2.7/doc/html/erlang.html#port_command/2"><code class="inline">erlang:port_command/2</code></a>, or pass it to
│ │ │  <a href="../../erts-15.2.7/doc/html/erl_nif.html#enif_inspect_binary">enif_inspect_binary</a> in a NIF.</p><p>Matching a binary will also cause it to shrink and the next append operation
│ │ │ -will copy the binary data:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8014110992-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8014110992-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8014110992-2">&lt;&lt;</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8014110992-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8014110992-3">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8014110992-3">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The reason is that a <a href="binaryhandling.html#match_context">match context</a> contains a
│ │ │ +will copy the binary data:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5636766139-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5636766139-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5636766139-2">&lt;&lt;</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5636766139-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5636766139-3">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5636766139-3">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The reason is that a <a href="binaryhandling.html#match_context">match context</a> contains a
│ │ │  direct pointer to the binary data.</p><p>If a process simply keeps binaries (either in &quot;loop data&quot; or in the process
│ │ │  dictionary), the garbage collector can eventually shrink the binaries. If only
│ │ │  one such binary is kept, it will not be shrunk. If the process later appends to
│ │ │  a binary that has been shrunk, the binary object will be reallocated to make
│ │ │  place for the data to be appended.</p><h2 id="matching-binaries" class="section-heading">
│ │ │    <a href="#matching-binaries" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Matching Binaries</span>
│ │ │  </h2>
│ │ │ -<p>Let us revisit the example in the beginning of the previous section:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="4782104684-1">(</span><span class="p" data-group-id="4782104684-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4782104684-2">&gt;&gt;</span><span class="p" data-group-id="4782104684-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4782104684-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="4782104684-4">(</span><span class="n">T</span><span class="p" data-group-id="4782104684-4">)</span><span class="p" data-group-id="4782104684-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="4782104684-5">(</span><span class="p" data-group-id="4782104684-6">&lt;&lt;</span><span class="p" data-group-id="4782104684-6">&gt;&gt;</span><span class="p" data-group-id="4782104684-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4782104684-7">[</span><span class="p" data-group-id="4782104684-7">]</span><span class="p">.</span></code></pre><p>The first time <code class="inline">my_binary_to_list/1</code> is called, a
│ │ │ +<p>Let us revisit the example in the beginning of the previous section:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="5206610621-1">(</span><span class="p" data-group-id="5206610621-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5206610621-2">&gt;&gt;</span><span class="p" data-group-id="5206610621-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5206610621-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="5206610621-4">(</span><span class="n">T</span><span class="p" data-group-id="5206610621-4">)</span><span class="p" data-group-id="5206610621-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="5206610621-5">(</span><span class="p" data-group-id="5206610621-6">&lt;&lt;</span><span class="p" data-group-id="5206610621-6">&gt;&gt;</span><span class="p" data-group-id="5206610621-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5206610621-7">[</span><span class="p" data-group-id="5206610621-7">]</span><span class="p">.</span></code></pre><p>The first time <code class="inline">my_binary_to_list/1</code> is called, a
│ │ │  <a href="binaryhandling.html#match_context">match context</a> is created. The match context
│ │ │  points to the first byte of the binary. 1 byte is matched out and the match
│ │ │  context is updated to point to the second byte in the binary.</p><p>At this point it would make sense to create a
│ │ │  <a href="binaryhandling.html#sub_binary">sub binary</a>, but in this particular example the
│ │ │  compiler sees that there will soon be a call to a function (in this case, to
│ │ │  <code class="inline">my_binary_to_list/1</code> itself) that immediately will create a new match context
│ │ │  and discard the sub binary.</p><p>Therefore <code class="inline">my_binary_to_list/1</code> calls itself with the match context instead of
│ │ │  with a sub binary. The instruction that initializes the matching operation
│ │ │  basically does nothing when it sees that it was passed a match context instead
│ │ │  of a binary.</p><p>When the end of the binary is reached and the second clause matches, the match
│ │ │  context will simply be discarded (removed in the next garbage collection, as
│ │ │  there is no longer any reference to it).</p><p>To summarize, <code class="inline">my_binary_to_list/1</code> only needs to create <em>one</em> match context and
│ │ │  no sub binaries.</p><p>Notice that the match context in <code class="inline">my_binary_to_list/1</code> was discarded when the
│ │ │  entire binary had been traversed. What happens if the iteration stops before it
│ │ │ -has reached the end of the binary? Will the optimization still work?</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="3076427028-1">(</span><span class="p" data-group-id="3076427028-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3076427028-2">&gt;&gt;</span><span class="p" data-group-id="3076427028-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +has reached the end of the binary? Will the optimization still work?</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="8111725047-1">(</span><span class="p" data-group-id="8111725047-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8111725047-2">&gt;&gt;</span><span class="p" data-group-id="8111725047-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="3076427028-3">(</span><span class="p" data-group-id="3076427028-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3076427028-4">&gt;&gt;</span><span class="p" data-group-id="3076427028-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="3076427028-5">(</span><span class="n">T</span><span class="p" data-group-id="3076427028-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="3076427028-6">(</span><span class="p" data-group-id="3076427028-7">&lt;&lt;</span><span class="p" data-group-id="3076427028-7">&gt;&gt;</span><span class="p" data-group-id="3076427028-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3076427028-8">&lt;&lt;</span><span class="p" data-group-id="3076427028-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>Yes, it will. The compiler will remove the building of the sub binary in the
│ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="8111725047-3">(</span><span class="p" data-group-id="8111725047-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8111725047-4">&gt;&gt;</span><span class="p" data-group-id="8111725047-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="8111725047-5">(</span><span class="n">T</span><span class="p" data-group-id="8111725047-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="8111725047-6">(</span><span class="p" data-group-id="8111725047-7">&lt;&lt;</span><span class="p" data-group-id="8111725047-7">&gt;&gt;</span><span class="p" data-group-id="8111725047-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8111725047-8">&lt;&lt;</span><span class="p" data-group-id="8111725047-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>Yes, it will. The compiler will remove the building of the sub binary in the
│ │ │  second clause:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="4161010592-1">(</span><span class="p" data-group-id="4161010592-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4161010592-2">&gt;&gt;</span><span class="p" data-group-id="4161010592-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="4161010592-3">(</span><span class="n">T</span><span class="p" data-group-id="4161010592-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>But it will generate code that builds a sub binary in the first clause:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="1820854880-1">(</span><span class="p" data-group-id="1820854880-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1820854880-2">&gt;&gt;</span><span class="p" data-group-id="1820854880-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="8856288994-1">(</span><span class="p" data-group-id="8856288994-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8856288994-2">&gt;&gt;</span><span class="p" data-group-id="8856288994-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="8856288994-3">(</span><span class="n">T</span><span class="p" data-group-id="8856288994-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>But it will generate code that builds a sub binary in the first clause:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="5101666214-1">(</span><span class="p" data-group-id="5101666214-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5101666214-2">&gt;&gt;</span><span class="p" data-group-id="5101666214-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Therefore, <code class="inline">after_zero/1</code> builds one match context and one sub binary (assuming
│ │ │ -it is passed a binary that contains a zero byte).</p><p>Code like the following will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="2250272016-1">(</span><span class="n">Buffer</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2250272016-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2250272016-2">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2250272016-3">(</span><span class="n">Acc</span><span class="p" data-group-id="2250272016-3">)</span><span class="p">,</span><span class="n">Buffer</span><span class="p" data-group-id="2250272016-2">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="2250272016-4">(</span><span class="p" data-group-id="2250272016-5">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2250272016-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="2250272016-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="2250272016-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="2250272016-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="2250272016-7">(</span><span class="p" data-group-id="2250272016-8">&lt;&lt;</span><span class="n">Byte</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2250272016-8">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="2250272016-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="2250272016-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2250272016-10">[</span><span class="n">Byte</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="2250272016-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="2250272016-9">)</span><span class="p">.</span></code></pre><p>The compiler removes building of sub binaries in the second and third clauses,
│ │ │ +it is passed a binary that contains a zero byte).</p><p>Code like the following will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="0374580668-1">(</span><span class="n">Buffer</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0374580668-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0374580668-2">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="0374580668-3">(</span><span class="n">Acc</span><span class="p" data-group-id="0374580668-3">)</span><span class="p">,</span><span class="n">Buffer</span><span class="p" data-group-id="0374580668-2">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="0374580668-4">(</span><span class="p" data-group-id="0374580668-5">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0374580668-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="0374580668-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="0374580668-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="0374580668-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="0374580668-7">(</span><span class="p" data-group-id="0374580668-8">&lt;&lt;</span><span class="n">Byte</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0374580668-8">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="0374580668-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="0374580668-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0374580668-10">[</span><span class="n">Byte</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="0374580668-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="0374580668-9">)</span><span class="p">.</span></code></pre><p>The compiler removes building of sub binaries in the second and third clauses,
│ │ │  and it adds an instruction to the first clause that converts <code class="inline">Buffer</code> from a
│ │ │  match context to a sub binary (or do nothing if <code class="inline">Buffer</code> is a binary already).</p><p>But in more complicated code, how can one know whether the optimization is
│ │ │  applied or not?</p><p><a href="" id="bin_opt_info"></a></p><h3 id="option-bin_opt_info" class="section-heading">
│ │ │    <a href="#option-bin_opt_info" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Option bin_opt_info</span>
│ │ │ @@ -354,38 +354,38 @@
│ │ │  <p>Use the <code class="inline">bin_opt_info</code> option to have the compiler print a lot of information
│ │ │  about binary optimizations. It can be given either to the compiler or <code class="inline">erlc</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">erlc</span><span class="w"> </span><span class="o">+</span><span class="ss">bin_opt_info</span><span class="w"> </span><span class="n">Mod</span><span class="p">.</span><span class="ss">erl</span></code></pre><p>or passed through an environment variable:</p><pre><code class="makeup erlang" translate="no"><span class="ss">export</span><span class="w"> </span><span class="n">ERL_COMPILER_OPTIONS</span><span class="o">=</span><span class="ss">bin_opt_info</span></code></pre><p>Notice that the <code class="inline">bin_opt_info</code> is not meant to be a permanent option added to
│ │ │  your <code class="inline">Makefile</code>s, because all messages that it generates cannot be eliminated.
│ │ │  Therefore, passing the option through the environment is in most cases the most
│ │ │  practical approach.</p><p>The warnings look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="o">/</span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">60</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">NOT</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">binary</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">returned</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">function</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="o">/</span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">62</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">context</span><span class="w"> </span><span class="ss">reused</span></code></pre><p>To make it clearer exactly what code the warnings refer to, the warnings in the
│ │ │  following examples are inserted as comments after the clause they refer to, for
│ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="5955136654-1">(</span><span class="p" data-group-id="5955136654-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5955136654-2">&gt;&gt;</span><span class="p" data-group-id="5955136654-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="3207963388-1">(</span><span class="p" data-group-id="3207963388-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3207963388-2">&gt;&gt;</span><span class="p" data-group-id="3207963388-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │           </span><span class="c1">%% BINARY CREATED: binary is returned from the function</span><span class="w">
│ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="5955136654-3">(</span><span class="p" data-group-id="5955136654-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5955136654-4">&gt;&gt;</span><span class="p" data-group-id="5955136654-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="3207963388-3">(</span><span class="p" data-group-id="3207963388-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3207963388-4">&gt;&gt;</span><span class="p" data-group-id="3207963388-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │           </span><span class="c1">%% OPTIMIZED: match context reused</span><span class="w">
│ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="5955136654-5">(</span><span class="n">T</span><span class="p" data-group-id="5955136654-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="5955136654-6">(</span><span class="p" data-group-id="5955136654-7">&lt;&lt;</span><span class="p" data-group-id="5955136654-7">&gt;&gt;</span><span class="p" data-group-id="5955136654-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5955136654-8">&lt;&lt;</span><span class="p" data-group-id="5955136654-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>The warning for the first clause says that the creation of a sub binary cannot
│ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="3207963388-5">(</span><span class="n">T</span><span class="p" data-group-id="3207963388-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="3207963388-6">(</span><span class="p" data-group-id="3207963388-7">&lt;&lt;</span><span class="p" data-group-id="3207963388-7">&gt;&gt;</span><span class="p" data-group-id="3207963388-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3207963388-8">&lt;&lt;</span><span class="p" data-group-id="3207963388-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>The warning for the first clause says that the creation of a sub binary cannot
│ │ │  be delayed, because it will be returned. The warning for the second clause says
│ │ │  that a sub binary will not be created (yet).</p><h3 id="unused-variables" class="section-heading">
│ │ │    <a href="#unused-variables" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Unused Variables</span>
│ │ │  </h3>
│ │ │  <p>The compiler figures out if a variable is unused. The same code is generated for
│ │ │ -each of the following functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">count1</span><span class="p" data-group-id="3651841065-1">(</span><span class="p" data-group-id="3651841065-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3651841065-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="3651841065-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count1</span><span class="p" data-group-id="3651841065-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="3651841065-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">count1</span><span class="p" data-group-id="3651841065-4">(</span><span class="p" data-group-id="3651841065-5">&lt;&lt;</span><span class="p" data-group-id="3651841065-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="3651841065-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ +each of the following functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">count1</span><span class="p" data-group-id="4738315115-1">(</span><span class="p" data-group-id="4738315115-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4738315115-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="4738315115-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count1</span><span class="p" data-group-id="4738315115-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="4738315115-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">count1</span><span class="p" data-group-id="4738315115-4">(</span><span class="p" data-group-id="4738315115-5">&lt;&lt;</span><span class="p" data-group-id="4738315115-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="4738315115-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">count2</span><span class="p" data-group-id="3651841065-6">(</span><span class="p" data-group-id="3651841065-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3651841065-7">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="3651841065-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count2</span><span class="p" data-group-id="3651841065-8">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="3651841065-8">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">count2</span><span class="p" data-group-id="3651841065-9">(</span><span class="p" data-group-id="3651841065-10">&lt;&lt;</span><span class="p" data-group-id="3651841065-10">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="3651841065-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">count2</span><span class="p" data-group-id="4738315115-6">(</span><span class="p" data-group-id="4738315115-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4738315115-7">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="4738315115-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count2</span><span class="p" data-group-id="4738315115-8">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="4738315115-8">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">count2</span><span class="p" data-group-id="4738315115-9">(</span><span class="p" data-group-id="4738315115-10">&lt;&lt;</span><span class="p" data-group-id="4738315115-10">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="4738315115-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">count3</span><span class="p" data-group-id="3651841065-11">(</span><span class="p" data-group-id="3651841065-12">&lt;&lt;</span><span class="p">_</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3651841065-12">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="3651841065-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count3</span><span class="p" data-group-id="3651841065-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="3651841065-13">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">count3</span><span class="p" data-group-id="3651841065-14">(</span><span class="p" data-group-id="3651841065-15">&lt;&lt;</span><span class="p" data-group-id="3651841065-15">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="3651841065-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span></code></pre><p>In each iteration, the first 8 bits in the binary will be skipped, not matched
│ │ │ +</span><span class="nf">count3</span><span class="p" data-group-id="4738315115-11">(</span><span class="p" data-group-id="4738315115-12">&lt;&lt;</span><span class="p">_</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4738315115-12">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="4738315115-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count3</span><span class="p" data-group-id="4738315115-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="4738315115-13">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">count3</span><span class="p" data-group-id="4738315115-14">(</span><span class="p" data-group-id="4738315115-15">&lt;&lt;</span><span class="p" data-group-id="4738315115-15">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="4738315115-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span></code></pre><p>In each iteration, the first 8 bits in the binary will be skipped, not matched
│ │ │  out.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="commoncaveats.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/bit_syntax.html
│ │ │ @@ -119,48 +119,48 @@
│ │ │    <a href="#introduction" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Introduction</span>
│ │ │  </h2>
│ │ │  <p>The complete specification for the bit syntax appears in the
│ │ │  <a href="../../doc/system/expressions.html#bit-syntax-expressions">Reference Manual</a>.</p><p>In Erlang, a Bin is used for constructing binaries and matching binary patterns.
│ │ │ -A Bin is written with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4511868680-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="4511868680-1">&gt;&gt;</span></code></pre><p>A Bin is a low-level sequence of bits or bytes. The purpose of a Bin is to
│ │ │ -enable construction of binaries:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9937146497-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="9937146497-1">&gt;&gt;</span></code></pre><p>All elements must be bound. Or match a binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4728978522-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="4728978522-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span></code></pre><p>Here, <code class="inline">Bin</code> is bound and the elements are bound or unbound, as in any match.</p><p>A Bin does not need to consist of a whole number of bytes.</p><p>A <em>bitstring</em> is a sequence of zero or more bits, where the number of bits does
│ │ │ +A Bin is written with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6820675185-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="6820675185-1">&gt;&gt;</span></code></pre><p>A Bin is a low-level sequence of bits or bytes. The purpose of a Bin is to
│ │ │ +enable construction of binaries:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8702143021-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="8702143021-1">&gt;&gt;</span></code></pre><p>All elements must be bound. Or match a binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4243481433-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="4243481433-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span></code></pre><p>Here, <code class="inline">Bin</code> is bound and the elements are bound or unbound, as in any match.</p><p>A Bin does not need to consist of a whole number of bytes.</p><p>A <em>bitstring</em> is a sequence of zero or more bits, where the number of bits does
│ │ │  not need to be divisible by 8. If the number of bits is divisible by 8, the
│ │ │  bitstring is also a binary.</p><p>Each element specifies a certain <em>segment</em> of the bitstring. A segment is a set
│ │ │  of contiguous bits of the binary (not necessarily on a byte boundary). The first
│ │ │  element specifies the initial segment, the second element specifies the
│ │ │  following segment, and so on.</p><p>The following examples illustrate how binaries are constructed, or matched, and
│ │ │  how elements and tails are specified.</p><h3 id="examples" class="section-heading">
│ │ │    <a href="#examples" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Examples</span>
│ │ │  </h3>
│ │ │  <p><em>Example 1:</em> A binary can be constructed from a set of constants or a string
│ │ │ -literal:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin11</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0402818164-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="0402818164-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Bin12</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0402818164-2">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0402818164-2">&gt;&gt;</span></code></pre><p>This gives two binaries of size 3, with the following evaluations:</p><ul><li><a href="../../erts-15.2.7/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin11)</code></a> evaluates to <code class="inline">[1, 17, 42]</code>.</li><li><a href="../../erts-15.2.7/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin12)</code></a> evaluates to <code class="inline">[97, 98, 99]</code>.</li></ul><p><em>Example 2:</em>Similarly, a binary can be constructed from a set of bound
│ │ │ +literal:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin11</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7068959732-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="7068959732-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Bin12</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7068959732-2">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="7068959732-2">&gt;&gt;</span></code></pre><p>This gives two binaries of size 3, with the following evaluations:</p><ul><li><a href="../../erts-15.2.7/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin11)</code></a> evaluates to <code class="inline">[1, 17, 42]</code>.</li><li><a href="../../erts-15.2.7/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin12)</code></a> evaluates to <code class="inline">[97, 98, 99]</code>.</li></ul><p><em>Example 2:</em>Similarly, a binary can be constructed from a set of bound
│ │ │  variables:</p><pre><code class="makeup erlang" translate="no"><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4939375022-1">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="4939375022-1">&gt;&gt;</span></code></pre><p>This gives a binary of size 4. Here, a <em>size expression</em> is used for the
│ │ │ +</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9201777962-1">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="9201777962-1">&gt;&gt;</span></code></pre><p>This gives a binary of size 4. Here, a <em>size expression</em> is used for the
│ │ │  variable <code class="inline">C</code> to specify a 16-bits segment of <code class="inline">Bin2</code>.</p><p><a href="../../erts-15.2.7/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin2)</code></a> evaluates to <code class="inline">[1, 17, 00, 42]</code>.</p><p><em>Example 3:</em> A Bin can also be used for matching. <code class="inline">D</code>, <code class="inline">E</code>, and <code class="inline">F</code> are unbound
│ │ │ -variables, and <code class="inline">Bin2</code> is bound, as in Example 2:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2466973250-1">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2466973250-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin2</span></code></pre><p>This gives <code class="inline">D = 273</code>, <code class="inline">E = 00</code>, and F binds to a binary of size 1:
│ │ │ +variables, and <code class="inline">Bin2</code> is bound, as in Example 2:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9724516060-1">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9724516060-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin2</span></code></pre><p>This gives <code class="inline">D = 273</code>, <code class="inline">E = 00</code>, and F binds to a binary of size 1:
│ │ │  <code class="inline">binary_to_list(F) = [42]</code>.</p><p><em>Example 4:</em> The following is a more elaborate example of matching. Here,
│ │ │  <code class="inline">Dgram</code> is bound to the consecutive bytes of an IP datagram of IP protocol
│ │ │ -version 4. The ambition is to extract the header and the data of the datagram:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5062365519-1">(</span><span class="n">IP_VERSION</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="5062365519-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5062365519-2">(</span><span class="n">IP_MIN_HDR_LEN</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="5062365519-2">)</span><span class="p">.</span><span class="w">
│ │ │ +version 4. The ambition is to extract the header and the data of the datagram:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5113047370-1">(</span><span class="n">IP_VERSION</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="5113047370-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5113047370-2">(</span><span class="n">IP_MIN_HDR_LEN</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="5113047370-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">DgramSize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="5062365519-3">(</span><span class="n">Dgram</span><span class="p" data-group-id="5062365519-3">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">DgramSize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="5113047370-3">(</span><span class="n">Dgram</span><span class="p" data-group-id="5113047370-3">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="k">case</span><span class="w"> </span><span class="n">Dgram</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5062365519-4">&lt;&lt;</span><span class="o">?</span><span class="n">IP_VERSION</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">HLen</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">SrvcType</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">TotLen</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5113047370-4">&lt;&lt;</span><span class="o">?</span><span class="n">IP_VERSION</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">HLen</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">SrvcType</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">TotLen</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │        </span><span class="n">ID</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">Flgs</span><span class="p">:</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">FragOff</span><span class="p">:</span><span class="mi">13</span><span class="p">,</span><span class="w">
│ │ │        </span><span class="n">TTL</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">Proto</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">HdrChkSum</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │        </span><span class="n">SrcIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w">
│ │ │ -      </span><span class="n">DestIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w"> </span><span class="n">RestDgram</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5062365519-4">&gt;&gt;</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">HLen</span><span class="o">&gt;=</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="n">HLen</span><span class="o">=&lt;</span><span class="n">DgramSize</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="n">OptsLen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="p" data-group-id="5062365519-5">(</span><span class="n">HLen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">?</span><span class="n">IP_MIN_HDR_LEN</span><span class="p" data-group-id="5062365519-5">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5062365519-6">&lt;&lt;</span><span class="n">Opts</span><span class="p">:</span><span class="n">OptsLen</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Data</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5062365519-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RestDgram</span><span class="p">,</span><span class="w">
│ │ │ +      </span><span class="n">DestIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w"> </span><span class="n">RestDgram</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5113047370-4">&gt;&gt;</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">HLen</span><span class="o">&gt;=</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="n">HLen</span><span class="o">=&lt;</span><span class="n">DgramSize</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="n">OptsLen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="p" data-group-id="5113047370-5">(</span><span class="n">HLen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">?</span><span class="n">IP_MIN_HDR_LEN</span><span class="p" data-group-id="5113047370-5">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5113047370-6">&lt;&lt;</span><span class="n">Opts</span><span class="p">:</span><span class="n">OptsLen</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Data</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5113047370-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RestDgram</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>Here, the segment corresponding to the <code class="inline">Opts</code> variable has a <em>type modifier</em>,
│ │ │  specifying that <code class="inline">Opts</code> is to bind to a binary. All other variables have the
│ │ │  default type equal to unsigned integer.</p><p>An IP datagram header is of variable length. This length is measured in the
│ │ │  number of 32-bit words and is given in the segment corresponding to <code class="inline">HLen</code>. The
│ │ │  minimum value of <code class="inline">HLen</code> is 5. It is the segment corresponding to <code class="inline">Opts</code> that is
│ │ │  variable, so if <code class="inline">HLen</code> is equal to 5, <code class="inline">Opts</code> becomes an empty binary.</p><p>The tail variables <code class="inline">RestDgram</code> and <code class="inline">Data</code> bind to binaries, as all tail
│ │ │ @@ -218,80 +218,80 @@
│ │ │  <p>This section describes the rules for constructing binaries using the bit syntax.
│ │ │  Unlike when constructing lists or tuples, the construction of a binary can fail
│ │ │  with a <code class="inline">badarg</code> exception.</p><p>There can be zero or more segments in a binary to be constructed. The expression
│ │ │  <code class="inline">&lt;&lt;&gt;&gt;</code> constructs a zero length binary.</p><p>Each segment in a binary can consist of zero or more bits. There are no
│ │ │  alignment rules for individual segments of type <code class="inline">integer</code> and <code class="inline">float</code>. For
│ │ │  binaries and bitstrings without size, the unit specifies the alignment. Since
│ │ │  the default alignment for the <code class="inline">binary</code> type is 8, the size of a binary segment
│ │ │ -must be a multiple of 8 bits, that is, only whole bytes.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4999003651-1">&lt;&lt;</span><span class="n">Bin</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Bitstring</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="4999003651-1">&gt;&gt;</span></code></pre><p>The variable <code class="inline">Bin</code> must contain a whole number of bytes, because the <code class="inline">binary</code>
│ │ │ +must be a multiple of 8 bits, that is, only whole bytes.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0677254263-1">&lt;&lt;</span><span class="n">Bin</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Bitstring</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="0677254263-1">&gt;&gt;</span></code></pre><p>The variable <code class="inline">Bin</code> must contain a whole number of bytes, because the <code class="inline">binary</code>
│ │ │  type defaults to <code class="inline">unit:8</code>. A <code class="inline">badarg</code> exception is generated if <code class="inline">Bin</code> consist
│ │ │  of, for example, 17 bits.</p><p>The <code class="inline">Bitstring</code> variable can consist of any number of bits, for example, 0, 1,
│ │ │  8, 11, 17, 42, and so on. This is because the default <code class="inline">unit</code> for bitstrings
│ │ │  is 1.</p><p>For clarity, it is recommended not to change the unit size for binaries.
│ │ │  Instead, use <code class="inline">binary</code> when you need byte alignment and <code class="inline">bitstring</code> when you need
│ │ │  bit alignment.</p><p>The following example successfully constructs a bitstring of 7 bits, provided
│ │ │ -that all of X and Y are integers:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9245754648-1">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">6</span><span class="p" data-group-id="9245754648-1">&gt;&gt;</span></code></pre><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When constructing binaries, <code class="inline">Value</code> and <code class="inline">Size</code> can be any Erlang expression.
│ │ │ +that all of X and Y are integers:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0967157888-1">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">6</span><span class="p" data-group-id="0967157888-1">&gt;&gt;</span></code></pre><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When constructing binaries, <code class="inline">Value</code> and <code class="inline">Size</code> can be any Erlang expression.
│ │ │  However, for syntactical reasons, both <code class="inline">Value</code> and <code class="inline">Size</code> must be enclosed in
│ │ │  parenthesis if the expression consists of anything more than a single literal or
│ │ │ -a variable. The following gives a compiler syntax error:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1250802972-1">&lt;&lt;</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="1250802972-1">&gt;&gt;</span></code></pre><p>This expression must be rewritten into the following, to be accepted by the
│ │ │ -compiler:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0916087665-1">&lt;&lt;</span><span class="p" data-group-id="0916087665-2">(</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="0916087665-2">)</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0916087665-1">&gt;&gt;</span></code></pre><h3 id="including-literal-strings" class="section-heading">
│ │ │ +a variable. The following gives a compiler syntax error:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6660223224-1">&lt;&lt;</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="6660223224-1">&gt;&gt;</span></code></pre><p>This expression must be rewritten into the following, to be accepted by the
│ │ │ +compiler:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6588893952-1">&lt;&lt;</span><span class="p" data-group-id="6588893952-2">(</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="6588893952-2">)</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="6588893952-1">&gt;&gt;</span></code></pre><h3 id="including-literal-strings" class="section-heading">
│ │ │    <a href="#including-literal-strings" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Including Literal Strings</span>
│ │ │  </h3>
│ │ │ -<p>A literal string can be written instead of an element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7018198895-1">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7018198895-1">&gt;&gt;</span></code></pre><p>This is syntactic sugar for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3083472937-1">&lt;&lt;</span><span class="sc">$h</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$o</span><span class="p" data-group-id="3083472937-1">&gt;&gt;</span></code></pre><h2 id="matching-binaries" class="section-heading">
│ │ │ +<p>A literal string can be written instead of an element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6376687125-1">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6376687125-1">&gt;&gt;</span></code></pre><p>This is syntactic sugar for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8221748137-1">&lt;&lt;</span><span class="sc">$h</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$o</span><span class="p" data-group-id="8221748137-1">&gt;&gt;</span></code></pre><h2 id="matching-binaries" class="section-heading">
│ │ │    <a href="#matching-binaries" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Matching Binaries</span>
│ │ │  </h2>
│ │ │  <p>This section describes the rules for matching binaries, using the bit syntax.</p><p>There can be zero or more segments in a binary pattern. A binary pattern can
│ │ │  occur wherever patterns are allowed, including inside other patterns. Binary
│ │ │  patterns cannot be nested. The pattern <code class="inline">&lt;&lt;&gt;&gt;</code> matches a zero length binary.</p><p>Each segment in a binary can consist of zero or more bits. A segment of type
│ │ │  <code class="inline">binary</code> must have a size evenly divisible by 8 (or divisible by the unit size,
│ │ │  if the unit size has been changed). A segment of type <code class="inline">bitstring</code> has no
│ │ │  restrictions on the size. A segment of type <code class="inline">float</code> must have size 64 or 32.</p><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When matching <code class="inline">Value</code>, value must be either a variable or an integer, or a
│ │ │  floating point literal. Expressions are not allowed.</p><p><code class="inline">Size</code> must be a
│ │ │  <a href="../../doc/system/expressions.html#guard-expressions">guard expression</a>, which can use
│ │ │ -literals and previously bound variables. The following is not allowed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="8572950994-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8572950994-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8572950994-2">&gt;&gt;</span><span class="p" data-group-id="8572950994-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8572950994-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="8572950994-3">}</span><span class="p">.</span></code></pre><p>The two occurrences of <code class="inline">N</code> are not related. The compiler will complain that the
│ │ │ -<code class="inline">N</code> in the size field is unbound.</p><p>The correct way to write this example is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="7856544641-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="7856544641-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="7856544641-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7856544641-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="7856544641-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="7856544641-3">}</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Before OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable bound to
│ │ │ +literals and previously bound variables. The following is not allowed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="7495512073-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7495512073-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7495512073-2">&gt;&gt;</span><span class="p" data-group-id="7495512073-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="7495512073-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="7495512073-3">}</span><span class="p">.</span></code></pre><p>The two occurrences of <code class="inline">N</code> are not related. The compiler will complain that the
│ │ │ +<code class="inline">N</code> in the size field is unbound.</p><p>The correct way to write this example is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="1952811339-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="1952811339-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="1952811339-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1952811339-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="1952811339-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="1952811339-3">}</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Before OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable bound to
│ │ │  an integer.</p></section><h3 id="binding-and-using-a-size-variable" class="section-heading">
│ │ │    <a href="#binding-and-using-a-size-variable" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Binding and Using a Size Variable</span>
│ │ │  </h3>
│ │ │  <p>There is one exception to the rule that a variable that is used as size must be
│ │ │  previously bound. It is possible to match and bind a variable, and use it as a
│ │ │ -size within the same binary pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="7108274253-1">(</span><span class="p" data-group-id="7108274253-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="n">Sz</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7108274253-2">&gt;&gt;</span><span class="p" data-group-id="7108274253-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="7108274253-3">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="7108274253-3">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is bound to the value in the first byte of the binary. <code class="inline">Sz</code> is then
│ │ │ -used at the number of bytes to match out as a binary.</p><p>Starting in OTP 23, the size can be a guard expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="0541387468-1">(</span><span class="p" data-group-id="0541387468-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="p" data-group-id="0541387468-3">(</span><span class="p" data-group-id="0541387468-4">(</span><span class="n">Sz</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="0541387468-4">)</span><span class="o">*</span><span class="mi">8</span><span class="p" data-group-id="0541387468-3">)</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0541387468-2">&gt;&gt;</span><span class="p" data-group-id="0541387468-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="0541387468-5">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="0541387468-5">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is the combined size of the header and the payload, so we will need to
│ │ │ +size within the same binary pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="5159229401-1">(</span><span class="p" data-group-id="5159229401-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="n">Sz</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5159229401-2">&gt;&gt;</span><span class="p" data-group-id="5159229401-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="5159229401-3">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="5159229401-3">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is bound to the value in the first byte of the binary. <code class="inline">Sz</code> is then
│ │ │ +used at the number of bytes to match out as a binary.</p><p>Starting in OTP 23, the size can be a guard expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="2145472700-1">(</span><span class="p" data-group-id="2145472700-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="p" data-group-id="2145472700-3">(</span><span class="p" data-group-id="2145472700-4">(</span><span class="n">Sz</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="2145472700-4">)</span><span class="o">*</span><span class="mi">8</span><span class="p" data-group-id="2145472700-3">)</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2145472700-2">&gt;&gt;</span><span class="p" data-group-id="2145472700-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2145472700-5">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="2145472700-5">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is the combined size of the header and the payload, so we will need to
│ │ │  subtract one byte to get the size of the payload.</p><h3 id="getting-the-rest-of-the-binary-or-bitstring" class="section-heading">
│ │ │    <a href="#getting-the-rest-of-the-binary-or-bitstring" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Getting the Rest of the Binary or Bitstring</span>
│ │ │  </h3>
│ │ │ -<p>To match out the rest of a binary, specify a binary field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="9991105587-1">(</span><span class="p" data-group-id="9991105587-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9991105587-2">&gt;&gt;</span><span class="p" data-group-id="9991105587-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>The size of the tail must be evenly divisible by 8.</p><p>To match out the rest of a bitstring, specify a field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="2354300167-1">(</span><span class="p" data-group-id="2354300167-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="2354300167-2">&gt;&gt;</span><span class="p" data-group-id="2354300167-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>There are no restrictions on the number of bits in the tail.</p><h2 id="appending-to-a-binary" class="section-heading">
│ │ │ +<p>To match out the rest of a binary, specify a binary field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="7816523416-1">(</span><span class="p" data-group-id="7816523416-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7816523416-2">&gt;&gt;</span><span class="p" data-group-id="7816523416-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>The size of the tail must be evenly divisible by 8.</p><p>To match out the rest of a bitstring, specify a field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="3369372810-1">(</span><span class="p" data-group-id="3369372810-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="3369372810-2">&gt;&gt;</span><span class="p" data-group-id="3369372810-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>There are no restrictions on the number of bits in the tail.</p><h2 id="appending-to-a-binary" class="section-heading">
│ │ │    <a href="#appending-to-a-binary" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Appending to a Binary</span>
│ │ │  </h2>
│ │ │ -<p>Appending to a binary in an efficient way can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">triples_to_bin</span><span class="p" data-group-id="3467180994-1">(</span><span class="n">T</span><span class="p" data-group-id="3467180994-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="3467180994-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3467180994-3">&lt;&lt;</span><span class="p" data-group-id="3467180994-3">&gt;&gt;</span><span class="p" data-group-id="3467180994-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Appending to a binary in an efficient way can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">triples_to_bin</span><span class="p" data-group-id="2477712116-1">(</span><span class="n">T</span><span class="p" data-group-id="2477712116-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="2477712116-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2477712116-3">&lt;&lt;</span><span class="p" data-group-id="2477712116-3">&gt;&gt;</span><span class="p" data-group-id="2477712116-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="3467180994-4">(</span><span class="p" data-group-id="3467180994-5">[</span><span class="p" data-group-id="3467180994-6">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p" data-group-id="3467180994-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3467180994-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3467180994-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="3467180994-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3467180994-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">X</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Z</span><span class="p">:</span><span class="mi">32</span><span class="p" data-group-id="3467180994-8">&gt;&gt;</span><span class="p" data-group-id="3467180994-7">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="3467180994-9">(</span><span class="p" data-group-id="3467180994-10">[</span><span class="p" data-group-id="3467180994-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="3467180994-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="2477712116-4">(</span><span class="p" data-group-id="2477712116-5">[</span><span class="p" data-group-id="2477712116-6">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p" data-group-id="2477712116-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2477712116-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2477712116-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="2477712116-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2477712116-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">X</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Z</span><span class="p">:</span><span class="mi">32</span><span class="p" data-group-id="2477712116-8">&gt;&gt;</span><span class="p" data-group-id="2477712116-7">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="2477712116-9">(</span><span class="p" data-group-id="2477712116-10">[</span><span class="p" data-group-id="2477712116-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2477712116-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="list_comprehensions.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/c_port.html
│ │ │ @@ -148,101 +148,101 @@
│ │ │  external program, if it is written properly).</p><p>The port is created using the BIF <a href="../../erts-15.2.7/doc/html/erlang.html#open_port/2"><code class="inline">open_port/2</code></a> with
│ │ │  <code class="inline">{spawn,ExtPrg}</code> as the first argument. The string <code class="inline">ExtPrg</code> is the name of the
│ │ │  external program, including any command line arguments. The second argument is a
│ │ │  list of options, in this case only <code class="inline">{packet,2}</code>. This option says that a 2 byte
│ │ │  length indicator is to be used to simplify the communication between C and
│ │ │  Erlang. The Erlang port automatically adds the length indicator, but this must
│ │ │  be done explicitly in the external C program.</p><p>The process is also set to trap exits, which enables detection of failure of the
│ │ │ -external program:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2702731708-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="2702731708-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2702731708-2">(</span><span class="p" data-group-id="2702731708-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2702731708-3">]</span><span class="p" data-group-id="2702731708-2">)</span><span class="p">.</span><span class="w">
│ │ │ +external program:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7633251253-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="7633251253-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7633251253-2">(</span><span class="p" data-group-id="7633251253-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7633251253-3">]</span><span class="p" data-group-id="7633251253-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="2702731708-4">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="2702731708-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nf">spawn</span><span class="p" data-group-id="2702731708-5">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2702731708-6">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="2702731708-6">]</span><span class="p" data-group-id="2702731708-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="7633251253-4">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="7633251253-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nf">spawn</span><span class="p" data-group-id="7633251253-5">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7633251253-6">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="7633251253-6">]</span><span class="p" data-group-id="7633251253-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="2702731708-7">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="2702731708-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nf">register</span><span class="p" data-group-id="2702731708-8">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2702731708-9">(</span><span class="p" data-group-id="2702731708-9">)</span><span class="p" data-group-id="2702731708-8">)</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="nf">process_flag</span><span class="p" data-group-id="2702731708-10">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2702731708-10">)</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="2702731708-11">(</span><span class="p" data-group-id="2702731708-12">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="2702731708-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2702731708-13">[</span><span class="p" data-group-id="2702731708-14">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2702731708-14">}</span><span class="p" data-group-id="2702731708-13">]</span><span class="p" data-group-id="2702731708-11">)</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="nf">loop</span><span class="p" data-group-id="2702731708-15">(</span><span class="n">Port</span><span class="p" data-group-id="2702731708-15">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex1:foo/1</code> and <code class="inline">complex1:bar/1</code> can be implemented. Both send a
│ │ │ -message to the <code class="inline">complex</code> process and receive the following replies:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="1346539913-1">(</span><span class="n">X</span><span class="p" data-group-id="1346539913-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nf">call_port</span><span class="p" data-group-id="1346539913-2">(</span><span class="p" data-group-id="1346539913-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1346539913-3">}</span><span class="p" data-group-id="1346539913-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="1346539913-4">(</span><span class="n">Y</span><span class="p" data-group-id="1346539913-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nf">call_port</span><span class="p" data-group-id="1346539913-5">(</span><span class="p" data-group-id="1346539913-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1346539913-6">}</span><span class="p" data-group-id="1346539913-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="7633251253-7">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="7633251253-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nf">register</span><span class="p" data-group-id="7633251253-8">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7633251253-9">(</span><span class="p" data-group-id="7633251253-9">)</span><span class="p" data-group-id="7633251253-8">)</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="nf">process_flag</span><span class="p" data-group-id="7633251253-10">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7633251253-10">)</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="7633251253-11">(</span><span class="p" data-group-id="7633251253-12">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="7633251253-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7633251253-13">[</span><span class="p" data-group-id="7633251253-14">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7633251253-14">}</span><span class="p" data-group-id="7633251253-13">]</span><span class="p" data-group-id="7633251253-11">)</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="nf">loop</span><span class="p" data-group-id="7633251253-15">(</span><span class="n">Port</span><span class="p" data-group-id="7633251253-15">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex1:foo/1</code> and <code class="inline">complex1:bar/1</code> can be implemented. Both send a
│ │ │ +message to the <code class="inline">complex</code> process and receive the following replies:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="5671871647-1">(</span><span class="n">X</span><span class="p" data-group-id="5671871647-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nf">call_port</span><span class="p" data-group-id="5671871647-2">(</span><span class="p" data-group-id="5671871647-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5671871647-3">}</span><span class="p" data-group-id="5671871647-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="5671871647-4">(</span><span class="n">Y</span><span class="p" data-group-id="5671871647-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nf">call_port</span><span class="p" data-group-id="5671871647-5">(</span><span class="p" data-group-id="5671871647-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5671871647-6">}</span><span class="p" data-group-id="5671871647-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="1346539913-7">(</span><span class="n">Msg</span><span class="p" data-group-id="1346539913-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1346539913-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1346539913-9">(</span><span class="p" data-group-id="1346539913-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1346539913-8">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="5671871647-7">(</span><span class="n">Msg</span><span class="p" data-group-id="5671871647-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5671871647-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5671871647-9">(</span><span class="p" data-group-id="5671871647-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="5671871647-8">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1346539913-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1346539913-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5671871647-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="5671871647-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │        </span><span class="n">Result</span><span class="w">
│ │ │ -  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process does the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="8558723685-1">(</span><span class="n">Port</span><span class="p" data-group-id="8558723685-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process does the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="5943665748-1">(</span><span class="n">Port</span><span class="p" data-group-id="5943665748-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8558723685-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8558723685-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -      </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8558723685-3">{</span><span class="nf">self</span><span class="p" data-group-id="8558723685-4">(</span><span class="p" data-group-id="8558723685-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8558723685-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="8558723685-6">(</span><span class="n">Msg</span><span class="p" data-group-id="8558723685-6">)</span><span class="p" data-group-id="8558723685-5">}</span><span class="p" data-group-id="8558723685-3">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5943665748-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="5943665748-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +      </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5943665748-3">{</span><span class="nf">self</span><span class="p" data-group-id="5943665748-4">(</span><span class="p" data-group-id="5943665748-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5943665748-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="5943665748-6">(</span><span class="n">Msg</span><span class="p" data-group-id="5943665748-6">)</span><span class="p" data-group-id="5943665748-5">}</span><span class="p" data-group-id="5943665748-3">}</span><span class="p">,</span><span class="w">
│ │ │        </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8558723685-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8558723685-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8558723685-8">}</span><span class="p" data-group-id="8558723685-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -          </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8558723685-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="8558723685-10">(</span><span class="n">Data</span><span class="p" data-group-id="8558723685-10">)</span><span class="p" data-group-id="8558723685-9">}</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5943665748-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5943665748-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5943665748-8">}</span><span class="p" data-group-id="5943665748-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +          </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5943665748-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="5943665748-10">(</span><span class="n">Data</span><span class="p" data-group-id="5943665748-10">)</span><span class="p" data-group-id="5943665748-9">}</span><span class="w">
│ │ │        </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -      </span><span class="nf">loop</span><span class="p" data-group-id="8558723685-11">(</span><span class="n">Port</span><span class="p" data-group-id="8558723685-11">)</span><span class="w">
│ │ │ +      </span><span class="nf">loop</span><span class="p" data-group-id="5943665748-11">(</span><span class="n">Port</span><span class="p" data-group-id="5943665748-11">)</span><span class="w">
│ │ │    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Assuming that both the arguments and the results from the C functions are less
│ │ │  than 256, a simple encoding/decoding scheme is employed. In this scheme, <code class="inline">foo</code>
│ │ │  is represented by byte 1, <code class="inline">bar</code> is represented by 2, and the argument/result is
│ │ │ -represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="6162758050-1">(</span><span class="p" data-group-id="6162758050-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6162758050-2">}</span><span class="p" data-group-id="6162758050-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6162758050-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6162758050-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="6162758050-4">(</span><span class="p" data-group-id="6162758050-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6162758050-5">}</span><span class="p" data-group-id="6162758050-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6162758050-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6162758050-6">]</span><span class="p">.</span><span class="w">
│ │ │ +represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="4144345706-1">(</span><span class="p" data-group-id="4144345706-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4144345706-2">}</span><span class="p" data-group-id="4144345706-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4144345706-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4144345706-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="4144345706-4">(</span><span class="p" data-group-id="4144345706-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4144345706-5">}</span><span class="p" data-group-id="4144345706-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4144345706-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4144345706-6">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="6162758050-7">(</span><span class="p" data-group-id="6162758050-8">[</span><span class="n">Int</span><span class="p" data-group-id="6162758050-8">]</span><span class="p" data-group-id="6162758050-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functionality for stopping the port and
│ │ │ -detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9088129792-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="9088129792-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9088129792-2">(</span><span class="p" data-group-id="9088129792-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9088129792-3">]</span><span class="p" data-group-id="9088129792-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9088129792-4">(</span><span class="p" data-group-id="9088129792-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9088129792-5">]</span><span class="p" data-group-id="9088129792-4">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="9088129792-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="9088129792-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9088129792-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9088129792-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="9088129792-8">]</span><span class="p" data-group-id="9088129792-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="9088129792-9">(</span><span class="p" data-group-id="9088129792-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="4144345706-7">(</span><span class="p" data-group-id="4144345706-8">[</span><span class="n">Int</span><span class="p" data-group-id="4144345706-8">]</span><span class="p" data-group-id="4144345706-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functionality for stopping the port and
│ │ │ +detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5137268292-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="5137268292-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5137268292-2">(</span><span class="p" data-group-id="5137268292-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5137268292-3">]</span><span class="p" data-group-id="5137268292-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5137268292-4">(</span><span class="p" data-group-id="5137268292-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5137268292-5">]</span><span class="p" data-group-id="5137268292-4">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="5137268292-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="5137268292-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="5137268292-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5137268292-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="5137268292-8">]</span><span class="p" data-group-id="5137268292-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="5137268292-9">(</span><span class="p" data-group-id="5137268292-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="9088129792-10">(</span><span class="n">X</span><span class="p" data-group-id="9088129792-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="9088129792-11">(</span><span class="p" data-group-id="9088129792-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9088129792-12">}</span><span class="p" data-group-id="9088129792-11">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="9088129792-13">(</span><span class="n">Y</span><span class="p" data-group-id="9088129792-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="9088129792-14">(</span><span class="p" data-group-id="9088129792-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9088129792-15">}</span><span class="p" data-group-id="9088129792-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="5137268292-10">(</span><span class="n">X</span><span class="p" data-group-id="5137268292-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="5137268292-11">(</span><span class="p" data-group-id="5137268292-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5137268292-12">}</span><span class="p" data-group-id="5137268292-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="5137268292-13">(</span><span class="n">Y</span><span class="p" data-group-id="5137268292-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="5137268292-14">(</span><span class="p" data-group-id="5137268292-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5137268292-15">}</span><span class="p" data-group-id="5137268292-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="9088129792-16">(</span><span class="n">Msg</span><span class="p" data-group-id="9088129792-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9088129792-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9088129792-18">(</span><span class="p" data-group-id="9088129792-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9088129792-17">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="5137268292-16">(</span><span class="n">Msg</span><span class="p" data-group-id="5137268292-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5137268292-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5137268292-18">(</span><span class="p" data-group-id="5137268292-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="5137268292-17">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="9088129792-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9088129792-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5137268292-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="5137268292-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="9088129792-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="9088129792-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9088129792-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9088129792-22">(</span><span class="p" data-group-id="9088129792-22">)</span><span class="p" data-group-id="9088129792-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9088129792-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9088129792-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="9088129792-24">(</span><span class="p" data-group-id="9088129792-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="9088129792-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9088129792-26">[</span><span class="p" data-group-id="9088129792-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9088129792-27">}</span><span class="p" data-group-id="9088129792-26">]</span><span class="p" data-group-id="9088129792-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="9088129792-28">(</span><span class="n">Port</span><span class="p" data-group-id="9088129792-28">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="5137268292-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="5137268292-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="5137268292-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5137268292-22">(</span><span class="p" data-group-id="5137268292-22">)</span><span class="p" data-group-id="5137268292-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="5137268292-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5137268292-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="5137268292-24">(</span><span class="p" data-group-id="5137268292-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="5137268292-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5137268292-26">[</span><span class="p" data-group-id="5137268292-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5137268292-27">}</span><span class="p" data-group-id="5137268292-26">]</span><span class="p" data-group-id="5137268292-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="5137268292-28">(</span><span class="n">Port</span><span class="p" data-group-id="5137268292-28">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="9088129792-29">(</span><span class="n">Port</span><span class="p" data-group-id="9088129792-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="5137268292-29">(</span><span class="n">Port</span><span class="p" data-group-id="5137268292-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="9088129792-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9088129792-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9088129792-31">{</span><span class="nf">self</span><span class="p" data-group-id="9088129792-32">(</span><span class="p" data-group-id="9088129792-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9088129792-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="9088129792-34">(</span><span class="n">Msg</span><span class="p" data-group-id="9088129792-34">)</span><span class="p" data-group-id="9088129792-33">}</span><span class="p" data-group-id="9088129792-31">}</span><span class="p">,</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5137268292-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="5137268292-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5137268292-31">{</span><span class="nf">self</span><span class="p" data-group-id="5137268292-32">(</span><span class="p" data-group-id="5137268292-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5137268292-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="5137268292-34">(</span><span class="n">Msg</span><span class="p" data-group-id="5137268292-34">)</span><span class="p" data-group-id="5137268292-33">}</span><span class="p" data-group-id="5137268292-31">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="9088129792-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9088129792-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9088129792-36">}</span><span class="p" data-group-id="9088129792-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9088129792-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="9088129792-38">(</span><span class="n">Data</span><span class="p" data-group-id="9088129792-38">)</span><span class="p" data-group-id="9088129792-37">}</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="5137268292-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5137268292-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5137268292-36">}</span><span class="p" data-group-id="5137268292-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5137268292-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="5137268292-38">(</span><span class="n">Data</span><span class="p" data-group-id="5137268292-38">)</span><span class="p" data-group-id="5137268292-37">}</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="9088129792-39">(</span><span class="n">Port</span><span class="p" data-group-id="9088129792-39">)</span><span class="p">;</span><span class="w">
│ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="5137268292-39">(</span><span class="n">Port</span><span class="p" data-group-id="5137268292-39">)</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9088129792-40">{</span><span class="nf">self</span><span class="p" data-group-id="9088129792-41">(</span><span class="p" data-group-id="9088129792-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="9088129792-40">}</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5137268292-40">{</span><span class="nf">self</span><span class="p" data-group-id="5137268292-41">(</span><span class="p" data-group-id="5137268292-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="5137268292-40">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="9088129792-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="9088129792-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="9088129792-43">(</span><span class="ss">normal</span><span class="p" data-group-id="9088129792-43">)</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="5137268292-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="5137268292-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="5137268292-43">(</span><span class="ss">normal</span><span class="p" data-group-id="5137268292-43">)</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="9088129792-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="9088129792-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="9088129792-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="9088129792-45">)</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5137268292-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5137268292-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="5137268292-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="5137268292-45">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="9088129792-46">(</span><span class="p" data-group-id="9088129792-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9088129792-47">}</span><span class="p" data-group-id="9088129792-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9088129792-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9088129792-48">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="9088129792-49">(</span><span class="p" data-group-id="9088129792-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9088129792-50">}</span><span class="p" data-group-id="9088129792-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9088129792-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9088129792-51">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="5137268292-46">(</span><span class="p" data-group-id="5137268292-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5137268292-47">}</span><span class="p" data-group-id="5137268292-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5137268292-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5137268292-48">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="5137268292-49">(</span><span class="p" data-group-id="5137268292-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5137268292-50">}</span><span class="p" data-group-id="5137268292-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5137268292-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5137268292-51">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="9088129792-52">(</span><span class="p" data-group-id="9088129792-53">[</span><span class="n">Int</span><span class="p" data-group-id="9088129792-53">]</span><span class="p" data-group-id="9088129792-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-program" class="section-heading">
│ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="5137268292-52">(</span><span class="p" data-group-id="5137268292-53">[</span><span class="n">Int</span><span class="p" data-group-id="5137268292-53">]</span><span class="p" data-group-id="5137268292-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-program" class="section-heading">
│ │ │    <a href="#c-program" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">C Program</span>
│ │ │  </h2>
│ │ │  <p>On the C side, it is necessary to write functions for receiving and sending data
│ │ │  with 2 byte length indicators from/to Erlang. By default, the C program is to
│ │ │ @@ -333,25 +333,25 @@
│ │ │  and terminates.</p><h2 id="running-the-example" class="section-heading">
│ │ │    <a href="#running-the-example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running the Example</span>
│ │ │  </h2>
│ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">$ gcc -o extprg complex.c erl_comm.c port.c</code></pre><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$ </span><span class="ss">erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="1824705370-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="1824705370-1">]</span><span class="w"> </span><span class="p" data-group-id="1824705370-2">[</span><span class="ss">source</span><span class="p" data-group-id="1824705370-2">]</span><span class="w"> </span><span class="p" data-group-id="1824705370-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="1824705370-3">]</span><span class="w"> </span><span class="p" data-group-id="1824705370-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="1824705370-4">]</span><span class="w"> </span><span class="p" data-group-id="1824705370-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="1824705370-5">]</span><span class="w"> </span><span class="p" data-group-id="1824705370-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="1824705370-6">]</span><span class="w"> </span><span class="p" data-group-id="1824705370-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="1824705370-7">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="4971109986-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="4971109986-1">]</span><span class="w"> </span><span class="p" data-group-id="4971109986-2">[</span><span class="ss">source</span><span class="p" data-group-id="4971109986-2">]</span><span class="w"> </span><span class="p" data-group-id="4971109986-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4971109986-3">]</span><span class="w"> </span><span class="p" data-group-id="4971109986-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4971109986-4">]</span><span class="w"> </span><span class="p" data-group-id="4971109986-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4971109986-5">]</span><span class="w"> </span><span class="p" data-group-id="4971109986-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4971109986-6">]</span><span class="w"> </span><span class="p" data-group-id="4971109986-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="4971109986-7">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="1824705370-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="1824705370-9">(</span><span class="p" data-group-id="1824705370-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="1824705370-8">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nf">c</span><span class="p" data-group-id="1824705370-10">(</span><span class="ss">complex1</span><span class="p" data-group-id="1824705370-10">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1824705370-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex1</span><span class="p" data-group-id="1824705370-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0262516485-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="0262516485-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="4971109986-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="4971109986-9">(</span><span class="p" data-group-id="4971109986-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="4971109986-8">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="nf">c</span><span class="p" data-group-id="4971109986-10">(</span><span class="ss">complex1</span><span class="p" data-group-id="4971109986-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4971109986-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex1</span><span class="p" data-group-id="4971109986-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0154586169-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="0154586169-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="0262516485-2">(</span><span class="mi">3</span><span class="p" data-group-id="0262516485-2">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="0154586169-2">(</span><span class="mi">3</span><span class="p" data-group-id="0154586169-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="0262516485-3">(</span><span class="mi">5</span><span class="p" data-group-id="0262516485-3">)</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="0154586169-3">(</span><span class="mi">5</span><span class="p" data-group-id="0154586169-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="0262516485-4">(</span><span class="p" data-group-id="0262516485-4">)</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="0154586169-4">(</span><span class="p" data-group-id="0154586169-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="example.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/c_portdriver.html
│ │ │ @@ -151,112 +151,112 @@
│ │ │  <p>Like a port program, the port communicates with an Erlang process. All
│ │ │  communication goes through one Erlang process that is the <em>connected process</em> of
│ │ │  the port driver. Terminating this process closes the port driver.</p><p>Before the port is created, the driver must be loaded. This is done with the
│ │ │  function <a href="../../lib/kernel-10.2.7.1/doc/html/erl_ddll.html#load_driver/2"><code class="inline">erl_ddll:load_driver/2</code></a>, with the name of the shared library as
│ │ │  argument.</p><p>The port is then created using the BIF <a href="../../erts-15.2.7/doc/html/erlang.html#open_port/2"><code class="inline">open_port/2</code></a>, with the
│ │ │  tuple <code class="inline">{spawn, DriverName}</code> as the first argument. The string <code class="inline">SharedLib</code> is the
│ │ │  name of the port driver. The second argument is a list of options, none in this
│ │ │ -case:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3048332660-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="3048332660-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3048332660-2">(</span><span class="p" data-group-id="3048332660-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3048332660-3">]</span><span class="p" data-group-id="3048332660-2">)</span><span class="p">.</span><span class="w">
│ │ │ +case:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8727629185-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="8727629185-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8727629185-2">(</span><span class="p" data-group-id="8727629185-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8727629185-3">]</span><span class="p" data-group-id="8727629185-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="3048332660-4">(</span><span class="n">SharedLib</span><span class="p" data-group-id="3048332660-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="3048332660-5">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="3048332660-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8727629185-4">(</span><span class="n">SharedLib</span><span class="p" data-group-id="8727629185-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="8727629185-5">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="8727629185-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3048332660-6">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="3048332660-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="3048332660-7">(</span><span class="p" data-group-id="3048332660-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="3048332660-8">}</span><span class="p" data-group-id="3048332660-7">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8727629185-6">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="8727629185-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="8727629185-7">(</span><span class="p" data-group-id="8727629185-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="8727629185-8">}</span><span class="p" data-group-id="8727629185-7">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="3048332660-9">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3048332660-10">[</span><span class="n">SharedLib</span><span class="p" data-group-id="3048332660-10">]</span><span class="p" data-group-id="3048332660-9">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="8727629185-9">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8727629185-10">[</span><span class="n">SharedLib</span><span class="p" data-group-id="8727629185-10">]</span><span class="p" data-group-id="8727629185-9">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="3048332660-11">(</span><span class="n">SharedLib</span><span class="p" data-group-id="3048332660-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nf">register</span><span class="p" data-group-id="3048332660-12">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3048332660-13">(</span><span class="p" data-group-id="3048332660-13">)</span><span class="p" data-group-id="3048332660-12">)</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="3048332660-14">(</span><span class="p" data-group-id="3048332660-15">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="3048332660-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3048332660-16">[</span><span class="p" data-group-id="3048332660-16">]</span><span class="p" data-group-id="3048332660-14">)</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="nf">loop</span><span class="p" data-group-id="3048332660-17">(</span><span class="n">Port</span><span class="p" data-group-id="3048332660-17">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex5:foo/1</code> and <code class="inline">complex5:bar/1</code> can be implemented. Both send a
│ │ │ -message to the <code class="inline">complex</code> process and receive the following reply:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="4503087840-1">(</span><span class="n">X</span><span class="p" data-group-id="4503087840-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="4503087840-2">(</span><span class="p" data-group-id="4503087840-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4503087840-3">}</span><span class="p" data-group-id="4503087840-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="4503087840-4">(</span><span class="n">Y</span><span class="p" data-group-id="4503087840-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="4503087840-5">(</span><span class="p" data-group-id="4503087840-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4503087840-6">}</span><span class="p" data-group-id="4503087840-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8727629185-11">(</span><span class="n">SharedLib</span><span class="p" data-group-id="8727629185-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nf">register</span><span class="p" data-group-id="8727629185-12">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8727629185-13">(</span><span class="p" data-group-id="8727629185-13">)</span><span class="p" data-group-id="8727629185-12">)</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="8727629185-14">(</span><span class="p" data-group-id="8727629185-15">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="8727629185-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8727629185-16">[</span><span class="p" data-group-id="8727629185-16">]</span><span class="p" data-group-id="8727629185-14">)</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="nf">loop</span><span class="p" data-group-id="8727629185-17">(</span><span class="n">Port</span><span class="p" data-group-id="8727629185-17">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex5:foo/1</code> and <code class="inline">complex5:bar/1</code> can be implemented. Both send a
│ │ │ +message to the <code class="inline">complex</code> process and receive the following reply:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="1572039186-1">(</span><span class="n">X</span><span class="p" data-group-id="1572039186-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="1572039186-2">(</span><span class="p" data-group-id="1572039186-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1572039186-3">}</span><span class="p" data-group-id="1572039186-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="1572039186-4">(</span><span class="n">Y</span><span class="p" data-group-id="1572039186-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="1572039186-5">(</span><span class="p" data-group-id="1572039186-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1572039186-6">}</span><span class="p" data-group-id="1572039186-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="4503087840-7">(</span><span class="n">Msg</span><span class="p" data-group-id="4503087840-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4503087840-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4503087840-9">(</span><span class="p" data-group-id="4503087840-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4503087840-8">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="1572039186-7">(</span><span class="n">Msg</span><span class="p" data-group-id="1572039186-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1572039186-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1572039186-9">(</span><span class="p" data-group-id="1572039186-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1572039186-8">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4503087840-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="4503087840-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="1572039186-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1572039186-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Result</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process performs the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="7023226781-1">(</span><span class="n">Port</span><span class="p" data-group-id="7023226781-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process performs the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="6819845773-1">(</span><span class="n">Port</span><span class="p" data-group-id="6819845773-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7023226781-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7023226781-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7023226781-3">{</span><span class="nf">self</span><span class="p" data-group-id="7023226781-4">(</span><span class="p" data-group-id="7023226781-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7023226781-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="7023226781-6">(</span><span class="n">Msg</span><span class="p" data-group-id="7023226781-6">)</span><span class="p" data-group-id="7023226781-5">}</span><span class="p" data-group-id="7023226781-3">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="6819845773-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6819845773-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6819845773-3">{</span><span class="nf">self</span><span class="p" data-group-id="6819845773-4">(</span><span class="p" data-group-id="6819845773-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6819845773-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="6819845773-6">(</span><span class="n">Msg</span><span class="p" data-group-id="6819845773-6">)</span><span class="p" data-group-id="6819845773-5">}</span><span class="p" data-group-id="6819845773-3">}</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="k">receive</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="7023226781-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7023226781-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7023226781-8">}</span><span class="p" data-group-id="7023226781-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7023226781-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="7023226781-10">(</span><span class="n">Data</span><span class="p" data-group-id="7023226781-10">)</span><span class="p" data-group-id="7023226781-9">}</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="6819845773-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6819845773-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6819845773-8">}</span><span class="p" data-group-id="6819845773-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6819845773-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="6819845773-10">(</span><span class="n">Data</span><span class="p" data-group-id="6819845773-10">)</span><span class="p" data-group-id="6819845773-9">}</span><span class="w">
│ │ │              </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="7023226781-11">(</span><span class="n">Port</span><span class="p" data-group-id="7023226781-11">)</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="6819845773-11">(</span><span class="n">Port</span><span class="p" data-group-id="6819845773-11">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Assuming that both the arguments and the results from the C functions are less
│ │ │  than 256, a simple encoding/decoding scheme is employed. In this scheme, <code class="inline">foo</code>
│ │ │  is represented by byte 1, <code class="inline">bar</code> is represented by 2, and the argument/result is
│ │ │ -represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="8391296407-1">(</span><span class="p" data-group-id="8391296407-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8391296407-2">}</span><span class="p" data-group-id="8391296407-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8391296407-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8391296407-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="8391296407-4">(</span><span class="p" data-group-id="8391296407-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8391296407-5">}</span><span class="p" data-group-id="8391296407-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8391296407-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8391296407-6">]</span><span class="p">.</span><span class="w">
│ │ │ +represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="1404287136-1">(</span><span class="p" data-group-id="1404287136-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1404287136-2">}</span><span class="p" data-group-id="1404287136-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1404287136-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1404287136-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="1404287136-4">(</span><span class="p" data-group-id="1404287136-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1404287136-5">}</span><span class="p" data-group-id="1404287136-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1404287136-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1404287136-6">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="8391296407-7">(</span><span class="p" data-group-id="8391296407-8">[</span><span class="n">Int</span><span class="p" data-group-id="8391296407-8">]</span><span class="p" data-group-id="8391296407-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functions for stopping the port and
│ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="1404287136-7">(</span><span class="p" data-group-id="1404287136-8">[</span><span class="n">Int</span><span class="p" data-group-id="1404287136-8">]</span><span class="p" data-group-id="1404287136-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functions for stopping the port and
│ │ │  detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9588535341-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="9588535341-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9588535341-2">(</span><span class="p" data-group-id="9588535341-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9588535341-3">]</span><span class="p" data-group-id="9588535341-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9588535341-4">(</span><span class="p" data-group-id="9588535341-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9588535341-5">]</span><span class="p" data-group-id="9588535341-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5696686420-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="5696686420-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5696686420-2">(</span><span class="p" data-group-id="5696686420-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5696686420-3">]</span><span class="p" data-group-id="5696686420-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5696686420-4">(</span><span class="p" data-group-id="5696686420-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5696686420-5">]</span><span class="p" data-group-id="5696686420-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="9588535341-6">(</span><span class="n">SharedLib</span><span class="p" data-group-id="9588535341-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="9588535341-7">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="9588535341-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="5696686420-6">(</span><span class="n">SharedLib</span><span class="p" data-group-id="5696686420-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="5696686420-7">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="5696686420-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │  	</span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="9588535341-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="9588535341-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="9588535341-9">(</span><span class="p" data-group-id="9588535341-10">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="9588535341-10">}</span><span class="p" data-group-id="9588535341-9">)</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5696686420-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="5696686420-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ +	</span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="5696686420-9">(</span><span class="p" data-group-id="5696686420-10">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="5696686420-10">}</span><span class="p" data-group-id="5696686420-9">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9588535341-11">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9588535341-12">[</span><span class="n">SharedLib</span><span class="p" data-group-id="9588535341-12">]</span><span class="p" data-group-id="9588535341-11">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="5696686420-11">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5696686420-12">[</span><span class="n">SharedLib</span><span class="p" data-group-id="5696686420-12">]</span><span class="p" data-group-id="5696686420-11">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="9588535341-13">(</span><span class="n">SharedLib</span><span class="p" data-group-id="9588535341-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9588535341-14">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9588535341-15">(</span><span class="p" data-group-id="9588535341-15">)</span><span class="p" data-group-id="9588535341-14">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="9588535341-16">(</span><span class="p" data-group-id="9588535341-17">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="9588535341-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9588535341-18">[</span><span class="p" data-group-id="9588535341-18">]</span><span class="p" data-group-id="9588535341-16">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="9588535341-19">(</span><span class="n">Port</span><span class="p" data-group-id="9588535341-19">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="5696686420-13">(</span><span class="n">SharedLib</span><span class="p" data-group-id="5696686420-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="5696686420-14">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5696686420-15">(</span><span class="p" data-group-id="5696686420-15">)</span><span class="p" data-group-id="5696686420-14">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="5696686420-16">(</span><span class="p" data-group-id="5696686420-17">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="5696686420-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5696686420-18">[</span><span class="p" data-group-id="5696686420-18">]</span><span class="p" data-group-id="5696686420-16">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="5696686420-19">(</span><span class="n">Port</span><span class="p" data-group-id="5696686420-19">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="9588535341-20">(</span><span class="p" data-group-id="9588535341-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="5696686420-20">(</span><span class="p" data-group-id="5696686420-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="9588535341-21">(</span><span class="n">X</span><span class="p" data-group-id="9588535341-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="9588535341-22">(</span><span class="p" data-group-id="9588535341-23">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9588535341-23">}</span><span class="p" data-group-id="9588535341-22">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="9588535341-24">(</span><span class="n">Y</span><span class="p" data-group-id="9588535341-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="9588535341-25">(</span><span class="p" data-group-id="9588535341-26">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9588535341-26">}</span><span class="p" data-group-id="9588535341-25">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="5696686420-21">(</span><span class="n">X</span><span class="p" data-group-id="5696686420-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="5696686420-22">(</span><span class="p" data-group-id="5696686420-23">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5696686420-23">}</span><span class="p" data-group-id="5696686420-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="5696686420-24">(</span><span class="n">Y</span><span class="p" data-group-id="5696686420-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="5696686420-25">(</span><span class="p" data-group-id="5696686420-26">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5696686420-26">}</span><span class="p" data-group-id="5696686420-25">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="9588535341-27">(</span><span class="n">Msg</span><span class="p" data-group-id="9588535341-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9588535341-28">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9588535341-29">(</span><span class="p" data-group-id="9588535341-29">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9588535341-28">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="5696686420-27">(</span><span class="n">Msg</span><span class="p" data-group-id="5696686420-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5696686420-28">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5696686420-29">(</span><span class="p" data-group-id="5696686420-29">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="5696686420-28">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="9588535341-30">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9588535341-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5696686420-30">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="5696686420-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="9588535341-31">(</span><span class="n">Port</span><span class="p" data-group-id="9588535341-31">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="5696686420-31">(</span><span class="n">Port</span><span class="p" data-group-id="5696686420-31">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="9588535341-32">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9588535341-32">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9588535341-33">{</span><span class="nf">self</span><span class="p" data-group-id="9588535341-34">(</span><span class="p" data-group-id="9588535341-34">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9588535341-35">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="9588535341-36">(</span><span class="n">Msg</span><span class="p" data-group-id="9588535341-36">)</span><span class="p" data-group-id="9588535341-35">}</span><span class="p" data-group-id="9588535341-33">}</span><span class="p">,</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5696686420-32">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="5696686420-32">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5696686420-33">{</span><span class="nf">self</span><span class="p" data-group-id="5696686420-34">(</span><span class="p" data-group-id="5696686420-34">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5696686420-35">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="5696686420-36">(</span><span class="n">Msg</span><span class="p" data-group-id="5696686420-36">)</span><span class="p" data-group-id="5696686420-35">}</span><span class="p" data-group-id="5696686420-33">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="9588535341-37">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9588535341-38">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9588535341-38">}</span><span class="p" data-group-id="9588535341-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9588535341-39">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="9588535341-40">(</span><span class="n">Data</span><span class="p" data-group-id="9588535341-40">)</span><span class="p" data-group-id="9588535341-39">}</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="5696686420-37">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5696686420-38">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5696686420-38">}</span><span class="p" data-group-id="5696686420-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5696686420-39">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="5696686420-40">(</span><span class="n">Data</span><span class="p" data-group-id="5696686420-40">)</span><span class="p" data-group-id="5696686420-39">}</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="9588535341-41">(</span><span class="n">Port</span><span class="p" data-group-id="9588535341-41">)</span><span class="p">;</span><span class="w">
│ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="5696686420-41">(</span><span class="n">Port</span><span class="p" data-group-id="5696686420-41">)</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9588535341-42">{</span><span class="nf">self</span><span class="p" data-group-id="9588535341-43">(</span><span class="p" data-group-id="9588535341-43">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="9588535341-42">}</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5696686420-42">{</span><span class="nf">self</span><span class="p" data-group-id="5696686420-43">(</span><span class="p" data-group-id="5696686420-43">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="5696686420-42">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="9588535341-44">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="9588535341-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="9588535341-45">(</span><span class="ss">normal</span><span class="p" data-group-id="9588535341-45">)</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="5696686420-44">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="5696686420-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="5696686420-45">(</span><span class="ss">normal</span><span class="p" data-group-id="5696686420-45">)</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="9588535341-46">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="9588535341-46">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9588535341-47">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9588535341-48">[</span><span class="n">Reason</span><span class="p" data-group-id="9588535341-48">]</span><span class="p" data-group-id="9588535341-47">)</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="9588535341-49">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="9588535341-49">)</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5696686420-46">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5696686420-46">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5696686420-47">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5696686420-48">[</span><span class="n">Reason</span><span class="p" data-group-id="5696686420-48">]</span><span class="p" data-group-id="5696686420-47">)</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="5696686420-49">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="5696686420-49">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="9588535341-50">(</span><span class="p" data-group-id="9588535341-51">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9588535341-51">}</span><span class="p" data-group-id="9588535341-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9588535341-52">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9588535341-52">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="9588535341-53">(</span><span class="p" data-group-id="9588535341-54">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9588535341-54">}</span><span class="p" data-group-id="9588535341-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9588535341-55">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9588535341-55">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="5696686420-50">(</span><span class="p" data-group-id="5696686420-51">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5696686420-51">}</span><span class="p" data-group-id="5696686420-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5696686420-52">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5696686420-52">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="5696686420-53">(</span><span class="p" data-group-id="5696686420-54">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5696686420-54">}</span><span class="p" data-group-id="5696686420-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5696686420-55">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5696686420-55">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="9588535341-56">(</span><span class="p" data-group-id="9588535341-57">[</span><span class="n">Int</span><span class="p" data-group-id="9588535341-57">]</span><span class="p" data-group-id="9588535341-56">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-driver" class="section-heading">
│ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="5696686420-56">(</span><span class="p" data-group-id="5696686420-57">[</span><span class="n">Int</span><span class="p" data-group-id="5696686420-57">]</span><span class="p" data-group-id="5696686420-56">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-driver" class="section-heading">
│ │ │    <a href="#c-driver" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">C Driver</span>
│ │ │  </h2>
│ │ │  <p>The C driver is a module that is compiled and linked into a shared library. It
│ │ │  uses a driver structure and includes the header file <code class="inline">erl_driver.h</code>.</p><p>The driver structure is filled with the driver name and function pointers. It is
│ │ │ @@ -347,25 +347,25 @@
│ │ │    <a href="#running-the-example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running the Example</span>
│ │ │  </h2>
│ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">unix&gt; gcc -o example_drv.so -fpic -shared complex.c port_driver.c
│ │ │  windows&gt; cl -LD -MD -Fe example_drv.dll complex.c port_driver.c</code></pre><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="ss">erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="0968494730-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="0968494730-1">]</span><span class="w"> </span><span class="p" data-group-id="0968494730-2">[</span><span class="ss">source</span><span class="p" data-group-id="0968494730-2">]</span><span class="w"> </span><span class="p" data-group-id="0968494730-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0968494730-3">]</span><span class="w"> </span><span class="p" data-group-id="0968494730-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0968494730-4">]</span><span class="w"> </span><span class="p" data-group-id="0968494730-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="0968494730-5">]</span><span class="w"> </span><span class="p" data-group-id="0968494730-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0968494730-6">]</span><span class="w"> </span><span class="p" data-group-id="0968494730-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="0968494730-7">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="2242922017-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="2242922017-1">]</span><span class="w"> </span><span class="p" data-group-id="2242922017-2">[</span><span class="ss">source</span><span class="p" data-group-id="2242922017-2">]</span><span class="w"> </span><span class="p" data-group-id="2242922017-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="2242922017-3">]</span><span class="w"> </span><span class="p" data-group-id="2242922017-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="2242922017-4">]</span><span class="w"> </span><span class="p" data-group-id="2242922017-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="2242922017-5">]</span><span class="w"> </span><span class="p" data-group-id="2242922017-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2242922017-6">]</span><span class="w"> </span><span class="p" data-group-id="2242922017-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="2242922017-7">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="0968494730-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="0968494730-9">(</span><span class="p" data-group-id="0968494730-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="0968494730-8">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nf">c</span><span class="p" data-group-id="0968494730-10">(</span><span class="ss">complex5</span><span class="p" data-group-id="0968494730-10">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0968494730-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex5</span><span class="p" data-group-id="0968494730-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1932464348-1">(</span><span class="s">&quot;example_drv&quot;</span><span class="p" data-group-id="1932464348-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="2242922017-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="2242922017-9">(</span><span class="p" data-group-id="2242922017-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="2242922017-8">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="nf">c</span><span class="p" data-group-id="2242922017-10">(</span><span class="ss">complex5</span><span class="p" data-group-id="2242922017-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2242922017-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex5</span><span class="p" data-group-id="2242922017-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7327072643-1">(</span><span class="s">&quot;example_drv&quot;</span><span class="p" data-group-id="7327072643-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="1932464348-2">(</span><span class="mi">3</span><span class="p" data-group-id="1932464348-2">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="7327072643-2">(</span><span class="mi">3</span><span class="p" data-group-id="7327072643-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="1932464348-3">(</span><span class="mi">5</span><span class="p" data-group-id="1932464348-3">)</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="7327072643-3">(</span><span class="mi">5</span><span class="p" data-group-id="7327072643-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="1932464348-4">(</span><span class="p" data-group-id="1932464348-4">)</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="7327072643-4">(</span><span class="p" data-group-id="7327072643-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="erl_interface.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/code_loading.html
│ │ │ @@ -122,16 +122,16 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Compilation</span>
│ │ │  </h2>
│ │ │  <p>Erlang programs must be <em>compiled</em> to object code. The compiler can generate a
│ │ │  new file that contains the object code. The current abstract machine, which runs
│ │ │  the object code, is called BEAM, therefore the object files get the suffix
│ │ │ -<code class="inline">.beam</code>. The compiler can also generate a binary which can be loaded directly.</p><p>The compiler is located in the module <a href="../../lib/compiler-8.6.1/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><pre><code class="makeup erlang" translate="no"><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="9799848744-1">(</span><span class="n">Module</span><span class="p" data-group-id="9799848744-1">)</span><span class="w">
│ │ │ -</span><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="9799848744-2">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="9799848744-2">)</span></code></pre><p>The Erlang shell understands the command <code class="inline">c(Module)</code>, which both compiles and
│ │ │ +<code class="inline">.beam</code>. The compiler can also generate a binary which can be loaded directly.</p><p>The compiler is located in the module <a href="../../lib/compiler-8.6.1/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><pre><code class="makeup erlang" translate="no"><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="4725836036-1">(</span><span class="n">Module</span><span class="p" data-group-id="4725836036-1">)</span><span class="w">
│ │ │ +</span><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="4725836036-2">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="4725836036-2">)</span></code></pre><p>The Erlang shell understands the command <code class="inline">c(Module)</code>, which both compiles and
│ │ │  loads <code class="inline">Module</code>.</p><p>There is also a module <code class="inline">make</code>, which provides a set of functions similar to the
│ │ │  UNIX type Make functions, see module <a href="../../lib/tools-4.1.1/doc/html/make.html"><code class="inline">make</code></a> in Tools.</p><p>The compiler can also be accessed from the OS prompt using the
│ │ │  <a href="../../erts-15.2.7/doc/html/erl_cmd.html">erl</a> executable in ERTS.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -compile Module1...ModuleN</span><span class="w">
│ │ │  </span><span class="c1">% erl -make</span></code></pre><p>The <code class="inline">erlc</code> program provides way to compile modules from the OS
│ │ │  shell, see the <a href="../../erts-15.2.7/doc/html/erlc_cmd.html">erlc</a> executable in ERTS. It
│ │ │  understands a number of flags that can be used to define macros, add search
│ │ │  paths for include files, and more.</p><pre><code class="text">% erlc &lt;flags&gt; File1.erl...FileN.erl</code></pre><p><a href="" id="loading"></a></p><h2 id="code-loading" class="section-heading">
│ │ │ @@ -156,54 +156,54 @@
│ │ │  When a module is loaded into the system for the first time, the code becomes
│ │ │  'current'. If then a new instance of the module is loaded, the code of the
│ │ │  previous instance becomes 'old' and the new instance becomes 'current'.</p><p>Both old and current code is valid, and can be evaluated concurrently. Fully
│ │ │  qualified function calls always refer to current code. Old code can still be
│ │ │  evaluated because of processes lingering in the old code.</p><p>If a third instance of the module is loaded, the code server removes (purges)
│ │ │  the old code and any processes lingering in it is terminated. Then the third
│ │ │  instance becomes 'current' and the previously current code becomes 'old'.</p><p>To change from old code to current code, a process must make a fully qualified
│ │ │ -function call.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3467715073-1">(</span><span class="ss">m</span><span class="p" data-group-id="3467715073-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3467715073-2">(</span><span class="p" data-group-id="3467715073-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3467715073-3">]</span><span class="p" data-group-id="3467715073-2">)</span><span class="p">.</span><span class="w">
│ │ │ +function call.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5277972552-1">(</span><span class="ss">m</span><span class="p" data-group-id="5277972552-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5277972552-2">(</span><span class="p" data-group-id="5277972552-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5277972552-3">]</span><span class="p" data-group-id="5277972552-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="3467715073-4">(</span><span class="p" data-group-id="3467715073-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="5277972552-4">(</span><span class="p" data-group-id="5277972552-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">code_switch</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">m</span><span class="p">:</span><span class="nf">loop</span><span class="p" data-group-id="3467715073-5">(</span><span class="p" data-group-id="3467715073-5">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="nc">m</span><span class="p">:</span><span class="nf">loop</span><span class="p" data-group-id="5277972552-5">(</span><span class="p" data-group-id="5277972552-5">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">Msg</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="3467715073-6">(</span><span class="p" data-group-id="3467715073-6">)</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="5277972552-6">(</span><span class="p" data-group-id="5277972552-6">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>To make the process change code, send the message <code class="inline">code_switch</code> to it. The
│ │ │  process then makes a fully qualified call to <code class="inline">m:loop()</code> and changes to current
│ │ │  code. Notice that <code class="inline">m:loop/0</code> must be exported.</p><p>For code replacement of funs to work, use the syntax
│ │ │  <code class="inline">fun Module:FunctionName/Arity</code>.</p><p><a href="" id="on_load"></a></p><h2 id="running-a-function-when-a-module-is-loaded" class="section-heading">
│ │ │    <a href="#running-a-function-when-a-module-is-loaded" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running a Function When a Module is Loaded</span>
│ │ │  </h2>
│ │ │  <p>The <code class="inline">-on_load()</code> directive names a function that is to be run automatically when
│ │ │ -a module is loaded.</p><p>Its syntax is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="7471039786-1">(</span><span class="n">Name</span><span class="o">/</span><span class="mi">0</span><span class="p" data-group-id="7471039786-1">)</span><span class="p">.</span></code></pre><p>It is not necessary to export the function. It is called in a freshly spawned
│ │ │ +a module is loaded.</p><p>Its syntax is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="6251301642-1">(</span><span class="n">Name</span><span class="o">/</span><span class="mi">0</span><span class="p" data-group-id="6251301642-1">)</span><span class="p">.</span></code></pre><p>It is not necessary to export the function. It is called in a freshly spawned
│ │ │  process (which terminates as soon as the function returns).</p><p>The function must return <code class="inline">ok</code> if the module is to become the new current code
│ │ │  for the module and become callable.</p><p>Returning any other value or generating an exception causes the new code to be
│ │ │  unloaded. If the return value is not an atom, a warning error report is sent to
│ │ │  the error logger.</p><p>If there already is current code for the module, that code will remain current
│ │ │  and can be called until the <code class="inline">on_load</code> function has returned. If the <code class="inline">on_load</code>
│ │ │  function fails, the current code (if any) will remain current. If there is no
│ │ │  current code for a module, any process that makes an external call to the module
│ │ │  before the <code class="inline">on_load</code> function has finished will be suspended until the <code class="inline">on_load</code>
│ │ │  function have finished.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 19, if the <code class="inline">on_load</code> function failed, any previously current
│ │ │  code would become old, essentially leaving the system without any working and
│ │ │  reachable instance of the module.</p></section><p>In embedded mode, first all modules are loaded. Then all <code class="inline">on_load</code> functions are
│ │ │  called. The system is terminated unless all of the <code class="inline">on_load</code> functions return
│ │ │ -<code class="inline">ok</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1067606296-1">(</span><span class="ss">m</span><span class="p" data-group-id="1067606296-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="1067606296-2">(</span><span class="ss">load_my_nifs</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1067606296-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">ok</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6255580804-1">(</span><span class="ss">m</span><span class="p" data-group-id="6255580804-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="6255580804-2">(</span><span class="ss">load_my_nifs</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6255580804-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">load_my_nifs</span><span class="p" data-group-id="1067606296-3">(</span><span class="p" data-group-id="1067606296-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">load_my_nifs</span><span class="p" data-group-id="6255580804-3">(</span><span class="p" data-group-id="6255580804-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NifPath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">    </span><span class="c1">%Set up the path to the NIF library.</span><span class="w">
│ │ │      </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">       </span><span class="c1">%Initialize the Info term</span><span class="w">
│ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="1067606296-4">(</span><span class="n">NifPath</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="1067606296-4">)</span><span class="p">.</span></code></pre><p>If the call to <a href="../../erts-15.2.7/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a> fails, the module is unloaded and a warning
│ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="6255580804-4">(</span><span class="n">NifPath</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="6255580804-4">)</span><span class="p">.</span></code></pre><p>If the call to <a href="../../erts-15.2.7/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a> fails, the module is unloaded and a warning
│ │ │  report is sent to the error loader.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="distributed.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/commoncaveats.html
│ │ │ @@ -118,31 +118,31 @@
│ │ │  <p>This section lists a few constructs to watch out for.</p><h2 id="operator" class="section-heading">
│ │ │    <a href="#operator" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Operator <code class="inline">++</code></span>
│ │ │  </h2>
│ │ │  <p>The <code class="inline">++</code> operator copies its left-hand side operand. That is clearly
│ │ │ -seen if we do our own implementation in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_plus_plus</span><span class="p" data-group-id="6718603407-1">(</span><span class="p" data-group-id="6718603407-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6718603407-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6718603407-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6718603407-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="6718603407-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6718603407-4">)</span><span class="p" data-group-id="6718603407-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="6718603407-5">(</span><span class="p" data-group-id="6718603407-6">[</span><span class="p" data-group-id="6718603407-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6718603407-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>We must be careful how we use <code class="inline">++</code> in a loop. First is how not to use it:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_reverse</span><span class="p" data-group-id="1122039742-1">(</span><span class="p" data-group-id="1122039742-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1122039742-2">]</span><span class="p" data-group-id="1122039742-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">naive_reverse</span><span class="p" data-group-id="1122039742-3">(</span><span class="n">T</span><span class="p" data-group-id="1122039742-3">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1122039742-4">[</span><span class="n">H</span><span class="p" data-group-id="1122039742-4">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">naive_reverse</span><span class="p" data-group-id="1122039742-5">(</span><span class="p" data-group-id="1122039742-6">[</span><span class="p" data-group-id="1122039742-6">]</span><span class="p" data-group-id="1122039742-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1122039742-7">[</span><span class="p" data-group-id="1122039742-7">]</span><span class="p">.</span></code></pre><p>As the <code class="inline">++</code> operator copies its left-hand side operand, the growing
│ │ │ -result is copied repeatedly, leading to quadratic complexity.</p><p>On the other hand, using <code class="inline">++</code> in loop like this is perfectly fine:</p><p><strong>OK</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8160653446-1">(</span><span class="n">List</span><span class="p" data-group-id="8160653446-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8160653446-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8160653446-3">[</span><span class="p" data-group-id="8160653446-3">]</span><span class="p" data-group-id="8160653446-2">)</span><span class="p">.</span><span class="w">
│ │ │ +seen if we do our own implementation in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_plus_plus</span><span class="p" data-group-id="6304053819-1">(</span><span class="p" data-group-id="6304053819-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6304053819-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6304053819-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6304053819-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="6304053819-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6304053819-4">)</span><span class="p" data-group-id="6304053819-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="6304053819-5">(</span><span class="p" data-group-id="6304053819-6">[</span><span class="p" data-group-id="6304053819-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6304053819-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>We must be careful how we use <code class="inline">++</code> in a loop. First is how not to use it:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_reverse</span><span class="p" data-group-id="7951914101-1">(</span><span class="p" data-group-id="7951914101-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7951914101-2">]</span><span class="p" data-group-id="7951914101-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">naive_reverse</span><span class="p" data-group-id="7951914101-3">(</span><span class="n">T</span><span class="p" data-group-id="7951914101-3">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="7951914101-4">[</span><span class="n">H</span><span class="p" data-group-id="7951914101-4">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">naive_reverse</span><span class="p" data-group-id="7951914101-5">(</span><span class="p" data-group-id="7951914101-6">[</span><span class="p" data-group-id="7951914101-6">]</span><span class="p" data-group-id="7951914101-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7951914101-7">[</span><span class="p" data-group-id="7951914101-7">]</span><span class="p">.</span></code></pre><p>As the <code class="inline">++</code> operator copies its left-hand side operand, the growing
│ │ │ +result is copied repeatedly, leading to quadratic complexity.</p><p>On the other hand, using <code class="inline">++</code> in loop like this is perfectly fine:</p><p><strong>OK</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="9499585345-1">(</span><span class="n">List</span><span class="p" data-group-id="9499585345-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="9499585345-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9499585345-3">[</span><span class="p" data-group-id="9499585345-3">]</span><span class="p" data-group-id="9499585345-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8160653446-4">(</span><span class="p" data-group-id="8160653446-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8160653446-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8160653446-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8160653446-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8160653446-7">[</span><span class="n">H</span><span class="p" data-group-id="8160653446-7">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8160653446-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8160653446-8">(</span><span class="p" data-group-id="8160653446-9">[</span><span class="p" data-group-id="8160653446-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8160653446-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="9499585345-4">(</span><span class="p" data-group-id="9499585345-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9499585345-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9499585345-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="9499585345-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9499585345-7">[</span><span class="n">H</span><span class="p" data-group-id="9499585345-7">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9499585345-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="9499585345-8">(</span><span class="p" data-group-id="9499585345-9">[</span><span class="p" data-group-id="9499585345-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9499585345-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Each list element is copied only once. The growing result <code class="inline">Acc</code> is the right-hand
│ │ │ -side operand, which it is <em>not</em> copied.</p><p>Experienced Erlang programmers would probably write as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">vanilla_reverse</span><span class="p" data-group-id="1195873124-1">(</span><span class="p" data-group-id="1195873124-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1195873124-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1195873124-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="1195873124-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1195873124-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="1195873124-4">]</span><span class="p" data-group-id="1195873124-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="1195873124-5">(</span><span class="p" data-group-id="1195873124-6">[</span><span class="p" data-group-id="1195873124-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1195873124-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +side operand, which it is <em>not</em> copied.</p><p>Experienced Erlang programmers would probably write as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">vanilla_reverse</span><span class="p" data-group-id="1862381020-1">(</span><span class="p" data-group-id="1862381020-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1862381020-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1862381020-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="1862381020-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1862381020-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="1862381020-4">]</span><span class="p" data-group-id="1862381020-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="1862381020-5">(</span><span class="p" data-group-id="1862381020-6">[</span><span class="p" data-group-id="1862381020-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1862381020-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>In principle, this is slightly more efficient because the list element <code class="inline">[H]</code>
│ │ │  is not built before being copied and discarded. In practice, the compiler
│ │ │  rewrites <code class="inline">[H] ++ Acc</code> to <code class="inline">[H|Acc]</code>.</p><h2 id="timer-module" class="section-heading">
│ │ │    <a href="#timer-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Timer Module</span>
│ │ │ @@ -160,77 +160,77 @@
│ │ │  therefore harmless.</p><h2 id="accidental-copying-and-loss-of-sharing" class="section-heading">
│ │ │    <a href="#accidental-copying-and-loss-of-sharing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Accidental Copying and Loss of Sharing</span>
│ │ │  </h2>
│ │ │  <p>When spawning a new process using a fun, one can accidentally copy more data to
│ │ │ -the process than intended. For example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental1</span><span class="p" data-group-id="1367918327-1">(</span><span class="n">State</span><span class="p" data-group-id="1367918327-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1367918327-2">(</span><span class="nf">fun</span><span class="p" data-group-id="1367918327-3">(</span><span class="p" data-group-id="1367918327-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1367918327-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1367918327-5">[</span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p" data-group-id="1367918327-5">]</span><span class="p" data-group-id="1367918327-4">)</span><span class="w">
│ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="1367918327-2">)</span><span class="p">.</span></code></pre><p>The code in the fun will extract one element from the record and print it. The
│ │ │ +the process than intended. For example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental1</span><span class="p" data-group-id="9437407551-1">(</span><span class="n">State</span><span class="p" data-group-id="9437407551-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9437407551-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9437407551-3">(</span><span class="p" data-group-id="9437407551-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9437407551-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9437407551-5">[</span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p" data-group-id="9437407551-5">]</span><span class="p" data-group-id="9437407551-4">)</span><span class="w">
│ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="9437407551-2">)</span><span class="p">.</span></code></pre><p>The code in the fun will extract one element from the record and print it. The
│ │ │  rest of the <code class="inline">state</code> record is not used. However, when the <a href="../../erts-15.2.7/doc/html/erlang.html#spawn/1"><code class="inline">spawn/1</code></a>
│ │ │ -function is executed, the entire record is copied to the newly created process.</p><p>The same kind of problem can happen with a map:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental2</span><span class="p" data-group-id="4558321951-1">(</span><span class="n">State</span><span class="p" data-group-id="4558321951-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="4558321951-2">(</span><span class="nf">fun</span><span class="p" data-group-id="4558321951-3">(</span><span class="p" data-group-id="4558321951-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4558321951-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4558321951-5">[</span><span class="nf">map_get</span><span class="p" data-group-id="4558321951-6">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4558321951-6">)</span><span class="p" data-group-id="4558321951-5">]</span><span class="p" data-group-id="4558321951-4">)</span><span class="w">
│ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="4558321951-2">)</span><span class="p">.</span></code></pre><p>In the following example (part of a module implementing the <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │ -behavior) the created fun is sent to another process:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="5399042491-1">(</span><span class="ss">give_me_a_fun</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5399042491-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5399042491-2">(</span><span class="p" data-group-id="5399042491-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="nb">size</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5399042491-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5399042491-3">}</span><span class="p">.</span></code></pre><p>How bad that unnecessary copy is depends on the contents of the record or the
│ │ │ -map.</p><p>For example, if the <code class="inline">state</code> record is initialized like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init1</span><span class="p" data-group-id="5130598324-1">(</span><span class="p" data-group-id="5130598324-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="5130598324-2">{</span><span class="ss">data</span><span class="o">=</span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5130598324-3">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">10000</span><span class="p" data-group-id="5130598324-3">)</span><span class="p" data-group-id="5130598324-2">}</span><span class="p">.</span></code></pre><p>a list with 10000 elements (or about 20000 heap words) will be copied to the
│ │ │ +function is executed, the entire record is copied to the newly created process.</p><p>The same kind of problem can happen with a map:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental2</span><span class="p" data-group-id="9842081350-1">(</span><span class="n">State</span><span class="p" data-group-id="9842081350-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9842081350-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9842081350-3">(</span><span class="p" data-group-id="9842081350-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9842081350-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9842081350-5">[</span><span class="nf">map_get</span><span class="p" data-group-id="9842081350-6">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9842081350-6">)</span><span class="p" data-group-id="9842081350-5">]</span><span class="p" data-group-id="9842081350-4">)</span><span class="w">
│ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="9842081350-2">)</span><span class="p">.</span></code></pre><p>In the following example (part of a module implementing the <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │ +behavior) the created fun is sent to another process:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="9084248605-1">(</span><span class="ss">give_me_a_fun</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9084248605-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9084248605-2">(</span><span class="p" data-group-id="9084248605-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="nb">size</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9084248605-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9084248605-3">}</span><span class="p">.</span></code></pre><p>How bad that unnecessary copy is depends on the contents of the record or the
│ │ │ +map.</p><p>For example, if the <code class="inline">state</code> record is initialized like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init1</span><span class="p" data-group-id="5041859992-1">(</span><span class="p" data-group-id="5041859992-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="5041859992-2">{</span><span class="ss">data</span><span class="o">=</span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5041859992-3">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">10000</span><span class="p" data-group-id="5041859992-3">)</span><span class="p" data-group-id="5041859992-2">}</span><span class="p">.</span></code></pre><p>a list with 10000 elements (or about 20000 heap words) will be copied to the
│ │ │  newly created process.</p><p>An unnecessary copy of 10000 element list can be bad enough, but it can get even
│ │ │  worse if the <code class="inline">state</code> record contains <em>shared subterms</em>. Here is a simple example
│ │ │ -of a term with a shared subterm:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5432093109-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="5432093109-1">}</span></code></pre><p>When a term is copied to another process, sharing of subterms will be lost and
│ │ │ -the copied term can be many times larger than the original term. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init2</span><span class="p" data-group-id="5545736235-1">(</span><span class="p" data-group-id="5545736235-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SharedSubTerms</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="5545736235-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5545736235-3">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="5545736235-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5545736235-4">[</span><span class="n">A</span><span class="p">|</span><span class="n">A</span><span class="p" data-group-id="5545736235-4">]</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5545736235-5">[</span><span class="mi">0</span><span class="p" data-group-id="5545736235-5">]</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5545736235-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">15</span><span class="p" data-group-id="5545736235-6">)</span><span class="p" data-group-id="5545736235-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="5545736235-7">{</span><span class="ss">data</span><span class="o">=</span><span class="n">Shared</span><span class="p" data-group-id="5545736235-7">}</span><span class="p">.</span></code></pre><p>In the process that calls <code class="inline">init2/0</code>, the size of the <code class="inline">data</code> field in the <code class="inline">state</code>
│ │ │ +of a term with a shared subterm:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0963224039-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="0963224039-1">}</span></code></pre><p>When a term is copied to another process, sharing of subterms will be lost and
│ │ │ +the copied term can be many times larger than the original term. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init2</span><span class="p" data-group-id="2811092686-1">(</span><span class="p" data-group-id="2811092686-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SharedSubTerms</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="2811092686-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2811092686-3">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2811092686-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2811092686-4">[</span><span class="n">A</span><span class="p">|</span><span class="n">A</span><span class="p" data-group-id="2811092686-4">]</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2811092686-5">[</span><span class="mi">0</span><span class="p" data-group-id="2811092686-5">]</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2811092686-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">15</span><span class="p" data-group-id="2811092686-6">)</span><span class="p" data-group-id="2811092686-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="2811092686-7">{</span><span class="ss">data</span><span class="o">=</span><span class="n">Shared</span><span class="p" data-group-id="2811092686-7">}</span><span class="p">.</span></code></pre><p>In the process that calls <code class="inline">init2/0</code>, the size of the <code class="inline">data</code> field in the <code class="inline">state</code>
│ │ │  record will be 32 heap words. When the record is copied to the newly created
│ │ │  process, sharing will be lost and the size of the copied <code class="inline">data</code> field will be
│ │ │  131070 heap words. More details about
│ │ │  <a href="eff_guide_processes.html#loss-of-sharing">loss off sharing</a> are found in a later
│ │ │  section.</p><p>To avoid the problem, outside of the fun extract only the fields of the record
│ │ │ -that are actually used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental1</span><span class="p" data-group-id="2451383703-1">(</span><span class="n">State</span><span class="p" data-group-id="2451383703-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +that are actually used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental1</span><span class="p" data-group-id="6909333492-1">(</span><span class="n">State</span><span class="p" data-group-id="6909333492-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2451383703-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2451383703-3">(</span><span class="p" data-group-id="2451383703-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2451383703-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2451383703-5">[</span><span class="n">Info</span><span class="p" data-group-id="2451383703-5">]</span><span class="p" data-group-id="2451383703-4">)</span><span class="w">
│ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="2451383703-2">)</span><span class="p">.</span></code></pre><p>Similarly, outside of the fun extract only the map elements that are actually
│ │ │ -used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental2</span><span class="p" data-group-id="0294578784-1">(</span><span class="n">State</span><span class="p" data-group-id="0294578784-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">map_get</span><span class="p" data-group-id="0294578784-2">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="0294578784-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="0294578784-3">(</span><span class="nf">fun</span><span class="p" data-group-id="0294578784-4">(</span><span class="p" data-group-id="0294578784-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0294578784-5">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0294578784-6">[</span><span class="n">Info</span><span class="p" data-group-id="0294578784-6">]</span><span class="p" data-group-id="0294578784-5">)</span><span class="w">
│ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="0294578784-3">)</span><span class="p">.</span></code></pre><h2 id="list_to_atom-1" class="section-heading">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="6909333492-2">(</span><span class="nf">fun</span><span class="p" data-group-id="6909333492-3">(</span><span class="p" data-group-id="6909333492-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6909333492-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6909333492-5">[</span><span class="n">Info</span><span class="p" data-group-id="6909333492-5">]</span><span class="p" data-group-id="6909333492-4">)</span><span class="w">
│ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="6909333492-2">)</span><span class="p">.</span></code></pre><p>Similarly, outside of the fun extract only the map elements that are actually
│ │ │ +used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental2</span><span class="p" data-group-id="9681356213-1">(</span><span class="n">State</span><span class="p" data-group-id="9681356213-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">map_get</span><span class="p" data-group-id="9681356213-2">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9681356213-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9681356213-3">(</span><span class="nf">fun</span><span class="p" data-group-id="9681356213-4">(</span><span class="p" data-group-id="9681356213-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9681356213-5">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9681356213-6">[</span><span class="n">Info</span><span class="p" data-group-id="9681356213-6">]</span><span class="p" data-group-id="9681356213-5">)</span><span class="w">
│ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="9681356213-3">)</span><span class="p">.</span></code></pre><h2 id="list_to_atom-1" class="section-heading">
│ │ │    <a href="#list_to_atom-1" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">list_to_atom/1</span>
│ │ │  </h2>
│ │ │  <p>Atoms are not garbage-collected. Once an atom is created, it is never removed.
│ │ │  The emulator terminates if the limit for the number of atoms (1,048,576 by
│ │ │  default) is reached.</p><p>Therefore, converting arbitrary input strings to atoms can be dangerous in a
│ │ │  system that runs continuously. If only certain well-defined atoms are allowed as
│ │ │  input, <a href="../../erts-15.2.7/doc/html/erlang.html#list_to_existing_atom/1"><code class="inline">list_to_existing_atom/1</code></a> or
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#binary_to_existing_atom/1"><code class="inline">binary_to_existing_atom/1</code></a> can be used
│ │ │  to guard against a denial-of-service attack. (All atoms that are allowed must
│ │ │  have been created earlier, for example, by using all of them in a module
│ │ │  and loading that module.)</p><p>Using <a href="../../erts-15.2.7/doc/html/erlang.html#list_to_atom/1"><code class="inline">list_to_atom/1</code></a> to construct an atom that
│ │ │ -is passed to <a href="../../erts-15.2.7/doc/html/erlang.html#apply/3"><code class="inline">apply/3</code></a> is quite expensive.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">apply</span><span class="p" data-group-id="0716643802-1">(</span><span class="nf">list_to_atom</span><span class="p" data-group-id="0716643802-2">(</span><span class="s">&quot;some_prefix&quot;</span><span class="o">++</span><span class="n">Var</span><span class="p" data-group-id="0716643802-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="0716643802-1">)</span></code></pre><h2 id="length-1" class="section-heading">
│ │ │ +is passed to <a href="../../erts-15.2.7/doc/html/erlang.html#apply/3"><code class="inline">apply/3</code></a> is quite expensive.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">apply</span><span class="p" data-group-id="0839810994-1">(</span><span class="nf">list_to_atom</span><span class="p" data-group-id="0839810994-2">(</span><span class="s">&quot;some_prefix&quot;</span><span class="o">++</span><span class="n">Var</span><span class="p" data-group-id="0839810994-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="0839810994-1">)</span></code></pre><h2 id="length-1" class="section-heading">
│ │ │    <a href="#length-1" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">length/1</span>
│ │ │  </h2>
│ │ │  <p>The time for calculating the length of a list is proportional to the length of
│ │ │  the list, as opposed to <a href="../../erts-15.2.7/doc/html/erlang.html#tuple_size/1"><code class="inline">tuple_size/1</code></a>,
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#byte_size/1"><code class="inline">byte_size/1</code></a>, and <a href="../../erts-15.2.7/doc/html/erlang.html#bit_size/1"><code class="inline">bit_size/1</code></a>, which all
│ │ │  execute in constant time.</p><p>Normally, there is no need to worry about the speed of <a href="../../erts-15.2.7/doc/html/erlang.html#length/1"><code class="inline">length/1</code></a>,
│ │ │  because it is efficiently implemented in C. In time-critical code, you might
│ │ │  want to avoid it if the input list could potentially be very long.</p><p>Some uses of <a href="../../erts-15.2.7/doc/html/erlang.html#length/1"><code class="inline">length/1</code></a> can be replaced by matching. For example,
│ │ │ -the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="5195518322-1">(</span><span class="n">L</span><span class="p" data-group-id="5195518322-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="5195518322-2">(</span><span class="n">L</span><span class="p" data-group-id="5195518322-2">)</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="4079347601-1">(</span><span class="p" data-group-id="4079347601-2">[</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="4079347601-2">]</span><span class="o">=</span><span class="n">L</span><span class="p" data-group-id="4079347601-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="1091981423-1">(</span><span class="n">L</span><span class="p" data-group-id="1091981423-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="1091981423-2">(</span><span class="n">L</span><span class="p" data-group-id="1091981423-2">)</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="6612933851-1">(</span><span class="p" data-group-id="6612933851-2">[</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="6612933851-2">]</span><span class="o">=</span><span class="n">L</span><span class="p" data-group-id="6612933851-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>One slight difference is that <a href="../../erts-15.2.7/doc/html/erlang.html#length/1"><code class="inline">length(L)</code></a> fails if <code class="inline">L</code> is an
│ │ │  improper list, while the pattern in the second code fragment accepts an improper
│ │ │  list.</p><h2 id="setelement-3" class="section-heading">
│ │ │    <a href="#setelement-3" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">setelement/3</span>
│ │ │ @@ -238,18 +238,18 @@
│ │ │  <p><a href="../../erts-15.2.7/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> copies the tuple it modifies. Therefore,
│ │ │  updating a tuple in a loop using <a href="../../erts-15.2.7/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> creates a new
│ │ │  copy of the tuple every time.</p><p>There is one exception to the rule that the tuple is copied. If the compiler
│ │ │  clearly can see that destructively updating the tuple would give the same result
│ │ │  as if the tuple was copied, the call to <a href="../../erts-15.2.7/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> is
│ │ │  replaced with a special destructive <code class="inline">setelement</code> instruction. In the following
│ │ │  code sequence, the first <a href="../../erts-15.2.7/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> call copies the tuple
│ │ │ -and modifies the ninth element:</p><pre><code class="makeup erlang" translate="no"><span class="nf">multiple_setelement</span><span class="p" data-group-id="5037021519-1">(</span><span class="n">T0</span><span class="p" data-group-id="5037021519-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="5037021519-2">(</span><span class="n">T0</span><span class="p" data-group-id="5037021519-2">)</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">T1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="5037021519-3">(</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p" data-group-id="5037021519-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">T2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="5037021519-4">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="ss">foobar</span><span class="p" data-group-id="5037021519-4">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">setelement</span><span class="p" data-group-id="5037021519-5">(</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p">,</span><span class="w"> </span><span class="ss">new_value</span><span class="p" data-group-id="5037021519-5">)</span><span class="p">.</span></code></pre><p>The two following <a href="../../erts-15.2.7/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> calls modify the tuple in
│ │ │ +and modifies the ninth element:</p><pre><code class="makeup erlang" translate="no"><span class="nf">multiple_setelement</span><span class="p" data-group-id="8552940311-1">(</span><span class="n">T0</span><span class="p" data-group-id="8552940311-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="8552940311-2">(</span><span class="n">T0</span><span class="p" data-group-id="8552940311-2">)</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">T1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="8552940311-3">(</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p" data-group-id="8552940311-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">T2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="8552940311-4">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="ss">foobar</span><span class="p" data-group-id="8552940311-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">setelement</span><span class="p" data-group-id="8552940311-5">(</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p">,</span><span class="w"> </span><span class="ss">new_value</span><span class="p" data-group-id="8552940311-5">)</span><span class="p">.</span></code></pre><p>The two following <a href="../../erts-15.2.7/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> calls modify the tuple in
│ │ │  place.</p><p>For the optimization to be applied, <em>all</em> the following conditions must be true:</p><ul><li>The tuple argument must be known to be a tuple of a known size.</li><li>The indices must be integer literals, not variables or expressions.</li><li>The indices must be given in descending order.</li><li>There must be no calls to another function in between the calls to
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a>.</li><li>The tuple returned from one <a href="../../erts-15.2.7/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> call must only be
│ │ │  used in the subsequent call to <a href="../../erts-15.2.7/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a>.</li></ul><p>If the code cannot be structured as in the <code class="inline">multiple_setelement/1</code> example, the
│ │ │  best way to modify multiple elements in a large tuple is to convert the tuple to
│ │ │  a list, modify the list, and convert it back to a tuple.</p><h2 id="size-1" class="section-heading">
│ │ │    <a href="#size-1" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/conc_prog.html
│ │ │ @@ -132,107 +132,107 @@
│ │ │  threads of execution in an Erlang program and to allow these threads to
│ │ │  communicate with each other. In Erlang, each thread of execution is called a
│ │ │  <em>process</em>.</p><p>(Aside: the term &quot;process&quot; is usually used when the threads of execution share
│ │ │  no data with each other and the term &quot;thread&quot; when they share data in some way.
│ │ │  Threads of execution in Erlang share no data, that is why they are called
│ │ │  processes).</p><p>The Erlang BIF <code class="inline">spawn</code> is used to create a new process:
│ │ │  <code class="inline">spawn(Module, Exported_Function, List of Arguments)</code>. Consider the following
│ │ │ -module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3241129880-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="3241129880-1">)</span><span class="p">.</span><span class="w">
│ │ │ +module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8362090309-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="8362090309-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3241129880-2">(</span><span class="p" data-group-id="3241129880-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3241129880-3">]</span><span class="p" data-group-id="3241129880-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8362090309-2">(</span><span class="p" data-group-id="8362090309-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8362090309-3">]</span><span class="p" data-group-id="8362090309-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">say_something</span><span class="p" data-group-id="3241129880-4">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3241129880-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">say_something</span><span class="p" data-group-id="8362090309-4">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8362090309-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">done</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">say_something</span><span class="p" data-group-id="3241129880-5">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="p" data-group-id="3241129880-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3241129880-6">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3241129880-7">[</span><span class="n">What</span><span class="p" data-group-id="3241129880-7">]</span><span class="p" data-group-id="3241129880-6">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">say_something</span><span class="p" data-group-id="3241129880-8">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3241129880-8">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="3241129880-9">(</span><span class="p" data-group-id="3241129880-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="3241129880-10">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3241129880-11">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3241129880-11">]</span><span class="p" data-group-id="3241129880-10">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="3241129880-12">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3241129880-13">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3241129880-13">]</span><span class="p" data-group-id="3241129880-12">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="4094959498-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="4094959498-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4094959498-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut14</span><span class="p" data-group-id="4094959498-2">}</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">say_something</span><span class="p" data-group-id="4094959498-3">(</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4094959498-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">say_something</span><span class="p" data-group-id="8362090309-5">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="p" data-group-id="8362090309-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8362090309-6">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8362090309-7">[</span><span class="n">What</span><span class="p" data-group-id="8362090309-7">]</span><span class="p" data-group-id="8362090309-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">say_something</span><span class="p" data-group-id="8362090309-8">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8362090309-8">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8362090309-9">(</span><span class="p" data-group-id="8362090309-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="8362090309-10">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8362090309-11">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8362090309-11">]</span><span class="p" data-group-id="8362090309-10">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="8362090309-12">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8362090309-13">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8362090309-13">]</span><span class="p" data-group-id="8362090309-12">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="3342088429-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="3342088429-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3342088429-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut14</span><span class="p" data-group-id="3342088429-2">}</span><span class="gp unselectable">
│ │ │ +6&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">say_something</span><span class="p" data-group-id="3342088429-3">(</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3342088429-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">done</span></code></pre><p>As shown, the function <code class="inline">say_something</code> writes its first argument the number of
│ │ │  times specified by second argument. The function <code class="inline">start</code> starts two Erlang
│ │ │  processes, one that writes &quot;hello&quot; three times and one that writes &quot;goodbye&quot;
│ │ │  three times. Both processes use the function <code class="inline">say_something</code>. Notice that a
│ │ │  function used in this way by <code class="inline">spawn</code>, to start a process, must be exported from
│ │ │ -the module (that is, in the <code class="inline">-export</code> at the start of the module).</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7018120277-1">(</span><span class="p" data-group-id="7018120277-1">)</span><span class="p">.</span><span class="w">
│ │ │ +the module (that is, in the <code class="inline">-export</code> at the start of the module).</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9598377853-1">(</span><span class="p" data-group-id="9598377853-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">goodbye</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.63</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">goodbye</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">goodbye</span></code></pre><p>Notice that it did not write &quot;hello&quot; three times and then &quot;goodbye&quot; three times.
│ │ │  Instead, the first process wrote a &quot;hello&quot;, the second a &quot;goodbye&quot;, the first
│ │ │  another &quot;hello&quot; and so forth. But where did the <code class="inline">&lt;0.63.0&gt;</code> come from? The return
│ │ │  value of a function is the return value of the last &quot;thing&quot; in the function. The
│ │ │ -last thing in the function <code class="inline">start</code> is</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="7591731344-1">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7591731344-2">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7591731344-2">]</span><span class="p" data-group-id="7591731344-1">)</span><span class="p">.</span></code></pre><p><code class="inline">spawn</code> returns a <em>process identifier</em>, or <em>pid</em>, which uniquely identifies the
│ │ │ +last thing in the function <code class="inline">start</code> is</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="6665715713-1">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6665715713-2">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6665715713-2">]</span><span class="p" data-group-id="6665715713-1">)</span><span class="p">.</span></code></pre><p><code class="inline">spawn</code> returns a <em>process identifier</em>, or <em>pid</em>, which uniquely identifies the
│ │ │  process. So <code class="inline">&lt;0.63.0&gt;</code> is the pid of the <code class="inline">spawn</code> function call above. The next
│ │ │  example shows how to use pids.</p><p>Notice also that ~p is used instead of ~w in <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a>. To quote <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#tilde_p">the manual</a>:</p><blockquote><p>~p Writes the data with standard syntax in the same way as ~w, but breaks terms
│ │ │  whose printed representation is longer than one line into many lines and indents
│ │ │  each line sensibly. It also tries to detect flat lists of printable characters and
│ │ │  to output these as strings</p></blockquote><h2 id="message-passing" class="section-heading">
│ │ │    <a href="#message-passing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Message Passing</span>
│ │ │  </h2>
│ │ │  <p>In the following example two processes are created and they send messages to
│ │ │ -each other a number of times.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9130891036-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="9130891036-1">)</span><span class="p">.</span><span class="w">
│ │ │ +each other a number of times.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1084634598-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="1084634598-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9130891036-2">(</span><span class="p" data-group-id="9130891036-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9130891036-3">]</span><span class="p" data-group-id="9130891036-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1084634598-2">(</span><span class="p" data-group-id="1084634598-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1084634598-3">]</span><span class="p" data-group-id="1084634598-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="9130891036-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="9130891036-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="1084634598-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="1084634598-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9130891036-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9130891036-6">[</span><span class="p" data-group-id="9130891036-6">]</span><span class="p" data-group-id="9130891036-5">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1084634598-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1084634598-6">[</span><span class="p" data-group-id="1084634598-6">]</span><span class="p" data-group-id="1084634598-5">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="9130891036-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="9130891036-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9130891036-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9130891036-9">(</span><span class="p" data-group-id="9130891036-9">)</span><span class="p" data-group-id="9130891036-8">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="1084634598-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="1084634598-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1084634598-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1084634598-9">(</span><span class="p" data-group-id="1084634598-9">)</span><span class="p" data-group-id="1084634598-8">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9130891036-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9130891036-11">[</span><span class="p" data-group-id="9130891036-11">]</span><span class="p" data-group-id="9130891036-10">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1084634598-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1084634598-11">[</span><span class="p" data-group-id="1084634598-11">]</span><span class="p" data-group-id="1084634598-10">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="9130891036-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="9130891036-12">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="1084634598-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="1084634598-12">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="9130891036-13">(</span><span class="p" data-group-id="9130891036-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="1084634598-13">(</span><span class="p" data-group-id="1084634598-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9130891036-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9130891036-15">[</span><span class="p" data-group-id="9130891036-15">]</span><span class="p" data-group-id="9130891036-14">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9130891036-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9130891036-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9130891036-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9130891036-18">[</span><span class="p" data-group-id="9130891036-18">]</span><span class="p" data-group-id="9130891036-17">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1084634598-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1084634598-15">[</span><span class="p" data-group-id="1084634598-15">]</span><span class="p" data-group-id="1084634598-14">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="1084634598-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="1084634598-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1084634598-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1084634598-18">[</span><span class="p" data-group-id="1084634598-18">]</span><span class="p" data-group-id="1084634598-17">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="9130891036-19">(</span><span class="p" data-group-id="9130891036-19">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="1084634598-19">(</span><span class="p" data-group-id="1084634598-19">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="9130891036-20">(</span><span class="p" data-group-id="9130891036-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9130891036-21">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9130891036-22">[</span><span class="p" data-group-id="9130891036-22">]</span><span class="p" data-group-id="9130891036-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9130891036-23">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9130891036-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="9130891036-24">]</span><span class="p" data-group-id="9130891036-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="3232580036-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="3232580036-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3232580036-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut15</span><span class="p" data-group-id="3232580036-2">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">tut15</span><span class="p">:</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="3232580036-3">(</span><span class="p" data-group-id="3232580036-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="1084634598-20">(</span><span class="p" data-group-id="1084634598-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1084634598-21">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1084634598-22">[</span><span class="p" data-group-id="1084634598-22">]</span><span class="p" data-group-id="1084634598-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="1084634598-23">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1084634598-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="1084634598-24">]</span><span class="p" data-group-id="1084634598-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="7673899987-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="7673899987-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7673899987-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut15</span><span class="p" data-group-id="7673899987-2">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nc">tut15</span><span class="p">:</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="7673899987-3">(</span><span class="p" data-group-id="7673899987-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.36</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span><span class="w">
│ │ │ -</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>The function <code class="inline">start</code> first creates a process, let us call it &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="5750249415-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5750249415-2">[</span><span class="p" data-group-id="5750249415-2">]</span><span class="p" data-group-id="5750249415-1">)</span></code></pre><p>This process executes <code class="inline">tut15:pong()</code>. <code class="inline">Pong_PID</code> is the process identity of the
│ │ │ -&quot;pong&quot; process. The function <code class="inline">start</code> now creates another process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="0658027529-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0658027529-2">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0658027529-2">]</span><span class="p" data-group-id="0658027529-1">)</span><span class="p">,</span></code></pre><p>This process executes:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="4671362815-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="4671362815-1">)</span></code></pre><p><code class="inline">&lt;0.36.0&gt;</code> is the return value from the <code class="inline">start</code> function.</p><p>The process &quot;pong&quot; now does:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ +</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>The function <code class="inline">start</code> first creates a process, let us call it &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1533618128-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1533618128-2">[</span><span class="p" data-group-id="1533618128-2">]</span><span class="p" data-group-id="1533618128-1">)</span></code></pre><p>This process executes <code class="inline">tut15:pong()</code>. <code class="inline">Pong_PID</code> is the process identity of the
│ │ │ +&quot;pong&quot; process. The function <code class="inline">start</code> now creates another process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="0364608668-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0364608668-2">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0364608668-2">]</span><span class="p" data-group-id="0364608668-1">)</span><span class="p">,</span></code></pre><p>This process executes:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="0737035154-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0737035154-1">)</span></code></pre><p><code class="inline">&lt;0.36.0&gt;</code> is the return value from the <code class="inline">start</code> function.</p><p>The process &quot;pong&quot; now does:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │      </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7483374220-1">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7483374220-2">[</span><span class="p" data-group-id="7483374220-2">]</span><span class="p" data-group-id="7483374220-1">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7483374220-3">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="7483374220-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7483374220-4">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7483374220-5">[</span><span class="p" data-group-id="7483374220-5">]</span><span class="p" data-group-id="7483374220-4">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0960011590-1">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0960011590-2">[</span><span class="p" data-group-id="0960011590-2">]</span><span class="p" data-group-id="0960011590-1">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0960011590-3">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="0960011590-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0960011590-4">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0960011590-5">[</span><span class="p" data-group-id="0960011590-5">]</span><span class="p" data-group-id="0960011590-4">)</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="nf">pong</span><span class="p" data-group-id="7483374220-6">(</span><span class="p" data-group-id="7483374220-6">)</span><span class="w">
│ │ │ +        </span><span class="nf">pong</span><span class="p" data-group-id="0960011590-6">(</span><span class="p" data-group-id="0960011590-6">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">receive</code> construct is used to allow processes to wait for messages from
│ │ │  other processes. It has the following format:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │     </span><span class="ss">pattern1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │         </span><span class="ss">actions1</span><span class="p">;</span><span class="w">
│ │ │     </span><span class="ss">pattern2</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │         </span><span class="ss">actions2</span><span class="p">;</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ @@ -253,84 +253,84 @@
│ │ │  queue (keeping the first message and any other messages in the queue). If the
│ │ │  second message does not match, the third message is tried, and so on, until the
│ │ │  end of the queue is reached. If the end of the queue is reached, the process
│ │ │  blocks (stops execution) and waits until a new message is received and this
│ │ │  procedure is repeated.</p><p>The Erlang implementation is &quot;clever&quot; and minimizes the number of times each
│ │ │  message is tested against the patterns in each <code class="inline">receive</code>.</p><p>Now back to the ping pong example.</p><p>&quot;Pong&quot; is waiting for messages. If the atom <code class="inline">finished</code> is received, &quot;pong&quot;
│ │ │  writes &quot;Pong finished&quot; to the output and, as it has nothing more to do,
│ │ │ -terminates. If it receives a message with the format:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9774544276-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9774544276-1">}</span></code></pre><p>it writes &quot;Pong received ping&quot; to the output and sends the atom <code class="inline">pong</code> to the
│ │ │ +terminates. If it receives a message with the format:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2814536269-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2814536269-1">}</span></code></pre><p>it writes &quot;Pong received ping&quot; to the output and sends the atom <code class="inline">pong</code> to the
│ │ │  process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span></code></pre><p>Notice how the operator &quot;!&quot; is used to send messages. The syntax of &quot;!&quot; is:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Message</span></code></pre><p>That is, <code class="inline">Message</code> (any Erlang term) is sent to the process with identity <code class="inline">Pid</code>.</p><p>After sending the message <code class="inline">pong</code> to the process &quot;ping&quot;, &quot;pong&quot; calls the <code class="inline">pong</code>
│ │ │  function again, which causes it to get back to the <code class="inline">receive</code> again and wait for
│ │ │ -another message.</p><p>Now let us look at the process &quot;ping&quot;. Recall that it was started by executing:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="9192732621-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="9192732621-1">)</span></code></pre><p>Looking at the function <code class="inline">ping/2</code>, the second clause of <code class="inline">ping/2</code> is executed
│ │ │ +another message.</p><p>Now let us look at the process &quot;ping&quot;. Recall that it was started by executing:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="2897526686-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="2897526686-1">)</span></code></pre><p>Looking at the function <code class="inline">ping/2</code>, the second clause of <code class="inline">ping/2</code> is executed
│ │ │  since the value of the first argument is 3 (not 0) (first clause head is
│ │ │ -<code class="inline">ping(0,Pong_PID)</code>, second clause head is <code class="inline">ping(N,Pong_PID)</code>, so <code class="inline">N</code> becomes 3).</p><p>The second clause sends a message to &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9989112992-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9989112992-2">(</span><span class="p" data-group-id="9989112992-2">)</span><span class="p" data-group-id="9989112992-1">}</span><span class="p">,</span></code></pre><p><a href="../../erts-15.2.7/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the pid of the process that executes <a href="../../erts-15.2.7/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a>, in this case the
│ │ │ +<code class="inline">ping(0,Pong_PID)</code>, second clause head is <code class="inline">ping(N,Pong_PID)</code>, so <code class="inline">N</code> becomes 3).</p><p>The second clause sends a message to &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3792079038-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3792079038-2">(</span><span class="p" data-group-id="3792079038-2">)</span><span class="p" data-group-id="3792079038-1">}</span><span class="p">,</span></code></pre><p><a href="../../erts-15.2.7/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the pid of the process that executes <a href="../../erts-15.2.7/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a>, in this case the
│ │ │  pid of &quot;ping&quot;. (Recall the code for &quot;pong&quot;, this lands up in the variable
│ │ │  <code class="inline">Ping_PID</code> in the <code class="inline">receive</code> previously explained.)</p><p>&quot;Ping&quot; now waits for a reply from &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │      </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7602093564-1">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7602093564-2">[</span><span class="p" data-group-id="7602093564-2">]</span><span class="p" data-group-id="7602093564-1">)</span><span class="w">
│ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0459724301-1">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0459724301-2">[</span><span class="p" data-group-id="0459724301-2">]</span><span class="p" data-group-id="0459724301-1">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre><p>It writes &quot;Ping received pong&quot; when this reply arrives, after which &quot;ping&quot; calls
│ │ │ -the <code class="inline">ping</code> function again.</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="8270394680-1">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="8270394680-1">)</span></code></pre><p><code class="inline">N-1</code> causes the first argument to be decremented until it becomes 0. When this
│ │ │ -occurs, the first clause of <code class="inline">ping/2</code> is executed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="3225393468-1">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="3225393468-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +the <code class="inline">ping</code> function again.</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="8984809823-1">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="8984809823-1">)</span></code></pre><p><code class="inline">N-1</code> causes the first argument to be decremented until it becomes 0. When this
│ │ │ +occurs, the first clause of <code class="inline">ping/2</code> is executed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="6753543650-1">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="6753543650-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3225393468-2">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3225393468-3">[</span><span class="p" data-group-id="3225393468-3">]</span><span class="p" data-group-id="3225393468-2">)</span><span class="p">;</span></code></pre><p>The atom <code class="inline">finished</code> is sent to &quot;pong&quot; (causing it to terminate as described
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6753543650-2">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6753543650-3">[</span><span class="p" data-group-id="6753543650-3">]</span><span class="p" data-group-id="6753543650-2">)</span><span class="p">;</span></code></pre><p>The atom <code class="inline">finished</code> is sent to &quot;pong&quot; (causing it to terminate as described
│ │ │  above) and &quot;ping finished&quot; is written to the output. &quot;Ping&quot; then terminates as
│ │ │  it has nothing left to do.</p><h2 id="registered-process-names" class="section-heading">
│ │ │    <a href="#registered-process-names" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Registered Process Names</span>
│ │ │  </h2>
│ │ │  <p>In the above example, &quot;pong&quot; was first created to be able to give the identity
│ │ │  of &quot;pong&quot; when &quot;ping&quot; was started. That is, in some way &quot;ping&quot; must be able to
│ │ │  know the identity of &quot;pong&quot; to be able to send a message to it. Sometimes
│ │ │  processes which need to know each other's identities are started independently
│ │ │  of each other. Erlang thus provides a mechanism for processes to be given names
│ │ │  so that these names can be used as identities instead of pids. This is done by
│ │ │ -using the <code class="inline">register</code> BIF:</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="6955093855-1">(</span><span class="ss">some_atom</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="6955093855-1">)</span></code></pre><p>Let us now rewrite the ping pong example using this and give the name <code class="inline">pong</code> to
│ │ │ -the &quot;pong&quot; process:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7953136472-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="7953136472-1">)</span><span class="p">.</span><span class="w">
│ │ │ +using the <code class="inline">register</code> BIF:</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="9058555552-1">(</span><span class="ss">some_atom</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="9058555552-1">)</span></code></pre><p>Let us now rewrite the ping pong example using this and give the name <code class="inline">pong</code> to
│ │ │ +the &quot;pong&quot; process:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1551176143-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="1551176143-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7953136472-2">(</span><span class="p" data-group-id="7953136472-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7953136472-3">]</span><span class="p" data-group-id="7953136472-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1551176143-2">(</span><span class="p" data-group-id="1551176143-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1551176143-3">]</span><span class="p" data-group-id="1551176143-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="7953136472-4">(</span><span class="mi">0</span><span class="p" data-group-id="7953136472-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="1551176143-4">(</span><span class="mi">0</span><span class="p" data-group-id="1551176143-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7953136472-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7953136472-6">[</span><span class="p" data-group-id="7953136472-6">]</span><span class="p" data-group-id="7953136472-5">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1551176143-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1551176143-6">[</span><span class="p" data-group-id="1551176143-6">]</span><span class="p" data-group-id="1551176143-5">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="7953136472-7">(</span><span class="n">N</span><span class="p" data-group-id="7953136472-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7953136472-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7953136472-9">(</span><span class="p" data-group-id="7953136472-9">)</span><span class="p" data-group-id="7953136472-8">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="1551176143-7">(</span><span class="n">N</span><span class="p" data-group-id="1551176143-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1551176143-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1551176143-9">(</span><span class="p" data-group-id="1551176143-9">)</span><span class="p" data-group-id="1551176143-8">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7953136472-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7953136472-11">[</span><span class="p" data-group-id="7953136472-11">]</span><span class="p" data-group-id="7953136472-10">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1551176143-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1551176143-11">[</span><span class="p" data-group-id="1551176143-11">]</span><span class="p" data-group-id="1551176143-10">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="7953136472-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7953136472-12">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="1551176143-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1551176143-12">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="7953136472-13">(</span><span class="p" data-group-id="7953136472-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="1551176143-13">(</span><span class="p" data-group-id="1551176143-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7953136472-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7953136472-15">[</span><span class="p" data-group-id="7953136472-15">]</span><span class="p" data-group-id="7953136472-14">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7953136472-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="7953136472-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7953136472-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7953136472-18">[</span><span class="p" data-group-id="7953136472-18">]</span><span class="p" data-group-id="7953136472-17">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1551176143-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1551176143-15">[</span><span class="p" data-group-id="1551176143-15">]</span><span class="p" data-group-id="1551176143-14">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="1551176143-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="1551176143-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1551176143-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1551176143-18">[</span><span class="p" data-group-id="1551176143-18">]</span><span class="p" data-group-id="1551176143-17">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="7953136472-19">(</span><span class="p" data-group-id="7953136472-19">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="1551176143-19">(</span><span class="p" data-group-id="1551176143-19">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="7953136472-20">(</span><span class="p" data-group-id="7953136472-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="7953136472-21">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7953136472-22">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7953136472-23">[</span><span class="p" data-group-id="7953136472-23">]</span><span class="p" data-group-id="7953136472-22">)</span><span class="p" data-group-id="7953136472-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="7953136472-24">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7953136472-25">[</span><span class="mi">3</span><span class="p" data-group-id="7953136472-25">]</span><span class="p" data-group-id="7953136472-24">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nf">c</span><span class="p" data-group-id="4310065658-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="4310065658-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4310065658-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut16</span><span class="p" data-group-id="4310065658-2">}</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nc">tut16</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4310065658-3">(</span><span class="p" data-group-id="4310065658-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="1551176143-20">(</span><span class="p" data-group-id="1551176143-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="1551176143-21">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1551176143-22">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1551176143-23">[</span><span class="p" data-group-id="1551176143-23">]</span><span class="p" data-group-id="1551176143-22">)</span><span class="p" data-group-id="1551176143-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="1551176143-24">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1551176143-25">[</span><span class="mi">3</span><span class="p" data-group-id="1551176143-25">]</span><span class="p" data-group-id="1551176143-24">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nf">c</span><span class="p" data-group-id="3308200570-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="3308200570-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3308200570-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut16</span><span class="p" data-group-id="3308200570-2">}</span><span class="gp unselectable">
│ │ │ +3&gt; </span><span class="nc">tut16</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3308200570-3">(</span><span class="p" data-group-id="3308200570-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.38</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span><span class="w">
│ │ │ -</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>Here the <code class="inline">start/0</code> function,</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="3500975862-1">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="3500975862-2">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3500975862-3">[</span><span class="p" data-group-id="3500975862-3">]</span><span class="p" data-group-id="3500975862-2">)</span><span class="p" data-group-id="3500975862-1">)</span><span class="p">,</span></code></pre><p>both spawns the &quot;pong&quot; process and gives it the name <code class="inline">pong</code>. In the &quot;ping&quot;
│ │ │ -process, messages can be sent to <code class="inline">pong</code> by:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3540582425-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3540582425-2">(</span><span class="p" data-group-id="3540582425-2">)</span><span class="p" data-group-id="3540582425-1">}</span><span class="p">,</span></code></pre><p><code class="inline">ping/2</code> now becomes <code class="inline">ping/1</code> as the argument <code class="inline">Pong_PID</code> is not needed.</p><h2 id="distributed-programming" class="section-heading">
│ │ │ +</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>Here the <code class="inline">start/0</code> function,</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="1892479100-1">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1892479100-2">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1892479100-3">[</span><span class="p" data-group-id="1892479100-3">]</span><span class="p" data-group-id="1892479100-2">)</span><span class="p" data-group-id="1892479100-1">)</span><span class="p">,</span></code></pre><p>both spawns the &quot;pong&quot; process and gives it the name <code class="inline">pong</code>. In the &quot;ping&quot;
│ │ │ +process, messages can be sent to <code class="inline">pong</code> by:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9609010808-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9609010808-2">(</span><span class="p" data-group-id="9609010808-2">)</span><span class="p" data-group-id="9609010808-1">}</span><span class="p">,</span></code></pre><p><code class="inline">ping/2</code> now becomes <code class="inline">ping/1</code> as the argument <code class="inline">Pong_PID</code> is not needed.</p><h2 id="distributed-programming" class="section-heading">
│ │ │    <a href="#distributed-programming" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Distributed Programming</span>
│ │ │  </h2>
│ │ │  <p>Let us rewrite the ping pong program with &quot;ping&quot; and &quot;pong&quot; on different
│ │ │  computers. First a few things are needed to set up to get this to work. The
│ │ │ @@ -350,106 +350,106 @@
│ │ │  of the file. This is a requirement.</p><p>When you start an Erlang system that is going to talk to other Erlang systems,
│ │ │  you must give it a name, for example:</p><pre><code class="text">$ erl -sname my_name</code></pre><p>We will see more details of this later. If you want to experiment with
│ │ │  distributed Erlang, but you only have one computer to work on, you can start two
│ │ │  separate Erlang systems on the same computer but give them different names. Each
│ │ │  Erlang system running on a computer is called an <em>Erlang node</em>.</p><p>(Note: <code class="inline">erl -sname</code> assumes that all nodes are in the same IP domain and we can
│ │ │  use only the first component of the IP address, if we want to use nodes in
│ │ │  different domains we use <code class="inline">-name</code> instead, but then all IP address must be given
│ │ │ -in full.)</p><p>Here is the ping pong example modified to run on two separate nodes:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8102392881-1">(</span><span class="ss">tut17</span><span class="p" data-group-id="8102392881-1">)</span><span class="p">.</span><span class="w">
│ │ │ +in full.)</p><p>Here is the ping pong example modified to run on two separate nodes:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5979015220-1">(</span><span class="ss">tut17</span><span class="p" data-group-id="5979015220-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8102392881-2">(</span><span class="p" data-group-id="8102392881-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8102392881-3">]</span><span class="p" data-group-id="8102392881-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5979015220-2">(</span><span class="p" data-group-id="5979015220-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5979015220-3">]</span><span class="p" data-group-id="5979015220-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="8102392881-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8102392881-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8102392881-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8102392881-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8102392881-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8102392881-7">[</span><span class="p" data-group-id="8102392881-7">]</span><span class="p" data-group-id="8102392881-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="5979015220-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5979015220-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5979015220-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5979015220-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5979015220-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5979015220-7">[</span><span class="p" data-group-id="5979015220-7">]</span><span class="p" data-group-id="5979015220-6">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="8102392881-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8102392881-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8102392881-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8102392881-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8102392881-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8102392881-11">(</span><span class="p" data-group-id="8102392881-11">)</span><span class="p" data-group-id="8102392881-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="5979015220-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5979015220-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5979015220-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5979015220-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5979015220-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5979015220-11">(</span><span class="p" data-group-id="5979015220-11">)</span><span class="p" data-group-id="5979015220-10">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8102392881-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8102392881-13">[</span><span class="p" data-group-id="8102392881-13">]</span><span class="p" data-group-id="8102392881-12">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5979015220-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5979015220-13">[</span><span class="p" data-group-id="5979015220-13">]</span><span class="p" data-group-id="5979015220-12">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="8102392881-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8102392881-14">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="5979015220-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5979015220-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="8102392881-15">(</span><span class="p" data-group-id="8102392881-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="5979015220-15">(</span><span class="p" data-group-id="5979015220-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8102392881-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8102392881-17">[</span><span class="p" data-group-id="8102392881-17">]</span><span class="p" data-group-id="8102392881-16">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8102392881-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="8102392881-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8102392881-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8102392881-20">[</span><span class="p" data-group-id="8102392881-20">]</span><span class="p" data-group-id="8102392881-19">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5979015220-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5979015220-17">[</span><span class="p" data-group-id="5979015220-17">]</span><span class="p" data-group-id="5979015220-16">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5979015220-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="5979015220-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5979015220-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5979015220-20">[</span><span class="p" data-group-id="5979015220-20">]</span><span class="p" data-group-id="5979015220-19">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="8102392881-21">(</span><span class="p" data-group-id="8102392881-21">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="5979015220-21">(</span><span class="p" data-group-id="5979015220-21">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_pong</span><span class="p" data-group-id="8102392881-22">(</span><span class="p" data-group-id="8102392881-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="8102392881-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="8102392881-24">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8102392881-25">[</span><span class="p" data-group-id="8102392881-25">]</span><span class="p" data-group-id="8102392881-24">)</span><span class="p" data-group-id="8102392881-23">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_pong</span><span class="p" data-group-id="5979015220-22">(</span><span class="p" data-group-id="5979015220-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="5979015220-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="5979015220-24">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5979015220-25">[</span><span class="p" data-group-id="5979015220-25">]</span><span class="p" data-group-id="5979015220-24">)</span><span class="p" data-group-id="5979015220-23">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_ping</span><span class="p" data-group-id="8102392881-26">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="8102392881-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="8102392881-27">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8102392881-28">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8102392881-28">]</span><span class="p" data-group-id="8102392881-27">)</span><span class="p">.</span></code></pre><p>Let us assume there are two computers called gollum and kosken. First a node is
│ │ │ +</span><span class="nf">start_ping</span><span class="p" data-group-id="5979015220-26">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="5979015220-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="5979015220-27">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5979015220-28">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5979015220-28">]</span><span class="p" data-group-id="5979015220-27">)</span><span class="p">.</span></code></pre><p>Let us assume there are two computers called gollum and kosken. First a node is
│ │ │  started on kosken, called ping, and then a node on gollum, called pong.</p><p>On kosken (on a Linux/UNIX system):</p><pre><code class="text">kosken&gt; erl -sname ping
│ │ │  Erlang (BEAM) emulator version 5.2.3.7 [hipe] [threads:0]
│ │ │  
│ │ │  Eshell V5.2.3.7  (abort with ^G)
│ │ │  (ping@kosken)1&gt;</code></pre><p>On gollum:</p><pre><code class="text">gollum&gt; erl -sname pong
│ │ │  Erlang (BEAM) emulator version 5.2.3.7 [hipe] [threads:0]
│ │ │  
│ │ │  Eshell V5.2.3.7  (abort with ^G)
│ │ │ -(pong@gollum)1&gt;</code></pre><p>Now the &quot;pong&quot; process on gollum is started:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_pong</span><span class="p" data-group-id="4886424020-1">(</span><span class="p" data-group-id="4886424020-1">)</span><span class="p">.</span><span class="w">
│ │ │ +(pong@gollum)1&gt;</code></pre><p>Now the &quot;pong&quot; process on gollum is started:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_pong</span><span class="p" data-group-id="5803302326-1">(</span><span class="p" data-group-id="5803302326-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><p>And the &quot;ping&quot; process on kosken is started (from the code above you can see
│ │ │  that a parameter of the <code class="inline">start_ping</code> function is the node name of the Erlang
│ │ │ -system where &quot;pong&quot; is running):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(ping@kosken)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_ping</span><span class="p" data-group-id="9237163029-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="9237163029-1">)</span><span class="p">.</span><span class="w">
│ │ │ +system where &quot;pong&quot; is running):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(ping@kosken)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_ping</span><span class="p" data-group-id="8983763103-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="8983763103-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.37</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>As shown, the ping pong program has run. On the &quot;pong&quot; side:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)2&gt; </span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="nf">finished</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6936311131-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="6936311131-1">)</span><span class="mi">2</span><span class="o">&gt;</span><span class="w"> </span></code></pre><p>Looking at the <code class="inline">tut17</code> code, you see that the <code class="inline">pong</code> function itself is
│ │ │ +</span><span class="p" data-group-id="2847976983-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="2847976983-1">)</span><span class="mi">2</span><span class="o">&gt;</span><span class="w"> </span></code></pre><p>Looking at the <code class="inline">tut17</code> code, you see that the <code class="inline">pong</code> function itself is
│ │ │  unchanged, the following lines work in the same way irrespective of on which
│ │ │ -node the &quot;ping&quot; process is executes:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0400717140-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="0400717140-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0400717140-2">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0400717140-3">[</span><span class="p" data-group-id="0400717140-3">]</span><span class="p" data-group-id="0400717140-2">)</span><span class="p">,</span><span class="w">
│ │ │ +node the &quot;ping&quot; process is executes:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6882803155-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="6882803155-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6882803155-2">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6882803155-3">[</span><span class="p" data-group-id="6882803155-3">]</span><span class="p" data-group-id="6882803155-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span></code></pre><p>Thus, Erlang pids contain information about where the process executes. So if
│ │ │  you know the pid of a process, the <code class="inline">!</code> operator can be used to send it a
│ │ │ -message disregarding if the process is on the same node or on a different node.</p><p>A difference is how messages are sent to a registered process on another node:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4760153520-1">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="4760153520-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4760153520-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4760153520-3">(</span><span class="p" data-group-id="4760153520-3">)</span><span class="p" data-group-id="4760153520-2">}</span><span class="p">,</span></code></pre><p>A tuple <code class="inline">{registered_name,node_name}</code> is used instead of just the
│ │ │ +message disregarding if the process is on the same node or on a different node.</p><p>A difference is how messages are sent to a registered process on another node:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2126570379-1">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2126570379-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2126570379-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2126570379-3">(</span><span class="p" data-group-id="2126570379-3">)</span><span class="p" data-group-id="2126570379-2">}</span><span class="p">,</span></code></pre><p>A tuple <code class="inline">{registered_name,node_name}</code> is used instead of just the
│ │ │  <code class="inline">registered_name</code>.</p><p>In the previous example, &quot;ping&quot; and &quot;pong&quot; were started from the shells of two
│ │ │  separate Erlang nodes. <code class="inline">spawn</code> can also be used to start processes in other
│ │ │  nodes.</p><p>The next example is the ping pong program, yet again, but this time &quot;ping&quot; is
│ │ │ -started in another node:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2900112517-1">(</span><span class="ss">tut18</span><span class="p" data-group-id="2900112517-1">)</span><span class="p">.</span><span class="w">
│ │ │ +started in another node:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8946195098-1">(</span><span class="ss">tut18</span><span class="p" data-group-id="8946195098-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2900112517-2">(</span><span class="p" data-group-id="2900112517-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2900112517-3">]</span><span class="p" data-group-id="2900112517-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8946195098-2">(</span><span class="p" data-group-id="8946195098-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8946195098-3">]</span><span class="p" data-group-id="8946195098-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="2900112517-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2900112517-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2900112517-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2900112517-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2900112517-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2900112517-7">[</span><span class="p" data-group-id="2900112517-7">]</span><span class="p" data-group-id="2900112517-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="8946195098-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8946195098-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8946195098-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8946195098-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8946195098-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8946195098-7">[</span><span class="p" data-group-id="8946195098-7">]</span><span class="p" data-group-id="8946195098-6">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="2900112517-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2900112517-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2900112517-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2900112517-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2900112517-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2900112517-11">(</span><span class="p" data-group-id="2900112517-11">)</span><span class="p" data-group-id="2900112517-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="8946195098-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8946195098-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8946195098-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8946195098-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8946195098-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8946195098-11">(</span><span class="p" data-group-id="8946195098-11">)</span><span class="p" data-group-id="8946195098-10">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2900112517-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2900112517-13">[</span><span class="p" data-group-id="2900112517-13">]</span><span class="p" data-group-id="2900112517-12">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8946195098-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8946195098-13">[</span><span class="p" data-group-id="8946195098-13">]</span><span class="p" data-group-id="8946195098-12">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="2900112517-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2900112517-14">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="8946195098-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8946195098-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="2900112517-15">(</span><span class="p" data-group-id="2900112517-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="8946195098-15">(</span><span class="p" data-group-id="8946195098-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2900112517-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2900112517-17">[</span><span class="p" data-group-id="2900112517-17">]</span><span class="p" data-group-id="2900112517-16">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2900112517-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2900112517-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2900112517-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2900112517-20">[</span><span class="p" data-group-id="2900112517-20">]</span><span class="p" data-group-id="2900112517-19">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8946195098-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8946195098-17">[</span><span class="p" data-group-id="8946195098-17">]</span><span class="p" data-group-id="8946195098-16">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8946195098-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="8946195098-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8946195098-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8946195098-20">[</span><span class="p" data-group-id="8946195098-20">]</span><span class="p" data-group-id="8946195098-19">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="2900112517-21">(</span><span class="p" data-group-id="2900112517-21">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="8946195098-21">(</span><span class="p" data-group-id="8946195098-21">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="2900112517-22">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="2900112517-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="2900112517-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2900112517-24">(</span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2900112517-25">[</span><span class="p" data-group-id="2900112517-25">]</span><span class="p" data-group-id="2900112517-24">)</span><span class="p" data-group-id="2900112517-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2900112517-26">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2900112517-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="2900112517-28">(</span><span class="p" data-group-id="2900112517-28">)</span><span class="p" data-group-id="2900112517-27">]</span><span class="p" data-group-id="2900112517-26">)</span><span class="p">.</span></code></pre><p>Assuming an Erlang system called ping (but not the &quot;ping&quot; process) has already
│ │ │ -been started on kosken, then on gollum this is done:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut18</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7338577930-1">(</span><span class="ss">ping@kosken</span><span class="p" data-group-id="7338577930-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8946195098-22">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="8946195098-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="8946195098-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="8946195098-24">(</span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8946195098-25">[</span><span class="p" data-group-id="8946195098-25">]</span><span class="p" data-group-id="8946195098-24">)</span><span class="p" data-group-id="8946195098-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="8946195098-26">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8946195098-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="8946195098-28">(</span><span class="p" data-group-id="8946195098-28">)</span><span class="p" data-group-id="8946195098-27">]</span><span class="p" data-group-id="8946195098-26">)</span><span class="p">.</span></code></pre><p>Assuming an Erlang system called ping (but not the &quot;ping&quot; process) has already
│ │ │ +been started on kosken, then on gollum this is done:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut18</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1124436813-1">(</span><span class="ss">ping@kosken</span><span class="p" data-group-id="1124436813-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">3934.39</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ @@ -516,188 +516,188 @@
│ │ │  </span><span class="c1">%%% Started: messenger:client(Server_Node, Name)</span><span class="w">
│ │ │  </span><span class="c1">%%% To client: logoff</span><span class="w">
│ │ │  </span><span class="c1">%%% To client: {message_to, ToName, Message}</span><span class="w">
│ │ │  </span><span class="c1">%%%</span><span class="w">
│ │ │  </span><span class="c1">%%% Configuration: change the server_node() function to return the</span><span class="w">
│ │ │  </span><span class="c1">%%% name of the node where the messenger server runs</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3260731430-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="3260731430-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3260731430-2">(</span><span class="p" data-group-id="3260731430-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3260731430-3">]</span><span class="p" data-group-id="3260731430-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0369705331-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="0369705331-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0369705331-2">(</span><span class="p" data-group-id="0369705331-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0369705331-3">]</span><span class="p" data-group-id="0369705331-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Change the function below to return the name of the node where the</span><span class="w">
│ │ │  </span><span class="c1">%%% messenger server runs</span><span class="w">
│ │ │ -</span><span class="nf">server_node</span><span class="p" data-group-id="3260731430-4">(</span><span class="p" data-group-id="3260731430-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_node</span><span class="p" data-group-id="0369705331-4">(</span><span class="p" data-group-id="0369705331-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">messenger@super</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% This is the server process for the &quot;messenger&quot;</span><span class="w">
│ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="3260731430-5">(</span><span class="n">User_List</span><span class="p" data-group-id="3260731430-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="0369705331-5">(</span><span class="n">User_List</span><span class="p" data-group-id="0369705331-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3260731430-6">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3260731430-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="3260731430-7">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-7">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="3260731430-8">(</span><span class="n">New_User_List</span><span class="p" data-group-id="3260731430-8">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3260731430-9">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="3260731430-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="3260731430-10">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-10">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="3260731430-11">(</span><span class="n">New_User_List</span><span class="p" data-group-id="3260731430-11">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3260731430-12">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3260731430-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="3260731430-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-13">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3260731430-14">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3260731430-15">[</span><span class="n">User_List</span><span class="p" data-group-id="3260731430-15">]</span><span class="p" data-group-id="3260731430-14">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="3260731430-16">(</span><span class="n">User_List</span><span class="p" data-group-id="3260731430-16">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0369705331-6">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0369705331-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="0369705331-7">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-7">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="0369705331-8">(</span><span class="n">New_User_List</span><span class="p" data-group-id="0369705331-8">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0369705331-9">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="0369705331-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="0369705331-10">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-10">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="0369705331-11">(</span><span class="n">New_User_List</span><span class="p" data-group-id="0369705331-11">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0369705331-12">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0369705331-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="0369705331-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-13">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0369705331-14">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369705331-15">[</span><span class="n">User_List</span><span class="p" data-group-id="0369705331-15">]</span><span class="p" data-group-id="0369705331-14">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="0369705331-16">(</span><span class="n">User_List</span><span class="p" data-group-id="0369705331-16">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="3260731430-17">(</span><span class="p" data-group-id="3260731430-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="3260731430-18">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="3260731430-19">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3260731430-20">[</span><span class="p" data-group-id="3260731430-21">[</span><span class="p" data-group-id="3260731430-21">]</span><span class="p" data-group-id="3260731430-20">]</span><span class="p" data-group-id="3260731430-19">)</span><span class="p" data-group-id="3260731430-18">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="0369705331-17">(</span><span class="p" data-group-id="0369705331-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="0369705331-18">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0369705331-19">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369705331-20">[</span><span class="p" data-group-id="0369705331-21">[</span><span class="p" data-group-id="0369705331-21">]</span><span class="p" data-group-id="0369705331-20">]</span><span class="p" data-group-id="0369705331-19">)</span><span class="p" data-group-id="0369705331-18">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="3260731430-22">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="0369705331-22">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="3260731430-23">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-23">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="0369705331-23">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-23">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3260731430-24">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="3260731430-24">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0369705331-24">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="0369705331-24">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3260731430-25">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="3260731430-25">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3260731430-26">[</span><span class="p" data-group-id="3260731430-27">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3260731430-27">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-26">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0369705331-25">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="0369705331-25">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="0369705331-26">[</span><span class="p" data-group-id="0369705331-27">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0369705331-27">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-26">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="3260731430-28">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="3260731430-29">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-29">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="0369705331-28">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="0369705331-29">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-29">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="3260731430-30">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="0369705331-30">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3260731430-31">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-31">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="0369705331-31">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-31">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3260731430-32">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="3260731430-32">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3260731430-33">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3260731430-34">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3260731430-34">}</span><span class="p" data-group-id="3260731430-33">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="3260731430-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-35">)</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0369705331-32">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="0369705331-32">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0369705331-33">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369705331-34">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0369705331-34">}</span><span class="p" data-group-id="0369705331-33">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="0369705331-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-35">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="3260731430-36">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="0369705331-36">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3260731430-37">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3260731430-37">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="0369705331-37">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0369705331-37">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3260731430-38">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="3260731430-38">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3260731430-39">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3260731430-40">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="3260731430-40">}</span><span class="p" data-group-id="3260731430-39">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3260731430-41">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3260731430-41">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3260731430-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="3260731430-42">}</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0369705331-38">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="0369705331-38">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0369705331-39">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369705331-40">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="0369705331-40">}</span><span class="p" data-group-id="0369705331-39">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0369705331-41">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0369705331-41">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0369705331-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="0369705331-42">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │  </span><span class="c1">%%% User Commands</span><span class="w">
│ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="3260731430-43">(</span><span class="n">Name</span><span class="p" data-group-id="3260731430-43">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="3260731430-44">(</span><span class="ss">mess_client</span><span class="p" data-group-id="3260731430-44">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="0369705331-43">(</span><span class="n">Name</span><span class="p" data-group-id="0369705331-43">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="0369705331-44">(</span><span class="ss">mess_client</span><span class="p" data-group-id="0369705331-44">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="3260731430-45">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="3260731430-46">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3260731430-47">[</span><span class="nf">server_node</span><span class="p" data-group-id="3260731430-48">(</span><span class="p" data-group-id="3260731430-48">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3260731430-47">]</span><span class="p" data-group-id="3260731430-46">)</span><span class="p" data-group-id="3260731430-45">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="0369705331-45">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="0369705331-46">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369705331-47">[</span><span class="nf">server_node</span><span class="p" data-group-id="0369705331-48">(</span><span class="p" data-group-id="0369705331-48">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0369705331-47">]</span><span class="p" data-group-id="0369705331-46">)</span><span class="p" data-group-id="0369705331-45">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="3260731430-49">(</span><span class="p" data-group-id="3260731430-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="0369705331-49">(</span><span class="p" data-group-id="0369705331-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="3260731430-50">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3260731430-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="3260731430-51">(</span><span class="ss">mess_client</span><span class="p" data-group-id="3260731430-51">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="0369705331-50">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0369705331-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="0369705331-51">(</span><span class="ss">mess_client</span><span class="p" data-group-id="0369705331-51">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3260731430-52">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3260731430-52">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0369705331-52">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0369705331-52">}</span><span class="p">,</span><span class="w">
│ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │  </span><span class="c1">%%% The client process which runs on each server node</span><span class="w">
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="3260731430-53">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3260731430-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3260731430-54">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="3260731430-54">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3260731430-55">{</span><span class="nf">self</span><span class="p" data-group-id="3260731430-56">(</span><span class="p" data-group-id="3260731430-56">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3260731430-55">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="3260731430-57">(</span><span class="p" data-group-id="3260731430-57">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="3260731430-58">(</span><span class="n">Server_Node</span><span class="p" data-group-id="3260731430-58">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="0369705331-53">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0369705331-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0369705331-54">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="0369705331-54">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0369705331-55">{</span><span class="nf">self</span><span class="p" data-group-id="0369705331-56">(</span><span class="p" data-group-id="0369705331-56">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0369705331-55">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="0369705331-57">(</span><span class="p" data-group-id="0369705331-57">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="0369705331-58">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0369705331-58">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="3260731430-59">(</span><span class="n">Server_Node</span><span class="p" data-group-id="3260731430-59">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="0369705331-59">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0369705331-59">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3260731430-60">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="3260731430-60">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3260731430-61">{</span><span class="nf">self</span><span class="p" data-group-id="3260731430-62">(</span><span class="p" data-group-id="3260731430-62">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="3260731430-61">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="3260731430-63">(</span><span class="ss">normal</span><span class="p" data-group-id="3260731430-63">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3260731430-64">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3260731430-64">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3260731430-65">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="3260731430-65">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3260731430-66">{</span><span class="nf">self</span><span class="p" data-group-id="3260731430-67">(</span><span class="p" data-group-id="3260731430-67">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3260731430-66">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="3260731430-68">(</span><span class="p" data-group-id="3260731430-68">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3260731430-69">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3260731430-69">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3260731430-70">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3260731430-71">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3260731430-71">]</span><span class="p" data-group-id="3260731430-70">)</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="0369705331-60">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="0369705331-60">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0369705331-61">{</span><span class="nf">self</span><span class="p" data-group-id="0369705331-62">(</span><span class="p" data-group-id="0369705331-62">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="0369705331-61">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="0369705331-63">(</span><span class="ss">normal</span><span class="p" data-group-id="0369705331-63">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0369705331-64">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0369705331-64">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="0369705331-65">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="0369705331-65">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0369705331-66">{</span><span class="nf">self</span><span class="p" data-group-id="0369705331-67">(</span><span class="p" data-group-id="0369705331-67">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0369705331-66">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="0369705331-68">(</span><span class="p" data-group-id="0369705331-68">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0369705331-69">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0369705331-69">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0369705331-70">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369705331-71">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0369705331-71">]</span><span class="p" data-group-id="0369705331-70">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="3260731430-72">(</span><span class="n">Server_Node</span><span class="p" data-group-id="3260731430-72">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="0369705331-72">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0369705331-72">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="3260731430-73">(</span><span class="p" data-group-id="3260731430-73">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="0369705331-73">(</span><span class="p" data-group-id="0369705331-73">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3260731430-74">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="3260731430-74">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3260731430-75">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3260731430-76">[</span><span class="n">Why</span><span class="p" data-group-id="3260731430-76">]</span><span class="p" data-group-id="3260731430-75">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="3260731430-77">(</span><span class="ss">normal</span><span class="p" data-group-id="3260731430-77">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3260731430-78">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="3260731430-78">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3260731430-79">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3260731430-80">[</span><span class="n">What</span><span class="p" data-group-id="3260731430-80">]</span><span class="p" data-group-id="3260731430-79">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0369705331-74">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="0369705331-74">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0369705331-75">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369705331-76">[</span><span class="n">Why</span><span class="p" data-group-id="0369705331-76">]</span><span class="p" data-group-id="0369705331-75">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="0369705331-77">(</span><span class="ss">normal</span><span class="p" data-group-id="0369705331-77">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0369705331-78">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="0369705331-78">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0369705331-79">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369705331-80">[</span><span class="n">What</span><span class="p" data-group-id="0369705331-80">]</span><span class="p" data-group-id="0369705331-79">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>To use this program, you need to:</p><ul><li>Configure the <code class="inline">server_node()</code> function.</li><li>Copy the compiled code (<code class="inline">messenger.beam</code>) to the directory on each computer
│ │ │  where you start Erlang.</li></ul><p>In the following example using this program, nodes are started on four different
│ │ │  computers. If you do not have that many machines available on your network, you
│ │ │  can start several nodes on the same machine.</p><p>Four Erlang nodes are started up: messenger@super, c1@bilbo, c2@kosken,
│ │ │ -c3@gollum.</p><p>First the server at messenger@super is started up:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(messenger@super)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">start_server</span><span class="p" data-group-id="3249967324-1">(</span><span class="p" data-group-id="3249967324-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">true</span></code></pre><p>Now Peter logs on at c1@bilbo:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="6572654130-1">(</span><span class="ss">peter</span><span class="p" data-group-id="6572654130-1">)</span><span class="p">.</span><span class="w">
│ │ │ +c3@gollum.</p><p>First the server at messenger@super is started up:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(messenger@super)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">start_server</span><span class="p" data-group-id="6299174328-1">(</span><span class="p" data-group-id="6299174328-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">true</span></code></pre><p>Now Peter logs on at c1@bilbo:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="3796742722-1">(</span><span class="ss">peter</span><span class="p" data-group-id="3796742722-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="ss">logged_on</span></code></pre><p>James logs on at c2@kosken:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="4940707012-1">(</span><span class="ss">james</span><span class="p" data-group-id="4940707012-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">logged_on</span></code></pre><p>James logs on at c2@kosken:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="9132361868-1">(</span><span class="ss">james</span><span class="p" data-group-id="9132361868-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="ss">logged_on</span></code></pre><p>And Fred logs on at c3@gollum:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c3@gollum)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="6233097900-1">(</span><span class="ss">fred</span><span class="p" data-group-id="6233097900-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">logged_on</span></code></pre><p>And Fred logs on at c3@gollum:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c3@gollum)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="2220935876-1">(</span><span class="ss">fred</span><span class="p" data-group-id="2220935876-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="ss">logged_on</span></code></pre><p>Now Peter sends Fred a message:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="6605187717-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6605187717-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">logged_on</span></code></pre><p>Now Peter sends Fred a message:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="9383278981-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="9383278981-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="ss">sent</span></code></pre><p>Fred receives the message and sends a message to Peter and logs off:</p><pre><code class="makeup erlang" translate="no"><span class="n">Message</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="nc">peter</span><span class="p">:</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="gp unselectable">
│ │ │ -(c3@gollum)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="4773325537-1">(</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;go away, I&#39;m busy&quot;</span><span class="p" data-group-id="4773325537-1">)</span><span class="p">.</span><span class="w">
│ │ │ +(c3@gollum)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="4114147687-1">(</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;go away, I&#39;m busy&quot;</span><span class="p" data-group-id="4114147687-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="nf">sent</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4773325537-2">(</span><span class="ss">c3@gollum</span><span class="p" data-group-id="4773325537-2">)</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logoff</span><span class="p" data-group-id="4773325537-3">(</span><span class="p" data-group-id="4773325537-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">logoff</span></code></pre><p>James now tries to send a message to Fred:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="4194713764-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;peter doesn&#39;t like you&quot;</span><span class="p" data-group-id="4194713764-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4114147687-2">(</span><span class="ss">c3@gollum</span><span class="p" data-group-id="4114147687-2">)</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logoff</span><span class="p" data-group-id="4114147687-3">(</span><span class="p" data-group-id="4114147687-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">logoff</span></code></pre><p>James now tries to send a message to Fred:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="2725906871-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;peter doesn&#39;t like you&quot;</span><span class="p" data-group-id="2725906871-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="ss">receiver_not_found</span></code></pre><p>But this fails as Fred has already logged off.</p><p>First let us look at some of the new concepts that have been introduced.</p><p>There are two versions of the <code class="inline">server_transfer</code> function: one with four
│ │ │  arguments (<code class="inline">server_transfer/4</code>) and one with five (<code class="inline">server_transfer/5</code>). These
│ │ │  are regarded by Erlang as two separate functions.</p><p>Notice how to write the <code class="inline">server</code> function so that it calls itself, through
│ │ │  <code class="inline">server(User_List)</code>, and thus creates a loop. The Erlang compiler is &quot;clever&quot;
│ │ │  and optimizes the code so that this really is a sort of loop and not a proper
│ │ │  function call. But this only works if there is no code after the call.
│ │ │  Otherwise, the compiler expects the call to return and make a proper function
│ │ │  call. This would result in the process getting bigger and bigger for every loop.</p><p>Functions in the <code class="inline">lists</code> module are used. This is a very useful module and a
│ │ │  study of the manual page is recommended (<code class="inline">erl -man lists</code>).
│ │ │  <code class="inline">lists:keymember(Key,Position,Lists)</code> looks through a list of tuples and looks
│ │ │  at <code class="inline">Position</code> in each tuple to see if it is the same as <code class="inline">Key</code>. The first element
│ │ │  is position 1. If it finds a tuple where the element at <code class="inline">Position</code> is the same
│ │ │ -as <code class="inline">Key</code>, it returns <code class="inline">true</code>, otherwise <code class="inline">false</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="3492583379-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3492583379-2">[</span><span class="p" data-group-id="3492583379-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="3492583379-3">}</span><span class="p">,</span><span class="p" data-group-id="3492583379-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3492583379-4">}</span><span class="p">,</span><span class="p" data-group-id="3492583379-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3492583379-5">}</span><span class="p">,</span><span class="p" data-group-id="3492583379-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="3492583379-6">}</span><span class="p" data-group-id="3492583379-2">]</span><span class="p" data-group-id="3492583379-1">)</span><span class="p">.</span><span class="w">
│ │ │ +as <code class="inline">Key</code>, it returns <code class="inline">true</code>, otherwise <code class="inline">false</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="7844705328-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7844705328-2">[</span><span class="p" data-group-id="7844705328-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="7844705328-3">}</span><span class="p">,</span><span class="p" data-group-id="7844705328-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7844705328-4">}</span><span class="p">,</span><span class="p" data-group-id="7844705328-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7844705328-5">}</span><span class="p">,</span><span class="p" data-group-id="7844705328-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="7844705328-6">}</span><span class="p" data-group-id="7844705328-2">]</span><span class="p" data-group-id="7844705328-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="3492583379-7">(</span><span class="ss">p</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3492583379-8">[</span><span class="p" data-group-id="3492583379-9">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="3492583379-9">}</span><span class="p">,</span><span class="p" data-group-id="3492583379-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3492583379-10">}</span><span class="p">,</span><span class="p" data-group-id="3492583379-11">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3492583379-11">}</span><span class="p">,</span><span class="p" data-group-id="3492583379-12">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="3492583379-12">}</span><span class="p" data-group-id="3492583379-8">]</span><span class="p" data-group-id="3492583379-7">)</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="7844705328-7">(</span><span class="ss">p</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7844705328-8">[</span><span class="p" data-group-id="7844705328-9">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="7844705328-9">}</span><span class="p">,</span><span class="p" data-group-id="7844705328-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7844705328-10">}</span><span class="p">,</span><span class="p" data-group-id="7844705328-11">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7844705328-11">}</span><span class="p">,</span><span class="p" data-group-id="7844705328-12">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="7844705328-12">}</span><span class="p" data-group-id="7844705328-8">]</span><span class="p" data-group-id="7844705328-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre><p><code class="inline">lists:keydelete</code> works in the same way but deletes the first tuple found (if
│ │ │ -any) and returns the remaining list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="5960013513-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5960013513-2">[</span><span class="p" data-group-id="5960013513-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="5960013513-3">}</span><span class="p">,</span><span class="p" data-group-id="5960013513-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5960013513-4">}</span><span class="p">,</span><span class="p" data-group-id="5960013513-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5960013513-5">}</span><span class="p">,</span><span class="p" data-group-id="5960013513-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="5960013513-6">}</span><span class="p" data-group-id="5960013513-2">]</span><span class="p" data-group-id="5960013513-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5960013513-7">[</span><span class="p" data-group-id="5960013513-8">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="5960013513-8">}</span><span class="p">,</span><span class="p" data-group-id="5960013513-9">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5960013513-9">}</span><span class="p">,</span><span class="p" data-group-id="5960013513-10">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="5960013513-10">}</span><span class="p" data-group-id="5960013513-7">]</span></code></pre><p><code class="inline">lists:keysearch</code> is like <code class="inline">lists:keymember</code>, but it returns
│ │ │ +any) and returns the remaining list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="8128640061-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8128640061-2">[</span><span class="p" data-group-id="8128640061-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="8128640061-3">}</span><span class="p">,</span><span class="p" data-group-id="8128640061-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8128640061-4">}</span><span class="p">,</span><span class="p" data-group-id="8128640061-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8128640061-5">}</span><span class="p">,</span><span class="p" data-group-id="8128640061-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="8128640061-6">}</span><span class="p" data-group-id="8128640061-2">]</span><span class="p" data-group-id="8128640061-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8128640061-7">[</span><span class="p" data-group-id="8128640061-8">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="8128640061-8">}</span><span class="p">,</span><span class="p" data-group-id="8128640061-9">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8128640061-9">}</span><span class="p">,</span><span class="p" data-group-id="8128640061-10">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="8128640061-10">}</span><span class="p" data-group-id="8128640061-7">]</span></code></pre><p><code class="inline">lists:keysearch</code> is like <code class="inline">lists:keymember</code>, but it returns
│ │ │  <code class="inline">{value,Tuple_Found}</code> or the atom <code class="inline">false</code>.</p><p>There are many very useful functions in the <code class="inline">lists</code> module.</p><p>An Erlang process (conceptually) runs until it does a <code class="inline">receive</code> and there is no
│ │ │  message which it wants to receive in the message queue. &quot;conceptually&quot; is used
│ │ │  here because the Erlang system shares the CPU time between the active processes
│ │ │  in the system.</p><p>A process terminates when there is nothing more for it to do, that is, the last
│ │ │  function it calls simply returns and does not call another function. Another way
│ │ │  for a process to terminate is for it to call <a href="../../erts-15.2.7/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a>. The argument
│ │ │  to <a href="../../erts-15.2.7/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a> has a special meaning, which is discussed later. In this
│ │ │  example, <a href="../../erts-15.2.7/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a> is done, which has the same effect as a
│ │ │  process running out of functions to call.</p><p>The BIF <a href="../../erts-15.2.7/doc/html/erlang.html#whereis/1"><code class="inline">whereis(RegisteredName)</code></a> checks if a registered process
│ │ │  of name <code class="inline">RegisteredName</code> exists. If it exists, the pid of that process is
│ │ │  returned. If it does not exist, the atom <code class="inline">undefined</code> is returned.</p><p>You should by now be able to understand most of the code in the
│ │ │  messenger-module. Let us study one case in detail: a message is sent from one
│ │ │ -user to another.</p><p>The first user &quot;sends&quot; the message in the example above by:</p><pre><code class="makeup erlang" translate="no"><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="2999881377-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="2999881377-1">)</span></code></pre><p>After testing that the client process exists:</p><pre><code class="makeup erlang" translate="no"><span class="nf">whereis</span><span class="p" data-group-id="2114505056-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="2114505056-1">)</span></code></pre><p>And a message is sent to <code class="inline">mess_client</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8453934192-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8453934192-1">}</span></code></pre><p>The client sends the message to the server by:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7748031144-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="7748031144-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7748031144-2">{</span><span class="nf">self</span><span class="p" data-group-id="7748031144-3">(</span><span class="p" data-group-id="7748031144-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7748031144-2">}</span><span class="p">,</span></code></pre><p>And waits for a reply from the server.</p><p>The server receives this message and calls:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="6291410114-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6291410114-1">)</span><span class="p">,</span></code></pre><p>This checks that the pid <code class="inline">From</code> is in the <code class="inline">User_List</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="0672533606-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0672533606-1">)</span></code></pre><p>If <code class="inline">keysearch</code> returns the atom <code class="inline">false</code>, some error has occurred and the server
│ │ │ -sends back the message:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5681769917-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="5681769917-1">}</span></code></pre><p>This is received by the client, which in turn does <a href="../../erts-15.2.7/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a>
│ │ │ +user to another.</p><p>The first user &quot;sends&quot; the message in the example above by:</p><pre><code class="makeup erlang" translate="no"><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="0340712915-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0340712915-1">)</span></code></pre><p>After testing that the client process exists:</p><pre><code class="makeup erlang" translate="no"><span class="nf">whereis</span><span class="p" data-group-id="2791410084-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="2791410084-1">)</span></code></pre><p>And a message is sent to <code class="inline">mess_client</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5496443666-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5496443666-1">}</span></code></pre><p>The client sends the message to the server by:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0633765964-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="0633765964-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0633765964-2">{</span><span class="nf">self</span><span class="p" data-group-id="0633765964-3">(</span><span class="p" data-group-id="0633765964-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0633765964-2">}</span><span class="p">,</span></code></pre><p>And waits for a reply from the server.</p><p>The server receives this message and calls:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="9981286165-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9981286165-1">)</span><span class="p">,</span></code></pre><p>This checks that the pid <code class="inline">From</code> is in the <code class="inline">User_List</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="4187489983-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4187489983-1">)</span></code></pre><p>If <code class="inline">keysearch</code> returns the atom <code class="inline">false</code>, some error has occurred and the server
│ │ │ +sends back the message:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1511379509-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="1511379509-1">}</span></code></pre><p>This is received by the client, which in turn does <a href="../../erts-15.2.7/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a>
│ │ │  and terminates. If <code class="inline">keysearch</code> returns <code class="inline">{value,{From,Name}}</code> it is certain that
│ │ │ -the user is logged on and that his name (peter) is in variable <code class="inline">Name</code>.</p><p>Let us now call:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="5274093185-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5274093185-1">)</span></code></pre><p>Notice that as this is <code class="inline">server_transfer/5</code>, it is not the same as the previous
│ │ │ +the user is logged on and that his name (peter) is in variable <code class="inline">Name</code>.</p><p>Let us now call:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="0625726752-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0625726752-1">)</span></code></pre><p>Notice that as this is <code class="inline">server_transfer/5</code>, it is not the same as the previous
│ │ │  function <code class="inline">server_transfer/4</code>. Another <code class="inline">keysearch</code> is done on <code class="inline">User_List</code> to find
│ │ │ -the pid of the client corresponding to fred:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="1743669243-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="1743669243-1">)</span></code></pre><p>This time argument 2 is used, which is the second element in the tuple. If this
│ │ │ +the pid of the client corresponding to fred:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3175543087-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3175543087-1">)</span></code></pre><p>This time argument 2 is used, which is the second element in the tuple. If this
│ │ │  returns the atom <code class="inline">false</code>, fred is not logged on and the following message is
│ │ │ -sent:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0974152217-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="0974152217-1">}</span><span class="p">;</span></code></pre><p>This is received by the client.</p><p>If <code class="inline">keysearch</code> returns:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5065206768-1">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5065206768-2">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p" data-group-id="5065206768-2">}</span><span class="p" data-group-id="5065206768-1">}</span></code></pre><p>The following message is sent to fred's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7634774888-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7634774888-1">}</span><span class="p">,</span></code></pre><p>The following message is sent to peter's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0685937774-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="0685937774-1">}</span></code></pre><p>Fred's client receives the message and prints it:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8807087464-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8807087464-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8807087464-2">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8807087464-3">[</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8807087464-3">]</span><span class="p" data-group-id="8807087464-2">)</span></code></pre><p>Peter's client receives the message in the <code class="inline">await_result</code> function.</p>
│ │ │ +sent:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9194582849-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="9194582849-1">}</span><span class="p">;</span></code></pre><p>This is received by the client.</p><p>If <code class="inline">keysearch</code> returns:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7075953524-1">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7075953524-2">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p" data-group-id="7075953524-2">}</span><span class="p" data-group-id="7075953524-1">}</span></code></pre><p>The following message is sent to fred's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4379665950-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4379665950-1">}</span><span class="p">,</span></code></pre><p>The following message is sent to peter's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7484090695-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="7484090695-1">}</span></code></pre><p>Fred's client receives the message and prints it:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0015705232-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0015705232-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0015705232-2">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0015705232-3">[</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0015705232-3">]</span><span class="p" data-group-id="0015705232-2">)</span></code></pre><p>Peter's client receives the message in the <code class="inline">await_result</code> function.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="seq_prog.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/create_target.html
│ │ │ @@ -138,21 +138,21 @@
│ │ │    <span class="text">Creating a Target System</span>
│ │ │  </h2>
│ │ │  <p>It is assumed that you have a working Erlang/OTP system structured according to
│ │ │  the OTP design principles.</p><p><em>Step 1.</em> Create a <code class="inline">.rel</code> file (see the <a href="../../lib/sasl-4.2.2/doc/html/rel.html">rel(4)</a> manual page in
│ │ │  SASL), which specifies the ERTS version and lists all applications that are to
│ │ │  be included in the new basic target system. An example is the following
│ │ │  <code class="inline">mysystem.rel</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% mysystem.rel</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0024962340-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0024962340-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;FIRST&quot;</span><span class="p" data-group-id="0024962340-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0024962340-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.10.4&quot;</span><span class="p" data-group-id="0024962340-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0024962340-4">[</span><span class="p" data-group-id="0024962340-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.16.4&quot;</span><span class="p" data-group-id="0024962340-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0024962340-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.19.4&quot;</span><span class="p" data-group-id="0024962340-6">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0024962340-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.3.4&quot;</span><span class="p" data-group-id="0024962340-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0024962340-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="0024962340-8">}</span><span class="p" data-group-id="0024962340-4">]</span><span class="p" data-group-id="0024962340-1">}</span><span class="p">.</span></code></pre><p>The listed applications are not only original Erlang/OTP applications but
│ │ │ +</span><span class="p" data-group-id="2664167120-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2664167120-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;FIRST&quot;</span><span class="p" data-group-id="2664167120-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2664167120-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.10.4&quot;</span><span class="p" data-group-id="2664167120-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2664167120-4">[</span><span class="p" data-group-id="2664167120-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.16.4&quot;</span><span class="p" data-group-id="2664167120-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2664167120-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.19.4&quot;</span><span class="p" data-group-id="2664167120-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2664167120-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.3.4&quot;</span><span class="p" data-group-id="2664167120-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2664167120-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="2664167120-8">}</span><span class="p" data-group-id="2664167120-4">]</span><span class="p" data-group-id="2664167120-1">}</span><span class="p">.</span></code></pre><p>The listed applications are not only original Erlang/OTP applications but
│ │ │  possibly also new applications that you have written (here exemplified by the
│ │ │  application Pea (<code class="inline">pea</code>)).</p><p><em>Step 2.</em> Start Erlang/OTP from the directory where the <code class="inline">mysystem.rel</code> file
│ │ │  resides:</p><pre><code class="text">% erl -pa /home/user/target_system/myapps/pea-1.0/ebin</code></pre><p>The <code class="inline">-pa</code> argument prepends the path to the <code class="inline">ebin</code> directory for
│ │ │  the Pea application to the code path.</p><p><em>Step 3.</em> Create the target system:</p><pre><code class="text">1&gt; target_system:create(&quot;mysystem&quot;).</code></pre><p>The function <code class="inline">target_system:create/1</code> performs the following:</p><ol><li><p>Reads the file <code class="inline">mysystem.rel</code> and creates a new file <code class="inline">plain.rel</code>.
│ │ │  The new file is identical to the original, except that it only
│ │ │  lists the Kernel and STDLIB applications.</p></li><li><p>From the files <code class="inline">mysystem.rel</code> and <code class="inline">plain.rel</code> creates the files
│ │ │  <code class="inline">mysystem.script</code>, <code class="inline">mysystem.boot</code>, <code class="inline">plain.script</code>, and <code class="inline">plain.boot</code>
│ │ │ @@ -242,25 +242,25 @@
│ │ │    <a href="#creating-the-next-version" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating the Next Version</span>
│ │ │  </h2>
│ │ │  <p>In this example the Pea application has been changed, and so are the
│ │ │  applications ERTS, Kernel, STDLIB and SASL.</p><p><em>Step 1.</em> Create the file <code class="inline">.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% mysystem2.rel</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4282881093-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4282881093-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;SECOND&quot;</span><span class="p" data-group-id="4282881093-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4282881093-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;6.0&quot;</span><span class="p" data-group-id="4282881093-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4282881093-4">[</span><span class="p" data-group-id="4282881093-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;3.0&quot;</span><span class="p" data-group-id="4282881093-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4282881093-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="4282881093-6">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4282881093-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.4&quot;</span><span class="p" data-group-id="4282881093-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4282881093-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="4282881093-8">}</span><span class="p" data-group-id="4282881093-4">]</span><span class="p" data-group-id="4282881093-1">}</span><span class="p">.</span></code></pre><p><em>Step 2.</em> Create the application upgrade file (see
│ │ │ +</span><span class="p" data-group-id="7491804784-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7491804784-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;SECOND&quot;</span><span class="p" data-group-id="7491804784-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7491804784-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;6.0&quot;</span><span class="p" data-group-id="7491804784-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7491804784-4">[</span><span class="p" data-group-id="7491804784-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;3.0&quot;</span><span class="p" data-group-id="7491804784-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="7491804784-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="7491804784-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="7491804784-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.4&quot;</span><span class="p" data-group-id="7491804784-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="7491804784-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="7491804784-8">}</span><span class="p" data-group-id="7491804784-4">]</span><span class="p" data-group-id="7491804784-1">}</span><span class="p">.</span></code></pre><p><em>Step 2.</em> Create the application upgrade file (see
│ │ │  <a href="../../lib/sasl-4.2.2/doc/html/appup.html">appup</a> in SASL) for Pea, for example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% pea.appup</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6627778194-1">{</span><span class="s">&quot;2.0&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6627778194-2">[</span><span class="p" data-group-id="6627778194-3">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="6627778194-4">[</span><span class="p" data-group-id="6627778194-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="6627778194-5">}</span><span class="p" data-group-id="6627778194-4">]</span><span class="p" data-group-id="6627778194-3">}</span><span class="p" data-group-id="6627778194-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6627778194-6">[</span><span class="p" data-group-id="6627778194-7">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="6627778194-8">[</span><span class="p" data-group-id="6627778194-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="6627778194-9">}</span><span class="p" data-group-id="6627778194-8">]</span><span class="p" data-group-id="6627778194-7">}</span><span class="p" data-group-id="6627778194-6">]</span><span class="p" data-group-id="6627778194-1">}</span><span class="p">.</span></code></pre><p><em>Step 3.</em> From the directory where the file <code class="inline">mysystem2.rel</code> resides, start the
│ │ │ +</span><span class="p" data-group-id="3814081871-1">{</span><span class="s">&quot;2.0&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3814081871-2">[</span><span class="p" data-group-id="3814081871-3">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="3814081871-4">[</span><span class="p" data-group-id="3814081871-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="3814081871-5">}</span><span class="p" data-group-id="3814081871-4">]</span><span class="p" data-group-id="3814081871-3">}</span><span class="p" data-group-id="3814081871-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3814081871-6">[</span><span class="p" data-group-id="3814081871-7">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="3814081871-8">[</span><span class="p" data-group-id="3814081871-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="3814081871-9">}</span><span class="p" data-group-id="3814081871-8">]</span><span class="p" data-group-id="3814081871-7">}</span><span class="p" data-group-id="3814081871-6">]</span><span class="p" data-group-id="3814081871-1">}</span><span class="p">.</span></code></pre><p><em>Step 3.</em> From the directory where the file <code class="inline">mysystem2.rel</code> resides, start the
│ │ │  Erlang/OTP system, giving the path to the new version of Pea:</p><pre><code class="text">% erl -pa /home/user/target_system/myapps/pea-2.0/ebin</code></pre><p><em>Step 4.</em> Create the release upgrade file (see <a href="../../lib/sasl-4.2.2/doc/html/relup.html">relup</a>
│ │ │  in SASL):</p><pre><code class="text">1&gt; systools:make_relup(&quot;mysystem2&quot;,[&quot;mysystem&quot;],[&quot;mysystem&quot;],
│ │ │      [{path,[&quot;/home/user/target_system/myapps/pea-1.0/ebin&quot;,
│ │ │      &quot;/my/old/erlang/lib/*/ebin&quot;]}]).</code></pre><p>Here <code class="inline">&quot;mysystem&quot;</code> is the base release and <code class="inline">&quot;mysystem2&quot;</code> is the release to
│ │ │  upgrade to.</p><p>The <code class="inline">path</code> option is used for pointing out the old version of all applications.
│ │ │  (The new versions are already in the code path - assuming of course that the
│ │ │  Erlang node on which this is executed is running the correct version of
│ │ │ @@ -292,21 +292,21 @@
│ │ │  {continue_after_restart,&quot;FIRST&quot;,[]}
│ │ │  heart: Tue Apr  1 12:15:10 2014: Erlang has closed.
│ │ │  heart: Tue Apr  1 12:15:11 2014: Executed &quot;/usr/local/erl-target/bin/start /usr/local/erl-target/releases/new_start_erl.data&quot; -&gt; 0. Terminating.
│ │ │  [End]</code></pre><p>The above return value and output after the call to
│ │ │  <a href="../../lib/sasl-4.2.2/doc/html/release_handler.html#install_release/1"><code class="inline">release_handler:install_release/1</code></a> means that the <code class="inline">release_handler</code> has
│ │ │  restarted the node by using <code class="inline">heart</code>. This is always done when the upgrade
│ │ │  involves a change of the applications ERTS, Kernel, STDLIB, or SASL. For more
│ │ │ -information, see <a href="upgrade.html">Upgrade when Erlang/OTP has Changed</a>.</p><p>The node is accessible through a new pipe:</p><pre><code class="text">% /usr/local/erl-target/bin/to_erl /tmp/erlang.pipe.2</code></pre><p>List the available releases in the system:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">which_releases</span><span class="p" data-group-id="6745675648-1">(</span><span class="p" data-group-id="6745675648-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6745675648-2">[</span><span class="p" data-group-id="6745675648-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6745675648-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="6745675648-4">]</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">current</span><span class="p" data-group-id="6745675648-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6745675648-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6745675648-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="6745675648-6">]</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">permanent</span><span class="p" data-group-id="6745675648-5">}</span><span class="p" data-group-id="6745675648-2">]</span></code></pre><p>Our new release, &quot;SECOND&quot;, is now the current release, but we can also see that
│ │ │ +information, see <a href="upgrade.html">Upgrade when Erlang/OTP has Changed</a>.</p><p>The node is accessible through a new pipe:</p><pre><code class="text">% /usr/local/erl-target/bin/to_erl /tmp/erlang.pipe.2</code></pre><p>List the available releases in the system:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">which_releases</span><span class="p" data-group-id="0608420183-1">(</span><span class="p" data-group-id="0608420183-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0608420183-2">[</span><span class="p" data-group-id="0608420183-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="0608420183-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="0608420183-4">]</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">current</span><span class="p" data-group-id="0608420183-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0608420183-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="0608420183-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="0608420183-6">]</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">permanent</span><span class="p" data-group-id="0608420183-5">}</span><span class="p" data-group-id="0608420183-2">]</span></code></pre><p>Our new release, &quot;SECOND&quot;, is now the current release, but we can also see that
│ │ │  our &quot;FIRST&quot; release is still permanent. This means that if the node would be
│ │ │  restarted now, it would come up running the &quot;FIRST&quot; release again.</p><p><em>Step 3.</em> Make the new release permanent:</p><pre><code class="text">2&gt; release_handler:make_permanent(&quot;SECOND&quot;).</code></pre><p>Check the releases again:</p><pre><code class="c">3&gt; release_handler:which_releases().
│ │ │  [{&quot;MYSYSTEM&quot;,&quot;SECOND&quot;,
│ │ │    [&quot;kernel-3.0&quot;,&quot;stdlib-2.0&quot;,&quot;sasl-2.4&quot;,&quot;pea-2.0&quot;],
│ │ │    permanent},
│ │ │   {&quot;MYSYSTEM&quot;,&quot;FIRST&quot;,
│ │ │    [&quot;kernel-2.16.4&quot;,&quot;stdlib-1.19.4&quot;,&quot;sasl-2.3.4&quot;,&quot;pea-1.0&quot;],
│ │ │ @@ -315,268 +315,268 @@
│ │ │    <a href="#listing-of-target_system-erl" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Listing of target_system.erl</span>
│ │ │  </h2>
│ │ │  <p>This module can also be found in the <code class="inline">examples</code> directory of the SASL
│ │ │  application.</p><pre><code class="makeup erlang" translate="no"><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6763615923-1">(</span><span class="ss">target_system</span><span class="p" data-group-id="6763615923-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6763615923-2">(</span><span class="p" data-group-id="6763615923-3">[</span><span class="ss">create</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">create</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">install</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6763615923-3">]</span><span class="p" data-group-id="6763615923-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2312876650-1">(</span><span class="ss">target_system</span><span class="p" data-group-id="2312876650-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2312876650-2">(</span><span class="p" data-group-id="2312876650-3">[</span><span class="ss">create</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">create</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">install</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2312876650-3">]</span><span class="p" data-group-id="2312876650-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% Note: RelFileName below is the *stem* without trailing .rel,</span><span class="w">
│ │ │  </span><span class="c1">%% .script etc.</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% create(RelFileName)</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">create</span><span class="p" data-group-id="6763615923-4">(</span><span class="n">RelFileName</span><span class="p" data-group-id="6763615923-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">create</span><span class="p" data-group-id="6763615923-5">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="p" data-group-id="6763615923-6">[</span><span class="p" data-group-id="6763615923-6">]</span><span class="p" data-group-id="6763615923-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">create</span><span class="p" data-group-id="2312876650-4">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2312876650-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">create</span><span class="p" data-group-id="2312876650-5">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="p" data-group-id="2312876650-6">[</span><span class="p" data-group-id="2312876650-6">]</span><span class="p" data-group-id="2312876650-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">create</span><span class="p" data-group-id="6763615923-7">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="6763615923-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">create</span><span class="p" data-group-id="2312876650-7">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2312876650-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">RelFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="6763615923-8">(</span><span class="n">RelFileName</span><span class="p" data-group-id="6763615923-8">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-9">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;plain&quot;</span><span class="p" data-group-id="6763615923-9">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="2312876650-8">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2312876650-8">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-9">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;plain&quot;</span><span class="p" data-group-id="2312876650-9">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">PlainRelFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-10">(</span><span class="s">&quot;Reading file: ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-11">[</span><span class="n">RelFile</span><span class="p" data-group-id="6763615923-11">]</span><span class="p" data-group-id="6763615923-10">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-13">[</span><span class="n">RelSpec</span><span class="p" data-group-id="6763615923-13">]</span><span class="p" data-group-id="6763615923-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">consult</span><span class="p" data-group-id="6763615923-14">(</span><span class="n">RelFile</span><span class="p" data-group-id="6763615923-14">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-15">(</span><span class="s">&quot;Creating file: ~ts from ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="6763615923-16">[</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="n">RelFile</span><span class="p" data-group-id="6763615923-16">]</span><span class="p" data-group-id="6763615923-15">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-17">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="6763615923-18">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="6763615923-18">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="6763615923-19">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="6763615923-19">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="n">AppVsns</span><span class="p" data-group-id="6763615923-17">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelSpec</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">PlainRelSpec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6763615923-20">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="6763615923-21">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="6763615923-21">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="6763615923-22">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="6763615923-22">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="6763615923-23">(</span><span class="nf">fun</span><span class="p" data-group-id="6763615923-24">(</span><span class="p" data-group-id="6763615923-25">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6763615923-25">}</span><span class="p" data-group-id="6763615923-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-10">(</span><span class="s">&quot;Reading file: ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-11">[</span><span class="n">RelFile</span><span class="p" data-group-id="2312876650-11">]</span><span class="p" data-group-id="2312876650-10">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-13">[</span><span class="n">RelSpec</span><span class="p" data-group-id="2312876650-13">]</span><span class="p" data-group-id="2312876650-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">consult</span><span class="p" data-group-id="2312876650-14">(</span><span class="n">RelFile</span><span class="p" data-group-id="2312876650-14">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-15">(</span><span class="s">&quot;Creating file: ~ts from ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2312876650-16">[</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="n">RelFile</span><span class="p" data-group-id="2312876650-16">]</span><span class="p" data-group-id="2312876650-15">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-17">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="2312876650-18">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="2312876650-18">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="2312876650-19">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="2312876650-19">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="n">AppVsns</span><span class="p" data-group-id="2312876650-17">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelSpec</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">PlainRelSpec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2312876650-20">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="2312876650-21">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="2312876650-21">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="2312876650-22">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="2312876650-22">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="2312876650-23">(</span><span class="nf">fun</span><span class="p" data-group-id="2312876650-24">(</span><span class="p" data-group-id="2312876650-25">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2312876650-25">}</span><span class="p" data-group-id="2312876650-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                                           </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ -                                    </span><span class="p" data-group-id="6763615923-26">(</span><span class="p" data-group-id="6763615923-27">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6763615923-27">}</span><span class="p" data-group-id="6763615923-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                                    </span><span class="p" data-group-id="2312876650-26">(</span><span class="p" data-group-id="2312876650-27">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2312876650-27">}</span><span class="p" data-group-id="2312876650-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                                           </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ -                                    </span><span class="p" data-group-id="6763615923-28">(</span><span class="p">_</span><span class="p" data-group-id="6763615923-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                                    </span><span class="p" data-group-id="2312876650-28">(</span><span class="p">_</span><span class="p" data-group-id="2312876650-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                                           </span><span class="ss">false</span><span class="w">
│ │ │ -                                 </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsns</span><span class="p" data-group-id="6763615923-23">)</span><span class="w">
│ │ │ -                   </span><span class="p" data-group-id="6763615923-20">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="6763615923-29">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="6763615923-30">(</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-31">[</span><span class="ss">write</span><span class="p" data-group-id="6763615923-31">]</span><span class="p" data-group-id="6763615923-30">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-32">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-33">[</span><span class="n">PlainRelSpec</span><span class="p" data-group-id="6763615923-33">]</span><span class="p" data-group-id="6763615923-32">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="6763615923-34">(</span><span class="n">Fd</span><span class="p" data-group-id="6763615923-34">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-35">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -	      </span><span class="p" data-group-id="6763615923-36">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">PlainRelFileName</span><span class="p" data-group-id="6763615923-36">]</span><span class="p" data-group-id="6763615923-35">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">make_script</span><span class="p" data-group-id="6763615923-37">(</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="6763615923-37">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-38">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="6763615923-39">[</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="6763615923-39">]</span><span class="p" data-group-id="6763615923-38">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">make_script</span><span class="p" data-group-id="6763615923-40">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="6763615923-40">)</span><span class="p">,</span><span class="w">
│ │ │ +                                 </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsns</span><span class="p" data-group-id="2312876650-23">)</span><span class="w">
│ │ │ +                   </span><span class="p" data-group-id="2312876650-20">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2312876650-29">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="2312876650-30">(</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-31">[</span><span class="ss">write</span><span class="p" data-group-id="2312876650-31">]</span><span class="p" data-group-id="2312876650-30">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-32">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-33">[</span><span class="n">PlainRelSpec</span><span class="p" data-group-id="2312876650-33">]</span><span class="p" data-group-id="2312876650-32">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2312876650-34">(</span><span class="n">Fd</span><span class="p" data-group-id="2312876650-34">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-35">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +	      </span><span class="p" data-group-id="2312876650-36">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">PlainRelFileName</span><span class="p" data-group-id="2312876650-36">]</span><span class="p" data-group-id="2312876650-35">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">make_script</span><span class="p" data-group-id="2312876650-37">(</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2312876650-37">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-38">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2312876650-39">[</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="2312876650-39">]</span><span class="p" data-group-id="2312876650-38">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">make_script</span><span class="p" data-group-id="2312876650-40">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2312876650-40">)</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │      </span><span class="n">TarFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.tar.gz&quot;</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-41">(</span><span class="s">&quot;Creating tar file ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-42">[</span><span class="n">TarFileName</span><span class="p" data-group-id="6763615923-42">]</span><span class="p" data-group-id="6763615923-41">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">make_tar</span><span class="p" data-group-id="6763615923-43">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="6763615923-43">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-41">(</span><span class="s">&quot;Creating tar file ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-42">[</span><span class="n">TarFileName</span><span class="p" data-group-id="2312876650-42">]</span><span class="p" data-group-id="2312876650-41">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">make_tar</span><span class="p" data-group-id="2312876650-43">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2312876650-43">)</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="n">TmpDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-44">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;tmp&quot;</span><span class="p" data-group-id="6763615923-44">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-45">(</span><span class="s">&quot;Creating directory ~tp ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="6763615923-46">[</span><span class="n">TmpDir</span><span class="p" data-group-id="6763615923-46">]</span><span class="p" data-group-id="6763615923-45">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="6763615923-47">(</span><span class="n">TmpDir</span><span class="p" data-group-id="6763615923-47">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-48">(</span><span class="s">&quot;Extracting ~ts into directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-49">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="6763615923-49">]</span><span class="p" data-group-id="6763615923-48">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">extract_tar</span><span class="p" data-group-id="6763615923-50">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="n">TmpDir</span><span class="p" data-group-id="6763615923-50">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="n">TmpBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-51">(</span><span class="p" data-group-id="6763615923-52">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="6763615923-52">]</span><span class="p" data-group-id="6763615923-51">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-53">(</span><span class="p" data-group-id="6763615923-54">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="6763615923-54">]</span><span class="p" data-group-id="6763615923-53">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-55">(</span><span class="s">&quot;Deleting \&quot;erl\&quot; and \&quot;start\&quot; in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="6763615923-56">[</span><span class="n">ErtsBinDir</span><span class="p" data-group-id="6763615923-56">]</span><span class="p" data-group-id="6763615923-55">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="6763615923-57">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-58">(</span><span class="p" data-group-id="6763615923-59">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erl&quot;</span><span class="p" data-group-id="6763615923-59">]</span><span class="p" data-group-id="6763615923-58">)</span><span class="p" data-group-id="6763615923-57">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="6763615923-60">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-61">(</span><span class="p" data-group-id="6763615923-62">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="6763615923-62">]</span><span class="p" data-group-id="6763615923-61">)</span><span class="p" data-group-id="6763615923-60">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-63">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-64">[</span><span class="n">TmpBinDir</span><span class="p" data-group-id="6763615923-64">]</span><span class="p" data-group-id="6763615923-63">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="6763615923-65">(</span><span class="n">TmpBinDir</span><span class="p" data-group-id="6763615923-65">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-66">(</span><span class="s">&quot;Copying file \&quot;~ts.boot\&quot; to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="6763615923-67">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-68">(</span><span class="p" data-group-id="6763615923-69">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="6763615923-69">]</span><span class="p" data-group-id="6763615923-68">)</span><span class="p" data-group-id="6763615923-67">]</span><span class="p" data-group-id="6763615923-66">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="6763615923-70">(</span><span class="n">PlainRelFileName</span><span class="o">++</span><span class="s">&quot;.boot&quot;</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-71">(</span><span class="p" data-group-id="6763615923-72">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="6763615923-72">]</span><span class="p" data-group-id="6763615923-71">)</span><span class="p" data-group-id="6763615923-70">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">TmpDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-44">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;tmp&quot;</span><span class="p" data-group-id="2312876650-44">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-45">(</span><span class="s">&quot;Creating directory ~tp ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="2312876650-46">[</span><span class="n">TmpDir</span><span class="p" data-group-id="2312876650-46">]</span><span class="p" data-group-id="2312876650-45">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="2312876650-47">(</span><span class="n">TmpDir</span><span class="p" data-group-id="2312876650-47">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-48">(</span><span class="s">&quot;Extracting ~ts into directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-49">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="2312876650-49">]</span><span class="p" data-group-id="2312876650-48">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">extract_tar</span><span class="p" data-group-id="2312876650-50">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="n">TmpDir</span><span class="p" data-group-id="2312876650-50">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="n">TmpBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-51">(</span><span class="p" data-group-id="2312876650-52">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2312876650-52">]</span><span class="p" data-group-id="2312876650-51">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-53">(</span><span class="p" data-group-id="2312876650-54">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2312876650-54">]</span><span class="p" data-group-id="2312876650-53">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-55">(</span><span class="s">&quot;Deleting \&quot;erl\&quot; and \&quot;start\&quot; in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2312876650-56">[</span><span class="n">ErtsBinDir</span><span class="p" data-group-id="2312876650-56">]</span><span class="p" data-group-id="2312876650-55">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2312876650-57">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-58">(</span><span class="p" data-group-id="2312876650-59">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erl&quot;</span><span class="p" data-group-id="2312876650-59">]</span><span class="p" data-group-id="2312876650-58">)</span><span class="p" data-group-id="2312876650-57">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2312876650-60">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-61">(</span><span class="p" data-group-id="2312876650-62">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="2312876650-62">]</span><span class="p" data-group-id="2312876650-61">)</span><span class="p" data-group-id="2312876650-60">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-63">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-64">[</span><span class="n">TmpBinDir</span><span class="p" data-group-id="2312876650-64">]</span><span class="p" data-group-id="2312876650-63">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="2312876650-65">(</span><span class="n">TmpBinDir</span><span class="p" data-group-id="2312876650-65">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-66">(</span><span class="s">&quot;Copying file \&quot;~ts.boot\&quot; to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2312876650-67">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-68">(</span><span class="p" data-group-id="2312876650-69">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="2312876650-69">]</span><span class="p" data-group-id="2312876650-68">)</span><span class="p" data-group-id="2312876650-67">]</span><span class="p" data-group-id="2312876650-66">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="2312876650-70">(</span><span class="n">PlainRelFileName</span><span class="o">++</span><span class="s">&quot;.boot&quot;</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-71">(</span><span class="p" data-group-id="2312876650-72">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="2312876650-72">]</span><span class="p" data-group-id="2312876650-71">)</span><span class="p" data-group-id="2312876650-70">)</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-73">(</span><span class="s">&quot;Copying files \&quot;epmd\&quot;, \&quot;run_erl\&quot; and \&quot;to_erl\&quot; from \n&quot;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-73">(</span><span class="s">&quot;Copying files \&quot;epmd\&quot;, \&quot;run_erl\&quot; and \&quot;to_erl\&quot; from \n&quot;</span><span class="w">
│ │ │                </span><span class="s">&quot;~ts to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="6763615923-74">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">TmpBinDir</span><span class="p" data-group-id="6763615923-74">]</span><span class="p" data-group-id="6763615923-73">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="6763615923-75">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-76">(</span><span class="p" data-group-id="6763615923-77">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="6763615923-77">]</span><span class="p" data-group-id="6763615923-76">)</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-78">(</span><span class="p" data-group-id="6763615923-79">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="6763615923-79">]</span><span class="p" data-group-id="6763615923-78">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-80">[</span><span class="ss">preserve</span><span class="p" data-group-id="6763615923-80">]</span><span class="p" data-group-id="6763615923-75">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="6763615923-81">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-82">(</span><span class="p" data-group-id="6763615923-83">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="6763615923-83">]</span><span class="p" data-group-id="6763615923-82">)</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-84">(</span><span class="p" data-group-id="6763615923-85">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="6763615923-85">]</span><span class="p" data-group-id="6763615923-84">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-86">[</span><span class="ss">preserve</span><span class="p" data-group-id="6763615923-86">]</span><span class="p" data-group-id="6763615923-81">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="6763615923-87">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-88">(</span><span class="p" data-group-id="6763615923-89">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="6763615923-89">]</span><span class="p" data-group-id="6763615923-88">)</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-90">(</span><span class="p" data-group-id="6763615923-91">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="6763615923-91">]</span><span class="p" data-group-id="6763615923-90">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-92">[</span><span class="ss">preserve</span><span class="p" data-group-id="6763615923-92">]</span><span class="p" data-group-id="6763615923-87">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2312876650-74">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">TmpBinDir</span><span class="p" data-group-id="2312876650-74">]</span><span class="p" data-group-id="2312876650-73">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="2312876650-75">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-76">(</span><span class="p" data-group-id="2312876650-77">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="2312876650-77">]</span><span class="p" data-group-id="2312876650-76">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-78">(</span><span class="p" data-group-id="2312876650-79">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="2312876650-79">]</span><span class="p" data-group-id="2312876650-78">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-80">[</span><span class="ss">preserve</span><span class="p" data-group-id="2312876650-80">]</span><span class="p" data-group-id="2312876650-75">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="2312876650-81">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-82">(</span><span class="p" data-group-id="2312876650-83">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="2312876650-83">]</span><span class="p" data-group-id="2312876650-82">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-84">(</span><span class="p" data-group-id="2312876650-85">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="2312876650-85">]</span><span class="p" data-group-id="2312876650-84">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-86">[</span><span class="ss">preserve</span><span class="p" data-group-id="2312876650-86">]</span><span class="p" data-group-id="2312876650-81">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="2312876650-87">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-88">(</span><span class="p" data-group-id="2312876650-89">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="2312876650-89">]</span><span class="p" data-group-id="2312876650-88">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-90">(</span><span class="p" data-group-id="2312876650-91">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="2312876650-91">]</span><span class="p" data-group-id="2312876650-90">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-92">[</span><span class="ss">preserve</span><span class="p" data-group-id="2312876650-92">]</span><span class="p" data-group-id="2312876650-87">)</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │      </span><span class="c1">%% This is needed if &#39;start&#39; script created from &#39;start.src&#39; shall</span><span class="w">
│ │ │      </span><span class="c1">%% be used as it points out this directory as log dir for &#39;run_erl&#39;</span><span class="w">
│ │ │ -    </span><span class="n">TmpLogDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-93">(</span><span class="p" data-group-id="6763615923-94">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="6763615923-94">]</span><span class="p" data-group-id="6763615923-93">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-95">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-96">[</span><span class="n">TmpLogDir</span><span class="p" data-group-id="6763615923-96">]</span><span class="p" data-group-id="6763615923-95">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="6763615923-97">(</span><span class="n">TmpLogDir</span><span class="p" data-group-id="6763615923-97">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-98">(</span><span class="p" data-group-id="6763615923-99">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="6763615923-99">]</span><span class="p" data-group-id="6763615923-98">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-100">(</span><span class="s">&quot;Creating ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-101">[</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="6763615923-101">]</span><span class="p" data-group-id="6763615923-100">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">StartErlData</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">io_lib</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-102">(</span><span class="s">&quot;</span><span class="si">~s</span><span class="s"> </span><span class="si">~s</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-103">[</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="6763615923-103">]</span><span class="p" data-group-id="6763615923-102">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">write_file</span><span class="p" data-group-id="6763615923-104">(</span><span class="n">StartErlDataFile</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="6763615923-104">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-105">(</span><span class="s">&quot;Recreating tar file ~ts from contents in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -	      </span><span class="p" data-group-id="6763615923-106">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="6763615923-106">]</span><span class="p" data-group-id="6763615923-105">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-107">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tar</span><span class="p" data-group-id="6763615923-107">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="6763615923-108">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-109">[</span><span class="ss">write</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="6763615923-109">]</span><span class="p" data-group-id="6763615923-108">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">TmpLogDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-93">(</span><span class="p" data-group-id="2312876650-94">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="2312876650-94">]</span><span class="p" data-group-id="2312876650-93">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-95">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-96">[</span><span class="n">TmpLogDir</span><span class="p" data-group-id="2312876650-96">]</span><span class="p" data-group-id="2312876650-95">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="2312876650-97">(</span><span class="n">TmpLogDir</span><span class="p" data-group-id="2312876650-97">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-98">(</span><span class="p" data-group-id="2312876650-99">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="2312876650-99">]</span><span class="p" data-group-id="2312876650-98">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-100">(</span><span class="s">&quot;Creating ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-101">[</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="2312876650-101">]</span><span class="p" data-group-id="2312876650-100">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">StartErlData</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">io_lib</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-102">(</span><span class="s">&quot;</span><span class="si">~s</span><span class="s"> </span><span class="si">~s</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-103">[</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="2312876650-103">]</span><span class="p" data-group-id="2312876650-102">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">write_file</span><span class="p" data-group-id="2312876650-104">(</span><span class="n">StartErlDataFile</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="2312876650-104">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-105">(</span><span class="s">&quot;Recreating tar file ~ts from contents in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +	      </span><span class="p" data-group-id="2312876650-106">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="2312876650-106">]</span><span class="p" data-group-id="2312876650-105">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-107">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tar</span><span class="p" data-group-id="2312876650-107">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="2312876650-108">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-109">[</span><span class="ss">write</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="2312876650-109">]</span><span class="p" data-group-id="2312876650-108">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%% {ok, Cwd} = file:get_cwd(),</span><span class="w">
│ │ │      </span><span class="c1">%% file:set_cwd(&quot;tmp&quot;),</span><span class="w">
│ │ │      </span><span class="n">ErtsDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="o">++</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="6763615923-110">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-111">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="6763615923-111">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-112">[</span><span class="p" data-group-id="6763615923-112">]</span><span class="p" data-group-id="6763615923-110">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="6763615923-113">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-114">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="n">ErtsDir</span><span class="p" data-group-id="6763615923-114">)</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsDir</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-115">[</span><span class="p" data-group-id="6763615923-115">]</span><span class="p" data-group-id="6763615923-113">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="6763615923-116">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-117">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;releases&quot;</span><span class="p" data-group-id="6763615923-117">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-118">[</span><span class="p" data-group-id="6763615923-118">]</span><span class="p" data-group-id="6763615923-116">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="6763615923-119">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-120">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;lib&quot;</span><span class="p" data-group-id="6763615923-120">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;lib&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-121">[</span><span class="p" data-group-id="6763615923-121">]</span><span class="p" data-group-id="6763615923-119">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="6763615923-122">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-123">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="6763615923-123">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-124">[</span><span class="p" data-group-id="6763615923-124">]</span><span class="p" data-group-id="6763615923-122">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="6763615923-125">(</span><span class="n">Tar</span><span class="p" data-group-id="6763615923-125">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2312876650-110">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-111">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2312876650-111">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-112">[</span><span class="p" data-group-id="2312876650-112">]</span><span class="p" data-group-id="2312876650-110">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2312876650-113">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-114">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="n">ErtsDir</span><span class="p" data-group-id="2312876650-114">)</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsDir</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-115">[</span><span class="p" data-group-id="2312876650-115">]</span><span class="p" data-group-id="2312876650-113">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2312876650-116">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-117">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;releases&quot;</span><span class="p" data-group-id="2312876650-117">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-118">[</span><span class="p" data-group-id="2312876650-118">]</span><span class="p" data-group-id="2312876650-116">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2312876650-119">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-120">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;lib&quot;</span><span class="p" data-group-id="2312876650-120">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;lib&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-121">[</span><span class="p" data-group-id="2312876650-121">]</span><span class="p" data-group-id="2312876650-119">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2312876650-122">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-123">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="2312876650-123">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-124">[</span><span class="p" data-group-id="2312876650-124">]</span><span class="p" data-group-id="2312876650-122">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2312876650-125">(</span><span class="n">Tar</span><span class="p" data-group-id="2312876650-125">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%% file:set_cwd(Cwd),</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-126">(</span><span class="s">&quot;Removing directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="6763615923-127">[</span><span class="n">TmpDir</span><span class="p" data-group-id="6763615923-127">]</span><span class="p" data-group-id="6763615923-126">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="6763615923-128">(</span><span class="n">TmpDir</span><span class="p" data-group-id="6763615923-128">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-126">(</span><span class="s">&quot;Removing directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="2312876650-127">[</span><span class="n">TmpDir</span><span class="p" data-group-id="2312876650-127">]</span><span class="p" data-group-id="2312876650-126">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="2312876650-128">(</span><span class="n">TmpDir</span><span class="p" data-group-id="2312876650-128">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │ -</span><span class="nf">install</span><span class="p" data-group-id="6763615923-129">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="6763615923-129">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">install</span><span class="p" data-group-id="2312876650-129">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2312876650-129">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">TarFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.tar.gz&quot;</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-130">(</span><span class="s">&quot;Extracting ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-131">[</span><span class="n">TarFile</span><span class="p" data-group-id="6763615923-131">]</span><span class="p" data-group-id="6763615923-130">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">extract_tar</span><span class="p" data-group-id="6763615923-132">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="6763615923-132">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-133">(</span><span class="p" data-group-id="6763615923-134">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="6763615923-134">]</span><span class="p" data-group-id="6763615923-133">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-135">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="6763615923-135">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="6763615923-136">(</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="6763615923-136">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-137">[</span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">RelVsn</span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6763615923-137">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">string</span><span class="p">:</span><span class="nf">tokens</span><span class="p" data-group-id="6763615923-138">(</span><span class="n">StartErlData</span><span class="p">,</span><span class="w"> </span><span class="s">&quot; \n&quot;</span><span class="p" data-group-id="6763615923-138">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-139">(</span><span class="p" data-group-id="6763615923-140">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="6763615923-140">]</span><span class="p" data-group-id="6763615923-139">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">BinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-141">(</span><span class="p" data-group-id="6763615923-142">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="6763615923-142">]</span><span class="p" data-group-id="6763615923-141">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-143">(</span><span class="s">&quot;Substituting in erl.src, start.src and start_erl.src to &quot;</span><span class="w">
│ │ │ -              </span><span class="s">&quot;form erl, start and start_erl ...\n&quot;</span><span class="p" data-group-id="6763615923-143">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="6763615923-144">(</span><span class="p" data-group-id="6763615923-145">[</span><span class="s">&quot;erl&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="6763615923-145">]</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">BinDir</span><span class="p">,</span><span class="w">
│ │ │ -                      </span><span class="p" data-group-id="6763615923-146">[</span><span class="p" data-group-id="6763615923-147">{</span><span class="s">&quot;FINAL_ROOTDIR&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="6763615923-147">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-148">{</span><span class="s">&quot;EMU&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;beam&quot;</span><span class="p" data-group-id="6763615923-148">}</span><span class="p" data-group-id="6763615923-146">]</span><span class="p">,</span><span class="w">
│ │ │ -                      </span><span class="p" data-group-id="6763615923-149">[</span><span class="ss">preserve</span><span class="p" data-group-id="6763615923-149">]</span><span class="p" data-group-id="6763615923-144">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-130">(</span><span class="s">&quot;Extracting ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-131">[</span><span class="n">TarFile</span><span class="p" data-group-id="2312876650-131">]</span><span class="p" data-group-id="2312876650-130">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">extract_tar</span><span class="p" data-group-id="2312876650-132">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2312876650-132">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-133">(</span><span class="p" data-group-id="2312876650-134">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="2312876650-134">]</span><span class="p" data-group-id="2312876650-133">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-135">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="2312876650-135">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="2312876650-136">(</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="2312876650-136">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-137">[</span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">RelVsn</span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2312876650-137">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">string</span><span class="p">:</span><span class="nf">tokens</span><span class="p" data-group-id="2312876650-138">(</span><span class="n">StartErlData</span><span class="p">,</span><span class="w"> </span><span class="s">&quot; \n&quot;</span><span class="p" data-group-id="2312876650-138">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-139">(</span><span class="p" data-group-id="2312876650-140">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2312876650-140">]</span><span class="p" data-group-id="2312876650-139">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">BinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-141">(</span><span class="p" data-group-id="2312876650-142">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2312876650-142">]</span><span class="p" data-group-id="2312876650-141">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-143">(</span><span class="s">&quot;Substituting in erl.src, start.src and start_erl.src to &quot;</span><span class="w">
│ │ │ +              </span><span class="s">&quot;form erl, start and start_erl ...\n&quot;</span><span class="p" data-group-id="2312876650-143">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="2312876650-144">(</span><span class="p" data-group-id="2312876650-145">[</span><span class="s">&quot;erl&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="2312876650-145">]</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">BinDir</span><span class="p">,</span><span class="w">
│ │ │ +                      </span><span class="p" data-group-id="2312876650-146">[</span><span class="p" data-group-id="2312876650-147">{</span><span class="s">&quot;FINAL_ROOTDIR&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2312876650-147">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-148">{</span><span class="s">&quot;EMU&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;beam&quot;</span><span class="p" data-group-id="2312876650-148">}</span><span class="p" data-group-id="2312876650-146">]</span><span class="p">,</span><span class="w">
│ │ │ +                      </span><span class="p" data-group-id="2312876650-149">[</span><span class="ss">preserve</span><span class="p" data-group-id="2312876650-149">]</span><span class="p" data-group-id="2312876650-144">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%%! Workaround for pre OTP 17.0: start.src and start_erl.src did</span><span class="w">
│ │ │      </span><span class="c1">%%! not have correct permissions, so the above &#39;preserve&#39; option did not help</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="6763615923-150">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-151">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="6763615923-151">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="6763615923-150">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="6763615923-152">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-153">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="6763615923-153">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="6763615923-152">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="2312876650-150">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-151">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="2312876650-151">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="2312876650-150">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="2312876650-152">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-153">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="2312876650-153">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="2312876650-152">)</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="6763615923-154">(</span><span class="s">&quot;Creating the RELEASES file ...\n&quot;</span><span class="p" data-group-id="6763615923-154">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">create_RELEASES</span><span class="p" data-group-id="6763615923-155">(</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-156">(</span><span class="p" data-group-id="6763615923-157">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w">
│ │ │ -					    </span><span class="nc">filename</span><span class="p">:</span><span class="nf">basename</span><span class="p" data-group-id="6763615923-158">(</span><span class="n">RelFileName</span><span class="p" data-group-id="6763615923-158">)</span><span class="p" data-group-id="6763615923-157">]</span><span class="p" data-group-id="6763615923-156">)</span><span class="p" data-group-id="6763615923-155">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2312876650-154">(</span><span class="s">&quot;Creating the RELEASES file ...\n&quot;</span><span class="p" data-group-id="2312876650-154">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">create_RELEASES</span><span class="p" data-group-id="2312876650-155">(</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-156">(</span><span class="p" data-group-id="2312876650-157">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w">
│ │ │ +					    </span><span class="nc">filename</span><span class="p">:</span><span class="nf">basename</span><span class="p" data-group-id="2312876650-158">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2312876650-158">)</span><span class="p" data-group-id="2312876650-157">]</span><span class="p" data-group-id="2312876650-156">)</span><span class="p" data-group-id="2312876650-155">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% LOCALS</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% make_script(RelFileName,Opts)</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">make_script</span><span class="p" data-group-id="6763615923-159">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="6763615923-159">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="6763615923-160">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-161">[</span><span class="ss">no_module_tests</span><span class="p">,</span><span class="w">
│ │ │ -				       </span><span class="p" data-group-id="6763615923-162">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="6763615923-163">(</span><span class="n">RelFileName</span><span class="p" data-group-id="6763615923-163">)</span><span class="p" data-group-id="6763615923-162">}</span><span class="w">
│ │ │ -				       </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="6763615923-161">]</span><span class="p" data-group-id="6763615923-160">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">make_script</span><span class="p" data-group-id="2312876650-159">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="2312876650-159">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="2312876650-160">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-161">[</span><span class="ss">no_module_tests</span><span class="p">,</span><span class="w">
│ │ │ +				       </span><span class="p" data-group-id="2312876650-162">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="2312876650-163">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2312876650-163">)</span><span class="p" data-group-id="2312876650-162">}</span><span class="w">
│ │ │ +				       </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="2312876650-161">]</span><span class="p" data-group-id="2312876650-160">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% make_tar(RelFileName,Opts)</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">make_tar</span><span class="p" data-group-id="6763615923-164">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="6763615923-164">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">RootDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">code</span><span class="p">:</span><span class="nf">root_dir</span><span class="p" data-group-id="6763615923-165">(</span><span class="p" data-group-id="6763615923-165">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="6763615923-166">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-167">[</span><span class="p" data-group-id="6763615923-168">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="6763615923-168">}</span><span class="p">,</span><span class="w">
│ │ │ -				    </span><span class="p" data-group-id="6763615923-169">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="6763615923-170">(</span><span class="n">RelFileName</span><span class="p" data-group-id="6763615923-170">)</span><span class="p" data-group-id="6763615923-169">}</span><span class="w">
│ │ │ -				    </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="6763615923-167">]</span><span class="p" data-group-id="6763615923-166">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">make_tar</span><span class="p" data-group-id="2312876650-164">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="2312876650-164">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">RootDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">code</span><span class="p">:</span><span class="nf">root_dir</span><span class="p" data-group-id="2312876650-165">(</span><span class="p" data-group-id="2312876650-165">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="2312876650-166">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-167">[</span><span class="p" data-group-id="2312876650-168">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2312876650-168">}</span><span class="p">,</span><span class="w">
│ │ │ +				    </span><span class="p" data-group-id="2312876650-169">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="2312876650-170">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2312876650-170">)</span><span class="p" data-group-id="2312876650-169">}</span><span class="w">
│ │ │ +				    </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="2312876650-167">]</span><span class="p" data-group-id="2312876650-166">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% extract_tar(TarFile, DestDir)</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">extract_tar</span><span class="p" data-group-id="6763615923-171">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="6763615923-171">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">extract</span><span class="p" data-group-id="6763615923-172">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-173">[</span><span class="p" data-group-id="6763615923-174">{</span><span class="ss">cwd</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="6763615923-174">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="6763615923-173">]</span><span class="p" data-group-id="6763615923-172">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">extract_tar</span><span class="p" data-group-id="2312876650-171">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="2312876650-171">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">extract</span><span class="p" data-group-id="2312876650-172">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-173">[</span><span class="p" data-group-id="2312876650-174">{</span><span class="ss">cwd</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="2312876650-174">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="2312876650-173">]</span><span class="p" data-group-id="2312876650-172">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="6763615923-175">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="6763615923-175">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="6763615923-176">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p" data-group-id="6763615923-176">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="2312876650-175">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="2312876650-175">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="2312876650-176">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p" data-group-id="2312876650-176">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="6763615923-177">(</span><span class="n">Scripts</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="6763615923-177">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="6763615923-178">(</span><span class="nf">fun</span><span class="p" data-group-id="6763615923-179">(</span><span class="n">Script</span><span class="p" data-group-id="6763615923-179">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                          </span><span class="nf">subst_src_script</span><span class="p" data-group-id="6763615923-180">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w">
│ │ │ -                                           </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="6763615923-180">)</span><span class="w">
│ │ │ -                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Scripts</span><span class="p" data-group-id="6763615923-178">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">subst_src_script</span><span class="p" data-group-id="6763615923-181">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="6763615923-181">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst_file</span><span class="p" data-group-id="6763615923-182">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-183">(</span><span class="p" data-group-id="6763615923-184">[</span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.src&quot;</span><span class="p" data-group-id="6763615923-184">]</span><span class="p" data-group-id="6763615923-183">)</span><span class="p">,</span><span class="w">
│ │ │ -               </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-185">(</span><span class="p" data-group-id="6763615923-186">[</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="p" data-group-id="6763615923-186">]</span><span class="p" data-group-id="6763615923-185">)</span><span class="p">,</span><span class="w">
│ │ │ -               </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="6763615923-182">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">subst_file</span><span class="p" data-group-id="6763615923-187">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="6763615923-187">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-188">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="6763615923-188">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="6763615923-189">(</span><span class="n">Src</span><span class="p" data-group-id="6763615923-189">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">NConts</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">subst</span><span class="p" data-group-id="6763615923-190">(</span><span class="n">Conts</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="6763615923-190">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">write_file</span><span class="p" data-group-id="6763615923-191">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">NConts</span><span class="p" data-group-id="6763615923-191">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="6763615923-192">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="6763615923-192">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="2312876650-177">(</span><span class="n">Scripts</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2312876650-177">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="2312876650-178">(</span><span class="nf">fun</span><span class="p" data-group-id="2312876650-179">(</span><span class="n">Script</span><span class="p" data-group-id="2312876650-179">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                          </span><span class="nf">subst_src_script</span><span class="p" data-group-id="2312876650-180">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w">
│ │ │ +                                           </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2312876650-180">)</span><span class="w">
│ │ │ +                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Scripts</span><span class="p" data-group-id="2312876650-178">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">subst_src_script</span><span class="p" data-group-id="2312876650-181">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2312876650-181">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst_file</span><span class="p" data-group-id="2312876650-182">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-183">(</span><span class="p" data-group-id="2312876650-184">[</span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.src&quot;</span><span class="p" data-group-id="2312876650-184">]</span><span class="p" data-group-id="2312876650-183">)</span><span class="p">,</span><span class="w">
│ │ │ +               </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-185">(</span><span class="p" data-group-id="2312876650-186">[</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="p" data-group-id="2312876650-186">]</span><span class="p" data-group-id="2312876650-185">)</span><span class="p">,</span><span class="w">
│ │ │ +               </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2312876650-182">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">subst_file</span><span class="p" data-group-id="2312876650-187">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2312876650-187">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-188">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="2312876650-188">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="2312876650-189">(</span><span class="n">Src</span><span class="p" data-group-id="2312876650-189">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">NConts</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">subst</span><span class="p" data-group-id="2312876650-190">(</span><span class="n">Conts</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="2312876650-190">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">write_file</span><span class="p" data-group-id="2312876650-191">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">NConts</span><span class="p" data-group-id="2312876650-191">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="2312876650-192">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2312876650-192">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="6763615923-193">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="6763615923-193">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="6763615923-194">(</span><span class="n">Src</span><span class="p" data-group-id="6763615923-194">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="6763615923-195">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="6763615923-195">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2312876650-193">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2312876650-193">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="2312876650-194">(</span><span class="n">Src</span><span class="p" data-group-id="2312876650-194">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="2312876650-195">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2312876650-195">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">ok</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% subst(Str, Vars)</span><span class="w">
│ │ │  </span><span class="c1">%% Vars = [{Var, Val}]</span><span class="w">
│ │ │  </span><span class="c1">%% Var = Val = string()</span><span class="w">
│ │ │  </span><span class="c1">%% Substitute all occurrences of %Var% for Val in Str, using the list</span><span class="w">
│ │ │  </span><span class="c1">%% of variables in Vars.</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="6763615923-196">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="6763615923-196">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="6763615923-197">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-198">[</span><span class="p" data-group-id="6763615923-198">]</span><span class="p" data-group-id="6763615923-197">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2312876650-196">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="2312876650-196">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="2312876650-197">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-198">[</span><span class="p" data-group-id="2312876650-198">]</span><span class="p" data-group-id="2312876650-197">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="6763615923-199">(</span><span class="p" data-group-id="6763615923-200">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6763615923-200">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6763615923-199">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$Z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="6763615923-201">(</span><span class="p" data-group-id="6763615923-202">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6763615923-202">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-203">[</span><span class="p" data-group-id="6763615923-203">]</span><span class="p" data-group-id="6763615923-201">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="6763615923-204">(</span><span class="p" data-group-id="6763615923-205">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6763615923-205">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6763615923-204">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="6763615923-206">(</span><span class="p" data-group-id="6763615923-207">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6763615923-207">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-208">[</span><span class="p" data-group-id="6763615923-208">]</span><span class="p" data-group-id="6763615923-206">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="6763615923-209">(</span><span class="p" data-group-id="6763615923-210">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6763615923-210">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6763615923-209">)</span><span class="w"> </span><span class="k">when</span><span class="w">  </span><span class="n">C</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">$_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="6763615923-211">(</span><span class="p" data-group-id="6763615923-212">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6763615923-212">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-213">[</span><span class="p" data-group-id="6763615923-213">]</span><span class="p" data-group-id="6763615923-211">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="6763615923-214">(</span><span class="p" data-group-id="6763615923-215">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6763615923-215">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6763615923-214">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="6763615923-216">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-217">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6763615923-217">]</span><span class="p" data-group-id="6763615923-216">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="6763615923-218">(</span><span class="p" data-group-id="6763615923-219">[</span><span class="p" data-group-id="6763615923-219">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6763615923-218">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="6763615923-220">(</span><span class="n">Result</span><span class="p" data-group-id="6763615923-220">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="6763615923-221">(</span><span class="p" data-group-id="6763615923-222">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6763615923-222">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="6763615923-221">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Key</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="6763615923-223">(</span><span class="n">VarAcc</span><span class="p" data-group-id="6763615923-223">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="6763615923-224">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="6763615923-224">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6763615923-225">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-226">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="6763615923-226">}</span><span class="p" data-group-id="6763615923-225">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">subst</span><span class="p" data-group-id="6763615923-227">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="6763615923-228">(</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6763615923-228">)</span><span class="p" data-group-id="6763615923-227">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2312876650-199">(</span><span class="p" data-group-id="2312876650-200">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2312876650-200">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2312876650-199">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$Z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="2312876650-201">(</span><span class="p" data-group-id="2312876650-202">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2312876650-202">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-203">[</span><span class="p" data-group-id="2312876650-203">]</span><span class="p" data-group-id="2312876650-201">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2312876650-204">(</span><span class="p" data-group-id="2312876650-205">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2312876650-205">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2312876650-204">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="2312876650-206">(</span><span class="p" data-group-id="2312876650-207">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2312876650-207">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-208">[</span><span class="p" data-group-id="2312876650-208">]</span><span class="p" data-group-id="2312876650-206">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2312876650-209">(</span><span class="p" data-group-id="2312876650-210">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2312876650-210">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2312876650-209">)</span><span class="w"> </span><span class="k">when</span><span class="w">  </span><span class="n">C</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">$_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="2312876650-211">(</span><span class="p" data-group-id="2312876650-212">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2312876650-212">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-213">[</span><span class="p" data-group-id="2312876650-213">]</span><span class="p" data-group-id="2312876650-211">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2312876650-214">(</span><span class="p" data-group-id="2312876650-215">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2312876650-215">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2312876650-214">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="2312876650-216">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-217">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2312876650-217">]</span><span class="p" data-group-id="2312876650-216">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2312876650-218">(</span><span class="p" data-group-id="2312876650-219">[</span><span class="p" data-group-id="2312876650-219">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2312876650-218">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2312876650-220">(</span><span class="n">Result</span><span class="p" data-group-id="2312876650-220">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="2312876650-221">(</span><span class="p" data-group-id="2312876650-222">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2312876650-222">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2312876650-221">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Key</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2312876650-223">(</span><span class="n">VarAcc</span><span class="p" data-group-id="2312876650-223">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="2312876650-224">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="2312876650-224">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2312876650-225">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-226">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="2312876650-226">}</span><span class="p" data-group-id="2312876650-225">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">subst</span><span class="p" data-group-id="2312876650-227">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2312876650-228">(</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2312876650-228">)</span><span class="p" data-group-id="2312876650-227">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">subst</span><span class="p" data-group-id="6763615923-229">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-230">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6763615923-231">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6763615923-231">]</span><span class="p" data-group-id="6763615923-230">]</span><span class="p" data-group-id="6763615923-229">)</span><span class="w">
│ │ │ +            </span><span class="nf">subst</span><span class="p" data-group-id="2312876650-229">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-230">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2312876650-231">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2312876650-231">]</span><span class="p" data-group-id="2312876650-230">]</span><span class="p" data-group-id="2312876650-229">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="6763615923-232">(</span><span class="p" data-group-id="6763615923-233">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6763615923-233">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="6763615923-232">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="6763615923-234">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-235">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="6763615923-235">]</span><span class="p" data-group-id="6763615923-234">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="6763615923-236">(</span><span class="p" data-group-id="6763615923-237">[</span><span class="p" data-group-id="6763615923-237">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="6763615923-236">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="6763615923-238">(</span><span class="p" data-group-id="6763615923-239">[</span><span class="p" data-group-id="6763615923-239">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-240">[</span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6763615923-241">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6763615923-241">]</span><span class="p" data-group-id="6763615923-240">]</span><span class="p" data-group-id="6763615923-238">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">copy_file</span><span class="p" data-group-id="6763615923-242">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="6763615923-242">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="6763615923-243">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-244">[</span><span class="p" data-group-id="6763615923-244">]</span><span class="p" data-group-id="6763615923-243">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">copy_file</span><span class="p" data-group-id="6763615923-245">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="6763615923-245">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-246">{</span><span class="ss">ok</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6763615923-246">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">copy</span><span class="p" data-group-id="6763615923-247">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="6763615923-247">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="6763615923-248">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="6763615923-248">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="2312876650-232">(</span><span class="p" data-group-id="2312876650-233">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2312876650-233">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2312876650-232">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="2312876650-234">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-235">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2312876650-235">]</span><span class="p" data-group-id="2312876650-234">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="2312876650-236">(</span><span class="p" data-group-id="2312876650-237">[</span><span class="p" data-group-id="2312876650-237">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2312876650-236">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="2312876650-238">(</span><span class="p" data-group-id="2312876650-239">[</span><span class="p" data-group-id="2312876650-239">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-240">[</span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2312876650-241">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2312876650-241">]</span><span class="p" data-group-id="2312876650-240">]</span><span class="p" data-group-id="2312876650-238">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">copy_file</span><span class="p" data-group-id="2312876650-242">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="2312876650-242">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="2312876650-243">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-244">[</span><span class="p" data-group-id="2312876650-244">]</span><span class="p" data-group-id="2312876650-243">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">copy_file</span><span class="p" data-group-id="2312876650-245">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2312876650-245">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-246">{</span><span class="ss">ok</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2312876650-246">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">copy</span><span class="p" data-group-id="2312876650-247">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="2312876650-247">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="2312876650-248">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2312876650-248">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="6763615923-249">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="6763615923-249">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="6763615923-250">(</span><span class="n">Src</span><span class="p" data-group-id="6763615923-250">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="6763615923-251">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="6763615923-251">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2312876650-249">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2312876650-249">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="2312876650-250">(</span><span class="n">Src</span><span class="p" data-group-id="2312876650-250">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="2312876650-251">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2312876650-251">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">ok</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">write_file</span><span class="p" data-group-id="6763615923-252">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="6763615923-252">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Enc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">native_name_encoding</span><span class="p" data-group-id="6763615923-253">(</span><span class="p" data-group-id="6763615923-253">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-254">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="6763615923-254">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="6763615923-255">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-256">[</span><span class="ss">write</span><span class="p" data-group-id="6763615923-256">]</span><span class="p" data-group-id="6763615923-255">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">write</span><span class="p" data-group-id="6763615923-257">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="nc">unicode</span><span class="p">:</span><span class="nf">characters_to_binary</span><span class="p" data-group-id="6763615923-258">(</span><span class="n">Conts</span><span class="p">,</span><span class="n">Enc</span><span class="p">,</span><span class="n">Enc</span><span class="p" data-group-id="6763615923-258">)</span><span class="p" data-group-id="6763615923-257">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="6763615923-259">(</span><span class="n">Fd</span><span class="p" data-group-id="6763615923-259">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">read_txt_file</span><span class="p" data-group-id="6763615923-260">(</span><span class="n">File</span><span class="p" data-group-id="6763615923-260">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-261">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="6763615923-261">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file</span><span class="p" data-group-id="6763615923-262">(</span><span class="n">File</span><span class="p" data-group-id="6763615923-262">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6763615923-263">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_list</span><span class="p" data-group-id="6763615923-264">(</span><span class="n">Bin</span><span class="p" data-group-id="6763615923-264">)</span><span class="p" data-group-id="6763615923-263">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="6763615923-265">(</span><span class="n">Dir</span><span class="p" data-group-id="6763615923-265">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">remove_all_files</span><span class="p" data-group-id="6763615923-266">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6763615923-267">[</span><span class="n">Dir</span><span class="p" data-group-id="6763615923-267">]</span><span class="p" data-group-id="6763615923-266">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">remove_all_files</span><span class="p" data-group-id="6763615923-268">(</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="6763615923-268">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="6763615923-269">(</span><span class="nf">fun</span><span class="p" data-group-id="6763615923-270">(</span><span class="n">File</span><span class="p" data-group-id="6763615923-270">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                          </span><span class="n">FilePath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6763615923-271">(</span><span class="p" data-group-id="6763615923-272">[</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">File</span><span class="p" data-group-id="6763615923-272">]</span><span class="p" data-group-id="6763615923-271">)</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="k">case</span><span class="w"> </span><span class="nc">filelib</span><span class="p">:</span><span class="nf">is_dir</span><span class="p" data-group-id="6763615923-273">(</span><span class="n">FilePath</span><span class="p" data-group-id="6763615923-273">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">write_file</span><span class="p" data-group-id="2312876650-252">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="2312876650-252">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Enc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">native_name_encoding</span><span class="p" data-group-id="2312876650-253">(</span><span class="p" data-group-id="2312876650-253">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-254">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2312876650-254">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="2312876650-255">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-256">[</span><span class="ss">write</span><span class="p" data-group-id="2312876650-256">]</span><span class="p" data-group-id="2312876650-255">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">write</span><span class="p" data-group-id="2312876650-257">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="nc">unicode</span><span class="p">:</span><span class="nf">characters_to_binary</span><span class="p" data-group-id="2312876650-258">(</span><span class="n">Conts</span><span class="p">,</span><span class="n">Enc</span><span class="p">,</span><span class="n">Enc</span><span class="p" data-group-id="2312876650-258">)</span><span class="p" data-group-id="2312876650-257">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2312876650-259">(</span><span class="n">Fd</span><span class="p" data-group-id="2312876650-259">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">read_txt_file</span><span class="p" data-group-id="2312876650-260">(</span><span class="n">File</span><span class="p" data-group-id="2312876650-260">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-261">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="2312876650-261">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file</span><span class="p" data-group-id="2312876650-262">(</span><span class="n">File</span><span class="p" data-group-id="2312876650-262">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2312876650-263">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_list</span><span class="p" data-group-id="2312876650-264">(</span><span class="n">Bin</span><span class="p" data-group-id="2312876650-264">)</span><span class="p" data-group-id="2312876650-263">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="2312876650-265">(</span><span class="n">Dir</span><span class="p" data-group-id="2312876650-265">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">remove_all_files</span><span class="p" data-group-id="2312876650-266">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312876650-267">[</span><span class="n">Dir</span><span class="p" data-group-id="2312876650-267">]</span><span class="p" data-group-id="2312876650-266">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">remove_all_files</span><span class="p" data-group-id="2312876650-268">(</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="2312876650-268">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="2312876650-269">(</span><span class="nf">fun</span><span class="p" data-group-id="2312876650-270">(</span><span class="n">File</span><span class="p" data-group-id="2312876650-270">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                          </span><span class="n">FilePath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2312876650-271">(</span><span class="p" data-group-id="2312876650-272">[</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">File</span><span class="p" data-group-id="2312876650-272">]</span><span class="p" data-group-id="2312876650-271">)</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="k">case</span><span class="w"> </span><span class="nc">filelib</span><span class="p">:</span><span class="nf">is_dir</span><span class="p" data-group-id="2312876650-273">(</span><span class="n">FilePath</span><span class="p" data-group-id="2312876650-273">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │                                </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                                  </span><span class="p" data-group-id="6763615923-274">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="6763615923-274">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">list_dir</span><span class="p" data-group-id="6763615923-275">(</span><span class="n">FilePath</span><span class="p" data-group-id="6763615923-275">)</span><span class="p">,</span><span class="w">
│ │ │ -                                  </span><span class="nf">remove_all_files</span><span class="p" data-group-id="6763615923-276">(</span><span class="n">FilePath</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="6763615923-276">)</span><span class="p">,</span><span class="w">
│ │ │ -                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">del_dir</span><span class="p" data-group-id="6763615923-277">(</span><span class="n">FilePath</span><span class="p" data-group-id="6763615923-277">)</span><span class="p">;</span><span class="w">
│ │ │ +                                  </span><span class="p" data-group-id="2312876650-274">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="2312876650-274">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">list_dir</span><span class="p" data-group-id="2312876650-275">(</span><span class="n">FilePath</span><span class="p" data-group-id="2312876650-275">)</span><span class="p">,</span><span class="w">
│ │ │ +                                  </span><span class="nf">remove_all_files</span><span class="p" data-group-id="2312876650-276">(</span><span class="n">FilePath</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="2312876650-276">)</span><span class="p">,</span><span class="w">
│ │ │ +                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">del_dir</span><span class="p" data-group-id="2312876650-277">(</span><span class="n">FilePath</span><span class="p" data-group-id="2312876650-277">)</span><span class="p">;</span><span class="w">
│ │ │                                </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="6763615923-278">(</span><span class="n">FilePath</span><span class="p" data-group-id="6763615923-278">)</span><span class="w">
│ │ │ +                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2312876650-278">(</span><span class="n">FilePath</span><span class="p" data-group-id="2312876650-278">)</span><span class="w">
│ │ │                            </span><span class="k">end</span><span class="w">
│ │ │ -                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="6763615923-269">)</span><span class="p">.</span></code></pre>
│ │ │ +                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="2312876650-269">)</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="error_logging.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/data_types.html
│ │ │ @@ -192,18 +192,18 @@
│ │ │    </a>
│ │ │    <span class="text">Representation of Floating Point Numbers</span>
│ │ │  </h3>
│ │ │  <p>When working with floats you may not see what you expect when printing or doing
│ │ │  arithmetic operations. This is because floats are represented by a fixed number
│ │ │  of bits in a base-2 system while printed floats are represented with a base-10
│ │ │  system. Erlang uses 64-bit floats. Here are examples of this phenomenon:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mf">0.30000000000000004</span></code></pre><p>The real numbers <code class="inline">0.1</code> and <code class="inline">0.2</code> cannot be represented exactly as floats.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5505243758-1">{</span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963968</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="mf">36028797018963970.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963970</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963970.0</span><span class="p" data-group-id="5505243758-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5505243758-2">{</span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="5505243758-2">}</span><span class="p">.</span></code></pre><p>The value <code class="inline">36028797018963968</code> can be represented exactly as a float value but
│ │ │ +</span><span class="mf">0.30000000000000004</span></code></pre><p>The real numbers <code class="inline">0.1</code> and <code class="inline">0.2</code> cannot be represented exactly as floats.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2631580919-1">{</span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963968</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="mf">36028797018963970.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963970</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963970.0</span><span class="p" data-group-id="2631580919-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2631580919-2">{</span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="2631580919-2">}</span><span class="p">.</span></code></pre><p>The value <code class="inline">36028797018963968</code> can be represented exactly as a float value but
│ │ │  Erlang's pretty printer rounds <code class="inline">36028797018963968.0</code> to <code class="inline">3.602879701896397e16</code>
│ │ │  (<code class="inline">=36028797018963970.0</code>) as all values in the range
│ │ │  <code class="inline">[36028797018963966.0, 36028797018963972.0]</code> are represented by
│ │ │  <code class="inline">36028797018963968.0</code>.</p><p>For more information about floats and issues with them see:</p><ul><li><a href="https://floating-point-gui.de/">What Every Programmer Should Know About Floating-Point Arithmetic</a></li><li><a href="https://0.30000000000000004.com/">0.30000000000000004.com/</a></li><li><a href="https://docs.python.org/3/tutorial/floatingpoint.html">Floating Point Arithmetic: Issues and Limitations</a></li></ul><p>If you need to work with exact decimal fractions, for instance to represent
│ │ │  money, it is recommended to use a library that handles that, or work in
│ │ │  cents instead of dollars or euros so that decimal fractions are not needed.</p><p>Also note that Erlang's floats do not exactly match IEEE 754 floats,
│ │ │  in that neither <em>Inf</em> nor <em>NaN</em> are supported in Erlang. Any
│ │ │ @@ -237,52 +237,52 @@
│ │ │  by eight are called <em>binaries</em>.</p><p><em>Examples:</em></p><pre><code class="text">1&gt; &lt;&lt;10,20&gt;&gt;.
│ │ │  &lt;&lt;10,20&gt;&gt;
│ │ │  2&gt; &lt;&lt;&quot;ABC&quot;&gt;&gt;.
│ │ │  &lt;&lt;&quot;ABC&quot;&gt;&gt;
│ │ │  3&gt; &lt;&lt;1:1,0:1&gt;&gt;.
│ │ │  &lt;&lt;2:2&gt;&gt;</code></pre><p>The <a href="../../erts-15.2.7/doc/html/erlang.html#is_bitstring/1"><code class="inline">is_bitstring/1</code></a> BIF tests whether a
│ │ │  term is a bit string, and the <a href="../../erts-15.2.7/doc/html/erlang.html#is_binary/1"><code class="inline">is_binary/1</code></a>
│ │ │ -BIF tests whether a term is a binary.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">is_bitstring</span><span class="p" data-group-id="3131119211-1">(</span><span class="p" data-group-id="3131119211-2">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="3131119211-2">&gt;&gt;</span><span class="p" data-group-id="3131119211-1">)</span><span class="p">.</span><span class="w">
│ │ │ +BIF tests whether a term is a binary.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">is_bitstring</span><span class="p" data-group-id="2311752538-1">(</span><span class="p" data-group-id="2311752538-2">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2311752538-2">&gt;&gt;</span><span class="p" data-group-id="2311752538-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="3131119211-3">(</span><span class="p" data-group-id="3131119211-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="3131119211-4">&gt;&gt;</span><span class="p" data-group-id="3131119211-3">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="2311752538-3">(</span><span class="p" data-group-id="2311752538-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2311752538-4">&gt;&gt;</span><span class="p" data-group-id="2311752538-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="3131119211-5">(</span><span class="p" data-group-id="3131119211-6">&lt;&lt;</span><span class="mi">42</span><span class="p" data-group-id="3131119211-6">&gt;&gt;</span><span class="p" data-group-id="3131119211-5">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="2311752538-5">(</span><span class="p" data-group-id="2311752538-6">&lt;&lt;</span><span class="mi">42</span><span class="p" data-group-id="2311752538-6">&gt;&gt;</span><span class="p" data-group-id="2311752538-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │  </span></code></pre><p>For more examples, see <a href="../../doc/system/bit_syntax.html">Programming Examples</a>.</p><h2 id="reference" class="section-heading">
│ │ │    <a href="#reference" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Reference</span>
│ │ │  </h2>
│ │ │  <p>A term that is <a href="../../doc/system/system_limits.html#unique_references">unique</a>
│ │ │  among connected nodes. A reference is created by calling the
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#make_ref/0"><code class="inline">make_ref/0</code></a> BIF. The
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#is_reference/1"><code class="inline">is_reference/1</code></a> BIF tests whether a term
│ │ │ -is a reference.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="0161294944-1">(</span><span class="p" data-group-id="0161294944-1">)</span><span class="p">.</span><span class="w">
│ │ │ +is a reference.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="6631579316-1">(</span><span class="p" data-group-id="6631579316-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Ref</span><span class="o">&lt;</span><span class="mf">0.76482849</span><span class="p">.</span><span class="mf">3801088007.198204</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nf">is_reference</span><span class="p" data-group-id="0161294944-2">(</span><span class="n">Ref</span><span class="p" data-group-id="0161294944-2">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="nf">is_reference</span><span class="p" data-group-id="6631579316-2">(</span><span class="n">Ref</span><span class="p" data-group-id="6631579316-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><h2 id="fun" class="section-heading">
│ │ │    <a href="#fun" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Fun</span>
│ │ │  </h2>
│ │ │  <p>A fun is a functional object. Funs make it possible to create an anonymous
│ │ │  function and pass the function itself — not its name — as argument to other
│ │ │ -functions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3395953370-1">(</span><span class="n">X</span><span class="p" data-group-id="3395953370-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +functions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5093394071-1">(</span><span class="n">X</span><span class="p" data-group-id="5093394071-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="3395953370-2">(</span><span class="mi">2</span><span class="p" data-group-id="3395953370-2">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="5093394071-2">(</span><span class="mi">2</span><span class="p" data-group-id="5093394071-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span></code></pre><p>The <a href="../../erts-15.2.7/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> and <a href="../../erts-15.2.7/doc/html/erlang.html#is_function/2"><code class="inline">is_function/2</code></a>
│ │ │ -BIFs tests whether a term is a fun.</p><p><em>Examples</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="7333141160-1">(</span><span class="p" data-group-id="7333141160-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +BIFs tests whether a term is a fun.</p><p><em>Examples</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9135962785-1">(</span><span class="p" data-group-id="9135962785-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">43.105768164</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="7333141160-2">(</span><span class="n">F</span><span class="p" data-group-id="7333141160-2">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="9135962785-2">(</span><span class="n">F</span><span class="p" data-group-id="9135962785-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="7333141160-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7333141160-3">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="9135962785-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="9135962785-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="7333141160-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7333141160-4">)</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="9135962785-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9135962785-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre><p>Read more about funs in <a href="expressions.html#fun-expressions">Fun Expressions</a>. For more
│ │ │  examples, see <a href="../../doc/system/funs.html">Programming Examples</a>.</p><h2 id="port-identifier" class="section-heading">
│ │ │    <a href="#port-identifier" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Port Identifier</span>
│ │ │  </h2>
│ │ │ @@ -300,94 +300,94 @@
│ │ │  for a new process after a while.</p><p>The BIF <a href="../../erts-15.2.7/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the Pid of the calling process. When
│ │ │  <a href="ref_man_processes.html#process-creation">creating a new process</a>, the parent
│ │ │  process will be able to get the Pid of the child process either via the return
│ │ │  value, as is the case when calling the <a href="../../erts-15.2.7/doc/html/erlang.html#spawn/3"><code class="inline">spawn/3</code></a> BIF, or via
│ │ │  a message, which is the case when calling the
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#spawn_request/5"><code class="inline">spawn_request/5</code></a> BIF. A Pid is typically used when
│ │ │  when sending a process a <a href="ref_man_processes.html#signals">signal</a>. The
│ │ │ -<a href="../../erts-15.2.7/doc/html/erlang.html#is_pid/1"><code class="inline">is_pid/1</code></a> BIF tests whether a term is a Pid.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4679555231-1">(</span><span class="ss">m</span><span class="p" data-group-id="4679555231-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4679555231-2">(</span><span class="p" data-group-id="4679555231-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4679555231-3">]</span><span class="p" data-group-id="4679555231-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="../../erts-15.2.7/doc/html/erlang.html#is_pid/1"><code class="inline">is_pid/1</code></a> BIF tests whether a term is a Pid.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1028320776-1">(</span><span class="ss">m</span><span class="p" data-group-id="1028320776-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1028320776-2">(</span><span class="p" data-group-id="1028320776-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1028320776-3">]</span><span class="p" data-group-id="1028320776-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="4679555231-4">(</span><span class="p" data-group-id="4679555231-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="1028320776-4">(</span><span class="p" data-group-id="1028320776-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">who_are_you</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4679555231-5">(</span><span class="s">&quot;I am </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4679555231-6">[</span><span class="nf">self</span><span class="p" data-group-id="4679555231-7">(</span><span class="p" data-group-id="4679555231-7">)</span><span class="p" data-group-id="4679555231-6">]</span><span class="p" data-group-id="4679555231-5">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="4679555231-8">(</span><span class="p" data-group-id="4679555231-8">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1028320776-5">(</span><span class="s">&quot;I am </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1028320776-6">[</span><span class="nf">self</span><span class="p" data-group-id="1028320776-7">(</span><span class="p" data-group-id="1028320776-7">)</span><span class="p" data-group-id="1028320776-6">]</span><span class="p" data-group-id="1028320776-5">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="1028320776-8">(</span><span class="p" data-group-id="1028320776-8">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="4679555231-9">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">loop</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4679555231-10">[</span><span class="p" data-group-id="4679555231-10">]</span><span class="p" data-group-id="4679555231-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1028320776-9">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">loop</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1028320776-10">[</span><span class="p" data-group-id="1028320776-10">]</span><span class="p" data-group-id="1028320776-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.58</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │  2&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">who_are_you</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">I</span><span class="w"> </span><span class="ss">am</span><span class="w"> </span><span class="o">&lt;</span><span class="mf">0.58</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="ss">who_are_you</span></code></pre><p>Read more about processes in <a href="ref_man_processes.html">Processes</a>.</p><h2 id="tuple" class="section-heading">
│ │ │    <a href="#tuple" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Tuple</span>
│ │ │  </h2>
│ │ │  <p>A tuple is a compound data type with a fixed number of terms:</p><pre><code class="text">{Term1,...,TermN}</code></pre><p>Each term <code class="inline">Term</code> in the tuple is called an <em>element</em>. The number of elements is
│ │ │ -said to be the <em>size</em> of the tuple.</p><p>There exists a number of BIFs to manipulate tuples.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3943973945-1">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="3943973945-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="3943973945-2">}</span><span class="p" data-group-id="3943973945-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3943973945-3">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="3943973945-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="3943973945-4">}</span><span class="p" data-group-id="3943973945-3">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nf">element</span><span class="p" data-group-id="3943973945-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="3943973945-5">)</span><span class="p">.</span><span class="w">
│ │ │ +said to be the <em>size</em> of the tuple.</p><p>There exists a number of BIFs to manipulate tuples.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4448080550-1">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="4448080550-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="4448080550-2">}</span><span class="p" data-group-id="4448080550-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4448080550-3">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="4448080550-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="4448080550-4">}</span><span class="p" data-group-id="4448080550-3">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nf">element</span><span class="p" data-group-id="4448080550-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="4448080550-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">adam</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nf">element</span><span class="p" data-group-id="3943973945-6">(</span><span class="mi">3</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="3943973945-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3943973945-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="3943973945-7">}</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="3943973945-8">(</span><span class="mi">2</span><span class="p">,</span><span class="n">P</span><span class="p">,</span><span class="mi">25</span><span class="p" data-group-id="3943973945-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3943973945-9">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">25</span><span class="p">,</span><span class="p" data-group-id="3943973945-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="3943973945-10">}</span><span class="p" data-group-id="3943973945-9">}</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="3943973945-11">(</span><span class="n">P</span><span class="p" data-group-id="3943973945-11">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nf">element</span><span class="p" data-group-id="4448080550-6">(</span><span class="mi">3</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="4448080550-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4448080550-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="4448080550-7">}</span><span class="gp unselectable">
│ │ │ +4&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="4448080550-8">(</span><span class="mi">2</span><span class="p">,</span><span class="n">P</span><span class="p">,</span><span class="mi">25</span><span class="p" data-group-id="4448080550-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4448080550-9">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">25</span><span class="p">,</span><span class="p" data-group-id="4448080550-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="4448080550-10">}</span><span class="p" data-group-id="4448080550-9">}</span><span class="gp unselectable">
│ │ │ +5&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="4448080550-11">(</span><span class="n">P</span><span class="p" data-group-id="4448080550-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="3943973945-12">(</span><span class="p" data-group-id="3943973945-13">{</span><span class="p" data-group-id="3943973945-13">}</span><span class="p" data-group-id="3943973945-12">)</span><span class="p">.</span><span class="w">
│ │ │ +6&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="4448080550-12">(</span><span class="p" data-group-id="4448080550-13">{</span><span class="p" data-group-id="4448080550-13">}</span><span class="p" data-group-id="4448080550-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">0</span><span class="gp unselectable">
│ │ │ -7&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="3943973945-14">(</span><span class="p" data-group-id="3943973945-15">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3943973945-15">}</span><span class="p" data-group-id="3943973945-14">)</span><span class="p">.</span><span class="w">
│ │ │ +7&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="4448080550-14">(</span><span class="p" data-group-id="4448080550-15">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4448080550-15">}</span><span class="p" data-group-id="4448080550-14">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><h2 id="map" class="section-heading">
│ │ │    <a href="#map" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Map</span>
│ │ │  </h2>
│ │ │  <p>A map is a compound data type with a variable number of key-value associations:</p><pre><code class="text">#{Key1 =&gt; Value1, ..., KeyN =&gt; ValueN}</code></pre><p>Each key-value association in the map is called an <em>association pair</em>. The key
│ │ │  and value parts of the pair are called <em>elements</em>. The number of association
│ │ │ -pairs is said to be the <em>size</em> of the map.</p><p>There exists a number of BIFs to manipulate maps.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4076887590-1">#{</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="w"> </span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4076887590-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="4076887590-2">}</span><span class="p" data-group-id="4076887590-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4076887590-3">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4076887590-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="4076887590-4">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="4076887590-3">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="4076887590-5">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="4076887590-5">)</span><span class="p">.</span><span class="w">
│ │ │ +pairs is said to be the <em>size</em> of the map.</p><p>There exists a number of BIFs to manipulate maps.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2368471608-1">#{</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="w"> </span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2368471608-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2368471608-2">}</span><span class="p" data-group-id="2368471608-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2368471608-3">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2368471608-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2368471608-4">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="2368471608-3">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="2368471608-5">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="2368471608-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">adam</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="4076887590-6">(</span><span class="ss">date</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="4076887590-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4076887590-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="4076887590-7">}</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="4076887590-8">(</span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="4076887590-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4076887590-9">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4076887590-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="4076887590-10">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="4076887590-9">}</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="4076887590-11">(</span><span class="n">M</span><span class="p" data-group-id="4076887590-11">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="2368471608-6">(</span><span class="ss">date</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="2368471608-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2368471608-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2368471608-7">}</span><span class="gp unselectable">
│ │ │ +4&gt; </span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="2368471608-8">(</span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="2368471608-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2368471608-9">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2368471608-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2368471608-10">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="2368471608-9">}</span><span class="gp unselectable">
│ │ │ +5&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="2368471608-11">(</span><span class="n">M</span><span class="p" data-group-id="2368471608-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="4076887590-12">(</span><span class="p" data-group-id="4076887590-13">#{</span><span class="p" data-group-id="4076887590-13">}</span><span class="p" data-group-id="4076887590-12">)</span><span class="p">.</span><span class="w">
│ │ │ +6&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="2368471608-12">(</span><span class="p" data-group-id="2368471608-13">#{</span><span class="p" data-group-id="2368471608-13">}</span><span class="p" data-group-id="2368471608-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">0</span></code></pre><p>A collection of maps processing functions are found in module <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html"><code class="inline">maps</code></a>
│ │ │  in STDLIB.</p><p>Read more about maps in <a href="expressions.html#map-expressions">Map Expressions</a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Maps were introduced as an experimental feature in Erlang/OTP R17. Their
│ │ │  functionality was extended and became fully supported in Erlang/OTP 18.</p></section><h2 id="list" class="section-heading">
│ │ │    <a href="#list" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">List</span>
│ │ │  </h2>
│ │ │  <p>A list is a compound data type with a variable number of terms.</p><pre><code class="text">[Term1,...,TermN]</code></pre><p>Each term <code class="inline">Term</code> in the list is called an <em>element</em>. The number of elements is
│ │ │  said to be the <em>length</em> of the list.</p><p>Formally, a list is either the empty list <code class="inline">[]</code> or consists of a <em>head</em> (first
│ │ │  element) and a <em>tail</em> (remainder of the list). The <em>tail</em> is also a list. The
│ │ │  latter can be expressed as <code class="inline">[H|T]</code>. The notation <code class="inline">[Term1,...,TermN]</code> above is
│ │ │  equivalent with the list <code class="inline">[Term1|[...|[TermN|[]]]]</code>.</p><p><em>Example:</em></p><p><code class="inline">[]</code> is a list, thus<br/><code class="inline">[c|[]]</code> is a list, thus<br/><code class="inline">[b|[c|[]]]</code> is a list, thus<br/><code class="inline">[a|[b|[c|[]]]]</code> is a list, or in short <code class="inline">[a,b,c]</code></p><p>A list where the tail is a list is sometimes called a <em>proper list</em>. It is
│ │ │  allowed to have a list where the tail is not a list, for example, <code class="inline">[a|b]</code>.
│ │ │ -However, this type of list is of little practical use.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1832546966-1">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1832546966-2">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1832546966-2">}</span><span class="p" data-group-id="1832546966-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1832546966-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1832546966-4">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1832546966-4">}</span><span class="p" data-group-id="1832546966-3">]</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="1832546966-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1832546966-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1832546966-6">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1832546966-7">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1832546966-7">}</span><span class="p" data-group-id="1832546966-6">]</span><span class="gp unselectable">
│ │ │ +However, this type of list is of little practical use.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0834374580-1">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="0834374580-2">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0834374580-2">}</span><span class="p" data-group-id="0834374580-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0834374580-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="0834374580-4">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0834374580-4">}</span><span class="p" data-group-id="0834374580-3">]</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="0834374580-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0834374580-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0834374580-6">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="0834374580-7">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0834374580-7">}</span><span class="p" data-group-id="0834374580-6">]</span><span class="gp unselectable">
│ │ │  3&gt; </span><span class="n">H</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">a</span><span class="gp unselectable">
│ │ │  4&gt; </span><span class="n">T</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1832546966-8">[</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1832546966-9">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1832546966-9">}</span><span class="p" data-group-id="1832546966-8">]</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="n">L2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1832546966-10">[</span><span class="ss">d</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1832546966-10">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1832546966-11">[</span><span class="ss">d</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1832546966-12">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1832546966-12">}</span><span class="p" data-group-id="1832546966-11">]</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nf">length</span><span class="p" data-group-id="1832546966-13">(</span><span class="n">L1</span><span class="p" data-group-id="1832546966-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0834374580-8">[</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="0834374580-9">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0834374580-9">}</span><span class="p" data-group-id="0834374580-8">]</span><span class="gp unselectable">
│ │ │ +5&gt; </span><span class="n">L2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0834374580-10">[</span><span class="ss">d</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0834374580-10">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0834374580-11">[</span><span class="ss">d</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="0834374580-12">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0834374580-12">}</span><span class="p" data-group-id="0834374580-11">]</span><span class="gp unselectable">
│ │ │ +6&gt; </span><span class="nf">length</span><span class="p" data-group-id="0834374580-13">(</span><span class="n">L1</span><span class="p" data-group-id="0834374580-13">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ -7&gt; </span><span class="nf">length</span><span class="p" data-group-id="1832546966-14">(</span><span class="p" data-group-id="1832546966-15">[</span><span class="p" data-group-id="1832546966-15">]</span><span class="p" data-group-id="1832546966-14">)</span><span class="p">.</span><span class="w">
│ │ │ +7&gt; </span><span class="nf">length</span><span class="p" data-group-id="0834374580-14">(</span><span class="p" data-group-id="0834374580-15">[</span><span class="p" data-group-id="0834374580-15">]</span><span class="p" data-group-id="0834374580-14">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">0</span></code></pre><p>A collection of list processing functions are found in module
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html"><code class="inline">lists</code></a> in STDLIB.</p><h2 id="string" class="section-heading">
│ │ │    <a href="#string" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">String</span>
│ │ │  </h2>
│ │ │ @@ -507,41 +507,41 @@
│ │ │    <span class="text">Record</span>
│ │ │  </h2>
│ │ │  <p>A record is a data structure for storing a fixed number of elements. It has
│ │ │  named fields and is similar to a struct in C. However, a record is not a true
│ │ │  data type. Instead, record expressions are translated to tuple expressions
│ │ │  during compilation. Therefore, record expressions are not understood by the
│ │ │  shell unless special actions are taken. For details, see module <a href="../../lib/stdlib-6.2.2.1/doc/html/shell.html"><code class="inline">shell</code></a>
│ │ │ -in STDLIB.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2988818847-1">(</span><span class="ss">person</span><span class="p" data-group-id="2988818847-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2988818847-2">(</span><span class="p" data-group-id="2988818847-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2988818847-3">]</span><span class="p" data-group-id="2988818847-2">)</span><span class="p">.</span><span class="w">
│ │ │ +in STDLIB.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1049769693-1">(</span><span class="ss">person</span><span class="p" data-group-id="1049769693-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1049769693-2">(</span><span class="p" data-group-id="1049769693-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1049769693-3">]</span><span class="p" data-group-id="1049769693-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2988818847-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2988818847-5">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="2988818847-5">}</span><span class="p" data-group-id="2988818847-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1049769693-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1049769693-5">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="1049769693-5">}</span><span class="p" data-group-id="1049769693-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">new</span><span class="p" data-group-id="2988818847-6">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="2988818847-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2988818847-7">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="o">=</span><span class="n">Age</span><span class="p" data-group-id="2988818847-7">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">new</span><span class="p" data-group-id="1049769693-6">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="1049769693-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1049769693-7">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="o">=</span><span class="n">Age</span><span class="p" data-group-id="1049769693-7">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">person</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="2988818847-8">(</span><span class="ss">ernie</span><span class="p">,</span><span class="w"> </span><span class="mi">44</span><span class="p" data-group-id="2988818847-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2988818847-9">{</span><span class="ss">person</span><span class="p">,</span><span class="ss">ernie</span><span class="p">,</span><span class="mi">44</span><span class="p" data-group-id="2988818847-9">}</span></code></pre><p>Read more about records in <a href="ref_man_records.html">Records</a>. More examples are
│ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">person</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="1049769693-8">(</span><span class="ss">ernie</span><span class="p">,</span><span class="w"> </span><span class="mi">44</span><span class="p" data-group-id="1049769693-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1049769693-9">{</span><span class="ss">person</span><span class="p">,</span><span class="ss">ernie</span><span class="p">,</span><span class="mi">44</span><span class="p" data-group-id="1049769693-9">}</span></code></pre><p>Read more about records in <a href="ref_man_records.html">Records</a>. More examples are
│ │ │  found in <a href="../../doc/system/prog_ex_records.html">Programming Examples</a>.</p><h2 id="boolean" class="section-heading">
│ │ │    <a href="#boolean" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Boolean</span>
│ │ │  </h2>
│ │ │  <p>There is no Boolean data type in Erlang. Instead the atoms <code class="inline">true</code> and <code class="inline">false</code>
│ │ │  are used to denote Boolean values. The <a href="../../erts-15.2.7/doc/html/erlang.html#is_boolean/1"><code class="inline">is_boolean/1</code></a>
│ │ │  BIF tests whether a term is a boolean.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mi">2</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │  2&gt; </span><span class="ss">true</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="ss">false</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="3979271445-1">(</span><span class="ss">true</span><span class="p" data-group-id="3979271445-1">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1966653120-1">(</span><span class="ss">true</span><span class="p" data-group-id="1966653120-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="3979271445-2">(</span><span class="ss">false</span><span class="p" data-group-id="3979271445-2">)</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1966653120-2">(</span><span class="ss">false</span><span class="p" data-group-id="1966653120-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="3979271445-3">(</span><span class="ss">ok</span><span class="p" data-group-id="3979271445-3">)</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1966653120-3">(</span><span class="ss">ok</span><span class="p" data-group-id="1966653120-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre><h2 id="escape-sequences" class="section-heading">
│ │ │    <a href="#escape-sequences" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Escape Sequences</span>
│ │ │  </h2>
│ │ │  <p>Within strings (<code class="inline">&quot;</code>-delimited), quoted atoms, and the content of
│ │ │ @@ -559,47 +559,47 @@
│ │ │  <a href="data_types.html#sigil"><code class="inline">~b</code> or <code class="inline">~s</code> sigils </a>the escape sequences for normal
│ │ │  strings, above, are used.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Triple-quoted strings and sigils were introduced in Erlang/OTP 27.</p></section><h2 id="type-conversions" class="section-heading">
│ │ │    <a href="#type-conversions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Type Conversions</span>
│ │ │  </h2>
│ │ │ -<p>There are a number of BIFs for type conversions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="4484885201-1">(</span><span class="ss">hello</span><span class="p" data-group-id="4484885201-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>There are a number of BIFs for type conversions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="6311494463-1">(</span><span class="ss">hello</span><span class="p" data-group-id="6311494463-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;hello&quot;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="4484885201-2">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4484885201-2">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="6311494463-2">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6311494463-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="4484885201-3">(</span><span class="p" data-group-id="4484885201-4">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4484885201-4">&gt;&gt;</span><span class="p" data-group-id="4484885201-3">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="6311494463-3">(</span><span class="p" data-group-id="6311494463-4">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6311494463-4">&gt;&gt;</span><span class="p" data-group-id="6311494463-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;hello&quot;</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="4484885201-5">(</span><span class="p" data-group-id="4484885201-6">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="4484885201-6">&gt;&gt;</span><span class="p" data-group-id="4484885201-5">)</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="6311494463-5">(</span><span class="p" data-group-id="6311494463-6">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="6311494463-6">&gt;&gt;</span><span class="p" data-group-id="6311494463-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;hello&quot;</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nf">list_to_binary</span><span class="p" data-group-id="4484885201-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4484885201-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4484885201-8">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="4484885201-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4484885201-9">(</span><span class="mf">7.0</span><span class="p" data-group-id="4484885201-9">)</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="nf">list_to_binary</span><span class="p" data-group-id="6311494463-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6311494463-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6311494463-8">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="6311494463-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +6&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="6311494463-9">(</span><span class="mf">7.0</span><span class="p" data-group-id="6311494463-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="gp unselectable">
│ │ │ -7&gt; </span><span class="nf">list_to_float</span><span class="p" data-group-id="4484885201-10">(</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="4484885201-10">)</span><span class="p">.</span><span class="w">
│ │ │ +7&gt; </span><span class="nf">list_to_float</span><span class="p" data-group-id="6311494463-10">(</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="6311494463-10">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">7.0</span><span class="gp unselectable">
│ │ │ -8&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="4484885201-11">(</span><span class="mi">77</span><span class="p" data-group-id="4484885201-11">)</span><span class="p">.</span><span class="w">
│ │ │ +8&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="6311494463-11">(</span><span class="mi">77</span><span class="p" data-group-id="6311494463-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;77&quot;</span><span class="gp unselectable">
│ │ │ -9&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="4484885201-12">(</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="4484885201-12">)</span><span class="p">.</span><span class="w">
│ │ │ +9&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="6311494463-12">(</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="6311494463-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">77</span><span class="gp unselectable">
│ │ │ -10&gt; </span><span class="nf">tuple_to_list</span><span class="p" data-group-id="4484885201-13">(</span><span class="p" data-group-id="4484885201-14">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4484885201-14">}</span><span class="p" data-group-id="4484885201-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4484885201-15">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4484885201-15">]</span><span class="gp unselectable">
│ │ │ -11&gt; </span><span class="nf">list_to_tuple</span><span class="p" data-group-id="4484885201-16">(</span><span class="p" data-group-id="4484885201-17">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4484885201-17">]</span><span class="p" data-group-id="4484885201-16">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4484885201-18">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4484885201-18">}</span><span class="gp unselectable">
│ │ │ -12&gt; </span><span class="nf">term_to_binary</span><span class="p" data-group-id="4484885201-19">(</span><span class="p" data-group-id="4484885201-20">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4484885201-20">}</span><span class="p" data-group-id="4484885201-19">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4484885201-21">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="4484885201-21">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -13&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="4484885201-22">(</span><span class="p" data-group-id="4484885201-23">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="4484885201-23">&gt;&gt;</span><span class="p" data-group-id="4484885201-22">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4484885201-24">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4484885201-24">}</span><span class="gp unselectable">
│ │ │ -14&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="4484885201-25">(</span><span class="p" data-group-id="4484885201-26">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="4484885201-26">&gt;&gt;</span><span class="p" data-group-id="4484885201-25">)</span><span class="p">.</span><span class="w">
│ │ │ +10&gt; </span><span class="nf">tuple_to_list</span><span class="p" data-group-id="6311494463-13">(</span><span class="p" data-group-id="6311494463-14">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6311494463-14">}</span><span class="p" data-group-id="6311494463-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6311494463-15">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6311494463-15">]</span><span class="gp unselectable">
│ │ │ +11&gt; </span><span class="nf">list_to_tuple</span><span class="p" data-group-id="6311494463-16">(</span><span class="p" data-group-id="6311494463-17">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6311494463-17">]</span><span class="p" data-group-id="6311494463-16">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6311494463-18">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6311494463-18">}</span><span class="gp unselectable">
│ │ │ +12&gt; </span><span class="nf">term_to_binary</span><span class="p" data-group-id="6311494463-19">(</span><span class="p" data-group-id="6311494463-20">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6311494463-20">}</span><span class="p" data-group-id="6311494463-19">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6311494463-21">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="6311494463-21">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +13&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="6311494463-22">(</span><span class="p" data-group-id="6311494463-23">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="6311494463-23">&gt;&gt;</span><span class="p" data-group-id="6311494463-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6311494463-24">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6311494463-24">}</span><span class="gp unselectable">
│ │ │ +14&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="6311494463-25">(</span><span class="p" data-group-id="6311494463-26">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="6311494463-26">&gt;&gt;</span><span class="p" data-group-id="6311494463-25">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">77</span><span class="gp unselectable">
│ │ │ -15&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="4484885201-27">(</span><span class="mi">77</span><span class="p" data-group-id="4484885201-27">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4484885201-28">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="4484885201-28">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -16&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="4484885201-29">(</span><span class="mf">7.0</span><span class="p" data-group-id="4484885201-29">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4484885201-30">&lt;&lt;</span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="p" data-group-id="4484885201-30">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -17&gt; </span><span class="nf">binary_to_float</span><span class="p" data-group-id="4484885201-31">(</span><span class="p" data-group-id="4484885201-32">&lt;&lt;</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="4484885201-32">&gt;&gt;</span><span class="p" data-group-id="4484885201-31">)</span><span class="p">.</span><span class="w">
│ │ │ +15&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="6311494463-27">(</span><span class="mi">77</span><span class="p" data-group-id="6311494463-27">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6311494463-28">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="6311494463-28">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +16&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="6311494463-29">(</span><span class="mf">7.0</span><span class="p" data-group-id="6311494463-29">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6311494463-30">&lt;&lt;</span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="p" data-group-id="6311494463-30">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +17&gt; </span><span class="nf">binary_to_float</span><span class="p" data-group-id="6311494463-31">(</span><span class="p" data-group-id="6311494463-32">&lt;&lt;</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="6311494463-32">&gt;&gt;</span><span class="p" data-group-id="6311494463-31">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">7.0</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="character_set.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/design_principles.html
│ │ │ @@ -152,135 +152,135 @@
│ │ │  the code for a process in a generic part (a behaviour module) and a specific
│ │ │  part (a <em>callback module</em>).</p><p>The behaviour module is part of Erlang/OTP. To implement a process such as a
│ │ │  supervisor, the user only needs to implement the callback module, which is to
│ │ │  export a pre-defined set of functions, the <em>callback functions</em>.</p><p>The following example illustrate how code can be divided into a generic and a
│ │ │  specific part. Consider the following code (written in plain Erlang) for a
│ │ │  simple server, which keeps track of a number of &quot;channels&quot;. Other processes can
│ │ │  allocate and free the channels by calling the functions <code class="inline">alloc/0</code> and <code class="inline">free/1</code>,
│ │ │ -respectively.</p><p><a href="" id="ch1"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3400854224-1">(</span><span class="ss">ch1</span><span class="p" data-group-id="3400854224-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3400854224-2">(</span><span class="p" data-group-id="3400854224-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3400854224-3">]</span><span class="p" data-group-id="3400854224-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3400854224-4">(</span><span class="p" data-group-id="3400854224-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3400854224-5">]</span><span class="p" data-group-id="3400854224-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3400854224-6">(</span><span class="p" data-group-id="3400854224-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3400854224-7">]</span><span class="p" data-group-id="3400854224-6">)</span><span class="p">.</span><span class="w">
│ │ │ +respectively.</p><p><a href="" id="ch1"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8051856319-1">(</span><span class="ss">ch1</span><span class="p" data-group-id="8051856319-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8051856319-2">(</span><span class="p" data-group-id="8051856319-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8051856319-3">]</span><span class="p" data-group-id="8051856319-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8051856319-4">(</span><span class="p" data-group-id="8051856319-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8051856319-5">]</span><span class="p" data-group-id="8051856319-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8051856319-6">(</span><span class="p" data-group-id="8051856319-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8051856319-7">]</span><span class="p" data-group-id="8051856319-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="3400854224-8">(</span><span class="p" data-group-id="3400854224-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="3400854224-9">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3400854224-10">[</span><span class="p" data-group-id="3400854224-10">]</span><span class="p" data-group-id="3400854224-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8051856319-8">(</span><span class="p" data-group-id="8051856319-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="8051856319-9">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8051856319-10">[</span><span class="p" data-group-id="8051856319-10">]</span><span class="p" data-group-id="8051856319-9">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="3400854224-11">(</span><span class="p" data-group-id="3400854224-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3400854224-12">{</span><span class="nf">self</span><span class="p" data-group-id="3400854224-13">(</span><span class="p" data-group-id="3400854224-13">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="3400854224-12">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="8051856319-11">(</span><span class="p" data-group-id="8051856319-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8051856319-12">{</span><span class="nf">self</span><span class="p" data-group-id="8051856319-13">(</span><span class="p" data-group-id="8051856319-13">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="8051856319-12">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3400854224-14">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="3400854224-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8051856319-14">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="8051856319-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Res</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="3400854224-15">(</span><span class="n">Ch</span><span class="p" data-group-id="3400854224-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3400854224-16">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3400854224-16">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="8051856319-15">(</span><span class="n">Ch</span><span class="p" data-group-id="8051856319-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8051856319-16">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8051856319-16">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="3400854224-17">(</span><span class="p" data-group-id="3400854224-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="3400854224-18">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3400854224-19">(</span><span class="p" data-group-id="3400854224-19">)</span><span class="p" data-group-id="3400854224-18">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="3400854224-20">(</span><span class="p" data-group-id="3400854224-20">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="3400854224-21">(</span><span class="n">Chs</span><span class="p" data-group-id="3400854224-21">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8051856319-17">(</span><span class="p" data-group-id="8051856319-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="8051856319-18">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8051856319-19">(</span><span class="p" data-group-id="8051856319-19">)</span><span class="p" data-group-id="8051856319-18">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="8051856319-20">(</span><span class="p" data-group-id="8051856319-20">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="8051856319-21">(</span><span class="n">Chs</span><span class="p" data-group-id="8051856319-21">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="3400854224-22">(</span><span class="n">Chs</span><span class="p" data-group-id="3400854224-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="8051856319-22">(</span><span class="n">Chs</span><span class="p" data-group-id="8051856319-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3400854224-23">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="3400854224-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3400854224-24">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="3400854224-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="3400854224-25">(</span><span class="n">Chs</span><span class="p" data-group-id="3400854224-25">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3400854224-26">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3400854224-26">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="3400854224-27">(</span><span class="n">Chs2</span><span class="p" data-group-id="3400854224-27">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3400854224-28">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3400854224-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="3400854224-29">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3400854224-29">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="3400854224-30">(</span><span class="n">Chs2</span><span class="p" data-group-id="3400854224-30">)</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The code for the server can be rewritten into a generic part <code class="inline">server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2856506890-1">(</span><span class="ss">server</span><span class="p" data-group-id="2856506890-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2856506890-2">(</span><span class="p" data-group-id="2856506890-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2856506890-3">]</span><span class="p" data-group-id="2856506890-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2856506890-4">(</span><span class="p" data-group-id="2856506890-5">[</span><span class="ss">call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2856506890-5">]</span><span class="p" data-group-id="2856506890-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2856506890-6">(</span><span class="p" data-group-id="2856506890-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2856506890-7">]</span><span class="p" data-group-id="2856506890-6">)</span><span class="p">.</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8051856319-23">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="8051856319-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8051856319-24">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="8051856319-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="8051856319-25">(</span><span class="n">Chs</span><span class="p" data-group-id="8051856319-25">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8051856319-26">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8051856319-26">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="8051856319-27">(</span><span class="n">Chs2</span><span class="p" data-group-id="8051856319-27">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8051856319-28">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8051856319-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="8051856319-29">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8051856319-29">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="8051856319-30">(</span><span class="n">Chs2</span><span class="p" data-group-id="8051856319-30">)</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The code for the server can be rewritten into a generic part <code class="inline">server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9804990310-1">(</span><span class="ss">server</span><span class="p" data-group-id="9804990310-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9804990310-2">(</span><span class="p" data-group-id="9804990310-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9804990310-3">]</span><span class="p" data-group-id="9804990310-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9804990310-4">(</span><span class="p" data-group-id="9804990310-5">[</span><span class="ss">call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9804990310-5">]</span><span class="p" data-group-id="9804990310-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9804990310-6">(</span><span class="p" data-group-id="9804990310-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9804990310-7">]</span><span class="p" data-group-id="9804990310-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="2856506890-8">(</span><span class="n">Mod</span><span class="p" data-group-id="2856506890-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2856506890-9">(</span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2856506890-10">[</span><span class="n">Mod</span><span class="p" data-group-id="2856506890-10">]</span><span class="p" data-group-id="2856506890-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="9804990310-8">(</span><span class="n">Mod</span><span class="p" data-group-id="9804990310-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9804990310-9">(</span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9804990310-10">[</span><span class="n">Mod</span><span class="p" data-group-id="9804990310-10">]</span><span class="p" data-group-id="9804990310-9">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call</span><span class="p" data-group-id="2856506890-11">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="2856506890-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2856506890-12">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2856506890-13">(</span><span class="p" data-group-id="2856506890-13">)</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="2856506890-12">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call</span><span class="p" data-group-id="9804990310-11">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9804990310-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9804990310-12">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9804990310-13">(</span><span class="p" data-group-id="9804990310-13">)</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9804990310-12">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2856506890-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="2856506890-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="9804990310-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="9804990310-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Res</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">cast</span><span class="p" data-group-id="2856506890-15">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="2856506890-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2856506890-16">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="2856506890-16">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">cast</span><span class="p" data-group-id="9804990310-15">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9804990310-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9804990310-16">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9804990310-16">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="2856506890-17">(</span><span class="n">Mod</span><span class="p" data-group-id="2856506890-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="2856506890-18">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2856506890-19">(</span><span class="p" data-group-id="2856506890-19">)</span><span class="p" data-group-id="2856506890-18">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">init</span><span class="p" data-group-id="2856506890-20">(</span><span class="p" data-group-id="2856506890-20">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="2856506890-21">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="2856506890-21">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="9804990310-17">(</span><span class="n">Mod</span><span class="p" data-group-id="9804990310-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="9804990310-18">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9804990310-19">(</span><span class="p" data-group-id="9804990310-19">)</span><span class="p" data-group-id="9804990310-18">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">init</span><span class="p" data-group-id="9804990310-20">(</span><span class="p" data-group-id="9804990310-20">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="9804990310-21">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9804990310-21">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="2856506890-22">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="2856506890-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="9804990310-22">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9804990310-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2856506890-23">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="2856506890-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="2856506890-24">{</span><span class="n">Res</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="2856506890-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_call</span><span class="p" data-group-id="2856506890-25">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="2856506890-25">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2856506890-26">{</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="2856506890-26">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="2856506890-27">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="2856506890-27">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2856506890-28">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="2856506890-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">State2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_cast</span><span class="p" data-group-id="2856506890-29">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="2856506890-29">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="2856506890-30">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="2856506890-30">)</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>And a callback module <code class="inline">ch2.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8389516300-1">(</span><span class="ss">ch2</span><span class="p" data-group-id="8389516300-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8389516300-2">(</span><span class="p" data-group-id="8389516300-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8389516300-3">]</span><span class="p" data-group-id="8389516300-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8389516300-4">(</span><span class="p" data-group-id="8389516300-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8389516300-5">]</span><span class="p" data-group-id="8389516300-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8389516300-6">(</span><span class="p" data-group-id="8389516300-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8389516300-7">]</span><span class="p" data-group-id="8389516300-6">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="8389516300-8">(</span><span class="p" data-group-id="8389516300-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8389516300-9">(</span><span class="ss">ch2</span><span class="p" data-group-id="8389516300-9">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="8389516300-10">(</span><span class="p" data-group-id="8389516300-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="8389516300-11">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="8389516300-11">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="8389516300-12">(</span><span class="n">Ch</span><span class="p" data-group-id="8389516300-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8389516300-13">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8389516300-14">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8389516300-14">}</span><span class="p" data-group-id="8389516300-13">)</span><span class="p">.</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="9804990310-23">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9804990310-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="9804990310-24">{</span><span class="n">Res</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="9804990310-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_call</span><span class="p" data-group-id="9804990310-25">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9804990310-25">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9804990310-26">{</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="9804990310-26">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="9804990310-27">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="9804990310-27">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="9804990310-28">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9804990310-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">State2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_cast</span><span class="p" data-group-id="9804990310-29">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9804990310-29">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="9804990310-30">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="9804990310-30">)</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>And a callback module <code class="inline">ch2.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0271866426-1">(</span><span class="ss">ch2</span><span class="p" data-group-id="0271866426-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0271866426-2">(</span><span class="p" data-group-id="0271866426-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0271866426-3">]</span><span class="p" data-group-id="0271866426-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0271866426-4">(</span><span class="p" data-group-id="0271866426-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0271866426-5">]</span><span class="p" data-group-id="0271866426-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0271866426-6">(</span><span class="p" data-group-id="0271866426-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0271866426-7">]</span><span class="p" data-group-id="0271866426-6">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="0271866426-8">(</span><span class="p" data-group-id="0271866426-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0271866426-9">(</span><span class="ss">ch2</span><span class="p" data-group-id="0271866426-9">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="0271866426-10">(</span><span class="p" data-group-id="0271866426-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="0271866426-11">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0271866426-11">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="0271866426-12">(</span><span class="n">Ch</span><span class="p" data-group-id="0271866426-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="0271866426-13">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0271866426-14">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0271866426-14">}</span><span class="p" data-group-id="0271866426-13">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8389516300-15">(</span><span class="p" data-group-id="8389516300-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">channels</span><span class="p" data-group-id="8389516300-16">(</span><span class="p" data-group-id="8389516300-16">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="0271866426-15">(</span><span class="p" data-group-id="0271866426-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">channels</span><span class="p" data-group-id="0271866426-16">(</span><span class="p" data-group-id="0271866426-16">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="8389516300-17">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8389516300-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">alloc</span><span class="p" data-group-id="8389516300-18">(</span><span class="n">Chs</span><span class="p" data-group-id="8389516300-18">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; {Ch,Chs2}</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="0271866426-17">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0271866426-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">alloc</span><span class="p" data-group-id="0271866426-18">(</span><span class="n">Chs</span><span class="p" data-group-id="0271866426-18">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; {Ch,Chs2}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="8389516300-19">(</span><span class="p" data-group-id="8389516300-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8389516300-20">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8389516300-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">free</span><span class="p" data-group-id="8389516300-21">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8389516300-21">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; Chs2</span></code></pre><p>Notice the following:</p><ul><li>The code in <code class="inline">server</code> can be reused to build many different servers.</li><li>The server name, in this example the atom <code class="inline">ch2</code>, is hidden from the users of
│ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="0271866426-19">(</span><span class="p" data-group-id="0271866426-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0271866426-20">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0271866426-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">free</span><span class="p" data-group-id="0271866426-21">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0271866426-21">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; Chs2</span></code></pre><p>Notice the following:</p><ul><li>The code in <code class="inline">server</code> can be reused to build many different servers.</li><li>The server name, in this example the atom <code class="inline">ch2</code>, is hidden from the users of
│ │ │  the client functions. This means that the name can be changed without
│ │ │  affecting them.</li><li>The protocol (messages sent to and received from the server) is also hidden.
│ │ │  This is good programming practice and allows one to change the protocol
│ │ │  without changing the code using the interface functions.</li><li>The functionality of <code class="inline">server</code> can be extended without having to change <code class="inline">ch2</code>
│ │ │  or any other callback module.</li></ul><p>In <code class="inline">ch1.erl</code> and <code class="inline">ch2.erl</code> above, the implementation of <code class="inline">channels/0</code>, <code class="inline">alloc/1</code>,
│ │ │  and <code class="inline">free/2</code> has been intentionally left out, as it is not relevant to the
│ │ │  example. For completeness, one way to write these functions is given below. This
│ │ │  is an example only, a realistic implementation must be able to handle situations
│ │ │ -like running out of channels to allocate, and so on.</p><p><a href="" id="channels-implementation"></a></p><pre><code class="makeup erlang" translate="no"><span class="nf">channels</span><span class="p" data-group-id="2822507317-1">(</span><span class="p" data-group-id="2822507317-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="2822507317-2">{</span><span class="p">_</span><span class="n">Allocated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2822507317-3">[</span><span class="p" data-group-id="2822507317-3">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2822507317-4">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="2822507317-4">)</span><span class="p" data-group-id="2822507317-2">}</span><span class="p">.</span><span class="w">
│ │ │ +like running out of channels to allocate, and so on.</p><p><a href="" id="channels-implementation"></a></p><pre><code class="makeup erlang" translate="no"><span class="nf">channels</span><span class="p" data-group-id="2075792642-1">(</span><span class="p" data-group-id="2075792642-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2075792642-2">{</span><span class="p">_</span><span class="n">Allocated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2075792642-3">[</span><span class="p" data-group-id="2075792642-3">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2075792642-4">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="2075792642-4">)</span><span class="p" data-group-id="2075792642-2">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="2822507317-5">(</span><span class="p" data-group-id="2822507317-6">{</span><span class="n">Allocated</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2822507317-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2822507317-7">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="p" data-group-id="2822507317-6">}</span><span class="p" data-group-id="2822507317-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="2822507317-8">{</span><span class="n">H</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2822507317-9">{</span><span class="p" data-group-id="2822507317-10">[</span><span class="n">H</span><span class="p">|</span><span class="n">Allocated</span><span class="p" data-group-id="2822507317-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2822507317-9">}</span><span class="p" data-group-id="2822507317-8">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="2075792642-5">(</span><span class="p" data-group-id="2075792642-6">{</span><span class="n">Allocated</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2075792642-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2075792642-7">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="p" data-group-id="2075792642-6">}</span><span class="p" data-group-id="2075792642-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2075792642-8">{</span><span class="n">H</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2075792642-9">{</span><span class="p" data-group-id="2075792642-10">[</span><span class="n">H</span><span class="p">|</span><span class="n">Allocated</span><span class="p" data-group-id="2075792642-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2075792642-9">}</span><span class="p" data-group-id="2075792642-8">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="2822507317-11">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2822507317-12">{</span><span class="n">Alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Free</span><span class="p" data-group-id="2822507317-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Channels</span><span class="p" data-group-id="2822507317-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="2822507317-13">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="2822507317-13">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="2075792642-11">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2075792642-12">{</span><span class="n">Alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Free</span><span class="p" data-group-id="2075792642-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Channels</span><span class="p" data-group-id="2075792642-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="2075792642-13">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="2075792642-13">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │        </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="2822507317-14">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2822507317-15">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="2822507317-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2822507317-16">[</span><span class="n">Ch</span><span class="p">|</span><span class="n">Free</span><span class="p" data-group-id="2822507317-16">]</span><span class="p" data-group-id="2822507317-14">}</span><span class="p">;</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="2075792642-14">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2075792642-15">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="2075792642-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2075792642-16">[</span><span class="n">Ch</span><span class="p">|</span><span class="n">Free</span><span class="p" data-group-id="2075792642-16">]</span><span class="p" data-group-id="2075792642-14">}</span><span class="p">;</span><span class="w">
│ │ │        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │           </span><span class="n">Channels</span><span class="w">
│ │ │     </span><span class="k">end</span><span class="p">.</span></code></pre><p>Code written without using behaviours can be more efficient, but the increased
│ │ │  efficiency is at the expense of generality. The ability to manage all
│ │ │  applications in the system in a consistent manner is important.</p><p>Using behaviours also makes it easier to read and understand code written by
│ │ │  other programmers. Improvised programming structures, while possibly more
│ │ │  efficient, are always more difficult to understand.</p><p>The <code class="inline">server</code> module corresponds, greatly simplified, to the Erlang/OTP behaviour
│ │ │  <code class="inline">gen_server</code>.</p><p>The standard Erlang/OTP behaviours are:</p><ul><li><p><a href="gen_server_concepts.html">gen_server</a></p><p>For implementing the server of a client-server relation</p></li><li><p><a href="statem.html">gen_statem</a></p><p>For implementing state machines</p></li><li><p><a href="events.html">gen_event</a></p><p>For implementing event handling functionality</p></li><li><p><a href="sup_princ.html">supervisor</a></p><p>For implementing a supervisor in a supervision tree</p></li></ul><p>The compiler understands the module attribute <code class="inline">-behaviour(Behaviour)</code> and issues
│ │ │ -warnings about missing callback functions, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2685775524-1">(</span><span class="ss">chs3</span><span class="p" data-group-id="2685775524-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="2685775524-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="2685775524-2">)</span><span class="p">.</span><span class="w">
│ │ │ +warnings about missing callback functions, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6611680237-1">(</span><span class="ss">chs3</span><span class="p" data-group-id="6611680237-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="6611680237-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="6611680237-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="2685775524-3">(</span><span class="ss">chs3</span><span class="p" data-group-id="2685775524-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="6611680237-3">(</span><span class="ss">chs3</span><span class="p" data-group-id="6611680237-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="o">/</span><span class="ss">chs3</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">10</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="ss">undefined</span><span class="w"> </span><span class="ss">call</span><span class="o">-</span><span class="ss">back</span><span class="w"> </span><span class="ss">function</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2685775524-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">chs3</span><span class="p" data-group-id="2685775524-4">}</span></code></pre><h2 id="applications" class="section-heading">
│ │ │ +</span><span class="p" data-group-id="6611680237-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">chs3</span><span class="p" data-group-id="6611680237-4">}</span></code></pre><h2 id="applications" class="section-heading">
│ │ │    <a href="#applications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Applications</span>
│ │ │  </h2>
│ │ │  <p>Erlang/OTP comes with a number of components, each implementing some specific
│ │ │  functionality. Components are with Erlang/OTP terminology called <em>applications</em>.
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/distributed.html
│ │ │ @@ -142,25 +142,25 @@
│ │ │  </h2>
│ │ │  <p>A <em>node</em> is an executing Erlang runtime system that has been given a name, using
│ │ │  the command-line flag <a href="../../erts-15.2.7/doc/html/erl_cmd.html#name"><code class="inline">-name</code></a> (long names) or
│ │ │  <a href="../../erts-15.2.7/doc/html/erl_cmd.html#sname"><code class="inline">-sname</code></a> (short names).</p><p>The format of the node name is an atom <code class="inline">name@host</code>. <code class="inline">name</code> is the name given by
│ │ │  the user. <code class="inline">host</code> is the full host name if long names are used, or the first part
│ │ │  of the host name if short names are used. Function <a href="../../erts-15.2.7/doc/html/erlang.html#node/0"><code class="inline">node()</code></a>
│ │ │  returns the name of the node.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -name dilbert</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6229818387-1">(</span><span class="ss">dilbert@uab</span><span class="p">.</span><span class="ss">ericsson</span><span class="p">.</span><span class="ss">se</span><span class="p" data-group-id="6229818387-1">)</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="6229818387-2">(</span><span class="p" data-group-id="6229818387-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1314831586-1">(</span><span class="ss">dilbert@uab</span><span class="p">.</span><span class="ss">ericsson</span><span class="p">.</span><span class="ss">se</span><span class="p" data-group-id="1314831586-1">)</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="1314831586-2">(</span><span class="p" data-group-id="1314831586-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">&#39;dilbert@uab.ericsson.se&#39;</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">% erl -sname dilbert</span><span class="gp unselectable">
│ │ │ -(dilbert@uab)1&gt; </span><span class="nf">node</span><span class="p" data-group-id="6229818387-3">(</span><span class="p" data-group-id="6229818387-3">)</span><span class="p">.</span><span class="w">
│ │ │ +(dilbert@uab)1&gt; </span><span class="nf">node</span><span class="p" data-group-id="1314831586-3">(</span><span class="p" data-group-id="1314831586-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">dilbert@uab</span></code></pre><p>The node name can also be given in runtime by calling <a href="../../lib/kernel-10.2.7.1/doc/html/net_kernel.html#start/1"><code class="inline">net_kernel:start/1</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nf">node</span><span class="p" data-group-id="6568666433-1">(</span><span class="p" data-group-id="6568666433-1">)</span><span class="p">.</span><span class="w">
│ │ │ +1&gt; </span><span class="nf">node</span><span class="p" data-group-id="5311157775-1">(</span><span class="p" data-group-id="5311157775-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">nonode@nohost</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">net_kernel</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6568666433-2">(</span><span class="p" data-group-id="6568666433-3">[</span><span class="ss">dilbert</span><span class="p">,</span><span class="ss">shortnames</span><span class="p" data-group-id="6568666433-3">]</span><span class="p" data-group-id="6568666433-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6568666433-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.102</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6568666433-4">}</span><span class="gp unselectable">
│ │ │ -(dilbert@uab)3&gt; </span><span class="nf">node</span><span class="p" data-group-id="6568666433-5">(</span><span class="p" data-group-id="6568666433-5">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="nc">net_kernel</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5311157775-2">(</span><span class="p" data-group-id="5311157775-3">[</span><span class="ss">dilbert</span><span class="p">,</span><span class="ss">shortnames</span><span class="p" data-group-id="5311157775-3">]</span><span class="p" data-group-id="5311157775-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5311157775-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.102</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5311157775-4">}</span><span class="gp unselectable">
│ │ │ +(dilbert@uab)3&gt; </span><span class="nf">node</span><span class="p" data-group-id="5311157775-5">(</span><span class="p" data-group-id="5311157775-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">dilbert@uab</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>A node with a long node name cannot communicate with a node with a short node
│ │ │  name.</p></section><h2 id="node-connections" class="section-heading">
│ │ │    <a href="#node-connections" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Node Connections</span>
│ │ │  </h2>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/distributed_applications.html
│ │ │ @@ -150,36 +150,36 @@
│ │ │  (within the time-out specified by <code class="inline">sync_nodes_timeout</code>).</li><li><p><code class="inline">sync_nodes_timeout = integer() | infinity</code> - Specifies how many milliseconds
│ │ │  to wait for the other nodes to start.</p></li></ul><p>When started, the node waits for all nodes specified by <code class="inline">sync_nodes_mandatory</code>
│ │ │  and <code class="inline">sync_nodes_optional</code> to come up. When all nodes are up, or when all
│ │ │  mandatory nodes are up and the time specified by <code class="inline">sync_nodes_timeout</code> has
│ │ │  elapsed, all applications start. If not all mandatory nodes are up, the node
│ │ │  terminates.</p><p><em>Example:</em></p><p>An application <code class="inline">myapp</code> is to run at the node <code class="inline">cp1@cave</code>. If this node goes down,
│ │ │  <code class="inline">myapp</code> is to be restarted at <code class="inline">cp2@cave</code> or <code class="inline">cp3@cave</code>. A system configuration
│ │ │ -file <code class="inline">cp1.config</code> for <code class="inline">cp1@cave</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9479971320-1">[</span><span class="p" data-group-id="9479971320-2">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9479971320-3">[</span><span class="p" data-group-id="9479971320-4">{</span><span class="ss">distributed</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479971320-5">[</span><span class="p" data-group-id="9479971320-6">{</span><span class="ss">myapp</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479971320-7">[</span><span class="ss">cp1@cave</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479971320-8">{</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="9479971320-8">}</span><span class="p" data-group-id="9479971320-7">]</span><span class="p" data-group-id="9479971320-6">}</span><span class="p" data-group-id="9479971320-5">]</span><span class="p" data-group-id="9479971320-4">}</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="9479971320-9">{</span><span class="ss">sync_nodes_mandatory</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479971320-10">[</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="9479971320-10">]</span><span class="p" data-group-id="9479971320-9">}</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="9479971320-11">{</span><span class="ss">sync_nodes_timeout</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p" data-group-id="9479971320-11">}</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9479971320-3">]</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9479971320-2">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9479971320-1">]</span><span class="p">.</span></code></pre><p>The system configuration files for <code class="inline">cp2@cave</code> and <code class="inline">cp3@cave</code> are identical,
│ │ │ +file <code class="inline">cp1.config</code> for <code class="inline">cp1@cave</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9601563488-1">[</span><span class="p" data-group-id="9601563488-2">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9601563488-3">[</span><span class="p" data-group-id="9601563488-4">{</span><span class="ss">distributed</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601563488-5">[</span><span class="p" data-group-id="9601563488-6">{</span><span class="ss">myapp</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601563488-7">[</span><span class="ss">cp1@cave</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601563488-8">{</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="9601563488-8">}</span><span class="p" data-group-id="9601563488-7">]</span><span class="p" data-group-id="9601563488-6">}</span><span class="p" data-group-id="9601563488-5">]</span><span class="p" data-group-id="9601563488-4">}</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="9601563488-9">{</span><span class="ss">sync_nodes_mandatory</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9601563488-10">[</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="9601563488-10">]</span><span class="p" data-group-id="9601563488-9">}</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="9601563488-11">{</span><span class="ss">sync_nodes_timeout</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p" data-group-id="9601563488-11">}</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9601563488-3">]</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9601563488-2">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9601563488-1">]</span><span class="p">.</span></code></pre><p>The system configuration files for <code class="inline">cp2@cave</code> and <code class="inline">cp3@cave</code> are identical,
│ │ │  except for the list of mandatory nodes, which is to be <code class="inline">[cp1@cave, cp3@cave]</code>
│ │ │  for <code class="inline">cp2@cave</code> and <code class="inline">[cp1@cave, cp2@cave]</code> for <code class="inline">cp3@cave</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>All involved nodes must have the same value for <code class="inline">distributed</code> and
│ │ │  <code class="inline">sync_nodes_timeout</code>. Otherwise the system behavior is undefined.</p></section><h2 id="starting-and-stopping-distributed-applications" class="section-heading">
│ │ │    <a href="#starting-and-stopping-distributed-applications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting and Stopping Distributed Applications</span>
│ │ │  </h2>
│ │ │  <p>When all involved (mandatory) nodes have been started, the distributed
│ │ │  application can be started by calling <code class="inline">application:start(Application)</code> at <em>all
│ │ │  of these nodes.</em></p><p>A boot script (see <a href="release_structure.html">Releases</a>) can be used that
│ │ │  automatically starts the application.</p><p>The application is started at the first operational node that is listed in the
│ │ │  list of nodes in the <code class="inline">distributed</code> configuration parameter. The application is
│ │ │  started as usual. That is, an application master is created and calls the
│ │ │ -application callback function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0605905602-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="0605905602-1">)</span></code></pre><p>Example:</p><p>Continuing the example from the previous section, the three nodes are started,
│ │ │ +application callback function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6134737063-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="6134737063-1">)</span></code></pre><p>Example:</p><p>Continuing the example from the previous section, the three nodes are started,
│ │ │  specifying the system configuration file:</p><pre><code class="text">&gt; erl -sname cp1 -config cp1
│ │ │  &gt; erl -sname cp2 -config cp2
│ │ │  &gt; erl -sname cp3 -config cp3</code></pre><p>When all nodes are operational, <code class="inline">myapp</code> can be started. This is achieved by
│ │ │  calling <code class="inline">application:start(myapp)</code> at all three nodes. It is then started at
│ │ │  <code class="inline">cp1</code>, as shown in the following figure:</p><p><a href="" id="dist1"></a></p><p><img src="assets/dist1.gif" alt="Application myapp - Situation 1" title="Application myapp - Situation 1"/></p><p>Similarly, the application must be stopped by calling
│ │ │  <code class="inline">application:stop(Application)</code> at all involved nodes.</p><h2 id="failover" class="section-heading">
│ │ │    <a href="#failover" class="hover-link">
│ │ │ @@ -187,30 +187,30 @@
│ │ │    </a>
│ │ │    <span class="text">Failover</span>
│ │ │  </h2>
│ │ │  <p>If the node where the application is running goes down, the application is
│ │ │  restarted (after the specified time-out) at the first operational node that is
│ │ │  listed in the list of nodes in the <code class="inline">distributed</code> configuration parameter. This
│ │ │  is called a <em>failover</em>.</p><p>The application is started the normal way at the new node, that is, by the
│ │ │ -application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1227669884-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="1227669884-1">)</span></code></pre><p>An exception is if the application has the <code class="inline">start_phases</code> key defined (see
│ │ │ +application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4732871711-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="4732871711-1">)</span></code></pre><p>An exception is if the application has the <code class="inline">start_phases</code> key defined (see
│ │ │  <a href="included_applications.html">Included Applications</a>). The application is then
│ │ │ -instead started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3291780721-1">(</span><span class="p" data-group-id="3291780721-2">{</span><span class="ss">failover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="3291780721-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="3291780721-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the terminated node.</p><p><em>Example:</em></p><p>If <code class="inline">cp1</code> goes down, the system checks which one of the other nodes, <code class="inline">cp2</code> or
│ │ │ +instead started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9544071183-1">(</span><span class="p" data-group-id="9544071183-2">{</span><span class="ss">failover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="9544071183-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="9544071183-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the terminated node.</p><p><em>Example:</em></p><p>If <code class="inline">cp1</code> goes down, the system checks which one of the other nodes, <code class="inline">cp2</code> or
│ │ │  <code class="inline">cp3</code>, has the least number of running applications, but waits for 5 seconds for
│ │ │  <code class="inline">cp1</code> to restart. If <code class="inline">cp1</code> does not restart and <code class="inline">cp2</code> runs fewer applications
│ │ │  than <code class="inline">cp3</code>, <code class="inline">myapp</code> is restarted on <code class="inline">cp2</code>.</p><p><a href="" id="dist2"></a></p><p><img src="assets/dist2.gif" alt="Application myapp - Situation 2" title="Application myapp - Situation 2"/></p><p>Suppose now that <code class="inline">cp2</code> goes also down and does not restart within 5 seconds.
│ │ │  <code class="inline">myapp</code> is now restarted on <code class="inline">cp3</code>.</p><p><a href="" id="dist3"></a></p><p><img src="assets/dist3.gif" alt="Application myapp - Situation 3" title="Application myapp - Situation 3"/></p><h2 id="takeover" class="section-heading">
│ │ │    <a href="#takeover" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Takeover</span>
│ │ │  </h2>
│ │ │  <p>If a node is started, which has higher priority according to <code class="inline">distributed</code> than
│ │ │  the node where a distributed application is running, the application is
│ │ │  restarted at the new node and stopped at the old node. This is called a
│ │ │ -<em>takeover</em>.</p><p>The application is started by the application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9864864495-1">(</span><span class="p" data-group-id="9864864495-2">{</span><span class="ss">takeover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="9864864495-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="9864864495-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the old node.</p><p><em>Example:</em></p><p>If <code class="inline">myapp</code> is running at <code class="inline">cp3</code>, and if <code class="inline">cp2</code> now restarts, it does not restart
│ │ │ +<em>takeover</em>.</p><p>The application is started by the application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1497753115-1">(</span><span class="p" data-group-id="1497753115-2">{</span><span class="ss">takeover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="1497753115-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="1497753115-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the old node.</p><p><em>Example:</em></p><p>If <code class="inline">myapp</code> is running at <code class="inline">cp3</code>, and if <code class="inline">cp2</code> now restarts, it does not restart
│ │ │  <code class="inline">myapp</code>, as the order between the <code class="inline">cp2</code> and <code class="inline">cp3</code> nodes is undefined.</p><p><a href="" id="dist4"></a></p><p><img src="assets/dist4.gif" alt="Application myapp - Situation 4" title="Application myapp - Situation 4"/></p><p>However, if <code class="inline">cp1</code> also restarts, the function <a href="../../lib/kernel-10.2.7.1/doc/html/application.html#takeover/2"><code class="inline">application:takeover/2</code></a> moves
│ │ │  <code class="inline">myapp</code> to <code class="inline">cp1</code>, as <code class="inline">cp1</code> has a higher priority than <code class="inline">cp3</code> for this
│ │ │  application. In this case, <code class="inline">Module:start({takeover, cp3@cave}, StartArgs)</code> is
│ │ │  executed at <code class="inline">cp1</code> to start the application.</p><p><a href="" id="dist5"></a></p><p><img src="assets/dist5.gif" alt="Application myapp - Situation 5" title="Application myapp - Situation 5"/></p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/documentation.html
│ │ │ @@ -112,23 +112,23 @@
│ │ │        </a>
│ │ │  
│ │ │  
│ │ │      <span>Documentation</span>
│ │ │    </h1>
│ │ │  
│ │ │  <p>Documentation in Erlang is done through the <code class="inline">-moduledoc</code> and <code class="inline">-doc</code>
│ │ │ -<a href="modules.html#module-attributes">attributes</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5862919845-1">(</span><span class="ss">arith</span><span class="p" data-group-id="5862919845-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="modules.html#module-attributes">attributes</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0366391311-1">(</span><span class="ss">arith</span><span class="p" data-group-id="0366391311-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │  A module for basic arithmetic.
│ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5862919845-2">(</span><span class="p" data-group-id="5862919845-3">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5862919845-3">]</span><span class="p" data-group-id="5862919845-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0366391311-2">(</span><span class="p" data-group-id="0366391311-3">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0366391311-3">]</span><span class="p" data-group-id="0366391311-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="5862919845-4">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5862919845-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The <code class="inline">-moduledoc</code> attribute has to be located before the first <code class="inline">-doc</code> attribute
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="0366391311-4">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="0366391311-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The <code class="inline">-moduledoc</code> attribute has to be located before the first <code class="inline">-doc</code> attribute
│ │ │  or function declaration. It documents the overall purpose of the module.</p><p>The <code class="inline">-doc</code> attribute always precedes the <a href="ref_man_functions.html">function</a> or
│ │ │  <a href="modules.html#module-attributes">attribute</a> it documents. The
│ │ │  attributes that can be documented are
│ │ │  <a href="typespec.html#type-declarations-of-user-defined-types">user-defined types</a>
│ │ │  (<code class="inline">-type</code> and <code class="inline">-opaque</code>) and
│ │ │  <a href="modules.html#behaviour-module-attribute">behaviour module attributes</a>
│ │ │  (<code class="inline">-callback</code>).</p><p>By default the format used for documentation attributes is
│ │ │ @@ -140,55 +140,55 @@
│ │ │  <a href="modules.html#documentation-attributes">Documentation Attributes</a>.</p><p><code class="inline">-doc</code> attributes have been available since Erlang/OTP 27.</p><h2 id="documentation-metadata" class="section-heading">
│ │ │    <a href="#documentation-metadata" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Documentation metadata</span>
│ │ │  </h2>
│ │ │  <p>It is possible to add metadata to the documentation entry. You do this by adding
│ │ │ -a <code class="inline">-moduledoc</code> or <code class="inline">-doc</code> attribute with a map as argument. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4624758845-1">(</span><span class="ss">arith</span><span class="p" data-group-id="4624758845-1">)</span><span class="p">.</span><span class="w">
│ │ │ +a <code class="inline">-moduledoc</code> or <code class="inline">-doc</code> attribute with a map as argument. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1246715677-1">(</span><span class="ss">arith</span><span class="p" data-group-id="1246715677-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │  A module for basic arithmetic.
│ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="4624758845-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="4624758845-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="1246715677-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="1246715677-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4624758845-3">(</span><span class="p" data-group-id="4624758845-4">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4624758845-4">]</span><span class="p" data-group-id="4624758845-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1246715677-3">(</span><span class="p" data-group-id="1246715677-4">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1246715677-4">]</span><span class="p" data-group-id="1246715677-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="4624758845-5">(</span><span class="p" data-group-id="4624758845-6">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="4624758845-6">}</span><span class="p" data-group-id="4624758845-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="4624758845-7">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4624758845-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The metadata is used by documentation tools to provide extra information to the
│ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="1246715677-5">(</span><span class="p" data-group-id="1246715677-6">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="1246715677-6">}</span><span class="p" data-group-id="1246715677-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="1246715677-7">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="1246715677-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The metadata is used by documentation tools to provide extra information to the
│ │ │  user. There can be multiple metadata documentation entries, in which case the
│ │ │  maps will be merged with the latest taking precedence if there are duplicate
│ │ │  keys. Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="3469142399-1">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">author</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p" data-group-id="3469142399-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="3469142399-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="3469142399-2">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="3469142399-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="3469142399-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>This will result in a metadata entry of <code class="inline">#{since =&gt; &quot;2.0&quot;, author =&gt; &quot;Joe&quot;}</code>.</p><p>The keys and values in the metadata map can be any type, but it is recommended
│ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="5303921669-1">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">author</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p" data-group-id="5303921669-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="5303921669-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="5303921669-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="5303921669-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5303921669-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>This will result in a metadata entry of <code class="inline">#{since =&gt; &quot;2.0&quot;, author =&gt; &quot;Joe&quot;}</code>.</p><p>The keys and values in the metadata map can be any type, but it is recommended
│ │ │  that only <a href="data_types.html#atom">atoms</a> are used for keys and
│ │ │  <a href="data_types.html#string">strings</a> for the values.</p><h2 id="external-documentation-files" class="section-heading">
│ │ │    <a href="#external-documentation-files" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">External documentation files</span>
│ │ │  </h2>
│ │ │  <p>The <code class="inline">-moduledoc</code> and <code class="inline">-doc</code> can also be placed in external files. To do so use
│ │ │  <code class="inline">-doc {file, &quot;path/to/doc.md&quot;}</code> to point to the documentation. The path used is
│ │ │  relative to the file where the <code class="inline">-doc</code> attribute is located. For example:</p><pre><code class="markdown">%% doc/add.md
│ │ │  Adds two numbers.</code></pre><p>and</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% src/arith.erl</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="1640774387-1">(</span><span class="p" data-group-id="1640774387-2">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/add.md&quot;</span><span class="p" data-group-id="1640774387-2">}</span><span class="p" data-group-id="1640774387-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="1640774387-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="1640774387-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><h2 id="documenting-a-module" class="section-heading">
│ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="2847593286-1">(</span><span class="p" data-group-id="2847593286-2">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/add.md&quot;</span><span class="p" data-group-id="2847593286-2">}</span><span class="p" data-group-id="2847593286-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="2847593286-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="2847593286-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><h2 id="documenting-a-module" class="section-heading">
│ │ │    <a href="#documenting-a-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Documenting a module</span>
│ │ │  </h2>
│ │ │  <p>The module description should include details on how to use the API and examples
│ │ │  of the different functions working together. Here is a good place to use images
│ │ │  and other diagrams to better show the usage of the module. Instead of writing a
│ │ │  long text in the <code class="inline">moduledoc</code> attribute, it could be better to break it out into
│ │ │  an external page.</p><p>The <code class="inline">moduledoc</code> attribute should start with a short paragraph describing the
│ │ │ -module and then go into greater details. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1418367738-1">(</span><span class="ss">arith</span><span class="p" data-group-id="1418367738-1">)</span><span class="p">.</span><span class="w">
│ │ │ +module and then go into greater details. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7809602492-1">(</span><span class="ss">arith</span><span class="p" data-group-id="7809602492-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="s">&quot;
│ │ │     A module for basic arithmetic.
│ │ │  
│ │ │     This module can be used to add and subtract values. For example:
│ │ │  
│ │ │     ```erlang
│ │ │     1&gt; arith:substract(arith:add(2, 3), 1).
│ │ │ @@ -203,94 +203,94 @@
│ │ │  <p>There are three reserved metadata keys for <code class="inline">-moduledoc</code>:</p><ul><li><code class="inline">since</code> - Shows in which version of the application the module was added.
│ │ │  If this is added, all functions, types, and callbacks within will also receive
│ │ │  the same <code class="inline">since</code> value unless specified in the metadata of the function, type
│ │ │  or callback.</li><li><code class="inline">deprecated</code> - Shows a text in the documentation explaining that it is
│ │ │  deprecated and what to use instead.</li><li><code class="inline">format</code> - The format to use for all documentation in this module. The
│ │ │  default is <code class="inline">text/markdown</code>. It should be written using the
│ │ │  <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types">mime type</a>
│ │ │ -of the format.</li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="7789950622-1">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/arith.asciidoc&quot;</span><span class="p" data-group-id="7789950622-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="7789950622-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;0.1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">format</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;text/asciidoc&quot;</span><span class="p" data-group-id="7789950622-2">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="7789950622-3">#{</span><span class="ss">deprecated</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Use the Erlang arithmetic operators instead.&quot;</span><span class="p" data-group-id="7789950622-3">}</span><span class="p">.</span></code></pre><h2 id="documenting-functions-user-defined-types-and-callbacks" class="section-heading">
│ │ │ +of the format.</li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="7319269385-1">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/arith.asciidoc&quot;</span><span class="p" data-group-id="7319269385-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="7319269385-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;0.1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">format</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;text/asciidoc&quot;</span><span class="p" data-group-id="7319269385-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="7319269385-3">#{</span><span class="ss">deprecated</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Use the Erlang arithmetic operators instead.&quot;</span><span class="p" data-group-id="7319269385-3">}</span><span class="p">.</span></code></pre><h2 id="documenting-functions-user-defined-types-and-callbacks" class="section-heading">
│ │ │    <a href="#documenting-functions-user-defined-types-and-callbacks" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Documenting functions, user-defined types, and callbacks</span>
│ │ │  </h2>
│ │ │  <p>Functions, types, and callbacks can be documented using the <code class="inline">-doc</code> attribute.
│ │ │  Each entry should start with a short paragraph describing the purpose of entity,
│ │ │  and then go into greater detail in needed.</p><p>It is not recommended to include images or diagrams in this documentation as it
│ │ │  is used by IDEs and <a href="../../lib/stdlib-6.2.2.1/doc/html/c.html#h/1"><code class="inline">c:h/1</code></a> to show the documentation to the user.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │  A number that can be used by the arith module.
│ │ │  
│ │ │  We use a special number here so that we know
│ │ │  that this number comes from this module.
│ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0659498643-1">(</span><span class="p" data-group-id="0659498643-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0659498643-2">{</span><span class="ss">arith</span><span class="p">,</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">number</span><span class="p" data-group-id="0659498643-3">(</span><span class="p" data-group-id="0659498643-3">)</span><span class="p" data-group-id="0659498643-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="5600864254-1">(</span><span class="p" data-group-id="5600864254-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="5600864254-2">{</span><span class="ss">arith</span><span class="p">,</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">number</span><span class="p" data-group-id="5600864254-3">(</span><span class="p" data-group-id="5600864254-3">)</span><span class="p" data-group-id="5600864254-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │  Adds two numbers.
│ │ │  
│ │ │  ### Example:
│ │ │  
│ │ │  ```
│ │ │  1&gt; arith:add(arith:number(1), arith:number(2)). {number, 3}
│ │ │  ```
│ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="0659498643-4">(</span><span class="nf">number</span><span class="p" data-group-id="0659498643-5">(</span><span class="p" data-group-id="0659498643-5">)</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0659498643-6">(</span><span class="p" data-group-id="0659498643-6">)</span><span class="p" data-group-id="0659498643-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0659498643-7">(</span><span class="p" data-group-id="0659498643-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="0659498643-8">(</span><span class="p" data-group-id="0659498643-9">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="p" data-group-id="0659498643-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0659498643-10">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="0659498643-10">}</span><span class="p" data-group-id="0659498643-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0659498643-11">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="0659498643-11">}</span><span class="p">.</span></code></pre><h3 id="doc-metadata" class="section-heading">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="5600864254-4">(</span><span class="nf">number</span><span class="p" data-group-id="5600864254-5">(</span><span class="p" data-group-id="5600864254-5">)</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="5600864254-6">(</span><span class="p" data-group-id="5600864254-6">)</span><span class="p" data-group-id="5600864254-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="5600864254-7">(</span><span class="p" data-group-id="5600864254-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="5600864254-8">(</span><span class="p" data-group-id="5600864254-9">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="p" data-group-id="5600864254-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5600864254-10">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5600864254-10">}</span><span class="p" data-group-id="5600864254-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5600864254-11">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5600864254-11">}</span><span class="p">.</span></code></pre><h3 id="doc-metadata" class="section-heading">
│ │ │    <a href="#doc-metadata" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Doc metadata</span>
│ │ │  </h3>
│ │ │  <p>There are four reserved metadata keys for <code class="inline">-doc</code>:</p><ul><li><p><code class="inline">since =&gt; unicode:chardata()</code> - Shows which version of the application the
│ │ │  module was added.</p></li><li><p><code class="inline">deprecated =&gt; unicode:chardata()</code> - Shows a text in the documentation
│ │ │  explaining that it is deprecated and what to use instead. The compiler will
│ │ │  automatically insert this key if there is a <code class="inline">-deprecated</code> attribute marking a
│ │ │  function as deprecated.</p></li><li><p><code class="inline">equiv =&gt; unicode:chardata() | F/A | F(...)</code> - Notes that this function is equivalent to
│ │ │  another function in this module. The equivalence can be described using either
│ │ │ -<code class="inline">Func/Arity</code>, <code class="inline">Func(Args)</code> or a <a href="../../lib/stdlib-6.2.2.1/doc/html/unicode.html#t:chardata/0">unicode string</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="5998742283-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">add</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="5998742283-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="5998742283-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5998742283-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="5998742283-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5998742283-4">[</span><span class="p" data-group-id="5998742283-4">]</span><span class="p" data-group-id="5998742283-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="5998742283-5">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="5998742283-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>or</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="3256604631-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="3256604631-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3256604631-3">[</span><span class="p" data-group-id="3256604631-3">]</span><span class="p" data-group-id="3256604631-2">)</span><span class="p" data-group-id="3256604631-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="3256604631-4">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3256604631-5">(</span><span class="p" data-group-id="3256604631-5">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3256604631-6">(</span><span class="p" data-group-id="3256604631-6">)</span><span class="p" data-group-id="3256604631-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3256604631-7">(</span><span class="p" data-group-id="3256604631-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="3256604631-8">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="3256604631-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="3256604631-9">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3256604631-10">[</span><span class="p" data-group-id="3256604631-10">]</span><span class="p" data-group-id="3256604631-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="3256604631-11">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="3256604631-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The entry into the <a href="../../lib/kernel-10.2.7.1/doc/html/eep48_chapter.html">EEP-48</a> doc chunk metadata is
│ │ │ +<code class="inline">Func/Arity</code>, <code class="inline">Func(Args)</code> or a <a href="../../lib/stdlib-6.2.2.1/doc/html/unicode.html#t:chardata/0">unicode string</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="7273493530-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">add</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="7273493530-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="7273493530-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="7273493530-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="7273493530-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7273493530-4">[</span><span class="p" data-group-id="7273493530-4">]</span><span class="p" data-group-id="7273493530-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="7273493530-5">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="7273493530-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>or</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="0295697863-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="0295697863-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0295697863-3">[</span><span class="p" data-group-id="0295697863-3">]</span><span class="p" data-group-id="0295697863-2">)</span><span class="p" data-group-id="0295697863-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="0295697863-4">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0295697863-5">(</span><span class="p" data-group-id="0295697863-5">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0295697863-6">(</span><span class="p" data-group-id="0295697863-6">)</span><span class="p" data-group-id="0295697863-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0295697863-7">(</span><span class="p" data-group-id="0295697863-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="0295697863-8">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="0295697863-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="0295697863-9">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0295697863-10">[</span><span class="p" data-group-id="0295697863-10">]</span><span class="p" data-group-id="0295697863-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="0295697863-11">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="0295697863-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The entry into the <a href="../../lib/kernel-10.2.7.1/doc/html/eep48_chapter.html">EEP-48</a> doc chunk metadata is
│ │ │  the value converted to a string.</p></li><li><p><code class="inline">exported =&gt; boolean()</code> - A <a href="../../erts-15.2.7/doc/html/erlang.html#t:boolean/0"><code class="inline">boolean/0</code></a> signifying if the entry is <code class="inline">exported</code>
│ │ │  or not. This value is automatically set by the compiler and should not be set
│ │ │  by the user.</p></li></ul><h3 id="doc-signatures" class="section-heading">
│ │ │    <a href="#doc-signatures" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Doc signatures</span>
│ │ │  </h3>
│ │ │  <p>The doc signature is a short text shown to describe the function and its arguments.
│ │ │  By default it is determined by looking at the names of the arguments in the
│ │ │ -<code class="inline">-spec</code> or function. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add</span><span class="p" data-group-id="4105333340-1">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4105333340-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">-spec</code> or function. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add</span><span class="p" data-group-id="6599726664-1">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="6599726664-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">sub</span><span class="p" data-group-id="4105333340-2">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4105333340-3">(</span><span class="p" data-group-id="4105333340-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4105333340-4">(</span><span class="p" data-group-id="4105333340-4">)</span><span class="p" data-group-id="4105333340-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4105333340-5">(</span><span class="p" data-group-id="4105333340-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">sub</span><span class="p" data-group-id="4105333340-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4105333340-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>will have a signature of <code class="inline">add(One, Two)</code> and <code class="inline">sub(One, Two)</code>.</p><p>For types or callbacks, the signature is derived from the type or callback
│ │ │ -specification. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0500916624-1">(</span><span class="n">Value</span><span class="p" data-group-id="0500916624-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0500916624-2">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="0500916624-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">sub</span><span class="p" data-group-id="6599726664-2">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="6599726664-3">(</span><span class="p" data-group-id="6599726664-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="6599726664-4">(</span><span class="p" data-group-id="6599726664-4">)</span><span class="p" data-group-id="6599726664-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="6599726664-5">(</span><span class="p" data-group-id="6599726664-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">sub</span><span class="p" data-group-id="6599726664-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6599726664-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>will have a signature of <code class="inline">add(One, Two)</code> and <code class="inline">sub(One, Two)</code>.</p><p>For types or callbacks, the signature is derived from the type or callback
│ │ │ +specification. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0966932645-1">(</span><span class="n">Value</span><span class="p" data-group-id="0966932645-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0966932645-2">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="0966932645-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% signature will be `number(Value)`</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0500916624-3">(</span><span class="p" data-group-id="0500916624-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0500916624-4">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0500916624-5">(</span><span class="p" data-group-id="0500916624-5">)</span><span class="p" data-group-id="0500916624-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0966932645-3">(</span><span class="p" data-group-id="0966932645-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0966932645-4">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0966932645-5">(</span><span class="p" data-group-id="0966932645-5">)</span><span class="p" data-group-id="0966932645-4">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% signature will be `number()`</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="0500916624-6">(</span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0500916624-7">(</span><span class="p" data-group-id="0500916624-7">)</span><span class="p" data-group-id="0500916624-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="0966932645-6">(</span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0966932645-7">(</span><span class="p" data-group-id="0966932645-7">)</span><span class="p" data-group-id="0966932645-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% signature will be `increment(In)`</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="0500916624-8">(</span><span class="n">In</span><span class="p" data-group-id="0500916624-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0500916624-9">(</span><span class="p" data-group-id="0500916624-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="0966932645-8">(</span><span class="n">In</span><span class="p" data-group-id="0966932645-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0966932645-9">(</span><span class="p" data-group-id="0966932645-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% signature will be `increment(In)`</span></code></pre><p>If it is not possible to &quot;easily&quot; figure out a nice signature from the code, the
│ │ │  MFA syntax is used instead. For example: <code class="inline">add/2</code>, <code class="inline">number/1</code>, <code class="inline">increment/1</code></p><p>It is possible to supply a custom signature by placing it as the first line of the
│ │ │  <code class="inline">-doc</code> attribute. The provided signature must be in the form of a function
│ │ │  declaration up until the <code class="inline">-&gt;</code>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │  add(One, Two)
│ │ │  
│ │ │  Adds two numbers.
│ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="3316029094-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="3316029094-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">.</span></code></pre><p>Will create the signature <code class="inline">add(One, Two)</code>. The signature will be removed from the
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="4187887081-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4187887081-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">.</span></code></pre><p>Will create the signature <code class="inline">add(One, Two)</code>. The signature will be removed from the
│ │ │  documentation string, so in the example above only the text <code class="inline">&quot;Adds two numbers&quot;</code>
│ │ │  will be part of the documentation. This works for functions, types, and
│ │ │  callbacks.</p><h2 id="links-in-markdown" class="section-heading">
│ │ │    <a href="#links-in-markdown" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Links in Markdown</span>
│ │ │ @@ -328,28 +328,28 @@
│ │ │  modules. That is, modules that should be used by other applications and modules
│ │ │  that should not. By default all modules in an application are visible, but by
│ │ │  setting <code class="inline">-moduledoc false.</code> specific modules can be hidden from being listed as
│ │ │  part of the available API.</p><p>An Erlang <a href="modules.html">module</a> consists of public and private functions and type
│ │ │  attributes. By default, all exported functions, exported types and callbacks are
│ │ │  considered visible and part of the modules public API. In addition, any
│ │ │  non-exported type that is referred to by any other visible type attribute is
│ │ │ -also visible, but not considered to be part of the public API. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6069701509-1">(</span><span class="p" data-group-id="6069701509-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6069701509-2">]</span><span class="p" data-group-id="6069701509-1">)</span><span class="p">.</span><span class="w">
│ │ │ +also visible, but not considered to be part of the public API. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1422210363-1">(</span><span class="p" data-group-id="1422210363-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1422210363-2">]</span><span class="p" data-group-id="1422210363-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="6069701509-3">(</span><span class="p" data-group-id="6069701509-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="6069701509-4">(</span><span class="p" data-group-id="6069701509-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="6069701509-5">(</span><span class="p" data-group-id="6069701509-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="6069701509-6">(</span><span class="p" data-group-id="6069701509-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>in the above code, the function <code class="inline">example/0</code> is exported and it referenced the
│ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="1422210363-3">(</span><span class="p" data-group-id="1422210363-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="1422210363-4">(</span><span class="p" data-group-id="1422210363-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="1422210363-5">(</span><span class="p" data-group-id="1422210363-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="1422210363-6">(</span><span class="p" data-group-id="1422210363-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>in the above code, the function <code class="inline">example/0</code> is exported and it referenced the
│ │ │  un-exported type <code class="inline">private/0</code>. Therefore both <code class="inline">example/0</code> and <code class="inline">private/0</code> will be
│ │ │  marked as visible. The <code class="inline">private/0</code> type will have the metadata field <code class="inline">exported</code>
│ │ │  set to <code class="inline">false</code> to show that it is not part of the public API.</p><p>If you want to make a visible entity hidden you need to set the <code class="inline">-doc</code> attribute
│ │ │ -to <code class="inline">false</code>. Let us revisit our previous example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3444171951-1">(</span><span class="p" data-group-id="3444171951-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3444171951-2">]</span><span class="p" data-group-id="3444171951-1">)</span><span class="p">.</span><span class="w">
│ │ │ +to <code class="inline">false</code>. Let us revisit our previous example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4173058050-1">(</span><span class="p" data-group-id="4173058050-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4173058050-2">]</span><span class="p" data-group-id="4173058050-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="3444171951-3">(</span><span class="p" data-group-id="3444171951-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="3444171951-4">(</span><span class="p" data-group-id="3444171951-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="3444171951-5">(</span><span class="p" data-group-id="3444171951-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="4173058050-3">(</span><span class="p" data-group-id="4173058050-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="4173058050-4">(</span><span class="p" data-group-id="4173058050-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="4173058050-5">(</span><span class="p" data-group-id="4173058050-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="ss">false</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="3444171951-6">(</span><span class="p" data-group-id="3444171951-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>The function <code class="inline">example/0</code> is exported but explicitly marked as hidden; therefore
│ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="4173058050-6">(</span><span class="p" data-group-id="4173058050-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>The function <code class="inline">example/0</code> is exported but explicitly marked as hidden; therefore
│ │ │  both <code class="inline">example/0</code> and <code class="inline">private/0</code> will be hidden.</p><p>Any documentation added to an automatically hidden entity (non-exported function
│ │ │  or type) is ignored and will generate a warning. Such functions can be
│ │ │  documented using comments.</p><h2 id="compiling-and-getting-documentation" class="section-heading">
│ │ │    <a href="#compiling-and-getting-documentation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Compiling and getting documentation</span>
│ │ │ @@ -375,21 +375,21 @@
│ │ │    <span class="text">Using ExDoc to generate HTML/ePub documentation</span>
│ │ │  </h2>
│ │ │  <p><a href="https://hexdocs.pm/ex_doc/">ExDoc</a> has built-in support to generate
│ │ │  documentation from Markdown. The simplest way is by using the
│ │ │  <a href="https://hexdocs.pm/rebar3_ex_doc">rebar3_ex_doc</a> plugin. To set up a
│ │ │  rebar3 project to use <a href="https://hexdocs.pm/ex_doc/">ExDoc</a> to generate
│ │ │  documentation add the following to your <code class="inline">rebar3.config</code>.</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Enable the plugin</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9311122770-1">{</span><span class="ss">plugins</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9311122770-2">[</span><span class="ss">rebar3_ex_doc</span><span class="p" data-group-id="9311122770-2">]</span><span class="p" data-group-id="9311122770-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8184259856-1">{</span><span class="ss">plugins</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8184259856-2">[</span><span class="ss">rebar3_ex_doc</span><span class="p" data-group-id="8184259856-2">]</span><span class="p" data-group-id="8184259856-1">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="9311122770-3">{</span><span class="ss">ex_doc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9311122770-4">[</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9311122770-5">{</span><span class="ss">extras</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9311122770-6">[</span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="9311122770-6">]</span><span class="p" data-group-id="9311122770-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9311122770-7">{</span><span class="ss">main</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="9311122770-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9311122770-8">{</span><span class="ss">source_url</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;https://github.com/namespace/your_app&quot;</span><span class="p" data-group-id="9311122770-8">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9311122770-4">]</span><span class="p" data-group-id="9311122770-3">}</span><span class="p">.</span></code></pre><p>When configured you can run <code class="inline">rebar3 ex_doc</code> to generate the
│ │ │ +</span><span class="p" data-group-id="8184259856-3">{</span><span class="ss">ex_doc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8184259856-4">[</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8184259856-5">{</span><span class="ss">extras</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8184259856-6">[</span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="8184259856-6">]</span><span class="p" data-group-id="8184259856-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8184259856-7">{</span><span class="ss">main</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="8184259856-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8184259856-8">{</span><span class="ss">source_url</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;https://github.com/namespace/your_app&quot;</span><span class="p" data-group-id="8184259856-8">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8184259856-4">]</span><span class="p" data-group-id="8184259856-3">}</span><span class="p">.</span></code></pre><p>When configured you can run <code class="inline">rebar3 ex_doc</code> to generate the
│ │ │  documentation to <code class="inline">doc/index.html</code>. For more details and options see
│ │ │  the <a href="https://hexdocs.pm/rebar3_ex_doc">rebar3_ex_doc</a> documentation.</p><p>You can also download the
│ │ │  <a href="https://github.com/elixir/ex_doc/releases/latest">release escript bundle</a> from
│ │ │  github and run it from the command line. The documentation for using the escript
│ │ │  is found by running <code class="inline">ex_doc --help</code>.</p><p>If you are writing documentation that will be using
│ │ │  <a href="https://hexdocs.pm/ex_doc/">ExDoc</a> to generate HTML/ePub it is highly
│ │ │  recommended to read its documentation.</p>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/drivers.html
│ │ │ @@ -122,23 +122,23 @@
│ │ │    <span class="text">Drivers and Concurrency</span>
│ │ │  </h2>
│ │ │  <p>The runtime system always takes a lock before running any code in a driver.</p><p>By default, that lock is at the driver level, that is, if several ports have
│ │ │  been opened to the same driver, only code for one port at the same time can be
│ │ │  running.</p><p>A driver can be configured to have one lock for each port instead.</p><p>If a driver is used in a functional way (that is, holds no state, but only does
│ │ │  some heavy calculation and returns a result), several ports with registered
│ │ │  names can be opened beforehand, and the port to be used can be chosen based on
│ │ │ -the scheduler ID as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8915748204-1">(</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="8915748204-2">(</span><span class="p" data-group-id="8915748204-2">)</span><span class="p">,</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="8915748204-3">{</span><span class="ss">some_driver_01</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_02</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_03</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_04</span><span class="p">,</span><span class="w">
│ │ │ +the scheduler ID as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4258524538-1">(</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="4258524538-2">(</span><span class="p" data-group-id="4258524538-2">)</span><span class="p">,</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="4258524538-3">{</span><span class="ss">some_driver_01</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_02</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_03</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_04</span><span class="p">,</span><span class="w">
│ │ │  	 </span><span class="ss">some_driver_05</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_06</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_07</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_08</span><span class="p">,</span><span class="w">
│ │ │  	 </span><span class="ss">some_driver_09</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_10</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_11</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_12</span><span class="p">,</span><span class="w">
│ │ │ -	 </span><span class="ss">some_driver_13</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_14</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_15</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_16</span><span class="p" data-group-id="8915748204-3">}</span><span class="p" data-group-id="8915748204-1">)</span><span class="p">.</span><span class="w">
│ │ │ +	 </span><span class="ss">some_driver_13</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_14</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_15</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_16</span><span class="p" data-group-id="4258524538-3">}</span><span class="p" data-group-id="4258524538-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client_port</span><span class="p" data-group-id="8915748204-4">(</span><span class="p" data-group-id="8915748204-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">element</span><span class="p" data-group-id="8915748204-5">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="8915748204-6">(</span><span class="ss">scheduler_id</span><span class="p" data-group-id="8915748204-6">)</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="8915748204-7">(</span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="8915748204-8">(</span><span class="p" data-group-id="8915748204-8">)</span><span class="p" data-group-id="8915748204-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="8915748204-9">(</span><span class="p" data-group-id="8915748204-9">)</span><span class="p" data-group-id="8915748204-5">)</span><span class="p">.</span></code></pre><p>As long as there are no more than 16 schedulers, there will never be any lock
│ │ │ +</span><span class="nf">client_port</span><span class="p" data-group-id="4258524538-4">(</span><span class="p" data-group-id="4258524538-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">element</span><span class="p" data-group-id="4258524538-5">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="4258524538-6">(</span><span class="ss">scheduler_id</span><span class="p" data-group-id="4258524538-6">)</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="4258524538-7">(</span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="4258524538-8">(</span><span class="p" data-group-id="4258524538-8">)</span><span class="p" data-group-id="4258524538-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="4258524538-9">(</span><span class="p" data-group-id="4258524538-9">)</span><span class="p" data-group-id="4258524538-5">)</span><span class="p">.</span></code></pre><p>As long as there are no more than 16 schedulers, there will never be any lock
│ │ │  contention on the port lock for the driver.</p><h2 id="avoiding-copying-binaries-when-calling-a-driver" class="section-heading">
│ │ │    <a href="#avoiding-copying-binaries-when-calling-a-driver" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Avoiding Copying Binaries When Calling a Driver</span>
│ │ │  </h2>
│ │ │  <p>There are basically two ways to avoid copying a binary that is sent to a driver:</p><ul><li><p>If the <code class="inline">Data</code> argument for <a href="../../erts-15.2.7/doc/html/erlang.html#port_control/3"><code class="inline">port_control/3</code></a> is a
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/eff_guide_functions.html
│ │ │ @@ -122,67 +122,67 @@
│ │ │    <span class="text">Pattern Matching</span>
│ │ │  </h2>
│ │ │  <p>Pattern matching in function head as well as in <code class="inline">case</code> and <code class="inline">receive</code> clauses are
│ │ │  optimized by the compiler. With a few exceptions, there is nothing to gain by
│ │ │  rearranging clauses.</p><p>One exception is pattern matching of binaries. The compiler does not rearrange
│ │ │  clauses that match binaries. Placing the clause that matches against the empty
│ │ │  binary <em>last</em> is usually slightly faster than placing it <em>first</em>.</p><p>The following is a rather unnatural example to show another exception where
│ │ │ -rearranging clauses is beneficial:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map1</span><span class="p" data-group-id="8994422813-1">(</span><span class="ss">one</span><span class="p" data-group-id="8994422813-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="8994422813-2">(</span><span class="ss">two</span><span class="p" data-group-id="8994422813-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="8994422813-3">(</span><span class="ss">three</span><span class="p" data-group-id="8994422813-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="8994422813-4">(</span><span class="n">Int</span><span class="p" data-group-id="8994422813-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="8994422813-5">(</span><span class="n">Int</span><span class="p" data-group-id="8994422813-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="8994422813-6">(</span><span class="ss">four</span><span class="p" data-group-id="8994422813-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="8994422813-7">(</span><span class="ss">five</span><span class="p" data-group-id="8994422813-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="8994422813-8">(</span><span class="ss">six</span><span class="p" data-group-id="8994422813-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>The problem is the clause with the variable <code class="inline">Int</code>. As a variable can match
│ │ │ +rearranging clauses is beneficial:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map1</span><span class="p" data-group-id="7268968366-1">(</span><span class="ss">one</span><span class="p" data-group-id="7268968366-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="7268968366-2">(</span><span class="ss">two</span><span class="p" data-group-id="7268968366-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="7268968366-3">(</span><span class="ss">three</span><span class="p" data-group-id="7268968366-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="7268968366-4">(</span><span class="n">Int</span><span class="p" data-group-id="7268968366-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="7268968366-5">(</span><span class="n">Int</span><span class="p" data-group-id="7268968366-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="7268968366-6">(</span><span class="ss">four</span><span class="p" data-group-id="7268968366-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="7268968366-7">(</span><span class="ss">five</span><span class="p" data-group-id="7268968366-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="7268968366-8">(</span><span class="ss">six</span><span class="p" data-group-id="7268968366-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>The problem is the clause with the variable <code class="inline">Int</code>. As a variable can match
│ │ │  anything, including the atoms <code class="inline">four</code>, <code class="inline">five</code>, and <code class="inline">six</code>, which the following
│ │ │  clauses also match, the compiler must generate suboptimal code that executes as
│ │ │  follows:</p><ul><li>First, the input value is compared to <code class="inline">one</code>, <code class="inline">two</code>, and <code class="inline">three</code> (using a
│ │ │  single instruction that does a binary search; thus, quite efficient even if
│ │ │  there are many values) to select which one of the first three clauses to
│ │ │  execute (if any).</li><li>If none of the first three clauses match, the fourth clause match as a
│ │ │  variable always matches.</li><li>If the guard test <a href="../../erts-15.2.7/doc/html/erlang.html#is_integer/1"><code class="inline">is_integer(Int)</code></a> succeeds, the fourth
│ │ │  clause is executed.</li><li>If the guard test fails, the input value is compared to <code class="inline">four</code>, <code class="inline">five</code>, and
│ │ │  <code class="inline">six</code>, and the appropriate clause is selected. (There is a <code class="inline">function_clause</code>
│ │ │ -exception if none of the values matched.)</li></ul><p>Rewriting to either:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map2</span><span class="p" data-group-id="1649779104-1">(</span><span class="ss">one</span><span class="p" data-group-id="1649779104-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="1649779104-2">(</span><span class="ss">two</span><span class="p" data-group-id="1649779104-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="1649779104-3">(</span><span class="ss">three</span><span class="p" data-group-id="1649779104-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="1649779104-4">(</span><span class="ss">four</span><span class="p" data-group-id="1649779104-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="1649779104-5">(</span><span class="ss">five</span><span class="p" data-group-id="1649779104-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="1649779104-6">(</span><span class="ss">six</span><span class="p" data-group-id="1649779104-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="1649779104-7">(</span><span class="n">Int</span><span class="p" data-group-id="1649779104-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="1649779104-8">(</span><span class="n">Int</span><span class="p" data-group-id="1649779104-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>or:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map3</span><span class="p" data-group-id="0827131561-1">(</span><span class="n">Int</span><span class="p" data-group-id="0827131561-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="0827131561-2">(</span><span class="n">Int</span><span class="p" data-group-id="0827131561-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="0827131561-3">(</span><span class="ss">one</span><span class="p" data-group-id="0827131561-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="0827131561-4">(</span><span class="ss">two</span><span class="p" data-group-id="0827131561-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="0827131561-5">(</span><span class="ss">three</span><span class="p" data-group-id="0827131561-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="0827131561-6">(</span><span class="ss">four</span><span class="p" data-group-id="0827131561-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="0827131561-7">(</span><span class="ss">five</span><span class="p" data-group-id="0827131561-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="0827131561-8">(</span><span class="ss">six</span><span class="p" data-group-id="0827131561-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>gives slightly more efficient matching code.</p><p>Another example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs1</span><span class="p" data-group-id="2834125952-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2834125952-2">[</span><span class="p" data-group-id="2834125952-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="2834125952-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +exception if none of the values matched.)</li></ul><p>Rewriting to either:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map2</span><span class="p" data-group-id="7573583234-1">(</span><span class="ss">one</span><span class="p" data-group-id="7573583234-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="7573583234-2">(</span><span class="ss">two</span><span class="p" data-group-id="7573583234-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="7573583234-3">(</span><span class="ss">three</span><span class="p" data-group-id="7573583234-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="7573583234-4">(</span><span class="ss">four</span><span class="p" data-group-id="7573583234-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="7573583234-5">(</span><span class="ss">five</span><span class="p" data-group-id="7573583234-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="7573583234-6">(</span><span class="ss">six</span><span class="p" data-group-id="7573583234-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="7573583234-7">(</span><span class="n">Int</span><span class="p" data-group-id="7573583234-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="7573583234-8">(</span><span class="n">Int</span><span class="p" data-group-id="7573583234-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>or:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map3</span><span class="p" data-group-id="9211860677-1">(</span><span class="n">Int</span><span class="p" data-group-id="9211860677-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="9211860677-2">(</span><span class="n">Int</span><span class="p" data-group-id="9211860677-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9211860677-3">(</span><span class="ss">one</span><span class="p" data-group-id="9211860677-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9211860677-4">(</span><span class="ss">two</span><span class="p" data-group-id="9211860677-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9211860677-5">(</span><span class="ss">three</span><span class="p" data-group-id="9211860677-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9211860677-6">(</span><span class="ss">four</span><span class="p" data-group-id="9211860677-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9211860677-7">(</span><span class="ss">five</span><span class="p" data-group-id="9211860677-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9211860677-8">(</span><span class="ss">six</span><span class="p" data-group-id="9211860677-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>gives slightly more efficient matching code.</p><p>Another example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs1</span><span class="p" data-group-id="8751305086-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8751305086-2">[</span><span class="p" data-group-id="8751305086-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="8751305086-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Ys</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map_pairs1</span><span class="p" data-group-id="2834125952-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2834125952-4">[</span><span class="p" data-group-id="2834125952-4">]</span><span class="p" data-group-id="2834125952-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">map_pairs1</span><span class="p" data-group-id="8751305086-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8751305086-4">[</span><span class="p" data-group-id="8751305086-4">]</span><span class="p" data-group-id="8751305086-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Xs</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map_pairs1</span><span class="p" data-group-id="2834125952-5">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2834125952-6">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="2834125952-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2834125952-7">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="2834125952-7">]</span><span class="p" data-group-id="2834125952-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2834125952-8">[</span><span class="n">Map</span><span class="p" data-group-id="2834125952-9">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2834125952-9">)</span><span class="p">|</span><span class="nf">map_pairs1</span><span class="p" data-group-id="2834125952-10">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="2834125952-10">)</span><span class="p" data-group-id="2834125952-8">]</span><span class="p">.</span></code></pre><p>The first argument is <em>not</em> a problem. It is variable, but it is a variable in
│ │ │ +</span><span class="nf">map_pairs1</span><span class="p" data-group-id="8751305086-5">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8751305086-6">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="8751305086-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8751305086-7">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="8751305086-7">]</span><span class="p" data-group-id="8751305086-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8751305086-8">[</span><span class="n">Map</span><span class="p" data-group-id="8751305086-9">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8751305086-9">)</span><span class="p">|</span><span class="nf">map_pairs1</span><span class="p" data-group-id="8751305086-10">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="8751305086-10">)</span><span class="p" data-group-id="8751305086-8">]</span><span class="p">.</span></code></pre><p>The first argument is <em>not</em> a problem. It is variable, but it is a variable in
│ │ │  all clauses. The problem is the variable in the second argument, <code class="inline">Xs</code>, in the
│ │ │  middle clause. Because the variable can match anything, the compiler is not
│ │ │  allowed to rearrange the clauses, but must generate code that matches them in
│ │ │  the order written.</p><p>If the function is rewritten as follows, the compiler is free to rearrange the
│ │ │ -clauses:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs2</span><span class="p" data-group-id="8855898590-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8855898590-2">[</span><span class="p" data-group-id="8855898590-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="8855898590-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +clauses:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs2</span><span class="p" data-group-id="5659588082-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5659588082-2">[</span><span class="p" data-group-id="5659588082-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="5659588082-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Ys</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map_pairs2</span><span class="p" data-group-id="8855898590-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8855898590-4">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="8855898590-4">]</span><span class="o">=</span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8855898590-5">[</span><span class="p" data-group-id="8855898590-5">]</span><span class="w"> </span><span class="p" data-group-id="8855898590-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">map_pairs2</span><span class="p" data-group-id="5659588082-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5659588082-4">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="5659588082-4">]</span><span class="o">=</span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5659588082-5">[</span><span class="p" data-group-id="5659588082-5">]</span><span class="w"> </span><span class="p" data-group-id="5659588082-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Xs</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map_pairs2</span><span class="p" data-group-id="8855898590-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8855898590-7">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="8855898590-7">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8855898590-8">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="8855898590-8">]</span><span class="p" data-group-id="8855898590-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8855898590-9">[</span><span class="n">Map</span><span class="p" data-group-id="8855898590-10">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8855898590-10">)</span><span class="p">|</span><span class="nf">map_pairs2</span><span class="p" data-group-id="8855898590-11">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="8855898590-11">)</span><span class="p" data-group-id="8855898590-9">]</span><span class="p">.</span></code></pre><p>The compiler will generate code similar to this:</p><p><strong>DO NOT (already done by the compiler)</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="3573805374-1">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs0</span><span class="p">,</span><span class="w"> </span><span class="n">Ys0</span><span class="p" data-group-id="3573805374-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">map_pairs2</span><span class="p" data-group-id="5659588082-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5659588082-7">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="5659588082-7">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5659588082-8">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="5659588082-8">]</span><span class="p" data-group-id="5659588082-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5659588082-9">[</span><span class="n">Map</span><span class="p" data-group-id="5659588082-10">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5659588082-10">)</span><span class="p">|</span><span class="nf">map_pairs2</span><span class="p" data-group-id="5659588082-11">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="5659588082-11">)</span><span class="p" data-group-id="5659588082-9">]</span><span class="p">.</span></code></pre><p>The compiler will generate code similar to this:</p><p><strong>DO NOT (already done by the compiler)</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="8866445512-1">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs0</span><span class="p">,</span><span class="w"> </span><span class="n">Ys0</span><span class="p" data-group-id="8866445512-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Xs0</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="3573805374-2">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="3573805374-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="8866445512-2">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="8866445512-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="k">case</span><span class="w"> </span><span class="n">Ys0</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="3573805374-3">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="3573805374-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="p" data-group-id="3573805374-4">[</span><span class="n">Map</span><span class="p" data-group-id="3573805374-5">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3573805374-5">)</span><span class="p">|</span><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="3573805374-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="3573805374-6">)</span><span class="p" data-group-id="3573805374-4">]</span><span class="p">;</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="3573805374-7">[</span><span class="p" data-group-id="3573805374-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="8866445512-3">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="8866445512-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="p" data-group-id="8866445512-4">[</span><span class="n">Map</span><span class="p" data-group-id="8866445512-5">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8866445512-5">)</span><span class="p">|</span><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="8866445512-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="8866445512-6">)</span><span class="p" data-group-id="8866445512-4">]</span><span class="p">;</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="8866445512-7">[</span><span class="p" data-group-id="8866445512-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  		    </span><span class="n">Xs0</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="3573805374-8">[</span><span class="p" data-group-id="3573805374-8">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="8866445512-8">[</span><span class="p" data-group-id="8866445512-8">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">Ys0</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>This is slightly faster for probably the most common case that the input lists
│ │ │  are not empty or very short. (Another advantage is that Dialyzer can deduce a
│ │ │  better type for the <code class="inline">Xs</code> variable.)</p><h2 id="function-calls" class="section-heading">
│ │ │    <a href="#function-calls" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/eff_guide_processes.html
│ │ │ @@ -119,45 +119,45 @@
│ │ │    <a href="#creating-an-erlang-process" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating an Erlang Process</span>
│ │ │  </h2>
│ │ │  <p>An Erlang process is lightweight compared to threads and processes in operating
│ │ │  systems.</p><p>A newly spawned Erlang process uses 327 words of memory. The size can be found
│ │ │ -as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="8923045255-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p">.</span><span class="mi">3</span><span class="p" data-group-id="8923045255-1">]</span><span class="w"> </span><span class="p" data-group-id="8923045255-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="8923045255-2">]</span><span class="w"> </span><span class="p" data-group-id="8923045255-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="8923045255-3">]</span><span class="w"> </span><span class="p" data-group-id="8923045255-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="8923045255-4">]</span><span class="w"> </span><span class="p" data-group-id="8923045255-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8923045255-5">]</span><span class="w"> </span><span class="p" data-group-id="8923045255-6">[</span><span class="ss">jit</span><span class="p" data-group-id="8923045255-6">]</span><span class="w">
│ │ │ +as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="0993745296-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p">.</span><span class="mi">3</span><span class="p" data-group-id="0993745296-1">]</span><span class="w"> </span><span class="p" data-group-id="0993745296-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0993745296-2">]</span><span class="w"> </span><span class="p" data-group-id="0993745296-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0993745296-3">]</span><span class="w"> </span><span class="p" data-group-id="0993745296-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="0993745296-4">]</span><span class="w"> </span><span class="p" data-group-id="0993745296-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0993745296-5">]</span><span class="w"> </span><span class="p" data-group-id="0993745296-6">[</span><span class="ss">jit</span><span class="p" data-group-id="0993745296-6">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mf">2.3</span><span class="w"> </span><span class="p" data-group-id="8923045255-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="8923045255-8">(</span><span class="p" data-group-id="8923045255-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="8923045255-7">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="8923045255-9">(</span><span class="p" data-group-id="8923045255-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="ss">infinity</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mf">2.3</span><span class="w"> </span><span class="p" data-group-id="0993745296-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="0993745296-8">(</span><span class="p" data-group-id="0993745296-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="0993745296-7">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0993745296-9">(</span><span class="p" data-group-id="0993745296-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="ss">infinity</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">43.39164016</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="8923045255-10">{</span><span class="p">_</span><span class="p">,</span><span class="n">Bytes</span><span class="p" data-group-id="8923045255-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">process_info</span><span class="p" data-group-id="8923045255-11">(</span><span class="nf">spawn</span><span class="p" data-group-id="8923045255-12">(</span><span class="n">Fun</span><span class="p" data-group-id="8923045255-12">)</span><span class="p">,</span><span class="w"> </span><span class="nb">memory</span><span class="p" data-group-id="8923045255-11">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8923045255-13">{</span><span class="nb">memory</span><span class="p">,</span><span class="mi">2616</span><span class="p" data-group-id="8923045255-13">}</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="n">Bytes</span><span class="w"> </span><span class="ow">div</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="8923045255-14">(</span><span class="ss">wordsize</span><span class="p" data-group-id="8923045255-14">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="p" data-group-id="0993745296-10">{</span><span class="p">_</span><span class="p">,</span><span class="n">Bytes</span><span class="p" data-group-id="0993745296-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">process_info</span><span class="p" data-group-id="0993745296-11">(</span><span class="nf">spawn</span><span class="p" data-group-id="0993745296-12">(</span><span class="n">Fun</span><span class="p" data-group-id="0993745296-12">)</span><span class="p">,</span><span class="w"> </span><span class="nb">memory</span><span class="p" data-group-id="0993745296-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0993745296-13">{</span><span class="nb">memory</span><span class="p">,</span><span class="mi">2616</span><span class="p" data-group-id="0993745296-13">}</span><span class="gp unselectable">
│ │ │ +3&gt; </span><span class="n">Bytes</span><span class="w"> </span><span class="ow">div</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="0993745296-14">(</span><span class="ss">wordsize</span><span class="p" data-group-id="0993745296-14">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">327</span></code></pre><p>The size includes 233 words for the heap area (which includes the stack). The
│ │ │  garbage collector increases the heap as needed.</p><p>The main (outer) loop for a process <em>must</em> be tail-recursive. Otherwise, the
│ │ │ -stack grows until the process terminates.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="3299621687-1">(</span><span class="p" data-group-id="3299621687-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +stack grows until the process terminates.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="8791589426-1">(</span><span class="p" data-group-id="8791589426-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="3299621687-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3299621687-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="3299621687-3">(</span><span class="n">Msg</span><span class="p" data-group-id="3299621687-3">)</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="3299621687-4">(</span><span class="p" data-group-id="3299621687-4">)</span><span class="p">;</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="3299621687-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3299621687-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -          </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="3299621687-6">(</span><span class="n">Msg</span><span class="p" data-group-id="3299621687-6">)</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="8791589426-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8791589426-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="8791589426-3">(</span><span class="n">Msg</span><span class="p" data-group-id="8791589426-3">)</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="8791589426-4">(</span><span class="p" data-group-id="8791589426-4">)</span><span class="p">;</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="8791589426-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8791589426-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +          </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8791589426-6">(</span><span class="n">Msg</span><span class="p" data-group-id="8791589426-6">)</span><span class="p">,</span><span class="w">
│ │ │            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Reply</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="nf">loop</span><span class="p" data-group-id="3299621687-7">(</span><span class="p" data-group-id="3299621687-7">)</span><span class="w">
│ │ │ +          </span><span class="nf">loop</span><span class="p" data-group-id="8791589426-7">(</span><span class="p" data-group-id="8791589426-7">)</span><span class="w">
│ │ │    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3299621687-8">(</span><span class="s">&quot;Message is processed</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3299621687-9">[</span><span class="p" data-group-id="3299621687-9">]</span><span class="p" data-group-id="3299621687-8">)</span><span class="p">.</span></code></pre><p>The call to <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> will never be executed, but a return address will
│ │ │ +  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8791589426-8">(</span><span class="s">&quot;Message is processed</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8791589426-9">[</span><span class="p" data-group-id="8791589426-9">]</span><span class="p" data-group-id="8791589426-8">)</span><span class="p">.</span></code></pre><p>The call to <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> will never be executed, but a return address will
│ │ │  still be pushed to the stack each time <code class="inline">loop/0</code> is called recursively. The
│ │ │ -correct tail-recursive version of the function looks as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="4593709926-1">(</span><span class="p" data-group-id="4593709926-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +correct tail-recursive version of the function looks as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="4410292953-1">(</span><span class="p" data-group-id="4410292953-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │     </span><span class="k">receive</span><span class="w">
│ │ │ -      </span><span class="p" data-group-id="4593709926-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4593709926-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="4593709926-3">(</span><span class="n">Msg</span><span class="p" data-group-id="4593709926-3">)</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="4593709926-4">(</span><span class="p" data-group-id="4593709926-4">)</span><span class="p">;</span><span class="w">
│ │ │ -      </span><span class="p" data-group-id="4593709926-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4593709926-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -         </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="4593709926-6">(</span><span class="n">Msg</span><span class="p" data-group-id="4593709926-6">)</span><span class="p">,</span><span class="w">
│ │ │ +      </span><span class="p" data-group-id="4410292953-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4410292953-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="4410292953-3">(</span><span class="n">Msg</span><span class="p" data-group-id="4410292953-3">)</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="4410292953-4">(</span><span class="p" data-group-id="4410292953-4">)</span><span class="p">;</span><span class="w">
│ │ │ +      </span><span class="p" data-group-id="4410292953-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4410292953-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +         </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="4410292953-6">(</span><span class="n">Msg</span><span class="p" data-group-id="4410292953-6">)</span><span class="p">,</span><span class="w">
│ │ │           </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Reply</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="4593709926-7">(</span><span class="p" data-group-id="4593709926-7">)</span><span class="w">
│ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="4410292953-7">(</span><span class="p" data-group-id="4410292953-7">)</span><span class="w">
│ │ │   </span><span class="k">end</span><span class="p">.</span></code></pre><h3 id="initial-heap-size" class="section-heading">
│ │ │    <a href="#initial-heap-size" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Initial Heap Size</span>
│ │ │  </h3>
│ │ │  <p>The default initial heap size of 233 words is quite conservative to support
│ │ │ @@ -189,30 +189,30 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Receiving messages</span>
│ │ │  </h2>
│ │ │  <p>The cost of receiving messages depends on how complicated the <code class="inline">receive</code>
│ │ │  expression is. A simple expression that matches any message is very cheap
│ │ │  because it retrieves the first message in the message queue:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="7794603838-1">(</span><span class="n">Message</span><span class="p" data-group-id="7794603838-1">)</span><span class="w">
│ │ │ +    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="9608244227-1">(</span><span class="n">Message</span><span class="p" data-group-id="9608244227-1">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>However, this is not always convenient: we can receive a message that we do not
│ │ │  know how to handle at this point, so it is common to only match the messages we
│ │ │  expect:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2286988083-1">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2286988083-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="2286988083-2">(</span><span class="n">Message</span><span class="p" data-group-id="2286988083-2">)</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7726166931-1">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7726166931-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="7726166931-2">(</span><span class="n">Message</span><span class="p" data-group-id="7726166931-2">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>While this is convenient it means that the entire message queue must be searched
│ │ │  until it finds a matching message. This is very expensive for processes with
│ │ │  long message queues, so there is an optimization for the common case of
│ │ │ -sending a request and waiting for a response shortly after:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="0543706319-1">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="0543706319-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0543706319-2">{</span><span class="nf">self</span><span class="p" data-group-id="0543706319-3">(</span><span class="p" data-group-id="0543706319-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0543706319-2">}</span><span class="p">,</span><span class="w">
│ │ │ +sending a request and waiting for a response shortly after:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="8329551703-1">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="8329551703-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8329551703-2">{</span><span class="nf">self</span><span class="p" data-group-id="8329551703-3">(</span><span class="p" data-group-id="8329551703-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="8329551703-2">}</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0543706319-4">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="0543706319-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="0543706319-5">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0543706319-6">[</span><span class="ss">flush</span><span class="p" data-group-id="0543706319-6">]</span><span class="p" data-group-id="0543706319-5">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="nf">handle_reply</span><span class="p" data-group-id="0543706319-7">(</span><span class="n">Reply</span><span class="p" data-group-id="0543706319-7">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0543706319-8">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="0543706319-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nf">handle_error</span><span class="p" data-group-id="0543706319-9">(</span><span class="n">Reason</span><span class="p" data-group-id="0543706319-9">)</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8329551703-4">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="8329551703-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="8329551703-5">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8329551703-6">[</span><span class="ss">flush</span><span class="p" data-group-id="8329551703-6">]</span><span class="p" data-group-id="8329551703-5">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="nf">handle_reply</span><span class="p" data-group-id="8329551703-7">(</span><span class="n">Reply</span><span class="p" data-group-id="8329551703-7">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8329551703-8">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="8329551703-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nf">handle_error</span><span class="p" data-group-id="8329551703-9">(</span><span class="n">Reason</span><span class="p" data-group-id="8329551703-9">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>Since the compiler knows that the reference created by
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#monitor/2"><code class="inline">monitor/2</code></a> cannot exist before the call (since it is a globally
│ │ │  unique identifier), and that the <code class="inline">receive</code> only matches messages that contain
│ │ │  said reference, it will tell the emulator to search only the messages that
│ │ │  arrived after the call to <a href="../../erts-15.2.7/doc/html/erlang.html#monitor/2"><code class="inline">monitor/2</code></a>.</p><p>The above is a simple example where one is but guaranteed that the optimization
│ │ │  will take, but what about more complicated code?</p><p><a href="" id="recv_opt_info"></a></p><h3 id="option-recv_opt_info" class="section-heading">
│ │ │    <a href="#option-recv_opt_info" class="hover-link">
│ │ │ @@ -228,101 +228,101 @@
│ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">200</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">NOT</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">do</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">suitable</span><span class="w"> </span><span class="ss">reference</span><span class="w">
│ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">206</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">used</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">mark</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">message</span><span class="w"> </span><span class="ss">queue</span><span class="w"> </span><span class="ss">position</span><span class="w">
│ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">208</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">created</span><span class="w"> </span><span class="ss">by</span><span class="w"> </span><span class="nb">monitor</span><span class="p">/</span><span class="mi">2</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">206</span><span class="w">
│ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">219</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">INFO</span><span class="p">:</span><span class="w"> </span><span class="ss">passing</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">created</span><span class="w"> </span><span class="ss">by</span><span class="w"> </span><span class="ss">make_ref</span><span class="p">/</span><span class="mi">0</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">218</span><span class="w">
│ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">222</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">function</span><span class="w"> </span><span class="ss">parameter</span><span class="w"> </span><span class="mi">1</span></code></pre><p>To make it clearer exactly what code the warnings refer to, the warnings in the
│ │ │  following examples are inserted as comments after the clause they refer to, for
│ │ │  example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% DO</span><span class="w">
│ │ │ -</span><span class="nf">simple_receive</span><span class="p" data-group-id="0291033812-1">(</span><span class="p" data-group-id="0291033812-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">simple_receive</span><span class="p" data-group-id="7646555847-1">(</span><span class="p" data-group-id="7646555847-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="c1">%% efficiency_guide.erl:194: Warning: INFO: not a selective receive, this is always fast</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="0291033812-2">(</span><span class="n">Message</span><span class="p" data-group-id="0291033812-2">)</span><span class="w">
│ │ │ +    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="7646555847-2">(</span><span class="n">Message</span><span class="p" data-group-id="7646555847-2">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% DO NOT, unless Tag is known to be a suitable reference: see</span><span class="w">
│ │ │  </span><span class="c1">%% cross_function_receive/0 further down.</span><span class="w">
│ │ │ -</span><span class="nf">selective_receive</span><span class="p" data-group-id="0291033812-3">(</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0291033812-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">selective_receive</span><span class="p" data-group-id="7646555847-3">(</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7646555847-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="c1">%% efficiency_guide.erl:200: Warning: NOT OPTIMIZED: all clauses do not match a suitable reference</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0291033812-4">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0291033812-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="0291033812-5">(</span><span class="n">Message</span><span class="p" data-group-id="0291033812-5">)</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7646555847-4">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7646555847-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="7646555847-5">(</span><span class="n">Message</span><span class="p" data-group-id="7646555847-5">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% DO</span><span class="w">
│ │ │ -</span><span class="nf">optimized_receive</span><span class="p" data-group-id="0291033812-6">(</span><span class="n">Process</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0291033812-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">optimized_receive</span><span class="p" data-group-id="7646555847-6">(</span><span class="n">Process</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="7646555847-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="c1">%% efficiency_guide.erl:206: Warning: OPTIMIZED: reference used to mark a message queue position</span><span class="w">
│ │ │ -    </span><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="0291033812-7">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="0291033812-7">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0291033812-8">{</span><span class="nf">self</span><span class="p" data-group-id="0291033812-9">(</span><span class="p" data-group-id="0291033812-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0291033812-8">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="7646555847-7">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="7646555847-7">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7646555847-8">{</span><span class="nf">self</span><span class="p" data-group-id="7646555847-9">(</span><span class="p" data-group-id="7646555847-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="7646555847-8">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%% efficiency_guide.erl:208: Warning: OPTIMIZED: matches reference created by monitor/2 at efficiency_guide.erl:206</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0291033812-10">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="0291033812-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="0291033812-11">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0291033812-12">[</span><span class="ss">flush</span><span class="p" data-group-id="0291033812-12">]</span><span class="p" data-group-id="0291033812-11">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="nf">handle_reply</span><span class="p" data-group-id="0291033812-13">(</span><span class="n">Reply</span><span class="p" data-group-id="0291033812-13">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0291033812-14">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="0291033812-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">handle_error</span><span class="p" data-group-id="0291033812-15">(</span><span class="n">Reason</span><span class="p" data-group-id="0291033812-15">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7646555847-10">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="7646555847-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="7646555847-11">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7646555847-12">[</span><span class="ss">flush</span><span class="p" data-group-id="7646555847-12">]</span><span class="p" data-group-id="7646555847-11">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="nf">handle_reply</span><span class="p" data-group-id="7646555847-13">(</span><span class="n">Reply</span><span class="p" data-group-id="7646555847-13">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7646555847-14">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="7646555847-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">handle_error</span><span class="p" data-group-id="7646555847-15">(</span><span class="n">Reason</span><span class="p" data-group-id="7646555847-15">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% DO</span><span class="w">
│ │ │ -</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="0291033812-16">(</span><span class="p" data-group-id="0291033812-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="7646555847-16">(</span><span class="p" data-group-id="7646555847-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% efficiency_guide.erl:218: Warning: OPTIMIZED: reference used to mark a message queue position</span><span class="w">
│ │ │ -    </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="0291033812-17">(</span><span class="p" data-group-id="0291033812-17">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="7646555847-17">(</span><span class="p" data-group-id="7646555847-17">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%% efficiency_guide.erl:219: Warning: INFO: passing reference created by make_ref/0 at efficiency_guide.erl:218</span><span class="w">
│ │ │ -    </span><span class="nf">cross_function_receive</span><span class="p" data-group-id="0291033812-18">(</span><span class="n">Ref</span><span class="p" data-group-id="0291033812-18">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">cross_function_receive</span><span class="p" data-group-id="7646555847-18">(</span><span class="n">Ref</span><span class="p" data-group-id="7646555847-18">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="0291033812-19">(</span><span class="n">Ref</span><span class="p" data-group-id="0291033812-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="7646555847-19">(</span><span class="n">Ref</span><span class="p" data-group-id="7646555847-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% efficiency_guide.erl:222: Warning: OPTIMIZED: all clauses match reference in function parameter 1</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0291033812-20">{</span><span class="n">Ref</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0291033812-20">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="0291033812-21">(</span><span class="n">Message</span><span class="p" data-group-id="0291033812-21">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7646555847-20">{</span><span class="n">Ref</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7646555847-20">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="7646555847-21">(</span><span class="n">Message</span><span class="p" data-group-id="7646555847-21">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="literal-pool" class="section-heading">
│ │ │    <a href="#literal-pool" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Literal Pool</span>
│ │ │  </h2>
│ │ │  <p>Constant Erlang terms (hereafter called <em>literals</em>) are kept in <em>literal pools</em>;
│ │ │  each loaded module has its own pool. The following function does not build the
│ │ │  tuple every time it is called (only to have it discarded the next time the
│ │ │  garbage collector was run), but the tuple is located in the module's literal
│ │ │ -pool:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">days_in_month</span><span class="p" data-group-id="8956664969-1">(</span><span class="n">M</span><span class="p" data-group-id="8956664969-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">element</span><span class="p" data-group-id="8956664969-2">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8956664969-3">{</span><span class="mi">31</span><span class="p">,</span><span class="mi">28</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p" data-group-id="8956664969-3">}</span><span class="p" data-group-id="8956664969-2">)</span><span class="p">.</span></code></pre><p>If a literal, or a term that contains a literal, is inserted into an Ets table,
│ │ │ +pool:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">days_in_month</span><span class="p" data-group-id="3648965530-1">(</span><span class="n">M</span><span class="p" data-group-id="3648965530-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">element</span><span class="p" data-group-id="3648965530-2">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3648965530-3">{</span><span class="mi">31</span><span class="p">,</span><span class="mi">28</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p" data-group-id="3648965530-3">}</span><span class="p" data-group-id="3648965530-2">)</span><span class="p">.</span></code></pre><p>If a literal, or a term that contains a literal, is inserted into an Ets table,
│ │ │  it is <em>copied</em>. The reason is that the module containing the literal can be
│ │ │  unloaded in the future.</p><p>When a literal is sent to another process, it is <em>not</em> copied. When a module
│ │ │  holding a literal is unloaded, the literal will be copied to the heap of all
│ │ │  processes that hold references to that literal.</p><p>There also exists a global literal pool that is managed by the
│ │ │  <a href="../../erts-15.2.7/doc/html/persistent_term.html"><code class="inline">persistent_term</code></a> module.</p><p>By default, 1 GB of virtual address space is reserved for all literal pools (in
│ │ │  BEAM code and persistent terms). The amount of virtual address space reserved
│ │ │  for literals can be changed by using the
│ │ │  <a href="../../erts-15.2.7/doc/html/erts_alloc.html#MIscs"><code class="inline">+MIscs option</code></a> when starting the emulator.</p><p>Here is an example how the reserved virtual address space for literals can be
│ │ │  raised to 2 GB (2048 MB):</p><pre><code class="text">erl +MIscs 2048</code></pre><h2 id="loss-of-sharing" class="section-heading">
│ │ │    <a href="#loss-of-sharing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Loss of Sharing</span>
│ │ │  </h2>
│ │ │ -<p>An Erlang term can have shared subterms. Here is a simple example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1751095243-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="1751095243-1">}</span></code></pre><p>Shared subterms are <em>not</em> preserved in the following cases:</p><ul><li>When a term is sent to another process</li><li>When a term is passed as the initial process arguments in the <code class="inline">spawn</code> call</li><li>When a term is stored in an Ets table</li></ul><p>That is an optimization. Most applications do not send messages with shared
│ │ │ -subterms.</p><p>The following example shows how a shared subterm can be created:</p><pre><code class="makeup erlang" translate="no"><span class="nf">kilo_byte</span><span class="p" data-group-id="0561056475-1">(</span><span class="p" data-group-id="0561056475-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="0561056475-2">(</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0561056475-3">[</span><span class="mi">42</span><span class="p" data-group-id="0561056475-3">]</span><span class="p" data-group-id="0561056475-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>An Erlang term can have shared subterms. Here is a simple example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8043492529-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="8043492529-1">}</span></code></pre><p>Shared subterms are <em>not</em> preserved in the following cases:</p><ul><li>When a term is sent to another process</li><li>When a term is passed as the initial process arguments in the <code class="inline">spawn</code> call</li><li>When a term is stored in an Ets table</li></ul><p>That is an optimization. Most applications do not send messages with shared
│ │ │ +subterms.</p><p>The following example shows how a shared subterm can be created:</p><pre><code class="makeup erlang" translate="no"><span class="nf">kilo_byte</span><span class="p" data-group-id="7290219443-1">(</span><span class="p" data-group-id="7290219443-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="7290219443-2">(</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7290219443-3">[</span><span class="mi">42</span><span class="p" data-group-id="7290219443-3">]</span><span class="p" data-group-id="7290219443-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">kilo_byte</span><span class="p" data-group-id="0561056475-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0561056475-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">kilo_byte</span><span class="p" data-group-id="7290219443-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7290219443-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">kilo_byte</span><span class="p" data-group-id="0561056475-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0561056475-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="0561056475-6">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0561056475-7">[</span><span class="n">Acc</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="0561056475-7">]</span><span class="p" data-group-id="0561056475-6">)</span><span class="p">.</span></code></pre><p><code class="inline">kilo_byte/1</code> creates a deep list. If <a href="../../erts-15.2.7/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a>
│ │ │ +</span><span class="nf">kilo_byte</span><span class="p" data-group-id="7290219443-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7290219443-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="7290219443-6">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7290219443-7">[</span><span class="n">Acc</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="7290219443-7">]</span><span class="p" data-group-id="7290219443-6">)</span><span class="p">.</span></code></pre><p><code class="inline">kilo_byte/1</code> creates a deep list. If <a href="../../erts-15.2.7/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a>
│ │ │  is called, the deep list can be converted to a binary of 1024 bytes:</p><pre><code class="text">1&gt; byte_size(list_to_binary(efficiency_guide:kilo_byte())).
│ │ │  1024</code></pre><p>Using the <code class="inline">erts_debug:size/1</code> BIF, it can be seen that the deep list only
│ │ │ -requires 22 words of heap space:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="8568886913-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="8568886913-2">(</span><span class="p" data-group-id="8568886913-2">)</span><span class="p" data-group-id="8568886913-1">)</span><span class="p">.</span><span class="w">
│ │ │ +requires 22 words of heap space:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="4769678677-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="4769678677-2">(</span><span class="p" data-group-id="4769678677-2">)</span><span class="p" data-group-id="4769678677-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">22</span></code></pre><p>Using the <code class="inline">erts_debug:flat_size/1</code> BIF, the size of the deep list can be
│ │ │  calculated if sharing is ignored. It becomes the size of the list when it has
│ │ │ -been sent to another process or stored in an Ets table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="9534324272-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="9534324272-2">(</span><span class="p" data-group-id="9534324272-2">)</span><span class="p" data-group-id="9534324272-1">)</span><span class="p">.</span><span class="w">
│ │ │ +been sent to another process or stored in an Ets table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="8176561897-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="8176561897-2">(</span><span class="p" data-group-id="8176561897-2">)</span><span class="p" data-group-id="8176561897-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4094</span></code></pre><p>It can be verified that sharing will be lost if the data is inserted into an Ets
│ │ │ -table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="4850739501-1">(</span><span class="ss">tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4850739501-2">[</span><span class="p" data-group-id="4850739501-2">]</span><span class="p" data-group-id="4850739501-1">)</span><span class="p">.</span><span class="w">
│ │ │ +table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="6500807379-1">(</span><span class="ss">tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6500807379-2">[</span><span class="p" data-group-id="6500807379-2">]</span><span class="p" data-group-id="6500807379-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Ref</span><span class="o">&lt;</span><span class="mf">0.1662103692</span><span class="p">.</span><span class="mf">2407923716.214181</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nc">ets</span><span class="p">:</span><span class="nf">insert</span><span class="p" data-group-id="4850739501-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4850739501-4">{</span><span class="ss">key</span><span class="p">,</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="4850739501-5">(</span><span class="p" data-group-id="4850739501-5">)</span><span class="p" data-group-id="4850739501-4">}</span><span class="p" data-group-id="4850739501-3">)</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="nc">ets</span><span class="p">:</span><span class="nf">insert</span><span class="p" data-group-id="6500807379-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6500807379-4">{</span><span class="ss">key</span><span class="p">,</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="6500807379-5">(</span><span class="p" data-group-id="6500807379-5">)</span><span class="p" data-group-id="6500807379-4">}</span><span class="p" data-group-id="6500807379-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="4850739501-6">(</span><span class="nf">element</span><span class="p" data-group-id="4850739501-7">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="4850739501-8">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="4850739501-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="4850739501-9">)</span><span class="p" data-group-id="4850739501-8">)</span><span class="p" data-group-id="4850739501-7">)</span><span class="p" data-group-id="4850739501-6">)</span><span class="p">.</span><span class="w">
│ │ │ +6&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="6500807379-6">(</span><span class="nf">element</span><span class="p" data-group-id="6500807379-7">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="6500807379-8">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="6500807379-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="6500807379-9">)</span><span class="p" data-group-id="6500807379-8">)</span><span class="p" data-group-id="6500807379-7">)</span><span class="p" data-group-id="6500807379-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4094</span><span class="gp unselectable">
│ │ │ -7&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="4850739501-10">(</span><span class="nf">element</span><span class="p" data-group-id="4850739501-11">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="4850739501-12">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="4850739501-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="4850739501-13">)</span><span class="p" data-group-id="4850739501-12">)</span><span class="p" data-group-id="4850739501-11">)</span><span class="p" data-group-id="4850739501-10">)</span><span class="p">.</span><span class="w">
│ │ │ +7&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="6500807379-10">(</span><span class="nf">element</span><span class="p" data-group-id="6500807379-11">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="6500807379-12">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="6500807379-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="6500807379-13">)</span><span class="p" data-group-id="6500807379-12">)</span><span class="p" data-group-id="6500807379-11">)</span><span class="p" data-group-id="6500807379-10">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4094</span></code></pre><p>When the data has passed through an Ets table, <code class="inline">erts_debug:size/1</code> and
│ │ │  <code class="inline">erts_debug:flat_size/1</code> return the same value. Sharing has been lost.</p><p>It is possible to build an <em>experimental</em> variant of the runtime system that
│ │ │  will preserve sharing when copying terms by giving the
│ │ │  <code class="inline">--enable-sharing-preserving</code> option to the <code class="inline">configure</code> script.</p><h2 id="smp-run-time-system" class="section-heading">
│ │ │    <a href="#smp-run-time-system" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/erl_interface.html
│ │ │ @@ -120,119 +120,119 @@
│ │ │  to read the port example in <a href="c_port.html">Ports</a> before reading this section.</p><h2 id="erlang-program" class="section-heading">
│ │ │    <a href="#erlang-program" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Erlang Program</span>
│ │ │  </h2>
│ │ │  <p>The following example shows an Erlang program communicating with a C program
│ │ │ -over a plain port with home made encoding:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6904919007-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="6904919007-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6904919007-2">(</span><span class="p" data-group-id="6904919007-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6904919007-3">]</span><span class="p" data-group-id="6904919007-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6904919007-4">(</span><span class="p" data-group-id="6904919007-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6904919007-5">]</span><span class="p" data-group-id="6904919007-4">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="6904919007-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="6904919007-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="6904919007-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6904919007-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="6904919007-8">]</span><span class="p" data-group-id="6904919007-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="6904919007-9">(</span><span class="p" data-group-id="6904919007-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +over a plain port with home made encoding:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9348280176-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="9348280176-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9348280176-2">(</span><span class="p" data-group-id="9348280176-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9348280176-3">]</span><span class="p" data-group-id="9348280176-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9348280176-4">(</span><span class="p" data-group-id="9348280176-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9348280176-5">]</span><span class="p" data-group-id="9348280176-4">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="9348280176-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="9348280176-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9348280176-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9348280176-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="9348280176-8">]</span><span class="p" data-group-id="9348280176-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="9348280176-9">(</span><span class="p" data-group-id="9348280176-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="6904919007-10">(</span><span class="n">X</span><span class="p" data-group-id="6904919007-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="6904919007-11">(</span><span class="p" data-group-id="6904919007-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6904919007-12">}</span><span class="p" data-group-id="6904919007-11">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="6904919007-13">(</span><span class="n">Y</span><span class="p" data-group-id="6904919007-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="6904919007-14">(</span><span class="p" data-group-id="6904919007-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6904919007-15">}</span><span class="p" data-group-id="6904919007-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="9348280176-10">(</span><span class="n">X</span><span class="p" data-group-id="9348280176-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="9348280176-11">(</span><span class="p" data-group-id="9348280176-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9348280176-12">}</span><span class="p" data-group-id="9348280176-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="9348280176-13">(</span><span class="n">Y</span><span class="p" data-group-id="9348280176-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="9348280176-14">(</span><span class="p" data-group-id="9348280176-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9348280176-15">}</span><span class="p" data-group-id="9348280176-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="6904919007-16">(</span><span class="n">Msg</span><span class="p" data-group-id="6904919007-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6904919007-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6904919007-18">(</span><span class="p" data-group-id="6904919007-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6904919007-17">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="9348280176-16">(</span><span class="n">Msg</span><span class="p" data-group-id="9348280176-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9348280176-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9348280176-18">(</span><span class="p" data-group-id="9348280176-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9348280176-17">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="6904919007-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6904919007-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="9348280176-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9348280176-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6904919007-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="6904919007-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="6904919007-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6904919007-22">(</span><span class="p" data-group-id="6904919007-22">)</span><span class="p" data-group-id="6904919007-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="6904919007-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6904919007-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="6904919007-24">(</span><span class="p" data-group-id="6904919007-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="6904919007-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6904919007-26">[</span><span class="p" data-group-id="6904919007-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6904919007-27">}</span><span class="p" data-group-id="6904919007-26">]</span><span class="p" data-group-id="6904919007-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="6904919007-28">(</span><span class="n">Port</span><span class="p" data-group-id="6904919007-28">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="9348280176-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="9348280176-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="9348280176-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9348280176-22">(</span><span class="p" data-group-id="9348280176-22">)</span><span class="p" data-group-id="9348280176-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="9348280176-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9348280176-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="9348280176-24">(</span><span class="p" data-group-id="9348280176-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="9348280176-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9348280176-26">[</span><span class="p" data-group-id="9348280176-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9348280176-27">}</span><span class="p" data-group-id="9348280176-26">]</span><span class="p" data-group-id="9348280176-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="9348280176-28">(</span><span class="n">Port</span><span class="p" data-group-id="9348280176-28">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="6904919007-29">(</span><span class="n">Port</span><span class="p" data-group-id="6904919007-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="9348280176-29">(</span><span class="n">Port</span><span class="p" data-group-id="9348280176-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="6904919007-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6904919007-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6904919007-31">{</span><span class="nf">self</span><span class="p" data-group-id="6904919007-32">(</span><span class="p" data-group-id="6904919007-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6904919007-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="6904919007-34">(</span><span class="n">Msg</span><span class="p" data-group-id="6904919007-34">)</span><span class="p" data-group-id="6904919007-33">}</span><span class="p" data-group-id="6904919007-31">}</span><span class="p">,</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="9348280176-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9348280176-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9348280176-31">{</span><span class="nf">self</span><span class="p" data-group-id="9348280176-32">(</span><span class="p" data-group-id="9348280176-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9348280176-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="9348280176-34">(</span><span class="n">Msg</span><span class="p" data-group-id="9348280176-34">)</span><span class="p" data-group-id="9348280176-33">}</span><span class="p" data-group-id="9348280176-31">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="6904919007-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6904919007-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6904919007-36">}</span><span class="p" data-group-id="6904919007-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6904919007-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="6904919007-38">(</span><span class="n">Data</span><span class="p" data-group-id="6904919007-38">)</span><span class="p" data-group-id="6904919007-37">}</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="9348280176-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9348280176-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9348280176-36">}</span><span class="p" data-group-id="9348280176-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9348280176-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="9348280176-38">(</span><span class="n">Data</span><span class="p" data-group-id="9348280176-38">)</span><span class="p" data-group-id="9348280176-37">}</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="6904919007-39">(</span><span class="n">Port</span><span class="p" data-group-id="6904919007-39">)</span><span class="p">;</span><span class="w">
│ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="9348280176-39">(</span><span class="n">Port</span><span class="p" data-group-id="9348280176-39">)</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6904919007-40">{</span><span class="nf">self</span><span class="p" data-group-id="6904919007-41">(</span><span class="p" data-group-id="6904919007-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="6904919007-40">}</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9348280176-40">{</span><span class="nf">self</span><span class="p" data-group-id="9348280176-41">(</span><span class="p" data-group-id="9348280176-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="9348280176-40">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="6904919007-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="6904919007-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="6904919007-43">(</span><span class="ss">normal</span><span class="p" data-group-id="6904919007-43">)</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="9348280176-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="9348280176-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="9348280176-43">(</span><span class="ss">normal</span><span class="p" data-group-id="9348280176-43">)</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="6904919007-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="6904919007-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="6904919007-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="6904919007-45">)</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="9348280176-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="9348280176-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="9348280176-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="9348280176-45">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="6904919007-46">(</span><span class="p" data-group-id="6904919007-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6904919007-47">}</span><span class="p" data-group-id="6904919007-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6904919007-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6904919007-48">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="6904919007-49">(</span><span class="p" data-group-id="6904919007-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6904919007-50">}</span><span class="p" data-group-id="6904919007-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6904919007-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6904919007-51">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="9348280176-46">(</span><span class="p" data-group-id="9348280176-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9348280176-47">}</span><span class="p" data-group-id="9348280176-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9348280176-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9348280176-48">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="9348280176-49">(</span><span class="p" data-group-id="9348280176-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9348280176-50">}</span><span class="p" data-group-id="9348280176-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9348280176-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9348280176-51">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="6904919007-52">(</span><span class="p" data-group-id="6904919007-53">[</span><span class="n">Int</span><span class="p" data-group-id="6904919007-53">]</span><span class="p" data-group-id="6904919007-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>There are two differences when using Erl_Interface on the C side compared to the
│ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="9348280176-52">(</span><span class="p" data-group-id="9348280176-53">[</span><span class="n">Int</span><span class="p" data-group-id="9348280176-53">]</span><span class="p" data-group-id="9348280176-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>There are two differences when using Erl_Interface on the C side compared to the
│ │ │  example in <a href="c_port.html">Ports</a>, using only the plain port:</p><ul><li>As Erl_Interface operates on the Erlang external term format, the port must be
│ │ │  set to use binaries.</li><li>Instead of inventing an encoding/decoding scheme, the
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#term_to_binary/1"><code class="inline">term_to_binary/1</code></a> and
│ │ │ -<a href="../../erts-15.2.7/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a> BIFs are to be used.</li></ul><p>That is:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="9005753559-1">(</span><span class="p" data-group-id="9005753559-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="9005753559-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9005753559-3">[</span><span class="p" data-group-id="9005753559-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9005753559-4">}</span><span class="p" data-group-id="9005753559-3">]</span><span class="p" data-group-id="9005753559-1">)</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="2585268620-1">(</span><span class="p" data-group-id="2585268620-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="2585268620-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2585268620-3">[</span><span class="p" data-group-id="2585268620-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2585268620-4">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="2585268620-3">]</span><span class="p" data-group-id="2585268620-1">)</span></code></pre><p>And:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6920915919-1">{</span><span class="nf">self</span><span class="p" data-group-id="6920915919-2">(</span><span class="p" data-group-id="6920915919-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6920915919-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="6920915919-4">(</span><span class="n">Msg</span><span class="p" data-group-id="6920915919-4">)</span><span class="p" data-group-id="6920915919-3">}</span><span class="p" data-group-id="6920915919-1">}</span><span class="p">,</span><span class="w">
│ │ │ +<a href="../../erts-15.2.7/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a> BIFs are to be used.</li></ul><p>That is:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="6603717842-1">(</span><span class="p" data-group-id="6603717842-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="6603717842-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6603717842-3">[</span><span class="p" data-group-id="6603717842-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6603717842-4">}</span><span class="p" data-group-id="6603717842-3">]</span><span class="p" data-group-id="6603717842-1">)</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="2957036060-1">(</span><span class="p" data-group-id="2957036060-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="2957036060-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2957036060-3">[</span><span class="p" data-group-id="2957036060-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2957036060-4">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="2957036060-3">]</span><span class="p" data-group-id="2957036060-1">)</span></code></pre><p>And:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3164689753-1">{</span><span class="nf">self</span><span class="p" data-group-id="3164689753-2">(</span><span class="p" data-group-id="3164689753-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3164689753-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="3164689753-4">(</span><span class="n">Msg</span><span class="p" data-group-id="3164689753-4">)</span><span class="p" data-group-id="3164689753-3">}</span><span class="p" data-group-id="3164689753-1">}</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6920915919-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6920915919-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6920915919-6">}</span><span class="p" data-group-id="6920915919-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6920915919-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="6920915919-8">(</span><span class="n">Data</span><span class="p" data-group-id="6920915919-8">)</span><span class="p" data-group-id="6920915919-7">}</span><span class="w">
│ │ │ -</span><span class="k">end</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2449647627-1">{</span><span class="nf">self</span><span class="p" data-group-id="2449647627-2">(</span><span class="p" data-group-id="2449647627-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2449647627-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="2449647627-4">(</span><span class="n">Msg</span><span class="p" data-group-id="2449647627-4">)</span><span class="p" data-group-id="2449647627-3">}</span><span class="p" data-group-id="2449647627-1">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3164689753-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3164689753-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3164689753-6">}</span><span class="p" data-group-id="3164689753-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3164689753-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="3164689753-8">(</span><span class="n">Data</span><span class="p" data-group-id="3164689753-8">)</span><span class="p" data-group-id="3164689753-7">}</span><span class="w">
│ │ │ +</span><span class="k">end</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0306087324-1">{</span><span class="nf">self</span><span class="p" data-group-id="0306087324-2">(</span><span class="p" data-group-id="0306087324-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0306087324-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="0306087324-4">(</span><span class="n">Msg</span><span class="p" data-group-id="0306087324-4">)</span><span class="p" data-group-id="0306087324-3">}</span><span class="p" data-group-id="0306087324-1">}</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="2449647627-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2449647627-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2449647627-6">}</span><span class="p" data-group-id="2449647627-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2449647627-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="2449647627-8">(</span><span class="n">Data</span><span class="p" data-group-id="2449647627-8">)</span><span class="p" data-group-id="2449647627-7">}</span><span class="w">
│ │ │ -</span><span class="k">end</span></code></pre><p>The resulting Erlang program is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8072456070-1">(</span><span class="ss">complex2</span><span class="p" data-group-id="8072456070-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8072456070-2">(</span><span class="p" data-group-id="8072456070-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8072456070-3">]</span><span class="p" data-group-id="8072456070-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8072456070-4">(</span><span class="p" data-group-id="8072456070-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8072456070-5">]</span><span class="p" data-group-id="8072456070-4">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="8072456070-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="8072456070-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="8072456070-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8072456070-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="8072456070-8">]</span><span class="p" data-group-id="8072456070-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="8072456070-9">(</span><span class="p" data-group-id="8072456070-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="0306087324-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0306087324-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0306087324-6">}</span><span class="p" data-group-id="0306087324-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0306087324-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="0306087324-8">(</span><span class="n">Data</span><span class="p" data-group-id="0306087324-8">)</span><span class="p" data-group-id="0306087324-7">}</span><span class="w">
│ │ │ +</span><span class="k">end</span></code></pre><p>The resulting Erlang program is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5107325467-1">(</span><span class="ss">complex2</span><span class="p" data-group-id="5107325467-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5107325467-2">(</span><span class="p" data-group-id="5107325467-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5107325467-3">]</span><span class="p" data-group-id="5107325467-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5107325467-4">(</span><span class="p" data-group-id="5107325467-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5107325467-5">]</span><span class="p" data-group-id="5107325467-4">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="5107325467-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="5107325467-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="5107325467-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5107325467-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="5107325467-8">]</span><span class="p" data-group-id="5107325467-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="5107325467-9">(</span><span class="p" data-group-id="5107325467-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="8072456070-10">(</span><span class="n">X</span><span class="p" data-group-id="8072456070-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="8072456070-11">(</span><span class="p" data-group-id="8072456070-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8072456070-12">}</span><span class="p" data-group-id="8072456070-11">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="8072456070-13">(</span><span class="n">Y</span><span class="p" data-group-id="8072456070-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="8072456070-14">(</span><span class="p" data-group-id="8072456070-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8072456070-15">}</span><span class="p" data-group-id="8072456070-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="5107325467-10">(</span><span class="n">X</span><span class="p" data-group-id="5107325467-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="5107325467-11">(</span><span class="p" data-group-id="5107325467-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5107325467-12">}</span><span class="p" data-group-id="5107325467-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="5107325467-13">(</span><span class="n">Y</span><span class="p" data-group-id="5107325467-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="5107325467-14">(</span><span class="p" data-group-id="5107325467-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5107325467-15">}</span><span class="p" data-group-id="5107325467-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="8072456070-16">(</span><span class="n">Msg</span><span class="p" data-group-id="8072456070-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8072456070-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8072456070-18">(</span><span class="p" data-group-id="8072456070-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8072456070-17">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="5107325467-16">(</span><span class="n">Msg</span><span class="p" data-group-id="5107325467-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5107325467-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5107325467-18">(</span><span class="p" data-group-id="5107325467-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="5107325467-17">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="8072456070-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8072456070-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5107325467-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="5107325467-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8072456070-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="8072456070-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="8072456070-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8072456070-22">(</span><span class="p" data-group-id="8072456070-22">)</span><span class="p" data-group-id="8072456070-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="8072456070-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8072456070-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="8072456070-24">(</span><span class="p" data-group-id="8072456070-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="8072456070-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8072456070-26">[</span><span class="p" data-group-id="8072456070-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8072456070-27">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="8072456070-26">]</span><span class="p" data-group-id="8072456070-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="8072456070-28">(</span><span class="n">Port</span><span class="p" data-group-id="8072456070-28">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="5107325467-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="5107325467-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="5107325467-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5107325467-22">(</span><span class="p" data-group-id="5107325467-22">)</span><span class="p" data-group-id="5107325467-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="5107325467-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5107325467-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="5107325467-24">(</span><span class="p" data-group-id="5107325467-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="5107325467-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5107325467-26">[</span><span class="p" data-group-id="5107325467-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5107325467-27">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="5107325467-26">]</span><span class="p" data-group-id="5107325467-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="5107325467-28">(</span><span class="n">Port</span><span class="p" data-group-id="5107325467-28">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="8072456070-29">(</span><span class="n">Port</span><span class="p" data-group-id="8072456070-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="5107325467-29">(</span><span class="n">Port</span><span class="p" data-group-id="5107325467-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="8072456070-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8072456070-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8072456070-31">{</span><span class="nf">self</span><span class="p" data-group-id="8072456070-32">(</span><span class="p" data-group-id="8072456070-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8072456070-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="8072456070-34">(</span><span class="n">Msg</span><span class="p" data-group-id="8072456070-34">)</span><span class="p" data-group-id="8072456070-33">}</span><span class="p" data-group-id="8072456070-31">}</span><span class="p">,</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5107325467-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="5107325467-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5107325467-31">{</span><span class="nf">self</span><span class="p" data-group-id="5107325467-32">(</span><span class="p" data-group-id="5107325467-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5107325467-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="5107325467-34">(</span><span class="n">Msg</span><span class="p" data-group-id="5107325467-34">)</span><span class="p" data-group-id="5107325467-33">}</span><span class="p" data-group-id="5107325467-31">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="8072456070-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8072456070-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8072456070-36">}</span><span class="p" data-group-id="8072456070-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8072456070-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="8072456070-38">(</span><span class="n">Data</span><span class="p" data-group-id="8072456070-38">)</span><span class="p" data-group-id="8072456070-37">}</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="5107325467-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5107325467-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5107325467-36">}</span><span class="p" data-group-id="5107325467-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5107325467-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="5107325467-38">(</span><span class="n">Data</span><span class="p" data-group-id="5107325467-38">)</span><span class="p" data-group-id="5107325467-37">}</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="8072456070-39">(</span><span class="n">Port</span><span class="p" data-group-id="8072456070-39">)</span><span class="p">;</span><span class="w">
│ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="5107325467-39">(</span><span class="n">Port</span><span class="p" data-group-id="5107325467-39">)</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8072456070-40">{</span><span class="nf">self</span><span class="p" data-group-id="8072456070-41">(</span><span class="p" data-group-id="8072456070-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="8072456070-40">}</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5107325467-40">{</span><span class="nf">self</span><span class="p" data-group-id="5107325467-41">(</span><span class="p" data-group-id="5107325467-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="5107325467-40">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="8072456070-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="8072456070-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="8072456070-43">(</span><span class="ss">normal</span><span class="p" data-group-id="8072456070-43">)</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="5107325467-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="5107325467-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="5107325467-43">(</span><span class="ss">normal</span><span class="p" data-group-id="5107325467-43">)</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="8072456070-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="8072456070-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="8072456070-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="8072456070-45">)</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5107325467-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5107325467-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="5107325467-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="5107325467-45">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Notice that calling <code class="inline">complex2:foo/1</code> and <code class="inline">complex2:bar/1</code> results in the tuple
│ │ │  <code class="inline">{foo,X}</code> or <code class="inline">{bar,Y}</code> being sent to the <code class="inline">complex</code> process, which codes them as
│ │ │  binaries and sends them to the port. This means that the C program must be able
│ │ │  to handle these two tuples.</p><h2 id="c-program" class="section-heading">
│ │ │    <a href="#c-program" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -362,27 +362,27 @@
│ │ │      -L/usr/local/otp/lib/erl_interface-3.9.2/lib \
│ │ │      complex.c erl_comm.c ei.c -lei -lpthread</code></pre><p>In Erlang/OTP R5B and later versions of OTP, the <code class="inline">include</code> and <code class="inline">lib</code> directories
│ │ │  are situated under <code class="inline">$OTPROOT/lib/erl_interface-VSN</code>, where <code class="inline">$OTPROOT</code> is the
│ │ │  root directory of the OTP installation (<code class="inline">/usr/local/otp</code> in the recent example)
│ │ │  and <code class="inline">VSN</code> is the version of the Erl_interface application (3.2.1 in the recent
│ │ │  example).</p><p>In R4B and earlier versions of OTP, <code class="inline">include</code> and <code class="inline">lib</code> are situated under
│ │ │  <code class="inline">$OTPROOT/usr</code>.</p><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$ </span><span class="ss">erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="4103882242-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="4103882242-1">]</span><span class="w"> </span><span class="p" data-group-id="4103882242-2">[</span><span class="ss">source</span><span class="p" data-group-id="4103882242-2">]</span><span class="w"> </span><span class="p" data-group-id="4103882242-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4103882242-3">]</span><span class="w"> </span><span class="p" data-group-id="4103882242-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4103882242-4">]</span><span class="w"> </span><span class="p" data-group-id="4103882242-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4103882242-5">]</span><span class="w"> </span><span class="p" data-group-id="4103882242-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4103882242-6">]</span><span class="w"> </span><span class="p" data-group-id="4103882242-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="4103882242-7">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="4176055112-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="4176055112-1">]</span><span class="w"> </span><span class="p" data-group-id="4176055112-2">[</span><span class="ss">source</span><span class="p" data-group-id="4176055112-2">]</span><span class="w"> </span><span class="p" data-group-id="4176055112-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4176055112-3">]</span><span class="w"> </span><span class="p" data-group-id="4176055112-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4176055112-4">]</span><span class="w"> </span><span class="p" data-group-id="4176055112-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4176055112-5">]</span><span class="w"> </span><span class="p" data-group-id="4176055112-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4176055112-6">]</span><span class="w"> </span><span class="p" data-group-id="4176055112-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="4176055112-7">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="4103882242-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="4103882242-9">(</span><span class="p" data-group-id="4103882242-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="4103882242-8">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nf">c</span><span class="p" data-group-id="4103882242-10">(</span><span class="ss">complex2</span><span class="p" data-group-id="4103882242-10">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4103882242-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex2</span><span class="p" data-group-id="4103882242-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="2046931507-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="2046931507-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="4176055112-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="4176055112-9">(</span><span class="p" data-group-id="4176055112-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="4176055112-8">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="nf">c</span><span class="p" data-group-id="4176055112-10">(</span><span class="ss">complex2</span><span class="p" data-group-id="4176055112-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4176055112-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex2</span><span class="p" data-group-id="4176055112-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0664485521-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="0664485521-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="2046931507-2">(</span><span class="mi">3</span><span class="p" data-group-id="2046931507-2">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="0664485521-2">(</span><span class="mi">3</span><span class="p" data-group-id="0664485521-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="2046931507-3">(</span><span class="mi">5</span><span class="p" data-group-id="2046931507-3">)</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="0664485521-3">(</span><span class="mi">5</span><span class="p" data-group-id="0664485521-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="2046931507-4">(</span><span class="mi">352</span><span class="p" data-group-id="2046931507-4">)</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="0664485521-4">(</span><span class="mi">352</span><span class="p" data-group-id="0664485521-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">704</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="2046931507-5">(</span><span class="p" data-group-id="2046931507-5">)</span><span class="p">.</span><span class="w">
│ │ │ +6&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="0664485521-5">(</span><span class="p" data-group-id="0664485521-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="c_port.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/error_logging.html
│ │ │ @@ -143,39 +143,39 @@
│ │ │  reports and other error and information reports are by default logged through
│ │ │  the log handler which is set up when the Kernel application is started.</p><p>Prior to Erlang/OTP 21.0, supervisor, crash, and progress reports were only
│ │ │  logged when the SASL application was running. This behaviour can, for backwards
│ │ │  compatibility, be enabled by setting the Kernel configuration parameter
│ │ │  <a href="../../lib/kernel-10.2.7.1/doc/html/kernel_app.html#logger_sasl_compatible"><code class="inline">logger_sasl_compatible</code></a> to
│ │ │  <code class="inline">true</code>. For more information, see
│ │ │  <a href="../../lib/sasl-4.2.2/doc/html/error_logging.html">SASL Error Logging</a> in the SASL User's Guide.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -kernel logger_level info</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">21</span><span class="w"> </span><span class="p" data-group-id="0811583245-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">10.0</span><span class="p" data-group-id="0811583245-1">]</span><span class="w"> </span><span class="p" data-group-id="0811583245-2">[</span><span class="ss">source</span><span class="o">-</span><span class="mi">13</span><span class="ss">c50db</span><span class="p" data-group-id="0811583245-2">]</span><span class="w"> </span><span class="p" data-group-id="0811583245-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0811583245-3">]</span><span class="w"> </span><span class="p" data-group-id="0811583245-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="0811583245-4">]</span><span class="w"> </span><span class="p" data-group-id="0811583245-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="0811583245-5">]</span><span class="w"> </span><span class="p" data-group-id="0811583245-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0811583245-6">]</span><span class="w"> </span><span class="p" data-group-id="0811583245-7">[</span><span class="ss">hipe</span><span class="p" data-group-id="0811583245-7">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">21</span><span class="w"> </span><span class="p" data-group-id="6517632704-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">10.0</span><span class="p" data-group-id="6517632704-1">]</span><span class="w"> </span><span class="p" data-group-id="6517632704-2">[</span><span class="ss">source</span><span class="o">-</span><span class="mi">13</span><span class="ss">c50db</span><span class="p" data-group-id="6517632704-2">]</span><span class="w"> </span><span class="p" data-group-id="6517632704-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="6517632704-3">]</span><span class="w"> </span><span class="p" data-group-id="6517632704-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="6517632704-4">]</span><span class="w"> </span><span class="p" data-group-id="6517632704-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="6517632704-5">]</span><span class="w"> </span><span class="p" data-group-id="6517632704-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6517632704-6">]</span><span class="w"> </span><span class="p" data-group-id="6517632704-7">[</span><span class="ss">hipe</span><span class="p" data-group-id="6517632704-7">]</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.916404</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │      </span><span class="nc">application</span><span class="p">:</span><span class="w"> </span><span class="ss">kernel</span><span class="w">
│ │ │      </span><span class="nc">started_at</span><span class="p">:</span><span class="w"> </span><span class="ss">nonode@nohost</span><span class="w">
│ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.922908</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │      </span><span class="nc">application</span><span class="p">:</span><span class="w"> </span><span class="ss">stdlib</span><span class="w">
│ │ │      </span><span class="nc">started_at</span><span class="p">:</span><span class="w"> </span><span class="ss">nonode@nohost</span><span class="w">
│ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.925755</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0811583245-8">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="0811583245-8">}</span><span class="w">
│ │ │ -    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0811583245-9">[</span><span class="p" data-group-id="0811583245-10">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.74</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0811583245-10">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0811583245-11">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_sup</span><span class="p" data-group-id="0811583245-11">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0811583245-12">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="0811583245-13">{</span><span class="ss">disk_log_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="0811583245-14">[</span><span class="p" data-group-id="0811583245-14">]</span><span class="p" data-group-id="0811583245-13">}</span><span class="p" data-group-id="0811583245-12">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0811583245-15">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="0811583245-15">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0811583245-16">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">1000</span><span class="p" data-group-id="0811583245-16">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0811583245-17">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">supervisor</span><span class="p" data-group-id="0811583245-17">}</span><span class="p" data-group-id="0811583245-9">]</span><span class="w">
│ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6517632704-8">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="6517632704-8">}</span><span class="w">
│ │ │ +    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6517632704-9">[</span><span class="p" data-group-id="6517632704-10">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.74</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6517632704-10">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="6517632704-11">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_sup</span><span class="p" data-group-id="6517632704-11">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="6517632704-12">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="6517632704-13">{</span><span class="ss">disk_log_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="6517632704-14">[</span><span class="p" data-group-id="6517632704-14">]</span><span class="p" data-group-id="6517632704-13">}</span><span class="p" data-group-id="6517632704-12">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="6517632704-15">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="6517632704-15">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="6517632704-16">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">1000</span><span class="p" data-group-id="6517632704-16">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="6517632704-17">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">supervisor</span><span class="p" data-group-id="6517632704-17">}</span><span class="p" data-group-id="6517632704-9">]</span><span class="w">
│ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.926056</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0811583245-18">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="0811583245-18">}</span><span class="w">
│ │ │ -    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0811583245-19">[</span><span class="p" data-group-id="0811583245-20">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.75</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0811583245-20">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0811583245-21">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_server</span><span class="p" data-group-id="0811583245-21">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0811583245-22">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="0811583245-23">{</span><span class="ss">disk_log_server</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="0811583245-24">[</span><span class="p" data-group-id="0811583245-24">]</span><span class="p" data-group-id="0811583245-23">}</span><span class="p" data-group-id="0811583245-22">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0811583245-25">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="0811583245-25">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0811583245-26">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">2000</span><span class="p" data-group-id="0811583245-26">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0811583245-27">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">worker</span><span class="p" data-group-id="0811583245-27">}</span><span class="p" data-group-id="0811583245-19">]</span><span class="w">
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V10</span><span class="p">.</span><span class="mi">0</span><span class="w">  </span><span class="p" data-group-id="0811583245-28">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="0811583245-28">)</span><span class="w">
│ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6517632704-18">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="6517632704-18">}</span><span class="w">
│ │ │ +    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6517632704-19">[</span><span class="p" data-group-id="6517632704-20">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.75</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6517632704-20">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="6517632704-21">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_server</span><span class="p" data-group-id="6517632704-21">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="6517632704-22">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="6517632704-23">{</span><span class="ss">disk_log_server</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="6517632704-24">[</span><span class="p" data-group-id="6517632704-24">]</span><span class="p" data-group-id="6517632704-23">}</span><span class="p" data-group-id="6517632704-22">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="6517632704-25">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="6517632704-25">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="6517632704-26">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">2000</span><span class="p" data-group-id="6517632704-26">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="6517632704-27">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">worker</span><span class="p" data-group-id="6517632704-27">}</span><span class="p" data-group-id="6517632704-19">]</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V10</span><span class="p">.</span><span class="mi">0</span><span class="w">  </span><span class="p" data-group-id="6517632704-28">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="6517632704-28">)</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="o">&gt;</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="system_principles.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/errors.html
│ │ │ @@ -151,22 +151,22 @@
│ │ │  classes, with different origins. The <a href="expressions.html#try">try</a> expression can
│ │ │  distinguish between the different classes, whereas the
│ │ │  <a href="expressions.html#catch-and-throw">catch</a> expression cannot. <code class="inline">try</code> and <code class="inline">catch</code> are described
│ │ │  in <a href="expressions.html">Expressions</a>.</p><table><thead><tr><th style="text-align: left;"><em>Class</em></th><th style="text-align: left;"><em>Origin</em></th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">error</code></td><td style="text-align: left;">Run-time error, for example, <code class="inline">1+a</code>, or the process called <a href="../../erts-15.2.7/doc/html/erlang.html#error/1"><code class="inline">error/1</code></a></td></tr><tr><td style="text-align: left;"><code class="inline">exit</code></td><td style="text-align: left;">The process called <a href="../../erts-15.2.7/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a></td></tr><tr><td style="text-align: left;"><code class="inline">throw</code></td><td style="text-align: left;">The process called <a href="../../erts-15.2.7/doc/html/erlang.html#throw/1"><code class="inline">throw/1</code></a></td></tr></tbody></table><p><em>Table: Exception Classes.</em></p><p>All of the above exceptions can also be generated by calling <a href="../../erts-15.2.7/doc/html/erlang.html#raise/3"><code class="inline">erlang:raise/3</code></a>.</p><p>An exception consists of its class, an exit reason (see
│ │ │  <a href="errors.html#exit_reasons">Exit Reason</a>), and a stack trace (which aids in finding
│ │ │  the code location of the exception).</p><p>The stack trace can be bound to a variable from within a <code class="inline">try</code> expression for
│ │ │  any exception class, or as part of the exit reason when a run-time error is
│ │ │ -caught by a <code class="inline">catch</code>. Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="9289319613-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="9289319613-2">{</span><span class="ss">test</span><span class="p">,</span><span class="n">Stacktrace</span><span class="p" data-group-id="9289319613-2">}</span><span class="p" data-group-id="9289319613-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9289319613-3">(</span><span class="k">catch</span><span class="w"> </span><span class="nf">error</span><span class="p" data-group-id="9289319613-4">(</span><span class="ss">test</span><span class="p" data-group-id="9289319613-4">)</span><span class="p" data-group-id="9289319613-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Stacktrace</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9289319613-5">[</span><span class="p" data-group-id="9289319613-6">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="9289319613-7">[</span><span class="p" data-group-id="9289319613-7">]</span><span class="p" data-group-id="9289319613-6">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9289319613-8">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="9289319613-9">[</span><span class="p" data-group-id="9289319613-9">]</span><span class="p" data-group-id="9289319613-8">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9289319613-5">]</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="k">try</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="9289319613-10">(</span><span class="ss">test</span><span class="p" data-group-id="9289319613-10">)</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="n">Class</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stacktrace</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Stacktrace</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9289319613-11">[</span><span class="p" data-group-id="9289319613-12">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="9289319613-13">[</span><span class="p" data-group-id="9289319613-13">]</span><span class="p" data-group-id="9289319613-12">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9289319613-14">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="9289319613-15">[</span><span class="p" data-group-id="9289319613-15">]</span><span class="p" data-group-id="9289319613-14">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9289319613-11">]</span></code></pre><p><a href="" id="stacktrace"></a></p><h3 id="the-call-stack-back-trace-stacktrace" class="section-heading">
│ │ │ +caught by a <code class="inline">catch</code>. Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="7896167126-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="7896167126-2">{</span><span class="ss">test</span><span class="p">,</span><span class="n">Stacktrace</span><span class="p" data-group-id="7896167126-2">}</span><span class="p" data-group-id="7896167126-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7896167126-3">(</span><span class="k">catch</span><span class="w"> </span><span class="nf">error</span><span class="p" data-group-id="7896167126-4">(</span><span class="ss">test</span><span class="p" data-group-id="7896167126-4">)</span><span class="p" data-group-id="7896167126-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Stacktrace</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7896167126-5">[</span><span class="p" data-group-id="7896167126-6">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="7896167126-7">[</span><span class="p" data-group-id="7896167126-7">]</span><span class="p" data-group-id="7896167126-6">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7896167126-8">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="7896167126-9">[</span><span class="p" data-group-id="7896167126-9">]</span><span class="p" data-group-id="7896167126-8">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7896167126-5">]</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="k">try</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="7896167126-10">(</span><span class="ss">test</span><span class="p" data-group-id="7896167126-10">)</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="n">Class</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stacktrace</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Stacktrace</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7896167126-11">[</span><span class="p" data-group-id="7896167126-12">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="7896167126-13">[</span><span class="p" data-group-id="7896167126-13">]</span><span class="p" data-group-id="7896167126-12">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7896167126-14">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="7896167126-15">[</span><span class="p" data-group-id="7896167126-15">]</span><span class="p" data-group-id="7896167126-14">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7896167126-11">]</span></code></pre><p><a href="" id="stacktrace"></a></p><h3 id="the-call-stack-back-trace-stacktrace" class="section-heading">
│ │ │    <a href="#the-call-stack-back-trace-stacktrace" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">The call-stack back trace (stacktrace)</span>
│ │ │  </h3>
│ │ │  <p>The stack back-trace (<a href="../../erts-15.2.7/doc/html/erlang.html#t:stacktrace/0"><em>stacktrace</em></a>) is a list that
│ │ │  contains <code class="inline">{Module, Function, Arity, ExtraInfo}</code> and/or <code class="inline">{Fun, Arity, ExtraInfo}</code>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/events.html
│ │ │ @@ -135,43 +135,43 @@
│ │ │  event handler.</p><h2 id="example" class="section-heading">
│ │ │    <a href="#example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example</span>
│ │ │  </h2>
│ │ │  <p>The callback module for the event handler writing error messages to the terminal
│ │ │ -can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7789070788-1">(</span><span class="ss">terminal_logger</span><span class="p" data-group-id="7789070788-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="7789070788-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="7789070788-2">)</span><span class="p">.</span><span class="w">
│ │ │ +can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4322135214-1">(</span><span class="ss">terminal_logger</span><span class="p" data-group-id="4322135214-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4322135214-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="4322135214-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7789070788-3">(</span><span class="p" data-group-id="7789070788-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7789070788-4">]</span><span class="p" data-group-id="7789070788-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4322135214-3">(</span><span class="p" data-group-id="4322135214-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4322135214-4">]</span><span class="p" data-group-id="4322135214-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="7789070788-5">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="7789070788-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7789070788-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7789070788-7">[</span><span class="p" data-group-id="7789070788-7">]</span><span class="p" data-group-id="7789070788-6">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="4322135214-5">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="4322135214-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4322135214-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4322135214-7">[</span><span class="p" data-group-id="4322135214-7">]</span><span class="p" data-group-id="4322135214-6">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="7789070788-8">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7789070788-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7789070788-9">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7789070788-10">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="7789070788-10">]</span><span class="p" data-group-id="7789070788-9">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7789070788-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7789070788-11">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="4322135214-8">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4322135214-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4322135214-9">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4322135214-10">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="4322135214-10">]</span><span class="p" data-group-id="4322135214-9">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4322135214-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4322135214-11">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="7789070788-12">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="7789070788-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="4322135214-12">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="4322135214-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The callback module for the event handler writing error messages to a file can
│ │ │ -look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8530466155-1">(</span><span class="ss">file_logger</span><span class="p" data-group-id="8530466155-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8530466155-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="8530466155-2">)</span><span class="p">.</span><span class="w">
│ │ │ +look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0157634348-1">(</span><span class="ss">file_logger</span><span class="p" data-group-id="0157634348-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="0157634348-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="0157634348-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8530466155-3">(</span><span class="p" data-group-id="8530466155-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8530466155-4">]</span><span class="p" data-group-id="8530466155-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0157634348-3">(</span><span class="p" data-group-id="0157634348-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0157634348-4">]</span><span class="p" data-group-id="0157634348-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8530466155-5">(</span><span class="n">File</span><span class="p" data-group-id="8530466155-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8530466155-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8530466155-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="8530466155-7">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="8530466155-7">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8530466155-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8530466155-8">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="8530466155-9">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8530466155-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8530466155-10">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8530466155-11">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="8530466155-11">]</span><span class="p" data-group-id="8530466155-10">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8530466155-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8530466155-12">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="0157634348-5">(</span><span class="n">File</span><span class="p" data-group-id="0157634348-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0157634348-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="0157634348-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="0157634348-7">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="0157634348-7">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0157634348-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="0157634348-8">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="0157634348-9">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="0157634348-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0157634348-10">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0157634348-11">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="0157634348-11">]</span><span class="p" data-group-id="0157634348-10">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0157634348-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="0157634348-12">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="8530466155-13">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8530466155-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="8530466155-14">(</span><span class="n">Fd</span><span class="p" data-group-id="8530466155-14">)</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><p><a href="" id="mgr"></a></p><h2 id="starting-an-event-manager" class="section-heading">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="0157634348-13">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="0157634348-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="0157634348-14">(</span><span class="n">Fd</span><span class="p" data-group-id="0157634348-14">)</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><p><a href="" id="mgr"></a></p><h2 id="starting-an-event-manager" class="section-heading">
│ │ │    <a href="#starting-an-event-manager" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting an Event Manager</span>
│ │ │  </h2>
│ │ │  <p>To start an event manager for handling errors, as described in the previous
│ │ │  example, call the following function:</p><pre><code class="text">gen_event:start_link({local, error_man})</code></pre><p><a href="../../lib/stdlib-6.2.2.1/doc/html/gen_event.html#start_link/1"><code class="inline">gen_event:start_link/1</code></a> spawns and links to a new event manager process.</p><p>The argument, <code class="inline">{local, error_man}</code>, specifies the name under which the
│ │ │ @@ -184,57 +184,57 @@
│ │ │  manager that is not part of a supervision tree.</p><h2 id="adding-an-event-handler" class="section-heading">
│ │ │    <a href="#adding-an-event-handler" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Adding an Event Handler</span>
│ │ │  </h2>
│ │ │  <p>The following example shows how to start an event manager and add an event
│ │ │ -handler to it by using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6950314577-1">(</span><span class="p" data-group-id="6950314577-2">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="6950314577-2">}</span><span class="p" data-group-id="6950314577-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6950314577-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.31</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6950314577-3">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">add_handler</span><span class="p" data-group-id="6950314577-4">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6950314577-5">[</span><span class="p" data-group-id="6950314577-5">]</span><span class="p" data-group-id="6950314577-4">)</span><span class="p">.</span><span class="w">
│ │ │ +handler to it by using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="2589895648-1">(</span><span class="p" data-group-id="2589895648-2">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="2589895648-2">}</span><span class="p" data-group-id="2589895648-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2589895648-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.31</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2589895648-3">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">add_handler</span><span class="p" data-group-id="2589895648-4">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2589895648-5">[</span><span class="p" data-group-id="2589895648-5">]</span><span class="p" data-group-id="2589895648-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>This function sends a message to the event manager registered as <code class="inline">error_man</code>,
│ │ │  telling it to add the event handler <code class="inline">terminal_logger</code>. The event manager calls
│ │ │  the callback function <code class="inline">terminal_logger:init([])</code>, where the argument <code class="inline">[]</code> is the
│ │ │  third argument to <code class="inline">add_handler</code>. <code class="inline">init/1</code> is expected to return <code class="inline">{ok, State}</code>,
│ │ │ -where <code class="inline">State</code> is the internal state of the event handler.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="2881475766-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="2881475766-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2881475766-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2881475766-3">[</span><span class="p" data-group-id="2881475766-3">]</span><span class="p" data-group-id="2881475766-2">}</span><span class="p">.</span></code></pre><p>Here, <code class="inline">init/1</code> does not need any input data and ignores its argument. For
│ │ │ +where <code class="inline">State</code> is the internal state of the event handler.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8265250356-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="8265250356-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8265250356-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8265250356-3">[</span><span class="p" data-group-id="8265250356-3">]</span><span class="p" data-group-id="8265250356-2">}</span><span class="p">.</span></code></pre><p>Here, <code class="inline">init/1</code> does not need any input data and ignores its argument. For
│ │ │  <code class="inline">terminal_logger</code>, the internal state is not used. For <code class="inline">file_logger</code>, the
│ │ │ -internal state is used to save the open file descriptor.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="3714001683-1">(</span><span class="n">File</span><span class="p" data-group-id="3714001683-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3714001683-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="3714001683-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="3714001683-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="3714001683-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3714001683-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="3714001683-4">}</span><span class="p">.</span></code></pre><h2 id="notifying-about-events" class="section-heading">
│ │ │ +internal state is used to save the open file descriptor.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5735696408-1">(</span><span class="n">File</span><span class="p" data-group-id="5735696408-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5735696408-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5735696408-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="5735696408-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="5735696408-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5735696408-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5735696408-4">}</span><span class="p">.</span></code></pre><h2 id="notifying-about-events" class="section-heading">
│ │ │    <a href="#notifying-about-events" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Notifying about Events</span>
│ │ │  </h2>
│ │ │  <pre><code class="text">3&gt; gen_event:notify(error_man, no_reply).
│ │ │  ***Error*** no_reply
│ │ │  ok</code></pre><p><code class="inline">error_man</code> is the name of the event manager and <code class="inline">no_reply</code> is the event.</p><p>The event is made into a message and sent to the event manager. When the event
│ │ │  is received, the event manager calls <code class="inline">handle_event(Event, State)</code> for each
│ │ │  installed event handler, in the same order as they were added. The function is
│ │ │  expected to return a tuple <code class="inline">{ok,State1}</code>, where <code class="inline">State1</code> is a new value for the
│ │ │ -state of the event handler.</p><p>In <code class="inline">terminal_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="9335109682-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9335109682-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9335109682-2">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9335109682-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="9335109682-3">]</span><span class="p" data-group-id="9335109682-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9335109682-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9335109682-4">}</span><span class="p">.</span></code></pre><p>In <code class="inline">file_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="6319949549-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="6319949549-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6319949549-2">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6319949549-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="6319949549-3">]</span><span class="p" data-group-id="6319949549-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6319949549-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="6319949549-4">}</span><span class="p">.</span></code></pre><h2 id="deleting-an-event-handler" class="section-heading">
│ │ │ +state of the event handler.</p><p>In <code class="inline">terminal_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="3771238699-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3771238699-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3771238699-2">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3771238699-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="3771238699-3">]</span><span class="p" data-group-id="3771238699-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3771238699-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3771238699-4">}</span><span class="p">.</span></code></pre><p>In <code class="inline">file_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="0143967909-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="0143967909-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0143967909-2">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0143967909-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="0143967909-3">]</span><span class="p" data-group-id="0143967909-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0143967909-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="0143967909-4">}</span><span class="p">.</span></code></pre><h2 id="deleting-an-event-handler" class="section-heading">
│ │ │    <a href="#deleting-an-event-handler" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Deleting an Event Handler</span>
│ │ │  </h2>
│ │ │ -<pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">delete_handler</span><span class="p" data-group-id="5083199321-1">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5083199321-2">[</span><span class="p" data-group-id="5083199321-2">]</span><span class="p" data-group-id="5083199321-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">delete_handler</span><span class="p" data-group-id="5741429910-1">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5741429910-2">[</span><span class="p" data-group-id="5741429910-2">]</span><span class="p" data-group-id="5741429910-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>This function sends a message to the event manager registered as <code class="inline">error_man</code>,
│ │ │  telling it to delete the event handler <code class="inline">terminal_logger</code>. The event manager
│ │ │  calls the callback function <code class="inline">terminal_logger:terminate([], State)</code>, where the
│ │ │  argument <code class="inline">[]</code> is the third argument to <code class="inline">delete_handler</code>. <code class="inline">terminate/2</code> is to be
│ │ │  the opposite of <code class="inline">init/1</code> and do any necessary cleaning up. Its return value is
│ │ │ -ignored.</p><p>For <code class="inline">terminal_logger</code>, no cleaning up is necessary:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="9852572209-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="9852572209-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>For <code class="inline">file_logger</code>, the file descriptor opened in <code class="inline">init</code> must be closed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="2369347737-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2369347737-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2369347737-2">(</span><span class="n">Fd</span><span class="p" data-group-id="2369347737-2">)</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │ +ignored.</p><p>For <code class="inline">terminal_logger</code>, no cleaning up is necessary:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="5450583434-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="5450583434-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>For <code class="inline">file_logger</code>, the file descriptor opened in <code class="inline">init</code> must be closed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="4795058300-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="4795058300-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="4795058300-2">(</span><span class="n">Fd</span><span class="p" data-group-id="4795058300-2">)</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │    <a href="#stopping" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Stopping</span>
│ │ │  </h2>
│ │ │  <p>When an event manager is stopped, it gives each of the installed event handlers
│ │ │  the chance to clean up by calling <code class="inline">terminate/2</code>, the same way as when deleting a
│ │ │ @@ -249,33 +249,33 @@
│ │ │  this is done is defined by a <a href="sup_princ.html#shutdown">shutdown strategy</a> set in
│ │ │  the supervisor.</p><h3 id="standalone-event-managers" class="section-heading">
│ │ │    <a href="#standalone-event-managers" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Standalone Event Managers</span>
│ │ │  </h3>
│ │ │ -<p>An event manager can also be stopped by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="9789134441-1">(</span><span class="ss">error_man</span><span class="p" data-group-id="9789134441-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>An event manager can also be stopped by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="5533480919-1">(</span><span class="ss">error_man</span><span class="p" data-group-id="5533480919-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><h2 id="handling-other-messages" class="section-heading">
│ │ │    <a href="#handling-other-messages" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Handling Other Messages</span>
│ │ │  </h2>
│ │ │  <p>If the <code class="inline">gen_event</code> process is to be able to receive other messages
│ │ │  than events, the callback function <code class="inline">handle_info(Info, State)</code> must be
│ │ │  implemented to handle them. Examples of other messages are exit
│ │ │  messages if the event manager is linked to other processes than the
│ │ │  supervisor (for example via <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_event.html#add_sup_handler/3"><code class="inline">gen_event:add_sup_handler/3</code></a>) and is
│ │ │ -trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="6109064228-1">(</span><span class="p" data-group-id="6109064228-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="6109064228-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6109064228-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="0145308320-1">(</span><span class="p" data-group-id="0145308320-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="0145308320-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="0145308320-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Code to handle exits here.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6109064228-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="6109064228-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="0185330573-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="0185330573-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0145308320-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="0145308320-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="9141357524-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="9141357524-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Code to convert state (and more) during code change.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0185330573-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="0185330573-2">}</span><span class="p">.</span></code></pre>
│ │ │ +    </span><span class="p" data-group-id="9141357524-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="9141357524-2">}</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="statem.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/example.html
│ │ │ @@ -131,15 +131,15 @@
│ │ │  
│ │ │  int bar(int y) {
│ │ │    return y*2;
│ │ │  }</code></pre><p>The functions are deliberately kept as simple as possible, for readability
│ │ │  reasons.</p><p>From an Erlang perspective, it is preferable to be able to call <code class="inline">foo</code> and <code class="inline">bar</code>
│ │ │  without having to bother about that they are C functions:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% Erlang code</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="n">Res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">complex</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="9060260022-1">(</span><span class="n">X</span><span class="p" data-group-id="9060260022-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">complex</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="7671419743-1">(</span><span class="n">X</span><span class="p" data-group-id="7671419743-1">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Here, the communication with C is hidden in the implementation of <code class="inline">complex.erl</code>.
│ │ │  In the following sections, it is shown how this module can be implemented using
│ │ │  the different interoperability mechanisms.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/expressions.html
│ │ │ @@ -151,81 +151,81 @@
│ │ │  </span><span class="n">Phone_number</span><span class="w">
│ │ │  </span><span class="p">_</span><span class="w">
│ │ │  </span><span class="p">_</span><span class="n">Height</span><span class="w">
│ │ │  </span><span class="ss">name@node</span></code></pre><p>Variables are bound to values using <a href="patterns.html">pattern matching</a>. Erlang uses
│ │ │  <em>single assignment</em>, that is, a variable can only be bound once.</p><p>The <em>anonymous variable</em> is denoted by underscore (_) and can be used when a
│ │ │  variable is required but its value can be ignored.</p><p><em>Example:</em></p><pre><code class="text">[H|_] = [1,2,3]</code></pre><p>Variables starting with underscore (<code class="inline">_</code>), for example, <code class="inline">_Height</code>, are normal
│ │ │  variables, not anonymous. However, they are ignored by the compiler in the sense
│ │ │ -that they do not generate warnings.</p><p><em>Example:</em></p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="4055990536-1">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4055990536-2">[</span><span class="p" data-group-id="4055990536-2">]</span><span class="p" data-group-id="4055990536-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4055990536-3">[</span><span class="p" data-group-id="4055990536-3">]</span><span class="p">.</span></code></pre><p>can be rewritten to be more readable:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="9913391127-1">(</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9913391127-2">[</span><span class="p" data-group-id="9913391127-2">]</span><span class="p" data-group-id="9913391127-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9913391127-3">[</span><span class="p" data-group-id="9913391127-3">]</span><span class="p">.</span></code></pre><p>This causes a warning for an unused variable, <code class="inline">Elem</code>. To avoid the warning,
│ │ │ -the code can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="9691557791-1">(</span><span class="p">_</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9691557791-2">[</span><span class="p" data-group-id="9691557791-2">]</span><span class="p" data-group-id="9691557791-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9691557791-3">[</span><span class="p" data-group-id="9691557791-3">]</span><span class="p">.</span></code></pre><p>Notice that since variables starting with an underscore are not anonymous, the
│ │ │ -following example matches:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5021570040-1">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5021570040-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5021570040-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5021570040-2">}</span></code></pre><p>But this example fails:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8724286200-1">{</span><span class="p">_</span><span class="n">N</span><span class="p">,</span><span class="p">_</span><span class="n">N</span><span class="p" data-group-id="8724286200-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8724286200-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8724286200-2">}</span></code></pre><p>The scope for a variable is its function clause. Variables bound in a branch of
│ │ │ +that they do not generate warnings.</p><p><em>Example:</em></p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="8580772660-1">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8580772660-2">[</span><span class="p" data-group-id="8580772660-2">]</span><span class="p" data-group-id="8580772660-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8580772660-3">[</span><span class="p" data-group-id="8580772660-3">]</span><span class="p">.</span></code></pre><p>can be rewritten to be more readable:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="9954353462-1">(</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9954353462-2">[</span><span class="p" data-group-id="9954353462-2">]</span><span class="p" data-group-id="9954353462-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9954353462-3">[</span><span class="p" data-group-id="9954353462-3">]</span><span class="p">.</span></code></pre><p>This causes a warning for an unused variable, <code class="inline">Elem</code>. To avoid the warning,
│ │ │ +the code can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="9181309265-1">(</span><span class="p">_</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9181309265-2">[</span><span class="p" data-group-id="9181309265-2">]</span><span class="p" data-group-id="9181309265-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9181309265-3">[</span><span class="p" data-group-id="9181309265-3">]</span><span class="p">.</span></code></pre><p>Notice that since variables starting with an underscore are not anonymous, the
│ │ │ +following example matches:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5854594212-1">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5854594212-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5854594212-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5854594212-2">}</span></code></pre><p>But this example fails:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5916506663-1">{</span><span class="p">_</span><span class="n">N</span><span class="p">,</span><span class="p">_</span><span class="n">N</span><span class="p" data-group-id="5916506663-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5916506663-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5916506663-2">}</span></code></pre><p>The scope for a variable is its function clause. Variables bound in a branch of
│ │ │  an <code class="inline">if</code>, <code class="inline">case</code>, or <code class="inline">receive</code> expression must be bound in all branches to have a
│ │ │  value outside the expression. Otherwise they are regarded as unsafe outside
│ │ │  the expression.</p><p>For the <code class="inline">try</code> expression variable scoping is limited so that variables bound in
│ │ │  the expression are always unsafe outside the expression.</p><h2 id="patterns" class="section-heading">
│ │ │    <a href="#patterns" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Patterns</span>
│ │ │  </h2>
│ │ │  <p>A pattern has the same structure as a term but can contain unbound variables.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">Name1</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0182282624-1">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0182282624-1">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0182282624-2">{</span><span class="ss">error</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="0182282624-2">}</span></code></pre><p>Patterns are allowed in clause heads, <a href="expressions.html#case">case expressions</a>,
│ │ │ +</span><span class="p" data-group-id="2384424792-1">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2384424792-1">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2384424792-2">{</span><span class="ss">error</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="2384424792-2">}</span></code></pre><p>Patterns are allowed in clause heads, <a href="expressions.html#case">case expressions</a>,
│ │ │  <a href="expressions.html#receive">receive expressions</a>, and
│ │ │  <a href="expressions.html#the-match-operator">match expressions</a>.</p><h3 id="the-compound-pattern-operator" class="section-heading">
│ │ │    <a href="#the-compound-pattern-operator" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">The Compound Pattern Operator</span>
│ │ │  </h3>
│ │ │  <p>If <code class="inline">Pattern1</code> and <code class="inline">Pattern2</code> are valid patterns, the following is also a valid
│ │ │  pattern:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Pattern2</span></code></pre><p>When matched against a term, both <code class="inline">Pattern1</code> and <code class="inline">Pattern2</code> are matched against
│ │ │ -the term. The idea behind this feature is to avoid reconstruction of terms.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="5027556064-1">(</span><span class="p" data-group-id="5027556064-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="5027556064-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="5027556064-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Signal</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5027556064-3">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="5027556064-3">}</span><span class="p">,</span><span class="w">
│ │ │ +the term. The idea behind this feature is to avoid reconstruction of terms.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4538676827-1">(</span><span class="p" data-group-id="4538676827-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="4538676827-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="4538676827-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Signal</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4538676827-3">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="4538676827-3">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="5027556064-4">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="5027556064-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>can instead be written as</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="3204156531-1">(</span><span class="p" data-group-id="3204156531-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3204156531-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="3204156531-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="4538676827-4">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="4538676827-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>can instead be written as</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4497530579-1">(</span><span class="p" data-group-id="4497530579-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4497530579-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="4497530579-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="3204156531-3">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="3204156531-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="4497530579-3">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="4497530579-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>The compound pattern operator does not imply that its operands are matched in
│ │ │  any particular order. That means that it is not legal to bind a variable in
│ │ │  <code class="inline">Pattern1</code> and use it in <code class="inline">Pattern2</code>, or vice versa.</p><h3 id="string-prefix-in-patterns" class="section-heading">
│ │ │    <a href="#string-prefix-in-patterns" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">String Prefix in Patterns</span>
│ │ │  </h3>
│ │ │ -<p>When matching strings, the following is a valid pattern:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0416651898-1">(</span><span class="s">&quot;prefix&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="0416651898-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This is syntactic sugar for the equivalent, but harder to read:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="2070228849-1">(</span><span class="p" data-group-id="2070228849-2">[</span><span class="sc">$p</span><span class="p">,</span><span class="sc">$r</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$f</span><span class="p">,</span><span class="sc">$i</span><span class="p">,</span><span class="sc">$x</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="2070228849-2">]</span><span class="p" data-group-id="2070228849-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h3 id="expressions-in-patterns" class="section-heading">
│ │ │ +<p>When matching strings, the following is a valid pattern:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="3879183805-1">(</span><span class="s">&quot;prefix&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="3879183805-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This is syntactic sugar for the equivalent, but harder to read:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="3953478964-1">(</span><span class="p" data-group-id="3953478964-2">[</span><span class="sc">$p</span><span class="p">,</span><span class="sc">$r</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$f</span><span class="p">,</span><span class="sc">$i</span><span class="p">,</span><span class="sc">$x</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="3953478964-2">]</span><span class="p" data-group-id="3953478964-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h3 id="expressions-in-patterns" class="section-heading">
│ │ │    <a href="#expressions-in-patterns" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Expressions in Patterns</span>
│ │ │  </h3>
│ │ │  <p>An arithmetic expression can be used within a pattern if it meets both of the
│ │ │ -following two conditions:</p><ul><li>It uses only numeric or bitwise operators.</li><li>Its value can be evaluated to a constant when complied.</li></ul><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="p" data-group-id="8877553870-1">{</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8877553870-1">}</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8877553870-2">{</span><span class="o">?</span><span class="n">THRESHOLD</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="8877553870-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="the-match-operator" class="section-heading">
│ │ │ +following two conditions:</p><ul><li>It uses only numeric or bitwise operators.</li><li>Its value can be evaluated to a constant when complied.</li></ul><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="p" data-group-id="5421338100-1">{</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="5421338100-1">}</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5421338100-2">{</span><span class="o">?</span><span class="n">THRESHOLD</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="5421338100-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="the-match-operator" class="section-heading">
│ │ │    <a href="#the-match-operator" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">The Match Operator</span>
│ │ │  </h2>
│ │ │  <p>The following matches <code class="inline">Pattern</code> against <code class="inline">Expr</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>If the matching succeeds, any unbound variable in the pattern becomes bound and
│ │ │  the value of <code class="inline">Expr</code> is returned.</p><p>If multiple match operators are applied in sequence, they will be evaluated from
│ │ │ -right to left.</p><p>If the matching fails, a <code class="inline">badmatch</code> run-time error occurs.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8102592906-1">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="8102592906-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8102592906-2">{</span><span class="ss">answer</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="8102592906-2">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8102592906-3">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="8102592906-3">}</span><span class="gp unselectable">
│ │ │ +right to left.</p><p>If the matching fails, a <code class="inline">badmatch</code> run-time error occurs.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6354700746-1">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="6354700746-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6354700746-2">{</span><span class="ss">answer</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="6354700746-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6354700746-3">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6354700746-3">}</span><span class="gp unselectable">
│ │ │  2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">answer</span><span class="gp unselectable">
│ │ │  3&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span><span class="gp unselectable">
│ │ │  4&gt; </span><span class="n">T</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8102592906-4">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="8102592906-4">}</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="p" data-group-id="8102592906-5">{</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="8102592906-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8102592906-6">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8102592906-6">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6354700746-4">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6354700746-4">}</span><span class="gp unselectable">
│ │ │ +5&gt; </span><span class="p" data-group-id="6354700746-5">{</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="6354700746-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6354700746-6">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6354700746-6">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right-hand side value [1,2]</span></code></pre><p>Because multiple match operators are evaluated from right to left, it means
│ │ │  that:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Pattern2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PatternN</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expression</span></code></pre><p>is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="n">Temporary</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expression</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="n">PatternN</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Temporary</span><span class="p">,</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="n">Pattern2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Temporary</span><span class="p">,</span><span class="w">
│ │ │ @@ -239,30 +239,30 @@
│ │ │  can safely be skipped on a first reading.</p></section><p>The <code class="inline">=</code> character is used to denote two similar but distinct operators: the
│ │ │  match operator and the compound pattern operator. Which one is meant is
│ │ │  determined by context.</p><p>The <em>compound pattern operator</em> is used to construct a compound pattern from two
│ │ │  patterns. Compound patterns are accepted everywhere a pattern is accepted. A
│ │ │  compound pattern matches if all of its constituent patterns match. It is not
│ │ │  legal for a pattern that is part of a compound pattern to use variables (as keys
│ │ │  in map patterns or sizes in binary patterns) bound in other sub patterns of the
│ │ │ -same compound pattern.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">fun</span><span class="p" data-group-id="9506917054-1">(</span><span class="p" data-group-id="9506917054-2">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="9506917054-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9506917054-3">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9506917054-3">}</span><span class="p" data-group-id="9506917054-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +same compound pattern.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">fun</span><span class="p" data-group-id="7107078567-1">(</span><span class="p" data-group-id="7107078567-2">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="7107078567-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7107078567-3">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="7107078567-3">}</span><span class="p" data-group-id="7107078567-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">* 1:7: variable &#39;Key&#39; is unbound</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9506917054-4">(</span><span class="p" data-group-id="9506917054-5">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9506917054-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">E</span><span class="p" data-group-id="9506917054-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9506917054-6">{</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9506917054-6">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="9506917054-7">(</span><span class="p" data-group-id="9506917054-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9506917054-8">}</span><span class="p" data-group-id="9506917054-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9506917054-9">{</span><span class="p" data-group-id="9506917054-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9506917054-10">}</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9506917054-9">}</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="n">G</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9506917054-11">(</span><span class="p" data-group-id="9506917054-12">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">B</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="9506917054-12">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9506917054-13">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="9506917054-13">&gt;&gt;</span><span class="p" data-group-id="9506917054-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9506917054-14">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="9506917054-14">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">G</span><span class="p" data-group-id="9506917054-15">(</span><span class="p" data-group-id="9506917054-16">&lt;&lt;</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p" data-group-id="9506917054-16">&gt;&gt;</span><span class="p" data-group-id="9506917054-15">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9506917054-17">{</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p">,</span><span class="mi">10795</span><span class="p" data-group-id="9506917054-17">}</span></code></pre><p>The <em>match operator</em> is allowed everywhere an expression is allowed. It is used
│ │ │ +2&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="7107078567-4">(</span><span class="p" data-group-id="7107078567-5">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="7107078567-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">E</span><span class="p" data-group-id="7107078567-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7107078567-6">{</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="7107078567-6">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="7107078567-7">(</span><span class="p" data-group-id="7107078567-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7107078567-8">}</span><span class="p" data-group-id="7107078567-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7107078567-9">{</span><span class="p" data-group-id="7107078567-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7107078567-10">}</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7107078567-9">}</span><span class="gp unselectable">
│ │ │ +3&gt; </span><span class="n">G</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="7107078567-11">(</span><span class="p" data-group-id="7107078567-12">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">B</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="7107078567-12">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7107078567-13">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7107078567-13">&gt;&gt;</span><span class="p" data-group-id="7107078567-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7107078567-14">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="7107078567-14">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">G</span><span class="p" data-group-id="7107078567-15">(</span><span class="p" data-group-id="7107078567-16">&lt;&lt;</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p" data-group-id="7107078567-16">&gt;&gt;</span><span class="p" data-group-id="7107078567-15">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7107078567-17">{</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p">,</span><span class="mi">10795</span><span class="p" data-group-id="7107078567-17">}</span></code></pre><p>The <em>match operator</em> is allowed everywhere an expression is allowed. It is used
│ │ │  to match the value of an expression to a pattern. If multiple match operators
│ │ │ -are applied in sequence, they will be evaluated from right to left.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5071792036-1">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="5071792036-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5071792036-2">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="5071792036-2">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nf">f</span><span class="p" data-group-id="5071792036-3">(</span><span class="n">Key</span><span class="p" data-group-id="5071792036-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5071792036-4">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="5071792036-4">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5071792036-5">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="5071792036-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ +are applied in sequence, they will be evaluated from right to left.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2897037114-1">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="2897037114-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2897037114-2">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="2897037114-2">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nf">f</span><span class="p" data-group-id="2897037114-3">(</span><span class="n">Key</span><span class="p" data-group-id="2897037114-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2897037114-4">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="2897037114-4">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2897037114-5">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="2897037114-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">value</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nf">f</span><span class="p" data-group-id="5071792036-6">(</span><span class="n">Key</span><span class="p" data-group-id="5071792036-6">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5071792036-7">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="5071792036-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5071792036-8">(</span><span class="p" data-group-id="5071792036-9">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="5071792036-9">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p" data-group-id="5071792036-8">)</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nf">f</span><span class="p" data-group-id="2897037114-6">(</span><span class="n">Key</span><span class="p" data-group-id="2897037114-6">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2897037114-7">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="2897037114-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2897037114-8">(</span><span class="p" data-group-id="2897037114-9">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="2897037114-9">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p" data-group-id="2897037114-8">)</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">value</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nf">f</span><span class="p" data-group-id="5071792036-10">(</span><span class="n">Key</span><span class="p" data-group-id="5071792036-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5071792036-11">(</span><span class="p" data-group-id="5071792036-12">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="5071792036-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5071792036-13">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="5071792036-13">}</span><span class="p" data-group-id="5071792036-11">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="nf">f</span><span class="p" data-group-id="2897037114-10">(</span><span class="n">Key</span><span class="p" data-group-id="2897037114-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2897037114-11">(</span><span class="p" data-group-id="2897037114-12">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="2897037114-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2897037114-13">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="2897037114-13">}</span><span class="p" data-group-id="2897037114-11">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">* 1:12: variable &#39;Key&#39; is unbound</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="p" data-group-id="5071792036-14">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">Y</span><span class="p" data-group-id="5071792036-14">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">begin</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5071792036-15">&lt;&lt;</span><span class="mi">42</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="5071792036-15">&gt;&gt;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="p" data-group-id="2897037114-14">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">Y</span><span class="p" data-group-id="2897037114-14">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">begin</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2897037114-15">&lt;&lt;</span><span class="mi">42</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="2897037114-15">&gt;&gt;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span></code></pre><p>The expression at prompt <code class="inline">2&gt;</code> first matches the value of variable <code class="inline">M</code> against
│ │ │  pattern <code class="inline">#{key := Key}</code>, binding variable <code class="inline">Key</code>. It then matches the value of
│ │ │  <code class="inline">M</code> against pattern <code class="inline">#{Key := Value}</code> using variable <code class="inline">Key</code> as the key, binding
│ │ │  variable <code class="inline">Value</code>.</p><p>The expression at prompt <code class="inline">3&gt;</code> matches expression <code class="inline">(#{key := Key} = M)</code> against
│ │ │  pattern <code class="inline">#{Key := Value}</code>. The expression inside the parentheses is evaluated
│ │ │  first. That is, <code class="inline">M</code> is matched against <code class="inline">#{key := Key}</code>, and then the value of
│ │ │  <code class="inline">M</code> is matched against pattern <code class="inline">#{Key := Value}</code>. That is the same evaluation
│ │ │ @@ -276,30 +276,30 @@
│ │ │  binding variable <code class="inline">Y</code> and creating a binary. The binary is then matched against
│ │ │  pattern <code class="inline">&lt;&lt;X:Y&gt;&gt;</code> using the value of <code class="inline">Y</code> as the size of the segment.</p><h2 id="function-calls" class="section-heading">
│ │ │    <a href="#function-calls" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Function Calls</span>
│ │ │  </h2>
│ │ │ -<pre><code class="makeup erlang" translate="no"><span class="n">ExprF</span><span class="p" data-group-id="7971750651-1">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="7971750651-1">)</span><span class="w">
│ │ │ -</span><span class="n">ExprM</span><span class="p">:</span><span class="n">ExprF</span><span class="p" data-group-id="7971750651-2">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="7971750651-2">)</span></code></pre><p>In the first form of function calls, <code class="inline">ExprM:ExprF(Expr1,...,ExprN)</code>, each of
│ │ │ +<pre><code class="makeup erlang" translate="no"><span class="n">ExprF</span><span class="p" data-group-id="3409274523-1">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="3409274523-1">)</span><span class="w">
│ │ │ +</span><span class="n">ExprM</span><span class="p">:</span><span class="n">ExprF</span><span class="p" data-group-id="3409274523-2">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="3409274523-2">)</span></code></pre><p>In the first form of function calls, <code class="inline">ExprM:ExprF(Expr1,...,ExprN)</code>, each of
│ │ │  <code class="inline">ExprM</code> and <code class="inline">ExprF</code> must be an atom or an expression that evaluates to an atom.
│ │ │  The function is said to be called by using the <em>fully qualified function name</em>.
│ │ │ -This is often referred to as a <em>remote</em> or <em>external function call</em>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="6871940177-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6871940177-1">)</span></code></pre><p>In the second form of function calls, <code class="inline">ExprF(Expr1,...,ExprN)</code>, <code class="inline">ExprF</code> must be
│ │ │ +This is often referred to as a <em>remote</em> or <em>external function call</em>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="6256455524-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6256455524-1">)</span></code></pre><p>In the second form of function calls, <code class="inline">ExprF(Expr1,...,ExprN)</code>, <code class="inline">ExprF</code> must be
│ │ │  an atom or evaluate to a fun.</p><p>If <code class="inline">ExprF</code> is an atom, the function is said to be called by using the
│ │ │  <em>implicitly qualified function name</em>. If the function <code class="inline">ExprF</code> is locally
│ │ │  defined, it is called. Alternatively, if <code class="inline">ExprF</code> is explicitly imported from the
│ │ │  <code class="inline">M</code> module, <code class="inline">M:ExprF(Expr1,...,ExprN)</code> is called. If <code class="inline">ExprF</code> is neither declared
│ │ │  locally nor explicitly imported, <code class="inline">ExprF</code> must be the name of an automatically
│ │ │ -imported BIF.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="5414699261-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5414699261-1">)</span><span class="w">
│ │ │ -</span><span class="nf">spawn</span><span class="p" data-group-id="5414699261-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5414699261-3">[</span><span class="p" data-group-id="5414699261-3">]</span><span class="p" data-group-id="5414699261-2">)</span></code></pre><p><em>Examples</em> where <code class="inline">ExprF</code> is a fun:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3540335479-1">(</span><span class="n">X</span><span class="p" data-group-id="3540335479-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Fun1</span><span class="p" data-group-id="3540335479-2">(</span><span class="mi">3</span><span class="p" data-group-id="3540335479-2">)</span><span class="p">.</span><span class="w">
│ │ │ +imported BIF.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="9467055202-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9467055202-1">)</span><span class="w">
│ │ │ +</span><span class="nf">spawn</span><span class="p" data-group-id="9467055202-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9467055202-3">[</span><span class="p" data-group-id="9467055202-3">]</span><span class="p" data-group-id="9467055202-2">)</span></code></pre><p><em>Examples</em> where <code class="inline">ExprF</code> is a fun:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4807002426-1">(</span><span class="n">X</span><span class="p" data-group-id="4807002426-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Fun1</span><span class="p" data-group-id="4807002426-2">(</span><span class="mi">3</span><span class="p" data-group-id="4807002426-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="k">fun</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="ss">append</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3540335479-3">(</span><span class="p" data-group-id="3540335479-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3540335479-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3540335479-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3540335479-5">]</span><span class="p" data-group-id="3540335479-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3540335479-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3540335479-6">]</span><span class="w">
│ │ │ +2&gt; </span><span class="k">fun</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="ss">append</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4807002426-3">(</span><span class="p" data-group-id="4807002426-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4807002426-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4807002426-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4807002426-5">]</span><span class="p" data-group-id="4807002426-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4807002426-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4807002426-6">]</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="o">&gt;</span></code></pre><p>Notice that when calling a local function, there is a difference between using
│ │ │  the implicitly or fully qualified function name. The latter always refers to the
│ │ │  latest version of the module. See
│ │ │  <a href="code_loading.html">Compilation and Code Loading </a>and
│ │ │  <a href="ref_man_functions.html#eval">Function Evaluation</a>.</p><h3 id="local-function-names-clashing-with-auto-imported-bifs" class="section-heading">
│ │ │    <a href="#local-function-names-clashing-with-auto-imported-bifs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -316,40 +316,40 @@
│ │ │  called instead. This is to avoid that future additions to the set of
│ │ │  auto-imported BIFs do not silently change the behavior of old code.</p></section><p>However, to avoid that old (pre R14) code changed its behavior when compiled
│ │ │  with Erlang/OTP version R14A or later, the following restriction applies: If you
│ │ │  override the name of a BIF that was auto-imported in OTP versions prior to R14A
│ │ │  (ERTS version 5.8) and have an implicitly qualified call to that function in
│ │ │  your code, you either need to explicitly remove the auto-import using a compiler
│ │ │  directive, or replace the call with a fully qualified function call. Otherwise
│ │ │ -you get a compilation error. See the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8381895037-1">(</span><span class="p" data-group-id="8381895037-2">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8381895037-2">]</span><span class="p" data-group-id="8381895037-1">)</span><span class="p">.</span><span class="w">
│ │ │ +you get a compilation error. See the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0551747865-1">(</span><span class="p" data-group-id="0551747865-2">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0551747865-2">]</span><span class="p" data-group-id="0551747865-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="8381895037-3">(</span><span class="p" data-group-id="8381895037-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="8381895037-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8381895037-5">]</span><span class="p" data-group-id="8381895037-4">}</span><span class="p" data-group-id="8381895037-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="0551747865-3">(</span><span class="p" data-group-id="0551747865-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="0551747865-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0551747865-5">]</span><span class="p" data-group-id="0551747865-4">}</span><span class="p" data-group-id="0551747865-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">length</span><span class="p" data-group-id="8381895037-6">(</span><span class="p" data-group-id="8381895037-7">[</span><span class="p" data-group-id="8381895037-7">]</span><span class="p" data-group-id="8381895037-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">length</span><span class="p" data-group-id="0551747865-6">(</span><span class="p" data-group-id="0551747865-7">[</span><span class="p" data-group-id="0551747865-7">]</span><span class="p" data-group-id="0551747865-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">length</span><span class="p" data-group-id="8381895037-8">(</span><span class="p" data-group-id="8381895037-9">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8381895037-9">]</span><span class="p" data-group-id="8381895037-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8381895037-10">(</span><span class="n">T</span><span class="p" data-group-id="8381895037-10">)</span><span class="p">.</span><span class="w"> </span><span class="c1">%% Calls the local function length/1</span><span class="w">
│ │ │ +</span><span class="nf">length</span><span class="p" data-group-id="0551747865-8">(</span><span class="p" data-group-id="0551747865-9">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0551747865-9">]</span><span class="p" data-group-id="0551747865-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0551747865-10">(</span><span class="n">T</span><span class="p" data-group-id="0551747865-10">)</span><span class="p">.</span><span class="w"> </span><span class="c1">%% Calls the local function length/1</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="8381895037-11">(</span><span class="n">X</span><span class="p" data-group-id="8381895037-11">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="8381895037-12">(</span><span class="n">X</span><span class="p" data-group-id="8381895037-12">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="0551747865-11">(</span><span class="n">X</span><span class="p" data-group-id="0551747865-11">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="0551747865-12">(</span><span class="n">X</span><span class="p" data-group-id="0551747865-12">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │                                    </span><span class="c1">%% which is allowed in guards</span><span class="w">
│ │ │      </span><span class="ss">long</span><span class="p">.</span></code></pre><p>The same logic applies to explicitly imported functions from other modules, as
│ │ │  to locally defined functions. It is not allowed to both import a function from
│ │ │ -another module and have the function declared in the module at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8401554511-1">(</span><span class="p" data-group-id="8401554511-2">[</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8401554511-2">]</span><span class="p" data-group-id="8401554511-1">)</span><span class="p">.</span><span class="w">
│ │ │ +another module and have the function declared in the module at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7878411166-1">(</span><span class="p" data-group-id="7878411166-2">[</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7878411166-2">]</span><span class="p" data-group-id="7878411166-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="8401554511-3">(</span><span class="p" data-group-id="8401554511-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="8401554511-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8401554511-5">]</span><span class="p" data-group-id="8401554511-4">}</span><span class="p" data-group-id="8401554511-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="7878411166-3">(</span><span class="p" data-group-id="7878411166-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="7878411166-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7878411166-5">]</span><span class="p" data-group-id="7878411166-4">}</span><span class="p" data-group-id="7878411166-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="8401554511-6">(</span><span class="ss">mod</span><span class="p">,</span><span class="p" data-group-id="8401554511-7">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8401554511-7">]</span><span class="p" data-group-id="8401554511-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="7878411166-6">(</span><span class="ss">mod</span><span class="p">,</span><span class="p" data-group-id="7878411166-7">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7878411166-7">]</span><span class="p" data-group-id="7878411166-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="8401554511-8">(</span><span class="n">X</span><span class="p" data-group-id="8401554511-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="8401554511-9">(</span><span class="n">X</span><span class="p" data-group-id="8401554511-9">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">33</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="7878411166-8">(</span><span class="n">X</span><span class="p" data-group-id="7878411166-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="7878411166-9">(</span><span class="n">X</span><span class="p" data-group-id="7878411166-9">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">33</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │                                     </span><span class="c1">%% which is allowed in guards</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="8401554511-10">(</span><span class="n">X</span><span class="p" data-group-id="8401554511-10">)</span><span class="p">;</span><span class="w">              </span><span class="c1">%% Explicit call to erlang:length in body</span><span class="w">
│ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="7878411166-10">(</span><span class="n">X</span><span class="p" data-group-id="7878411166-10">)</span><span class="p">;</span><span class="w">              </span><span class="c1">%% Explicit call to erlang:length in body</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="8401554511-11">(</span><span class="n">X</span><span class="p" data-group-id="8401554511-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">length</span><span class="p" data-group-id="8401554511-12">(</span><span class="n">X</span><span class="p" data-group-id="8401554511-12">)</span><span class="p">.</span><span class="w">                     </span><span class="c1">%% mod:length/1 is called</span></code></pre><p>For auto-imported BIFs added in Erlang/OTP R14A and thereafter, overriding the
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="7878411166-11">(</span><span class="n">X</span><span class="p" data-group-id="7878411166-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">length</span><span class="p" data-group-id="7878411166-12">(</span><span class="n">X</span><span class="p" data-group-id="7878411166-12">)</span><span class="p">.</span><span class="w">                     </span><span class="c1">%% mod:length/1 is called</span></code></pre><p>For auto-imported BIFs added in Erlang/OTP R14A and thereafter, overriding the
│ │ │  name with a local function or explicit import is always allowed. However, if the
│ │ │  <code class="inline">-compile({no_auto_import,[F/A])</code> directive is not used, the compiler issues a
│ │ │  warning whenever the function is called in the module using the implicitly
│ │ │  qualified function name.</p><h2 id="if" class="section-heading">
│ │ │    <a href="#if" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -361,40 +361,40 @@
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">GuardSeqN</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The branches of an <code class="inline">if</code>-expression are scanned sequentially until a guard
│ │ │  sequence <code class="inline">GuardSeq</code> that evaluates to true is found. Then the corresponding
│ │ │  <code class="inline">Body</code> (a sequence of expressions separated by <code class="inline">,</code>) is evaluated.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">if</code> expression.</p><p>If no guard sequence is evaluated as true, an <code class="inline">if_clause</code> run-time error occurs.
│ │ │  If necessary, the guard expression <code class="inline">true</code> can be used in the last branch, as
│ │ │ -that guard sequence is always true.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_greater_than</span><span class="p" data-group-id="9562393242-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9562393242-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +that guard sequence is always true.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_greater_than</span><span class="p" data-group-id="5593680301-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5593680301-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% works as an &#39;else&#39; branch</span><span class="w">
│ │ │              </span><span class="ss">false</span><span class="w">
│ │ │      </span><span class="k">end</span></code></pre><h2 id="case" class="section-heading">
│ │ │    <a href="#case" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Case</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">Expr</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="9476292349-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9476292349-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="9472239635-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9472239635-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="9476292349-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="9476292349-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="9472239635-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="9472239635-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The expression <code class="inline">Expr</code> is evaluated and the patterns <code class="inline">Pattern</code> are sequentially
│ │ │  matched against the result. If a match succeeds and the optional guard sequence
│ │ │  <code class="inline">GuardSeq</code> is true, the corresponding <code class="inline">Body</code> is evaluated.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">case</code> expression.</p><p>If there is no matching pattern with a true guard sequence, a <code class="inline">case_clause</code>
│ │ │ -run-time error occurs.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_valid_signal</span><span class="p" data-group-id="0260685266-1">(</span><span class="n">Signal</span><span class="p" data-group-id="0260685266-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +run-time error occurs.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_valid_signal</span><span class="p" data-group-id="5675981438-1">(</span><span class="n">Signal</span><span class="p" data-group-id="5675981438-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Signal</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0260685266-2">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="0260685266-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5675981438-2">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="5675981438-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0260685266-3">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="0260685266-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5675981438-3">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="5675981438-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">_</span><span class="n">Else</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">false</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="maybe" class="section-heading">
│ │ │    <a href="#maybe" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -412,57 +412,57 @@
│ │ │  the top-level of a <code class="inline">maybe</code> block. It matches the pattern <code class="inline">Expr1</code> against
│ │ │  <code class="inline">Expr2</code>. If the matching succeeds, any unbound variable in the pattern becomes
│ │ │  bound. If the expression is the last expression in the <code class="inline">maybe</code> block, it also
│ │ │  returns the value of <code class="inline">Expr2</code>. If the matching is unsuccessful, the rest of the
│ │ │  expressions in the <code class="inline">maybe</code> block are skipped and the return value of the <code class="inline">maybe</code>
│ │ │  block is <code class="inline">Expr2</code>.</p><p>None of the variables bound in a <code class="inline">maybe</code> block must be used in the code that
│ │ │  follows the block.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5757920145-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="5757920145-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="5757920145-2">(</span><span class="p" data-group-id="5757920145-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3965142415-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="3965142415-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="3965142415-2">(</span><span class="p" data-group-id="3965142415-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5757920145-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="5757920145-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="5757920145-4">(</span><span class="p" data-group-id="5757920145-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3965142415-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="3965142415-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="3965142415-4">(</span><span class="p" data-group-id="3965142415-4">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>Let us first assume that <code class="inline">a()</code> returns <code class="inline">{ok,42}</code> and <code class="inline">b()</code> returns <code class="inline">{ok,58}</code>.
│ │ │  With those return values, all of the match operators will succeed, and the
│ │ │  return value of the <code class="inline">maybe</code> block is <code class="inline">A + B</code>, which is equal to <code class="inline">42 + 58 = 100</code>.</p><p>Now let us assume that <code class="inline">a()</code> returns <code class="inline">error</code>. The conditional match operator in
│ │ │  <code class="inline">{ok, A} ?= a()</code> fails to match, and the return value of the <code class="inline">maybe</code> block is
│ │ │  the value of the expression that failed to match, namely <code class="inline">error</code>. Similarly, if
│ │ │  <code class="inline">b()</code> returns <code class="inline">wrong</code>, the return value of the <code class="inline">maybe</code> block is <code class="inline">wrong</code>.</p><p>Finally, let us assume that <code class="inline">a()</code> returns <code class="inline">{ok,-1}</code>. Because <code class="inline">true = A &gt;= 0</code> uses
│ │ │  the match operator <code class="inline">=</code>, a <code class="inline">{badmatch,false}</code> run-time error occurs when the
│ │ │ -expression fails to match the pattern.</p><p>The example can be written in a less succient way using nested case expressions:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="7204400394-1">(</span><span class="p" data-group-id="7204400394-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7204400394-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="7204400394-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +expression fails to match the pattern.</p><p>The example can be written in a less succient way using nested case expressions:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="1689369347-1">(</span><span class="p" data-group-id="1689369347-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1689369347-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="1689369347-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="7204400394-3">(</span><span class="p" data-group-id="7204400394-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="7204400394-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="7204400394-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="1689369347-3">(</span><span class="p" data-group-id="1689369347-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="1689369347-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="1689369347-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="n">Other1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Other1</span><span class="w">
│ │ │          </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Other2</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Other2</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">maybe</code> block can be augmented with <code class="inline">else</code> clauses:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │      </span><span class="n">Expr1</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">ExprN</span><span class="w">
│ │ │  </span><span class="k">else</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="3752605130-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="3752605130-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="4513192329-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="4513192329-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="3752605130-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="3752605130-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="4513192329-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="4513192329-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>If a conditional match operator fails, the failed expression is matched against
│ │ │  the patterns in all clauses between the <code class="inline">else</code> and <code class="inline">end</code> keywords. If a match
│ │ │  succeeds and the optional guard sequence <code class="inline">GuardSeq</code> is true, the corresponding
│ │ │  <code class="inline">Body</code> is evaluated. The value returned from the body is the return value of the
│ │ │  <code class="inline">maybe</code> block.</p><p>If there is no matching pattern with a true guard sequence, an <code class="inline">else_clause</code>
│ │ │  run-time error occurs.</p><p>None of the variables bound in a <code class="inline">maybe</code> block must be used in the <code class="inline">else</code>
│ │ │  clauses. None of the variables bound in the <code class="inline">else</code> clauses must be used in the
│ │ │  code that follows the <code class="inline">maybe</code> block.</p><p>Here is the previous example augmented with <code class="inline">else</code> clauses:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5262679087-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="5262679087-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="5262679087-2">(</span><span class="p" data-group-id="5262679087-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8951892397-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="8951892397-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="8951892397-2">(</span><span class="p" data-group-id="8951892397-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5262679087-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="5262679087-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="5262679087-4">(</span><span class="p" data-group-id="5262679087-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8951892397-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="8951892397-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="8951892397-4">(</span><span class="p" data-group-id="8951892397-4">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="w">
│ │ │  </span><span class="k">else</span><span class="w">
│ │ │      </span><span class="ss">error</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">wrong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">else</code> clauses translate the failing value from the conditional match
│ │ │  operators to the value <code class="inline">error</code>. If the failing value is not one of the
│ │ │  recognized values, a <code class="inline">else_clause</code> run-time error occurs.</p><h2 id="send" class="section-heading">
│ │ │ @@ -481,75 +481,75 @@
│ │ │  <code class="inline">{Name,Node}</code> (or a pid located at another node), also never fails.</li></ul><h2 id="receive" class="section-heading">
│ │ │    <a href="#receive" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Receive</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="5125324906-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="5125324906-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="6743173063-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="6743173063-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="5125324906-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="5125324906-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="6743173063-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="6743173063-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>Fetches a received message present in the message queue of the process. The
│ │ │  first message in the message queue is matched sequentially against the patterns
│ │ │  from top to bottom. If no match was found, the matching sequence is repeated for
│ │ │  the second message in the queue, and so on. Messages are queued in the
│ │ │  <a href="ref_man_processes.html#message-queue-order">order they were received</a>. If a match
│ │ │  succeeds, that is, if the <code class="inline">Pattern</code> matches and the optional guard sequence
│ │ │  <code class="inline">GuardSeq</code> is true, then the message is removed from the message queue and the
│ │ │  corresponding <code class="inline">Body</code> is evaluated. All other messages in the message queue
│ │ │  remain unchanged.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">receive</code> expression.</p><p><code class="inline">receive</code> never fails. The execution is suspended, possibly indefinitely, until
│ │ │  a message arrives that matches one of the patterns and with a true guard
│ │ │ -sequence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="9013926550-1">(</span><span class="p" data-group-id="9013926550-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +sequence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="2060826820-1">(</span><span class="p" data-group-id="2060826820-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">onhook</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="9013926550-2">(</span><span class="p" data-group-id="9013926550-2">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">idle</span><span class="p" data-group-id="9013926550-3">(</span><span class="p" data-group-id="9013926550-3">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9013926550-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9013926550-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9013926550-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9013926550-6">(</span><span class="p" data-group-id="9013926550-6">)</span><span class="p" data-group-id="9013926550-5">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="9013926550-7">(</span><span class="p" data-group-id="9013926550-7">)</span><span class="w">
│ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="2060826820-2">(</span><span class="p" data-group-id="2060826820-2">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">idle</span><span class="p" data-group-id="2060826820-3">(</span><span class="p" data-group-id="2060826820-3">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2060826820-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2060826820-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2060826820-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2060826820-6">(</span><span class="p" data-group-id="2060826820-6">)</span><span class="p" data-group-id="2060826820-5">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="2060826820-7">(</span><span class="p" data-group-id="2060826820-7">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">receive</code> expression can be augmented with a timeout:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="3117529563-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="3117529563-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="8033153822-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="8033153822-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="3117529563-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="3117529563-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="8033153822-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="8033153822-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">after</span><span class="w">
│ │ │      </span><span class="n">ExprT</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyT</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p><code class="inline">receive...after</code> works exactly as <code class="inline">receive</code>, except that if no matching message
│ │ │  has arrived within <code class="inline">ExprT</code> milliseconds, then <code class="inline">BodyT</code> is evaluated instead. The
│ │ │  return value of <code class="inline">BodyT</code> then becomes the return value of the <code class="inline">receive...after</code>
│ │ │  expression. <code class="inline">ExprT</code> is to evaluate to an integer, or the atom <code class="inline">infinity</code>. The
│ │ │  allowed integer range is from 0 to 4294967295, that is, the longest possible
│ │ │  timeout is almost 50 days. With a zero value the timeout occurs immediately if
│ │ │  there is no matching message in the message queue.</p><p>The atom <code class="inline">infinity</code> will make the process wait indefinitely for a matching
│ │ │  message. This is the same as not using a timeout. It can be useful for timeout
│ │ │ -values that are calculated at runtime.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="4259555035-1">(</span><span class="p" data-group-id="4259555035-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +values that are calculated at runtime.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="0236847143-1">(</span><span class="p" data-group-id="0236847143-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">onhook</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="4259555035-2">(</span><span class="p" data-group-id="4259555035-2">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">idle</span><span class="p" data-group-id="4259555035-3">(</span><span class="p" data-group-id="4259555035-3">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4259555035-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4259555035-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4259555035-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4259555035-6">(</span><span class="p" data-group-id="4259555035-6">)</span><span class="p" data-group-id="4259555035-5">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="4259555035-7">(</span><span class="p" data-group-id="4259555035-7">)</span><span class="w">
│ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="0236847143-2">(</span><span class="p" data-group-id="0236847143-2">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">idle</span><span class="p" data-group-id="0236847143-3">(</span><span class="p" data-group-id="0236847143-3">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0236847143-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="0236847143-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0236847143-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0236847143-6">(</span><span class="p" data-group-id="0236847143-6">)</span><span class="p" data-group-id="0236847143-5">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="0236847143-7">(</span><span class="p" data-group-id="0236847143-7">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w">
│ │ │          </span><span class="mi">60000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="4259555035-8">(</span><span class="p" data-group-id="4259555035-8">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">error</span><span class="p" data-group-id="4259555035-9">(</span><span class="p" data-group-id="4259555035-9">)</span><span class="w">
│ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="0236847143-8">(</span><span class="p" data-group-id="0236847143-8">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">error</span><span class="p" data-group-id="0236847143-9">(</span><span class="p" data-group-id="0236847143-9">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>It is legal to use a <code class="inline">receive...after</code> expression with no branches:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │  </span><span class="k">after</span><span class="w">
│ │ │      </span><span class="n">ExprT</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyT</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>This construction does not consume any messages, only suspends execution in the
│ │ │ -process for <code class="inline">ExprT</code> milliseconds. This can be used to implement simple timers.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">timer</span><span class="p" data-group-id="9118101166-1">(</span><span class="p" data-group-id="9118101166-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9118101166-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9118101166-3">[</span><span class="nf">self</span><span class="p" data-group-id="9118101166-4">(</span><span class="p" data-group-id="9118101166-4">)</span><span class="p" data-group-id="9118101166-3">]</span><span class="p" data-group-id="9118101166-2">)</span><span class="p">.</span><span class="w">
│ │ │ +process for <code class="inline">ExprT</code> milliseconds. This can be used to implement simple timers.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">timer</span><span class="p" data-group-id="4852125327-1">(</span><span class="p" data-group-id="4852125327-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="4852125327-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4852125327-3">[</span><span class="nf">self</span><span class="p" data-group-id="4852125327-4">(</span><span class="p" data-group-id="4852125327-4">)</span><span class="p" data-group-id="4852125327-3">]</span><span class="p" data-group-id="4852125327-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">timer</span><span class="p" data-group-id="9118101166-5">(</span><span class="n">Pid</span><span class="p" data-group-id="9118101166-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">timer</span><span class="p" data-group-id="4852125327-5">(</span><span class="n">Pid</span><span class="p" data-group-id="4852125327-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w">
│ │ │          </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">timeout</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>For more information on timers in Erlang in general, see the
│ │ │  <a href="../../erts-15.2.7/doc/html/time_correction.html#timers"><em>Timers</em></a> section of the
│ │ │  <a href="../../erts-15.2.7/doc/html/time_correction.html"><em>Time and Time Correction in Erlang</em></a>
│ │ │ @@ -591,21 +591,21 @@
│ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │  4&gt; </span><span class="mf">0.0</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">-</span><span class="mf">0.0</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │  5&gt; </span><span class="mf">0.0</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">+</span><span class="mf">0.0</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │  6&gt; </span><span class="mi">1</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ -7&gt; </span><span class="p" data-group-id="9733218406-1">#{</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="9733218406-1">}</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="9733218406-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9733218406-2">}</span><span class="p">.</span><span class="w">
│ │ │ +7&gt; </span><span class="p" data-group-id="8433803041-1">#{</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8433803041-1">}</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="8433803041-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8433803041-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ -8&gt; </span><span class="p" data-group-id="9733218406-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9733218406-3">}</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="p" data-group-id="9733218406-4">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">2.0</span><span class="p" data-group-id="9733218406-4">}</span><span class="p">.</span><span class="w">
│ │ │ +8&gt; </span><span class="p" data-group-id="8433803041-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8433803041-3">}</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="p" data-group-id="8433803041-4">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">2.0</span><span class="p" data-group-id="8433803041-4">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -9&gt; </span><span class="p" data-group-id="9733218406-5">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="9733218406-5">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="9733218406-6">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="9733218406-6">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +9&gt; </span><span class="p" data-group-id="8433803041-5">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="8433803041-5">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="8433803041-6">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="8433803041-6">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -10&gt; </span><span class="p" data-group-id="9733218406-7">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="9733218406-7">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="9733218406-8">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="9733218406-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +10&gt; </span><span class="p" data-group-id="8433803041-7">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="8433803041-7">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="8433803041-8">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="8433803041-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Prior to OTP 27, the term equivalence operators considered <code class="inline">0.0</code>
│ │ │  and <code class="inline">-0.0</code> to be the same term.</p><p>This was changed in OTP 27 but legacy code may have expected them to be
│ │ │  considered the same. To help users catch errors that may arise from an
│ │ │  upgrade, the compiler raises a warning when <code class="inline">0.0</code> is pattern-matched or used
│ │ │  in a term equivalence test.</p><p>If you need to match <code class="inline">0.0</code> specifically, the warning can be silenced by
│ │ │  writing <code class="inline">+0.0</code> instead, which produces the same term but makes the compiler
│ │ │  interpret the match as being done on purpose.</p></section><h2 id="arithmetic-expressions" class="section-heading">
│ │ │ @@ -631,15 +631,15 @@
│ │ │  </span><span class="mi">0</span><span class="gp unselectable">
│ │ │  8&gt; </span><span class="mi">2#10</span><span class="w"> </span><span class="ow">bor</span><span class="w"> </span><span class="mi">2#01</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │  9&gt; </span><span class="ss">a</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">10</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: an error occurred when evaluating an arithmetic expression
│ │ │       in operator  +/2
│ │ │          called as a + 10</span><span class="gp unselectable">
│ │ │ -10&gt; </span><span class="mi">1</span><span class="w"> </span><span class="nf">bsl</span><span class="w"> </span><span class="p" data-group-id="5144533334-1">(</span><span class="mi">1</span><span class="w"> </span><span class="ow">bsl</span><span class="w"> </span><span class="mi">64</span><span class="p" data-group-id="5144533334-1">)</span><span class="p">.</span><span class="w">
│ │ │ +10&gt; </span><span class="mi">1</span><span class="w"> </span><span class="nf">bsl</span><span class="w"> </span><span class="p" data-group-id="1432027857-1">(</span><span class="mi">1</span><span class="w"> </span><span class="ow">bsl</span><span class="w"> </span><span class="mi">64</span><span class="p" data-group-id="1432027857-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: a system limit has been reached
│ │ │       in operator  bsl/2
│ │ │          called as 1 bsl 18446744073709551616</span></code></pre><h2 id="boolean-expressions" class="section-heading">
│ │ │    <a href="#boolean-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Boolean Expressions</span>
│ │ │ @@ -658,136 +658,136 @@
│ │ │    <a href="#short-circuit-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Short-Circuit Expressions</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="n">Expr1</span><span class="w"> </span><span class="ow">orelse</span><span class="w"> </span><span class="n">Expr2</span><span class="w">
│ │ │  </span><span class="n">Expr1</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">Expr2</span></code></pre><p><code class="inline">Expr2</code> is evaluated only if necessary. That is, <code class="inline">Expr2</code> is evaluated only if:</p><ul><li><code class="inline">Expr1</code> evaluates to <code class="inline">false</code> in an <code class="inline">orelse</code> expression.</li></ul><p>or</p><ul><li><code class="inline">Expr1</code> evaluates to <code class="inline">true</code> in an <code class="inline">andalso</code> expression.</li></ul><p>Returns either the value of <code class="inline">Expr1</code> (that is, <code class="inline">true</code> or <code class="inline">false</code>) or the value of
│ │ │ -<code class="inline">Expr2</code> (if <code class="inline">Expr2</code> is evaluated).</p><p><em>Example 1:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="o">-</span><span class="mf">1.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nc">math</span><span class="p">:</span><span class="nf">sqrt</span><span class="p" data-group-id="6138176231-1">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="6138176231-1">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span></code></pre><p>This works even if <code class="inline">A</code> is less than <code class="inline">-1.0</code>, since in that case, <a href="../../lib/stdlib-6.2.2.1/doc/html/math.html#sqrt/1"><code class="inline">math:sqrt/1</code></a> is
│ │ │ -never evaluated.</p><p><em>Example 2:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">OnlyOne</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">is_atom</span><span class="p" data-group-id="7047115772-1">(</span><span class="n">L</span><span class="p" data-group-id="7047115772-1">)</span><span class="w"> </span><span class="nf">orelse</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="7047115772-2">(</span><span class="nf">is_list</span><span class="p" data-group-id="7047115772-3">(</span><span class="n">L</span><span class="p" data-group-id="7047115772-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7047115772-4">(</span><span class="n">L</span><span class="p" data-group-id="7047115772-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7047115772-2">)</span><span class="p">,</span></code></pre><p><code class="inline">Expr2</code> is not required to evaluate to a Boolean value. Because of that,
│ │ │ -<code class="inline">andalso</code> and <code class="inline">orelse</code> are tail-recursive.</p><p><em>Example 3 (tail-recursive function):</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="3438264136-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3438264136-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="3438264136-2">]</span><span class="p" data-group-id="3438264136-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Pred</span><span class="p" data-group-id="3438264136-3">(</span><span class="n">Hd</span><span class="p" data-group-id="3438264136-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">all</span><span class="p" data-group-id="3438264136-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="3438264136-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">all</span><span class="p" data-group-id="3438264136-5">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3438264136-6">[</span><span class="p" data-group-id="3438264136-6">]</span><span class="p" data-group-id="3438264136-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<code class="inline">Expr2</code> (if <code class="inline">Expr2</code> is evaluated).</p><p><em>Example 1:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="o">-</span><span class="mf">1.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nc">math</span><span class="p">:</span><span class="nf">sqrt</span><span class="p" data-group-id="5840961288-1">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="5840961288-1">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span></code></pre><p>This works even if <code class="inline">A</code> is less than <code class="inline">-1.0</code>, since in that case, <a href="../../lib/stdlib-6.2.2.1/doc/html/math.html#sqrt/1"><code class="inline">math:sqrt/1</code></a> is
│ │ │ +never evaluated.</p><p><em>Example 2:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">OnlyOne</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">is_atom</span><span class="p" data-group-id="5489018013-1">(</span><span class="n">L</span><span class="p" data-group-id="5489018013-1">)</span><span class="w"> </span><span class="nf">orelse</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="5489018013-2">(</span><span class="nf">is_list</span><span class="p" data-group-id="5489018013-3">(</span><span class="n">L</span><span class="p" data-group-id="5489018013-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="5489018013-4">(</span><span class="n">L</span><span class="p" data-group-id="5489018013-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5489018013-2">)</span><span class="p">,</span></code></pre><p><code class="inline">Expr2</code> is not required to evaluate to a Boolean value. Because of that,
│ │ │ +<code class="inline">andalso</code> and <code class="inline">orelse</code> are tail-recursive.</p><p><em>Example 3 (tail-recursive function):</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="7213190352-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7213190352-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="7213190352-2">]</span><span class="p" data-group-id="7213190352-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pred</span><span class="p" data-group-id="7213190352-3">(</span><span class="n">Hd</span><span class="p" data-group-id="7213190352-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">all</span><span class="p" data-group-id="7213190352-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="7213190352-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">all</span><span class="p" data-group-id="7213190352-5">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7213190352-6">[</span><span class="p" data-group-id="7213190352-6">]</span><span class="p" data-group-id="7213190352-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">true</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R13A, <code class="inline">Expr2</code> was required to evaluate to a Boolean value,
│ │ │  and as consequence, <code class="inline">andalso</code> and <code class="inline">orelse</code> were <strong>not</strong> tail-recursive.</p></section><h2 id="list-operations" class="section-heading">
│ │ │    <a href="#list-operations" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">List Operations</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="n">Expr1</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Expr2</span><span class="w">
│ │ │  </span><span class="n">Expr1</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="n">Expr2</span></code></pre><p>The list concatenation operator <code class="inline">++</code> appends its second argument to its first
│ │ │  and returns the resulting list.</p><p>The list subtraction operator <code class="inline">--</code> produces a list that is a copy of the first
│ │ │  argument. The procedure is as follows: for each element in the second argument,
│ │ │ -the first occurrence of this element (if any) is removed.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4943456064-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4943456064-1">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4943456064-2">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4943456064-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4943456064-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4943456064-3">]</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="4943456064-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4943456064-4">]</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="p" data-group-id="4943456064-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4943456064-5">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4943456064-6">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4943456064-6">]</span></code></pre><h2 id="map-expressions" class="section-heading">
│ │ │ +the first occurrence of this element (if any) is removed.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9149747083-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9149747083-1">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9149747083-2">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9149747083-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9149747083-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9149747083-3">]</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="9149747083-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9149747083-4">]</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="p" data-group-id="9149747083-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9149747083-5">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9149747083-6">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9149747083-6">]</span></code></pre><h2 id="map-expressions" class="section-heading">
│ │ │    <a href="#map-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Map Expressions</span>
│ │ │  </h2>
│ │ │  <h3 id="creating-maps" class="section-heading">
│ │ │    <a href="#creating-maps" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating Maps</span>
│ │ │  </h3>
│ │ │  <p>Constructing a new map is done by letting an expression <code class="inline">K</code> be associated with
│ │ │ -another expression <code class="inline">V</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1376445552-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="1376445552-1">}</span></code></pre><p>New maps can include multiple associations at construction by listing every
│ │ │ -association:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0679201593-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="0679201593-1">}</span></code></pre><p>An empty map is constructed by not associating any terms with each other:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5915557463-1">#{</span><span class="p" data-group-id="5915557463-1">}</span></code></pre><p>All keys and values in the map are terms. Any expression is first evaluated and
│ │ │ +another expression <code class="inline">V</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6813107620-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="6813107620-1">}</span></code></pre><p>New maps can include multiple associations at construction by listing every
│ │ │ +association:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9863247806-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="9863247806-1">}</span></code></pre><p>An empty map is constructed by not associating any terms with each other:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8123790822-1">#{</span><span class="p" data-group-id="8123790822-1">}</span></code></pre><p>All keys and values in the map are terms. Any expression is first evaluated and
│ │ │  then the resulting terms are used as <em>key</em> and <em>value</em> respectively.</p><p>Keys and values are separated by the <code class="inline">=&gt;</code> arrow and associations are separated
│ │ │ -by a comma (<code class="inline">,</code>).</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2808038317-1">#{</span><span class="p" data-group-id="2808038317-1">}</span><span class="p">,</span><span class="w">                 </span><span class="c1">% empty map</span><span class="w">
│ │ │ -</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2808038317-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2808038317-3">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="2808038317-3">&gt;&gt;</span><span class="p" data-group-id="2808038317-2">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% single association with literals</span><span class="w">
│ │ │ -</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2808038317-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="2808038317-4">}</span><span class="p">,</span><span class="w">   </span><span class="c1">% multiple associations with literals</span><span class="w">
│ │ │ -</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2808038317-5">#{</span><span class="ss">k</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2808038317-6">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="2808038317-6">}</span><span class="p" data-group-id="2808038317-5">}</span><span class="p">,</span><span class="w">       </span><span class="c1">% single association with variables</span><span class="w">
│ │ │ -</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2808038317-7">#{</span><span class="p" data-group-id="2808038317-8">{</span><span class="s">&quot;w&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2808038317-8">}</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="2808038317-9">(</span><span class="p" data-group-id="2808038317-9">)</span><span class="p" data-group-id="2808038317-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% compound key associated with an evaluated expression</span></code></pre><p>Here, <code class="inline">A</code> and <code class="inline">B</code> are any expressions and <code class="inline">M0</code> through <code class="inline">M4</code> are the resulting
│ │ │ -map terms.</p><p>If two matching keys are declared, the latter key takes precedence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3030954158-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3030954158-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3030954158-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p" data-group-id="3030954158-2">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="3030954158-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3030954158-3">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3030954158-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="3030954158-4">}</span></code></pre><p>The order in which the expressions constructing the keys (and their associated
│ │ │ +by a comma (<code class="inline">,</code>).</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1720972639-1">#{</span><span class="p" data-group-id="1720972639-1">}</span><span class="p">,</span><span class="w">                 </span><span class="c1">% empty map</span><span class="w">
│ │ │ +</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1720972639-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1720972639-3">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="1720972639-3">&gt;&gt;</span><span class="p" data-group-id="1720972639-2">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% single association with literals</span><span class="w">
│ │ │ +</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1720972639-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1720972639-4">}</span><span class="p">,</span><span class="w">   </span><span class="c1">% multiple associations with literals</span><span class="w">
│ │ │ +</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1720972639-5">#{</span><span class="ss">k</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1720972639-6">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="1720972639-6">}</span><span class="p" data-group-id="1720972639-5">}</span><span class="p">,</span><span class="w">       </span><span class="c1">% single association with variables</span><span class="w">
│ │ │ +</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1720972639-7">#{</span><span class="p" data-group-id="1720972639-8">{</span><span class="s">&quot;w&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1720972639-8">}</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="1720972639-9">(</span><span class="p" data-group-id="1720972639-9">)</span><span class="p" data-group-id="1720972639-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% compound key associated with an evaluated expression</span></code></pre><p>Here, <code class="inline">A</code> and <code class="inline">B</code> are any expressions and <code class="inline">M0</code> through <code class="inline">M4</code> are the resulting
│ │ │ +map terms.</p><p>If two matching keys are declared, the latter key takes precedence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0657658473-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="0657658473-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0657658473-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p" data-group-id="0657658473-2">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="0657658473-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="0657658473-3">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0657658473-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="0657658473-4">}</span></code></pre><p>The order in which the expressions constructing the keys (and their associated
│ │ │  values) are evaluated is not defined. The syntactic order of the key-value pairs
│ │ │  in the construction is of no relevance, except in the recently mentioned case of
│ │ │  two matching keys.</p><h3 id="updating-maps" class="section-heading">
│ │ │    <a href="#updating-maps" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Updating Maps</span>
│ │ │  </h3>
│ │ │  <p>Updating a map has a similar syntax as constructing it.</p><p>An expression defining the map to be updated is put in front of the expression
│ │ │ -defining the keys to be updated and their respective values:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="8380088279-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="8380088279-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map and <code class="inline">K</code> and <code class="inline">V</code> are any expression.</p><p>If key <code class="inline">K</code> does not match any existing key in the map, a new association is
│ │ │ +defining the keys to be updated and their respective values:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="8076032771-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="8076032771-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map and <code class="inline">K</code> and <code class="inline">V</code> are any expression.</p><p>If key <code class="inline">K</code> does not match any existing key in the map, a new association is
│ │ │  created from key <code class="inline">K</code> to value <code class="inline">V</code>.</p><p>If key <code class="inline">K</code> matches an existing key in map <code class="inline">M</code>, its associated value is replaced
│ │ │  by the new value <code class="inline">V</code>. In both cases, the evaluated map expression returns a new
│ │ │ -map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p>To only update an existing value, the following syntax is used:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="6505991167-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="6505991167-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map, <code class="inline">V</code> is an expression and <code class="inline">K</code> is an expression
│ │ │ +map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p>To only update an existing value, the following syntax is used:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="3683298150-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="3683298150-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map, <code class="inline">V</code> is an expression and <code class="inline">K</code> is an expression
│ │ │  that evaluates to an existing key in <code class="inline">M</code>.</p><p>If key <code class="inline">K</code> does not match any existing keys in map <code class="inline">M</code>, an exception of type
│ │ │  <code class="inline">badkey</code> is raised at runtime. If a matching key <code class="inline">K</code> is present in map <code class="inline">M</code>,
│ │ │  its associated value is replaced by the new value <code class="inline">V</code>, and the evaluated map
│ │ │ -expression returns a new map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4231777954-1">#{</span><span class="p" data-group-id="4231777954-1">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M0</span><span class="p" data-group-id="4231777954-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4231777954-2">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="4231777954-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4231777954-3">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M2</span><span class="p" data-group-id="4231777954-4">#{</span><span class="s">&quot;function&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4231777954-5">(</span><span class="p" data-group-id="4231777954-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="4231777954-6">(</span><span class="p" data-group-id="4231777954-6">)</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="4231777954-4">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M3</span><span class="p" data-group-id="4231777954-7">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4231777954-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% &#39;a&#39; and &#39;b&#39; was added in `M1` and `M2`.</span></code></pre><p>Here <code class="inline">M0</code> is any map. It follows that <code class="inline">M1</code> through <code class="inline">M4</code> are maps as well.</p><p><em>More examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3055667763-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="3055667763-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3055667763-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="p" data-group-id="3055667763-2">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="n">M</span><span class="p" data-group-id="3055667763-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3055667763-3">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3055667763-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3055667763-4">}</span><span class="p">.</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="n">M</span><span class="p" data-group-id="3055667763-5">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3055667763-5">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3055667763-6">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3055667763-6">}</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="n">M</span><span class="p" data-group-id="3055667763-7">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3055667763-7">}</span><span class="p">.</span><span class="w">
│ │ │ +expression returns a new map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6810583339-1">#{</span><span class="p" data-group-id="6810583339-1">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M0</span><span class="p" data-group-id="6810583339-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6810583339-2">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="6810583339-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6810583339-3">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M2</span><span class="p" data-group-id="6810583339-4">#{</span><span class="s">&quot;function&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6810583339-5">(</span><span class="p" data-group-id="6810583339-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="6810583339-6">(</span><span class="p" data-group-id="6810583339-6">)</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="6810583339-4">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M3</span><span class="p" data-group-id="6810583339-7">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6810583339-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% &#39;a&#39; and &#39;b&#39; was added in `M1` and `M2`.</span></code></pre><p>Here <code class="inline">M0</code> is any map. It follows that <code class="inline">M1</code> through <code class="inline">M4</code> are maps as well.</p><p><em>More examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4476760220-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="4476760220-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4476760220-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="p" data-group-id="4476760220-2">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="n">M</span><span class="p" data-group-id="4476760220-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="4476760220-3">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4476760220-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="4476760220-4">}</span><span class="p">.</span><span class="gp unselectable">
│ │ │ +3&gt; </span><span class="n">M</span><span class="p" data-group-id="4476760220-5">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="4476760220-5">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4476760220-6">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="4476760220-6">}</span><span class="gp unselectable">
│ │ │ +4&gt; </span><span class="n">M</span><span class="p" data-group-id="4476760220-7">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="4476760220-7">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: bad argument</span></code></pre><p>As in construction, the order in which the key and value expressions are
│ │ │  evaluated is not defined. The syntactic order of the key-value pairs in the
│ │ │  update is of no relevance, except in the case where two keys match. In that
│ │ │  case, the latter value is used.</p><h3 id="maps-in-patterns" class="section-heading">
│ │ │    <a href="#maps-in-patterns" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Maps in Patterns</span>
│ │ │  </h3>
│ │ │ -<p>Matching of key-value associations from maps is done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5667821076-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="5667821076-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here <code class="inline">M</code> is any map. The key <code class="inline">K</code> must be a
│ │ │ +<p>Matching of key-value associations from maps is done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5136395252-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="5136395252-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here <code class="inline">M</code> is any map. The key <code class="inline">K</code> must be a
│ │ │  <a href="expressions.html#guard-expressions">guard expression</a>, with all variables already
│ │ │  bound. <code class="inline">V</code> can be any pattern with either bound or unbound variables.</p><p>If the variable <code class="inline">V</code> is unbound, it becomes bound to the value associated with
│ │ │  the key <code class="inline">K</code>, which must exist in the map <code class="inline">M</code>. If the variable <code class="inline">V</code> is bound, it
│ │ │  must match the value associated with <code class="inline">K</code> in <code class="inline">M</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 23, the expression defining the key <code class="inline">K</code> was restricted to be
│ │ │ -either a single variable or a literal.</p></section><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1011243453-1">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1011243453-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1011243453-2">}</span><span class="p" data-group-id="1011243453-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1011243453-3">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1011243453-4">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1011243453-4">}</span><span class="p" data-group-id="1011243453-3">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="1011243453-5">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1011243453-6">{</span><span class="mi">1</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="1011243453-6">}</span><span class="p" data-group-id="1011243453-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1011243453-7">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1011243453-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1011243453-8">}</span><span class="p" data-group-id="1011243453-7">}</span><span class="gp unselectable">
│ │ │ +either a single variable or a literal.</p></section><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3409470775-1">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3409470775-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3409470775-2">}</span><span class="p" data-group-id="3409470775-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3409470775-3">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3409470775-4">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3409470775-4">}</span><span class="p" data-group-id="3409470775-3">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="3409470775-5">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3409470775-6">{</span><span class="mi">1</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="3409470775-6">}</span><span class="p" data-group-id="3409470775-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3409470775-7">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3409470775-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3409470775-8">}</span><span class="p" data-group-id="3409470775-7">}</span><span class="gp unselectable">
│ │ │  3&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">2</span><span class="p">.</span></code></pre><p>This binds variable <code class="inline">B</code> to integer <code class="inline">2</code>.</p><p>Similarly, multiple values from the map can be matched:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6490250429-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="6490250429-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here keys <code class="inline">K1</code> through <code class="inline">Kn</code> are any expressions with literals or bound
│ │ │ +</span><span class="mi">2</span><span class="p">.</span></code></pre><p>This binds variable <code class="inline">B</code> to integer <code class="inline">2</code>.</p><p>Similarly, multiple values from the map can be matched:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6135607630-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="6135607630-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here keys <code class="inline">K1</code> through <code class="inline">Kn</code> are any expressions with literals or bound
│ │ │  variables. If all key expressions evaluate successfully and all keys
│ │ │  exist in map <code class="inline">M</code>, all variables in <code class="inline">V1 .. Vn</code> is matched to the
│ │ │  associated values of their respective keys.</p><p>If the matching conditions are not met the match fails.</p><p>Note that when matching a map, only the <code class="inline">:=</code> operator (not the <code class="inline">=&gt;</code>) is allowed
│ │ │  as a delimiter for the associations.</p><p>The order in which keys are declared in matching has no relevance.</p><p>Duplicate keys are allowed in matching and match each pattern associated to the
│ │ │ -keys:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8106050884-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V2</span><span class="p" data-group-id="8106050884-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>The empty map literal (<code class="inline">#{}</code>) matches any map when used as a pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4091904419-1">#{</span><span class="p" data-group-id="4091904419-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>This expression matches if the expression <code class="inline">Expr</code> is of type map, otherwise it
│ │ │ -fails with an exception <code class="inline">badmatch</code>.</p><p>Here the key to be retrieved is constructed from an expression:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5353118844-1">#{</span><span class="p" data-group-id="5353118844-2">{</span><span class="ss">tag</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="5353118844-3">(</span><span class="n">List</span><span class="p" data-group-id="5353118844-3">)</span><span class="p" data-group-id="5353118844-2">}</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="5353118844-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map</span></code></pre><p><code class="inline">List</code> must be an already bound variable.</p><h4>Matching Syntax</h4><p>Matching of literals as keys are allowed in function heads:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% only start if not_started</span><span class="w">
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="9159957839-1">(</span><span class="ss">start</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9159957839-2">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">not_started</span><span class="p" data-group-id="9159957839-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="9159957839-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +keys:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3952920415-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V2</span><span class="p" data-group-id="3952920415-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>The empty map literal (<code class="inline">#{}</code>) matches any map when used as a pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3359035059-1">#{</span><span class="p" data-group-id="3359035059-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>This expression matches if the expression <code class="inline">Expr</code> is of type map, otherwise it
│ │ │ +fails with an exception <code class="inline">badmatch</code>.</p><p>Here the key to be retrieved is constructed from an expression:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1798118769-1">#{</span><span class="p" data-group-id="1798118769-2">{</span><span class="ss">tag</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="1798118769-3">(</span><span class="n">List</span><span class="p" data-group-id="1798118769-3">)</span><span class="p" data-group-id="1798118769-2">}</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="1798118769-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map</span></code></pre><p><code class="inline">List</code> must be an already bound variable.</p><h4>Matching Syntax</h4><p>Matching of literals as keys are allowed in function heads:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% only start if not_started</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="7403782587-1">(</span><span class="ss">start</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7403782587-2">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">not_started</span><span class="p" data-group-id="7403782587-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7403782587-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9159957839-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="9159957839-4">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="9159957839-4">}</span><span class="p" data-group-id="9159957839-3">}</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7403782587-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7403782587-4">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="7403782587-4">}</span><span class="p" data-group-id="7403782587-3">}</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% only change if started</span><span class="w">
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="9159957839-5">(</span><span class="ss">change</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9159957839-6">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="9159957839-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="9159957839-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="7403782587-5">(</span><span class="ss">change</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7403782587-6">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="7403782587-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7403782587-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9159957839-7">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="9159957839-8">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">changed</span><span class="p" data-group-id="9159957839-8">}</span><span class="p" data-group-id="9159957839-7">}</span><span class="p">;</span></code></pre><h3 id="maps-in-guards" class="section-heading">
│ │ │ +    </span><span class="p" data-group-id="7403782587-7">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7403782587-8">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">changed</span><span class="p" data-group-id="7403782587-8">}</span><span class="p" data-group-id="7403782587-7">}</span><span class="p">;</span></code></pre><h3 id="maps-in-guards" class="section-heading">
│ │ │    <a href="#maps-in-guards" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Maps in Guards</span>
│ │ │  </h3>
│ │ │  <p>Maps are allowed in guards as long as all subexpressions are valid guard
│ │ │  expressions.</p><p>The following guard BIFs handle maps:</p><ul><li><a href="../../erts-15.2.7/doc/html/erlang.html#is_map/1">is_map/1</a> in the <code class="inline">erlang</code> module</li><li><a href="../../erts-15.2.7/doc/html/erlang.html#is_map_key/2">is_map_key/2</a> in the <code class="inline">erlang</code> module</li><li><a href="../../erts-15.2.7/doc/html/erlang.html#map_get/2">map_get/2</a> in the <code class="inline">erlang</code> module</li><li><a href="../../erts-15.2.7/doc/html/erlang.html#map_size/1">map_size/1</a> in the <code class="inline">erlang</code> module</li></ul><h2 id="bit-syntax-expressions" class="section-heading">
│ │ │    <a href="#bit-syntax-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Bit Syntax Expressions</span>
│ │ │  </h2>
│ │ │  <p>The bit syntax operates on <em>bit strings</em>. A bit string is a sequence of bits
│ │ │ -ordered from the most significant bit to the least significant bit.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8647951213-1">&lt;&lt;</span><span class="p" data-group-id="8647951213-1">&gt;&gt;</span><span class="w">  </span><span class="c1">% The empty bit string, zero length</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8647951213-2">&lt;&lt;</span><span class="n">E1</span><span class="p" data-group-id="8647951213-2">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8647951213-3">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">En</span><span class="p" data-group-id="8647951213-3">&gt;&gt;</span></code></pre><p>Each element <code class="inline">Ei</code> specifies a <em>segment</em> of the bit string. The segments are
│ │ │ +ordered from the most significant bit to the least significant bit.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4016356147-1">&lt;&lt;</span><span class="p" data-group-id="4016356147-1">&gt;&gt;</span><span class="w">  </span><span class="c1">% The empty bit string, zero length</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4016356147-2">&lt;&lt;</span><span class="n">E1</span><span class="p" data-group-id="4016356147-2">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4016356147-3">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">En</span><span class="p" data-group-id="4016356147-3">&gt;&gt;</span></code></pre><p>Each element <code class="inline">Ei</code> specifies a <em>segment</em> of the bit string. The segments are
│ │ │  ordered left to right from the most significant bit to the least significant bit
│ │ │  of the bit string.</p><p>Each segment specification <code class="inline">Ei</code> is a value, whose default type is <code class="inline">integer</code>,
│ │ │  followed by an optional <em>size expression</em> and an optional <em>type specifier list</em>.</p><pre><code class="makeup erlang" translate="no"><span class="n">Ei</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │       </span><span class="n">Value</span><span class="p">:</span><span class="n">Size</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │       </span><span class="n">Value</span><span class="o">/</span><span class="n">TypeSpecifierList</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │       </span><span class="n">Value</span><span class="p">:</span><span class="n">Size</span><span class="o">/</span><span class="n">TypeSpecifierList</span></code></pre><p>When used in a bit string construction, <code class="inline">Value</code> is an expression that is to
│ │ │  evaluate to an integer, float, or bit string. If the expression is not a single
│ │ │ @@ -798,34 +798,34 @@
│ │ │  <a href="expressions.html#guard-expressions">guard expression</a> that evaluates to an
│ │ │  integer. All variables in the guard expression must be already bound.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable
│ │ │  bound to an integer.</p></section><p>The value of <code class="inline">Size</code> specifies the size of the segment in units (see below). The
│ │ │  default value depends on the type (see below):</p><ul><li>For <code class="inline">integer</code> it is 8.</li><li>For <code class="inline">float</code> it is 64.</li><li>For <code class="inline">binary</code> and <code class="inline">bitstring</code> it is the whole binary or bit string.</li></ul><p>In matching, the default value for a binary or bit string segment is only valid
│ │ │  for the last element. All other bit string or binary elements in the matching
│ │ │  must have a size specification.</p><p><a href="" id="binaries"></a></p><p><strong>Binaries</strong></p><p>A bit string with a length that is a multiple of 8 bits is known as a <em>binary</em>,
│ │ │  which is the most common and useful type of bit string.</p><p>A binary has a canonical representation in memory. Here follows a sequence of
│ │ │ -bytes where each byte's value is its sequence number:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3834356366-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p" data-group-id="3834356366-1">&gt;&gt;</span></code></pre><p>Bit strings are a later generalization of binaries, so many texts and much
│ │ │ -information about binaries apply just as well for bit strings.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0826382687-1">&lt;&lt;</span><span class="n">A</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0826382687-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0826382687-2">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="0826382687-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +bytes where each byte's value is its sequence number:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8807512166-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p" data-group-id="8807512166-1">&gt;&gt;</span></code></pre><p>Bit strings are a later generalization of binaries, so many texts and much
│ │ │ +information about binaries apply just as well for bit strings.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8851529529-1">&lt;&lt;</span><span class="n">A</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8851529529-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8851529529-2">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="8851529529-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">* 1:3: a binary field without size is only allowed at the end of a binary pattern</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="0826382687-3">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">3</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0826382687-3">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0826382687-4">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="0826382687-4">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0826382687-5">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="0826382687-5">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="8851529529-3">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">3</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8851529529-3">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8851529529-4">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="8851529529-4">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8851529529-5">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="8851529529-5">&gt;&gt;</span><span class="gp unselectable">
│ │ │  3&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0826382687-6">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0826382687-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +</span><span class="p" data-group-id="8851529529-6">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="8851529529-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │  4&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0826382687-7">&lt;&lt;</span><span class="s">&quot;de&quot;</span><span class="p" data-group-id="0826382687-7">&gt;&gt;</span></code></pre><p>For the <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code> types, <code class="inline">Size</code> must not be given. The size
│ │ │ +</span><span class="p" data-group-id="8851529529-7">&lt;&lt;</span><span class="s">&quot;de&quot;</span><span class="p" data-group-id="8851529529-7">&gt;&gt;</span></code></pre><p>For the <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code> types, <code class="inline">Size</code> must not be given. The size
│ │ │  of the segment is implicitly determined by the type and value itself.</p><p><code class="inline">TypeSpecifierList</code> is a list of type specifiers, in any order, separated by
│ │ │  hyphens (-). Default values are used for any omitted type specifiers.</p><ul><li><p><strong><code class="inline">Type</code>= <code class="inline">integer</code> | <code class="inline">float</code> | <code class="inline">binary</code> | <code class="inline">bytes</code> | <code class="inline">bitstring</code> | <code class="inline">bits</code> |
│ │ │  <code class="inline">utf8</code> | <code class="inline">utf16</code> | <code class="inline">utf32</code></strong> - The default is <code class="inline">integer</code>. <code class="inline">bytes</code> is a
│ │ │  shorthand for <code class="inline">binary</code> and <code class="inline">bits</code> is a shorthand for <code class="inline">bitstring</code>. See below
│ │ │  for more information about the <code class="inline">utf</code> types.</p></li><li><p><strong><code class="inline">Signedness</code>= <code class="inline">signed</code> | <code class="inline">unsigned</code></strong> - Only matters for matching and when
│ │ │  the type is <code class="inline">integer</code>. The default is <code class="inline">unsigned</code>.</p></li><li><p><strong><code class="inline">Endianness</code>= <code class="inline">big</code> | <code class="inline">little</code> | <code class="inline">native</code></strong> - Specifies byte level (octet
│ │ │  level) endianness (byte order). Native-endian means that the endianness is
│ │ │  resolved at load time to be either big-endian or little-endian, depending on
│ │ │  what is native for the CPU that the Erlang machine is run on. Endianness only
│ │ │  matters when the <strong>Type</strong> is either <code class="inline">integer</code>, <code class="inline">utf16</code>, <code class="inline">utf32</code>, or <code class="inline">float</code>. The
│ │ │ -default is <code class="inline">big</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3436305952-1">&lt;&lt;</span><span class="mi">16#1234</span><span class="p">:</span><span class="mi">16</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="3436305952-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3436305952-2">&lt;&lt;</span><span class="mi">16#3412</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="3436305952-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3436305952-3">&lt;&lt;</span><span class="mi">16#34</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">16#12</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="3436305952-3">&gt;&gt;</span></code></pre></li><li><p><strong><code class="inline">Unit</code>= <code class="inline">unit:IntegerLiteral</code></strong> - The allowed range is 1 through 256.
│ │ │ +default is <code class="inline">big</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6306978200-1">&lt;&lt;</span><span class="mi">16#1234</span><span class="p">:</span><span class="mi">16</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="6306978200-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6306978200-2">&lt;&lt;</span><span class="mi">16#3412</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="6306978200-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6306978200-3">&lt;&lt;</span><span class="mi">16#34</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">16#12</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="6306978200-3">&gt;&gt;</span></code></pre></li><li><p><strong><code class="inline">Unit</code>= <code class="inline">unit:IntegerLiteral</code></strong> - The allowed range is 1 through 256.
│ │ │  Defaults to 1 for <code class="inline">integer</code>, <code class="inline">float</code>, and <code class="inline">bitstring</code>, and to 8 for <code class="inline">binary</code>.
│ │ │  For types <code class="inline">bitstring</code>, <code class="inline">bits</code>, and <code class="inline">bytes</code>, it is not allowed to specify a
│ │ │  unit value different from the default value. No unit specifier must be given
│ │ │  for the types <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code>.</p></li></ul><h3 id="integer-segments" class="section-heading">
│ │ │    <a href="#integer-segments" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -850,41 +850,41 @@
│ │ │    </a>
│ │ │    <span class="text">Binary segments</span>
│ │ │  </h3>
│ │ │  <p>In this section, the phrase &quot;binary segment&quot; refers to any one of the segment
│ │ │  types <code class="inline">binary</code>, <code class="inline">bitstring</code>, <code class="inline">bytes</code>, and <code class="inline">bits</code>.</p><p>See also the paragraphs about <a href="expressions.html#binaries">Binaries</a>.</p><p>When constructing binaries and no size is specified for a binary segment, the
│ │ │  entire binary value is interpolated into the binary being constructed. However,
│ │ │  the size in bits of the binary being interpolated must be evenly divisible by
│ │ │ -the unit value for the segment; otherwise an exception is raised.</p><p>For example, the following examples all succeed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2915777622-1">&lt;&lt;</span><span class="p" data-group-id="2915777622-2">(</span><span class="p" data-group-id="2915777622-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2915777622-3">&gt;&gt;</span><span class="p" data-group-id="2915777622-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="2915777622-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2915777622-4">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2915777622-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="2915777622-5">&lt;&lt;</span><span class="p" data-group-id="2915777622-6">(</span><span class="p" data-group-id="2915777622-7">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2915777622-7">&gt;&gt;</span><span class="p" data-group-id="2915777622-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2915777622-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2915777622-8">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2915777622-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="p" data-group-id="2915777622-9">&lt;&lt;</span><span class="p" data-group-id="2915777622-10">(</span><span class="p" data-group-id="2915777622-11">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2915777622-11">&gt;&gt;</span><span class="p" data-group-id="2915777622-10">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2915777622-9">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2915777622-12">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2915777622-12">&gt;&gt;</span></code></pre><p>The first two examples have a unit value of 1 for the segment, while the third
│ │ │ +the unit value for the segment; otherwise an exception is raised.</p><p>For example, the following examples all succeed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8800745889-1">&lt;&lt;</span><span class="p" data-group-id="8800745889-2">(</span><span class="p" data-group-id="8800745889-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="8800745889-3">&gt;&gt;</span><span class="p" data-group-id="8800745889-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="8800745889-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8800745889-4">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="8800745889-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="8800745889-5">&lt;&lt;</span><span class="p" data-group-id="8800745889-6">(</span><span class="p" data-group-id="8800745889-7">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="8800745889-7">&gt;&gt;</span><span class="p" data-group-id="8800745889-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8800745889-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8800745889-8">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="8800745889-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +3&gt; </span><span class="p" data-group-id="8800745889-9">&lt;&lt;</span><span class="p" data-group-id="8800745889-10">(</span><span class="p" data-group-id="8800745889-11">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="8800745889-11">&gt;&gt;</span><span class="p" data-group-id="8800745889-10">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8800745889-9">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8800745889-12">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="8800745889-12">&gt;&gt;</span></code></pre><p>The first two examples have a unit value of 1 for the segment, while the third
│ │ │  segment has a unit value of 8.</p><p>Attempting to interpolate a bit string of size 1 into a binary segment with unit
│ │ │ -8 (the default unit for <code class="inline">binary</code>) fails as shown in this example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1976261675-1">&lt;&lt;</span><span class="p" data-group-id="1976261675-2">(</span><span class="p" data-group-id="1976261675-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="1976261675-3">&gt;&gt;</span><span class="p" data-group-id="1976261675-2">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1976261675-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="gt">** exception error: bad argument</span></code></pre><p>For the construction to succeed, the unit value of the segment must be 1:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4302106611-1">&lt;&lt;</span><span class="p" data-group-id="4302106611-2">(</span><span class="p" data-group-id="4302106611-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4302106611-3">&gt;&gt;</span><span class="p" data-group-id="4302106611-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="4302106611-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4302106611-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4302106611-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="p" data-group-id="4302106611-5">&lt;&lt;</span><span class="p" data-group-id="4302106611-6">(</span><span class="p" data-group-id="4302106611-7">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4302106611-7">&gt;&gt;</span><span class="p" data-group-id="4302106611-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4302106611-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4302106611-8">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4302106611-8">&gt;&gt;</span></code></pre><p>Similarly, when matching a binary segment with no size specified, the match
│ │ │ +8 (the default unit for <code class="inline">binary</code>) fails as shown in this example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7434713786-1">&lt;&lt;</span><span class="p" data-group-id="7434713786-2">(</span><span class="p" data-group-id="7434713786-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="7434713786-3">&gt;&gt;</span><span class="p" data-group-id="7434713786-2">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7434713786-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gt">** exception error: bad argument</span></code></pre><p>For the construction to succeed, the unit value of the segment must be 1:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="2271165194-1">&lt;&lt;</span><span class="p" data-group-id="2271165194-2">(</span><span class="p" data-group-id="2271165194-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2271165194-3">&gt;&gt;</span><span class="p" data-group-id="2271165194-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="2271165194-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2271165194-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2271165194-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +3&gt; </span><span class="p" data-group-id="2271165194-5">&lt;&lt;</span><span class="p" data-group-id="2271165194-6">(</span><span class="p" data-group-id="2271165194-7">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2271165194-7">&gt;&gt;</span><span class="p" data-group-id="2271165194-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2271165194-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2271165194-8">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2271165194-8">&gt;&gt;</span></code></pre><p>Similarly, when matching a binary segment with no size specified, the match
│ │ │  succeeds if and only if the size in bits of the rest of the binary is evenly
│ │ │ -divisible by the unit value:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0473847134-1">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0473847134-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0473847134-2">&lt;&lt;</span><span class="s">&quot;&quot;</span><span class="p" data-group-id="0473847134-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0473847134-3">&lt;&lt;</span><span class="p" data-group-id="0473847134-3">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="0473847134-4">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0473847134-4">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0473847134-5">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="0473847134-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +divisible by the unit value:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2381400880-1">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="2381400880-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2381400880-2">&lt;&lt;</span><span class="s">&quot;&quot;</span><span class="p" data-group-id="2381400880-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2381400880-3">&lt;&lt;</span><span class="p" data-group-id="2381400880-3">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="2381400880-4">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="2381400880-4">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2381400880-5">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="2381400880-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value &lt;&lt;&quot;a&quot;&gt;&gt;</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="p" data-group-id="0473847134-6">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0473847134-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0473847134-7">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="0473847134-7">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0473847134-8">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="0473847134-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="p" data-group-id="0473847134-9">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0473847134-9">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0473847134-10">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0473847134-10">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="p" data-group-id="2381400880-6">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="2381400880-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2381400880-7">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="2381400880-7">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2381400880-8">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="2381400880-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +4&gt; </span><span class="p" data-group-id="2381400880-9">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="2381400880-9">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2381400880-10">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2381400880-10">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value &lt;&lt;&quot;abc&quot;&gt;&gt;</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="p" data-group-id="0473847134-11">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0473847134-11">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0473847134-12">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="0473847134-12">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0473847134-13">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="0473847134-13">&gt;&gt;</span></code></pre><p>When a size is explicitly specified for a binary segment, the segment size in
│ │ │ +5&gt; </span><span class="p" data-group-id="2381400880-11">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="2381400880-11">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2381400880-12">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="2381400880-12">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2381400880-13">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="2381400880-13">&gt;&gt;</span></code></pre><p>When a size is explicitly specified for a binary segment, the segment size in
│ │ │  bits is the value of <code class="inline">Size</code> multiplied by the default or explicit unit value.</p><p>When constructing binaries, the size of the binary being interpolated into the
│ │ │ -constructed binary must be at least as large as the size of the binary segment.</p><p><strong>Examples:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6825582341-1">&lt;&lt;</span><span class="p" data-group-id="6825582341-2">(</span><span class="p" data-group-id="6825582341-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6825582341-3">&gt;&gt;</span><span class="p" data-group-id="6825582341-2">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6825582341-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6825582341-4">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="6825582341-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="6825582341-5">&lt;&lt;</span><span class="p" data-group-id="6825582341-6">(</span><span class="p" data-group-id="6825582341-7">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="6825582341-7">&gt;&gt;</span><span class="p" data-group-id="6825582341-6">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6825582341-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +constructed binary must be at least as large as the size of the binary segment.</p><p><strong>Examples:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2326588197-1">&lt;&lt;</span><span class="p" data-group-id="2326588197-2">(</span><span class="p" data-group-id="2326588197-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2326588197-3">&gt;&gt;</span><span class="p" data-group-id="2326588197-2">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2326588197-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2326588197-4">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="2326588197-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="2326588197-5">&lt;&lt;</span><span class="p" data-group-id="2326588197-6">(</span><span class="p" data-group-id="2326588197-7">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="2326588197-7">&gt;&gt;</span><span class="p" data-group-id="2326588197-6">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2326588197-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: construction of binary failed
│ │ │          *** segment 1 of type &#39;binary&#39;: the value &lt;&lt;&quot;a&quot;&gt;&gt; is shorter than the size of the segment</span></code></pre><h3 id="unicode-segments" class="section-heading">
│ │ │    <a href="#unicode-segments" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Unicode segments</span>
│ │ │  </h3>
│ │ │ @@ -900,78 +900,78 @@
│ │ │  range <code class="inline">0</code> through <code class="inline">16#D7FF</code> or <code class="inline">16#E000</code> through <code class="inline">16#10FFFF</code>. The match fails if the
│ │ │  returned value falls outside those ranges.</p><p>A segment of type <code class="inline">utf8</code> matches 1-4 bytes in the bit string, if the bit string
│ │ │  at the match position contains a valid UTF-8 sequence. (See RFC-3629 or the
│ │ │  Unicode standard.)</p><p>A segment of type <code class="inline">utf16</code> can match 2 or 4 bytes in the bit string. The match
│ │ │  fails if the bit string at the match position does not contain a legal UTF-16
│ │ │  encoding of a Unicode code point. (See RFC-2781 or the Unicode standard.)</p><p>A segment of type <code class="inline">utf32</code> can match 4 bytes in the bit string in the same way as
│ │ │  an <code class="inline">integer</code> segment matches 32 bits. The match fails if the resulting integer
│ │ │ -is outside the legal ranges previously mentioned.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4239799373-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="4239799373-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="4239799373-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4239799373-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="4239799373-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-4">&lt;&lt;</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="4239799373-4">&gt;&gt;</span><span class="w">
│ │ │ +is outside the legal ranges previously mentioned.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7315979964-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7315979964-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7315979964-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7315979964-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="7315979964-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-4">&lt;&lt;</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="7315979964-4">&gt;&gt;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4239799373-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="4239799373-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-6">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="4239799373-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="p" data-group-id="4239799373-7">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="4239799373-7">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4239799373-8">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="4239799373-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-9">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="4239799373-9">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7315979964-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7315979964-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-6">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7315979964-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +4&gt; </span><span class="p" data-group-id="7315979964-7">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7315979964-7">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7315979964-8">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7315979964-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-9">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7315979964-9">&gt;&gt;</span><span class="gp unselectable">
│ │ │  5&gt; </span><span class="n">C</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="p" data-group-id="4239799373-10">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="n">E</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="4239799373-10">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4239799373-11">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="4239799373-11">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-12">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="4239799373-12">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +6&gt; </span><span class="p" data-group-id="7315979964-10">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="n">E</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="7315979964-10">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7315979964-11">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7315979964-11">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-12">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7315979964-12">&gt;&gt;</span><span class="gp unselectable">
│ │ │  7&gt; </span><span class="n">D</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">273</span><span class="gp unselectable">
│ │ │  8&gt; </span><span class="n">F</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span><span class="gp unselectable">
│ │ │ -9&gt; </span><span class="p" data-group-id="4239799373-13">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">H</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4239799373-13">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4239799373-14">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="4239799373-14">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-15">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="4239799373-15">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +9&gt; </span><span class="p" data-group-id="7315979964-13">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">H</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7315979964-13">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7315979964-14">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7315979964-14">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-15">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7315979964-15">&gt;&gt;</span><span class="gp unselectable">
│ │ │  10&gt; </span><span class="n">H</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-16">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="4239799373-16">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -11&gt; </span><span class="p" data-group-id="4239799373-17">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">J</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="4239799373-17">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4239799373-18">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="4239799373-18">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-19">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="4239799373-19">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +</span><span class="p" data-group-id="7315979964-16">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7315979964-16">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +11&gt; </span><span class="p" data-group-id="7315979964-17">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">J</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="7315979964-17">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7315979964-18">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="7315979964-18">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-19">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="7315979964-19">&gt;&gt;</span><span class="gp unselectable">
│ │ │  12&gt; </span><span class="n">J</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-20">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="4239799373-20">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-20">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="7315979964-20">&gt;&gt;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">13</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="4239799373-21">&lt;&lt;</span><span class="mi">1024</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="4239799373-21">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-22">&lt;&lt;</span><span class="mi">208</span><span class="p">,</span><span class="mi">128</span><span class="p" data-group-id="4239799373-22">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="mi">13</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="7315979964-21">&lt;&lt;</span><span class="mi">1024</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="7315979964-21">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-22">&lt;&lt;</span><span class="mi">208</span><span class="p">,</span><span class="mi">128</span><span class="p" data-group-id="7315979964-22">&gt;&gt;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">14</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="4239799373-23">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">:</span><span class="mi">7</span><span class="p" data-group-id="4239799373-23">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-24">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="4239799373-24">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -15&gt; </span><span class="p" data-group-id="4239799373-25">&lt;&lt;</span><span class="mi">16#123</span><span class="p">:</span><span class="mi">12</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="4239799373-25">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4239799373-26">&lt;&lt;</span><span class="mi">16#231</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="4239799373-26">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4239799373-27">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="4239799373-27">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4239799373-28">&lt;&lt;</span><span class="mi">35</span><span class="p">,</span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="4239799373-28">&gt;&gt;</span></code></pre><p>Notice that bit string patterns cannot be nested.</p><p>Notice also that &quot;<code class="inline">B=&lt;&lt;1&gt;&gt;</code>&quot; is interpreted as &quot;<code class="inline">B =&lt; &lt;1&gt;&gt;</code>&quot; which is a syntax
│ │ │ +</span><span class="mi">14</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="7315979964-23">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">:</span><span class="mi">7</span><span class="p" data-group-id="7315979964-23">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-24">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="7315979964-24">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +15&gt; </span><span class="p" data-group-id="7315979964-25">&lt;&lt;</span><span class="mi">16#123</span><span class="p">:</span><span class="mi">12</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="7315979964-25">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7315979964-26">&lt;&lt;</span><span class="mi">16#231</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="7315979964-26">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7315979964-27">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="7315979964-27">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7315979964-28">&lt;&lt;</span><span class="mi">35</span><span class="p">,</span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="7315979964-28">&gt;&gt;</span></code></pre><p>Notice that bit string patterns cannot be nested.</p><p>Notice also that &quot;<code class="inline">B=&lt;&lt;1&gt;&gt;</code>&quot; is interpreted as &quot;<code class="inline">B =&lt; &lt;1&gt;&gt;</code>&quot; which is a syntax
│ │ │  error. The correct way is to write a space after <code class="inline">=</code>: &quot;<code class="inline">B = &lt;&lt;1&gt;&gt;</code>.</p><p>More examples are provided in <a href="../../doc/system/bit_syntax.html">Programming Examples</a>.</p><h2 id="fun-expressions" class="section-heading">
│ │ │    <a href="#fun-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Fun Expressions</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">fun</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9609356392-1">[</span><span class="n">Name</span><span class="p" data-group-id="9609356392-1">]</span><span class="p" data-group-id="9609356392-2">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="9609356392-2">)</span><span class="w"> </span><span class="p" data-group-id="9609356392-3">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9609356392-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0338283064-1">[</span><span class="n">Name</span><span class="p" data-group-id="0338283064-1">]</span><span class="p" data-group-id="0338283064-2">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="0338283064-2">)</span><span class="w"> </span><span class="p" data-group-id="0338283064-3">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="0338283064-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9609356392-4">[</span><span class="n">Name</span><span class="p" data-group-id="9609356392-4">]</span><span class="p" data-group-id="9609356392-5">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="9609356392-5">)</span><span class="w"> </span><span class="p" data-group-id="9609356392-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="9609356392-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0338283064-4">[</span><span class="n">Name</span><span class="p" data-group-id="0338283064-4">]</span><span class="p" data-group-id="0338283064-5">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="0338283064-5">)</span><span class="w"> </span><span class="p" data-group-id="0338283064-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="0338283064-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                </span><span class="n">BodyK</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>A fun expression begins with the keyword <code class="inline">fun</code> and ends with the keyword <code class="inline">end</code>.
│ │ │  Between them is to be a function declaration, similar to a
│ │ │  <a href="ref_man_functions.html#function-declaration-syntax">regular function declaration</a>,
│ │ │  except that the function name is optional and is to be a variable, if any.</p><p>Variables in a fun head shadow the function name and both shadow variables in
│ │ │  the function clause surrounding the fun expression. Variables bound in a fun
│ │ │ -body are local to the fun body.</p><p>The return value of the expression is the resulting fun.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5492971741-1">(</span><span class="n">X</span><span class="p" data-group-id="5492971741-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +body are local to the fun body.</p><p>The return value of the expression is the resulting fun.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8882036921-1">(</span><span class="n">X</span><span class="p" data-group-id="8882036921-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="5492971741-2">(</span><span class="mi">2</span><span class="p" data-group-id="5492971741-2">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="8882036921-2">(</span><span class="mi">2</span><span class="p" data-group-id="8882036921-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="n">Fun2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5492971741-3">(</span><span class="n">X</span><span class="p" data-group-id="5492971741-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="o">&gt;=</span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">gt</span><span class="p">;</span><span class="w"> </span><span class="p" data-group-id="5492971741-4">(</span><span class="n">X</span><span class="p" data-group-id="5492971741-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">lt</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="n">Fun2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8882036921-3">(</span><span class="n">X</span><span class="p" data-group-id="8882036921-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="o">&gt;=</span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">gt</span><span class="p">;</span><span class="w"> </span><span class="p" data-group-id="8882036921-4">(</span><span class="n">X</span><span class="p" data-group-id="8882036921-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">lt</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="n">Fun2</span><span class="p" data-group-id="5492971741-5">(</span><span class="mi">7</span><span class="p" data-group-id="5492971741-5">)</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="n">Fun2</span><span class="p" data-group-id="8882036921-5">(</span><span class="mi">7</span><span class="p" data-group-id="8882036921-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">gt</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="n">Fun3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="5492971741-6">(</span><span class="mi">1</span><span class="p" data-group-id="5492971741-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="5492971741-7">(</span><span class="n">X</span><span class="p" data-group-id="5492971741-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="5492971741-8">(</span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5492971741-8">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="n">Fun3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="8882036921-6">(</span><span class="mi">1</span><span class="p" data-group-id="8882036921-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="8882036921-7">(</span><span class="n">X</span><span class="p" data-group-id="8882036921-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="8882036921-8">(</span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8882036921-8">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="n">Fun3</span><span class="p" data-group-id="5492971741-9">(</span><span class="mi">4</span><span class="p" data-group-id="5492971741-9">)</span><span class="p">.</span><span class="w">
│ │ │ +6&gt; </span><span class="n">Fun3</span><span class="p" data-group-id="8882036921-9">(</span><span class="mi">4</span><span class="p" data-group-id="8882036921-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">24</span></code></pre><p>The following fun expressions are also allowed:</p><pre><code class="makeup erlang" translate="no"><span class="k">fun</span><span class="w"> </span><span class="n">Name</span><span class="o">/</span><span class="n">Arity</span><span class="w">
│ │ │  </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">Name</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In <code class="inline">Name/Arity</code>, <code class="inline">Name</code> is an atom and <code class="inline">Arity</code> is an integer. <code class="inline">Name/Arity</code> must
│ │ │ -specify an existing local function. The expression is syntactic sugar for:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5736247238-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="5736247238-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="5736247238-2">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="5736247238-2">)</span><span class="w"> </span><span class="k">end</span></code></pre><p>In <code class="inline">Module:Name/Arity</code>, <code class="inline">Module</code>, and <code class="inline">Name</code> are atoms and <code class="inline">Arity</code> is an
│ │ │ +specify an existing local function. The expression is syntactic sugar for:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="9784870619-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="9784870619-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9784870619-2">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="9784870619-2">)</span><span class="w"> </span><span class="k">end</span></code></pre><p>In <code class="inline">Module:Name/Arity</code>, <code class="inline">Module</code>, and <code class="inline">Name</code> are atoms and <code class="inline">Arity</code> is an
│ │ │  integer. <code class="inline">Module</code>, <code class="inline">Name</code>, and <code class="inline">Arity</code> can also be variables. A fun defined in
│ │ │  this way refers to the function <code class="inline">Name</code> with arity <code class="inline">Arity</code> in the <em>latest</em>
│ │ │  version of module <code class="inline">Module</code>. A fun defined in this way is not dependent on the
│ │ │  code for the module in which it is defined.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R15, <code class="inline">Module</code>, <code class="inline">Name</code>, and <code class="inline">Arity</code> were not allowed to be
│ │ │  variables.</p></section><p>More examples are provided in <a href="../../doc/system/funs.html">Programming Examples</a>.</p><h2 id="catch-and-throw" class="section-heading">
│ │ │    <a href="#catch-and-throw" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -981,35 +981,35 @@
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">catch</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>Returns the value of <code class="inline">Expr</code> unless an exception is raised during the evaluation. In
│ │ │  that case, the exception is caught. The return value depends on the class of the
│ │ │  exception:</p><ul><li><p><strong><code class="inline">error</code></strong> (a run-time error or the code called <a href="../../erts-15.2.7/doc/html/erlang.html#error/1"><code class="inline">error(Term)</code></a>) -
│ │ │  <code class="inline">{'EXIT',{Reason,Stack}}</code> is returned.</p></li><li><p><strong><code class="inline">exit</code></strong> (the code called <a href="../../erts-15.2.7/doc/html/erlang.html#exit/1"><code class="inline">exit(Term)</code></a>) - <code class="inline">{'EXIT',Term}</code> is returned.</p></li><li><p><strong><code class="inline">throw</code></strong> (the code called <a href="../../erts-15.2.7/doc/html/erlang.html#throw/1"><code class="inline">throw(Term)</code></a>): <code class="inline">Term</code> is returned.</p></li></ul><p><code class="inline">Reason</code> depends on the type of error that occurred, and <code class="inline">Stack</code> is the stack of
│ │ │  recent function calls, see <a href="errors.html#exit_reasons">Exit Reasons</a>.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="k">catch</span><span class="w"> </span><span class="mi">1</span><span class="o">+</span><span class="mi">2</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │  2&gt; </span><span class="k">catch</span><span class="w"> </span><span class="mi">1</span><span class="o">+</span><span class="ss">a</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6599516456-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="6599516456-2">{</span><span class="ss">badarith</span><span class="p">,</span><span class="p" data-group-id="6599516456-3">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6599516456-3">]</span><span class="p" data-group-id="6599516456-2">}</span><span class="p" data-group-id="6599516456-1">}</span></code></pre><p>The BIF <a href="../../erts-15.2.7/doc/html/erlang.html#throw/1"><code class="inline">throw(Any)</code></a> can be used for non-local return from a
│ │ │ -function. It must be evaluated within a <code class="inline">catch</code>, which returns the value <code class="inline">Any</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="4217324514-1">(</span><span class="ss">hello</span><span class="p" data-group-id="4217324514-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8976907428-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="8976907428-2">{</span><span class="ss">badarith</span><span class="p">,</span><span class="p" data-group-id="8976907428-3">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8976907428-3">]</span><span class="p" data-group-id="8976907428-2">}</span><span class="p" data-group-id="8976907428-1">}</span></code></pre><p>The BIF <a href="../../erts-15.2.7/doc/html/erlang.html#throw/1"><code class="inline">throw(Any)</code></a> can be used for non-local return from a
│ │ │ +function. It must be evaluated within a <code class="inline">catch</code>, which returns the value <code class="inline">Any</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="6749734644-1">(</span><span class="ss">hello</span><span class="p" data-group-id="6749734644-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span></code></pre><p>If <a href="../../erts-15.2.7/doc/html/erlang.html#throw/1"><code class="inline">throw/1</code></a> is not evaluated within a catch, a <code class="inline">nocatch</code> run-time
│ │ │  error occurs.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 24, the <code class="inline">catch</code> operator had the lowest precedence, making
│ │ │ -it necessary to add parentheses when combining it with the <code class="inline">match</code> operator:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9863129312-1">(</span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="9863129312-1">)</span><span class="p">.</span><span class="w">
│ │ │ +it necessary to add parentheses when combining it with the <code class="inline">match</code> operator:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2177119002-1">(</span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="2177119002-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span><span class="gp unselectable">
│ │ │  2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span></code></pre><p>Starting from Erlang/OTP 24, the parentheses can be omitted:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span><span class="gp unselectable">
│ │ │  2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span></code></pre></section><h2 id="try" class="section-heading">
│ │ │    <a href="#try" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Try</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="5627779208-1">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="5627779208-1">]</span><span class="w"> </span><span class="p" data-group-id="5627779208-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="5627779208-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="6804203481-1">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="6804203481-1">]</span><span class="w"> </span><span class="p" data-group-id="6804203481-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="6804203481-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="5627779208-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="5627779208-3">]</span><span class="w"> </span><span class="p" data-group-id="5627779208-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="5627779208-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="6804203481-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="6804203481-3">]</span><span class="w"> </span><span class="p" data-group-id="6804203481-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="6804203481-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>This is an enhancement of <a href="expressions.html#catch-and-throw">catch</a>. It gives the
│ │ │  possibility to:</p><ul><li>Distinguish between different exception classes.</li><li>Choose to handle only the desired ones.</li><li>Passing the others on to an enclosing <code class="inline">try</code> or <code class="inline">catch</code>, or to default error
│ │ │  handling.</li></ul><p>Notice that although the keyword <code class="inline">catch</code> is used in the <code class="inline">try</code> expression, there
│ │ │  is not a <code class="inline">catch</code> expression within the <code class="inline">try</code> expression.</p><p>It returns the value of <code class="inline">Exprs</code> (a sequence of expressions <code class="inline">Expr1, ..., ExprN</code>)
│ │ │  unless an exception occurs during the evaluation. In that case the exception is
│ │ │  caught and the patterns <code class="inline">ExceptionPattern</code> with the right exception class
│ │ │ @@ -1019,47 +1019,47 @@
│ │ │  stack trace is bound to the variable when the corresponding <code class="inline">ExceptionPattern</code>
│ │ │  matches.</p><p>If an exception occurs during evaluation of <code class="inline">Exprs</code> but there is no matching
│ │ │  <code class="inline">ExceptionPattern</code> of the right <code class="inline">Class</code> with a true guard sequence, the
│ │ │  exception is passed on as if <code class="inline">Exprs</code> had not been enclosed in a <code class="inline">try</code>
│ │ │  expression.</p><p>If an exception occurs during evaluation of <code class="inline">ExceptionBody</code>, it is not caught.</p><p>It is allowed to omit <code class="inline">Class</code> and <code class="inline">Stacktrace</code>. An omitted <code class="inline">Class</code> is shorthand
│ │ │  for <code class="inline">throw</code>:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ -    </span><span class="n">ExceptionPattern1</span><span class="w"> </span><span class="p" data-group-id="7067865446-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="7067865446-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ExceptionPattern1</span><span class="w"> </span><span class="p" data-group-id="9942726962-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="9942726962-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ExceptionPatternN</span><span class="w"> </span><span class="p" data-group-id="7067865446-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="7067865446-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ExceptionPatternN</span><span class="w"> </span><span class="p" data-group-id="9942726962-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="9942726962-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">try</code> expression can have an <code class="inline">of</code> section:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="8514593080-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="8514593080-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="4347476019-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="4347476019-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="8514593080-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="8514593080-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="4347476019-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="4347476019-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="8514593080-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="8514593080-3">]</span><span class="w"> </span><span class="p" data-group-id="8514593080-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="8514593080-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="4347476019-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="4347476019-3">]</span><span class="w"> </span><span class="p" data-group-id="4347476019-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="4347476019-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="8514593080-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="8514593080-5">]</span><span class="w"> </span><span class="p" data-group-id="8514593080-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="8514593080-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="4347476019-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="4347476019-5">]</span><span class="w"> </span><span class="p" data-group-id="4347476019-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="4347476019-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>If the evaluation of <code class="inline">Exprs</code> succeeds without an exception, the patterns
│ │ │  <code class="inline">Pattern</code> are sequentially matched against the result in the same way as for a
│ │ │  <a href="expressions.html#case">case</a> expression, except that if the matching fails, a
│ │ │  <code class="inline">try_clause</code> run-time error occurs instead of a <code class="inline">case_clause</code>.</p><p>Only exceptions occurring during the evaluation of <code class="inline">Exprs</code> can be caught by the
│ │ │  <code class="inline">catch</code> section. Exceptions occurring in a <code class="inline">Body</code> or due to a failed match are
│ │ │  not caught.</p><p>The <code class="inline">try</code> expression can also be augmented with an <code class="inline">after</code> section, intended to
│ │ │  be used for cleanup with side effects:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="9609851156-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9609851156-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="2195570923-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="2195570923-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="9609851156-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="9609851156-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="2195570923-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="2195570923-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="9609851156-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="9609851156-3">]</span><span class="w"> </span><span class="p" data-group-id="9609851156-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="9609851156-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="2195570923-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="2195570923-3">]</span><span class="w"> </span><span class="p" data-group-id="2195570923-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="2195570923-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="9609851156-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="9609851156-5">]</span><span class="w"> </span><span class="p" data-group-id="9609851156-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="9609851156-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="2195570923-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="2195570923-5">]</span><span class="w"> </span><span class="p" data-group-id="2195570923-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="2195570923-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │  </span><span class="k">after</span><span class="w">
│ │ │      </span><span class="n">AfterBody</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p><code class="inline">AfterBody</code> is evaluated after either <code class="inline">Body</code> or <code class="inline">ExceptionBody</code>, no matter which
│ │ │  one. The evaluated value of <code class="inline">AfterBody</code> is lost; the return value of the <code class="inline">try</code>
│ │ │  expression is the same with an <code class="inline">after</code> section as without.</p><p>Even if an exception occurs during evaluation of <code class="inline">Body</code> or <code class="inline">ExceptionBody</code>,
│ │ │  <code class="inline">AfterBody</code> is evaluated. In this case the exception is passed on after
│ │ │ @@ -1082,40 +1082,40 @@
│ │ │          </span><span class="n">ExpressionBody</span><span class="w">
│ │ │  </span><span class="k">after</span><span class="w">
│ │ │      </span><span class="n">AfterBody</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="w">
│ │ │  
│ │ │  </span><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="n">AfterBody</span><span class="w"> </span><span class="k">end</span></code></pre><p>Next is an example of using <code class="inline">after</code>. This closes the file, even in the event of
│ │ │  exceptions in <a href="../../lib/kernel-10.2.7.1/doc/html/file.html#read/2"><code class="inline">file:read/2</code></a> or in <a href="../../erts-15.2.7/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a>. The
│ │ │ -exceptions are the same as without the <code class="inline">try</code>...<code class="inline">after</code>...<code class="inline">end</code> expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">termize_file</span><span class="p" data-group-id="7727256411-1">(</span><span class="n">Name</span><span class="p" data-group-id="7727256411-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7727256411-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="7727256411-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="7727256411-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7727256411-4">[</span><span class="ss">read</span><span class="p">,</span><span class="ss">binary</span><span class="p" data-group-id="7727256411-4">]</span><span class="p" data-group-id="7727256411-3">)</span><span class="p">,</span><span class="w">
│ │ │ +exceptions are the same as without the <code class="inline">try</code>...<code class="inline">after</code>...<code class="inline">end</code> expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">termize_file</span><span class="p" data-group-id="7320188804-1">(</span><span class="n">Name</span><span class="p" data-group-id="7320188804-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7320188804-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="7320188804-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="7320188804-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7320188804-4">[</span><span class="ss">read</span><span class="p">,</span><span class="ss">binary</span><span class="p" data-group-id="7320188804-4">]</span><span class="p" data-group-id="7320188804-3">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">try</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7727256411-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">Bin</span><span class="p" data-group-id="7727256411-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="7727256411-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="p" data-group-id="7727256411-6">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="nf">binary_to_term</span><span class="p" data-group-id="7727256411-7">(</span><span class="n">Bin</span><span class="p" data-group-id="7727256411-7">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7320188804-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">Bin</span><span class="p" data-group-id="7320188804-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="7320188804-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="p" data-group-id="7320188804-6">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="nf">binary_to_term</span><span class="p" data-group-id="7320188804-7">(</span><span class="n">Bin</span><span class="p" data-group-id="7320188804-7">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w">
│ │ │ -        </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="7727256411-8">(</span><span class="n">F</span><span class="p" data-group-id="7727256411-8">)</span><span class="w">
│ │ │ +        </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="7320188804-8">(</span><span class="n">F</span><span class="p" data-group-id="7320188804-8">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Next is an example of using <code class="inline">try</code> to emulate <code class="inline">catch Expr</code>:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Expr</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │      </span><span class="nc">throw</span><span class="p">:</span><span class="n">Term</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Term</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nc">exit</span><span class="p">:</span><span class="n">Reason</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5135895812-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="5135895812-1">}</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nc">error</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stk</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5135895812-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="5135895812-3">{</span><span class="n">Reason</span><span class="p">,</span><span class="n">Stk</span><span class="p" data-group-id="5135895812-3">}</span><span class="p" data-group-id="5135895812-2">}</span><span class="w">
│ │ │ +    </span><span class="nc">exit</span><span class="p">:</span><span class="n">Reason</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3875561306-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="3875561306-1">}</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nc">error</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stk</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3875561306-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="3875561306-3">{</span><span class="n">Reason</span><span class="p">,</span><span class="n">Stk</span><span class="p" data-group-id="3875561306-3">}</span><span class="p" data-group-id="3875561306-2">}</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>Variables bound in the various parts of these expressions have different scopes.
│ │ │  Variables bound just after the <code class="inline">try</code> keyword are:</p><ul><li>bound in the <code class="inline">of</code> section</li><li>unsafe in both the <code class="inline">catch</code> and <code class="inline">after</code> sections, as well as after the whole
│ │ │  construct</li></ul><p>Variables bound in <code class="inline">of</code> section are:</p><ul><li>unbound in the <code class="inline">catch</code> section</li><li>unsafe in both the <code class="inline">after</code> section, as well as after the whole construct</li></ul><p>Variables bound in the <code class="inline">catch</code> section are unsafe in the <code class="inline">after</code> section, as
│ │ │  well as after the whole construct.</p><p>Variables bound in the <code class="inline">after</code> section are unsafe after the whole construct.</p><h2 id="parenthesized-expressions" class="section-heading">
│ │ │    <a href="#parenthesized-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Parenthesized Expressions</span>
│ │ │  </h2>
│ │ │ -<pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9593762925-1">(</span><span class="n">Expr</span><span class="p" data-group-id="9593762925-1">)</span></code></pre><p>Parenthesized expressions are useful to override
│ │ │ +<pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4211843410-1">(</span><span class="n">Expr</span><span class="p" data-group-id="4211843410-1">)</span></code></pre><p>Parenthesized expressions are useful to override
│ │ │  <a href="expressions.html#prec">operator precedences</a>, for example, in arithmetic
│ │ │  expressions:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">7</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="5030793628-1">(</span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5030793628-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="p" data-group-id="2964084288-1">(</span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2964084288-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">9</span></code></pre><h2 id="block-expressions" class="section-heading">
│ │ │    <a href="#block-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Block Expressions</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">begin</span><span class="w">
│ │ │ @@ -1127,71 +1127,71 @@
│ │ │    <a href="#comprehensions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Comprehensions</span>
│ │ │  </h2>
│ │ │  <p>Comprehensions provide a succinct notation for iterating over one or more terms
│ │ │  and constructing a new term. Comprehensions come in three different flavors,
│ │ │ -depending on the type of term they build.</p><p>List comprehensions construct lists. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8587925800-1">[</span><span class="n">Expr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="8587925800-1">]</span></code></pre><p>Here, <code class="inline">Expr</code> is an arbitrary expression, and each <code class="inline">Qualifier</code> is either a
│ │ │ +depending on the type of term they build.</p><p>List comprehensions construct lists. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4299245042-1">[</span><span class="n">Expr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="4299245042-1">]</span></code></pre><p>Here, <code class="inline">Expr</code> is an arbitrary expression, and each <code class="inline">Qualifier</code> is either a
│ │ │  <strong>generator</strong> or a <strong>filter</strong>.</p><p>Bit string comprehensions construct bit strings or binaries. They have the
│ │ │ -following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6062108591-1">&lt;&lt;</span><span class="w"> </span><span class="n">BitStringExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="w"> </span><span class="p" data-group-id="6062108591-1">&gt;&gt;</span></code></pre><p><code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string. If
│ │ │ +following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4426345044-1">&lt;&lt;</span><span class="w"> </span><span class="n">BitStringExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="w"> </span><span class="p" data-group-id="4426345044-1">&gt;&gt;</span></code></pre><p><code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string. If
│ │ │  <code class="inline">BitStringExpr</code> is a function call, it must be enclosed in parentheses. Each
│ │ │ -<code class="inline">Qualifier</code> is either a <strong>generator</strong> or a <strong>filter</strong>.</p><p>Map comprehensions construct maps. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5139753182-1">#{</span><span class="n">KeyExpr</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="5139753182-1">}</span></code></pre><p>Here, <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> are arbitrary expressions, and each <code class="inline">Qualifier</code>
│ │ │ +<code class="inline">Qualifier</code> is either a <strong>generator</strong> or a <strong>filter</strong>.</p><p>Map comprehensions construct maps. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5327168350-1">#{</span><span class="n">KeyExpr</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="5327168350-1">}</span></code></pre><p>Here, <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> are arbitrary expressions, and each <code class="inline">Qualifier</code>
│ │ │  is either a <strong>generator</strong> or a <strong>filter</strong>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Map comprehensions and map generators were introduced in Erlang/OTP 26.</p></section><p>There are three kinds of generators.</p><p>A <em>list generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">ListExpr</span></code></pre><p>where <code class="inline">ListExpr</code> is an expression that evaluates to a list of terms.</p><p>A <em>bit string generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">BitstringPattern</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="n">BitStringExpr</span></code></pre><p>where <code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string.</p><p>A <em>map generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">KeyPattern</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">ValuePattern</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">MapExpression</span></code></pre><p>where <code class="inline">MapExpr</code> is an expression that evaluates to a map, or a map iterator
│ │ │  obtained by calling <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html#iterator/1"><code class="inline">maps:iterator/1</code></a> or <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html#iterator/2"><code class="inline">maps:iterator/2</code></a>.</p><p>A <em>filter</em> is an expression that evaluates to <code class="inline">true</code> or <code class="inline">false</code>.</p><p>The variables in the generator patterns shadow previously bound variables,
│ │ │  including variables bound in a previous generator pattern.</p><p>Variables bound in a generator expression are not visible outside the
│ │ │ -expression:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7064007443-1">[</span><span class="p" data-group-id="7064007443-2">{</span><span class="n">E</span><span class="p">,</span><span class="n">L</span><span class="p" data-group-id="7064007443-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="o">=</span><span class="p" data-group-id="7064007443-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7064007443-3">]</span><span class="p" data-group-id="7064007443-1">]</span><span class="p">.</span><span class="w">
│ │ │ +expression:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2644159035-1">[</span><span class="p" data-group-id="2644159035-2">{</span><span class="n">E</span><span class="p">,</span><span class="n">L</span><span class="p" data-group-id="2644159035-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="o">=</span><span class="p" data-group-id="2644159035-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2644159035-3">]</span><span class="p" data-group-id="2644159035-1">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">* 1:5: variable &#39;L&#39; is unbound</span></code></pre><p>A <strong>list comprehension</strong> returns a list, where the list elements are the result
│ │ │  of evaluating <code class="inline">Expr</code> for each combination of generator elements for which all
│ │ │  filters are true.</p><p>A <strong>bit string comprehension</strong> returns a bit string, which is created by
│ │ │  concatenating the results of evaluating <code class="inline">BitStringExpr</code> for each combination of
│ │ │  bit string generator elements for which all filters are true.</p><p>A <strong>map comprehension</strong> returns a map, where the map elements are the result of
│ │ │  evaluating <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> for each combination of generator elements
│ │ │  for which all filters are true. If the key expressions are not unique, the last
│ │ │ -occurrence is stored in the map.</p><p><strong>Examples:</strong></p><p>Multiplying each element in a list by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9506106838-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9506106838-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9506106838-2">]</span><span class="p" data-group-id="9506106838-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9506106838-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9506106838-3">]</span></code></pre><p>Multiplying each byte in a binary by two, returning a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2316123461-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="2316123461-2">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="2316123461-2">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="2316123461-3">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2316123461-3">&gt;&gt;</span><span class="p" data-group-id="2316123461-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2316123461-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2316123461-4">]</span></code></pre><p>Multiplying each byte in a binary by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4027758364-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="4027758364-2">&lt;&lt;</span><span class="p" data-group-id="4027758364-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="4027758364-3">)</span><span class="p" data-group-id="4027758364-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="4027758364-4">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="4027758364-4">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="4027758364-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4027758364-5">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="4027758364-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4027758364-6">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4027758364-6">&gt;&gt;</span></code></pre><p>Multiplying each element in a list by two, returning a binary:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1283167943-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="1283167943-2">&lt;&lt;</span><span class="p" data-group-id="1283167943-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="1283167943-3">)</span><span class="p" data-group-id="1283167943-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="1283167943-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1283167943-4">]</span><span class="w"> </span><span class="p" data-group-id="1283167943-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1283167943-5">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1283167943-5">&gt;&gt;</span></code></pre><p>Creating a mapping from an integer to its square:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5047270698-1">#{</span><span class="n">X</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="5047270698-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5047270698-2">]</span><span class="p" data-group-id="5047270698-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047270698-3">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="5047270698-3">}</span></code></pre><p>Multiplying the value of each element in a map by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0960908247-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">V</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0960908247-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="0960908247-2">}</span><span class="p" data-group-id="0960908247-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0960908247-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="0960908247-3">}</span></code></pre><p>Filtering a list, keeping odd numbers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8268605128-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="8268605128-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8268605128-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8268605128-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8268605128-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8268605128-3">]</span></code></pre><p>Filtering a list, keeping only elements that match:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8079467937-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="8079467937-2">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8079467937-2">}</span><span class="o">=</span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="8079467937-3">[</span><span class="p" data-group-id="8079467937-4">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8079467937-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8079467937-5">[</span><span class="ss">a</span><span class="p" data-group-id="8079467937-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8079467937-6">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="8079467937-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8079467937-7">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8079467937-7">}</span><span class="p" data-group-id="8079467937-3">]</span><span class="p" data-group-id="8079467937-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8079467937-8">[</span><span class="p" data-group-id="8079467937-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8079467937-9">}</span><span class="p">,</span><span class="p" data-group-id="8079467937-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8079467937-10">}</span><span class="p" data-group-id="8079467937-8">]</span></code></pre><p>Combining elements from two list generators:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0879411405-1">[</span><span class="p" data-group-id="0879411405-2">{</span><span class="n">P</span><span class="p">,</span><span class="n">Q</span><span class="p" data-group-id="0879411405-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0879411405-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0879411405-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0879411405-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0879411405-4">]</span><span class="p" data-group-id="0879411405-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0879411405-5">[</span><span class="p" data-group-id="0879411405-6">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0879411405-6">}</span><span class="p">,</span><span class="p" data-group-id="0879411405-7">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0879411405-7">}</span><span class="p">,</span><span class="p" data-group-id="0879411405-8">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0879411405-8">}</span><span class="p">,</span><span class="p" data-group-id="0879411405-9">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0879411405-9">}</span><span class="p">,</span><span class="p" data-group-id="0879411405-10">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0879411405-10">}</span><span class="p">,</span><span class="p" data-group-id="0879411405-11">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0879411405-11">}</span><span class="p" data-group-id="0879411405-5">]</span></code></pre><p>More examples are provided in
│ │ │ +occurrence is stored in the map.</p><p><strong>Examples:</strong></p><p>Multiplying each element in a list by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0957264394-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0957264394-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0957264394-2">]</span><span class="p" data-group-id="0957264394-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0957264394-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="0957264394-3">]</span></code></pre><p>Multiplying each byte in a binary by two, returning a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1468966093-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="1468966093-2">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="1468966093-2">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="1468966093-3">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1468966093-3">&gt;&gt;</span><span class="p" data-group-id="1468966093-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1468966093-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1468966093-4">]</span></code></pre><p>Multiplying each byte in a binary by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7582642188-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="7582642188-2">&lt;&lt;</span><span class="p" data-group-id="7582642188-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="7582642188-3">)</span><span class="p" data-group-id="7582642188-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="7582642188-4">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="7582642188-4">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="7582642188-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7582642188-5">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="7582642188-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7582642188-6">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7582642188-6">&gt;&gt;</span></code></pre><p>Multiplying each element in a list by two, returning a binary:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1881169849-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="1881169849-2">&lt;&lt;</span><span class="p" data-group-id="1881169849-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="1881169849-3">)</span><span class="p" data-group-id="1881169849-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="1881169849-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1881169849-4">]</span><span class="w"> </span><span class="p" data-group-id="1881169849-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1881169849-5">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1881169849-5">&gt;&gt;</span></code></pre><p>Creating a mapping from an integer to its square:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0563768381-1">#{</span><span class="n">X</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0563768381-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0563768381-2">]</span><span class="p" data-group-id="0563768381-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0563768381-3">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="0563768381-3">}</span></code></pre><p>Multiplying the value of each element in a map by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5028847984-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">V</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="5028847984-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5028847984-2">}</span><span class="p" data-group-id="5028847984-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5028847984-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="5028847984-3">}</span></code></pre><p>Filtering a list, keeping odd numbers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0009061770-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0009061770-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0009061770-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0009061770-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0009061770-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0009061770-3">]</span></code></pre><p>Filtering a list, keeping only elements that match:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2683553377-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="2683553377-2">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2683553377-2">}</span><span class="o">=</span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="2683553377-3">[</span><span class="p" data-group-id="2683553377-4">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2683553377-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2683553377-5">[</span><span class="ss">a</span><span class="p" data-group-id="2683553377-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2683553377-6">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="2683553377-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2683553377-7">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2683553377-7">}</span><span class="p" data-group-id="2683553377-3">]</span><span class="p" data-group-id="2683553377-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2683553377-8">[</span><span class="p" data-group-id="2683553377-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2683553377-9">}</span><span class="p">,</span><span class="p" data-group-id="2683553377-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2683553377-10">}</span><span class="p" data-group-id="2683553377-8">]</span></code></pre><p>Combining elements from two list generators:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0480967335-1">[</span><span class="p" data-group-id="0480967335-2">{</span><span class="n">P</span><span class="p">,</span><span class="n">Q</span><span class="p" data-group-id="0480967335-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0480967335-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0480967335-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0480967335-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0480967335-4">]</span><span class="p" data-group-id="0480967335-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0480967335-5">[</span><span class="p" data-group-id="0480967335-6">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0480967335-6">}</span><span class="p">,</span><span class="p" data-group-id="0480967335-7">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0480967335-7">}</span><span class="p">,</span><span class="p" data-group-id="0480967335-8">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0480967335-8">}</span><span class="p">,</span><span class="p" data-group-id="0480967335-9">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0480967335-9">}</span><span class="p">,</span><span class="p" data-group-id="0480967335-10">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0480967335-10">}</span><span class="p">,</span><span class="p" data-group-id="0480967335-11">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0480967335-11">}</span><span class="p" data-group-id="0480967335-5">]</span></code></pre><p>More examples are provided in
│ │ │  <a href="../../doc/system/list_comprehensions.html">Programming Examples.</a></p><p>When there are no generators, a comprehension returns either a term constructed
│ │ │  from a single element (the result of evaluating <code class="inline">Expr</code>) if all filters are true,
│ │ │  or a term constructed from no elements (that is, <code class="inline">[]</code> for list comprehension,
│ │ │ -<code class="inline">&lt;&lt;&gt;&gt;</code> for a bit string comprehension, and <code class="inline">#{}</code> for a map comprehension).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7914218737-1">[</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="7914218737-2">(</span><span class="mi">2</span><span class="p" data-group-id="7914218737-2">)</span><span class="p" data-group-id="7914218737-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7914218737-3">[</span><span class="mi">2</span><span class="p" data-group-id="7914218737-3">]</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="7914218737-4">[</span><span class="ss">x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="7914218737-5">(</span><span class="ss">x</span><span class="p" data-group-id="7914218737-5">)</span><span class="p" data-group-id="7914218737-4">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7914218737-6">[</span><span class="p" data-group-id="7914218737-6">]</span></code></pre><p>What happens when the filter expression does not evaluate to a boolean value
│ │ │ +<code class="inline">&lt;&lt;&gt;&gt;</code> for a bit string comprehension, and <code class="inline">#{}</code> for a map comprehension).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2458872206-1">[</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="2458872206-2">(</span><span class="mi">2</span><span class="p" data-group-id="2458872206-2">)</span><span class="p" data-group-id="2458872206-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2458872206-3">[</span><span class="mi">2</span><span class="p" data-group-id="2458872206-3">]</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="2458872206-4">[</span><span class="ss">x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="2458872206-5">(</span><span class="ss">x</span><span class="p" data-group-id="2458872206-5">)</span><span class="p" data-group-id="2458872206-4">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2458872206-6">[</span><span class="p" data-group-id="2458872206-6">]</span></code></pre><p>What happens when the filter expression does not evaluate to a boolean value
│ │ │  depends on the expression:</p><ul><li>If the expression is a <a href="expressions.html#guard-expressions">guard expression</a>,
│ │ │  failure to evaluate or evaluating to a non-boolean value is equivalent to
│ │ │  evaluating to <code class="inline">false</code>.</li><li>If the expression is not a guard expression and evaluates to a non-Boolean
│ │ │  value <code class="inline">Val</code>, an exception <code class="inline">{bad_filter, Val}</code> is triggered at runtime. If the
│ │ │  evaluation of the expression raises an exception, it is not caught by the
│ │ │ -comprehension.</li></ul><p><strong>Examples</strong> (using a guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5595692393-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5595692393-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5595692393-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5595692393-2">]</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="5595692393-3">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5595692393-3">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5595692393-4">[</span><span class="p" data-group-id="5595692393-4">]</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="p" data-group-id="5595692393-5">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5595692393-5">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5595692393-6">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5595692393-6">]</span></code></pre><p><strong>Examples</strong> (using a non-guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2731955162-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2731955162-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2731955162-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2731955162-2">]</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="n">FaultyIsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="2731955162-3">(</span><span class="n">E</span><span class="p" data-group-id="2731955162-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +comprehension.</li></ul><p><strong>Examples</strong> (using a guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2418387687-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2418387687-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2418387687-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2418387687-2">]</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="2418387687-3">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2418387687-3">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2418387687-4">[</span><span class="p" data-group-id="2418387687-4">]</span><span class="gp unselectable">
│ │ │ +3&gt; </span><span class="p" data-group-id="2418387687-5">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2418387687-5">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2418387687-6">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2418387687-6">]</span></code></pre><p><strong>Examples</strong> (using a non-guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1896560138-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1896560138-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1896560138-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1896560138-2">]</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="n">FaultyIsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1896560138-3">(</span><span class="n">E</span><span class="p" data-group-id="1896560138-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">42.17316486</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="p" data-group-id="2731955162-4">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">FaultyIsEven</span><span class="p" data-group-id="2731955162-5">(</span><span class="n">E</span><span class="p" data-group-id="2731955162-5">)</span><span class="p" data-group-id="2731955162-4">]</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="p" data-group-id="1896560138-4">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">FaultyIsEven</span><span class="p" data-group-id="1896560138-5">(</span><span class="n">E</span><span class="p" data-group-id="1896560138-5">)</span><span class="p" data-group-id="1896560138-4">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: bad filter 1</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="n">IsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="2731955162-6">(</span><span class="n">E</span><span class="p" data-group-id="2731955162-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="n">IsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1896560138-6">(</span><span class="n">E</span><span class="p" data-group-id="1896560138-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">42.17316486</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="p" data-group-id="2731955162-7">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="2731955162-8">(</span><span class="n">E</span><span class="p" data-group-id="2731955162-8">)</span><span class="p" data-group-id="2731955162-7">]</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="p" data-group-id="1896560138-7">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="1896560138-8">(</span><span class="n">E</span><span class="p" data-group-id="1896560138-8">)</span><span class="p" data-group-id="1896560138-7">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: an error occurred when evaluating an arithmetic expression
│ │ │       in operator  rem/2
│ │ │          called as a rem 2</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="p" data-group-id="2731955162-9">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="2731955162-10">(</span><span class="n">E</span><span class="p" data-group-id="2731955162-10">)</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="2731955162-11">(</span><span class="n">E</span><span class="p" data-group-id="2731955162-11">)</span><span class="p" data-group-id="2731955162-9">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2731955162-12">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2731955162-12">]</span></code></pre><p><a href="" id="guards"></a></p><h2 id="guard-sequences" class="section-heading">
│ │ │ +6&gt; </span><span class="p" data-group-id="1896560138-9">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="1896560138-10">(</span><span class="n">E</span><span class="p" data-group-id="1896560138-10">)</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="1896560138-11">(</span><span class="n">E</span><span class="p" data-group-id="1896560138-11">)</span><span class="p" data-group-id="1896560138-9">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1896560138-12">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1896560138-12">]</span></code></pre><p><a href="" id="guards"></a></p><h2 id="guard-sequences" class="section-heading">
│ │ │    <a href="#guard-sequences" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Guard Sequences</span>
│ │ │  </h2>
│ │ │  <p>A <em>guard sequence</em> is a sequence of guards, separated by semicolon (<code class="inline">;</code>). The
│ │ │  guard sequence is true if at least one of the guards is true. (The remaining
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/funs.html
│ │ │ @@ -117,402 +117,402 @@
│ │ │  
│ │ │  <h2 id="map" class="section-heading">
│ │ │    <a href="#map" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">map</span>
│ │ │  </h2>
│ │ │ -<p>The following function, <code class="inline">double</code>, doubles every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="3643441499-1">(</span><span class="p" data-group-id="3643441499-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3643441499-2">]</span><span class="p" data-group-id="3643441499-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3643441499-3">[</span><span class="mi">2</span><span class="o">*</span><span class="n">H</span><span class="p">|</span><span class="nf">double</span><span class="p" data-group-id="3643441499-4">(</span><span class="n">T</span><span class="p" data-group-id="3643441499-4">)</span><span class="p" data-group-id="3643441499-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="3643441499-5">(</span><span class="p" data-group-id="3643441499-6">[</span><span class="p" data-group-id="3643441499-6">]</span><span class="p" data-group-id="3643441499-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3643441499-7">[</span><span class="p" data-group-id="3643441499-7">]</span><span class="p">.</span></code></pre><p>Hence, the argument entered as input is doubled as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">double</span><span class="p" data-group-id="7136663556-1">(</span><span class="p" data-group-id="7136663556-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7136663556-2">]</span><span class="p" data-group-id="7136663556-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7136663556-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p" data-group-id="7136663556-3">]</span></code></pre><p>The following function, <code class="inline">add_one</code>, adds one to every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add_one</span><span class="p" data-group-id="8654421215-1">(</span><span class="p" data-group-id="8654421215-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8654421215-2">]</span><span class="p" data-group-id="8654421215-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8654421215-3">[</span><span class="n">H</span><span class="o">+</span><span class="mi">1</span><span class="p">|</span><span class="nf">add_one</span><span class="p" data-group-id="8654421215-4">(</span><span class="n">T</span><span class="p" data-group-id="8654421215-4">)</span><span class="p" data-group-id="8654421215-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">add_one</span><span class="p" data-group-id="8654421215-5">(</span><span class="p" data-group-id="8654421215-6">[</span><span class="p" data-group-id="8654421215-6">]</span><span class="p" data-group-id="8654421215-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8654421215-7">[</span><span class="p" data-group-id="8654421215-7">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> have a similar structure. This can be used
│ │ │ -by writing a function <code class="inline">map</code> that expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="3785006034-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3785006034-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3785006034-2">]</span><span class="p" data-group-id="3785006034-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3785006034-3">[</span><span class="n">F</span><span class="p" data-group-id="3785006034-4">(</span><span class="n">H</span><span class="p" data-group-id="3785006034-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="3785006034-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3785006034-5">)</span><span class="p" data-group-id="3785006034-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="3785006034-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3785006034-7">[</span><span class="p" data-group-id="3785006034-7">]</span><span class="p" data-group-id="3785006034-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3785006034-8">[</span><span class="p" data-group-id="3785006034-8">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> can now be expressed in terms of <code class="inline">map</code> as
│ │ │ -follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="2162098537-1">(</span><span class="n">L</span><span class="p" data-group-id="2162098537-1">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="2162098537-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2162098537-3">(</span><span class="n">X</span><span class="p" data-group-id="2162098537-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2162098537-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add_one</span><span class="p" data-group-id="2162098537-4">(</span><span class="n">L</span><span class="p" data-group-id="2162098537-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="2162098537-5">(</span><span class="nf">fun</span><span class="p" data-group-id="2162098537-6">(</span><span class="n">X</span><span class="p" data-group-id="2162098537-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2162098537-5">)</span><span class="p">.</span></code></pre><p><code class="inline">map(F, List)</code> is a function that takes a function <code class="inline">F</code> and a list <code class="inline">L</code> as
│ │ │ +<p>The following function, <code class="inline">double</code>, doubles every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="1227182006-1">(</span><span class="p" data-group-id="1227182006-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1227182006-2">]</span><span class="p" data-group-id="1227182006-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1227182006-3">[</span><span class="mi">2</span><span class="o">*</span><span class="n">H</span><span class="p">|</span><span class="nf">double</span><span class="p" data-group-id="1227182006-4">(</span><span class="n">T</span><span class="p" data-group-id="1227182006-4">)</span><span class="p" data-group-id="1227182006-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="1227182006-5">(</span><span class="p" data-group-id="1227182006-6">[</span><span class="p" data-group-id="1227182006-6">]</span><span class="p" data-group-id="1227182006-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1227182006-7">[</span><span class="p" data-group-id="1227182006-7">]</span><span class="p">.</span></code></pre><p>Hence, the argument entered as input is doubled as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">double</span><span class="p" data-group-id="2790953077-1">(</span><span class="p" data-group-id="2790953077-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2790953077-2">]</span><span class="p" data-group-id="2790953077-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2790953077-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p" data-group-id="2790953077-3">]</span></code></pre><p>The following function, <code class="inline">add_one</code>, adds one to every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add_one</span><span class="p" data-group-id="8250643622-1">(</span><span class="p" data-group-id="8250643622-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8250643622-2">]</span><span class="p" data-group-id="8250643622-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8250643622-3">[</span><span class="n">H</span><span class="o">+</span><span class="mi">1</span><span class="p">|</span><span class="nf">add_one</span><span class="p" data-group-id="8250643622-4">(</span><span class="n">T</span><span class="p" data-group-id="8250643622-4">)</span><span class="p" data-group-id="8250643622-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">add_one</span><span class="p" data-group-id="8250643622-5">(</span><span class="p" data-group-id="8250643622-6">[</span><span class="p" data-group-id="8250643622-6">]</span><span class="p" data-group-id="8250643622-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8250643622-7">[</span><span class="p" data-group-id="8250643622-7">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> have a similar structure. This can be used
│ │ │ +by writing a function <code class="inline">map</code> that expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="1921879019-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1921879019-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1921879019-2">]</span><span class="p" data-group-id="1921879019-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1921879019-3">[</span><span class="n">F</span><span class="p" data-group-id="1921879019-4">(</span><span class="n">H</span><span class="p" data-group-id="1921879019-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="1921879019-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="1921879019-5">)</span><span class="p" data-group-id="1921879019-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="1921879019-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1921879019-7">[</span><span class="p" data-group-id="1921879019-7">]</span><span class="p" data-group-id="1921879019-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1921879019-8">[</span><span class="p" data-group-id="1921879019-8">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> can now be expressed in terms of <code class="inline">map</code> as
│ │ │ +follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="5517799966-1">(</span><span class="n">L</span><span class="p" data-group-id="5517799966-1">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="5517799966-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5517799966-3">(</span><span class="n">X</span><span class="p" data-group-id="5517799966-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5517799966-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add_one</span><span class="p" data-group-id="5517799966-4">(</span><span class="n">L</span><span class="p" data-group-id="5517799966-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="5517799966-5">(</span><span class="nf">fun</span><span class="p" data-group-id="5517799966-6">(</span><span class="n">X</span><span class="p" data-group-id="5517799966-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5517799966-5">)</span><span class="p">.</span></code></pre><p><code class="inline">map(F, List)</code> is a function that takes a function <code class="inline">F</code> and a list <code class="inline">L</code> as
│ │ │  arguments and returns a new list, obtained by applying <code class="inline">F</code> to each of the
│ │ │  elements in <code class="inline">L</code>.</p><p>The process of abstracting out the common features of a number of different
│ │ │  programs is called <em>procedural abstraction</em>. Procedural abstraction can be used
│ │ │  to write several different functions that have a similar structure, but differ
│ │ │  in some minor detail. This is done as follows:</p><ol><li><em>Step 1.</em> Write one function that represents the common features of these
│ │ │  functions.</li><li><em>Step 2.</em> Parameterize the difference in terms of functions that are passed
│ │ │  as arguments to the common function.</li></ol><h2 id="foreach" class="section-heading">
│ │ │    <a href="#foreach" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">foreach</span>
│ │ │  </h2>
│ │ │  <p>This section illustrates procedural abstraction. Initially, the following two
│ │ │ -examples are written as conventional functions.</p><p>This function prints all elements of a list onto a stream:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="9409777090-1">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9409777090-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9409777090-2">]</span><span class="p" data-group-id="9409777090-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9409777090-3">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9409777090-4">[</span><span class="n">H</span><span class="p" data-group-id="9409777090-4">]</span><span class="p" data-group-id="9409777090-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_list</span><span class="p" data-group-id="9409777090-5">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9409777090-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">print_list</span><span class="p" data-group-id="9409777090-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9409777090-7">[</span><span class="p" data-group-id="9409777090-7">]</span><span class="p" data-group-id="9409777090-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>This function broadcasts a message to a list of processes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">broadcast</span><span class="p" data-group-id="6755708767-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6755708767-2">[</span><span class="n">Pid</span><span class="p">|</span><span class="n">Pids</span><span class="p" data-group-id="6755708767-2">]</span><span class="p" data-group-id="6755708767-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +examples are written as conventional functions.</p><p>This function prints all elements of a list onto a stream:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="8797807230-1">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8797807230-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8797807230-2">]</span><span class="p" data-group-id="8797807230-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8797807230-3">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8797807230-4">[</span><span class="n">H</span><span class="p" data-group-id="8797807230-4">]</span><span class="p" data-group-id="8797807230-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_list</span><span class="p" data-group-id="8797807230-5">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8797807230-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">print_list</span><span class="p" data-group-id="8797807230-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8797807230-7">[</span><span class="p" data-group-id="8797807230-7">]</span><span class="p" data-group-id="8797807230-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>This function broadcasts a message to a list of processes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">broadcast</span><span class="p" data-group-id="1875578355-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1875578355-2">[</span><span class="n">Pid</span><span class="p">|</span><span class="n">Pids</span><span class="p" data-group-id="1875578355-2">]</span><span class="p" data-group-id="1875578355-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Msg</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">broadcast</span><span class="p" data-group-id="6755708767-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">Pids</span><span class="p" data-group-id="6755708767-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">broadcast</span><span class="p" data-group-id="6755708767-4">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6755708767-5">[</span><span class="p" data-group-id="6755708767-5">]</span><span class="p" data-group-id="6755708767-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">broadcast</span><span class="p" data-group-id="1875578355-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">Pids</span><span class="p" data-group-id="1875578355-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">broadcast</span><span class="p" data-group-id="1875578355-4">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1875578355-5">[</span><span class="p" data-group-id="1875578355-5">]</span><span class="p" data-group-id="1875578355-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">true</span><span class="p">.</span></code></pre><p>These two functions have a similar structure. They both iterate over a list and
│ │ │  do something to each element in the list. The &quot;something&quot; is passed on as an
│ │ │ -extra argument to the function that does this.</p><p>The function <code class="inline">foreach</code> expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="8218479816-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8218479816-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8218479816-2">]</span><span class="p" data-group-id="8218479816-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">F</span><span class="p" data-group-id="8218479816-3">(</span><span class="n">H</span><span class="p" data-group-id="8218479816-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="8218479816-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8218479816-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="8218479816-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8218479816-6">[</span><span class="p" data-group-id="8218479816-6">]</span><span class="p" data-group-id="8218479816-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">print_list</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="4562301465-1">(</span><span class="nf">fun</span><span class="p" data-group-id="4562301465-2">(</span><span class="n">H</span><span class="p" data-group-id="4562301465-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4562301465-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="4562301465-4">[</span><span class="n">H</span><span class="p" data-group-id="4562301465-4">]</span><span class="p" data-group-id="4562301465-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4562301465-1">)</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">broadcast</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="7582735700-1">(</span><span class="nf">fun</span><span class="p" data-group-id="7582735700-2">(</span><span class="n">Pid</span><span class="p" data-group-id="7582735700-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7582735700-1">)</span></code></pre><p><code class="inline">foreach</code> is evaluated for its side-effect and not its value. <code class="inline">foreach(Fun ,L)</code>
│ │ │ +extra argument to the function that does this.</p><p>The function <code class="inline">foreach</code> expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="8473096994-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8473096994-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8473096994-2">]</span><span class="p" data-group-id="8473096994-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">F</span><span class="p" data-group-id="8473096994-3">(</span><span class="n">H</span><span class="p" data-group-id="8473096994-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="8473096994-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8473096994-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="8473096994-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8473096994-6">[</span><span class="p" data-group-id="8473096994-6">]</span><span class="p" data-group-id="8473096994-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">print_list</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="5029387357-1">(</span><span class="nf">fun</span><span class="p" data-group-id="5029387357-2">(</span><span class="n">H</span><span class="p" data-group-id="5029387357-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5029387357-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="5029387357-4">[</span><span class="n">H</span><span class="p" data-group-id="5029387357-4">]</span><span class="p" data-group-id="5029387357-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5029387357-1">)</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">broadcast</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="9655993662-1">(</span><span class="nf">fun</span><span class="p" data-group-id="9655993662-2">(</span><span class="n">Pid</span><span class="p" data-group-id="9655993662-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="9655993662-1">)</span></code></pre><p><code class="inline">foreach</code> is evaluated for its side-effect and not its value. <code class="inline">foreach(Fun ,L)</code>
│ │ │  calls <code class="inline">Fun(X)</code> for each element <code class="inline">X</code> in <code class="inline">L</code> and the processing occurs in the
│ │ │  order that the elements were defined in <code class="inline">L</code>. <code class="inline">map</code> does not define the order in
│ │ │  which its elements are processed.</p><h2 id="syntax-of-funs" class="section-heading">
│ │ │    <a href="#syntax-of-funs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Syntax of Funs</span>
│ │ │  </h2>
│ │ │  <p>Funs are written with the following syntax (see
│ │ │ -<a href="../../doc/system/expressions.html#fun-expressions">Fun Expressions </a>for full description):</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3280469335-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">ArgN</span><span class="p" data-group-id="3280469335-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<a href="../../doc/system/expressions.html#fun-expressions">Fun Expressions </a>for full description):</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3986544493-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">ArgN</span><span class="p" data-group-id="3986544493-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">end</span></code></pre><p>This creates an anonymous function of <code class="inline">N</code> arguments and binds it to the variable
│ │ │  <code class="inline">F</code>.</p><p>Another function, <code class="inline">FunctionName</code>, written in the same module, can be passed as
│ │ │  an argument, using the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>With this form of function reference, the function that is referred to does not
│ │ │  need to be exported from the module.</p><p>It is also possible to refer to a function defined in a different module, with
│ │ │ -the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In this case, the function must be exported from the module in question.</p><p>The following program illustrates the different ways of creating funs:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4790353553-1">(</span><span class="ss">fun_test</span><span class="p" data-group-id="4790353553-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4790353553-2">(</span><span class="p" data-group-id="4790353553-3">[</span><span class="ss">t1</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">t2</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4790353553-3">]</span><span class="p" data-group-id="4790353553-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="4790353553-4">(</span><span class="ss">lists</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4790353553-5">[</span><span class="ss">map</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4790353553-5">]</span><span class="p" data-group-id="4790353553-4">)</span><span class="p">.</span><span class="w">
│ │ │ +the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In this case, the function must be exported from the module in question.</p><p>The following program illustrates the different ways of creating funs:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2462849660-1">(</span><span class="ss">fun_test</span><span class="p" data-group-id="2462849660-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2462849660-2">(</span><span class="p" data-group-id="2462849660-3">[</span><span class="ss">t1</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">t2</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2462849660-3">]</span><span class="p" data-group-id="2462849660-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="2462849660-4">(</span><span class="ss">lists</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2462849660-5">[</span><span class="ss">map</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2462849660-5">]</span><span class="p" data-group-id="2462849660-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">t1</span><span class="p" data-group-id="4790353553-6">(</span><span class="p" data-group-id="4790353553-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="4790353553-7">(</span><span class="nf">fun</span><span class="p" data-group-id="4790353553-8">(</span><span class="n">X</span><span class="p" data-group-id="4790353553-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4790353553-9">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4790353553-9">]</span><span class="p" data-group-id="4790353553-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">t1</span><span class="p" data-group-id="2462849660-6">(</span><span class="p" data-group-id="2462849660-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="2462849660-7">(</span><span class="nf">fun</span><span class="p" data-group-id="2462849660-8">(</span><span class="n">X</span><span class="p" data-group-id="2462849660-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2462849660-9">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2462849660-9">]</span><span class="p" data-group-id="2462849660-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">t2</span><span class="p" data-group-id="4790353553-10">(</span><span class="p" data-group-id="4790353553-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="4790353553-11">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4790353553-12">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4790353553-12">]</span><span class="p" data-group-id="4790353553-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">t2</span><span class="p" data-group-id="2462849660-10">(</span><span class="p" data-group-id="2462849660-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="2462849660-11">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2462849660-12">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2462849660-12">]</span><span class="p" data-group-id="2462849660-11">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="4790353553-13">(</span><span class="n">X</span><span class="p" data-group-id="4790353553-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span></code></pre><p>The fun <code class="inline">F</code> can be evaluated with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="p" data-group-id="5428331771-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Argn</span><span class="p" data-group-id="5428331771-1">)</span></code></pre><p>To check whether a term is a fun, use the test
│ │ │ -<a href="../../erts-15.2.7/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> in a guard.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="5077652267-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="5077652267-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_function</span><span class="p" data-group-id="5077652267-2">(</span><span class="n">F</span><span class="p" data-group-id="5077652267-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="nf">apply</span><span class="p" data-group-id="5077652267-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="5077652267-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="5077652267-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="5077652267-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="5077652267-5">(</span><span class="n">N</span><span class="p" data-group-id="5077652267-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="2462849660-13">(</span><span class="n">X</span><span class="p" data-group-id="2462849660-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span></code></pre><p>The fun <code class="inline">F</code> can be evaluated with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="p" data-group-id="9159603383-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Argn</span><span class="p" data-group-id="9159603383-1">)</span></code></pre><p>To check whether a term is a fun, use the test
│ │ │ +<a href="../../erts-15.2.7/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> in a guard.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="6987436721-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="6987436721-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_function</span><span class="p" data-group-id="6987436721-2">(</span><span class="n">F</span><span class="p" data-group-id="6987436721-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="nf">apply</span><span class="p" data-group-id="6987436721-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="6987436721-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="6987436721-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6987436721-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="6987436721-5">(</span><span class="n">N</span><span class="p" data-group-id="6987436721-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │     </span><span class="n">N</span><span class="p">.</span></code></pre><p>Funs are a distinct type. The BIFs <code class="inline">erlang:fun_info/1,2</code> can be used to retrieve
│ │ │  information about a fun, and the BIF <a href="../../erts-15.2.7/doc/html/erlang.html#fun_to_list/1"><code class="inline">erlang:fun_to_list/1</code></a> returns a textual
│ │ │  representation of a fun. The <a href="../../erts-15.2.7/doc/html/erlang.html#check_process_code/2"><code class="inline">check_process_code/2</code></a>
│ │ │  BIF returns <code class="inline">true</code> if the process contains funs that depend on the old version
│ │ │  of a module.</p><h2 id="variable-bindings-within-a-fun" class="section-heading">
│ │ │    <a href="#variable-bindings-within-a-fun" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Variable Bindings Within a Fun</span>
│ │ │  </h2>
│ │ │  <p>The scope rules for variables that occur in funs are as follows:</p><ul><li>All variables that occur in the head of a fun are assumed to be &quot;fresh&quot;
│ │ │  variables.</li><li>Variables that are defined before the fun, and that occur in function calls or
│ │ │ -guard tests within the fun, have the values they had outside the fun.</li><li>Variables cannot be exported from a fun.</li></ul><p>The following examples illustrate these rules:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="8624896392-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="8624896392-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8624896392-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="8624896392-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="8624896392-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="8624896392-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="8624896392-4">(</span><span class="nf">fun</span><span class="p" data-group-id="8624896392-5">(</span><span class="n">X</span><span class="p" data-group-id="8624896392-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8624896392-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="8624896392-7">[</span><span class="n">X</span><span class="p" data-group-id="8624896392-7">]</span><span class="p" data-group-id="8624896392-6">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="8624896392-4">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="8624896392-8">(</span><span class="n">Stream</span><span class="p" data-group-id="8624896392-8">)</span><span class="p">.</span></code></pre><p>Here, the variable <code class="inline">X</code>, defined in the head of the fun, is a new variable. The
│ │ │ +guard tests within the fun, have the values they had outside the fun.</li><li>Variables cannot be exported from a fun.</li></ul><p>The following examples illustrate these rules:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="7066948596-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7066948596-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7066948596-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="7066948596-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="7066948596-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="7066948596-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="7066948596-4">(</span><span class="nf">fun</span><span class="p" data-group-id="7066948596-5">(</span><span class="n">X</span><span class="p" data-group-id="7066948596-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7066948596-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="7066948596-7">[</span><span class="n">X</span><span class="p" data-group-id="7066948596-7">]</span><span class="p" data-group-id="7066948596-6">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7066948596-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="7066948596-8">(</span><span class="n">Stream</span><span class="p" data-group-id="7066948596-8">)</span><span class="p">.</span></code></pre><p>Here, the variable <code class="inline">X</code>, defined in the head of the fun, is a new variable. The
│ │ │  variable <code class="inline">Stream</code>, which is used within the fun, gets its value from the
│ │ │  <code class="inline">file:open</code> line.</p><p>As any variable that occurs in the head of a fun is considered a new variable,
│ │ │ -it is equally valid to write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="3093506686-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3093506686-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3093506686-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="3093506686-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="3093506686-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="3093506686-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="3093506686-4">(</span><span class="nf">fun</span><span class="p" data-group-id="3093506686-5">(</span><span class="n">File</span><span class="p" data-group-id="3093506686-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3093506686-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="3093506686-7">[</span><span class="n">File</span><span class="p" data-group-id="3093506686-7">]</span><span class="p" data-group-id="3093506686-6">)</span><span class="w">
│ │ │ -            </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3093506686-4">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="3093506686-8">(</span><span class="n">Stream</span><span class="p" data-group-id="3093506686-8">)</span><span class="p">.</span></code></pre><p>Here, <code class="inline">File</code> is used as the new variable instead of <code class="inline">X</code>. This is not so wise
│ │ │ +it is equally valid to write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="5911033408-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="5911033408-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5911033408-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="5911033408-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="5911033408-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="5911033408-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="5911033408-4">(</span><span class="nf">fun</span><span class="p" data-group-id="5911033408-5">(</span><span class="n">File</span><span class="p" data-group-id="5911033408-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5911033408-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="5911033408-7">[</span><span class="n">File</span><span class="p" data-group-id="5911033408-7">]</span><span class="p" data-group-id="5911033408-6">)</span><span class="w">
│ │ │ +            </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="5911033408-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="5911033408-8">(</span><span class="n">Stream</span><span class="p" data-group-id="5911033408-8">)</span><span class="p">.</span></code></pre><p>Here, <code class="inline">File</code> is used as the new variable instead of <code class="inline">X</code>. This is not so wise
│ │ │  because code in the fun body cannot refer to the variable <code class="inline">File</code>, which is
│ │ │  defined outside of the fun. Compiling this example gives the following
│ │ │  diagnostic:</p><pre><code class="text">./FileName.erl:Line: Warning: variable 'File'
│ │ │        shadowed in 'fun'</code></pre><p>This indicates that the variable <code class="inline">File</code>, which is defined inside the fun,
│ │ │  collides with the variable <code class="inline">File</code>, which is defined outside the fun.</p><p>The rules for importing variables into a fun has the consequence that certain
│ │ │  pattern matching operations must be moved into guard expressions and cannot be
│ │ │  written in the head of the fun. For example, you might write the following code
│ │ │  if you intend the first clause of <code class="inline">F</code> to be evaluated when the value of its
│ │ │ -argument is <code class="inline">Y</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="7599190131-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7599190131-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +argument is <code class="inline">Y</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="7810785775-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7810785775-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="nf">map</span><span class="p" data-group-id="7599190131-2">(</span><span class="nf">fun</span><span class="p" data-group-id="7599190131-3">(</span><span class="n">X</span><span class="p" data-group-id="7599190131-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">map</span><span class="p" data-group-id="7810785775-2">(</span><span class="nf">fun</span><span class="p" data-group-id="7810785775-3">(</span><span class="n">X</span><span class="p" data-group-id="7810785775-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │               </span><span class="p">;</span><span class="w">
│ │ │ -           </span><span class="p" data-group-id="7599190131-4">(</span><span class="p">_</span><span class="p" data-group-id="7599190131-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +           </span><span class="p" data-group-id="7810785775-4">(</span><span class="p">_</span><span class="p" data-group-id="7810785775-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │               </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7599190131-2">)</span><span class="w">
│ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>instead of writing the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0583116183-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0583116183-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7810785775-2">)</span><span class="w">
│ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>instead of writing the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0944460451-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0944460451-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="nf">map</span><span class="p" data-group-id="0583116183-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0583116183-3">(</span><span class="n">Y</span><span class="p" data-group-id="0583116183-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">map</span><span class="p" data-group-id="0944460451-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0944460451-3">(</span><span class="n">Y</span><span class="p" data-group-id="0944460451-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │               </span><span class="p">;</span><span class="w">
│ │ │ -           </span><span class="p" data-group-id="0583116183-4">(</span><span class="p">_</span><span class="p" data-group-id="0583116183-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +           </span><span class="p" data-group-id="0944460451-4">(</span><span class="p">_</span><span class="p" data-group-id="0944460451-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │               </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0583116183-2">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0944460451-2">)</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="funs-and-module-lists" class="section-heading">
│ │ │    <a href="#funs-and-module-lists" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Funs and Module Lists</span>
│ │ │  </h2>
│ │ │  <p>The following examples show a dialogue with the Erlang shell. All the higher
│ │ │  order functions discussed are exported from the module <a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html"><code class="inline">lists</code></a>.</p><h3 id="map-1" class="section-heading">
│ │ │    <a href="#map-1" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">map</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="3530359337-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3530359337-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3530359337-2">]</span><span class="p" data-group-id="3530359337-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3530359337-3">[</span><span class="n">F</span><span class="p" data-group-id="3530359337-4">(</span><span class="n">H</span><span class="p" data-group-id="3530359337-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="3530359337-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3530359337-5">)</span><span class="p" data-group-id="3530359337-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="3530359337-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3530359337-7">[</span><span class="p" data-group-id="3530359337-7">]</span><span class="p" data-group-id="3530359337-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3530359337-8">[</span><span class="p" data-group-id="3530359337-8">]</span><span class="p">.</span></code></pre><p>It returns the list obtained by applying the function to every argument in the
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="8021177328-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8021177328-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8021177328-2">]</span><span class="p" data-group-id="8021177328-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8021177328-3">[</span><span class="n">F</span><span class="p" data-group-id="8021177328-4">(</span><span class="n">H</span><span class="p" data-group-id="8021177328-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="8021177328-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8021177328-5">)</span><span class="p" data-group-id="8021177328-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="8021177328-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8021177328-7">[</span><span class="p" data-group-id="8021177328-7">]</span><span class="p" data-group-id="8021177328-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8021177328-8">[</span><span class="p" data-group-id="8021177328-8">]</span><span class="p">.</span></code></pre><p>It returns the list obtained by applying the function to every argument in the
│ │ │  list.</p><p>When a new fun is defined in the shell, the value of the fun is printed as
│ │ │ -<code class="inline">Fun#&lt;erl_eval&gt;</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Double</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0249869594-1">(</span><span class="n">X</span><span class="p" data-group-id="0249869594-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">Fun#&lt;erl_eval&gt;</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Double</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="7575198727-1">(</span><span class="n">X</span><span class="p" data-group-id="7575198727-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0249869594-2">(</span><span class="n">Double</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0249869594-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0249869594-3">]</span><span class="p" data-group-id="0249869594-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0249869594-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="0249869594-4">]</span></code></pre><h3 id="any" class="section-heading">
│ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7575198727-2">(</span><span class="n">Double</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7575198727-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7575198727-3">]</span><span class="p" data-group-id="7575198727-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7575198727-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="7575198727-4">]</span></code></pre><h3 id="any" class="section-heading">
│ │ │    <a href="#any" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">any</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#any/2"><code class="inline">lists:any/2</code></a> takes a predicate <code class="inline">P</code> of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">any</span><span class="p" data-group-id="8327345751-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8327345751-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8327345751-2">]</span><span class="p" data-group-id="8327345751-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="8327345751-3">(</span><span class="n">H</span><span class="p" data-group-id="8327345751-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#any/2"><code class="inline">lists:any/2</code></a> takes a predicate <code class="inline">P</code> of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">any</span><span class="p" data-group-id="6196464748-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6196464748-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6196464748-2">]</span><span class="p" data-group-id="6196464748-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="6196464748-3">(</span><span class="n">H</span><span class="p" data-group-id="6196464748-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">any</span><span class="p" data-group-id="8327345751-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8327345751-4">)</span><span class="w">
│ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">any</span><span class="p" data-group-id="6196464748-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6196464748-4">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">any</span><span class="p" data-group-id="8327345751-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8327345751-6">[</span><span class="p" data-group-id="8327345751-6">]</span><span class="p" data-group-id="8327345751-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">any</span><span class="p" data-group-id="6196464748-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6196464748-6">[</span><span class="p" data-group-id="6196464748-6">]</span><span class="p" data-group-id="6196464748-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">false</span><span class="p">.</span></code></pre><p>A predicate is a function that returns <code class="inline">true</code> or <code class="inline">false</code>. <code class="inline">any</code> is <code class="inline">true</code> if
│ │ │  there is a term <code class="inline">X</code> in the list such that <code class="inline">P(X)</code> is <code class="inline">true</code>.</p><p>A predicate <code class="inline">Big(X)</code> is defined, which is <code class="inline">true</code> if its argument is greater that
│ │ │ -10:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Big</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="1365906017-1">(</span><span class="n">X</span><span class="p" data-group-id="1365906017-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="p">;</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +10:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Big</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="9023062312-1">(</span><span class="n">X</span><span class="p" data-group-id="9023062312-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="p">;</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="1365906017-2">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1365906017-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1365906017-3">]</span><span class="p" data-group-id="1365906017-2">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="9023062312-2">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9023062312-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="9023062312-3">]</span><span class="p" data-group-id="9023062312-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="1365906017-4">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1365906017-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1365906017-5">]</span><span class="p" data-group-id="1365906017-4">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="9023062312-4">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9023062312-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9023062312-5">]</span><span class="p" data-group-id="9023062312-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><h3 id="all" class="section-heading">
│ │ │    <a href="#all" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">all</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#all/2"><code class="inline">lists:all/2</code></a> has the same arguments as <code class="inline">any</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="8067155618-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8067155618-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8067155618-2">]</span><span class="p" data-group-id="8067155618-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="8067155618-3">(</span><span class="n">H</span><span class="p" data-group-id="8067155618-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">all</span><span class="p" data-group-id="8067155618-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8067155618-4">)</span><span class="p">;</span><span class="w">
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#all/2"><code class="inline">lists:all/2</code></a> has the same arguments as <code class="inline">any</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="4129245494-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4129245494-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4129245494-2">]</span><span class="p" data-group-id="4129245494-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="4129245494-3">(</span><span class="n">H</span><span class="p" data-group-id="4129245494-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">all</span><span class="p" data-group-id="4129245494-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4129245494-4">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="ss">false</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">all</span><span class="p" data-group-id="8067155618-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8067155618-6">[</span><span class="p" data-group-id="8067155618-6">]</span><span class="p" data-group-id="8067155618-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>It is <code class="inline">true</code> if the predicate applied to all elements in the list is <code class="inline">true</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="1915836387-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1915836387-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1915836387-2">]</span><span class="p" data-group-id="1915836387-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">all</span><span class="p" data-group-id="4129245494-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4129245494-6">[</span><span class="p" data-group-id="4129245494-6">]</span><span class="p" data-group-id="4129245494-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>It is <code class="inline">true</code> if the predicate applied to all elements in the list is <code class="inline">true</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="8999828520-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8999828520-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8999828520-2">]</span><span class="p" data-group-id="8999828520-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="1915836387-3">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1915836387-4">[</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="1915836387-4">]</span><span class="p" data-group-id="1915836387-3">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="8999828520-3">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8999828520-4">[</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="8999828520-4">]</span><span class="p" data-group-id="8999828520-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><h3 id="foreach-1" class="section-heading">
│ │ │    <a href="#foreach-1" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">foreach</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#foreach/2"><code class="inline">lists:foreach/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="8718025396-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8718025396-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8718025396-2">]</span><span class="p" data-group-id="8718025396-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">F</span><span class="p" data-group-id="8718025396-3">(</span><span class="n">H</span><span class="p" data-group-id="8718025396-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="8718025396-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8718025396-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="8718025396-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8718025396-6">[</span><span class="p" data-group-id="8718025396-6">]</span><span class="p" data-group-id="8718025396-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#foreach/2"><code class="inline">lists:foreach/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="1853660819-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1853660819-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1853660819-2">]</span><span class="p" data-group-id="1853660819-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">F</span><span class="p" data-group-id="1853660819-3">(</span><span class="n">H</span><span class="p" data-group-id="1853660819-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="1853660819-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="1853660819-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="1853660819-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1853660819-6">[</span><span class="p" data-group-id="1853660819-6">]</span><span class="p" data-group-id="1853660819-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The function is applied to each argument in the list. <code class="inline">foreach</code> returns <code class="inline">ok</code>. It
│ │ │ -is only used for its side-effect:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="3916337785-1">(</span><span class="nf">fun</span><span class="p" data-group-id="3916337785-2">(</span><span class="n">X</span><span class="p" data-group-id="3916337785-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3916337785-3">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="3916337785-4">[</span><span class="n">X</span><span class="p" data-group-id="3916337785-4">]</span><span class="p" data-group-id="3916337785-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3916337785-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3916337785-5">]</span><span class="p" data-group-id="3916337785-1">)</span><span class="p">.</span><span class="w">
│ │ │ +is only used for its side-effect:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="5840767301-1">(</span><span class="nf">fun</span><span class="p" data-group-id="5840767301-2">(</span><span class="n">X</span><span class="p" data-group-id="5840767301-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5840767301-3">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="5840767301-4">[</span><span class="n">X</span><span class="p" data-group-id="5840767301-4">]</span><span class="p" data-group-id="5840767301-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5840767301-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5840767301-5">]</span><span class="p" data-group-id="5840767301-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="w">
│ │ │  </span><span class="mi">2</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><h3 id="foldl" class="section-heading">
│ │ │    <a href="#foldl" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">foldl</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> takes a function of two arguments, an accumulator and a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foldl</span><span class="p" data-group-id="3815038782-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3815038782-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="3815038782-2">]</span><span class="p" data-group-id="3815038782-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">foldl</span><span class="p" data-group-id="3815038782-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="3815038782-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="3815038782-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="3815038782-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">foldl</span><span class="p" data-group-id="3815038782-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3815038782-6">[</span><span class="p" data-group-id="3815038782-6">]</span><span class="p" data-group-id="3815038782-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Accu</span><span class="p">.</span></code></pre><p>The function is called with two arguments. The first argument is the successive
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> takes a function of two arguments, an accumulator and a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foldl</span><span class="p" data-group-id="6972082396-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6972082396-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="6972082396-2">]</span><span class="p" data-group-id="6972082396-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">foldl</span><span class="p" data-group-id="6972082396-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="6972082396-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="6972082396-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6972082396-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">foldl</span><span class="p" data-group-id="6972082396-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6972082396-6">[</span><span class="p" data-group-id="6972082396-6">]</span><span class="p" data-group-id="6972082396-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Accu</span><span class="p">.</span></code></pre><p>The function is called with two arguments. The first argument is the successive
│ │ │  elements in the list. The second argument is the accumulator. The function must
│ │ │  return a new accumulator, which is used the next time the function is called.</p><p>If you have a list of lists <code class="inline">L = [&quot;I&quot;,&quot;like&quot;,&quot;Erlang&quot;]</code>, then you can sum the
│ │ │ -lengths of all the strings in <code class="inline">L</code> as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3278850411-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="3278850411-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3278850411-2">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="3278850411-2">]</span><span class="gp unselectable">
│ │ │ -10&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="3278850411-3">(</span><span class="nf">fun</span><span class="p" data-group-id="3278850411-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="3278850411-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="3278850411-5">(</span><span class="n">X</span><span class="p" data-group-id="3278850411-5">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="3278850411-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">11</span></code></pre><p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> works like a <code class="inline">while</code> loop in an imperative language:</p><pre><code class="makeup erlang" translate="no"><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="p" data-group-id="4682814680-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="4682814680-1">]</span><span class="p">,</span><span class="w">
│ │ │ +lengths of all the strings in <code class="inline">L</code> as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3949030794-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="3949030794-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3949030794-2">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="3949030794-2">]</span><span class="gp unselectable">
│ │ │ +10&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="3949030794-3">(</span><span class="nf">fun</span><span class="p" data-group-id="3949030794-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="3949030794-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="3949030794-5">(</span><span class="n">X</span><span class="p" data-group-id="3949030794-5">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="3949030794-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">11</span></code></pre><p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> works like a <code class="inline">while</code> loop in an imperative language:</p><pre><code class="makeup erlang" translate="no"><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="p" data-group-id="8019105204-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="8019105204-1">]</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="n">Sum</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">while</span><span class="p" data-group-id="4682814680-2">(</span><span class="w"> </span><span class="n">L</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4682814680-3">[</span><span class="p" data-group-id="4682814680-3">]</span><span class="p" data-group-id="4682814680-2">)</span><span class="p" data-group-id="4682814680-4">{</span><span class="w">
│ │ │ -    </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="4682814680-5">(</span><span class="nf">head</span><span class="p" data-group-id="4682814680-6">(</span><span class="n">L</span><span class="p" data-group-id="4682814680-6">)</span><span class="p" data-group-id="4682814680-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tail</span><span class="p" data-group-id="4682814680-7">(</span><span class="n">L</span><span class="p" data-group-id="4682814680-7">)</span><span class="w">
│ │ │ +</span><span class="nf">while</span><span class="p" data-group-id="8019105204-2">(</span><span class="w"> </span><span class="n">L</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8019105204-3">[</span><span class="p" data-group-id="8019105204-3">]</span><span class="p" data-group-id="8019105204-2">)</span><span class="p" data-group-id="8019105204-4">{</span><span class="w">
│ │ │ +    </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8019105204-5">(</span><span class="nf">head</span><span class="p" data-group-id="8019105204-6">(</span><span class="n">L</span><span class="p" data-group-id="8019105204-6">)</span><span class="p" data-group-id="8019105204-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tail</span><span class="p" data-group-id="8019105204-7">(</span><span class="n">L</span><span class="p" data-group-id="8019105204-7">)</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><h3 id="mapfoldl" class="section-heading">
│ │ │    <a href="#mapfoldl" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">mapfoldl</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#mapfoldl/3"><code class="inline">lists:mapfoldl/3</code></a> simultaneously maps and folds over a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mapfoldl</span><span class="p" data-group-id="9576653830-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9576653830-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="9576653830-2">]</span><span class="p" data-group-id="9576653830-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9576653830-3">{</span><span class="n">R</span><span class="p">,</span><span class="n">Accu1</span><span class="p" data-group-id="9576653830-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="9576653830-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p" data-group-id="9576653830-4">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9576653830-5">{</span><span class="n">Rs</span><span class="p">,</span><span class="n">Accu2</span><span class="p" data-group-id="9576653830-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">mapfoldl</span><span class="p" data-group-id="9576653830-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu1</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="9576653830-6">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9576653830-7">{</span><span class="p" data-group-id="9576653830-8">[</span><span class="n">R</span><span class="p">|</span><span class="n">Rs</span><span class="p" data-group-id="9576653830-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu2</span><span class="p" data-group-id="9576653830-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">mapfoldl</span><span class="p" data-group-id="9576653830-9">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9576653830-10">[</span><span class="p" data-group-id="9576653830-10">]</span><span class="p" data-group-id="9576653830-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9576653830-11">{</span><span class="p" data-group-id="9576653830-12">[</span><span class="p" data-group-id="9576653830-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="9576653830-11">}</span><span class="p">.</span></code></pre><p>The following example shows how to change all letters in <code class="inline">L</code> to upper case and
│ │ │ -then count them.</p><p>First the change to upper case:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Upcase</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="1940292592-1">(</span><span class="n">X</span><span class="p" data-group-id="1940292592-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w">  </span><span class="n">X</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="sc">$a</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1940292592-2">(</span><span class="n">X</span><span class="p" data-group-id="1940292592-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w">
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#mapfoldl/3"><code class="inline">lists:mapfoldl/3</code></a> simultaneously maps and folds over a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mapfoldl</span><span class="p" data-group-id="2009751987-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2009751987-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="2009751987-2">]</span><span class="p" data-group-id="2009751987-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2009751987-3">{</span><span class="n">R</span><span class="p">,</span><span class="n">Accu1</span><span class="p" data-group-id="2009751987-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="2009751987-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p" data-group-id="2009751987-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2009751987-5">{</span><span class="n">Rs</span><span class="p">,</span><span class="n">Accu2</span><span class="p" data-group-id="2009751987-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">mapfoldl</span><span class="p" data-group-id="2009751987-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu1</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="2009751987-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2009751987-7">{</span><span class="p" data-group-id="2009751987-8">[</span><span class="n">R</span><span class="p">|</span><span class="n">Rs</span><span class="p" data-group-id="2009751987-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu2</span><span class="p" data-group-id="2009751987-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">mapfoldl</span><span class="p" data-group-id="2009751987-9">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2009751987-10">[</span><span class="p" data-group-id="2009751987-10">]</span><span class="p" data-group-id="2009751987-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2009751987-11">{</span><span class="p" data-group-id="2009751987-12">[</span><span class="p" data-group-id="2009751987-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="2009751987-11">}</span><span class="p">.</span></code></pre><p>The following example shows how to change all letters in <code class="inline">L</code> to upper case and
│ │ │ +then count them.</p><p>First the change to upper case:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Upcase</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="0593411045-1">(</span><span class="n">X</span><span class="p" data-group-id="0593411045-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w">  </span><span class="n">X</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="sc">$a</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0593411045-2">(</span><span class="n">X</span><span class="p" data-group-id="0593411045-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │  &gt; </span><span class="n">Upcase_word</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ -</span><span class="nf">fun</span><span class="p" data-group-id="1940292592-3">(</span><span class="n">X</span><span class="p" data-group-id="1940292592-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1940292592-4">(</span><span class="n">Upcase</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1940292592-4">)</span><span class="w">
│ │ │ +</span><span class="nf">fun</span><span class="p" data-group-id="0593411045-3">(</span><span class="n">X</span><span class="p" data-group-id="0593411045-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0593411045-4">(</span><span class="n">Upcase</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0593411045-4">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Upcase_word</span><span class="p" data-group-id="1940292592-5">(</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="1940292592-5">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="n">Upcase_word</span><span class="p" data-group-id="0593411045-5">(</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="0593411045-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;ERLANG&quot;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1940292592-6">(</span><span class="n">Upcase_word</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1940292592-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1940292592-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="1940292592-7">]</span></code></pre><p>Now, the fold and the map can be done at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">mapfoldl</span><span class="p" data-group-id="9814912686-1">(</span><span class="nf">fun</span><span class="p" data-group-id="9814912686-2">(</span><span class="n">Word</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="9814912686-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9814912686-3">{</span><span class="n">Upcase_word</span><span class="p" data-group-id="9814912686-4">(</span><span class="n">Word</span><span class="p" data-group-id="9814912686-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9814912686-5">(</span><span class="n">Word</span><span class="p" data-group-id="9814912686-5">)</span><span class="p" data-group-id="9814912686-3">}</span><span class="w">
│ │ │ -</span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="9814912686-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9814912686-6">{</span><span class="p" data-group-id="9814912686-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="9814912686-7">]</span><span class="p">,</span><span class="mi">11</span><span class="p" data-group-id="9814912686-6">}</span></code></pre><h3 id="filter" class="section-heading">
│ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0593411045-6">(</span><span class="n">Upcase_word</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0593411045-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0593411045-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="0593411045-7">]</span></code></pre><p>Now, the fold and the map can be done at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">mapfoldl</span><span class="p" data-group-id="4406872453-1">(</span><span class="nf">fun</span><span class="p" data-group-id="4406872453-2">(</span><span class="n">Word</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="4406872453-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4406872453-3">{</span><span class="n">Upcase_word</span><span class="p" data-group-id="4406872453-4">(</span><span class="n">Word</span><span class="p" data-group-id="4406872453-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="4406872453-5">(</span><span class="n">Word</span><span class="p" data-group-id="4406872453-5">)</span><span class="p" data-group-id="4406872453-3">}</span><span class="w">
│ │ │ +</span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4406872453-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4406872453-6">{</span><span class="p" data-group-id="4406872453-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="4406872453-7">]</span><span class="p">,</span><span class="mi">11</span><span class="p" data-group-id="4406872453-6">}</span></code></pre><h3 id="filter" class="section-heading">
│ │ │    <a href="#filter" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">filter</span>
│ │ │  </h3>
│ │ │  <p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#filter/2"><code class="inline">lists:filter/2</code></a> takes a predicate of one argument and a list and returns all elements
│ │ │ -in the list that satisfy the predicate:</p><pre><code class="makeup erlang" translate="no"><span class="nf">filter</span><span class="p" data-group-id="5121639917-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5121639917-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5121639917-2">]</span><span class="p" data-group-id="5121639917-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="5121639917-3">(</span><span class="n">H</span><span class="p" data-group-id="5121639917-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5121639917-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">filter</span><span class="p" data-group-id="5121639917-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5121639917-5">)</span><span class="p" data-group-id="5121639917-4">]</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="5121639917-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5121639917-6">)</span><span class="w">
│ │ │ +in the list that satisfy the predicate:</p><pre><code class="makeup erlang" translate="no"><span class="nf">filter</span><span class="p" data-group-id="8858750652-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8858750652-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8858750652-2">]</span><span class="p" data-group-id="8858750652-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="8858750652-3">(</span><span class="n">H</span><span class="p" data-group-id="8858750652-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8858750652-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">filter</span><span class="p" data-group-id="8858750652-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8858750652-5">)</span><span class="p" data-group-id="8858750652-4">]</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="8858750652-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8858750652-6">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">filter</span><span class="p" data-group-id="5121639917-7">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5121639917-8">[</span><span class="p" data-group-id="5121639917-8">]</span><span class="p" data-group-id="5121639917-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5121639917-9">[</span><span class="p" data-group-id="5121639917-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="1982597160-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1982597160-2">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="1982597160-2">]</span><span class="p" data-group-id="1982597160-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1982597160-3">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="1982597160-3">]</span></code></pre><p>Combining maps and filters enables writing of very succinct code. For example,
│ │ │ +</span><span class="nf">filter</span><span class="p" data-group-id="8858750652-7">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8858750652-8">[</span><span class="p" data-group-id="8858750652-8">]</span><span class="p" data-group-id="8858750652-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8858750652-9">[</span><span class="p" data-group-id="8858750652-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="3410248724-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3410248724-2">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3410248724-2">]</span><span class="p" data-group-id="3410248724-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3410248724-3">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="3410248724-3">]</span></code></pre><p>Combining maps and filters enables writing of very succinct code. For example,
│ │ │  to define a set difference function <code class="inline">diff(L1, L2)</code> to be the difference between
│ │ │ -the lists <code class="inline">L1</code> and <code class="inline">L2</code>, the code can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">diff</span><span class="p" data-group-id="4251741211-1">(</span><span class="n">L1</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="4251741211-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">filter</span><span class="p" data-group-id="4251741211-2">(</span><span class="nf">fun</span><span class="p" data-group-id="4251741211-3">(</span><span class="n">X</span><span class="p" data-group-id="4251741211-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="4251741211-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="4251741211-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="4251741211-2">)</span><span class="p">.</span></code></pre><p>This gives the list of all elements in L1 that are not contained in L2.</p><p>The AND intersection of the list <code class="inline">L1</code> and <code class="inline">L2</code> is also easily defined:</p><pre><code class="makeup erlang" translate="no"><span class="nf">intersection</span><span class="p" data-group-id="5476507248-1">(</span><span class="n">L1</span><span class="p">,</span><span class="n">L2</span><span class="p" data-group-id="5476507248-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="5476507248-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5476507248-3">(</span><span class="n">X</span><span class="p" data-group-id="5476507248-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="5476507248-4">(</span><span class="n">X</span><span class="p">,</span><span class="n">L1</span><span class="p" data-group-id="5476507248-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="5476507248-2">)</span><span class="p">.</span></code></pre><h3 id="takewhile" class="section-heading">
│ │ │ +the lists <code class="inline">L1</code> and <code class="inline">L2</code>, the code can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">diff</span><span class="p" data-group-id="8893911595-1">(</span><span class="n">L1</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="8893911595-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">filter</span><span class="p" data-group-id="8893911595-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8893911595-3">(</span><span class="n">X</span><span class="p" data-group-id="8893911595-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="8893911595-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="8893911595-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="8893911595-2">)</span><span class="p">.</span></code></pre><p>This gives the list of all elements in L1 that are not contained in L2.</p><p>The AND intersection of the list <code class="inline">L1</code> and <code class="inline">L2</code> is also easily defined:</p><pre><code class="makeup erlang" translate="no"><span class="nf">intersection</span><span class="p" data-group-id="6683610419-1">(</span><span class="n">L1</span><span class="p">,</span><span class="n">L2</span><span class="p" data-group-id="6683610419-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="6683610419-2">(</span><span class="nf">fun</span><span class="p" data-group-id="6683610419-3">(</span><span class="n">X</span><span class="p" data-group-id="6683610419-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="6683610419-4">(</span><span class="n">X</span><span class="p">,</span><span class="n">L1</span><span class="p" data-group-id="6683610419-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="6683610419-2">)</span><span class="p">.</span></code></pre><h3 id="takewhile" class="section-heading">
│ │ │    <a href="#takewhile" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">takewhile</span>
│ │ │  </h3>
│ │ │  <p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#takewhile/2"><code class="inline">lists:takewhile/2</code></a> takes elements <code class="inline">X</code> from a list <code class="inline">L</code> as long as the predicate
│ │ │ -<code class="inline">P(X)</code> is true:</p><pre><code class="makeup erlang" translate="no"><span class="nf">takewhile</span><span class="p" data-group-id="0926908427-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0926908427-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0926908427-2">]</span><span class="p" data-group-id="0926908427-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="0926908427-3">(</span><span class="n">H</span><span class="p" data-group-id="0926908427-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0926908427-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">takewhile</span><span class="p" data-group-id="0926908427-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="0926908427-5">)</span><span class="p" data-group-id="0926908427-4">]</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0926908427-6">[</span><span class="p" data-group-id="0926908427-6">]</span><span class="w">
│ │ │ +<code class="inline">P(X)</code> is true:</p><pre><code class="makeup erlang" translate="no"><span class="nf">takewhile</span><span class="p" data-group-id="2335108931-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2335108931-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2335108931-2">]</span><span class="p" data-group-id="2335108931-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="2335108931-3">(</span><span class="n">H</span><span class="p" data-group-id="2335108931-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2335108931-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">takewhile</span><span class="p" data-group-id="2335108931-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2335108931-5">)</span><span class="p" data-group-id="2335108931-4">]</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2335108931-6">[</span><span class="p" data-group-id="2335108931-6">]</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">takewhile</span><span class="p" data-group-id="0926908427-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0926908427-8">[</span><span class="p" data-group-id="0926908427-8">]</span><span class="p" data-group-id="0926908427-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0926908427-9">[</span><span class="p" data-group-id="0926908427-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">takewhile</span><span class="p" data-group-id="5990600930-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5990600930-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5990600930-2">]</span><span class="p" data-group-id="5990600930-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5990600930-3">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="5990600930-3">]</span></code></pre><h3 id="dropwhile" class="section-heading">
│ │ │ +</span><span class="nf">takewhile</span><span class="p" data-group-id="2335108931-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2335108931-8">[</span><span class="p" data-group-id="2335108931-8">]</span><span class="p" data-group-id="2335108931-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2335108931-9">[</span><span class="p" data-group-id="2335108931-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">takewhile</span><span class="p" data-group-id="3248533583-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3248533583-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="3248533583-2">]</span><span class="p" data-group-id="3248533583-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3248533583-3">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="3248533583-3">]</span></code></pre><h3 id="dropwhile" class="section-heading">
│ │ │    <a href="#dropwhile" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">dropwhile</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#dropwhile/2"><code class="inline">lists:dropwhile/2</code></a> is the complement of <code class="inline">takewhile</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">dropwhile</span><span class="p" data-group-id="5840561337-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5840561337-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5840561337-2">]</span><span class="p" data-group-id="5840561337-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="5840561337-3">(</span><span class="n">H</span><span class="p" data-group-id="5840561337-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">dropwhile</span><span class="p" data-group-id="5840561337-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5840561337-4">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5840561337-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5840561337-5">]</span><span class="w">
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#dropwhile/2"><code class="inline">lists:dropwhile/2</code></a> is the complement of <code class="inline">takewhile</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">dropwhile</span><span class="p" data-group-id="8664477141-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8664477141-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8664477141-2">]</span><span class="p" data-group-id="8664477141-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="8664477141-3">(</span><span class="n">H</span><span class="p" data-group-id="8664477141-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">dropwhile</span><span class="p" data-group-id="8664477141-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8664477141-4">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8664477141-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8664477141-5">]</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">dropwhile</span><span class="p" data-group-id="5840561337-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5840561337-7">[</span><span class="p" data-group-id="5840561337-7">]</span><span class="p" data-group-id="5840561337-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5840561337-8">[</span><span class="p" data-group-id="5840561337-8">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">dropwhile</span><span class="p" data-group-id="1826716639-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1826716639-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1826716639-2">]</span><span class="p" data-group-id="1826716639-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1826716639-3">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1826716639-3">]</span></code></pre><h3 id="splitwith" class="section-heading">
│ │ │ +</span><span class="nf">dropwhile</span><span class="p" data-group-id="8664477141-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8664477141-7">[</span><span class="p" data-group-id="8664477141-7">]</span><span class="p" data-group-id="8664477141-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8664477141-8">[</span><span class="p" data-group-id="8664477141-8">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">dropwhile</span><span class="p" data-group-id="5694271115-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5694271115-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5694271115-2">]</span><span class="p" data-group-id="5694271115-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5694271115-3">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5694271115-3">]</span></code></pre><h3 id="splitwith" class="section-heading">
│ │ │    <a href="#splitwith" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">splitwith</span>
│ │ │  </h3>
│ │ │  <p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#splitwith/2"><code class="inline">lists:splitwith/2</code></a> splits the list <code class="inline">L</code> into the two sublists <code class="inline">{L1, L2}</code>, where
│ │ │ -<code class="inline">L = takewhile(P, L)</code> and <code class="inline">L2 = dropwhile(P, L)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">splitwith</span><span class="p" data-group-id="2780286844-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2780286844-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">splitwith</span><span class="p" data-group-id="2780286844-2">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2780286844-3">[</span><span class="p" data-group-id="2780286844-3">]</span><span class="p" data-group-id="2780286844-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">L = takewhile(P, L)</code> and <code class="inline">L2 = dropwhile(P, L)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">splitwith</span><span class="p" data-group-id="9813875783-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="9813875783-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">splitwith</span><span class="p" data-group-id="9813875783-2">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9813875783-3">[</span><span class="p" data-group-id="9813875783-3">]</span><span class="p" data-group-id="9813875783-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">splitwith</span><span class="p" data-group-id="2780286844-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2780286844-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2780286844-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2780286844-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="2780286844-6">(</span><span class="n">H</span><span class="p" data-group-id="2780286844-6">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">splitwith</span><span class="p" data-group-id="2780286844-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2780286844-8">[</span><span class="n">H</span><span class="p">|</span><span class="n">L</span><span class="p" data-group-id="2780286844-8">]</span><span class="p" data-group-id="2780286844-7">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2780286844-9">{</span><span class="nf">reverse</span><span class="p" data-group-id="2780286844-10">(</span><span class="n">L</span><span class="p" data-group-id="2780286844-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2780286844-11">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2780286844-11">]</span><span class="p" data-group-id="2780286844-9">}</span><span class="w">
│ │ │ +</span><span class="nf">splitwith</span><span class="p" data-group-id="9813875783-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9813875783-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9813875783-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="9813875783-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="9813875783-6">(</span><span class="n">H</span><span class="p" data-group-id="9813875783-6">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">splitwith</span><span class="p" data-group-id="9813875783-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9813875783-8">[</span><span class="n">H</span><span class="p">|</span><span class="n">L</span><span class="p" data-group-id="9813875783-8">]</span><span class="p" data-group-id="9813875783-7">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9813875783-9">{</span><span class="nf">reverse</span><span class="p" data-group-id="9813875783-10">(</span><span class="n">L</span><span class="p" data-group-id="9813875783-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9813875783-11">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9813875783-11">]</span><span class="p" data-group-id="9813875783-9">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">splitwith</span><span class="p" data-group-id="2780286844-12">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2780286844-13">[</span><span class="p" data-group-id="2780286844-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2780286844-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2780286844-14">{</span><span class="nf">reverse</span><span class="p" data-group-id="2780286844-15">(</span><span class="n">L</span><span class="p" data-group-id="2780286844-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2780286844-16">[</span><span class="p" data-group-id="2780286844-16">]</span><span class="p" data-group-id="2780286844-14">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">splitwith</span><span class="p" data-group-id="0246540698-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0246540698-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="0246540698-2">]</span><span class="p" data-group-id="0246540698-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0246540698-3">{</span><span class="p" data-group-id="0246540698-4">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="0246540698-4">]</span><span class="p">,</span><span class="p" data-group-id="0246540698-5">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="0246540698-5">]</span><span class="p" data-group-id="0246540698-3">}</span></code></pre><h2 id="funs-returning-funs" class="section-heading">
│ │ │ +</span><span class="nf">splitwith</span><span class="p" data-group-id="9813875783-12">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9813875783-13">[</span><span class="p" data-group-id="9813875783-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="9813875783-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9813875783-14">{</span><span class="nf">reverse</span><span class="p" data-group-id="9813875783-15">(</span><span class="n">L</span><span class="p" data-group-id="9813875783-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9813875783-16">[</span><span class="p" data-group-id="9813875783-16">]</span><span class="p" data-group-id="9813875783-14">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">splitwith</span><span class="p" data-group-id="8666737395-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8666737395-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8666737395-2">]</span><span class="p" data-group-id="8666737395-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8666737395-3">{</span><span class="p" data-group-id="8666737395-4">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="8666737395-4">]</span><span class="p">,</span><span class="p" data-group-id="8666737395-5">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8666737395-5">]</span><span class="p" data-group-id="8666737395-3">}</span></code></pre><h2 id="funs-returning-funs" class="section-heading">
│ │ │    <a href="#funs-returning-funs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Funs Returning Funs</span>
│ │ │  </h2>
│ │ │  <p>So far, only functions that take funs as arguments have been described. More
│ │ │  powerful functions, that themselves return funs, can also be written. The
│ │ │  following examples illustrate these type of functions.</p><h3 id="simple-higher-order-functions" class="section-heading">
│ │ │    <a href="#simple-higher-order-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Simple Higher Order Functions</span>
│ │ │  </h3>
│ │ │  <p><code class="inline">Adder(X)</code> is a function that given <code class="inline">X</code>, returns a new function <code class="inline">G</code> such that
│ │ │ -<code class="inline">G(K)</code> returns <code class="inline">K + X</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Adder</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3987860453-1">(</span><span class="n">X</span><span class="p" data-group-id="3987860453-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3987860453-2">(</span><span class="n">Y</span><span class="p" data-group-id="3987860453-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">G(K)</code> returns <code class="inline">K + X</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Adder</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1348482655-1">(</span><span class="n">X</span><span class="p" data-group-id="1348482655-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1348482655-2">(</span><span class="n">Y</span><span class="p" data-group-id="1348482655-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Add6</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Adder</span><span class="p" data-group-id="3987860453-3">(</span><span class="mi">6</span><span class="p" data-group-id="3987860453-3">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="n">Add6</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Adder</span><span class="p" data-group-id="1348482655-3">(</span><span class="mi">6</span><span class="p" data-group-id="1348482655-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Add6</span><span class="p" data-group-id="3987860453-4">(</span><span class="mi">10</span><span class="p" data-group-id="3987860453-4">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="n">Add6</span><span class="p" data-group-id="1348482655-4">(</span><span class="mi">10</span><span class="p" data-group-id="1348482655-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">16</span></code></pre><h3 id="infinite-lists" class="section-heading">
│ │ │    <a href="#infinite-lists" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Infinite Lists</span>
│ │ │  </h3>
│ │ │ -<p>The idea is to write something like:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8786350864-1">(</span><span class="ss">lazy</span><span class="p" data-group-id="8786350864-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8786350864-2">(</span><span class="p" data-group-id="8786350864-3">[</span><span class="ss">ints_from</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8786350864-3">]</span><span class="p" data-group-id="8786350864-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">ints_from</span><span class="p" data-group-id="8786350864-4">(</span><span class="n">N</span><span class="p" data-group-id="8786350864-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">fun</span><span class="p" data-group-id="8786350864-5">(</span><span class="p" data-group-id="8786350864-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="8786350864-6">[</span><span class="n">N</span><span class="p">|</span><span class="nf">ints_from</span><span class="p" data-group-id="8786350864-7">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="8786350864-7">)</span><span class="p" data-group-id="8786350864-6">]</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Then proceed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lazy</span><span class="p">:</span><span class="nf">ints_from</span><span class="p" data-group-id="0207555652-1">(</span><span class="mi">1</span><span class="p" data-group-id="0207555652-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>The idea is to write something like:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0103597607-1">(</span><span class="ss">lazy</span><span class="p" data-group-id="0103597607-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0103597607-2">(</span><span class="p" data-group-id="0103597607-3">[</span><span class="ss">ints_from</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0103597607-3">]</span><span class="p" data-group-id="0103597607-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">ints_from</span><span class="p" data-group-id="0103597607-4">(</span><span class="n">N</span><span class="p" data-group-id="0103597607-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">fun</span><span class="p" data-group-id="0103597607-5">(</span><span class="p" data-group-id="0103597607-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="0103597607-6">[</span><span class="n">N</span><span class="p">|</span><span class="nf">ints_from</span><span class="p" data-group-id="0103597607-7">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="0103597607-7">)</span><span class="p" data-group-id="0103597607-6">]</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Then proceed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lazy</span><span class="p">:</span><span class="nf">ints_from</span><span class="p" data-group-id="7410641100-1">(</span><span class="mi">1</span><span class="p" data-group-id="7410641100-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">XX</span><span class="p" data-group-id="0207555652-2">(</span><span class="p" data-group-id="0207555652-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0207555652-3">[</span><span class="mi">1</span><span class="p">|</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="p" data-group-id="0207555652-3">]</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">hd</span><span class="p" data-group-id="0207555652-4">(</span><span class="n">XX</span><span class="p" data-group-id="0207555652-5">(</span><span class="p" data-group-id="0207555652-5">)</span><span class="p" data-group-id="0207555652-4">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="n">XX</span><span class="p" data-group-id="7410641100-2">(</span><span class="p" data-group-id="7410641100-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7410641100-3">[</span><span class="mi">1</span><span class="p">|</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="p" data-group-id="7410641100-3">]</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">hd</span><span class="p" data-group-id="7410641100-4">(</span><span class="n">XX</span><span class="p" data-group-id="7410641100-5">(</span><span class="p" data-group-id="7410641100-5">)</span><span class="p" data-group-id="7410641100-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tl</span><span class="p" data-group-id="0207555652-6">(</span><span class="n">XX</span><span class="p" data-group-id="0207555652-7">(</span><span class="p" data-group-id="0207555652-7">)</span><span class="p" data-group-id="0207555652-6">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tl</span><span class="p" data-group-id="7410641100-6">(</span><span class="n">XX</span><span class="p" data-group-id="7410641100-7">(</span><span class="p" data-group-id="7410641100-7">)</span><span class="p" data-group-id="7410641100-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">hd</span><span class="p" data-group-id="0207555652-8">(</span><span class="n">Y</span><span class="p" data-group-id="0207555652-9">(</span><span class="p" data-group-id="0207555652-9">)</span><span class="p" data-group-id="0207555652-8">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">hd</span><span class="p" data-group-id="7410641100-8">(</span><span class="n">Y</span><span class="p" data-group-id="7410641100-9">(</span><span class="p" data-group-id="7410641100-9">)</span><span class="p" data-group-id="7410641100-8">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">2</span></code></pre><p>And so on. This is an example of &quot;lazy embedding&quot;.</p><h3 id="parsing" class="section-heading">
│ │ │    <a href="#parsing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Parsing</span>
│ │ │  </h3>
│ │ │ -<p>The following examples show parsers of the following type:</p><pre><code class="makeup erlang" translate="no"><span class="n">Parser</span><span class="p" data-group-id="1132459894-1">(</span><span class="n">Toks</span><span class="p" data-group-id="1132459894-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1132459894-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tree</span><span class="p">,</span><span class="w"> </span><span class="n">Toks1</span><span class="p" data-group-id="1132459894-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">fail</span></code></pre><p><code class="inline">Toks</code> is the list of tokens to be parsed. A successful parse returns
│ │ │ +<p>The following examples show parsers of the following type:</p><pre><code class="makeup erlang" translate="no"><span class="n">Parser</span><span class="p" data-group-id="3323177112-1">(</span><span class="n">Toks</span><span class="p" data-group-id="3323177112-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3323177112-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tree</span><span class="p">,</span><span class="w"> </span><span class="n">Toks1</span><span class="p" data-group-id="3323177112-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">fail</span></code></pre><p><code class="inline">Toks</code> is the list of tokens to be parsed. A successful parse returns
│ │ │  <code class="inline">{ok, Tree, Toks1}</code>.</p><ul><li><code class="inline">Tree</code> is a parse tree.</li><li><code class="inline">Toks1</code> is a tail of <code class="inline">Tree</code> that contains symbols encountered after the
│ │ │  structure that was correctly parsed.</li></ul><p>An unsuccessful parse returns <code class="inline">fail</code>.</p><p>The following example illustrates a simple, functional parser that parses the
│ │ │  grammar:</p><pre><code class="text">(a | b) &amp; (c | d)</code></pre><p>The following code defines a function <code class="inline">pconst(X)</code> in the module <code class="inline">funparse</code>,
│ │ │ -which returns a fun that parses a list of tokens:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pconst</span><span class="p" data-group-id="8355399211-1">(</span><span class="n">X</span><span class="p" data-group-id="8355399211-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8355399211-2">(</span><span class="n">T</span><span class="p" data-group-id="8355399211-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +which returns a fun that parses a list of tokens:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pconst</span><span class="p" data-group-id="4809666091-1">(</span><span class="n">X</span><span class="p" data-group-id="4809666091-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4809666091-2">(</span><span class="n">T</span><span class="p" data-group-id="4809666091-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │         </span><span class="k">case</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -           </span><span class="p" data-group-id="8355399211-3">[</span><span class="n">X</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="8355399211-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8355399211-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8355399211-5">{</span><span class="ss">const</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8355399211-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="8355399211-4">}</span><span class="p">;</span><span class="w">
│ │ │ +           </span><span class="p" data-group-id="4809666091-3">[</span><span class="n">X</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="4809666091-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4809666091-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4809666091-5">{</span><span class="ss">const</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4809666091-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4809666091-4">}</span><span class="p">;</span><span class="w">
│ │ │             </span><span class="p">_</span><span class="w">      </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">fail</span><span class="w">
│ │ │         </span><span class="k">end</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>This function can be used as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">pconst</span><span class="p" data-group-id="4015761749-1">(</span><span class="ss">a</span><span class="p" data-group-id="4015761749-1">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>This function can be used as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">pconst</span><span class="p" data-group-id="2762530774-1">(</span><span class="ss">a</span><span class="p" data-group-id="2762530774-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">funparse</span><span class="p">.</span><span class="mf">0.22674075</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">P1</span><span class="p" data-group-id="4015761749-2">(</span><span class="p" data-group-id="4015761749-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4015761749-3">]</span><span class="p" data-group-id="4015761749-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4015761749-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="4015761749-5">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4015761749-5">}</span><span class="p">,</span><span class="p" data-group-id="4015761749-6">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4015761749-6">]</span><span class="p" data-group-id="4015761749-4">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">P1</span><span class="p" data-group-id="4015761749-7">(</span><span class="p" data-group-id="4015761749-8">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="4015761749-8">]</span><span class="p" data-group-id="4015761749-7">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="n">P1</span><span class="p" data-group-id="2762530774-2">(</span><span class="p" data-group-id="2762530774-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="2762530774-3">]</span><span class="p" data-group-id="2762530774-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2762530774-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="2762530774-5">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="2762530774-5">}</span><span class="p">,</span><span class="p" data-group-id="2762530774-6">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="2762530774-6">]</span><span class="p" data-group-id="2762530774-4">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">P1</span><span class="p" data-group-id="2762530774-7">(</span><span class="p" data-group-id="2762530774-8">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="2762530774-8">]</span><span class="p" data-group-id="2762530774-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">fail</span></code></pre><p>Next, the two higher order functions <code class="inline">pand</code> and <code class="inline">por</code> are defined. They combine
│ │ │ -primitive parsers to produce more complex parsers.</p><p>First <code class="inline">pand</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pand</span><span class="p" data-group-id="4927596394-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="4927596394-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4927596394-2">(</span><span class="n">T</span><span class="p" data-group-id="4927596394-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="4927596394-3">(</span><span class="n">T</span><span class="p" data-group-id="4927596394-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4927596394-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4927596394-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="4927596394-5">(</span><span class="n">T1</span><span class="p" data-group-id="4927596394-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="4927596394-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="4927596394-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                        </span><span class="p" data-group-id="4927596394-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4927596394-8">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="4927596394-8">}</span><span class="p" data-group-id="4927596394-7">}</span><span class="p">;</span><span class="w">
│ │ │ +primitive parsers to produce more complex parsers.</p><p>First <code class="inline">pand</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pand</span><span class="p" data-group-id="8728148256-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="8728148256-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8728148256-2">(</span><span class="n">T</span><span class="p" data-group-id="8728148256-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="8728148256-3">(</span><span class="n">T</span><span class="p" data-group-id="8728148256-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8728148256-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="8728148256-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="8728148256-5">(</span><span class="n">T1</span><span class="p" data-group-id="8728148256-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="8728148256-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="8728148256-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                        </span><span class="p" data-group-id="8728148256-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8728148256-8">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="8728148256-8">}</span><span class="p" data-group-id="8728148256-7">}</span><span class="p">;</span><span class="w">
│ │ │                      </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                          </span><span class="ss">fail</span><span class="w">
│ │ │                  </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="ss">fail</span><span class="w">
│ │ │          </span><span class="k">end</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Given a parser <code class="inline">P1</code> for grammar <code class="inline">G1</code>, and a parser <code class="inline">P2</code> for grammar <code class="inline">G2</code>,
│ │ │  <code class="inline">pand(P1, P2)</code> returns a parser for the grammar, which consists of sequences of
│ │ │  tokens that satisfy <code class="inline">G1</code>, followed by sequences of tokens that satisfy <code class="inline">G2</code>.</p><p><code class="inline">por(P1, P2)</code> returns a parser for the language described by the grammar <code class="inline">G1</code> or
│ │ │ -<code class="inline">G2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">por</span><span class="p" data-group-id="4261564119-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="4261564119-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4261564119-2">(</span><span class="n">T</span><span class="p" data-group-id="4261564119-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="4261564119-3">(</span><span class="n">T</span><span class="p" data-group-id="4261564119-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4261564119-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4261564119-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="4261564119-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4261564119-6">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="n">R</span><span class="p" data-group-id="4261564119-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4261564119-5">}</span><span class="p">;</span><span class="w">
│ │ │ +<code class="inline">G2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">por</span><span class="p" data-group-id="0989316062-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="0989316062-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0989316062-2">(</span><span class="n">T</span><span class="p" data-group-id="0989316062-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="0989316062-3">(</span><span class="n">T</span><span class="p" data-group-id="0989316062-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="0989316062-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="0989316062-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="0989316062-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0989316062-6">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="n">R</span><span class="p" data-group-id="0989316062-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="0989316062-5">}</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="4261564119-7">(</span><span class="n">T</span><span class="p" data-group-id="4261564119-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="4261564119-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4261564119-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                        </span><span class="p" data-group-id="4261564119-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4261564119-10">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="n">R1</span><span class="p" data-group-id="4261564119-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4261564119-9">}</span><span class="p">;</span><span class="w">
│ │ │ +                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="0989316062-7">(</span><span class="n">T</span><span class="p" data-group-id="0989316062-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="0989316062-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="0989316062-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                        </span><span class="p" data-group-id="0989316062-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0989316062-10">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="n">R1</span><span class="p" data-group-id="0989316062-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="0989316062-9">}</span><span class="p">;</span><span class="w">
│ │ │                      </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                          </span><span class="ss">fail</span><span class="w">
│ │ │                  </span><span class="k">end</span><span class="w">
│ │ │          </span><span class="k">end</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The original problem was to parse the grammar <code class="inline">(a | b) &amp; (c | d)</code>. The following
│ │ │ -code addresses this problem:</p><pre><code class="makeup erlang" translate="no"><span class="nf">grammar</span><span class="p" data-group-id="6253749833-1">(</span><span class="p" data-group-id="6253749833-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">pand</span><span class="p" data-group-id="6253749833-2">(</span><span class="w">
│ │ │ -         </span><span class="nf">por</span><span class="p" data-group-id="6253749833-3">(</span><span class="nf">pconst</span><span class="p" data-group-id="6253749833-4">(</span><span class="ss">a</span><span class="p" data-group-id="6253749833-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="6253749833-5">(</span><span class="ss">b</span><span class="p" data-group-id="6253749833-5">)</span><span class="p" data-group-id="6253749833-3">)</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="nf">por</span><span class="p" data-group-id="6253749833-6">(</span><span class="nf">pconst</span><span class="p" data-group-id="6253749833-7">(</span><span class="ss">c</span><span class="p" data-group-id="6253749833-7">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="6253749833-8">(</span><span class="ss">d</span><span class="p" data-group-id="6253749833-8">)</span><span class="p" data-group-id="6253749833-6">)</span><span class="p" data-group-id="6253749833-2">)</span><span class="p">.</span></code></pre><p>The following code adds a parser interface to the grammar:</p><pre><code class="makeup erlang" translate="no"><span class="nf">parse</span><span class="p" data-group-id="8881213759-1">(</span><span class="n">List</span><span class="p" data-group-id="8881213759-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8881213759-2">(</span><span class="nf">grammar</span><span class="p" data-group-id="8881213759-3">(</span><span class="p" data-group-id="8881213759-3">)</span><span class="p" data-group-id="8881213759-2">)</span><span class="p" data-group-id="8881213759-4">(</span><span class="n">List</span><span class="p" data-group-id="8881213759-4">)</span><span class="p">.</span></code></pre><p>The parser can be tested as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="2232105806-1">(</span><span class="p" data-group-id="2232105806-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="2232105806-2">]</span><span class="p" data-group-id="2232105806-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2232105806-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="2232105806-4">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="2232105806-5">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="2232105806-6">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="2232105806-6">}</span><span class="p" data-group-id="2232105806-5">}</span><span class="p">,</span><span class="p" data-group-id="2232105806-7">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="2232105806-8">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="2232105806-8">}</span><span class="p" data-group-id="2232105806-7">}</span><span class="p" data-group-id="2232105806-4">}</span><span class="p" data-group-id="2232105806-3">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="2232105806-9">(</span><span class="p" data-group-id="2232105806-10">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="2232105806-10">]</span><span class="p" data-group-id="2232105806-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2232105806-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="2232105806-12">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="2232105806-13">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="2232105806-14">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="2232105806-14">}</span><span class="p" data-group-id="2232105806-13">}</span><span class="p">,</span><span class="p" data-group-id="2232105806-15">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="2232105806-16">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="2232105806-16">}</span><span class="p" data-group-id="2232105806-15">}</span><span class="p" data-group-id="2232105806-12">}</span><span class="p" data-group-id="2232105806-11">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="2232105806-17">(</span><span class="p" data-group-id="2232105806-18">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="2232105806-18">]</span><span class="p" data-group-id="2232105806-17">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2232105806-19">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="2232105806-20">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="2232105806-21">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="2232105806-22">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2232105806-22">}</span><span class="p" data-group-id="2232105806-21">}</span><span class="p">,</span><span class="p" data-group-id="2232105806-23">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="2232105806-24">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="2232105806-24">}</span><span class="p" data-group-id="2232105806-23">}</span><span class="p" data-group-id="2232105806-20">}</span><span class="p" data-group-id="2232105806-19">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="2232105806-25">(</span><span class="p" data-group-id="2232105806-26">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="2232105806-26">]</span><span class="p" data-group-id="2232105806-25">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2232105806-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="2232105806-28">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="2232105806-29">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="2232105806-30">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2232105806-30">}</span><span class="p" data-group-id="2232105806-29">}</span><span class="p">,</span><span class="p" data-group-id="2232105806-31">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="2232105806-32">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="2232105806-32">}</span><span class="p" data-group-id="2232105806-31">}</span><span class="p" data-group-id="2232105806-28">}</span><span class="p" data-group-id="2232105806-27">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="2232105806-33">(</span><span class="p" data-group-id="2232105806-34">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2232105806-34">]</span><span class="p" data-group-id="2232105806-33">)</span><span class="p">.</span><span class="w">
│ │ │ +code addresses this problem:</p><pre><code class="makeup erlang" translate="no"><span class="nf">grammar</span><span class="p" data-group-id="4938087604-1">(</span><span class="p" data-group-id="4938087604-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">pand</span><span class="p" data-group-id="4938087604-2">(</span><span class="w">
│ │ │ +         </span><span class="nf">por</span><span class="p" data-group-id="4938087604-3">(</span><span class="nf">pconst</span><span class="p" data-group-id="4938087604-4">(</span><span class="ss">a</span><span class="p" data-group-id="4938087604-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="4938087604-5">(</span><span class="ss">b</span><span class="p" data-group-id="4938087604-5">)</span><span class="p" data-group-id="4938087604-3">)</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="nf">por</span><span class="p" data-group-id="4938087604-6">(</span><span class="nf">pconst</span><span class="p" data-group-id="4938087604-7">(</span><span class="ss">c</span><span class="p" data-group-id="4938087604-7">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="4938087604-8">(</span><span class="ss">d</span><span class="p" data-group-id="4938087604-8">)</span><span class="p" data-group-id="4938087604-6">)</span><span class="p" data-group-id="4938087604-2">)</span><span class="p">.</span></code></pre><p>The following code adds a parser interface to the grammar:</p><pre><code class="makeup erlang" translate="no"><span class="nf">parse</span><span class="p" data-group-id="3662256881-1">(</span><span class="n">List</span><span class="p" data-group-id="3662256881-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3662256881-2">(</span><span class="nf">grammar</span><span class="p" data-group-id="3662256881-3">(</span><span class="p" data-group-id="3662256881-3">)</span><span class="p" data-group-id="3662256881-2">)</span><span class="p" data-group-id="3662256881-4">(</span><span class="n">List</span><span class="p" data-group-id="3662256881-4">)</span><span class="p">.</span></code></pre><p>The parser can be tested as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="5910239920-1">(</span><span class="p" data-group-id="5910239920-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5910239920-2">]</span><span class="p" data-group-id="5910239920-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5910239920-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="5910239920-4">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="5910239920-5">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="5910239920-6">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="5910239920-6">}</span><span class="p" data-group-id="5910239920-5">}</span><span class="p">,</span><span class="p" data-group-id="5910239920-7">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="5910239920-8">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5910239920-8">}</span><span class="p" data-group-id="5910239920-7">}</span><span class="p" data-group-id="5910239920-4">}</span><span class="p" data-group-id="5910239920-3">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="5910239920-9">(</span><span class="p" data-group-id="5910239920-10">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="5910239920-10">]</span><span class="p" data-group-id="5910239920-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5910239920-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="5910239920-12">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="5910239920-13">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="5910239920-14">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="5910239920-14">}</span><span class="p" data-group-id="5910239920-13">}</span><span class="p">,</span><span class="p" data-group-id="5910239920-15">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5910239920-16">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="5910239920-16">}</span><span class="p" data-group-id="5910239920-15">}</span><span class="p" data-group-id="5910239920-12">}</span><span class="p" data-group-id="5910239920-11">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="5910239920-17">(</span><span class="p" data-group-id="5910239920-18">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5910239920-18">]</span><span class="p" data-group-id="5910239920-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5910239920-19">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="5910239920-20">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="5910239920-21">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5910239920-22">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5910239920-22">}</span><span class="p" data-group-id="5910239920-21">}</span><span class="p">,</span><span class="p" data-group-id="5910239920-23">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="5910239920-24">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5910239920-24">}</span><span class="p" data-group-id="5910239920-23">}</span><span class="p" data-group-id="5910239920-20">}</span><span class="p" data-group-id="5910239920-19">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="5910239920-25">(</span><span class="p" data-group-id="5910239920-26">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="5910239920-26">]</span><span class="p" data-group-id="5910239920-25">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5910239920-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="5910239920-28">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="5910239920-29">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5910239920-30">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5910239920-30">}</span><span class="p" data-group-id="5910239920-29">}</span><span class="p">,</span><span class="p" data-group-id="5910239920-31">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5910239920-32">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="5910239920-32">}</span><span class="p" data-group-id="5910239920-31">}</span><span class="p" data-group-id="5910239920-28">}</span><span class="p" data-group-id="5910239920-27">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="5910239920-33">(</span><span class="p" data-group-id="5910239920-34">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5910239920-34">]</span><span class="p" data-group-id="5910239920-33">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">fail</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="prog_ex_records.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/gen_server_concepts.html
│ │ │ @@ -157,63 +157,63 @@
│ │ │    <a href="#example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example</span>
│ │ │  </h2>
│ │ │  <p>An example of a simple server written in plain Erlang is provided in
│ │ │  <a href="design_principles.html#ch1">Overview</a>. The server can be reimplemented using
│ │ │ -<code class="inline">gen_server</code>, resulting in this callback module:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6555041491-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="6555041491-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="6555041491-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="6555041491-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">gen_server</code>, resulting in this callback module:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9129845487-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="9129845487-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="9129845487-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="9129845487-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6555041491-3">(</span><span class="p" data-group-id="6555041491-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6555041491-4">]</span><span class="p" data-group-id="6555041491-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6555041491-5">(</span><span class="p" data-group-id="6555041491-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6555041491-6">]</span><span class="p" data-group-id="6555041491-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6555041491-7">(</span><span class="p" data-group-id="6555041491-8">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6555041491-8">]</span><span class="p" data-group-id="6555041491-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9129845487-3">(</span><span class="p" data-group-id="9129845487-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9129845487-4">]</span><span class="p" data-group-id="9129845487-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9129845487-5">(</span><span class="p" data-group-id="9129845487-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9129845487-6">]</span><span class="p" data-group-id="9129845487-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9129845487-7">(</span><span class="p" data-group-id="9129845487-8">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9129845487-8">]</span><span class="p" data-group-id="9129845487-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="6555041491-9">(</span><span class="p" data-group-id="6555041491-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6555041491-10">(</span><span class="p" data-group-id="6555041491-11">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6555041491-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6555041491-12">[</span><span class="p" data-group-id="6555041491-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6555041491-13">[</span><span class="p" data-group-id="6555041491-13">]</span><span class="p" data-group-id="6555041491-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="9129845487-9">(</span><span class="p" data-group-id="9129845487-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="9129845487-10">(</span><span class="p" data-group-id="9129845487-11">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="9129845487-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9129845487-12">[</span><span class="p" data-group-id="9129845487-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9129845487-13">[</span><span class="p" data-group-id="9129845487-13">]</span><span class="p" data-group-id="9129845487-10">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="6555041491-14">(</span><span class="p" data-group-id="6555041491-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="6555041491-15">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="6555041491-15">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="9129845487-14">(</span><span class="p" data-group-id="9129845487-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="9129845487-15">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="9129845487-15">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="6555041491-16">(</span><span class="n">Ch</span><span class="p" data-group-id="6555041491-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6555041491-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6555041491-18">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6555041491-18">}</span><span class="p" data-group-id="6555041491-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="9129845487-16">(</span><span class="n">Ch</span><span class="p" data-group-id="9129845487-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="9129845487-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9129845487-18">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9129845487-18">}</span><span class="p" data-group-id="9129845487-17">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6555041491-19">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6555041491-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6555041491-20">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="6555041491-21">(</span><span class="p" data-group-id="6555041491-21">)</span><span class="p" data-group-id="6555041491-20">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="9129845487-19">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="9129845487-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9129845487-20">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="9129845487-21">(</span><span class="p" data-group-id="9129845487-21">)</span><span class="p" data-group-id="9129845487-20">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="6555041491-22">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6555041491-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6555041491-23">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6555041491-23">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="6555041491-24">(</span><span class="n">Chs</span><span class="p" data-group-id="6555041491-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6555041491-25">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6555041491-25">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="9129845487-22">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="9129845487-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9129845487-23">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="9129845487-23">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="9129845487-24">(</span><span class="n">Chs</span><span class="p" data-group-id="9129845487-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9129845487-25">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="9129845487-25">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="6555041491-26">(</span><span class="p" data-group-id="6555041491-27">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6555041491-27">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6555041491-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="6555041491-28">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6555041491-28">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6555041491-29">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6555041491-29">}</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-a-gen_server" class="section-heading">
│ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="9129845487-26">(</span><span class="p" data-group-id="9129845487-27">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9129845487-27">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="9129845487-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="9129845487-28">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="9129845487-28">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9129845487-29">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="9129845487-29">}</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-a-gen_server" class="section-heading">
│ │ │    <a href="#starting-a-gen_server" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting a Gen_Server</span>
│ │ │  </h2>
│ │ │  <p>In the example in the previous section, <code class="inline">gen_server</code> is started by calling
│ │ │ -<code class="inline">ch3:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="0576862023-1">(</span><span class="p" data-group-id="0576862023-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0576862023-2">(</span><span class="p" data-group-id="0576862023-3">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0576862023-3">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0576862023-4">[</span><span class="p" data-group-id="0576862023-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0576862023-5">[</span><span class="p" data-group-id="0576862023-5">]</span><span class="p" data-group-id="0576862023-2">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0576862023-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="0576862023-6">}</span></code></pre><p><code class="inline">start_link/0</code> calls function <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a>.  This function
│ │ │ +<code class="inline">ch3:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="1480311477-1">(</span><span class="p" data-group-id="1480311477-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1480311477-2">(</span><span class="p" data-group-id="1480311477-3">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="1480311477-3">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1480311477-4">[</span><span class="p" data-group-id="1480311477-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1480311477-5">[</span><span class="p" data-group-id="1480311477-5">]</span><span class="p" data-group-id="1480311477-2">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1480311477-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="1480311477-6">}</span></code></pre><p><code class="inline">start_link/0</code> calls function <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a>.  This function
│ │ │  spawns and links to a new process, a <code class="inline">gen_server</code>.</p><ul><li><p>The first argument, <code class="inline">{local, ch3}</code>, specifies the name.
│ │ │  The gen_server is then locally registered as <code class="inline">ch3</code>.</p><p>If the name is omitted, the <code class="inline">gen_server</code> is not registered. Instead its pid
│ │ │  must be used. The name can also be given as <code class="inline">{global, Name}</code>, in which case
│ │ │  the <code class="inline">gen_server</code> is registered using <a href="../../lib/kernel-10.2.7.1/doc/html/global.html#register_name/2"><code class="inline">global:register_name/2</code></a>.</p></li><li><p>The second argument, <code class="inline">ch3</code>, is the name of the callback module, which is
│ │ │  the module where the callback functions are located.</p><p>The interface functions (<code class="inline">start_link/0</code>, <code class="inline">alloc/0</code>, and <code class="inline">free/1</code>) are located
│ │ │  in the same module as the callback functions (<code class="inline">init/1</code>, <code class="inline">handle_call/3</code>, and
│ │ │  <code class="inline">handle_cast/2</code>). It is usually good programming practice to have the code
│ │ │  corresponding to one process contained in a single module.</p></li><li><p>The third argument, <code class="inline">[]</code>, is a term that is passed as is to the callback
│ │ │  function <code class="inline">init</code>. Here, <code class="inline">init</code> does not need any indata and ignores the
│ │ │  argument.</p></li><li><p>The fourth argument, <code class="inline">[]</code>, is a list of options. See <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │  for the available options.</p></li></ul><p>If name registration succeeds, the new <code class="inline">gen_server</code> process calls the callback
│ │ │  function <code class="inline">ch3:init([])</code>. <code class="inline">init</code> is expected to return <code class="inline">{ok, State}</code>, where
│ │ │  <code class="inline">State</code> is the internal state of the <code class="inline">gen_server</code>. In this case, the state is
│ │ │ -the available channels.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="2080428421-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="2080428421-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2080428421-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="2080428421-3">(</span><span class="p" data-group-id="2080428421-3">)</span><span class="p" data-group-id="2080428421-2">}</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> is synchronous. It does not return until the
│ │ │ +the available channels.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1115772630-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="1115772630-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1115772630-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="1115772630-3">(</span><span class="p" data-group-id="1115772630-3">)</span><span class="p" data-group-id="1115772630-2">}</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> is synchronous. It does not return until the
│ │ │  <code class="inline">gen_server</code> has been initialized and is ready to receive requests.</p><p><a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> must be used if the <code class="inline">gen_server</code> is part of
│ │ │  a supervision tree, meaning that it was started by a supervisor. There
│ │ │  is another function, <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#start/4"><code class="inline">gen_server:start/4</code></a>, to start a standalone
│ │ │  <code class="inline">gen_server</code> that is not part of a supervision tree.</p><h2 id="synchronous-requests-call" class="section-heading">
│ │ │    <a href="#synchronous-requests-call" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -221,32 +221,32 @@
│ │ │  </h2>
│ │ │  <p>The synchronous request <code class="inline">alloc()</code> is implemented using <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#call/2"><code class="inline">gen_server:call/2</code></a>:</p><pre><code class="text">alloc() -&gt;
│ │ │      gen_server:call(ch3, alloc).</code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code> and must agree with the name
│ │ │  used to start it. <code class="inline">alloc</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │  When the request is received, the <code class="inline">gen_server</code> calls
│ │ │  <code class="inline">handle_call(Request, From, State)</code>, which is expected to return
│ │ │  a tuple <code class="inline">{reply,Reply,State1}</code>. <code class="inline">Reply</code> is the reply that is to be sent back
│ │ │ -to the client, and <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="8246797578-1">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8246797578-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8246797578-2">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="8246797578-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="8246797578-3">(</span><span class="n">Chs</span><span class="p" data-group-id="8246797578-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8246797578-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="8246797578-4">}</span><span class="p">.</span></code></pre><p>In this case, the reply is the allocated channel <code class="inline">Ch</code> and the new state is the
│ │ │ +to the client, and <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="6542668075-1">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6542668075-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6542668075-2">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6542668075-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="6542668075-3">(</span><span class="n">Chs</span><span class="p" data-group-id="6542668075-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6542668075-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6542668075-4">}</span><span class="p">.</span></code></pre><p>In this case, the reply is the allocated channel <code class="inline">Ch</code> and the new state is the
│ │ │  set of remaining available channels <code class="inline">Chs2</code>.</p><p>Thus, the call <code class="inline">ch3:alloc()</code> returns the allocated channel <code class="inline">Ch</code> and the
│ │ │  <code class="inline">gen_server</code> then waits for new requests, now with an updated list of
│ │ │  available channels.</p><h2 id="asynchronous-requests-cast" class="section-heading">
│ │ │    <a href="#asynchronous-requests-cast" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Asynchronous Requests - Cast</span>
│ │ │  </h2>
│ │ │ -<p>The asynchronous request <code class="inline">free(Ch)</code> is implemented using <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#cast/2"><code class="inline">gen_server:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">free</span><span class="p" data-group-id="3402960399-1">(</span><span class="n">Ch</span><span class="p" data-group-id="3402960399-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="3402960399-2">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3402960399-3">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3402960399-3">}</span><span class="p" data-group-id="3402960399-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code>. <code class="inline">{free, Ch}</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │ +<p>The asynchronous request <code class="inline">free(Ch)</code> is implemented using <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#cast/2"><code class="inline">gen_server:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">free</span><span class="p" data-group-id="6610928990-1">(</span><span class="n">Ch</span><span class="p" data-group-id="6610928990-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6610928990-2">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6610928990-3">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6610928990-3">}</span><span class="p" data-group-id="6610928990-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code>. <code class="inline">{free, Ch}</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │  <code class="inline">cast</code>, and thus <code class="inline">free</code>, then returns <code class="inline">ok</code>.</p><p>When the request is received, the <code class="inline">gen_server</code> calls
│ │ │  <code class="inline">handle_cast(Request, State)</code>, which is expected to return a tuple
│ │ │ -<code class="inline">{noreply,State1}</code>. <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_cast</span><span class="p" data-group-id="6254534592-1">(</span><span class="p" data-group-id="6254534592-2">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6254534592-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6254534592-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="6254534592-3">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6254534592-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6254534592-4">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6254534592-4">}</span><span class="p">.</span></code></pre><p>In this case, the new state is the updated list of available channels <code class="inline">Chs2</code>.
│ │ │ +<code class="inline">{noreply,State1}</code>. <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_cast</span><span class="p" data-group-id="2190548151-1">(</span><span class="p" data-group-id="2190548151-2">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="2190548151-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2190548151-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="2190548151-3">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2190548151-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2190548151-4">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="2190548151-4">}</span><span class="p">.</span></code></pre><p>In this case, the new state is the updated list of available channels <code class="inline">Chs2</code>.
│ │ │  The <code class="inline">gen_server</code> is now ready for new requests.</p><h2 id="stopping" class="section-heading">
│ │ │    <a href="#stopping" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Stopping</span>
│ │ │  </h2>
│ │ │  <h3 id="in-a-supervision-tree" class="section-heading">
│ │ │ @@ -257,69 +257,69 @@
│ │ │  </h3>
│ │ │  <p>If the <code class="inline">gen_server</code> is part of a supervision tree, no stop function is needed.
│ │ │  The <code class="inline">gen_server</code> is automatically terminated by its supervisor.  Exactly how
│ │ │  this is done is defined by a <a href="sup_princ.html#shutdown">shutdown strategy</a>
│ │ │  set in the supervisor.</p><p>If it is necessary to clean up before termination, the shutdown strategy
│ │ │  must be a time-out value and the <code class="inline">gen_server</code> must be set to trap exit signals
│ │ │  in function <code class="inline">init</code>. When ordered to shutdown, the <code class="inline">gen_server</code> then calls
│ │ │ -the callback function <code class="inline">terminate(shutdown, State)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8570684301-1">(</span><span class="n">Args</span><span class="p" data-group-id="8570684301-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +the callback function <code class="inline">terminate(shutdown, State)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1210981921-1">(</span><span class="n">Args</span><span class="p" data-group-id="1210981921-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="8570684301-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8570684301-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="1210981921-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1210981921-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8570684301-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8570684301-3">}</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1210981921-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1210981921-3">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="8570684301-4">(</span><span class="ss">shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8570684301-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="1210981921-4">(</span><span class="ss">shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1210981921-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Code for cleaning up here</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="standalone-gen_servers" class="section-heading">
│ │ │    <a href="#standalone-gen_servers" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Standalone Gen_Servers</span>
│ │ │  </h3>
│ │ │  <p>If the <code class="inline">gen_server</code> is not part of a supervision tree, a stop function
│ │ │  can be useful, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">export</span><span class="p" data-group-id="8117791795-1">(</span><span class="p" data-group-id="8117791795-2">[</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8117791795-2">]</span><span class="p" data-group-id="8117791795-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">export</span><span class="p" data-group-id="8775336343-1">(</span><span class="p" data-group-id="8775336343-2">[</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8775336343-2">]</span><span class="p" data-group-id="8775336343-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="8117791795-3">(</span><span class="p" data-group-id="8117791795-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8117791795-4">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p" data-group-id="8117791795-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="8775336343-3">(</span><span class="p" data-group-id="8775336343-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8775336343-4">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p" data-group-id="8775336343-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="8117791795-5">(</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8117791795-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8117791795-6">{</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8117791795-6">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="8117791795-7">(</span><span class="p" data-group-id="8117791795-8">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8117791795-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8117791795-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="8775336343-5">(</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8775336343-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8775336343-6">{</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8775336343-6">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="8775336343-7">(</span><span class="p" data-group-id="8775336343-8">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8775336343-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8775336343-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="8117791795-9">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8117791795-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="8775336343-9">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8775336343-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The callback function handling the <code class="inline">stop</code> request returns a tuple
│ │ │  <code class="inline">{stop,normal,State1}</code>, where <code class="inline">normal</code> specifies that it is
│ │ │  a normal termination and <code class="inline">State1</code> is a new value for the state
│ │ │  of the <code class="inline">gen_server</code>.  This causes the <code class="inline">gen_server</code> to call
│ │ │  <code class="inline">terminate(normal, State1)</code> and then it terminates gracefully.</p><h2 id="handling-other-messages" class="section-heading">
│ │ │    <a href="#handling-other-messages" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Handling Other Messages</span>
│ │ │  </h2>
│ │ │  <p>If the <code class="inline">gen_server</code> is to be able to receive other messages than requests,
│ │ │  the callback function <code class="inline">handle_info(Info, State)</code> must be implemented
│ │ │  to handle them.  Examples of other messages are exit messages,
│ │ │  if the <code class="inline">gen_server</code> is linked to other processes than the supervisor
│ │ │ -and it is trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="4632366654-1">(</span><span class="p" data-group-id="4632366654-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="4632366654-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4632366654-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +and it is trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="0245103293-1">(</span><span class="p" data-group-id="0245103293-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="0245103293-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="0245103293-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Code to handle exits here.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4632366654-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="4632366654-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="5207617178-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="5207617178-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0245103293-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="0245103293-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="9908444271-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="9908444271-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Code to convert state (and more) during code change.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5207617178-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="5207617178-2">}</span><span class="p">.</span></code></pre>
│ │ │ +    </span><span class="p" data-group-id="9908444271-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="9908444271-2">}</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="design_principles.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/included_applications.html
│ │ │ @@ -161,75 +161,75 @@
│ │ │  belonging to the primary application.</p><h2 id="specifying-included-applications" class="section-heading">
│ │ │    <a href="#specifying-included-applications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Specifying Included Applications</span>
│ │ │  </h2>
│ │ │  <p>Which applications to include is defined by the <code class="inline">included_applications</code> key in
│ │ │ -the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6046255110-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6046255110-2">[</span><span class="p" data-group-id="6046255110-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="6046255110-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6046255110-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6046255110-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6046255110-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6046255110-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="6046255110-6">]</span><span class="p" data-group-id="6046255110-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6046255110-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6046255110-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="6046255110-8">]</span><span class="p" data-group-id="6046255110-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6046255110-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6046255110-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="6046255110-10">]</span><span class="p" data-group-id="6046255110-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6046255110-11">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6046255110-12">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="6046255110-12">]</span><span class="p" data-group-id="6046255110-11">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6046255110-13">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6046255110-14">{</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="6046255110-15">[</span><span class="p" data-group-id="6046255110-15">]</span><span class="p" data-group-id="6046255110-14">}</span><span class="p" data-group-id="6046255110-13">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6046255110-16">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6046255110-17">[</span><span class="p" data-group-id="6046255110-18">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="6046255110-18">}</span><span class="p" data-group-id="6046255110-17">]</span><span class="p" data-group-id="6046255110-16">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6046255110-2">]</span><span class="p" data-group-id="6046255110-1">}</span><span class="p">.</span></code></pre><h2 id="synchronizing-processes-during-startup" class="section-heading">
│ │ │ +the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6208849284-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6208849284-2">[</span><span class="p" data-group-id="6208849284-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="6208849284-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6208849284-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6208849284-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6208849284-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6208849284-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="6208849284-6">]</span><span class="p" data-group-id="6208849284-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6208849284-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6208849284-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="6208849284-8">]</span><span class="p" data-group-id="6208849284-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6208849284-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6208849284-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="6208849284-10">]</span><span class="p" data-group-id="6208849284-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6208849284-11">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6208849284-12">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="6208849284-12">]</span><span class="p" data-group-id="6208849284-11">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6208849284-13">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6208849284-14">{</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="6208849284-15">[</span><span class="p" data-group-id="6208849284-15">]</span><span class="p" data-group-id="6208849284-14">}</span><span class="p" data-group-id="6208849284-13">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6208849284-16">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6208849284-17">[</span><span class="p" data-group-id="6208849284-18">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="6208849284-18">}</span><span class="p" data-group-id="6208849284-17">]</span><span class="p" data-group-id="6208849284-16">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6208849284-2">]</span><span class="p" data-group-id="6208849284-1">}</span><span class="p">.</span></code></pre><h2 id="synchronizing-processes-during-startup" class="section-heading">
│ │ │    <a href="#synchronizing-processes-during-startup" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Synchronizing Processes during Startup</span>
│ │ │  </h2>
│ │ │  <p>The supervisor tree of an included application is started as part of the
│ │ │  supervisor tree of the including application. If there is a need for
│ │ │  synchronization between processes in the including and included applications,
│ │ │  this can be achieved by using <em>start phases</em>.</p><p>Start phases are defined by the <code class="inline">start_phases</code> key in the <code class="inline">.app</code> file as a list
│ │ │  of tuples <code class="inline">{Phase,PhaseArgs}</code>, where <code class="inline">Phase</code> is an atom and <code class="inline">PhaseArgs</code> is a
│ │ │  term.</p><p>The value of the <code class="inline">mod</code> key of the including application must be set to
│ │ │  <code class="inline">{application_starter,[Module,StartArgs]}</code>, where <code class="inline">Module</code> as usual is the
│ │ │  application callback module. <code class="inline">StartArgs</code> is a term provided as argument to the
│ │ │ -callback function <code class="inline">Module:start/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8210133515-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8210133515-2">[</span><span class="p" data-group-id="8210133515-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="8210133515-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="8210133515-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="8210133515-6">]</span><span class="p" data-group-id="8210133515-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="8210133515-8">]</span><span class="p" data-group-id="8210133515-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="8210133515-10">]</span><span class="p" data-group-id="8210133515-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-11">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-12">[</span><span class="p" data-group-id="8210133515-13">{</span><span class="ss">init</span><span class="p">,</span><span class="p" data-group-id="8210133515-14">[</span><span class="p" data-group-id="8210133515-14">]</span><span class="p" data-group-id="8210133515-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-15">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="8210133515-16">[</span><span class="p" data-group-id="8210133515-16">]</span><span class="p" data-group-id="8210133515-15">}</span><span class="p" data-group-id="8210133515-12">]</span><span class="p" data-group-id="8210133515-11">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-17">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-18">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="8210133515-18">]</span><span class="p" data-group-id="8210133515-17">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-19">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-20">{</span><span class="ss">application_starter</span><span class="p">,</span><span class="p" data-group-id="8210133515-21">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="8210133515-22">[</span><span class="p" data-group-id="8210133515-22">]</span><span class="p" data-group-id="8210133515-21">]</span><span class="p" data-group-id="8210133515-20">}</span><span class="p" data-group-id="8210133515-19">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-23">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-24">[</span><span class="p" data-group-id="8210133515-25">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="8210133515-25">}</span><span class="p" data-group-id="8210133515-24">]</span><span class="p" data-group-id="8210133515-23">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8210133515-2">]</span><span class="p" data-group-id="8210133515-1">}</span><span class="p">.</span><span class="w">
│ │ │ +callback function <code class="inline">Module:start/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2679322657-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2679322657-2">[</span><span class="p" data-group-id="2679322657-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="2679322657-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="2679322657-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="2679322657-6">]</span><span class="p" data-group-id="2679322657-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="2679322657-8">]</span><span class="p" data-group-id="2679322657-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="2679322657-10">]</span><span class="p" data-group-id="2679322657-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-11">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-12">[</span><span class="p" data-group-id="2679322657-13">{</span><span class="ss">init</span><span class="p">,</span><span class="p" data-group-id="2679322657-14">[</span><span class="p" data-group-id="2679322657-14">]</span><span class="p" data-group-id="2679322657-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-15">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="2679322657-16">[</span><span class="p" data-group-id="2679322657-16">]</span><span class="p" data-group-id="2679322657-15">}</span><span class="p" data-group-id="2679322657-12">]</span><span class="p" data-group-id="2679322657-11">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-17">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-18">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="2679322657-18">]</span><span class="p" data-group-id="2679322657-17">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-19">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-20">{</span><span class="ss">application_starter</span><span class="p">,</span><span class="p" data-group-id="2679322657-21">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="2679322657-22">[</span><span class="p" data-group-id="2679322657-22">]</span><span class="p" data-group-id="2679322657-21">]</span><span class="p" data-group-id="2679322657-20">}</span><span class="p" data-group-id="2679322657-19">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-23">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-24">[</span><span class="p" data-group-id="2679322657-25">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="2679322657-25">}</span><span class="p" data-group-id="2679322657-24">]</span><span class="p" data-group-id="2679322657-23">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2679322657-2">]</span><span class="p" data-group-id="2679322657-1">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="8210133515-26">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8210133515-27">[</span><span class="p" data-group-id="8210133515-28">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Included application&quot;</span><span class="p" data-group-id="8210133515-28">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-29">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="8210133515-29">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-30">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-31">[</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_server</span><span class="p" data-group-id="8210133515-31">]</span><span class="p" data-group-id="8210133515-30">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-32">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-33">[</span><span class="p" data-group-id="8210133515-33">]</span><span class="p" data-group-id="8210133515-32">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-34">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-35">[</span><span class="p" data-group-id="8210133515-36">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="8210133515-37">[</span><span class="p" data-group-id="8210133515-37">]</span><span class="p" data-group-id="8210133515-36">}</span><span class="p" data-group-id="8210133515-35">]</span><span class="p" data-group-id="8210133515-34">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-38">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-39">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="8210133515-39">]</span><span class="p" data-group-id="8210133515-38">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8210133515-40">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8210133515-41">{</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="p" data-group-id="8210133515-42">[</span><span class="p" data-group-id="8210133515-42">]</span><span class="p" data-group-id="8210133515-41">}</span><span class="p" data-group-id="8210133515-40">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8210133515-27">]</span><span class="p" data-group-id="8210133515-26">}</span><span class="p">.</span></code></pre><p>When starting a primary application with included applications, the primary
│ │ │ +</span><span class="p" data-group-id="2679322657-26">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2679322657-27">[</span><span class="p" data-group-id="2679322657-28">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Included application&quot;</span><span class="p" data-group-id="2679322657-28">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-29">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="2679322657-29">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-30">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-31">[</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_server</span><span class="p" data-group-id="2679322657-31">]</span><span class="p" data-group-id="2679322657-30">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-32">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-33">[</span><span class="p" data-group-id="2679322657-33">]</span><span class="p" data-group-id="2679322657-32">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-34">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-35">[</span><span class="p" data-group-id="2679322657-36">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="2679322657-37">[</span><span class="p" data-group-id="2679322657-37">]</span><span class="p" data-group-id="2679322657-36">}</span><span class="p" data-group-id="2679322657-35">]</span><span class="p" data-group-id="2679322657-34">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-38">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-39">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="2679322657-39">]</span><span class="p" data-group-id="2679322657-38">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2679322657-40">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2679322657-41">{</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="p" data-group-id="2679322657-42">[</span><span class="p" data-group-id="2679322657-42">]</span><span class="p" data-group-id="2679322657-41">}</span><span class="p" data-group-id="2679322657-40">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2679322657-27">]</span><span class="p" data-group-id="2679322657-26">}</span><span class="p">.</span></code></pre><p>When starting a primary application with included applications, the primary
│ │ │  application is started the normal way, that is:</p><ul><li>The application controller creates an application master for the application</li><li>The application master calls <code class="inline">Module:start(normal, StartArgs)</code> to start the
│ │ │  top supervisor.</li></ul><p>Then, for the primary application and each included application in top-down,
│ │ │  left-to-right order, the application master calls
│ │ │  <code class="inline">Module:start_phase(Phase, Type, PhaseArgs)</code> for each phase defined for the
│ │ │  primary application, in that order. If a phase is not defined for an included
│ │ │  application, the function is not called for this phase and application.</p><p>The following requirements apply to the <code class="inline">.app</code> file for an included application:</p><ul><li>The <code class="inline">{mod, {Module,StartArgs}}</code> option must be included. This option is used
│ │ │  to find the callback module <code class="inline">Module</code> of the application. <code class="inline">StartArgs</code> is
│ │ │  ignored, as <code class="inline">Module:start/2</code> is called only for the primary application.</li><li>If the included application itself contains included applications, instead the
│ │ │  <code class="inline">{mod, {application_starter, [Module,StartArgs]}}</code> option must be included.</li><li>The <code class="inline">{start_phases, [{Phase,PhaseArgs}]}</code> option must be included, and the set
│ │ │  of specified phases must be a subset of the set of phases specified for the
│ │ │  primary application.</li></ul><p>When starting <code class="inline">prim_app</code> as defined above, the application controller calls the
│ │ │  following callback functions before <code class="inline">application:start(prim_app)</code> returns a
│ │ │ -value:</p><pre><code class="makeup erlang" translate="no"><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4333805126-1">(</span><span class="ss">prim_app</span><span class="p" data-group-id="4333805126-1">)</span><span class="w">
│ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4333805126-2">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4333805126-3">[</span><span class="p" data-group-id="4333805126-3">]</span><span class="p" data-group-id="4333805126-2">)</span><span class="w">
│ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="4333805126-4">(</span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4333805126-5">[</span><span class="p" data-group-id="4333805126-5">]</span><span class="p" data-group-id="4333805126-4">)</span><span class="w">
│ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="4333805126-6">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4333805126-7">[</span><span class="p" data-group-id="4333805126-7">]</span><span class="p" data-group-id="4333805126-6">)</span><span class="w">
│ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">incl_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="4333805126-8">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4333805126-9">[</span><span class="p" data-group-id="4333805126-9">]</span><span class="p" data-group-id="4333805126-8">)</span><span class="w">
│ │ │ +value:</p><pre><code class="makeup erlang" translate="no"><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1583560502-1">(</span><span class="ss">prim_app</span><span class="p" data-group-id="1583560502-1">)</span><span class="w">
│ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1583560502-2">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1583560502-3">[</span><span class="p" data-group-id="1583560502-3">]</span><span class="p" data-group-id="1583560502-2">)</span><span class="w">
│ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="1583560502-4">(</span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1583560502-5">[</span><span class="p" data-group-id="1583560502-5">]</span><span class="p" data-group-id="1583560502-4">)</span><span class="w">
│ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="1583560502-6">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1583560502-7">[</span><span class="p" data-group-id="1583560502-7">]</span><span class="p" data-group-id="1583560502-6">)</span><span class="w">
│ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">incl_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="1583560502-8">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1583560502-9">[</span><span class="p" data-group-id="1583560502-9">]</span><span class="p" data-group-id="1583560502-8">)</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="applications.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/install-win32.html
│ │ │ @@ -295,15 +295,15 @@
│ │ │  </span><span class="gp unselectable">$ </span><span class="">cd erts/emulator
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make debug
│ │ │  </span><span class="gp unselectable">$ </span><span class="">cd ../etc
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make debug
│ │ │  </span></code></pre><p>and sometimes</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make local_setup
│ │ │  </span></code></pre><p>So now when you run <code class="inline">$ERL_TOP/erl.exe</code>, you should have a debug compiled
│ │ │ -emulator, which you will see if you do a:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="1550681930-1">(</span><span class="ss">system_version</span><span class="p" data-group-id="1550681930-1">)</span><span class="p">.</span></code></pre><p>in the erlang shell. If the returned string contains <code class="inline">[debug]</code>, you
│ │ │ +emulator, which you will see if you do a:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="9442300960-1">(</span><span class="ss">system_version</span><span class="p" data-group-id="9442300960-1">)</span><span class="p">.</span></code></pre><p>in the erlang shell. If the returned string contains <code class="inline">[debug]</code>, you
│ │ │  got a debug compiled emulator.</p><p>To hack the erlang libraries, you simply do a <code class="inline">make opt</code> in the
│ │ │  specific &quot;applications&quot; directory, like:</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make opt
│ │ │  </span></code></pre><p>or even in the source directory...</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib/src
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make opt
│ │ │  </span></code></pre><p>Note that you're expected to have a fresh Erlang in your path when
│ │ │  doing this, preferably the plain 27 you have built in the previous
│ │ │ @@ -318,19 +318,19 @@
│ │ │  </span><span class="">:$ERL_TOP/erts/etc/win32/wsl_tools:$ERL_TOP/bootstrap/bin:$PATH
│ │ │  </span></code></pre><p>That should make it possible to rebuild any library without hassle...</p><p>If you want to copy a library (an application) newly built, to a
│ │ │  release area, you do like with the emulator:</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make TESTROOT=/tmp/erlang_release release
│ │ │  </span></code></pre><p>Remember that:</p><ul><li><p>  Windows specific C-code goes in the <code class="inline">$ERL_TOP/erts/emulator/sys/win32</code>,
│ │ │  <code class="inline">$ERL_TOP/erts/emulator/drivers/win32</code> or <code class="inline">$ERL_TOP/erts/etc/win32</code>.</p></li><li><p>  Windows specific erlang code should be used conditionally and the
│ │ │  host OS tested in <em>runtime</em>, the exactly same beam files should be
│ │ │ -distributed for every platform! So write code like:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">os</span><span class="p">:</span><span class="nf">type</span><span class="p" data-group-id="6607518955-1">(</span><span class="p" data-group-id="6607518955-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6607518955-2">{</span><span class="ss">win32</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6607518955-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nf">do_windows_specific</span><span class="p" data-group-id="6607518955-3">(</span><span class="p" data-group-id="6607518955-3">)</span><span class="p">;</span><span class="w">
│ │ │ +distributed for every platform! So write code like:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">os</span><span class="p">:</span><span class="nf">type</span><span class="p" data-group-id="5499959635-1">(</span><span class="p" data-group-id="5499959635-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5499959635-2">{</span><span class="ss">win32</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5499959635-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nf">do_windows_specific</span><span class="p" data-group-id="5499959635-3">(</span><span class="p" data-group-id="5499959635-3">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Other</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nf">do_fallback_or_exit</span><span class="p" data-group-id="6607518955-4">(</span><span class="p" data-group-id="6607518955-4">)</span><span class="w">
│ │ │ +        </span><span class="nf">do_fallback_or_exit</span><span class="p" data-group-id="5499959635-4">(</span><span class="p" data-group-id="5499959635-4">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre></li></ul><p>That's basically all you need to get going.</p><h2 id="frequently-asked-questions" class="section-heading">
│ │ │    <a href="#frequently-asked-questions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Frequently Asked Questions</span>
│ │ │  </h2>
│ │ │  <ul><li><p>  Q: So, now I can build Erlang using GCC on Windows?</p><p>A: No, unfortunately not. You'll need Microsoft's Visual C++
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/list_comprehensions.html
│ │ │ @@ -117,33 +117,33 @@
│ │ │  
│ │ │  <h2 id="simple-examples" class="section-heading">
│ │ │    <a href="#simple-examples" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Simple Examples</span>
│ │ │  </h2>
│ │ │ -<p>This section starts with a simple example, showing a generator and a filter:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="7111995273-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7111995273-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7111995273-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7111995273-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7111995273-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7111995273-3">]</span></code></pre><p>This is read as follows: The list of X such that X is taken from the list
│ │ │ +<p>This section starts with a simple example, showing a generator and a filter:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="3335845673-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="3335845673-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="3335845673-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3335845673-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3335845673-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="3335845673-3">]</span></code></pre><p>This is read as follows: The list of X such that X is taken from the list
│ │ │  <code class="inline">[1,2,a,...]</code> and X is greater than 3.</p><p>The notation <code class="inline">X &lt;- [1,2,a,...]</code> is a generator and the expression <code class="inline">X &gt; 3</code> is a
│ │ │  filter.</p><p>An additional filter, <a href="../../erts-15.2.7/doc/html/erlang.html#is_integer/1"><code class="inline">is_integer(X)</code></a>, can be added to
│ │ │ -restrict the result to integers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="2470578569-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="2470578569-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2470578569-2">]</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="2470578569-3">(</span><span class="n">X</span><span class="p" data-group-id="2470578569-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2470578569-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2470578569-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2470578569-4">]</span></code></pre><p>Generators can be combined. For example, the Cartesian product of two lists can
│ │ │ -be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="4190570128-1">[</span><span class="p" data-group-id="4190570128-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4190570128-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4190570128-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4190570128-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4190570128-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4190570128-4">]</span><span class="p" data-group-id="4190570128-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4190570128-5">[</span><span class="p" data-group-id="4190570128-6">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4190570128-6">}</span><span class="p">,</span><span class="p" data-group-id="4190570128-7">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4190570128-7">}</span><span class="p">,</span><span class="p" data-group-id="4190570128-8">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4190570128-8">}</span><span class="p">,</span><span class="p" data-group-id="4190570128-9">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4190570128-9">}</span><span class="p">,</span><span class="p" data-group-id="4190570128-10">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4190570128-10">}</span><span class="p">,</span><span class="p" data-group-id="4190570128-11">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4190570128-11">}</span><span class="p" data-group-id="4190570128-5">]</span></code></pre><h2 id="quick-sort" class="section-heading">
│ │ │ +restrict the result to integers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="6466562942-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="6466562942-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6466562942-2">]</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="6466562942-3">(</span><span class="n">X</span><span class="p" data-group-id="6466562942-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6466562942-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6466562942-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6466562942-4">]</span></code></pre><p>Generators can be combined. For example, the Cartesian product of two lists can
│ │ │ +be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="7486822666-1">[</span><span class="p" data-group-id="7486822666-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7486822666-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7486822666-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7486822666-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7486822666-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7486822666-4">]</span><span class="p" data-group-id="7486822666-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7486822666-5">[</span><span class="p" data-group-id="7486822666-6">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7486822666-6">}</span><span class="p">,</span><span class="p" data-group-id="7486822666-7">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7486822666-7">}</span><span class="p">,</span><span class="p" data-group-id="7486822666-8">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7486822666-8">}</span><span class="p">,</span><span class="p" data-group-id="7486822666-9">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7486822666-9">}</span><span class="p">,</span><span class="p" data-group-id="7486822666-10">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7486822666-10">}</span><span class="p">,</span><span class="p" data-group-id="7486822666-11">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7486822666-11">}</span><span class="p" data-group-id="7486822666-5">]</span></code></pre><h2 id="quick-sort" class="section-heading">
│ │ │    <a href="#quick-sort" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Quick Sort</span>
│ │ │  </h2>
│ │ │ -<p>The well-known quick sort routine can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sort</span><span class="p" data-group-id="1791632821-1">(</span><span class="p" data-group-id="1791632821-2">[</span><span class="p" data-group-id="1791632821-2">]</span><span class="p" data-group-id="1791632821-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1791632821-3">[</span><span class="p" data-group-id="1791632821-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">sort</span><span class="p" data-group-id="1791632821-4">(</span><span class="p" data-group-id="1791632821-5">[</span><span class="p">_</span><span class="p" data-group-id="1791632821-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1791632821-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">L</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">sort</span><span class="p" data-group-id="1791632821-6">(</span><span class="p" data-group-id="1791632821-7">[</span><span class="n">Pivot</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1791632821-7">]</span><span class="p" data-group-id="1791632821-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">sort</span><span class="p" data-group-id="1791632821-8">(</span><span class="p" data-group-id="1791632821-9">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="1791632821-9">]</span><span class="p" data-group-id="1791632821-8">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1791632821-10">[</span><span class="n">Pivot</span><span class="p" data-group-id="1791632821-10">]</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ -    </span><span class="nf">sort</span><span class="p" data-group-id="1791632821-11">(</span><span class="p" data-group-id="1791632821-12">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="1791632821-12">]</span><span class="p" data-group-id="1791632821-11">)</span><span class="p">.</span></code></pre><p>The expression <code class="inline">[X || X &lt;- T, X &lt; Pivot]</code> is the list of all elements in <code class="inline">T</code>
│ │ │ +<p>The well-known quick sort routine can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sort</span><span class="p" data-group-id="3232584121-1">(</span><span class="p" data-group-id="3232584121-2">[</span><span class="p" data-group-id="3232584121-2">]</span><span class="p" data-group-id="3232584121-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3232584121-3">[</span><span class="p" data-group-id="3232584121-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">sort</span><span class="p" data-group-id="3232584121-4">(</span><span class="p" data-group-id="3232584121-5">[</span><span class="p">_</span><span class="p" data-group-id="3232584121-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="3232584121-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">L</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">sort</span><span class="p" data-group-id="3232584121-6">(</span><span class="p" data-group-id="3232584121-7">[</span><span class="n">Pivot</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3232584121-7">]</span><span class="p" data-group-id="3232584121-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">sort</span><span class="p" data-group-id="3232584121-8">(</span><span class="p" data-group-id="3232584121-9">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="3232584121-9">]</span><span class="p" data-group-id="3232584121-8">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3232584121-10">[</span><span class="n">Pivot</span><span class="p" data-group-id="3232584121-10">]</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ +    </span><span class="nf">sort</span><span class="p" data-group-id="3232584121-11">(</span><span class="p" data-group-id="3232584121-12">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="3232584121-12">]</span><span class="p" data-group-id="3232584121-11">)</span><span class="p">.</span></code></pre><p>The expression <code class="inline">[X || X &lt;- T, X &lt; Pivot]</code> is the list of all elements in <code class="inline">T</code>
│ │ │  that are less than <code class="inline">Pivot</code>.</p><p><code class="inline">[X || X &lt;- T, X &gt;= Pivot]</code> is the list of all elements in <code class="inline">T</code> that are greater
│ │ │  than or equal to <code class="inline">Pivot</code>.</p><p>With the algorithm above, a list is sorted as follows:</p><ul><li>A list with zero or one element is trivially sorted.</li><li>For lists with more than one element:<ol><li>The first element in the list is isolated as the pivot element.</li><li>The remaining list is partitioned into two sublists, such that:</li></ol><ul><li>The first sublist contains all elements that are smaller than the pivot
│ │ │  element.</li><li>The second sublist contains all elements that are greater than or equal to
│ │ │  the pivot element.</li></ul><ol><li>The sublists are recursively sorted by the same algorithm and the results
│ │ │  are combined, resulting in a list consisting of:</li></ol><ul><li>All elements from the first sublist, that is all elements smaller than the
│ │ │  pivot element, in sorted order.</li><li>The pivot element.</li><li>All elements from the second sublist, that is all elements greater than or
│ │ │  equal to the pivot element, in sorted order.</li></ul></li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>While the sorting algorithm as shown above serves as a nice example to
│ │ │ @@ -151,93 +151,93 @@
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html"><code class="inline">lists</code></a> module contains sorting functions that are implemented in a more
│ │ │  efficient way.</p></section><h2 id="permutations" class="section-heading">
│ │ │    <a href="#permutations" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Permutations</span>
│ │ │  </h2>
│ │ │ -<p>The following example generates all permutations of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">perms</span><span class="p" data-group-id="5850862786-1">(</span><span class="p" data-group-id="5850862786-2">[</span><span class="p" data-group-id="5850862786-2">]</span><span class="p" data-group-id="5850862786-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5850862786-3">[</span><span class="p" data-group-id="5850862786-4">[</span><span class="p" data-group-id="5850862786-4">]</span><span class="p" data-group-id="5850862786-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">perms</span><span class="p" data-group-id="5850862786-5">(</span><span class="n">L</span><span class="p" data-group-id="5850862786-5">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5850862786-6">[</span><span class="p" data-group-id="5850862786-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5850862786-7">]</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nf">perms</span><span class="p" data-group-id="5850862786-8">(</span><span class="n">L</span><span class="o">--</span><span class="p" data-group-id="5850862786-9">[</span><span class="n">H</span><span class="p" data-group-id="5850862786-9">]</span><span class="p" data-group-id="5850862786-8">)</span><span class="p" data-group-id="5850862786-6">]</span><span class="p">.</span></code></pre><p>This takes <code class="inline">H</code> from <code class="inline">L</code> in all possible ways. The result is the set of all lists
│ │ │ +<p>The following example generates all permutations of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">perms</span><span class="p" data-group-id="7677925123-1">(</span><span class="p" data-group-id="7677925123-2">[</span><span class="p" data-group-id="7677925123-2">]</span><span class="p" data-group-id="7677925123-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7677925123-3">[</span><span class="p" data-group-id="7677925123-4">[</span><span class="p" data-group-id="7677925123-4">]</span><span class="p" data-group-id="7677925123-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">perms</span><span class="p" data-group-id="7677925123-5">(</span><span class="n">L</span><span class="p" data-group-id="7677925123-5">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7677925123-6">[</span><span class="p" data-group-id="7677925123-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7677925123-7">]</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nf">perms</span><span class="p" data-group-id="7677925123-8">(</span><span class="n">L</span><span class="o">--</span><span class="p" data-group-id="7677925123-9">[</span><span class="n">H</span><span class="p" data-group-id="7677925123-9">]</span><span class="p" data-group-id="7677925123-8">)</span><span class="p" data-group-id="7677925123-6">]</span><span class="p">.</span></code></pre><p>This takes <code class="inline">H</code> from <code class="inline">L</code> in all possible ways. The result is the set of all lists
│ │ │  <code class="inline">[H|T]</code>, where <code class="inline">T</code> is the set of all possible permutations of <code class="inline">L</code>, with <code class="inline">H</code>
│ │ │ -removed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">perms</span><span class="p" data-group-id="6800737022-1">(</span><span class="p" data-group-id="6800737022-2">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="6800737022-2">]</span><span class="p" data-group-id="6800737022-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6800737022-3">[</span><span class="p" data-group-id="6800737022-4">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="6800737022-4">]</span><span class="p">,</span><span class="p" data-group-id="6800737022-5">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="6800737022-5">]</span><span class="p">,</span><span class="p" data-group-id="6800737022-6">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="6800737022-6">]</span><span class="p">,</span><span class="p" data-group-id="6800737022-7">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6800737022-7">]</span><span class="p">,</span><span class="p" data-group-id="6800737022-8">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="6800737022-8">]</span><span class="p">,</span><span class="p" data-group-id="6800737022-9">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6800737022-9">]</span><span class="p" data-group-id="6800737022-3">]</span></code></pre><h2 id="pythagorean-triplets" class="section-heading">
│ │ │ +removed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">perms</span><span class="p" data-group-id="7869288598-1">(</span><span class="p" data-group-id="7869288598-2">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="7869288598-2">]</span><span class="p" data-group-id="7869288598-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7869288598-3">[</span><span class="p" data-group-id="7869288598-4">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="7869288598-4">]</span><span class="p">,</span><span class="p" data-group-id="7869288598-5">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="7869288598-5">]</span><span class="p">,</span><span class="p" data-group-id="7869288598-6">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="7869288598-6">]</span><span class="p">,</span><span class="p" data-group-id="7869288598-7">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7869288598-7">]</span><span class="p">,</span><span class="p" data-group-id="7869288598-8">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="7869288598-8">]</span><span class="p">,</span><span class="p" data-group-id="7869288598-9">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7869288598-9">]</span><span class="p" data-group-id="7869288598-3">]</span></code></pre><h2 id="pythagorean-triplets" class="section-heading">
│ │ │    <a href="#pythagorean-triplets" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Pythagorean Triplets</span>
│ │ │  </h2>
│ │ │  <p>Pythagorean triplets are sets of integers <code class="inline">{A,B,C}</code> such that
│ │ │  <code class="inline">A**2 + B**2 = C**2</code>.</p><p>The function <code class="inline">pyth(N)</code> generates a list of all integers <code class="inline">{A,B,C}</code> such that
│ │ │  <code class="inline">A**2 + B**2 = C**2</code> and where the sum of the sides is equal to, or less than,
│ │ │ -<code class="inline">N</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth</span><span class="p" data-group-id="2221443162-1">(</span><span class="n">N</span><span class="p" data-group-id="2221443162-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2221443162-2">[</span><span class="w"> </span><span class="p" data-group-id="2221443162-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="2221443162-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ -        </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2221443162-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="2221443162-4">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2221443162-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="2221443162-5">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2221443162-6">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="2221443162-6">)</span><span class="p">,</span><span class="w">
│ │ │ +<code class="inline">N</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth</span><span class="p" data-group-id="5800255512-1">(</span><span class="n">N</span><span class="p" data-group-id="5800255512-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5800255512-2">[</span><span class="w"> </span><span class="p" data-group-id="5800255512-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="5800255512-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ +        </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5800255512-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="5800255512-4">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5800255512-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="5800255512-5">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5800255512-6">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="5800255512-6">)</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">+</span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2221443162-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="9237589313-1">(</span><span class="mi">3</span><span class="p" data-group-id="9237589313-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9237589313-2">[</span><span class="p" data-group-id="9237589313-2">]</span><span class="p">.</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="9237589313-3">(</span><span class="mi">11</span><span class="p" data-group-id="9237589313-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9237589313-4">[</span><span class="p" data-group-id="9237589313-4">]</span><span class="p">.</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="9237589313-5">(</span><span class="mi">12</span><span class="p" data-group-id="9237589313-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9237589313-6">[</span><span class="p" data-group-id="9237589313-7">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9237589313-7">}</span><span class="p">,</span><span class="p" data-group-id="9237589313-8">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9237589313-8">}</span><span class="p" data-group-id="9237589313-6">]</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="9237589313-9">(</span><span class="mi">50</span><span class="p" data-group-id="9237589313-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9237589313-10">[</span><span class="p" data-group-id="9237589313-11">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9237589313-11">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-12">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9237589313-12">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-13">{</span><span class="mi">5</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="9237589313-13">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-14">{</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="9237589313-14">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-15">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="9237589313-15">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-16">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="9237589313-16">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-17">{</span><span class="mi">9</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="9237589313-17">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-18">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="9237589313-18">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-19">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="9237589313-19">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-20">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="9237589313-20">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-21">{</span><span class="mi">15</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="9237589313-21">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9237589313-22">{</span><span class="mi">16</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="9237589313-22">}</span><span class="p" data-group-id="9237589313-10">]</span></code></pre><p>The following code reduces the search space and is more efficient:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth1</span><span class="p" data-group-id="1019897263-1">(</span><span class="n">N</span><span class="p" data-group-id="1019897263-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="1019897263-2">[</span><span class="p" data-group-id="1019897263-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="1019897263-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ -       </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1019897263-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="1019897263-4">)</span><span class="p">,</span><span class="w">
│ │ │ -       </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1019897263-5">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="1019897263-5">)</span><span class="p">,</span><span class="w">
│ │ │ -       </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1019897263-6">(</span><span class="n">B</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="1019897263-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5800255512-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="3175481881-1">(</span><span class="mi">3</span><span class="p" data-group-id="3175481881-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3175481881-2">[</span><span class="p" data-group-id="3175481881-2">]</span><span class="p">.</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="3175481881-3">(</span><span class="mi">11</span><span class="p" data-group-id="3175481881-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3175481881-4">[</span><span class="p" data-group-id="3175481881-4">]</span><span class="p">.</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="3175481881-5">(</span><span class="mi">12</span><span class="p" data-group-id="3175481881-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3175481881-6">[</span><span class="p" data-group-id="3175481881-7">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3175481881-7">}</span><span class="p">,</span><span class="p" data-group-id="3175481881-8">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3175481881-8">}</span><span class="p" data-group-id="3175481881-6">]</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="3175481881-9">(</span><span class="mi">50</span><span class="p" data-group-id="3175481881-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3175481881-10">[</span><span class="p" data-group-id="3175481881-11">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3175481881-11">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-12">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3175481881-12">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-13">{</span><span class="mi">5</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="3175481881-13">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-14">{</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="3175481881-14">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-15">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="3175481881-15">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-16">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="3175481881-16">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-17">{</span><span class="mi">9</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="3175481881-17">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-18">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="3175481881-18">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-19">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="3175481881-19">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-20">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="3175481881-20">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-21">{</span><span class="mi">15</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="3175481881-21">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3175481881-22">{</span><span class="mi">16</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="3175481881-22">}</span><span class="p" data-group-id="3175481881-10">]</span></code></pre><p>The following code reduces the search space and is more efficient:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth1</span><span class="p" data-group-id="5341839999-1">(</span><span class="n">N</span><span class="p" data-group-id="5341839999-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="5341839999-2">[</span><span class="p" data-group-id="5341839999-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="5341839999-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ +       </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5341839999-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="5341839999-4">)</span><span class="p">,</span><span class="w">
│ │ │ +       </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5341839999-5">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5341839999-5">)</span><span class="p">,</span><span class="w">
│ │ │ +       </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="5341839999-6">(</span><span class="n">B</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="5341839999-6">)</span><span class="p">,</span><span class="w">
│ │ │         </span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">+</span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w">
│ │ │ -       </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w"> </span><span class="p" data-group-id="1019897263-2">]</span><span class="p">.</span></code></pre><h2 id="simplifications-with-list-comprehensions" class="section-heading">
│ │ │ +       </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w"> </span><span class="p" data-group-id="5341839999-2">]</span><span class="p">.</span></code></pre><h2 id="simplifications-with-list-comprehensions" class="section-heading">
│ │ │    <a href="#simplifications-with-list-comprehensions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Simplifications With List Comprehensions</span>
│ │ │  </h2>
│ │ │  <p>As an example, list comprehensions can be used to simplify some of the functions
│ │ │ -in <code class="inline">lists.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="5958754594-1">(</span><span class="n">L</span><span class="p" data-group-id="5958754594-1">)</span><span class="w">   </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="5958754594-2">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">L1</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="5958754594-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="5958754594-3">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5958754594-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5958754594-4">[</span><span class="n">Fun</span><span class="p" data-group-id="5958754594-5">(</span><span class="n">X</span><span class="p" data-group-id="5958754594-5">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5958754594-4">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">filter</span><span class="p" data-group-id="5958754594-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5958754594-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5958754594-7">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="5958754594-8">(</span><span class="n">X</span><span class="p" data-group-id="5958754594-8">)</span><span class="p" data-group-id="5958754594-7">]</span><span class="p">.</span></code></pre><h2 id="variable-bindings-in-list-comprehensions" class="section-heading">
│ │ │ +in <code class="inline">lists.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="8979647306-1">(</span><span class="n">L</span><span class="p" data-group-id="8979647306-1">)</span><span class="w">   </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="8979647306-2">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">L1</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="8979647306-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="8979647306-3">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="8979647306-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8979647306-4">[</span><span class="n">Fun</span><span class="p" data-group-id="8979647306-5">(</span><span class="n">X</span><span class="p" data-group-id="8979647306-5">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="8979647306-4">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">filter</span><span class="p" data-group-id="8979647306-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="8979647306-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8979647306-7">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="8979647306-8">(</span><span class="n">X</span><span class="p" data-group-id="8979647306-8">)</span><span class="p" data-group-id="8979647306-7">]</span><span class="p">.</span></code></pre><h2 id="variable-bindings-in-list-comprehensions" class="section-heading">
│ │ │    <a href="#variable-bindings-in-list-comprehensions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Variable Bindings in List Comprehensions</span>
│ │ │  </h2>
│ │ │  <p>The scope rules for variables that occur in list comprehensions are as follows:</p><ul><li>All variables that occur in a generator pattern are assumed to be &quot;fresh&quot;
│ │ │  variables.</li><li>Any variables that are defined before the list comprehension, and that are
│ │ │  used in filters, have the values they had before the list comprehension.</li><li>Variables cannot be exported from a list comprehension.</li></ul><p>As an example of these rules, suppose you want to write the function <code class="inline">select</code>,
│ │ │  which selects certain elements from a list of tuples. Suppose you write
│ │ │  <code class="inline">select(X, L) -&gt; [Y || {X, Y} &lt;- L].</code> with the intention of extracting all
│ │ │  tuples from <code class="inline">L</code>, where the first item is <code class="inline">X</code>.</p><p>Compiling this gives the following diagnostic:</p><pre><code class="text">./FileName.erl:Line: Warning: variable 'X' shadowed in generate</code></pre><p>This diagnostic warns that the variable <code class="inline">X</code> in the pattern is not the same as
│ │ │ -the variable <code class="inline">X</code> that occurs in the function head.</p><p>Evaluating <code class="inline">select</code> gives the following result:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="8723693635-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="8723693635-2">[</span><span class="p" data-group-id="8723693635-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8723693635-3">}</span><span class="p">,</span><span class="p" data-group-id="8723693635-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8723693635-4">}</span><span class="p">,</span><span class="p" data-group-id="8723693635-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8723693635-5">}</span><span class="p">,</span><span class="p" data-group-id="8723693635-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="8723693635-6">}</span><span class="p" data-group-id="8723693635-2">]</span><span class="p" data-group-id="8723693635-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8723693635-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="8723693635-7">]</span></code></pre><p>This is not the wanted result. To achieve the desired effect, <code class="inline">select</code> must be
│ │ │ -written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="4262708041-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4262708041-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="4262708041-2">[</span><span class="n">Y</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="4262708041-3">{</span><span class="n">X1</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4262708041-3">}</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">X1</span><span class="p" data-group-id="4262708041-2">]</span><span class="p">.</span></code></pre><p>The generator now contains unbound variables and the test has been moved into
│ │ │ -the filter.</p><p>This now works as expected:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="0262291295-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="0262291295-2">[</span><span class="p" data-group-id="0262291295-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0262291295-3">}</span><span class="p">,</span><span class="p" data-group-id="0262291295-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0262291295-4">}</span><span class="p">,</span><span class="p" data-group-id="0262291295-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0262291295-5">}</span><span class="p">,</span><span class="p" data-group-id="0262291295-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="0262291295-6">}</span><span class="p" data-group-id="0262291295-2">]</span><span class="p" data-group-id="0262291295-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0262291295-7">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="0262291295-7">]</span></code></pre><p>Also note that a variable in a generator pattern will shadow a variable with the
│ │ │ -same name bound in a previous generator pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="4902304508-1">[</span><span class="p" data-group-id="4902304508-2">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p" data-group-id="4902304508-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4902304508-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4902304508-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="o">=</span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4902304508-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4902304508-4">]</span><span class="p" data-group-id="4902304508-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4902304508-5">[</span><span class="p" data-group-id="4902304508-6">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4902304508-6">}</span><span class="p">,</span><span class="p" data-group-id="4902304508-7">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4902304508-7">}</span><span class="p">,</span><span class="p" data-group-id="4902304508-8">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4902304508-8">}</span><span class="p">,</span><span class="p" data-group-id="4902304508-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4902304508-9">}</span><span class="p">,</span><span class="p" data-group-id="4902304508-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4902304508-10">}</span><span class="p">,</span><span class="p" data-group-id="4902304508-11">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4902304508-11">}</span><span class="p">,</span><span class="p" data-group-id="4902304508-12">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4902304508-12">}</span><span class="p">,</span><span class="p" data-group-id="4902304508-13">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4902304508-13">}</span><span class="p">,</span><span class="p" data-group-id="4902304508-14">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4902304508-14">}</span><span class="p" data-group-id="4902304508-5">]</span></code></pre><p>A consequence of the rules for importing variables into a list comprehensions is
│ │ │ +the variable <code class="inline">X</code> that occurs in the function head.</p><p>Evaluating <code class="inline">select</code> gives the following result:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="3345948590-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="3345948590-2">[</span><span class="p" data-group-id="3345948590-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3345948590-3">}</span><span class="p">,</span><span class="p" data-group-id="3345948590-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3345948590-4">}</span><span class="p">,</span><span class="p" data-group-id="3345948590-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3345948590-5">}</span><span class="p">,</span><span class="p" data-group-id="3345948590-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3345948590-6">}</span><span class="p" data-group-id="3345948590-2">]</span><span class="p" data-group-id="3345948590-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3345948590-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3345948590-7">]</span></code></pre><p>This is not the wanted result. To achieve the desired effect, <code class="inline">select</code> must be
│ │ │ +written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="8857283333-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="8857283333-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="8857283333-2">[</span><span class="n">Y</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="8857283333-3">{</span><span class="n">X1</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8857283333-3">}</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">X1</span><span class="p" data-group-id="8857283333-2">]</span><span class="p">.</span></code></pre><p>The generator now contains unbound variables and the test has been moved into
│ │ │ +the filter.</p><p>This now works as expected:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="4512711082-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="4512711082-2">[</span><span class="p" data-group-id="4512711082-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4512711082-3">}</span><span class="p">,</span><span class="p" data-group-id="4512711082-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4512711082-4">}</span><span class="p">,</span><span class="p" data-group-id="4512711082-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4512711082-5">}</span><span class="p">,</span><span class="p" data-group-id="4512711082-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4512711082-6">}</span><span class="p" data-group-id="4512711082-2">]</span><span class="p" data-group-id="4512711082-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4512711082-7">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4512711082-7">]</span></code></pre><p>Also note that a variable in a generator pattern will shadow a variable with the
│ │ │ +same name bound in a previous generator pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="3992108291-1">[</span><span class="p" data-group-id="3992108291-2">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p" data-group-id="3992108291-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="3992108291-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3992108291-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="o">=</span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="3992108291-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3992108291-4">]</span><span class="p" data-group-id="3992108291-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3992108291-5">[</span><span class="p" data-group-id="3992108291-6">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="3992108291-6">}</span><span class="p">,</span><span class="p" data-group-id="3992108291-7">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3992108291-7">}</span><span class="p">,</span><span class="p" data-group-id="3992108291-8">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3992108291-8">}</span><span class="p">,</span><span class="p" data-group-id="3992108291-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="3992108291-9">}</span><span class="p">,</span><span class="p" data-group-id="3992108291-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3992108291-10">}</span><span class="p">,</span><span class="p" data-group-id="3992108291-11">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3992108291-11">}</span><span class="p">,</span><span class="p" data-group-id="3992108291-12">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="3992108291-12">}</span><span class="p">,</span><span class="p" data-group-id="3992108291-13">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3992108291-13">}</span><span class="p">,</span><span class="p" data-group-id="3992108291-14">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3992108291-14">}</span><span class="p" data-group-id="3992108291-5">]</span></code></pre><p>A consequence of the rules for importing variables into a list comprehensions is
│ │ │  that certain pattern matching operations must be moved into the filters and
│ │ │ -cannot be written directly in the generators.</p><p>To illustrate this, do <em>not</em> write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="1436138016-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1436138016-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +cannot be written directly in the generators.</p><p>To illustrate this, do <em>not</em> write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4351093953-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4351093953-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1436138016-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1436138016-2">]</span><span class="w">
│ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Instead, write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="6475884249-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6475884249-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4351093953-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4351093953-2">]</span><span class="w">
│ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Instead, write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="5421487198-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5421487198-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6475884249-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y1</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6475884249-2">]</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5421487198-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y1</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5421487198-2">]</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="funs.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/listhandling.html
│ │ │ @@ -120,105 +120,105 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating a List</span>
│ │ │  </h2>
│ │ │  <p>Lists can only be built starting from the end and attaching list elements at the
│ │ │  beginning. If you use the <code class="inline">++</code> operator as follows, a new list is created that
│ │ │  is a copy of the elements in <code class="inline">List1</code>, followed by <code class="inline">List2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">List1</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">List2</span></code></pre><p>Looking at how <a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#append/2"><code class="inline">lists:append/2</code></a> or <code class="inline">++</code> would be implemented in plain Erlang,
│ │ │ -clearly the first list is copied:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="7725365373-1">(</span><span class="p" data-group-id="7725365373-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7725365373-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="7725365373-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7725365373-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">append</span><span class="p" data-group-id="7725365373-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="7725365373-4">)</span><span class="p" data-group-id="7725365373-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">append</span><span class="p" data-group-id="7725365373-5">(</span><span class="p" data-group-id="7725365373-6">[</span><span class="p" data-group-id="7725365373-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="7725365373-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +clearly the first list is copied:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="3064053264-1">(</span><span class="p" data-group-id="3064053264-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3064053264-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="3064053264-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3064053264-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">append</span><span class="p" data-group-id="3064053264-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="3064053264-4">)</span><span class="p" data-group-id="3064053264-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">append</span><span class="p" data-group-id="3064053264-5">(</span><span class="p" data-group-id="3064053264-6">[</span><span class="p" data-group-id="3064053264-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="3064053264-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>When recursing and building a list, it is important to ensure that you attach
│ │ │  the new elements to the beginning of the list. In this way, you will build <em>one</em>
│ │ │ -list, not hundreds or thousands of copies of the growing result list.</p><p>Let us first see how it is not to be done:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">bad_fib</span><span class="p" data-group-id="9802890486-1">(</span><span class="n">N</span><span class="p" data-group-id="9802890486-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">bad_fib</span><span class="p" data-group-id="9802890486-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9802890486-3">[</span><span class="p" data-group-id="9802890486-3">]</span><span class="p" data-group-id="9802890486-2">)</span><span class="p">.</span><span class="w">
│ │ │ +list, not hundreds or thousands of copies of the growing result list.</p><p>Let us first see how it is not to be done:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">bad_fib</span><span class="p" data-group-id="1320442199-1">(</span><span class="n">N</span><span class="p" data-group-id="1320442199-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">bad_fib</span><span class="p" data-group-id="1320442199-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1320442199-3">[</span><span class="p" data-group-id="1320442199-3">]</span><span class="p" data-group-id="1320442199-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">bad_fib</span><span class="p" data-group-id="9802890486-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="9802890486-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">bad_fib</span><span class="p" data-group-id="1320442199-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="1320442199-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Fibs</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">bad_fib</span><span class="p" data-group-id="9802890486-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="9802890486-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">bad_fib</span><span class="p" data-group-id="9802890486-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9802890486-7">[</span><span class="n">Current</span><span class="p" data-group-id="9802890486-7">]</span><span class="p" data-group-id="9802890486-6">)</span><span class="p">.</span></code></pre><p>Here more than one list is built. In each iteration step a new list is created
│ │ │ +</span><span class="nf">bad_fib</span><span class="p" data-group-id="1320442199-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="1320442199-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">bad_fib</span><span class="p" data-group-id="1320442199-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1320442199-7">[</span><span class="n">Current</span><span class="p" data-group-id="1320442199-7">]</span><span class="p" data-group-id="1320442199-6">)</span><span class="p">.</span></code></pre><p>Here more than one list is built. In each iteration step a new list is created
│ │ │  that is one element longer than the new previous list.</p><p>To avoid copying the result in each iteration, build the list in reverse order
│ │ │ -and reverse the list when you are done:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8851135751-1">(</span><span class="n">N</span><span class="p" data-group-id="8851135751-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8851135751-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8851135751-3">[</span><span class="p" data-group-id="8851135751-3">]</span><span class="p" data-group-id="8851135751-2">)</span><span class="p">.</span><span class="w">
│ │ │ +and reverse the list when you are done:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="5439914361-1">(</span><span class="n">N</span><span class="p" data-group-id="5439914361-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="5439914361-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5439914361-3">[</span><span class="p" data-group-id="5439914361-3">]</span><span class="p" data-group-id="5439914361-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8851135751-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="8851135751-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="8851135751-5">(</span><span class="n">Fibs</span><span class="p" data-group-id="8851135751-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8851135751-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="8851135751-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8851135751-7">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8851135751-8">[</span><span class="n">Current</span><span class="p">|</span><span class="n">Fibs</span><span class="p" data-group-id="8851135751-8">]</span><span class="p" data-group-id="8851135751-7">)</span><span class="p">.</span></code></pre><h2 id="list-comprehensions" class="section-heading">
│ │ │ +</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="5439914361-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="5439914361-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="5439914361-5">(</span><span class="n">Fibs</span><span class="p" data-group-id="5439914361-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="5439914361-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="5439914361-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="5439914361-7">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5439914361-8">[</span><span class="n">Current</span><span class="p">|</span><span class="n">Fibs</span><span class="p" data-group-id="5439914361-8">]</span><span class="p" data-group-id="5439914361-7">)</span><span class="p">.</span></code></pre><h2 id="list-comprehensions" class="section-heading">
│ │ │    <a href="#list-comprehensions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">List Comprehensions</span>
│ │ │  </h2>
│ │ │ -<p>A list comprehension:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7839001331-1">[</span><span class="n">Expr</span><span class="p" data-group-id="7839001331-2">(</span><span class="n">E</span><span class="p" data-group-id="7839001331-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7839001331-1">]</span></code></pre><p>is basically translated to a local function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="9082800767-1">(</span><span class="p" data-group-id="9082800767-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="9082800767-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="9082800767-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9082800767-3">[</span><span class="n">Expr</span><span class="p" data-group-id="9082800767-4">(</span><span class="n">E</span><span class="p" data-group-id="9082800767-4">)</span><span class="p">|</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="9082800767-5">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="9082800767-5">)</span><span class="p" data-group-id="9082800767-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="9082800767-6">(</span><span class="p" data-group-id="9082800767-7">[</span><span class="p" data-group-id="9082800767-7">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="9082800767-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9082800767-8">[</span><span class="p" data-group-id="9082800767-8">]</span><span class="p">.</span></code></pre><p>If the result of the list comprehension will <em>obviously</em> not be used, a list
│ │ │ -will not be constructed. For example, in this code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2953408288-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="2953408288-2">(</span><span class="n">E</span><span class="p" data-group-id="2953408288-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="2953408288-1">]</span><span class="p">,</span><span class="w">
│ │ │ +<p>A list comprehension:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6678122120-1">[</span><span class="n">Expr</span><span class="p" data-group-id="6678122120-2">(</span><span class="n">E</span><span class="p" data-group-id="6678122120-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6678122120-1">]</span></code></pre><p>is basically translated to a local function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="0782634203-1">(</span><span class="p" data-group-id="0782634203-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="0782634203-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="0782634203-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0782634203-3">[</span><span class="n">Expr</span><span class="p" data-group-id="0782634203-4">(</span><span class="n">E</span><span class="p" data-group-id="0782634203-4">)</span><span class="p">|</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="0782634203-5">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="0782634203-5">)</span><span class="p" data-group-id="0782634203-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="0782634203-6">(</span><span class="p" data-group-id="0782634203-7">[</span><span class="p" data-group-id="0782634203-7">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="0782634203-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0782634203-8">[</span><span class="p" data-group-id="0782634203-8">]</span><span class="p">.</span></code></pre><p>If the result of the list comprehension will <em>obviously</em> not be used, a list
│ │ │ +will not be constructed. For example, in this code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6573510997-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="6573510997-2">(</span><span class="n">E</span><span class="p" data-group-id="6573510997-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6573510997-1">]</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>or in this code:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">Var</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2207076786-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="2207076786-2">(</span><span class="n">E</span><span class="p" data-group-id="2207076786-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="2207076786-1">]</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="4834572954-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="4834572954-2">(</span><span class="n">E</span><span class="p" data-group-id="4834572954-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="4834572954-1">]</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">some_function</span><span class="p" data-group-id="2207076786-3">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2207076786-3">)</span><span class="p">,</span></code></pre><p>the value is not assigned to a variable, not passed to another function, and not
│ │ │ +</span><span class="nf">some_function</span><span class="p" data-group-id="4834572954-3">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4834572954-3">)</span><span class="p">,</span></code></pre><p>the value is not assigned to a variable, not passed to another function, and not
│ │ │  returned. This means that there is no need to construct a list and the compiler
│ │ │ -will simplify the code for the list comprehension to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5256178217-1">(</span><span class="p" data-group-id="5256178217-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="5256178217-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="5256178217-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Expr</span><span class="p" data-group-id="5256178217-3">(</span><span class="n">E</span><span class="p" data-group-id="5256178217-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5256178217-4">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="5256178217-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5256178217-5">(</span><span class="p" data-group-id="5256178217-6">[</span><span class="p" data-group-id="5256178217-6">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="5256178217-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5256178217-7">[</span><span class="p" data-group-id="5256178217-7">]</span><span class="p">.</span></code></pre><p>The compiler also understands that assigning to <code class="inline">_</code> means that the value will
│ │ │ -not be used. Therefore, the code in the following example will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6989861127-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="6989861127-2">(</span><span class="n">E</span><span class="p" data-group-id="6989861127-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6989861127-1">]</span><span class="p">,</span><span class="w">
│ │ │ +will simplify the code for the list comprehension to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="1964650863-1">(</span><span class="p" data-group-id="1964650863-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="1964650863-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="1964650863-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Expr</span><span class="p" data-group-id="1964650863-3">(</span><span class="n">E</span><span class="p" data-group-id="1964650863-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="1964650863-4">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="1964650863-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="1964650863-5">(</span><span class="p" data-group-id="1964650863-6">[</span><span class="p" data-group-id="1964650863-6">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="1964650863-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1964650863-7">[</span><span class="p" data-group-id="1964650863-7">]</span><span class="p">.</span></code></pre><p>The compiler also understands that assigning to <code class="inline">_</code> means that the value will
│ │ │ +not be used. Therefore, the code in the following example will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4972572523-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="4972572523-2">(</span><span class="n">E</span><span class="p" data-group-id="4972572523-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="4972572523-1">]</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="p">.</span></code></pre><h2 id="deep-and-flat-lists" class="section-heading">
│ │ │    <a href="#deep-and-flat-lists" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Deep and Flat Lists</span>
│ │ │  </h2>
│ │ │  <p><a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#flatten/1"><code class="inline">lists:flatten/1</code></a> builds an entirely new list. It is therefore expensive, and
│ │ │  even <em>more</em> expensive than the <code class="inline">++</code> operator (which copies its left argument,
│ │ │  but not its right argument).</p><p>In the following situations it is unnecessary to call <a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#flatten/1"><code class="inline">lists:flatten/1</code></a>:</p><ul><li>When sending data to a port. Ports understand deep lists so there is no reason
│ │ │  to flatten the list before sending it to the port.</li><li>When calling BIFs that accept deep lists, such as
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a> or
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#iolist_to_binary/1"><code class="inline">iolist_to_binary/1</code></a>.</li><li>When you know that your list is only one level deep. Use <a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#append/1"><code class="inline">lists:append/1</code></a>
│ │ │ -instead.</li></ul><p><em>Examples:</em></p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="4959578714-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">DeepList</span><span class="p" data-group-id="4959578714-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="5839538608-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="5839538608-2">(</span><span class="n">DeepList</span><span class="p" data-group-id="5839538608-2">)</span><span class="p" data-group-id="5839538608-1">)</span></code></pre><p>A common way to send a zero-terminated string to a port is the following:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0662795571-1">[</span><span class="mi">0</span><span class="p" data-group-id="0662795571-1">]</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">port_command</span><span class="p" data-group-id="0662795571-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="0662795571-2">)</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4326987682-1">[</span><span class="n">String</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4326987682-1">]</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">port_command</span><span class="p" data-group-id="4326987682-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="4326987682-2">)</span></code></pre><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">append</span><span class="p" data-group-id="3955747136-1">(</span><span class="p" data-group-id="3955747136-2">[</span><span class="p" data-group-id="3955747136-3">[</span><span class="mi">1</span><span class="p" data-group-id="3955747136-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3955747136-4">[</span><span class="mi">2</span><span class="p" data-group-id="3955747136-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3955747136-5">[</span><span class="mi">3</span><span class="p" data-group-id="3955747136-5">]</span><span class="p" data-group-id="3955747136-2">]</span><span class="p" data-group-id="3955747136-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3955747136-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3955747136-6">]</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="8687590201-1">(</span><span class="p" data-group-id="8687590201-2">[</span><span class="p" data-group-id="8687590201-3">[</span><span class="mi">1</span><span class="p" data-group-id="8687590201-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8687590201-4">[</span><span class="mi">2</span><span class="p" data-group-id="8687590201-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8687590201-5">[</span><span class="mi">3</span><span class="p" data-group-id="8687590201-5">]</span><span class="p" data-group-id="8687590201-2">]</span><span class="p" data-group-id="8687590201-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8687590201-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8687590201-6">]</span></code></pre><h2 id="recursive-list-functions" class="section-heading">
│ │ │ +instead.</li></ul><p><em>Examples:</em></p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="1507318400-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">DeepList</span><span class="p" data-group-id="1507318400-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="9977425605-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="9977425605-2">(</span><span class="n">DeepList</span><span class="p" data-group-id="9977425605-2">)</span><span class="p" data-group-id="9977425605-1">)</span></code></pre><p>A common way to send a zero-terminated string to a port is the following:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6334891918-1">[</span><span class="mi">0</span><span class="p" data-group-id="6334891918-1">]</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">port_command</span><span class="p" data-group-id="6334891918-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="6334891918-2">)</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9143487948-1">[</span><span class="n">String</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="9143487948-1">]</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">port_command</span><span class="p" data-group-id="9143487948-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="9143487948-2">)</span></code></pre><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">append</span><span class="p" data-group-id="1523080079-1">(</span><span class="p" data-group-id="1523080079-2">[</span><span class="p" data-group-id="1523080079-3">[</span><span class="mi">1</span><span class="p" data-group-id="1523080079-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1523080079-4">[</span><span class="mi">2</span><span class="p" data-group-id="1523080079-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1523080079-5">[</span><span class="mi">3</span><span class="p" data-group-id="1523080079-5">]</span><span class="p" data-group-id="1523080079-2">]</span><span class="p" data-group-id="1523080079-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1523080079-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1523080079-6">]</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="9743710109-1">(</span><span class="p" data-group-id="9743710109-2">[</span><span class="p" data-group-id="9743710109-3">[</span><span class="mi">1</span><span class="p" data-group-id="9743710109-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9743710109-4">[</span><span class="mi">2</span><span class="p" data-group-id="9743710109-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9743710109-5">[</span><span class="mi">3</span><span class="p" data-group-id="9743710109-5">]</span><span class="p" data-group-id="9743710109-2">]</span><span class="p" data-group-id="9743710109-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9743710109-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9743710109-6">]</span></code></pre><h2 id="recursive-list-functions" class="section-heading">
│ │ │    <a href="#recursive-list-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Recursive List Functions</span>
│ │ │  </h2>
│ │ │  <p>There are two basic ways to write a function that traverses a list and
│ │ │  produces a new list.</p><p>The first way is writing a <em>body-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ -</span><span class="nf">add_42_body</span><span class="p" data-group-id="0733960360-1">(</span><span class="p" data-group-id="0733960360-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0733960360-2">]</span><span class="p" data-group-id="0733960360-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0733960360-3">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">add_42_body</span><span class="p" data-group-id="0733960360-4">(</span><span class="n">T</span><span class="p" data-group-id="0733960360-4">)</span><span class="p" data-group-id="0733960360-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">add_42_body</span><span class="p" data-group-id="0733960360-5">(</span><span class="p" data-group-id="0733960360-6">[</span><span class="p" data-group-id="0733960360-6">]</span><span class="p" data-group-id="0733960360-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0733960360-7">[</span><span class="p" data-group-id="0733960360-7">]</span><span class="p">.</span></code></pre><p>The second way is writing a <em>tail-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="4004369833-1">(</span><span class="n">List</span><span class="p" data-group-id="4004369833-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="4004369833-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4004369833-3">[</span><span class="p" data-group-id="4004369833-3">]</span><span class="p" data-group-id="4004369833-2">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="4004369833-4">(</span><span class="p" data-group-id="4004369833-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4004369833-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4004369833-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="4004369833-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4004369833-7">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4004369833-7">]</span><span class="p" data-group-id="4004369833-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="4004369833-8">(</span><span class="p" data-group-id="4004369833-9">[</span><span class="p" data-group-id="4004369833-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="4004369833-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="4004369833-10">(</span><span class="n">Acc</span><span class="p" data-group-id="4004369833-10">)</span><span class="p">.</span></code></pre><p>In early version of Erlang the tail-recursive function would typically
│ │ │ +</span><span class="nf">add_42_body</span><span class="p" data-group-id="4826516763-1">(</span><span class="p" data-group-id="4826516763-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4826516763-2">]</span><span class="p" data-group-id="4826516763-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4826516763-3">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">add_42_body</span><span class="p" data-group-id="4826516763-4">(</span><span class="n">T</span><span class="p" data-group-id="4826516763-4">)</span><span class="p" data-group-id="4826516763-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">add_42_body</span><span class="p" data-group-id="4826516763-5">(</span><span class="p" data-group-id="4826516763-6">[</span><span class="p" data-group-id="4826516763-6">]</span><span class="p" data-group-id="4826516763-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4826516763-7">[</span><span class="p" data-group-id="4826516763-7">]</span><span class="p">.</span></code></pre><p>The second way is writing a <em>tail-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="8777945980-1">(</span><span class="n">List</span><span class="p" data-group-id="8777945980-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="8777945980-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8777945980-3">[</span><span class="p" data-group-id="8777945980-3">]</span><span class="p" data-group-id="8777945980-2">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="8777945980-4">(</span><span class="p" data-group-id="8777945980-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8777945980-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8777945980-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="8777945980-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8777945980-7">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8777945980-7">]</span><span class="p" data-group-id="8777945980-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="8777945980-8">(</span><span class="p" data-group-id="8777945980-9">[</span><span class="p" data-group-id="8777945980-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8777945980-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="8777945980-10">(</span><span class="n">Acc</span><span class="p" data-group-id="8777945980-10">)</span><span class="p">.</span></code></pre><p>In early version of Erlang the tail-recursive function would typically
│ │ │  be more efficient. In modern versions of Erlang, there is usually not
│ │ │  much difference in performance between a body-recursive list function and
│ │ │  tail-recursive function that reverses the list at the end. Therefore,
│ │ │  concentrate on writing beautiful code and forget about the performance
│ │ │  of your list functions. In the time-critical parts of your code,
│ │ │  <em>measure</em> before rewriting your code.</p><p>For a thorough discussion about tail and body recursion, see
│ │ │  <a href="http://ferd.ca/erlang-s-tail-recursion-is-not-a-silver-bullet.html">Erlang's Tail Recursion is Not a Silver Bullet</a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>This section is about list functions that <em>construct</em> lists. A tail-recursive
│ │ │  function that does not construct a list runs in constant space, while the
│ │ │  corresponding body-recursive function uses stack space proportional to the
│ │ │  length of the list.</p></section><p>For example, a function that sums a list of integers, is <em>not</em> to be written as
│ │ │ -follows:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">recursive_sum</span><span class="p" data-group-id="6308306541-1">(</span><span class="p" data-group-id="6308306541-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6308306541-2">]</span><span class="p" data-group-id="6308306541-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">H</span><span class="o">+</span><span class="nf">recursive_sum</span><span class="p" data-group-id="6308306541-3">(</span><span class="n">T</span><span class="p" data-group-id="6308306541-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">recursive_sum</span><span class="p" data-group-id="6308306541-4">(</span><span class="p" data-group-id="6308306541-5">[</span><span class="p" data-group-id="6308306541-5">]</span><span class="p" data-group-id="6308306541-4">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">sum</span><span class="p" data-group-id="3638821575-1">(</span><span class="n">L</span><span class="p" data-group-id="3638821575-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="3638821575-2">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3638821575-2">)</span><span class="p">.</span><span class="w">
│ │ │ +follows:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">recursive_sum</span><span class="p" data-group-id="8604523572-1">(</span><span class="p" data-group-id="8604523572-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8604523572-2">]</span><span class="p" data-group-id="8604523572-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">H</span><span class="o">+</span><span class="nf">recursive_sum</span><span class="p" data-group-id="8604523572-3">(</span><span class="n">T</span><span class="p" data-group-id="8604523572-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">recursive_sum</span><span class="p" data-group-id="8604523572-4">(</span><span class="p" data-group-id="8604523572-5">[</span><span class="p" data-group-id="8604523572-5">]</span><span class="p" data-group-id="8604523572-4">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">sum</span><span class="p" data-group-id="8022197530-1">(</span><span class="n">L</span><span class="p" data-group-id="8022197530-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="8022197530-2">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8022197530-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">sum</span><span class="p" data-group-id="3638821575-3">(</span><span class="p" data-group-id="3638821575-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3638821575-4">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="3638821575-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="3638821575-5">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">H</span><span class="p" data-group-id="3638821575-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">sum</span><span class="p" data-group-id="3638821575-6">(</span><span class="p" data-group-id="3638821575-7">[</span><span class="p" data-group-id="3638821575-7">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="3638821575-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Sum</span><span class="p">.</span></code></pre>
│ │ │ +</span><span class="nf">sum</span><span class="p" data-group-id="8022197530-3">(</span><span class="p" data-group-id="8022197530-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8022197530-4">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="8022197530-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="8022197530-5">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">H</span><span class="p" data-group-id="8022197530-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">sum</span><span class="p" data-group-id="8022197530-6">(</span><span class="p" data-group-id="8022197530-7">[</span><span class="p" data-group-id="8022197530-7">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="8022197530-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Sum</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="maps.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/macros.html
│ │ │ @@ -117,56 +117,56 @@
│ │ │  
│ │ │  <h2 id="file-inclusion" class="section-heading">
│ │ │    <a href="#file-inclusion" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">File Inclusion</span>
│ │ │  </h2>
│ │ │ -<p>A file can be included as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2645057981-1">(</span><span class="n">File</span><span class="p" data-group-id="2645057981-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="2645057981-2">(</span><span class="n">File</span><span class="p" data-group-id="2645057981-2">)</span><span class="p">.</span></code></pre><p><code class="inline">File</code>, a string, is to point out a file. The contents of this file are included
│ │ │ +<p>A file can be included as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4936874754-1">(</span><span class="n">File</span><span class="p" data-group-id="4936874754-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="4936874754-2">(</span><span class="n">File</span><span class="p" data-group-id="4936874754-2">)</span><span class="p">.</span></code></pre><p><code class="inline">File</code>, a string, is to point out a file. The contents of this file are included
│ │ │  as is, at the position of the directive.</p><p>Include files are typically used for record and macro definitions that are
│ │ │  shared by several modules. It is recommended to use the file name extension
│ │ │  <code class="inline">.hrl</code> for include files.</p><p><code class="inline">File</code> can start with a path component <code class="inline">$VAR</code>, for some string <code class="inline">VAR</code>. If that is
│ │ │  the case, the value of the environment variable <code class="inline">VAR</code> as returned by
│ │ │  <code class="inline">os:getenv(VAR)</code> is substituted for <code class="inline">$VAR</code>. If <code class="inline">os:getenv(VAR)</code> returns <code class="inline">false</code>,
│ │ │  <code class="inline">$VAR</code> is left as is.</p><p>If the filename <code class="inline">File</code> is absolute (possibly after variable substitution), the
│ │ │  include file with that name is included. Otherwise, the specified file is
│ │ │  searched for in the following directories, and in this order:</p><ol><li>The current working directory</li><li>The directory where the module is being compiled</li><li>The directories given by the <code class="inline">include</code> option</li></ol><p>For details, see <a href="../../erts-15.2.7/doc/html/erlc_cmd.html">erlc</a> in ERTS and
│ │ │ -<a href="../../lib/compiler-8.6.1/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3966869121-1">(</span><span class="s">&quot;my_records.hrl&quot;</span><span class="p" data-group-id="3966869121-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3966869121-2">(</span><span class="s">&quot;incdir/my_records.hrl&quot;</span><span class="p" data-group-id="3966869121-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3966869121-3">(</span><span class="s">&quot;/home/user/proj/my_records.hrl&quot;</span><span class="p" data-group-id="3966869121-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3966869121-4">(</span><span class="s">&quot;$PROJ_ROOT/my_records.hrl&quot;</span><span class="p" data-group-id="3966869121-4">)</span><span class="p">.</span></code></pre><p><code class="inline">include_lib</code> is similar to <code class="inline">include</code>, but is not to point out an absolute file.
│ │ │ +<a href="../../lib/compiler-8.6.1/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1465556447-1">(</span><span class="s">&quot;my_records.hrl&quot;</span><span class="p" data-group-id="1465556447-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1465556447-2">(</span><span class="s">&quot;incdir/my_records.hrl&quot;</span><span class="p" data-group-id="1465556447-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1465556447-3">(</span><span class="s">&quot;/home/user/proj/my_records.hrl&quot;</span><span class="p" data-group-id="1465556447-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1465556447-4">(</span><span class="s">&quot;$PROJ_ROOT/my_records.hrl&quot;</span><span class="p" data-group-id="1465556447-4">)</span><span class="p">.</span></code></pre><p><code class="inline">include_lib</code> is similar to <code class="inline">include</code>, but is not to point out an absolute file.
│ │ │  Instead, the first path component (possibly after variable substitution) is
│ │ │ -assumed to be the name of an application.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="4517203406-1">(</span><span class="s">&quot;kernel/include/file.hrl&quot;</span><span class="p" data-group-id="4517203406-1">)</span><span class="p">.</span></code></pre><p>The code server uses <code class="inline">code:lib_dir(kernel)</code> to find the directory of the current
│ │ │ +assumed to be the name of an application.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="2179923252-1">(</span><span class="s">&quot;kernel/include/file.hrl&quot;</span><span class="p" data-group-id="2179923252-1">)</span><span class="p">.</span></code></pre><p>The code server uses <code class="inline">code:lib_dir(kernel)</code> to find the directory of the current
│ │ │  (latest) version of Kernel, and then the subdirectory <code class="inline">include</code> is searched for
│ │ │  the file <code class="inline">file.hrl</code>.</p><h2 id="defining-and-using-macros" class="section-heading">
│ │ │    <a href="#defining-and-using-macros" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Defining and Using Macros</span>
│ │ │  </h2>
│ │ │ -<p>A macro is defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4837384218-1">(</span><span class="n">Const</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="4837384218-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4837384218-2">(</span><span class="n">Func</span><span class="p" data-group-id="4837384218-3">(</span><span class="n">Var1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">VarN</span><span class="p" data-group-id="4837384218-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="4837384218-2">)</span><span class="p">.</span></code></pre><p>A macro definition can be placed anywhere among the attributes and function
│ │ │ +<p>A macro is defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0710275564-1">(</span><span class="n">Const</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="0710275564-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0710275564-2">(</span><span class="n">Func</span><span class="p" data-group-id="0710275564-3">(</span><span class="n">Var1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">VarN</span><span class="p" data-group-id="0710275564-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="0710275564-2">)</span><span class="p">.</span></code></pre><p>A macro definition can be placed anywhere among the attributes and function
│ │ │  declarations of a module, but the definition must come before any usage of the
│ │ │  macro.</p><p>If a macro is used in several modules, it is recommended that the macro
│ │ │  definition is placed in an include file.</p><p>A macro is used as follows:</p><pre><code class="text">?Const
│ │ │  ?Func(Arg1,...,ArgN)</code></pre><p>Macros are expanded during compilation. A simple macro <code class="inline">?Const</code> is replaced with
│ │ │ -<code class="inline">Replacement</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4913582831-1">(</span><span class="n">TIMEOUT</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="4913582831-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">Replacement</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6666807558-1">(</span><span class="n">TIMEOUT</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="6666807558-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">call</span><span class="p" data-group-id="4913582831-2">(</span><span class="n">Request</span><span class="p" data-group-id="4913582831-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4913582831-3">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">TIMEOUT</span><span class="p" data-group-id="4913582831-3">)</span><span class="p">.</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">call</span><span class="p" data-group-id="4782990333-1">(</span><span class="n">Request</span><span class="p" data-group-id="4782990333-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4782990333-2">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="4782990333-2">)</span><span class="p">.</span></code></pre><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> is replaced with <code class="inline">Replacement</code>, where all
│ │ │ +</span><span class="nf">call</span><span class="p" data-group-id="6666807558-2">(</span><span class="n">Request</span><span class="p" data-group-id="6666807558-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="6666807558-3">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">TIMEOUT</span><span class="p" data-group-id="6666807558-3">)</span><span class="p">.</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">call</span><span class="p" data-group-id="3507640135-1">(</span><span class="n">Request</span><span class="p" data-group-id="3507640135-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="3507640135-2">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="3507640135-2">)</span><span class="p">.</span></code></pre><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> is replaced with <code class="inline">Replacement</code>, where all
│ │ │  occurrences of a variable <code class="inline">Var</code> from the macro definition are replaced with the
│ │ │ -corresponding argument <code class="inline">Arg</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3422746585-1">(</span><span class="n">MACRO1</span><span class="p" data-group-id="3422746585-2">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3422746585-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3422746585-3">{</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3422746585-3">}</span><span class="p" data-group-id="3422746585-1">)</span><span class="p">.</span><span class="w">
│ │ │ +corresponding argument <code class="inline">Arg</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1104013566-1">(</span><span class="n">MACRO1</span><span class="p" data-group-id="1104013566-2">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1104013566-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1104013566-3">{</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1104013566-3">}</span><span class="p" data-group-id="1104013566-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="3422746585-4">(</span><span class="n">X</span><span class="p" data-group-id="3422746585-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="3422746585-5">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3422746585-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="3422746585-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="p" data-group-id="3422746585-6">)</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="6390557503-1">(</span><span class="n">X</span><span class="p" data-group-id="6390557503-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6390557503-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6390557503-2">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6390557503-3">{</span><span class="ss">a</span><span class="p">,</span><span class="n">X</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">123</span><span class="p" data-group-id="6390557503-3">}</span><span class="p">.</span></code></pre><p>It is good programming practice, but not mandatory, to ensure that a macro
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="1104013566-4">(</span><span class="n">X</span><span class="p" data-group-id="1104013566-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="1104013566-5">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1104013566-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="1104013566-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="p" data-group-id="1104013566-6">)</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="0801513183-1">(</span><span class="n">X</span><span class="p" data-group-id="0801513183-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0801513183-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="0801513183-2">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0801513183-3">{</span><span class="ss">a</span><span class="p">,</span><span class="n">X</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">123</span><span class="p" data-group-id="0801513183-3">}</span><span class="p">.</span></code></pre><p>It is good programming practice, but not mandatory, to ensure that a macro
│ │ │  definition is a valid Erlang syntactic form.</p><p>To view the result of macro expansion, a module can be compiled with the <code class="inline">'P'</code>
│ │ │  option. <code class="inline">compile:file(File, ['P'])</code>. This produces a listing of the parsed code
│ │ │  after preprocessing and parse transforms, in the file <code class="inline">File.P</code>.</p><h2 id="predefined-macros" class="section-heading">
│ │ │    <a href="#predefined-macros" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Predefined Macros</span>
│ │ │ @@ -185,29 +185,29 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Macros Overloading</span>
│ │ │  </h2>
│ │ │  <p>It is possible to overload macros, except for predefined macros. An overloaded
│ │ │  macro has more than one definition, each with a different number of arguments.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Support for overloading of macros was added in Erlang 5.7.5/OTP R13B04.</p></section><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> with a (possibly empty) list of arguments results
│ │ │  in an error message if there is at least one definition of <code class="inline">Func</code> with
│ │ │ -arguments, but none with N arguments.</p><p>Assuming these definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0857184882-1">(</span><span class="n">F0</span><span class="p" data-group-id="0857184882-2">(</span><span class="p" data-group-id="0857184882-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="0857184882-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0857184882-3">(</span><span class="n">F1</span><span class="p" data-group-id="0857184882-4">(</span><span class="n">A</span><span class="p" data-group-id="0857184882-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="0857184882-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0857184882-5">(</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="nc">m</span><span class="p">:</span><span class="ss">f</span><span class="p" data-group-id="0857184882-5">)</span><span class="p">.</span></code></pre><p>the following does not work:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f0</span><span class="p" data-group-id="3872925962-1">(</span><span class="p" data-group-id="3872925962-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +arguments, but none with N arguments.</p><p>Assuming these definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4468119768-1">(</span><span class="n">F0</span><span class="p" data-group-id="4468119768-2">(</span><span class="p" data-group-id="4468119768-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="4468119768-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4468119768-3">(</span><span class="n">F1</span><span class="p" data-group-id="4468119768-4">(</span><span class="n">A</span><span class="p" data-group-id="4468119768-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="4468119768-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4468119768-5">(</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="nc">m</span><span class="p">:</span><span class="ss">f</span><span class="p" data-group-id="4468119768-5">)</span><span class="p">.</span></code></pre><p>the following does not work:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f0</span><span class="p" data-group-id="6998503838-1">(</span><span class="p" data-group-id="6998503838-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="o">?</span><span class="n">F0</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, an empty list of arguments expected.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">f1</span><span class="p" data-group-id="3872925962-2">(</span><span class="n">A</span><span class="p" data-group-id="3872925962-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">F1</span><span class="p" data-group-id="3872925962-3">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="3872925962-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, exactly one argument expected.</span></code></pre><p>On the other hand,</p><pre><code class="text">f() -&gt;
│ │ │ -    ?C().</code></pre><p>is expanded to</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4149589923-1">(</span><span class="p" data-group-id="4149589923-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">m</span><span class="p">:</span><span class="nf">f</span><span class="p" data-group-id="4149589923-2">(</span><span class="p" data-group-id="4149589923-2">)</span><span class="p">.</span></code></pre><h2 id="removing-a-macro-definition" class="section-heading">
│ │ │ +</span><span class="nf">f1</span><span class="p" data-group-id="6998503838-2">(</span><span class="n">A</span><span class="p" data-group-id="6998503838-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">F1</span><span class="p" data-group-id="6998503838-3">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="6998503838-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, exactly one argument expected.</span></code></pre><p>On the other hand,</p><pre><code class="text">f() -&gt;
│ │ │ +    ?C().</code></pre><p>is expanded to</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="3025455697-1">(</span><span class="p" data-group-id="3025455697-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">m</span><span class="p">:</span><span class="nf">f</span><span class="p" data-group-id="3025455697-2">(</span><span class="p" data-group-id="3025455697-2">)</span><span class="p">.</span></code></pre><h2 id="removing-a-macro-definition" class="section-heading">
│ │ │    <a href="#removing-a-macro-definition" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Removing a macro definition</span>
│ │ │  </h2>
│ │ │ -<p>A definition of macro can be removed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">undef</span><span class="p" data-group-id="3382517910-1">(</span><span class="n">Macro</span><span class="p" data-group-id="3382517910-1">)</span><span class="p">.</span></code></pre><h2 id="conditional-compilation" class="section-heading">
│ │ │ +<p>A definition of macro can be removed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">undef</span><span class="p" data-group-id="3172747453-1">(</span><span class="n">Macro</span><span class="p" data-group-id="3172747453-1">)</span><span class="p">.</span></code></pre><h2 id="conditional-compilation" class="section-heading">
│ │ │    <a href="#conditional-compilation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Conditional Compilation</span>
│ │ │  </h2>
│ │ │  <p>The following macro directives support conditional compilation:</p><ul><li><p><strong><code class="inline">-ifdef(Macro).</code></strong> - Evaluate the following lines only if <code class="inline">Macro</code> is
│ │ │  defined.</p></li><li><p><strong><code class="inline">-ifndef(Macro).</code></strong> - Evaluate the following lines only if <code class="inline">Macro</code> is not
│ │ │ @@ -219,43 +219,43 @@
│ │ │  true, and the <code class="inline">Condition</code> evaluates to true, the lines following the <code class="inline">elif</code>
│ │ │  are evaluated instead.</p></li><li><p><strong><code class="inline">-endif.</code></strong> - Specifies the end of a series of control flow directives.</p></li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Macro directives cannot be used inside functions.</p></section><p>Syntactically, the <code class="inline">Condition</code> in <code class="inline">if</code> and <code class="inline">elif</code> must be a
│ │ │  <a href="expressions.html#guard-expressions">guard expression</a>. Other constructs (such as
│ │ │  a <code class="inline">case</code> expression) result in a compilation error.</p><p>As opposed to the standard guard expressions, an expression in an <code class="inline">if</code> and
│ │ │  <code class="inline">elif</code> also supports calling the psuedo-function <code class="inline">defined(Name)</code>, which tests
│ │ │  whether the <code class="inline">Name</code> argument is the name of a previously defined macro.
│ │ │  <code class="inline">defined(Name)</code> evaluates to <code class="inline">true</code> if the macro is defined and <code class="inline">false</code>
│ │ │ -otherwise. An attempt to call other functions results in a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0437608748-1">(</span><span class="ss">m</span><span class="p" data-group-id="0437608748-1">)</span><span class="p">.</span><span class="w">
│ │ │ +otherwise. An attempt to call other functions results in a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9621970512-1">(</span><span class="ss">m</span><span class="p" data-group-id="9621970512-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="0437608748-2">(</span><span class="ss">debug</span><span class="p" data-group-id="0437608748-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0437608748-3">(</span><span class="n">LOG</span><span class="p" data-group-id="0437608748-4">(</span><span class="n">X</span><span class="p" data-group-id="0437608748-4">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0437608748-5">(</span><span class="s">&quot;{</span><span class="si">~p</span><span class="s">,</span><span class="si">~p</span><span class="s">}: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0437608748-6">[</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="o">?</span><span class="n">LINE</span><span class="p">,</span><span class="n">X</span><span class="p" data-group-id="0437608748-6">]</span><span class="p" data-group-id="0437608748-5">)</span><span class="p" data-group-id="0437608748-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="9621970512-2">(</span><span class="ss">debug</span><span class="p" data-group-id="9621970512-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9621970512-3">(</span><span class="n">LOG</span><span class="p" data-group-id="9621970512-4">(</span><span class="n">X</span><span class="p" data-group-id="9621970512-4">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9621970512-5">(</span><span class="s">&quot;{</span><span class="si">~p</span><span class="s">,</span><span class="si">~p</span><span class="s">}: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9621970512-6">[</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="o">?</span><span class="n">LINE</span><span class="p">,</span><span class="n">X</span><span class="p" data-group-id="9621970512-6">]</span><span class="p" data-group-id="9621970512-5">)</span><span class="p" data-group-id="9621970512-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0437608748-7">(</span><span class="n">LOG</span><span class="p" data-group-id="0437608748-8">(</span><span class="n">X</span><span class="p" data-group-id="0437608748-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0437608748-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9621970512-7">(</span><span class="n">LOG</span><span class="p" data-group-id="9621970512-8">(</span><span class="n">X</span><span class="p" data-group-id="9621970512-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9621970512-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>When trace output is desired, <code class="inline">debug</code> is to be defined when the module <code class="inline">m</code> is
│ │ │  compiled:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erlc -Ddebug m.erl</span><span class="w">
│ │ │  
│ │ │  </span><span class="ow">or</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="4890265901-1">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4890265901-2">{</span><span class="ss">d</span><span class="p">,</span><span class="w"> </span><span class="ss">debug</span><span class="p" data-group-id="4890265901-2">}</span><span class="p" data-group-id="4890265901-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4890265901-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">m</span><span class="p" data-group-id="4890265901-3">}</span></code></pre><p><code class="inline">?LOG(Arg)</code> is then expanded to a call to <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> and provide the user
│ │ │ -with some simple trace output.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0425391517-1">(</span><span class="ss">m</span><span class="p" data-group-id="0425391517-1">)</span><span class="w">
│ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="9580787501-1">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9580787501-2">{</span><span class="ss">d</span><span class="p">,</span><span class="w"> </span><span class="ss">debug</span><span class="p" data-group-id="9580787501-2">}</span><span class="p" data-group-id="9580787501-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9580787501-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">m</span><span class="p" data-group-id="9580787501-3">}</span></code></pre><p><code class="inline">?LOG(Arg)</code> is then expanded to a call to <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> and provide the user
│ │ │ +with some simple trace output.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3744270756-1">(</span><span class="ss">m</span><span class="p" data-group-id="3744270756-1">)</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="0425391517-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">25</span><span class="p" data-group-id="0425391517-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="3744270756-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">25</span><span class="p" data-group-id="3744270756-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Code that will work in OTP 25 or higher</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">elif</span><span class="p" data-group-id="0425391517-3">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="p" data-group-id="0425391517-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">elif</span><span class="p" data-group-id="3744270756-3">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="p" data-group-id="3744270756-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Code that will work in OTP 26 or higher</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Code that will work in OTP 24 or lower.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This code uses the <code class="inline">OTP_RELEASE</code> macro to conditionally select code depending on
│ │ │ -release.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2160298234-1">(</span><span class="ss">m</span><span class="p" data-group-id="2160298234-1">)</span><span class="w">
│ │ │ +release.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3634165815-1">(</span><span class="ss">m</span><span class="p" data-group-id="3634165815-1">)</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="2160298234-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">defined</span><span class="p" data-group-id="2160298234-3">(</span><span class="ss">debug</span><span class="p" data-group-id="2160298234-3">)</span><span class="p" data-group-id="2160298234-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="3634165815-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">defined</span><span class="p" data-group-id="3634165815-3">(</span><span class="ss">debug</span><span class="p" data-group-id="3634165815-3">)</span><span class="p" data-group-id="3634165815-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Debugging code that requires OTP 26 or later.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Non-debug code that works in any release.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This code uses the <code class="inline">OTP_RELEASE</code> macro and <code class="inline">defined(debug)</code> to compile debug
│ │ │  code only for OTP 26 or later.</p><h2 id="the-feature-directive" class="section-heading">
│ │ │    <a href="#the-feature-directive" class="hover-link">
│ │ │ @@ -270,44 +270,44 @@
│ │ │  used. In practice this means it should appear before any <code class="inline">-export(..)</code> or record
│ │ │  definitions.</p><h2 id="error-and-warning-directives" class="section-heading">
│ │ │    <a href="#error-and-warning-directives" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">-error() and -warning() directives</span>
│ │ │  </h2>
│ │ │ -<p>The directive <code class="inline">-error(Term)</code> causes a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9938261184-1">(</span><span class="ss">t</span><span class="p" data-group-id="9938261184-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9938261184-2">(</span><span class="p" data-group-id="9938261184-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9938261184-3">]</span><span class="p" data-group-id="9938261184-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>The directive <code class="inline">-error(Term)</code> causes a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2677102800-1">(</span><span class="ss">t</span><span class="p" data-group-id="2677102800-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2677102800-2">(</span><span class="p" data-group-id="2677102800-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2677102800-3">]</span><span class="p" data-group-id="2677102800-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="9938261184-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="9938261184-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="9938261184-5">(</span><span class="p" data-group-id="9938261184-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="2677102800-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="2677102800-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="2677102800-5">(</span><span class="p" data-group-id="2677102800-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">error</span><span class="p" data-group-id="9938261184-6">(</span><span class="s">&quot;Macro VERSION must be defined.&quot;</span><span class="p" data-group-id="9938261184-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="9938261184-7">(</span><span class="p" data-group-id="9938261184-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">error</span><span class="p" data-group-id="2677102800-6">(</span><span class="s">&quot;Macro VERSION must be defined.&quot;</span><span class="p" data-group-id="2677102800-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="2677102800-7">(</span><span class="p" data-group-id="2677102800-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span></code></pre><p>The error message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │ -t.erl:7: -error(&quot;Macro VERSION must be defined.&quot;).</code></pre><p>The directive <code class="inline">-warning(Term)</code> causes a compilation warning.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0368672004-1">(</span><span class="ss">t</span><span class="p" data-group-id="0368672004-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0368672004-2">(</span><span class="p" data-group-id="0368672004-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0368672004-3">]</span><span class="p" data-group-id="0368672004-2">)</span><span class="p">.</span><span class="w">
│ │ │ +t.erl:7: -error(&quot;Macro VERSION must be defined.&quot;).</code></pre><p>The directive <code class="inline">-warning(Term)</code> causes a compilation warning.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2223492777-1">(</span><span class="ss">t</span><span class="p" data-group-id="2223492777-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2223492777-2">(</span><span class="p" data-group-id="2223492777-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2223492777-3">]</span><span class="p" data-group-id="2223492777-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">ifndef</span><span class="p" data-group-id="0368672004-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="0368672004-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">warning</span><span class="p" data-group-id="0368672004-5">(</span><span class="s">&quot;Macro VERSION not defined -- using default version.&quot;</span><span class="p" data-group-id="0368672004-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0368672004-6">(</span><span class="n">VERSION</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;0&quot;</span><span class="p" data-group-id="0368672004-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">ifndef</span><span class="p" data-group-id="2223492777-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="2223492777-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">warning</span><span class="p" data-group-id="2223492777-5">(</span><span class="s">&quot;Macro VERSION not defined -- using default version.&quot;</span><span class="p" data-group-id="2223492777-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2223492777-6">(</span><span class="n">VERSION</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;0&quot;</span><span class="p" data-group-id="2223492777-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="0368672004-7">(</span><span class="p" data-group-id="0368672004-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span></code></pre><p>The warning message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="2223492777-7">(</span><span class="p" data-group-id="2223492777-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span></code></pre><p>The warning message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │  t.erl:5: Warning: -warning(&quot;Macro VERSION not defined -- using default version.&quot;).</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>The <code class="inline">-error()</code> and <code class="inline">-warning()</code> directives were added in Erlang/OTP 19.</p></section><h2 id="stringifying-macro-arguments" class="section-heading">
│ │ │    <a href="#stringifying-macro-arguments" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Stringifying Macro Arguments</span>
│ │ │  </h2>
│ │ │  <p>The construction <code class="inline">??Arg</code>, where <code class="inline">Arg</code> is a macro argument, is expanded to a
│ │ │  string containing the tokens of the argument. This is similar to the <code class="inline">#arg</code>
│ │ │ -stringifying construction in C.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3161288349-1">(</span><span class="n">TESTCALL</span><span class="p" data-group-id="3161288349-2">(</span><span class="n">Call</span><span class="p" data-group-id="3161288349-2">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3161288349-3">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3161288349-4">[</span><span class="o">?</span><span class="o">?</span><span class="n">Call</span><span class="p">,</span><span class="w"> </span><span class="n">Call</span><span class="p" data-group-id="3161288349-4">]</span><span class="p" data-group-id="3161288349-3">)</span><span class="p" data-group-id="3161288349-1">)</span><span class="p">.</span><span class="w">
│ │ │ +stringifying construction in C.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5606291110-1">(</span><span class="n">TESTCALL</span><span class="p" data-group-id="5606291110-2">(</span><span class="n">Call</span><span class="p" data-group-id="5606291110-2">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5606291110-3">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5606291110-4">[</span><span class="o">?</span><span class="o">?</span><span class="n">Call</span><span class="p">,</span><span class="w"> </span><span class="n">Call</span><span class="p" data-group-id="5606291110-4">]</span><span class="p" data-group-id="5606291110-3">)</span><span class="p" data-group-id="5606291110-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="3161288349-5">(</span><span class="nf">myfunction</span><span class="p" data-group-id="3161288349-6">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3161288349-6">)</span><span class="p" data-group-id="3161288349-5">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="3161288349-7">(</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="3161288349-8">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3161288349-8">)</span><span class="p" data-group-id="3161288349-7">)</span><span class="p">.</span></code></pre><p>results in</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7573581348-1">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="7573581348-2">[</span><span class="s">&quot;myfunction ( 1 , 2 )&quot;</span><span class="p">,</span><span class="nf">myfunction</span><span class="p" data-group-id="7573581348-3">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7573581348-3">)</span><span class="p" data-group-id="7573581348-2">]</span><span class="p" data-group-id="7573581348-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7573581348-4">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="7573581348-5">[</span><span class="s">&quot;you : function ( 2 , 1 )&quot;</span><span class="p">,</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="7573581348-6">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7573581348-6">)</span><span class="p" data-group-id="7573581348-5">]</span><span class="p" data-group-id="7573581348-4">)</span><span class="p">.</span></code></pre><p>That is, a trace output, with both the function called and the resulting value.</p>
│ │ │ +</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="5606291110-5">(</span><span class="nf">myfunction</span><span class="p" data-group-id="5606291110-6">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5606291110-6">)</span><span class="p" data-group-id="5606291110-5">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="5606291110-7">(</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="5606291110-8">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5606291110-8">)</span><span class="p" data-group-id="5606291110-7">)</span><span class="p">.</span></code></pre><p>results in</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2536910905-1">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="2536910905-2">[</span><span class="s">&quot;myfunction ( 1 , 2 )&quot;</span><span class="p">,</span><span class="nf">myfunction</span><span class="p" data-group-id="2536910905-3">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2536910905-3">)</span><span class="p" data-group-id="2536910905-2">]</span><span class="p" data-group-id="2536910905-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2536910905-4">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="2536910905-5">[</span><span class="s">&quot;you : function ( 2 , 1 )&quot;</span><span class="p">,</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="2536910905-6">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2536910905-6">)</span><span class="p" data-group-id="2536910905-5">]</span><span class="p" data-group-id="2536910905-4">)</span><span class="p">.</span></code></pre><p>That is, a trace output, with both the function called and the resulting value.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="expressions.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/maps.html
│ │ │ @@ -148,16 +148,16 @@
│ │ │  single function that constructs the map using the map syntax and always use
│ │ │  it.</p></li><li><p>Always update the map using the <code class="inline">:=</code> operator (that is, requiring that an
│ │ │  element with that key already exists). The <code class="inline">:=</code> operator is slightly more
│ │ │  efficient, and it helps catching mispellings of keys.</p></li><li><p>Whenever possible, match multiple map elements at once.</p></li><li><p>Whenever possible, update multiple map elements at once.</p></li><li><p>Avoid default values and the <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> function. If there are default
│ │ │  values, sharing of keys between different instances of the map will be less
│ │ │  effective, and it is not possible to match multiple elements having default
│ │ │  values in one go.</p></li><li><p>To avoid having to deal with a map that may lack some keys, <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html#merge/2"><code class="inline">maps:merge/2</code></a> can
│ │ │ -efficiently add multiple default values. For example:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6734429998-1">#{</span><span class="ss">shoe_size</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="ss">editor</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">emacs</span><span class="p" data-group-id="6734429998-1">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="6734429998-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="6734429998-2">)</span></code></pre></li></ul><h2 id="using-maps-as-dictionaries" class="section-heading">
│ │ │ +efficiently add multiple default values. For example:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0275222741-1">#{</span><span class="ss">shoe_size</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="ss">editor</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">emacs</span><span class="p" data-group-id="0275222741-1">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="0275222741-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="0275222741-2">)</span></code></pre></li></ul><h2 id="using-maps-as-dictionaries" class="section-heading">
│ │ │    <a href="#using-maps-as-dictionaries" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Using Maps as Dictionaries</span>
│ │ │  </h2>
│ │ │  <p>Using a map as a dictionary implies the following usage pattern:</p><ul><li>Keys are usually variables not known at compile-time.</li><li>There can be any number of elements in the map.</li><li>Usually, no more than one element is looked up or updated at once.</li></ul><p>Given that usage pattern, the difference in performance between using the map
│ │ │  syntax and the maps module is usually small. Therefore, which one to use is
│ │ │ @@ -167,18 +167,18 @@
│ │ │  choice.</li></ul><h2 id="using-maps-as-sets" class="section-heading">
│ │ │    <a href="#using-maps-as-sets" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Using Maps as Sets</span>
│ │ │  </h2>
│ │ │  <p>Starting in OTP 24, the <a href="../../lib/stdlib-6.2.2.1/doc/html/sets.html"><code class="inline">sets</code></a> module has an option to represent sets as maps.
│ │ │ -Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="7679444452-1">(</span><span class="p" data-group-id="7679444452-2">[</span><span class="p" data-group-id="7679444452-3">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7679444452-3">}</span><span class="p" data-group-id="7679444452-2">]</span><span class="p" data-group-id="7679444452-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7679444452-4">#{</span><span class="p" data-group-id="7679444452-4">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">from_list</span><span class="p" data-group-id="7679444452-5">(</span><span class="p" data-group-id="7679444452-6">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="7679444452-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7679444452-7">[</span><span class="p" data-group-id="7679444452-8">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7679444452-8">}</span><span class="p" data-group-id="7679444452-7">]</span><span class="p" data-group-id="7679444452-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7679444452-9">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7679444452-10">[</span><span class="p" data-group-id="7679444452-10">]</span><span class="p">,</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7679444452-11">[</span><span class="p" data-group-id="7679444452-11">]</span><span class="p">,</span><span class="ss">z</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7679444452-12">[</span><span class="p" data-group-id="7679444452-12">]</span><span class="p" data-group-id="7679444452-9">}</span></code></pre><p><code class="inline">sets</code> backed by maps is generally the most efficient set representation, with a
│ │ │ +Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="3970039750-1">(</span><span class="p" data-group-id="3970039750-2">[</span><span class="p" data-group-id="3970039750-3">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3970039750-3">}</span><span class="p" data-group-id="3970039750-2">]</span><span class="p" data-group-id="3970039750-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3970039750-4">#{</span><span class="p" data-group-id="3970039750-4">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">from_list</span><span class="p" data-group-id="3970039750-5">(</span><span class="p" data-group-id="3970039750-6">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="3970039750-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3970039750-7">[</span><span class="p" data-group-id="3970039750-8">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3970039750-8">}</span><span class="p" data-group-id="3970039750-7">]</span><span class="p" data-group-id="3970039750-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3970039750-9">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3970039750-10">[</span><span class="p" data-group-id="3970039750-10">]</span><span class="p">,</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3970039750-11">[</span><span class="p" data-group-id="3970039750-11">]</span><span class="p">,</span><span class="ss">z</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3970039750-12">[</span><span class="p" data-group-id="3970039750-12">]</span><span class="p" data-group-id="3970039750-9">}</span></code></pre><p><code class="inline">sets</code> backed by maps is generally the most efficient set representation, with a
│ │ │  few possible exceptions:</p><ul><li><a href="../../lib/stdlib-6.2.2.1/doc/html/ordsets.html#intersection/2"><code class="inline">ordsets:intersection/2</code></a> can be more efficient than <a href="../../lib/stdlib-6.2.2.1/doc/html/sets.html#intersection/2"><code class="inline">sets:intersection/2</code></a>. If
│ │ │  the intersection operation is frequently used and operations that operate on a
│ │ │  single element in a set (such as <code class="inline">is_element/2</code>) are avoided, <a href="../../lib/stdlib-6.2.2.1/doc/html/ordsets.html"><code class="inline">ordsets</code></a> can
│ │ │  be a better choice than <a href="../../lib/stdlib-6.2.2.1/doc/html/sets.html"><code class="inline">sets</code></a>.</li><li>If the intersection operation is frequently used and operations that operate
│ │ │  on a single element in a set (such as <code class="inline">is_element/2</code>) must also be efficient,
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/gb_sets.html"><code class="inline">gb_sets</code></a> can potentially be a better choice than <a href="../../lib/stdlib-6.2.2.1/doc/html/sets.html"><code class="inline">sets</code></a>.</li><li>If the elements of the set are integers in a fairly compact range, the set can
│ │ │  be represented as an integer where each bit represents an element in the set.
│ │ │ @@ -203,18 +203,18 @@
│ │ │  for the runtime system).</p></li><li><p><strong>N</strong> - The number of elements in the map.</p></li><li><p><strong>Keys</strong> - A tuple with keys of the map: <code class="inline">{Key1,...,KeyN}</code>. The keys are
│ │ │  sorted.</p></li><li><p><strong>Value1</strong> - The value corresponding to the first key in the key tuple.</p></li><li><p><strong>ValueN</strong> - The value corresponding to the last key in the key tuple.</p></li></ul><p>As an example, let us look at how the map <code class="inline">#{a =&gt; foo, z =&gt; bar}</code> is
│ │ │  represented:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: left;">4</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>2</em></td><td style="text-align: center;"><code class="inline">{a,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: left;"><code class="inline">bar</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, z =&gt; bar}</em></p><p>Let us update the map: <code class="inline">M#{q =&gt; baz}</code>. The map now looks like this:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: center;">4</th><th style="text-align: center;">5</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>3</em></td><td style="text-align: center;"><code class="inline">{a,q,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: center;"><code class="inline">baz</code></td><td style="text-align: center;"><code class="inline">bar</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, q =&gt; baz, z =&gt; bar}</em></p><p>Finally, change the value of one element: <code class="inline">M#{z := bird}</code>. The map now looks
│ │ │  like this:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: center;">4</th><th style="text-align: center;">5</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>3</em></td><td style="text-align: center;"><code class="inline">{a,q,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: center;"><code class="inline">baz</code></td><td style="text-align: center;"><code class="inline">bird</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, q =&gt; baz, z =&gt; bird}</em></p><p>When the value for an existing key is updated, the key tuple is not updated,
│ │ │  allowing the key tuple to be shared with other instances of the map that have
│ │ │  the same keys. In fact, the key tuple can be shared between all maps with the
│ │ │  same keys with some care. To arrange that, define a function that returns a map.
│ │ │ -For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="0885195576-1">(</span><span class="p" data-group-id="0885195576-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0885195576-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p" data-group-id="0885195576-2">}</span><span class="p">.</span></code></pre><p>Defined like this, the key tuple <code class="inline">{a,b,c}</code> will be a global literal. To ensure
│ │ │ +For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="7464792883-1">(</span><span class="p" data-group-id="7464792883-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7464792883-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p" data-group-id="7464792883-2">}</span><span class="p">.</span></code></pre><p>Defined like this, the key tuple <code class="inline">{a,b,c}</code> will be a global literal. To ensure
│ │ │  that the key tuple is shared when creating an instance of the map, always call
│ │ │ -<code class="inline">new()</code> and modify the returned map:</p><pre><code class="makeup erlang" translate="no"><span class="w">    </span><span class="p" data-group-id="2033254412-1">(</span><span class="n">SOME_MODULE</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="2033254412-2">(</span><span class="p" data-group-id="2033254412-2">)</span><span class="p" data-group-id="2033254412-1">)</span><span class="p" data-group-id="2033254412-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="2033254412-3">}</span><span class="p">.</span></code></pre><p>Using the map syntax with small maps is particularly efficient. As long as the
│ │ │ +<code class="inline">new()</code> and modify the returned map:</p><pre><code class="makeup erlang" translate="no"><span class="w">    </span><span class="p" data-group-id="8062318237-1">(</span><span class="n">SOME_MODULE</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="8062318237-2">(</span><span class="p" data-group-id="8062318237-2">)</span><span class="p" data-group-id="8062318237-1">)</span><span class="p" data-group-id="8062318237-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="8062318237-3">}</span><span class="p">.</span></code></pre><p>Using the map syntax with small maps is particularly efficient. As long as the
│ │ │  keys are known at compile-time, the map is updated in one go, making the time to
│ │ │  update a map essentially constant regardless of the number of keys updated. The
│ │ │  same goes for matching. (When the keys are variables, one or more of the keys
│ │ │  could be identical, so the operations need to be performed sequentially from
│ │ │  left to right.)</p><p>The memory size for a small map is the size of all keys and values plus 5 words.
│ │ │  See <a href="memory.html">Memory</a> for more information about memory sizes.</p><h3 id="how-large-maps-are-implemented" class="section-heading">
│ │ │    <a href="#how-large-maps-are-implemented" class="hover-link">
│ │ │ @@ -241,21 +241,21 @@
│ │ │    <a href="#using-the-map-syntax" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Using the Map Syntax</span>
│ │ │  </h2>
│ │ │  <p>Using the map syntax is usually slightly more efficient than using the
│ │ │  corresponding function in the <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html"><code class="inline">maps</code></a> module.</p><p>The gain in efficiency for the map syntax is more noticeable for the following
│ │ │ -operations that can only be achieved using the map syntax:</p><ul><li>Matching multiple literal keys</li><li>Updating multiple literal keys</li><li>Adding multiple literal keys to a map</li></ul><p>For example:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="1533432110-1">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="ss">z</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="1533432110-1">}</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="5611029904-1">(</span><span class="ss">x</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="5611029904-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="5611029904-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="5611029904-2">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="5611029904-3">(</span><span class="ss">z</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p">,</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="5611029904-3">)</span></code></pre><p>If the map is a small map, the first example runs roughly three times as fast.</p><p>Note that for variable keys, the elements are updated sequentially from left to
│ │ │ -right. For example, given the following update with variable keys:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="8193333596-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="8193333596-1">}</span></code></pre><p>the compiler rewrites it like this to ensure that the updates are applied from
│ │ │ -left to right:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="1912827912-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1912827912-1">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="1912827912-2">#{</span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1912827912-2">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="1912827912-3">#{</span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="1912827912-3">}</span></code></pre><p>If a key is known to exist in a map, using the <code class="inline">:=</code> operator is slightly more
│ │ │ +operations that can only be achieved using the map syntax:</p><ul><li>Matching multiple literal keys</li><li>Updating multiple literal keys</li><li>Adding multiple literal keys to a map</li></ul><p>For example:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="8762268495-1">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="ss">z</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="8762268495-1">}</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="8465540770-1">(</span><span class="ss">x</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="8465540770-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="8465540770-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="8465540770-2">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="8465540770-3">(</span><span class="ss">z</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p">,</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="8465540770-3">)</span></code></pre><p>If the map is a small map, the first example runs roughly three times as fast.</p><p>Note that for variable keys, the elements are updated sequentially from left to
│ │ │ +right. For example, given the following update with variable keys:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="1298823506-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="1298823506-1">}</span></code></pre><p>the compiler rewrites it like this to ensure that the updates are applied from
│ │ │ +left to right:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="4391193701-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4391193701-1">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="4391193701-2">#{</span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4391193701-2">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="4391193701-3">#{</span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="4391193701-3">}</span></code></pre><p>If a key is known to exist in a map, using the <code class="inline">:=</code> operator is slightly more
│ │ │  efficient than using the <code class="inline">=&gt;</code> operator for a small map.</p><h2 id="using-the-functions-in-the-maps-module" class="section-heading">
│ │ │    <a href="#using-the-functions-in-the-maps-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Using the Functions in the maps Module</span>
│ │ │  </h2>
│ │ │  <p>Here follows some notes about most of the functions in the <code class="inline">maps</code> module. For
│ │ │ @@ -306,23 +306,23 @@
│ │ │    <a href="#maps-get-3" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">maps:get/3</span>
│ │ │  </h3>
│ │ │  <p>As an optimization, the compiler will rewrite a call to <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> to Erlang
│ │ │  code similar to the following:</p><pre><code class="makeup erlang" translate="no"><span class="n">Result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">Map</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="7379169237-1">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="7379169237-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="p">;</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="7379169237-2">#{</span><span class="p" data-group-id="7379169237-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Default</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="7454902301-1">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="7454902301-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="p">;</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="7454902301-2">#{</span><span class="p" data-group-id="7454902301-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Default</span><span class="w">
│ │ │           </span><span class="k">end</span></code></pre><p>This is reasonably efficient, but if a small map is used as an alternative to
│ │ │  using a record it is often better not to rely on default values as it prevents
│ │ │  sharing of keys, which may in the end use more memory than what you save from
│ │ │  not storing default values in the map.</p><p>If default values are nevertheless required, instead of calling <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a>
│ │ │  multiple times, consider putting the default values in a map and merging that
│ │ │ -map with the other map:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7582773918-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">KeyN</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueN</span><span class="p" data-group-id="7582773918-1">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="7582773918-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="7582773918-2">)</span></code></pre><p>This helps share keys between the default map and the one you applied defaults
│ │ │ +map with the other map:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7706021243-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">KeyN</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueN</span><span class="p" data-group-id="7706021243-1">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="7706021243-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="7706021243-2">)</span></code></pre><p>This helps share keys between the default map and the one you applied defaults
│ │ │  to, as long as the default map contains <em>all</em> the keys that will ever be used
│ │ │  and not just the ones with default values. Whether this is faster than calling
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> multiple times depends on the size of the map and the number of
│ │ │  default values.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before OTP 26.0 <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> was implemented by calling the function instead
│ │ │  of rewriting it as an Erlang expression. It is now slightly faster but can no
│ │ │  longer be traced.</p></section><h3 id="maps-intersect-2-maps-intersect_with-3" class="section-heading">
│ │ │    <a href="#maps-intersect-2-maps-intersect_with-3" class="hover-link">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/modules.html
│ │ │ @@ -118,20 +118,20 @@
│ │ │  <h2 id="module-syntax" class="section-heading">
│ │ │    <a href="#module-syntax" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Module Syntax</span>
│ │ │  </h2>
│ │ │  <p>Erlang code is divided into <em>modules</em>. A module consists of a sequence of
│ │ │ -attributes and function declarations, each terminated by a period (<code class="inline">.</code>).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7671977198-1">(</span><span class="ss">m</span><span class="p" data-group-id="7671977198-1">)</span><span class="p">.</span><span class="w">          </span><span class="c1">% module attribute</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7671977198-2">(</span><span class="p" data-group-id="7671977198-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7671977198-3">]</span><span class="p" data-group-id="7671977198-2">)</span><span class="p">.</span><span class="w">   </span><span class="c1">% module attribute</span><span class="w">
│ │ │ +attributes and function declarations, each terminated by a period (<code class="inline">.</code>).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9222454716-1">(</span><span class="ss">m</span><span class="p" data-group-id="9222454716-1">)</span><span class="p">.</span><span class="w">          </span><span class="c1">% module attribute</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9222454716-2">(</span><span class="p" data-group-id="9222454716-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9222454716-3">]</span><span class="p" data-group-id="9222454716-2">)</span><span class="p">.</span><span class="w">   </span><span class="c1">% module attribute</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="7671977198-4">(</span><span class="n">N</span><span class="p" data-group-id="7671977198-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% beginning of function declaration</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="7671977198-5">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="7671977198-5">)</span><span class="p">;</span><span class="w">   </span><span class="c1">%  |</span><span class="w">
│ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="7671977198-6">(</span><span class="mi">0</span><span class="p" data-group-id="7671977198-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">           </span><span class="c1">%  |</span><span class="w">
│ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="9222454716-4">(</span><span class="n">N</span><span class="p" data-group-id="9222454716-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% beginning of function declaration</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="9222454716-5">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="9222454716-5">)</span><span class="p">;</span><span class="w">   </span><span class="c1">%  |</span><span class="w">
│ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="9222454716-6">(</span><span class="mi">0</span><span class="p" data-group-id="9222454716-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">           </span><span class="c1">%  |</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">.</span><span class="w">               </span><span class="c1">% end of function declaration</span></code></pre><p>For a description of function declarations, see
│ │ │  <a href="ref_man_functions.html">Function Declaration Syntax</a>.</p><h2 id="module-attributes" class="section-heading">
│ │ │    <a href="#module-attributes" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Module Attributes</span>
│ │ │  </h2>
│ │ │ @@ -176,71 +176,71 @@
│ │ │  meaning.</p></section></li></ul><h3 id="behaviour-module-attribute" class="section-heading">
│ │ │    <a href="#behaviour-module-attribute" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Behaviour Module Attribute</span>
│ │ │  </h3>
│ │ │  <p>It is possible to specify that the module is the callback module for a
│ │ │ -<em>behaviour</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="7303519863-1">(</span><span class="n">Behaviour</span><span class="p" data-group-id="7303519863-1">)</span><span class="p">.</span></code></pre><p>The atom <code class="inline">Behaviour</code> gives the name of the behaviour, which can be a
│ │ │ +<em>behaviour</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5946290226-1">(</span><span class="n">Behaviour</span><span class="p" data-group-id="5946290226-1">)</span><span class="p">.</span></code></pre><p>The atom <code class="inline">Behaviour</code> gives the name of the behaviour, which can be a
│ │ │  user-defined behaviour or one of the following OTP standard behaviours:</p><ul><li><code class="inline">gen_server</code></li><li><code class="inline">gen_statem</code></li><li><code class="inline">gen_event</code></li><li><code class="inline">supervisor</code></li></ul><p>The spelling <code class="inline">behavior</code> is also accepted.</p><p>The callback functions of the module can be specified either directly by the
│ │ │ -exported function <code class="inline">behaviour_info/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="1233823670-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="1233823670-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Callbacks</span><span class="p">.</span></code></pre><p>or by a <code class="inline">-callback</code> attribute for each callback function:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4597804859-1">(</span><span class="n">Arguments</span><span class="p" data-group-id="4597804859-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="p">.</span></code></pre><p>Here, <code class="inline">Arguments</code> is a list of zero or more arguments. The <code class="inline">-callback</code> attribute
│ │ │ +exported function <code class="inline">behaviour_info/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="1422325605-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="1422325605-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Callbacks</span><span class="p">.</span></code></pre><p>or by a <code class="inline">-callback</code> attribute for each callback function:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4151343681-1">(</span><span class="n">Arguments</span><span class="p" data-group-id="4151343681-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="p">.</span></code></pre><p>Here, <code class="inline">Arguments</code> is a list of zero or more arguments. The <code class="inline">-callback</code> attribute
│ │ │  is to be preferred since the extra type information can be used by tools to
│ │ │  produce documentation or find discrepancies.</p><p>Read more about behaviours and callback modules in
│ │ │  <a href="../../doc/system/spec_proc.html#behaviours">OTP Design Principles</a>.</p><h3 id="record-definitions" class="section-heading">
│ │ │    <a href="#record-definitions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Record Definitions</span>
│ │ │  </h3>
│ │ │ -<p>The same syntax as for module attributes is used for record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3360738457-1">(</span><span class="n">Record</span><span class="p">,</span><span class="w"> </span><span class="n">Fields</span><span class="p" data-group-id="3360738457-1">)</span><span class="p">.</span></code></pre><p>Record definitions are allowed anywhere in a module, also among the function
│ │ │ +<p>The same syntax as for module attributes is used for record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0908059310-1">(</span><span class="n">Record</span><span class="p">,</span><span class="w"> </span><span class="n">Fields</span><span class="p" data-group-id="0908059310-1">)</span><span class="p">.</span></code></pre><p>Record definitions are allowed anywhere in a module, also among the function
│ │ │  declarations. Read more in <a href="ref_man_records.html">Records</a>.</p><h3 id="preprocessor" class="section-heading">
│ │ │    <a href="#preprocessor" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Preprocessor</span>
│ │ │  </h3>
│ │ │  <p>The same syntax as for module attributes is used by the preprocessor, which
│ │ │ -supports file inclusion, macros, and conditional compilation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4352214010-1">(</span><span class="s">&quot;SomeFile.hrl&quot;</span><span class="p" data-group-id="4352214010-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4352214010-2">(</span><span class="n">Macro</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="4352214010-2">)</span><span class="p">.</span></code></pre><p>Read more in <a href="macros.html">Preprocessor</a>.</p><h3 id="setting-file-and-line" class="section-heading">
│ │ │ +supports file inclusion, macros, and conditional compilation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="8974157288-1">(</span><span class="s">&quot;SomeFile.hrl&quot;</span><span class="p" data-group-id="8974157288-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8974157288-2">(</span><span class="n">Macro</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="8974157288-2">)</span><span class="p">.</span></code></pre><p>Read more in <a href="macros.html">Preprocessor</a>.</p><h3 id="setting-file-and-line" class="section-heading">
│ │ │    <a href="#setting-file-and-line" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Setting File and Line</span>
│ │ │  </h3>
│ │ │  <p>The same syntax as for module attributes is used for changing the pre-defined
│ │ │ -macros <code class="inline">?FILE</code> and <code class="inline">?LINE</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">file</span><span class="p" data-group-id="1292626748-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">Line</span><span class="p" data-group-id="1292626748-1">)</span><span class="p">.</span></code></pre><p>This attribute is used by tools, such as Yecc, to inform the compiler that the
│ │ │ +macros <code class="inline">?FILE</code> and <code class="inline">?LINE</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">file</span><span class="p" data-group-id="2952200061-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">Line</span><span class="p" data-group-id="2952200061-1">)</span><span class="p">.</span></code></pre><p>This attribute is used by tools, such as Yecc, to inform the compiler that the
│ │ │  source program is generated by another tool. It also indicates the
│ │ │  correspondence of source files to lines of the original user-written file, from
│ │ │  which the source program is produced.</p><h3 id="types-and-function-specifications" class="section-heading">
│ │ │    <a href="#types-and-function-specifications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Types and function specifications</span>
│ │ │  </h3>
│ │ │  <p>A similar syntax as for module attributes is used for specifying types and
│ │ │ -function specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_type</span><span class="p" data-group-id="1946383441-1">(</span><span class="p" data-group-id="1946383441-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="1946383441-2">(</span><span class="p" data-group-id="1946383441-2">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1946383441-3">(</span><span class="p" data-group-id="1946383441-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">my_function</span><span class="p" data-group-id="1946383441-4">(</span><span class="nf">integer</span><span class="p" data-group-id="1946383441-5">(</span><span class="p" data-group-id="1946383441-5">)</span><span class="p" data-group-id="1946383441-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1946383441-6">(</span><span class="p" data-group-id="1946383441-6">)</span><span class="p">.</span></code></pre><p>Read more in <a href="typespec.html">Types and Function specifications</a>.</p><p>The description is based on
│ │ │ +function specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_type</span><span class="p" data-group-id="1548590948-1">(</span><span class="p" data-group-id="1548590948-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="1548590948-2">(</span><span class="p" data-group-id="1548590948-2">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1548590948-3">(</span><span class="p" data-group-id="1548590948-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">my_function</span><span class="p" data-group-id="1548590948-4">(</span><span class="nf">integer</span><span class="p" data-group-id="1548590948-5">(</span><span class="p" data-group-id="1548590948-5">)</span><span class="p" data-group-id="1548590948-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1548590948-6">(</span><span class="p" data-group-id="1548590948-6">)</span><span class="p">.</span></code></pre><p>Read more in <a href="typespec.html">Types and Function specifications</a>.</p><p>The description is based on
│ │ │  <a href="http://www.erlang.org/eeps/eep-0008.html">EEP8 - Types and function specifications</a>,
│ │ │  which is not to be further updated.</p><h3 id="documentation-attributes" class="section-heading">
│ │ │    <a href="#documentation-attributes" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Documentation attributes</span>
│ │ │  </h3>
│ │ │  <p>The module attribute <code class="inline">-doc(Documentation)</code> is used to provide user documentation
│ │ │ -for a function/type/callback:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="1207415589-1">(</span><span class="s">&quot;Example documentation&quot;</span><span class="p" data-group-id="1207415589-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="1207415589-2">(</span><span class="p" data-group-id="1207415589-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The attribute should be placed just before the entity it documents.The
│ │ │ +for a function/type/callback:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="9874758460-1">(</span><span class="s">&quot;Example documentation&quot;</span><span class="p" data-group-id="9874758460-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="9874758460-2">(</span><span class="p" data-group-id="9874758460-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The attribute should be placed just before the entity it documents.The
│ │ │  parenthesis are optional around <code class="inline">Documentation</code>. The allowed values for
│ │ │  <code class="inline">Documentation</code> are:</p><ul><li><p><strong><a href="data_types.html#string">literal string</a> or
│ │ │  <a href="expressions.html#unicode-segments">utf-8 encoded binary string</a></strong> - The string
│ │ │  documenting the entity. Any literal string is allowed, so both
│ │ │  <a href="data_types.html#tqstring">triple quoted strings</a> and
│ │ │  <a href="data_types.html#sigil">sigils</a> that translate to literal strings can be used.
│ │ │ -The following examples are equivalent:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="9371310890-1">(</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="p" data-group-id="9371310890-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="9371310890-2">(</span><span class="p" data-group-id="9371310890-3">&lt;&lt;</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="9371310890-3">&gt;&gt;</span><span class="p" data-group-id="9371310890-2">)</span><span class="p">.</span><span class="w">
│ │ │ +The following examples are equivalent:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7573370067-1">(</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="p" data-group-id="7573370067-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7573370067-2">(</span><span class="p" data-group-id="7573370067-3">&lt;&lt;</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="7573370067-3">&gt;&gt;</span><span class="p" data-group-id="7573370067-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">~S/Example &quot;docs&quot;/</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="s">&quot;
│ │ │     Example &quot;</span><span class="ss">docs</span><span class="s">&quot;
│ │ │     &quot;</span><span class="s">&quot;&quot;</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">~B|Example &quot;docs&quot;|</span><span class="p">.</span></code></pre><p>For clarity it is recommended to use either normal <code class="inline">&quot;strings&quot;</code> or triple
│ │ │  quoted strings for documentation attributes.</p></li><li><p><strong><code class="inline">{file,</code> <a href="../../lib/kernel-10.2.7.1/doc/html/file.html#t:name/0"><code class="inline">file:name/0</code></a> <code class="inline">}</code></strong> - Read the contents of filename and use
│ │ │  that as the documentation string.</p></li><li><p><strong><code class="inline">false</code></strong> - Set the current entity as hidden, that is, it should not be
│ │ │ @@ -253,15 +253,15 @@
│ │ │    <a href="#the-feature-directive" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">The feature directive</span>
│ │ │  </h2>
│ │ │  <p>While not a module attribute, but rather a directive (since it might affect
│ │ │  syntax), there is the <code class="inline">-feature(..)</code> directive used for enabling and disabling
│ │ │ -<a href="../../doc/system/features.html#features">features</a>.</p><p>The syntax is similar to that of an attribute, but has two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">feature</span><span class="p" data-group-id="7052632148-1">(</span><span class="n">FeatureName</span><span class="p">,</span><span class="w"> </span><span class="ss">enable</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">disable</span><span class="p" data-group-id="7052632148-1">)</span><span class="p">.</span></code></pre><p>Note that the <a href="macros.html#feature-directive">feature directive</a> can only appear
│ │ │ +<a href="../../doc/system/features.html#features">features</a>.</p><p>The syntax is similar to that of an attribute, but has two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">feature</span><span class="p" data-group-id="8644781107-1">(</span><span class="n">FeatureName</span><span class="p">,</span><span class="w"> </span><span class="ss">enable</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">disable</span><span class="p" data-group-id="8644781107-1">)</span><span class="p">.</span></code></pre><p>Note that the <a href="macros.html#feature-directive">feature directive</a> can only appear
│ │ │  in a prefix of the module.</p><h2 id="comments" class="section-heading">
│ │ │    <a href="#comments" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Comments</span>
│ │ │  </h2>
│ │ │  <p>Comments can be placed anywhere in a module except within strings and
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/nif.html
│ │ │ @@ -133,26 +133,26 @@
│ │ │    <span class="text">Erlang Program</span>
│ │ │  </h2>
│ │ │  <p>Even if all functions of a module are NIFs, an Erlang module is still needed for
│ │ │  two reasons:</p><ul><li>The NIF library must be explicitly loaded by Erlang code in the same module.</li><li>All NIFs of a module must have an Erlang implementation as well.</li></ul><p>Normally these are minimal stub implementations that throw an exception. But
│ │ │  they can also be used as fallback implementations for functions that do not have
│ │ │  native implementations on some architectures.</p><p>NIF libraries are loaded by calling <a href="../../erts-15.2.7/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a>, with the name of the
│ │ │  shared library as argument. The second argument can be any term that will be
│ │ │ -passed on to the library and used for initialization:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3730762021-1">(</span><span class="ss">complex6</span><span class="p" data-group-id="3730762021-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3730762021-2">(</span><span class="p" data-group-id="3730762021-3">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3730762021-3">]</span><span class="p" data-group-id="3730762021-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">nifs</span><span class="p" data-group-id="3730762021-4">(</span><span class="p" data-group-id="3730762021-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3730762021-5">]</span><span class="p" data-group-id="3730762021-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="3730762021-6">(</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3730762021-6">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="3730762021-7">(</span><span class="p" data-group-id="3730762021-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="3730762021-8">(</span><span class="s">&quot;./complex6_nif&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3730762021-8">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="3730762021-9">(</span><span class="p">_</span><span class="n">X</span><span class="p" data-group-id="3730762021-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="3730762021-10">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="3730762021-10">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="3730762021-11">(</span><span class="p">_</span><span class="n">Y</span><span class="p" data-group-id="3730762021-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="3730762021-12">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="3730762021-12">)</span><span class="p">.</span></code></pre><p>Here, the directive <code class="inline">on_load</code> is used to get function <code class="inline">init</code> to be automatically
│ │ │ +passed on to the library and used for initialization:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8891306383-1">(</span><span class="ss">complex6</span><span class="p" data-group-id="8891306383-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8891306383-2">(</span><span class="p" data-group-id="8891306383-3">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8891306383-3">]</span><span class="p" data-group-id="8891306383-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">nifs</span><span class="p" data-group-id="8891306383-4">(</span><span class="p" data-group-id="8891306383-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8891306383-5">]</span><span class="p" data-group-id="8891306383-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="8891306383-6">(</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8891306383-6">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8891306383-7">(</span><span class="p" data-group-id="8891306383-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="8891306383-8">(</span><span class="s">&quot;./complex6_nif&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8891306383-8">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="8891306383-9">(</span><span class="p">_</span><span class="n">X</span><span class="p" data-group-id="8891306383-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="8891306383-10">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="8891306383-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="8891306383-11">(</span><span class="p">_</span><span class="n">Y</span><span class="p" data-group-id="8891306383-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="8891306383-12">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="8891306383-12">)</span><span class="p">.</span></code></pre><p>Here, the directive <code class="inline">on_load</code> is used to get function <code class="inline">init</code> to be automatically
│ │ │  called when the module is loaded. If <code class="inline">init</code> returns anything other than <code class="inline">ok</code>,
│ │ │  such when the loading of the NIF library fails in this example, the module is
│ │ │  unloaded and calls to functions within it, fail.</p><p>Loading the NIF library overrides the stub implementations and cause calls to
│ │ │  <code class="inline">foo</code> and <code class="inline">bar</code> to be dispatched to the NIF implementations instead.</p><h2 id="nif-library-code" class="section-heading">
│ │ │    <a href="#nif-library-code" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -209,23 +209,23 @@
│ │ │    <a href="#running-the-example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running the Example</span>
│ │ │  </h2>
│ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">unix&gt; gcc -o complex6_nif.so -fpic -shared complex.c complex6_nif.c
│ │ │  windows&gt; cl -LD -MD -Fe complex6_nif.dll complex.c complex6_nif.c</code></pre><p><em>Step 2:</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="ss">erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="n">R13B04</span><span class="w"> </span><span class="p" data-group-id="6198498006-1">(</span><span class="ss">erts</span><span class="o">-</span><span class="mf">5.7</span><span class="p">.</span><span class="mi">5</span><span class="p" data-group-id="6198498006-1">)</span><span class="w"> </span><span class="p" data-group-id="6198498006-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="6198498006-2">]</span><span class="w"> </span><span class="p" data-group-id="6198498006-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="6198498006-3">]</span><span class="w"> </span><span class="p" data-group-id="6198498006-4">[</span><span class="nc">rq</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="6198498006-4">]</span><span class="w"> </span><span class="p" data-group-id="6198498006-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="6198498006-5">]</span><span class="w"> </span><span class="p" data-group-id="6198498006-6">[</span><span class="ss">kernel</span><span class="o">-</span><span class="nc">poll</span><span class="p">:</span><span class="ss">false</span><span class="p" data-group-id="6198498006-6">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="n">R13B04</span><span class="w"> </span><span class="p" data-group-id="0419600681-1">(</span><span class="ss">erts</span><span class="o">-</span><span class="mf">5.7</span><span class="p">.</span><span class="mi">5</span><span class="p" data-group-id="0419600681-1">)</span><span class="w"> </span><span class="p" data-group-id="0419600681-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0419600681-2">]</span><span class="w"> </span><span class="p" data-group-id="0419600681-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="0419600681-3">]</span><span class="w"> </span><span class="p" data-group-id="0419600681-4">[</span><span class="nc">rq</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="0419600681-4">]</span><span class="w"> </span><span class="p" data-group-id="0419600681-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="0419600681-5">]</span><span class="w"> </span><span class="p" data-group-id="0419600681-6">[</span><span class="ss">kernel</span><span class="o">-</span><span class="nc">poll</span><span class="p">:</span><span class="ss">false</span><span class="p" data-group-id="0419600681-6">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">7.5</span><span class="w">  </span><span class="p" data-group-id="6198498006-7">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="6198498006-7">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nf">c</span><span class="p" data-group-id="6198498006-8">(</span><span class="ss">complex6</span><span class="p" data-group-id="6198498006-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6198498006-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex6</span><span class="p" data-group-id="6198498006-9">}</span></code></pre><p><em>Step 3:</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="4056941588-1">(</span><span class="mi">3</span><span class="p" data-group-id="4056941588-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">7.5</span><span class="w">  </span><span class="p" data-group-id="0419600681-7">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="0419600681-7">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="nf">c</span><span class="p" data-group-id="0419600681-8">(</span><span class="ss">complex6</span><span class="p" data-group-id="0419600681-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0419600681-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex6</span><span class="p" data-group-id="0419600681-9">}</span></code></pre><p><em>Step 3:</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="0800918601-1">(</span><span class="mi">3</span><span class="p" data-group-id="0800918601-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="4056941588-2">(</span><span class="mi">5</span><span class="p" data-group-id="4056941588-2">)</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="0800918601-2">(</span><span class="mi">5</span><span class="p" data-group-id="0800918601-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="4056941588-3">(</span><span class="s">&quot;not an integer&quot;</span><span class="p" data-group-id="4056941588-3">)</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="0800918601-3">(</span><span class="s">&quot;not an integer&quot;</span><span class="p" data-group-id="0800918601-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: bad argument
│ │ │       in function  complex6:foo/1
│ │ │          called as comlpex6:foo(&quot;not an integer&quot;)</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/opaques.html
│ │ │ @@ -122,24 +122,24 @@
│ │ │    <span class="text">Opaque Type Aliases</span>
│ │ │  </h2>
│ │ │  <p>The main use case for opacity in Erlang is to hide the implementation of a data
│ │ │  type, enabling evolving the API while minimizing the risk of breaking consumers.
│ │ │  The runtime does not check opacity. Dialyzer provides some opacity-checking, but
│ │ │  the rest is up to convention.</p><p>This document explains what Erlang opacity is (and the trade-offs involved) via
│ │ │  the example of the <a href="../../lib/stdlib-6.2.2.1/doc/html/sets.html#t:set/0"><code class="inline">sets:set()</code></a> data type. This type <em>was</em>
│ │ │ -defined in the <code class="inline">sets</code> module like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="9166561636-1">(</span><span class="n">Element</span><span class="p" data-group-id="9166561636-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="9166561636-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="9166561636-3">(</span><span class="n">Element</span><span class="p" data-group-id="9166561636-3">)</span><span class="p" data-group-id="9166561636-2">}</span><span class="p">.</span></code></pre><p>OTP 24 changed the definition to the following in
│ │ │ -<a href="https://github.com/erlang/otp/commit/e66941e8d7c47b973dff94c0308ea85a6be1958e">this commit</a>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="9912677790-1">(</span><span class="n">Element</span><span class="p" data-group-id="9912677790-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="9912677790-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="9912677790-3">(</span><span class="n">Element</span><span class="p" data-group-id="9912677790-3">)</span><span class="p" data-group-id="9912677790-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="9912677790-4">#{</span><span class="n">Element</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VALUE</span><span class="p" data-group-id="9912677790-4">}</span><span class="p">.</span></code></pre><p>And this change was safer and more backwards-compatible than if the type had
│ │ │ +defined in the <code class="inline">sets</code> module like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="9119727232-1">(</span><span class="n">Element</span><span class="p" data-group-id="9119727232-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="9119727232-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="9119727232-3">(</span><span class="n">Element</span><span class="p" data-group-id="9119727232-3">)</span><span class="p" data-group-id="9119727232-2">}</span><span class="p">.</span></code></pre><p>OTP 24 changed the definition to the following in
│ │ │ +<a href="https://github.com/erlang/otp/commit/e66941e8d7c47b973dff94c0308ea85a6be1958e">this commit</a>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="8241651526-1">(</span><span class="n">Element</span><span class="p" data-group-id="8241651526-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="8241651526-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="8241651526-3">(</span><span class="n">Element</span><span class="p" data-group-id="8241651526-3">)</span><span class="p" data-group-id="8241651526-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8241651526-4">#{</span><span class="n">Element</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VALUE</span><span class="p" data-group-id="8241651526-4">}</span><span class="p">.</span></code></pre><p>And this change was safer and more backwards-compatible than if the type had
│ │ │  been defined with <code class="inline">-type</code> instead of <code class="inline">-opaque</code>. Here is why: when a module
│ │ │  defines an <code class="inline">-opaque</code>, the contract is that only the defining module should rely
│ │ │  on the definition of the type: no other modules should rely on the definition.</p><p>This means that code that pattern-matched on <code class="inline">set</code> as a record/tuple technically
│ │ │  broke the contract, and opted in to being potentially broken when the definition
│ │ │  of <code class="inline">set()</code> changed. Before OTP 24, this code printed <code class="inline">ok</code>. In OTP 24 it may
│ │ │ -error:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="0923628794-1">(</span><span class="p" data-group-id="0923628794-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="n">Set</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_tuple</span><span class="p" data-group-id="0923628794-2">(</span><span class="n">Set</span><span class="p" data-group-id="0923628794-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0923628794-3">(</span><span class="s">&quot;ok&quot;</span><span class="p" data-group-id="0923628794-3">)</span><span class="w">
│ │ │ +error:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="2323884020-1">(</span><span class="p" data-group-id="2323884020-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="n">Set</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_tuple</span><span class="p" data-group-id="2323884020-2">(</span><span class="n">Set</span><span class="p" data-group-id="2323884020-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2323884020-3">(</span><span class="s">&quot;ok&quot;</span><span class="p" data-group-id="2323884020-3">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p><strong>When working with an opaque defined in another module, here are some
│ │ │  recommendations:</strong></p><ul><li>Don't examine the underlying type using pattern-matching, guards, or functions
│ │ │  that reveal the type, such as <a href="../../erts-15.2.7/doc/html/erlang.html#tuple_size/1"><code class="inline">tuple_size/1</code></a> .</li><li>Instead, use functions provided by the module for working with the type. For
│ │ │  example, <code class="inline">sets</code> module provides <a href="../../lib/stdlib-6.2.2.1/doc/html/sets.html#new/0"><code class="inline">sets:new/0</code></a>, <a href="../../lib/stdlib-6.2.2.1/doc/html/sets.html#add_element/2"><code class="inline">sets:add_element/2</code></a>,
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/sets.html#is_element/2"><code class="inline">sets:is_element/2</code></a>, and so on.</li><li><p><a href="../../lib/stdlib-6.2.2.1/doc/html/sets.html#t:set/1"><code class="inline">sets:set(a)</code></a> is a subtype of <code class="inline">sets:set(a | b)</code> and not the
│ │ │  other way around. Generally, you can rely on the property that <code class="inline">the_opaque(T)</code>
│ │ │  is a subtype of <code class="inline">the_opaque(U)</code> when T is a subtype of U.</p></li></ul><p><strong>When defining your own opaques, here are some recommendations:</strong></p><ul><li>Since consumers are expected to not rely on the definition of the opaque type,
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/otp-patch-apply.html
│ │ │ @@ -201,15 +201,15 @@
│ │ │    </a>
│ │ │    <span class="text">Sanity check</span>
│ │ │  </h2>
│ │ │  <p>The application dependencies can be checked using the Erlang shell.
│ │ │  Application dependencies are verified among installed applications by
│ │ │  <code class="inline">otp_patch_apply</code>, but these are not necessarily those actually loaded.
│ │ │  By calling <code class="inline">system_information:sanity_check()</code> one can validate
│ │ │ -dependencies among applications actually loaded.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">system_information</span><span class="p">:</span><span class="nf">sanity_check</span><span class="p" data-group-id="4233913828-1">(</span><span class="p" data-group-id="4233913828-1">)</span><span class="p">.</span><span class="w">
│ │ │ +dependencies among applications actually loaded.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">system_information</span><span class="p">:</span><span class="nf">sanity_check</span><span class="p" data-group-id="8284444814-1">(</span><span class="p" data-group-id="8284444814-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>Please take a look at the reference of <a href="../../lib/runtime_tools-2.1.1/doc/html/system_information.html#sanity_check/0" title="">sanity_check()</a> for more
│ │ │  information.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/patterns.html
│ │ │ @@ -128,18 +128,18 @@
│ │ │  succeeds, any unbound variables in the pattern become bound. If the matching
│ │ │  fails, an exception is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** 1:1: variable &#39;X&#39; is unbound **</span><span class="gp unselectable">
│ │ │  2&gt; </span><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">2</span><span class="gp unselectable">
│ │ │  3&gt; </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="p" data-group-id="7842590583-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7842590583-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7842590583-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7842590583-2">}</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="p" data-group-id="2008503956-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2008503956-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2008503956-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2008503956-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value {1,2}</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="p" data-group-id="7842590583-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7842590583-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7842590583-4">{</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7842590583-4">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7842590583-5">{</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7842590583-5">}</span><span class="gp unselectable">
│ │ │ +5&gt; </span><span class="p" data-group-id="2008503956-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2008503956-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2008503956-4">{</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2008503956-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2008503956-5">{</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2008503956-5">}</span><span class="gp unselectable">
│ │ │  6&gt; </span><span class="n">Y</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/prog_ex_records.html
│ │ │ @@ -122,105 +122,105 @@
│ │ │    <span class="text">Records and Tuples</span>
│ │ │  </h2>
│ │ │  <p>The main advantage of using records rather than tuples is that fields in a
│ │ │  record are accessed by name, whereas fields in a tuple are accessed by position.
│ │ │  To illustrate these differences, suppose that you want to represent a person
│ │ │  with the tuple <code class="inline">{Name, Address, Phone}</code>.</p><p>To write functions that manipulate this data, remember the following:</p><ul><li>The <code class="inline">Name</code> field is the first element of the tuple.</li><li>The <code class="inline">Address</code> field is the second element.</li><li>The <code class="inline">Phone</code> field is the third element.</li></ul><p>For example, to extract data from a variable <code class="inline">P</code> that contains such a tuple, you
│ │ │  can write the following code and then use pattern matching to extract the
│ │ │ -relevant fields:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="5854986233-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="5854986233-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="5854986233-2">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="5854986233-2">)</span><span class="p">,</span><span class="w">
│ │ │ +relevant fields:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="6907119394-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="6907119394-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="6907119394-2">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="6907119394-2">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Such code is difficult to read and understand, and errors occur if the numbering
│ │ │  of the elements in the tuple is wrong. If the data representation of the fields
│ │ │  is changed, by re-ordering, adding, or removing fields, all references to the
│ │ │  person tuple must be checked and possibly modified.</p><p>Records allow references to the fields by name, instead of by position. In the
│ │ │ -following example, a record instead of a tuple is used to store the data:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8217041593-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8217041593-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="8217041593-2">}</span><span class="p" data-group-id="8217041593-1">)</span><span class="p">.</span></code></pre><p>This enables references to the fields of the record by name. For example, if <code class="inline">P</code>
│ │ │ +following example, a record instead of a tuple is used to store the data:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5768174655-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5768174655-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="5768174655-2">}</span><span class="p" data-group-id="5768174655-1">)</span><span class="p">.</span></code></pre><p>This enables references to the fields of the record by name. For example, if <code class="inline">P</code>
│ │ │  is a variable whose value is a <code class="inline">person</code> record, the following code access the
│ │ │  name and address fields of the records:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">address</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Internally, records are represented using tagged tuples:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4228970313-1">{</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p" data-group-id="4228970313-1">}</span></code></pre><h2 id="defining-a-record" class="section-heading">
│ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Internally, records are represented using tagged tuples:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0414093564-1">{</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p" data-group-id="0414093564-1">}</span></code></pre><h2 id="defining-a-record" class="section-heading">
│ │ │    <a href="#defining-a-record" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Defining a Record</span>
│ │ │  </h2>
│ │ │  <p>This following definition of a <code class="inline">person</code> is used in several examples in this
│ │ │  section. Three fields are included, <code class="inline">name</code>, <code class="inline">phone</code>, and <code class="inline">address</code>. The default
│ │ │  values for <code class="inline">name</code> and <code class="inline">phone</code> is &quot;&quot; and [], respectively. The default value for
│ │ │  <code class="inline">address</code> is the atom <code class="inline">undefined</code>, since no default value is supplied for this
│ │ │ -field:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9687989740-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9687989740-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9687989740-3">[</span><span class="p" data-group-id="9687989740-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="9687989740-2">}</span><span class="p" data-group-id="9687989740-1">)</span><span class="p">.</span></code></pre><p>The record must be defined in the shell to enable use of the record syntax in
│ │ │ -the examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">rd</span><span class="p" data-group-id="7426444310-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7426444310-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7426444310-3">[</span><span class="p" data-group-id="7426444310-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="7426444310-2">}</span><span class="p" data-group-id="7426444310-1">)</span><span class="p">.</span><span class="w">
│ │ │ +field:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3720473619-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3720473619-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3720473619-3">[</span><span class="p" data-group-id="3720473619-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="3720473619-2">}</span><span class="p" data-group-id="3720473619-1">)</span><span class="p">.</span></code></pre><p>The record must be defined in the shell to enable use of the record syntax in
│ │ │ +the examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">rd</span><span class="p" data-group-id="6645921160-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6645921160-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6645921160-3">[</span><span class="p" data-group-id="6645921160-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="6645921160-2">}</span><span class="p" data-group-id="6645921160-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">person</span></code></pre><p>This is because record definitions are only available at compile time, not at
│ │ │  runtime. For details on records in the shell, see the <a href="../../lib/stdlib-6.2.2.1/doc/html/shell.html"><code class="inline">shell</code></a> manual page in
│ │ │  STDLIB.</p><h2 id="creating-a-record" class="section-heading">
│ │ │    <a href="#creating-a-record" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating a Record</span>
│ │ │  </h2>
│ │ │ -<p>A new <code class="inline">person</code> record is created as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4088055289-1">{</span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="4088055289-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4088055289-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="4088055289-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4088055289-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4088055289-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4088055289-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="4088055289-3">}</span></code></pre><p>As the <code class="inline">address</code> field was omitted, its default value is used.</p><p>From Erlang 5.1/OTP R8B, a value to all fields in a record can be set with the
│ │ │ -special field <code class="inline">_</code>. <code class="inline">_</code> means &quot;all fields not explicitly specified&quot;.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6879254842-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6879254842-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6879254842-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6879254842-2">}</span></code></pre><p>It is primarily intended to be used in <a href="../../lib/stdlib-6.2.2.1/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a> and
│ │ │ +<p>A new <code class="inline">person</code> record is created as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9216069797-1">{</span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="9216069797-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9216069797-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="9216069797-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9216069797-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9216069797-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9216069797-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="9216069797-3">}</span></code></pre><p>As the <code class="inline">address</code> field was omitted, its default value is used.</p><p>From Erlang 5.1/OTP R8B, a value to all fields in a record can be set with the
│ │ │ +special field <code class="inline">_</code>. <code class="inline">_</code> means &quot;all fields not explicitly specified&quot;.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8280669707-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="8280669707-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8280669707-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="8280669707-2">}</span></code></pre><p>It is primarily intended to be used in <a href="../../lib/stdlib-6.2.2.1/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a> and
│ │ │  <a href="../../lib/mnesia-4.23.5/doc/html/mnesia.html#match_object/3"><code class="inline">mnesia:match_object/3</code></a>, to set record fields to the atom <code class="inline">'_'</code>. (This is a
│ │ │  wildcard in <a href="../../lib/stdlib-6.2.2.1/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>.)</p><h2 id="accessing-a-record-field" class="section-heading">
│ │ │    <a href="#accessing-a-record-field" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Accessing a Record Field</span>
│ │ │  </h2>
│ │ │ -<p>The following example shows how to access a record field:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1927319543-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1927319543-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1927319543-2">]</span><span class="p" data-group-id="1927319543-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1927319543-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1927319543-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1927319543-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="1927319543-3">}</span><span class="gp unselectable">
│ │ │ +<p>The following example shows how to access a record field:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6441074576-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6441074576-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6441074576-2">]</span><span class="p" data-group-id="6441074576-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6441074576-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6441074576-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6441074576-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="6441074576-3">}</span><span class="gp unselectable">
│ │ │  &gt; </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;Joe&quot;</span></code></pre><h2 id="updating-a-record" class="section-heading">
│ │ │    <a href="#updating-a-record" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Updating a Record</span>
│ │ │  </h2>
│ │ │ -<p>The following example shows how to update a record:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8976710630-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="8976710630-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8976710630-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="8976710630-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8976710630-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8976710630-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8976710630-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="8976710630-3">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P1</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8976710630-5">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="8976710630-5">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8976710630-6">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8976710630-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8976710630-7">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="8976710630-6">}</span></code></pre><h2 id="type-testing" class="section-heading">
│ │ │ +<p>The following example shows how to update a record:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5353567166-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="5353567166-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5353567166-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="5353567166-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5353567166-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5353567166-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5353567166-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="5353567166-3">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P1</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5353567166-5">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="5353567166-5">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5353567166-6">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5353567166-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5353567166-7">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="5353567166-6">}</span></code></pre><h2 id="type-testing" class="section-heading">
│ │ │    <a href="#type-testing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Type Testing</span>
│ │ │  </h2>
│ │ │  <p>The following example shows that the guard succeeds if <code class="inline">P</code> is record of type
│ │ │ -<code class="inline">person</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="7782589435-1">(</span><span class="n">P</span><span class="p" data-group-id="7782589435-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="7782589435-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="7782589435-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">a_person</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="7782589435-3">(</span><span class="p">_</span><span class="p" data-group-id="7782589435-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">not_a_person</span><span class="p">.</span></code></pre><h2 id="pattern-matching" class="section-heading">
│ │ │ +<code class="inline">person</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="7457381904-1">(</span><span class="n">P</span><span class="p" data-group-id="7457381904-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="7457381904-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="7457381904-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">a_person</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="7457381904-3">(</span><span class="p">_</span><span class="p" data-group-id="7457381904-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">not_a_person</span><span class="p">.</span></code></pre><h2 id="pattern-matching" class="section-heading">
│ │ │    <a href="#pattern-matching" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Pattern Matching</span>
│ │ │  </h2>
│ │ │  <p>Matching can be used in combination with records, as shown in the following
│ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4465206739-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="4465206739-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4465206739-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="4465206739-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4465206739-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4465206739-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4465206739-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="4465206739-3">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4465206739-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4465206739-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P3</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">.</span><span class="w">
│ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3004239417-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="3004239417-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3004239417-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="3004239417-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3004239417-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3004239417-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3004239417-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="3004239417-3">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3004239417-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3004239417-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P3</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;Joe&quot;</span></code></pre><p>The following function takes a list of <code class="inline">person</code> records and searches for the
│ │ │ -phone number of a person with a particular name:</p><pre><code class="makeup erlang" translate="no"><span class="nf">find_phone</span><span class="p" data-group-id="4284429743-1">(</span><span class="p" data-group-id="4284429743-2">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4284429743-3">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="n">Phone</span><span class="p" data-group-id="4284429743-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="4284429743-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4284429743-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4284429743-4">{</span><span class="ss">found</span><span class="p">,</span><span class="w">  </span><span class="n">Phone</span><span class="p" data-group-id="4284429743-4">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">find_phone</span><span class="p" data-group-id="4284429743-5">(</span><span class="p" data-group-id="4284429743-6">[</span><span class="p">_</span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4284429743-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4284429743-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">find_phone</span><span class="p" data-group-id="4284429743-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4284429743-7">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">find_phone</span><span class="p" data-group-id="4284429743-8">(</span><span class="p" data-group-id="4284429743-9">[</span><span class="p" data-group-id="4284429743-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4284429743-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +phone number of a person with a particular name:</p><pre><code class="makeup erlang" translate="no"><span class="nf">find_phone</span><span class="p" data-group-id="9574145450-1">(</span><span class="p" data-group-id="9574145450-2">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9574145450-3">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="n">Phone</span><span class="p" data-group-id="9574145450-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9574145450-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9574145450-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9574145450-4">{</span><span class="ss">found</span><span class="p">,</span><span class="w">  </span><span class="n">Phone</span><span class="p" data-group-id="9574145450-4">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">find_phone</span><span class="p" data-group-id="9574145450-5">(</span><span class="p" data-group-id="9574145450-6">[</span><span class="p">_</span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9574145450-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9574145450-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">find_phone</span><span class="p" data-group-id="9574145450-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9574145450-7">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">find_phone</span><span class="p" data-group-id="9574145450-8">(</span><span class="p" data-group-id="9574145450-9">[</span><span class="p" data-group-id="9574145450-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9574145450-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">not_found</span><span class="p">.</span></code></pre><p>The fields referred to in the pattern can be given in any order.</p><h2 id="nested-records" class="section-heading">
│ │ │    <a href="#nested-records" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Nested Records</span>
│ │ │  </h2>
│ │ │  <p>The value of a field in a record can be an instance of a record. Retrieval of
│ │ │  nested data can be done stepwise, or in a single step, as shown in the following
│ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7879158106-1">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7879158106-2">{</span><span class="ss">first</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">last</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Ericsson&quot;</span><span class="p" data-group-id="7879158106-2">}</span><span class="p" data-group-id="7879158106-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7879158106-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7879158106-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="7879158106-5">{</span><span class="p" data-group-id="7879158106-5">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p" data-group-id="7879158106-4">}</span><span class="p" data-group-id="7879158106-3">)</span><span class="p">.</span><span class="w">
│ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2124811511-1">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2124811511-2">{</span><span class="ss">first</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">last</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Ericsson&quot;</span><span class="p" data-group-id="2124811511-2">}</span><span class="p" data-group-id="2124811511-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2124811511-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2124811511-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="2124811511-5">{</span><span class="p" data-group-id="2124811511-5">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p" data-group-id="2124811511-4">}</span><span class="p" data-group-id="2124811511-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">demo</span><span class="p" data-group-id="7879158106-6">(</span><span class="p" data-group-id="7879158106-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7879158106-7">{</span><span class="ss">name</span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="7879158106-8">{</span><span class="ss">first</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">last</span><span class="o">=</span><span class="s">&quot;Virding&quot;</span><span class="p" data-group-id="7879158106-8">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="mi">123</span><span class="p" data-group-id="7879158106-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="n">First</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7879158106-9">(</span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="7879158106-9">)</span><span class="o">#</span><span class="ss">name</span><span class="p">.</span><span class="ss">first</span><span class="p">.</span></code></pre><p>Here, <code class="inline">demo()</code> evaluates to <code class="inline">&quot;Robert&quot;</code>.</p><h2 id="a-longer-example" class="section-heading">
│ │ │ +</span><span class="nf">demo</span><span class="p" data-group-id="2124811511-6">(</span><span class="p" data-group-id="2124811511-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2124811511-7">{</span><span class="ss">name</span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="2124811511-8">{</span><span class="ss">first</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">last</span><span class="o">=</span><span class="s">&quot;Virding&quot;</span><span class="p" data-group-id="2124811511-8">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="mi">123</span><span class="p" data-group-id="2124811511-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="n">First</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2124811511-9">(</span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="2124811511-9">)</span><span class="o">#</span><span class="ss">name</span><span class="p">.</span><span class="ss">first</span><span class="p">.</span></code></pre><p>Here, <code class="inline">demo()</code> evaluates to <code class="inline">&quot;Robert&quot;</code>.</p><h2 id="a-longer-example" class="section-heading">
│ │ │    <a href="#a-longer-example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">A Longer Example</span>
│ │ │  </h2>
│ │ │  <p>Comments are embedded in the following example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% File: person.hrl</span><span class="w">
│ │ │  
│ │ │ @@ -230,48 +230,48 @@
│ │ │  </span><span class="c1">%%    name:  A string (default is undefined).</span><span class="w">
│ │ │  </span><span class="c1">%%    age:   An integer (default is undefined).</span><span class="w">
│ │ │  </span><span class="c1">%%    phone: A list of integers (default is []).</span><span class="w">
│ │ │  </span><span class="c1">%%    dict:  A dictionary containing various information</span><span class="w">
│ │ │  </span><span class="c1">%%           about the person.</span><span class="w">
│ │ │  </span><span class="c1">%%           A {Key, Value} list (default is the empty list).</span><span class="w">
│ │ │  </span><span class="c1">%%------------------------------------------------------------</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6409808129-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6409808129-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6409808129-3">[</span><span class="p" data-group-id="6409808129-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6409808129-4">[</span><span class="p" data-group-id="6409808129-4">]</span><span class="p" data-group-id="6409808129-2">}</span><span class="p" data-group-id="6409808129-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1102861514-1">(</span><span class="ss">person</span><span class="p" data-group-id="1102861514-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1102861514-2">(</span><span class="s">&quot;person.hrl&quot;</span><span class="p" data-group-id="1102861514-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="1102861514-3">(</span><span class="ss">export_all</span><span class="p" data-group-id="1102861514-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% For test purposes only.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6300375527-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6300375527-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6300375527-3">[</span><span class="p" data-group-id="6300375527-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6300375527-4">[</span><span class="p" data-group-id="6300375527-4">]</span><span class="p" data-group-id="6300375527-2">}</span><span class="p" data-group-id="6300375527-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3547886957-1">(</span><span class="ss">person</span><span class="p" data-group-id="3547886957-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3547886957-2">(</span><span class="s">&quot;person.hrl&quot;</span><span class="p" data-group-id="3547886957-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="3547886957-3">(</span><span class="ss">export_all</span><span class="p" data-group-id="3547886957-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% For test purposes only.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% This creates an instance of a person.</span><span class="w">
│ │ │  </span><span class="c1">%%   Note: The phone number is not supplied so the</span><span class="w">
│ │ │  </span><span class="c1">%%         default value [] will be used.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="1102861514-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="1102861514-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1102861514-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ -           </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1102861514-6">[</span><span class="p" data-group-id="1102861514-7">{</span><span class="ss">computer_knowledge</span><span class="p">,</span><span class="w"> </span><span class="ss">excellent</span><span class="p" data-group-id="1102861514-7">}</span><span class="p">,</span><span class="w">
│ │ │ -                   </span><span class="p" data-group-id="1102861514-8">{</span><span class="ss">drinks</span><span class="p">,</span><span class="w"> </span><span class="ss">coke</span><span class="p" data-group-id="1102861514-8">}</span><span class="p" data-group-id="1102861514-6">]</span><span class="p" data-group-id="1102861514-5">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="3547886957-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="3547886957-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3547886957-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ +           </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3547886957-6">[</span><span class="p" data-group-id="3547886957-7">{</span><span class="ss">computer_knowledge</span><span class="p">,</span><span class="w"> </span><span class="ss">excellent</span><span class="p" data-group-id="3547886957-7">}</span><span class="p">,</span><span class="w">
│ │ │ +                   </span><span class="p" data-group-id="3547886957-8">{</span><span class="ss">drinks</span><span class="p">,</span><span class="w"> </span><span class="ss">coke</span><span class="p" data-group-id="3547886957-8">}</span><span class="p" data-group-id="3547886957-6">]</span><span class="p" data-group-id="3547886957-5">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% This demonstrates matching in arguments</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">print</span><span class="p" data-group-id="1102861514-9">(</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1102861514-10">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="1102861514-10">}</span><span class="p" data-group-id="1102861514-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1102861514-11">(</span><span class="s">&quot;Name: </span><span class="si">~s</span><span class="s">, Age: </span><span class="si">~w</span><span class="s">, Phone: </span><span class="si">~w</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="w">
│ │ │ -            </span><span class="s">&quot;Dictionary: </span><span class="si">~w</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1102861514-12">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="1102861514-12">]</span><span class="p" data-group-id="1102861514-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">print</span><span class="p" data-group-id="3547886957-9">(</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3547886957-10">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="3547886957-10">}</span><span class="p" data-group-id="3547886957-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3547886957-11">(</span><span class="s">&quot;Name: </span><span class="si">~s</span><span class="s">, Age: </span><span class="si">~w</span><span class="s">, Phone: </span><span class="si">~w</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="w">
│ │ │ +            </span><span class="s">&quot;Dictionary: </span><span class="si">~w</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3547886957-12">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="3547886957-12">]</span><span class="p" data-group-id="3547886957-11">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% Demonstrates type testing, selector, updating.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">birthday</span><span class="p" data-group-id="1102861514-13">(</span><span class="n">P</span><span class="p" data-group-id="1102861514-13">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="1102861514-14">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="1102861514-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1102861514-15">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1102861514-15">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">birthday</span><span class="p" data-group-id="3547886957-13">(</span><span class="n">P</span><span class="p" data-group-id="3547886957-13">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="3547886957-14">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="3547886957-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3547886957-15">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3547886957-15">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">register_two_hackers</span><span class="p" data-group-id="1102861514-16">(</span><span class="p" data-group-id="1102861514-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="n">Hacker1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="1102861514-17">(</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">29</span><span class="p" data-group-id="1102861514-17">)</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="n">OldHacker</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">birthday</span><span class="p" data-group-id="1102861514-18">(</span><span class="n">Hacker1</span><span class="p" data-group-id="1102861514-18">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">register_two_hackers</span><span class="p" data-group-id="3547886957-16">(</span><span class="p" data-group-id="3547886957-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="n">Hacker1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="3547886957-17">(</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">29</span><span class="p" data-group-id="3547886957-17">)</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="n">OldHacker</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">birthday</span><span class="p" data-group-id="3547886957-18">(</span><span class="n">Hacker1</span><span class="p" data-group-id="3547886957-18">)</span><span class="p">,</span><span class="w">
│ │ │     </span><span class="c1">% The central_register_server should have</span><span class="w">
│ │ │     </span><span class="c1">% an interface function for this.</span><span class="w">
│ │ │ -   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1102861514-19">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w"> </span><span class="n">Hacker1</span><span class="p" data-group-id="1102861514-19">}</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1102861514-20">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="n">OldHacker</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1102861514-21">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w">
│ │ │ -                              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1102861514-22">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1102861514-22">]</span><span class="p" data-group-id="1102861514-21">}</span><span class="p" data-group-id="1102861514-20">}</span><span class="p">.</span></code></pre>
│ │ │ +   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3547886957-19">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w"> </span><span class="n">Hacker1</span><span class="p" data-group-id="3547886957-19">}</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3547886957-20">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="n">OldHacker</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3547886957-21">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w">
│ │ │ +                              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3547886957-22">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3547886957-22">]</span><span class="p" data-group-id="3547886957-21">}</span><span class="p" data-group-id="3547886957-20">}</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="programming_examples.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/records_macros.html
│ │ │ @@ -124,40 +124,40 @@
│ │ │  </h2>
│ │ │  <p>To illustrate this, the messenger example from the previous section is divided
│ │ │  into the following five files:</p><ul><li><p><code class="inline">mess_config.hrl</code></p><p>Header file for configuration data</p></li><li><p><code class="inline">mess_interface.hrl</code></p><p>Interface definitions between the client and the messenger</p></li><li><p><code class="inline">user_interface.erl</code></p><p>Functions for the user interface</p></li><li><p><code class="inline">mess_client.erl</code></p><p>Functions for the client side of the messenger</p></li><li><p><code class="inline">mess_server.erl</code></p><p>Functions for the server side of the messenger</p></li></ul><p>While doing this, the message passing interface between the shell, the client,
│ │ │  and the server is cleaned up and is defined using <em>records</em>. Also, <em>macros</em> are
│ │ │  introduced:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_config.hrl----</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Configure the location of the server node,</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3305044691-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="3305044691-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4552321323-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="4552321323-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_interface.hrl----</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Message interface between client and server and client shell for</span><span class="w">
│ │ │  </span><span class="c1">%%% messenger program</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%Messages from Client to server received in server/1 function.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3597346557-1">(</span><span class="ss">logon</span><span class="p">,</span><span class="p" data-group-id="3597346557-2">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="p" data-group-id="3597346557-2">}</span><span class="p" data-group-id="3597346557-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3597346557-3">(</span><span class="ss">message</span><span class="p">,</span><span class="p" data-group-id="3597346557-4">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="3597346557-4">}</span><span class="p" data-group-id="3597346557-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7303521043-1">(</span><span class="ss">logon</span><span class="p">,</span><span class="p" data-group-id="7303521043-2">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="p" data-group-id="7303521043-2">}</span><span class="p" data-group-id="7303521043-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7303521043-3">(</span><span class="ss">message</span><span class="p">,</span><span class="p" data-group-id="7303521043-4">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="7303521043-4">}</span><span class="p" data-group-id="7303521043-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% {&#39;EXIT&#39;, ClientPid, Reason}  (client terminated or unreachable.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Messages from Server to Client, received in await_result/0 function</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3597346557-5">(</span><span class="ss">abort_client</span><span class="p">,</span><span class="p" data-group-id="3597346557-6">{</span><span class="ss">message</span><span class="p" data-group-id="3597346557-6">}</span><span class="p" data-group-id="3597346557-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7303521043-5">(</span><span class="ss">abort_client</span><span class="p">,</span><span class="p" data-group-id="7303521043-6">{</span><span class="ss">message</span><span class="p" data-group-id="7303521043-6">}</span><span class="p" data-group-id="7303521043-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% Messages are: user_exists_at_other_node,</span><span class="w">
│ │ │  </span><span class="c1">%%%               you_are_not_logged_on</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3597346557-7">(</span><span class="ss">server_reply</span><span class="p">,</span><span class="p" data-group-id="3597346557-8">{</span><span class="ss">message</span><span class="p" data-group-id="3597346557-8">}</span><span class="p" data-group-id="3597346557-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7303521043-7">(</span><span class="ss">server_reply</span><span class="p">,</span><span class="p" data-group-id="7303521043-8">{</span><span class="ss">message</span><span class="p" data-group-id="7303521043-8">}</span><span class="p" data-group-id="7303521043-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% Messages are: logged_on</span><span class="w">
│ │ │  </span><span class="c1">%%%               receiver_not_found</span><span class="w">
│ │ │  </span><span class="c1">%%%               sent  (Message has been sent (no guarantee)</span><span class="w">
│ │ │  </span><span class="c1">%%% Messages from Server to Client received in client/1 function</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3597346557-9">(</span><span class="ss">message_from</span><span class="p">,</span><span class="p" data-group-id="3597346557-10">{</span><span class="ss">from_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="3597346557-10">}</span><span class="p" data-group-id="3597346557-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7303521043-9">(</span><span class="ss">message_from</span><span class="p">,</span><span class="p" data-group-id="7303521043-10">{</span><span class="ss">from_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="7303521043-10">}</span><span class="p" data-group-id="7303521043-9">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Messages from shell to Client received in client/1 function</span><span class="w">
│ │ │  </span><span class="c1">%%% spawn(mess_client, client, [server_node(), Name])</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3597346557-11">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="3597346557-12">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="3597346557-12">}</span><span class="p" data-group-id="3597346557-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7303521043-11">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="7303521043-12">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="7303521043-12">}</span><span class="p" data-group-id="7303521043-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% logoff</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE user_interface.erl----</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% User interface to the messenger program</span><span class="w">
│ │ │  </span><span class="c1">%%% login(Name)</span><span class="w">
│ │ │  </span><span class="c1">%%%     One user at a time can log in from each Erlang node in the</span><span class="w">
│ │ │ @@ -170,177 +170,177 @@
│ │ │  </span><span class="c1">%%%     Logs off anybody at that node</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% message(ToName, Message)</span><span class="w">
│ │ │  </span><span class="c1">%%%     sends Message to ToName. Error messages if the user of this</span><span class="w">
│ │ │  </span><span class="c1">%%%     function is not logged on or if ToName is not logged on at</span><span class="w">
│ │ │  </span><span class="c1">%%%     any node.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1770075609-1">(</span><span class="ss">user_interface</span><span class="p" data-group-id="1770075609-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1770075609-2">(</span><span class="p" data-group-id="1770075609-3">[</span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1770075609-3">]</span><span class="p" data-group-id="1770075609-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1770075609-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="1770075609-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1770075609-5">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="1770075609-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6814473935-1">(</span><span class="ss">user_interface</span><span class="p" data-group-id="6814473935-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6814473935-2">(</span><span class="p" data-group-id="6814473935-3">[</span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6814473935-3">]</span><span class="p" data-group-id="6814473935-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="6814473935-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="6814473935-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="6814473935-5">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="6814473935-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="1770075609-6">(</span><span class="n">Name</span><span class="p" data-group-id="1770075609-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="1770075609-7">(</span><span class="ss">mess_client</span><span class="p" data-group-id="1770075609-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="6814473935-6">(</span><span class="n">Name</span><span class="p" data-group-id="6814473935-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="6814473935-7">(</span><span class="ss">mess_client</span><span class="p" data-group-id="6814473935-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="1770075609-8">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="1770075609-9">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1770075609-10">[</span><span class="o">?</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="1770075609-10">]</span><span class="p" data-group-id="1770075609-9">)</span><span class="p" data-group-id="1770075609-8">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="6814473935-8">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="6814473935-9">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6814473935-10">[</span><span class="o">?</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6814473935-10">]</span><span class="p" data-group-id="6814473935-9">)</span><span class="p" data-group-id="6814473935-8">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="1770075609-11">(</span><span class="p" data-group-id="1770075609-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="6814473935-11">(</span><span class="p" data-group-id="6814473935-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="1770075609-12">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="1770075609-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="1770075609-13">(</span><span class="ss">mess_client</span><span class="p" data-group-id="1770075609-13">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="6814473935-12">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6814473935-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="6814473935-13">(</span><span class="ss">mess_client</span><span class="p" data-group-id="6814473935-13">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="1770075609-14">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="1770075609-14">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="6814473935-14">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="6814473935-14">}</span><span class="p">,</span><span class="w">
│ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_client.erl----</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% The client process which runs on each user node</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2173589799-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="2173589799-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2173589799-2">(</span><span class="p" data-group-id="2173589799-3">[</span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2173589799-3">]</span><span class="p" data-group-id="2173589799-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2173589799-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="2173589799-4">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="2173589799-5">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2173589799-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2173589799-6">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="2173589799-6">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="2173589799-7">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="2173589799-8">(</span><span class="p" data-group-id="2173589799-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="2173589799-7">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="2173589799-9">(</span><span class="p" data-group-id="2173589799-9">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="2173589799-10">(</span><span class="n">Server_Node</span><span class="p" data-group-id="2173589799-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1226690915-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="1226690915-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1226690915-2">(</span><span class="p" data-group-id="1226690915-3">[</span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1226690915-3">]</span><span class="p" data-group-id="1226690915-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1226690915-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="1226690915-4">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="1226690915-5">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="1226690915-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1226690915-6">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="1226690915-6">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="1226690915-7">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="1226690915-8">(</span><span class="p" data-group-id="1226690915-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="1226690915-7">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="1226690915-9">(</span><span class="p" data-group-id="1226690915-9">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="1226690915-10">(</span><span class="n">Server_Node</span><span class="p" data-group-id="1226690915-10">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="2173589799-11">(</span><span class="n">Server_Node</span><span class="p" data-group-id="2173589799-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="1226690915-11">(</span><span class="n">Server_Node</span><span class="p" data-group-id="1226690915-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="2173589799-12">(</span><span class="ss">normal</span><span class="p" data-group-id="2173589799-12">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="2173589799-13">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="2173589799-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="2173589799-14">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="2173589799-14">}</span><span class="w"> </span><span class="o">!</span><span class="w">
│ │ │ -                </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="2173589799-15">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="2173589799-16">(</span><span class="p" data-group-id="2173589799-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="2173589799-15">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="2173589799-17">(</span><span class="p" data-group-id="2173589799-17">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2173589799-18">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2173589799-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2173589799-19">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2173589799-20">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2173589799-20">]</span><span class="p" data-group-id="2173589799-19">)</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="1226690915-12">(</span><span class="ss">normal</span><span class="p" data-group-id="1226690915-12">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="1226690915-13">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="1226690915-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="1226690915-14">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="1226690915-14">}</span><span class="w"> </span><span class="o">!</span><span class="w">
│ │ │ +                </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="1226690915-15">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="1226690915-16">(</span><span class="p" data-group-id="1226690915-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="1226690915-15">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="1226690915-17">(</span><span class="p" data-group-id="1226690915-17">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="1226690915-18">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="1226690915-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1226690915-19">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1226690915-20">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="1226690915-20">]</span><span class="p" data-group-id="1226690915-19">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="2173589799-21">(</span><span class="n">Server_Node</span><span class="p" data-group-id="2173589799-21">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="1226690915-21">(</span><span class="n">Server_Node</span><span class="p" data-group-id="1226690915-21">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="2173589799-22">(</span><span class="p" data-group-id="2173589799-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="1226690915-22">(</span><span class="p" data-group-id="1226690915-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="2173589799-23">{</span><span class="ss">message</span><span class="o">=</span><span class="n">Why</span><span class="p" data-group-id="2173589799-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2173589799-24">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2173589799-25">[</span><span class="n">Why</span><span class="p" data-group-id="2173589799-25">]</span><span class="p" data-group-id="2173589799-24">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="2173589799-26">(</span><span class="ss">normal</span><span class="p" data-group-id="2173589799-26">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="2173589799-27">{</span><span class="ss">message</span><span class="o">=</span><span class="n">What</span><span class="p" data-group-id="2173589799-27">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2173589799-28">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2173589799-29">[</span><span class="n">What</span><span class="p" data-group-id="2173589799-29">]</span><span class="p" data-group-id="2173589799-28">)</span><span class="w">
│ │ │ +        </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="1226690915-23">{</span><span class="ss">message</span><span class="o">=</span><span class="n">Why</span><span class="p" data-group-id="1226690915-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1226690915-24">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1226690915-25">[</span><span class="n">Why</span><span class="p" data-group-id="1226690915-25">]</span><span class="p" data-group-id="1226690915-24">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="1226690915-26">(</span><span class="ss">normal</span><span class="p" data-group-id="1226690915-26">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="1226690915-27">{</span><span class="ss">message</span><span class="o">=</span><span class="n">What</span><span class="p" data-group-id="1226690915-27">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1226690915-28">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1226690915-29">[</span><span class="n">What</span><span class="p" data-group-id="1226690915-29">]</span><span class="p" data-group-id="1226690915-28">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2173589799-30">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2173589799-31">[</span><span class="p" data-group-id="2173589799-31">]</span><span class="p" data-group-id="2173589799-30">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="2173589799-32">(</span><span class="ss">timeout</span><span class="p" data-group-id="2173589799-32">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1226690915-30">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1226690915-31">[</span><span class="p" data-group-id="1226690915-31">]</span><span class="p" data-group-id="1226690915-30">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="1226690915-32">(</span><span class="ss">timeout</span><span class="p" data-group-id="1226690915-32">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%----END FILE---</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_server.erl----</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% This is the server process of the messenger service</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6717536042-1">(</span><span class="ss">mess_server</span><span class="p" data-group-id="6717536042-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6717536042-2">(</span><span class="p" data-group-id="6717536042-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6717536042-3">]</span><span class="p" data-group-id="6717536042-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="6717536042-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="6717536042-4">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="6717536042-5">(</span><span class="p" data-group-id="6717536042-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="6717536042-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6717536042-6">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="6717536042-7">(</span><span class="p" data-group-id="6717536042-8">[</span><span class="p" data-group-id="6717536042-8">]</span><span class="p" data-group-id="6717536042-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2656601192-1">(</span><span class="ss">mess_server</span><span class="p" data-group-id="2656601192-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2656601192-2">(</span><span class="p" data-group-id="2656601192-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2656601192-3">]</span><span class="p" data-group-id="2656601192-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2656601192-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="2656601192-4">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="2656601192-5">(</span><span class="p" data-group-id="2656601192-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="2656601192-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2656601192-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="2656601192-7">(</span><span class="p" data-group-id="2656601192-8">[</span><span class="p" data-group-id="2656601192-8">]</span><span class="p" data-group-id="2656601192-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="6717536042-9">(</span><span class="n">User_List</span><span class="p" data-group-id="6717536042-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6717536042-10">(</span><span class="s">&quot;User list = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6717536042-11">[</span><span class="n">User_List</span><span class="p" data-group-id="6717536042-11">]</span><span class="p" data-group-id="6717536042-10">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="2656601192-9">(</span><span class="n">User_List</span><span class="p" data-group-id="2656601192-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2656601192-10">(</span><span class="s">&quot;User list = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2656601192-11">[</span><span class="n">User_List</span><span class="p" data-group-id="2656601192-11">]</span><span class="p" data-group-id="2656601192-10">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="6717536042-12">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="6717536042-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="6717536042-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-13">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="6717536042-14">(</span><span class="n">New_User_List</span><span class="p" data-group-id="6717536042-14">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6717536042-15">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6717536042-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="6717536042-16">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-16">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="6717536042-17">(</span><span class="n">New_User_List</span><span class="p" data-group-id="6717536042-17">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="6717536042-18">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="6717536042-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="6717536042-19">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-19">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="6717536042-20">(</span><span class="n">User_List</span><span class="p" data-group-id="6717536042-20">)</span><span class="w">
│ │ │ +        </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="2656601192-12">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="2656601192-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="2656601192-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-13">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="2656601192-14">(</span><span class="n">New_User_List</span><span class="p" data-group-id="2656601192-14">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2656601192-15">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2656601192-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="2656601192-16">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-16">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="2656601192-17">(</span><span class="n">New_User_List</span><span class="p" data-group-id="2656601192-17">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="2656601192-18">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="2656601192-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="2656601192-19">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-19">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="2656601192-20">(</span><span class="n">User_List</span><span class="p" data-group-id="2656601192-20">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="6717536042-21">(</span><span class="p" data-group-id="6717536042-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="6717536042-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="6717536042-23">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6717536042-24">[</span><span class="p" data-group-id="6717536042-24">]</span><span class="p" data-group-id="6717536042-23">)</span><span class="p" data-group-id="6717536042-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="2656601192-21">(</span><span class="p" data-group-id="2656601192-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="2656601192-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2656601192-23">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2656601192-24">[</span><span class="p" data-group-id="2656601192-24">]</span><span class="p" data-group-id="2656601192-23">)</span><span class="p" data-group-id="2656601192-22">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="6717536042-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="2656601192-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="6717536042-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="2656601192-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="6717536042-27">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="6717536042-27">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="2656601192-27">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="2656601192-27">}</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="6717536042-28">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">logged_on</span><span class="p" data-group-id="6717536042-28">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">link</span><span class="p" data-group-id="6717536042-29">(</span><span class="n">From</span><span class="p" data-group-id="6717536042-29">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="6717536042-30">[</span><span class="p" data-group-id="6717536042-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6717536042-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="2656601192-28">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">logged_on</span><span class="p" data-group-id="2656601192-28">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">link</span><span class="p" data-group-id="2656601192-29">(</span><span class="n">From</span><span class="p" data-group-id="2656601192-29">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2656601192-30">[</span><span class="p" data-group-id="2656601192-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2656601192-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="6717536042-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="6717536042-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-33">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="2656601192-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="2656601192-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-33">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="6717536042-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="2656601192-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="6717536042-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="2656601192-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="6717536042-36">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="6717536042-36">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6717536042-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6717536042-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6717536042-38">}</span><span class="p" data-group-id="6717536042-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="6717536042-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-39">)</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="2656601192-36">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="2656601192-36">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2656601192-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2656601192-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2656601192-38">}</span><span class="p" data-group-id="2656601192-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="2656601192-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-39">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="6717536042-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="2656601192-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="6717536042-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6717536042-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="2656601192-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2656601192-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="6717536042-42">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">receiver_not_found</span><span class="p" data-group-id="6717536042-42">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6717536042-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6717536042-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="6717536042-44">}</span><span class="p" data-group-id="6717536042-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_from</span><span class="p" data-group-id="6717536042-45">{</span><span class="ss">from_name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="6717536042-45">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="6717536042-46">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">sent</span><span class="p" data-group-id="6717536042-46">}</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="2656601192-42">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">receiver_not_found</span><span class="p" data-group-id="2656601192-42">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2656601192-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2656601192-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="2656601192-44">}</span><span class="p" data-group-id="2656601192-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_from</span><span class="p" data-group-id="2656601192-45">{</span><span class="ss">from_name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="2656601192-45">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="2656601192-46">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">sent</span><span class="p" data-group-id="2656601192-46">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%----END FILE---</span></code></pre><h2 id="header-files" class="section-heading">
│ │ │    <a href="#header-files" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Header Files</span>
│ │ │  </h2>
│ │ │  <p>As shown above, some files have extension <code class="inline">.hrl</code>. These are header files that
│ │ │ -are included in the <code class="inline">.erl</code> files by:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2910214655-1">(</span><span class="s">&quot;File_Name&quot;</span><span class="p" data-group-id="2910214655-1">)</span><span class="p">.</span></code></pre><p>for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="9883267403-1">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="9883267403-1">)</span><span class="p">.</span></code></pre><p>In the case above the file is fetched from the same directory as all the other
│ │ │ +are included in the <code class="inline">.erl</code> files by:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="9133154261-1">(</span><span class="s">&quot;File_Name&quot;</span><span class="p" data-group-id="9133154261-1">)</span><span class="p">.</span></code></pre><p>for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="7845555148-1">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="7845555148-1">)</span><span class="p">.</span></code></pre><p>In the case above the file is fetched from the same directory as all the other
│ │ │  files in the messenger example. (<em>manual</em>).</p><p>.hrl files can contain any valid Erlang code but are most often used for record
│ │ │  and macro definitions.</p><h2 id="records" class="section-heading">
│ │ │    <a href="#records" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Records</span>
│ │ │  </h2>
│ │ │ -<p>A record is defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0895378529-1">(</span><span class="ss">name_of_record</span><span class="p">,</span><span class="p" data-group-id="0895378529-2">{</span><span class="ss">field_name1</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name2</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0895378529-2">}</span><span class="p" data-group-id="0895378529-1">)</span><span class="p">.</span></code></pre><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1122445693-1">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="1122445693-2">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="1122445693-2">}</span><span class="p" data-group-id="1122445693-1">)</span><span class="p">.</span></code></pre><p>This is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4417729274-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To_Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4417729274-1">}</span></code></pre><p>Creating a record is best illustrated by an example:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="6499011664-1">{</span><span class="ss">message</span><span class="o">=</span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="ss">fred</span><span class="p">)</span></code></pre><p>This creates:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3148932521-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="3148932521-1">}</span></code></pre><p>Notice that you do not have to worry about the order you assign values to the
│ │ │ +<p>A record is defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2140738275-1">(</span><span class="ss">name_of_record</span><span class="p">,</span><span class="p" data-group-id="2140738275-2">{</span><span class="ss">field_name1</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name2</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2140738275-2">}</span><span class="p" data-group-id="2140738275-1">)</span><span class="p">.</span></code></pre><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7102985182-1">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="7102985182-2">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="7102985182-2">}</span><span class="p" data-group-id="7102985182-1">)</span><span class="p">.</span></code></pre><p>This is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9570236988-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To_Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9570236988-1">}</span></code></pre><p>Creating a record is best illustrated by an example:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="4519722025-1">{</span><span class="ss">message</span><span class="o">=</span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="ss">fred</span><span class="p">)</span></code></pre><p>This creates:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3399228414-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="3399228414-1">}</span></code></pre><p>Notice that you do not have to worry about the order you assign values to the
│ │ │  various parts of the records when you create it. The advantage of using records
│ │ │  is that by placing their definitions in header files you can conveniently define
│ │ │  interfaces that are easy to change. For example, if you want to add a new field
│ │ │  to the record, you only have to change the code where the new field is used and
│ │ │  not at every place the record is referred to. If you leave out a field when
│ │ │  creating a record, it gets the value of the atom <code class="inline">undefined</code>. (<em>manual</em>)</p><p>Pattern matching with records is very similar to creating records. For example,
│ │ │ -inside a <code class="inline">case</code> or <code class="inline">receive</code>:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="1252235949-1">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="1252235949-1">}</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>This is the same as:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1624198512-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="1624198512-1">}</span></code></pre><h2 id="macros" class="section-heading">
│ │ │ +inside a <code class="inline">case</code> or <code class="inline">receive</code>:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="5009499940-1">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="5009499940-1">}</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>This is the same as:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1732734683-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="1732734683-1">}</span></code></pre><h2 id="macros" class="section-heading">
│ │ │    <a href="#macros" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Macros</span>
│ │ │  </h2>
│ │ │  <p>Another thing that has been added to the messenger is a macro. The file
│ │ │  <code class="inline">mess_config.hrl</code> contains the definition:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Configure the location of the server node,</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4382373937-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="4382373937-1">)</span><span class="p">.</span></code></pre><p>This file is included in <code class="inline">mess_server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="0311565072-1">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="0311565072-1">)</span><span class="p">.</span></code></pre><p>Every occurrence of <code class="inline">?server_node</code> in <code class="inline">mess_server.erl</code> is now replaced by
│ │ │ -<code class="inline">messenger@super</code>.</p><p>A macro is also used when spawning the server process:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="9522797925-1">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9522797925-2">[</span><span class="p" data-group-id="9522797925-2">]</span><span class="p" data-group-id="9522797925-1">)</span></code></pre><p>This is a standard macro (that is, defined by the system, not by the user).
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9031069262-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="9031069262-1">)</span><span class="p">.</span></code></pre><p>This file is included in <code class="inline">mess_server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4130310479-1">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="4130310479-1">)</span><span class="p">.</span></code></pre><p>Every occurrence of <code class="inline">?server_node</code> in <code class="inline">mess_server.erl</code> is now replaced by
│ │ │ +<code class="inline">messenger@super</code>.</p><p>A macro is also used when spawning the server process:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="3973844694-1">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3973844694-2">[</span><span class="p" data-group-id="3973844694-2">]</span><span class="p" data-group-id="3973844694-1">)</span></code></pre><p>This is a standard macro (that is, defined by the system, not by the user).
│ │ │  <code class="inline">?MODULE</code> is always replaced by the name of the current module (that is, the
│ │ │  <code class="inline">-module</code> definition near the start of the file). There are more advanced ways
│ │ │  of using macros with, for example, <a href="macros.html#defining-and-using-macros">parameters</a>.</p><p>The three Erlang (<code class="inline">.erl</code>) files in the messenger example are individually
│ │ │  compiled into object code file (<code class="inline">.beam</code>). The Erlang system loads and links
│ │ │  these files into the system when they are referred to during execution of the
│ │ │  code. In this case, they are simply put in our current working directory (that
│ │ │  is, the place you have done &quot;cd&quot; to). There are ways of putting the <code class="inline">.beam</code>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/ref_man_functions.html
│ │ │ @@ -120,51 +120,51 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Function Declaration Syntax</span>
│ │ │  </h2>
│ │ │  <p>A <em>function declaration</em> is a sequence of function clauses separated by
│ │ │  semicolons, and terminated by a period (<code class="inline">.</code>).</p><p>A <em>function clause</em> consists of a <em>clause head</em> and a <em>clause body</em>, separated by
│ │ │  <code class="inline">-&gt;</code>.</p><p>A clause <em>head</em> consists of the function name, an argument list, and an optional
│ │ │ -guard sequence beginning with the keyword <code class="inline">when</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="p" data-group-id="5759652623-1">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="5759652623-1">)</span><span class="w"> </span><span class="p" data-group-id="5759652623-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="5759652623-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +guard sequence beginning with the keyword <code class="inline">when</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="p" data-group-id="9783560582-1">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="9783560582-1">)</span><span class="w"> </span><span class="p" data-group-id="9783560582-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9783560582-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="n">Name</span><span class="p" data-group-id="5759652623-3">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="5759652623-3">)</span><span class="w"> </span><span class="p" data-group-id="5759652623-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="5759652623-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="n">Name</span><span class="p" data-group-id="9783560582-3">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="9783560582-3">)</span><span class="w"> </span><span class="p" data-group-id="9783560582-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="9783560582-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">BodyK</span><span class="p">.</span></code></pre><p>The function name is an atom. Each argument is a pattern.</p><p>The number of arguments <code class="inline">N</code> is the <em>arity</em> of the function. A function is
│ │ │  uniquely defined by the module name, function name, and arity. That is, two
│ │ │  functions with the same name and in the same module, but with different arities
│ │ │  are two different functions.</p><p>A function named <code class="inline">f</code> in module <code class="inline">mod</code> and with arity <code class="inline">N</code> is often denoted as
│ │ │  <code class="inline">mod:f/N</code>.</p><p>A clause <em>body</em> consists of a sequence of expressions separated by comma (<code class="inline">,</code>):</p><pre><code class="text">Expr1,
│ │ │  ...,
│ │ │  ExprN</code></pre><p>Valid Erlang expressions and guard sequences are described in
│ │ │ -<a href="expressions.html">Expressions</a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">fact</span><span class="p" data-group-id="2177040286-1">(</span><span class="n">N</span><span class="p" data-group-id="2177040286-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% first clause head</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="2177040286-2">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="2177040286-2">)</span><span class="p">;</span><span class="w">     </span><span class="c1">% first clause body</span><span class="w">
│ │ │ +<a href="expressions.html">Expressions</a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">fact</span><span class="p" data-group-id="7984442377-1">(</span><span class="n">N</span><span class="p" data-group-id="7984442377-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% first clause head</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="7984442377-2">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="7984442377-2">)</span><span class="p">;</span><span class="w">     </span><span class="c1">% first clause body</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="2177040286-3">(</span><span class="mi">0</span><span class="p" data-group-id="2177040286-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">             </span><span class="c1">% second clause head</span><span class="w">
│ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="7984442377-3">(</span><span class="mi">0</span><span class="p" data-group-id="7984442377-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">             </span><span class="c1">% second clause head</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">.</span><span class="w">                 </span><span class="c1">% second clause body</span></code></pre><p><a href="" id="eval"></a></p><h2 id="function-evaluation" class="section-heading">
│ │ │    <a href="#function-evaluation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Function Evaluation</span>
│ │ │  </h2>
│ │ │  <p>When a function <code class="inline">M:F/N</code> is called, first the code for the function is located.
│ │ │  If the function cannot be found, an <code class="inline">undef</code> runtime error occurs. Notice that
│ │ │  the function must be exported to be visible outside the module it is defined in.</p><p>If the function is found, the function clauses are scanned sequentially until a
│ │ │  clause is found that fulfills both of the following two conditions:</p><ol><li>The patterns in the clause head can be successfully matched against the given
│ │ │  arguments.</li><li>The guard sequence, if any, is true.</li></ol><p>If such a clause cannot be found, a <code class="inline">function_clause</code> runtime error occurs.</p><p>If such a clause is found, the corresponding clause body is evaluated. That is,
│ │ │  the expressions in the body are evaluated sequentially and the value of the last
│ │ │ -expression is returned.</p><p>Consider the function <code class="inline">fact</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0569805129-1">(</span><span class="ss">mod</span><span class="p" data-group-id="0569805129-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0569805129-2">(</span><span class="p" data-group-id="0569805129-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0569805129-3">]</span><span class="p" data-group-id="0569805129-2">)</span><span class="p">.</span><span class="w">
│ │ │ +expression is returned.</p><p>Consider the function <code class="inline">fact</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2588561857-1">(</span><span class="ss">mod</span><span class="p" data-group-id="2588561857-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2588561857-2">(</span><span class="p" data-group-id="2588561857-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2588561857-3">]</span><span class="p" data-group-id="2588561857-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="0569805129-4">(</span><span class="n">N</span><span class="p" data-group-id="0569805129-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="0569805129-5">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0569805129-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="0569805129-6">(</span><span class="mi">0</span><span class="p" data-group-id="0569805129-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="2588561857-4">(</span><span class="n">N</span><span class="p" data-group-id="2588561857-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="2588561857-5">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2588561857-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="2588561857-6">(</span><span class="mi">0</span><span class="p" data-group-id="2588561857-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">.</span></code></pre><p>Assume that you want to calculate the factorial for 1:</p><pre><code class="text">1&gt; mod:fact(1).</code></pre><p>Evaluation starts at the first clause. The pattern <code class="inline">N</code> is matched against
│ │ │  argument 1. The matching succeeds and the guard (<code class="inline">N &gt; 0</code>) is true, thus <code class="inline">N</code> is
│ │ │ -bound to 1, and the corresponding body is evaluated:</p><pre><code class="makeup erlang" translate="no"><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="3367389370-1">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="3367389370-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3367389370-2">(</span><span class="n">N</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">bound</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3367389370-2">)</span><span class="w">
│ │ │ -</span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="3367389370-3">(</span><span class="mi">0</span><span class="p" data-group-id="3367389370-3">)</span></code></pre><p>Now, <code class="inline">fact(0)</code> is called, and the function clauses are scanned
│ │ │ +bound to 1, and the corresponding body is evaluated:</p><pre><code class="makeup erlang" translate="no"><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="0596761519-1">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="0596761519-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0596761519-2">(</span><span class="n">N</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">bound</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0596761519-2">)</span><span class="w">
│ │ │ +</span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="0596761519-3">(</span><span class="mi">0</span><span class="p" data-group-id="0596761519-3">)</span></code></pre><p>Now, <code class="inline">fact(0)</code> is called, and the function clauses are scanned
│ │ │  sequentially again. First, the pattern <code class="inline">N</code> is matched against 0. The
│ │ │  matching succeeds, but the guard (<code class="inline">N &gt; 0</code>) is false. Second, the
│ │ │  pattern <code class="inline">0</code> is matched against the argument <code class="inline">0</code>. The matching succeeds
│ │ │  and the body is evaluated:</p><pre><code class="text">1 * fact(0) =&gt;
│ │ │  1 * 1 =&gt;
│ │ │  1</code></pre><p>Evaluation has succeed and <code class="inline">mod:fact(1)</code> returns 1.</p><p>If <code class="inline">mod:fact/1</code> is called with a negative number as argument, no clause head
│ │ │  matches. A <code class="inline">function_clause</code> runtime error occurs.</p><h2 id="tail-recursion" class="section-heading">
│ │ │ @@ -173,17 +173,17 @@
│ │ │    </a>
│ │ │    <span class="text">Tail recursion</span>
│ │ │  </h2>
│ │ │  <p>If the last expression of a function body is a function call, a
│ │ │  <em>tail-recursive call</em> is done. This is to ensure that no system
│ │ │  resources, for example, call stack, are consumed. This means that an
│ │ │  infinite loop using tail-recursive calls will not exhaust the call
│ │ │ -stack and can (in principle) run forever.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="9111385573-1">(</span><span class="n">N</span><span class="p" data-group-id="9111385573-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9111385573-2">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9111385573-3">[</span><span class="n">N</span><span class="p" data-group-id="9111385573-3">]</span><span class="p" data-group-id="9111385573-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="9111385573-4">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="9111385573-4">)</span><span class="p">.</span></code></pre><p>The earlier factorial example is a counter-example. It is not
│ │ │ +stack and can (in principle) run forever.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="7538810453-1">(</span><span class="n">N</span><span class="p" data-group-id="7538810453-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7538810453-2">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7538810453-3">[</span><span class="n">N</span><span class="p" data-group-id="7538810453-3">]</span><span class="p" data-group-id="7538810453-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="7538810453-4">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="7538810453-4">)</span><span class="p">.</span></code></pre><p>The earlier factorial example is a counter-example. It is not
│ │ │  tail-recursive, since a multiplication is done on the result of the recursive
│ │ │  call to <code class="inline">fact(N-1)</code>.</p><h2 id="built-in-functions-bifs" class="section-heading">
│ │ │    <a href="#built-in-functions-bifs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Built-In Functions (BIFs)</span>
│ │ │  </h2>
│ │ │ @@ -191,17 +191,17 @@
│ │ │  system. BIFs do things that are difficult or impossible to implement
│ │ │  in Erlang. Most of the BIFs belong to module <a href="../../erts-15.2.7/doc/html/erlang.html"><code class="inline">erlang</code></a>, but there
│ │ │  are also BIFs belonging to a few other modules, for example <a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html"><code class="inline">lists</code></a>
│ │ │  and <a href="../../lib/stdlib-6.2.2.1/doc/html/ets.html"><code class="inline">ets</code></a>.</p><p>The most commonly used BIFs belonging to <a href="../../erts-15.2.7/doc/html/erlang.html"><code class="inline">erlang</code></a> are <em>auto-imported</em>. They do
│ │ │  not need to be prefixed with the module name. Which BIFs that are auto-imported
│ │ │  is specified in the <a href="../../erts-15.2.7/doc/html/erlang.html"><code class="inline">erlang</code></a> module in ERTS. For example, standard-type
│ │ │  conversion BIFs like <code class="inline">atom_to_list</code> and BIFs allowed in guards can be called
│ │ │ -without specifying the module name.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="9372204681-1">(</span><span class="p" data-group-id="9372204681-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9372204681-2">}</span><span class="p" data-group-id="9372204681-1">)</span><span class="p">.</span><span class="w">
│ │ │ +without specifying the module name.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="9116515259-1">(</span><span class="p" data-group-id="9116515259-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9116515259-2">}</span><span class="p" data-group-id="9116515259-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="9372204681-3">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="9372204681-3">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="9116515259-3">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="9116515259-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;Erlang&quot;</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="documentation.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/ref_man_processes.html
│ │ │ @@ -125,18 +125,18 @@
│ │ │  (grow and shrink dynamically) with small memory footprint, fast to create and
│ │ │  terminate, and the scheduling overhead is low.</p><h2 id="process-creation" class="section-heading">
│ │ │    <a href="#process-creation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Process Creation</span>
│ │ │  </h2>
│ │ │ -<p>A process is created by calling <a href="../../erts-15.2.7/doc/html/erlang.html#spawn/3"><code class="inline">spawn()</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="5415438731-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="5415438731-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pid</span><span class="p" data-group-id="5415438731-2">(</span><span class="p" data-group-id="5415438731-2">)</span><span class="w">
│ │ │ -  </span><span class="n">Module</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="5415438731-3">(</span><span class="p" data-group-id="5415438731-3">)</span><span class="w">
│ │ │ -  </span><span class="n">Args</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5415438731-4">[</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="5415438731-4">]</span><span class="w">
│ │ │ -    </span><span class="n">ArgI</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="5415438731-5">(</span><span class="p" data-group-id="5415438731-5">)</span></code></pre><p><code class="inline">spawn()</code> creates a new process and returns the pid.</p><p>The new process starts executing in <code class="inline">Module:Name(Arg1,...,ArgN)</code> where the
│ │ │ +<p>A process is created by calling <a href="../../erts-15.2.7/doc/html/erlang.html#spawn/3"><code class="inline">spawn()</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="7825983199-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="7825983199-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pid</span><span class="p" data-group-id="7825983199-2">(</span><span class="p" data-group-id="7825983199-2">)</span><span class="w">
│ │ │ +  </span><span class="n">Module</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="7825983199-3">(</span><span class="p" data-group-id="7825983199-3">)</span><span class="w">
│ │ │ +  </span><span class="n">Args</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7825983199-4">[</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="7825983199-4">]</span><span class="w">
│ │ │ +    </span><span class="n">ArgI</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7825983199-5">(</span><span class="p" data-group-id="7825983199-5">)</span></code></pre><p><code class="inline">spawn()</code> creates a new process and returns the pid.</p><p>The new process starts executing in <code class="inline">Module:Name(Arg1,...,ArgN)</code> where the
│ │ │  arguments are the elements of the (possible empty) <code class="inline">Args</code> argument list.</p><p>There exist a number of different <code class="inline">spawn</code> BIFs:</p><ul><li><a href="../../erts-15.2.7/doc/html/erlang.html#spawn/4"><code class="inline">spawn/1,2,3,4</code></a></li><li><a href="../../erts-15.2.7/doc/html/erlang.html#spawn_link/4"><code class="inline">spawn_link/1,2,3,4</code></a></li><li><a href="../../erts-15.2.7/doc/html/erlang.html#spawn_monitor/4"><code class="inline">spawn_monitor/1,2,3,4</code></a></li><li><a href="../../erts-15.2.7/doc/html/erlang.html#spawn_opt/5"><code class="inline">spawn_opt/2,3,4,5</code></a></li><li><a href="../../erts-15.2.7/doc/html/erlang.html#spawn_request/5"><code class="inline">spawn_request/1,2,3,4,5</code></a></li></ul><h2 id="registered-processes" class="section-heading">
│ │ │    <a href="#registered-processes" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Registered Processes</span>
│ │ │  </h2>
│ │ │  <p>Besides addressing a process by using its pid, there are also BIFs for
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/ref_man_records.html
│ │ │ @@ -123,17 +123,17 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Defining Records</span>
│ │ │  </h2>
│ │ │  <p>A record definition consists of the name of the record, followed by the field
│ │ │  names of the record. Record and field names must be atoms. Each field can be
│ │ │  given an optional default value. If no default value is supplied, <code class="inline">undefined</code> is
│ │ │ -used.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2396366860-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2396366860-2">{</span><span class="n">Field1</span><span class="w"> </span><span class="p" data-group-id="2396366860-3">[</span><span class="o">=</span><span class="w"> </span><span class="n">Expr1</span><span class="p" data-group-id="2396366860-3">]</span><span class="p">,</span><span class="w">
│ │ │ +used.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6434930018-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6434930018-2">{</span><span class="n">Field1</span><span class="w"> </span><span class="p" data-group-id="6434930018-3">[</span><span class="o">=</span><span class="w"> </span><span class="n">Expr1</span><span class="p" data-group-id="6434930018-3">]</span><span class="p">,</span><span class="w">
│ │ │                 </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -               </span><span class="n">FieldN</span><span class="w"> </span><span class="p" data-group-id="2396366860-4">[</span><span class="o">=</span><span class="w"> </span><span class="n">ExprN</span><span class="p" data-group-id="2396366860-4">]</span><span class="p" data-group-id="2396366860-2">}</span><span class="p" data-group-id="2396366860-1">)</span><span class="p">.</span></code></pre><p>The default value for a field is an arbitrary expression, except that it must
│ │ │ +               </span><span class="n">FieldN</span><span class="w"> </span><span class="p" data-group-id="6434930018-4">[</span><span class="o">=</span><span class="w"> </span><span class="n">ExprN</span><span class="p" data-group-id="6434930018-4">]</span><span class="p" data-group-id="6434930018-2">}</span><span class="p" data-group-id="6434930018-1">)</span><span class="p">.</span></code></pre><p>The default value for a field is an arbitrary expression, except that it must
│ │ │  not use any variables.</p><p>A record definition can be placed anywhere among the attributes and function
│ │ │  declarations of a module, but the definition must come before any usage of the
│ │ │  record.</p><p>If a record is used in several modules, it is recommended that the record
│ │ │  definition is placed in an include file.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Starting from Erlang/OTP 26, records can be defined in the Erlang shell
│ │ │  using the syntax described in this section. In earlier releases, it was
│ │ │  necessary to use the <a href="../../lib/stdlib-6.2.2.1/doc/html/shell.html"><code class="inline">shell</code></a> built-in function <code class="inline">rd/2</code>.</p></section><h2 id="creating-records" class="section-heading">
│ │ │    <a href="#creating-records" class="hover-link">
│ │ │ @@ -143,32 +143,32 @@
│ │ │  </h2>
│ │ │  <p>The following expression creates a new <code class="inline">Name</code> record where the value of each
│ │ │  field <code class="inline">FieldI</code> is the value of evaluating the corresponding expression <code class="inline">ExprI</code>:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p>The fields can be in any order, not necessarily the same order as in the record
│ │ │  definition, and fields can be omitted. Omitted fields get their respective
│ │ │  default value instead.</p><p>If several fields are to be assigned the same value, the following construction
│ │ │  can be used:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK, _=ExprL}</code></pre><p>Omitted fields then get the value of evaluating <code class="inline">ExprL</code> instead of their default
│ │ │  values. This feature is primarily intended to be used to create patterns for ETS
│ │ │ -and Mnesia match functions.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3757716629-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3757716629-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="3757716629-2">}</span><span class="p" data-group-id="3757716629-1">)</span><span class="p">.</span><span class="w">
│ │ │ +and Mnesia match functions.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5654232229-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5654232229-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="5654232229-2">}</span><span class="p" data-group-id="5654232229-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="3757716629-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="3757716629-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="3757716629-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3757716629-5">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="3757716629-5">}</span><span class="p" data-group-id="3757716629-4">)</span><span class="p">.</span></code></pre><h2 id="accessing-record-fields" class="section-heading">
│ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="5654232229-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="5654232229-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="5654232229-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5654232229-5">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="5654232229-5">}</span><span class="p" data-group-id="5654232229-4">)</span><span class="p">.</span></code></pre><h2 id="accessing-record-fields" class="section-heading">
│ │ │    <a href="#accessing-record-fields" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Accessing Record Fields</span>
│ │ │  </h2>
│ │ │  <pre><code class="text">Expr#Name.Field</code></pre><p>Returns the value of the specified field. <code class="inline">Expr</code> is to evaluate to a <code class="inline">Name</code>
│ │ │ -record.</p><p><em>Example</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3190297260-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3190297260-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="3190297260-2">}</span><span class="p" data-group-id="3190297260-1">)</span><span class="p">.</span><span class="w">
│ │ │ +record.</p><p><em>Example</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0104985023-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0104985023-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="0104985023-2">}</span><span class="p" data-group-id="0104985023-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">get_person_name</span><span class="p" data-group-id="3190297260-3">(</span><span class="n">Person</span><span class="p" data-group-id="3190297260-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">get_person_name</span><span class="p" data-group-id="0104985023-3">(</span><span class="n">Person</span><span class="p" data-group-id="0104985023-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">.</span></code></pre><p>The following expression returns the position of the specified field in the
│ │ │ -tuple representation of the record:</p><pre><code class="text">#Name.Field</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1065523441-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1065523441-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="1065523441-2">}</span><span class="p" data-group-id="1065523441-1">)</span><span class="p">.</span><span class="w">
│ │ │ +tuple representation of the record:</p><pre><code class="text">#Name.Field</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4972301692-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4972301692-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="4972301692-2">}</span><span class="p" data-group-id="4972301692-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="1065523441-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1065523441-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="1065523441-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1065523441-4">)</span><span class="p">.</span></code></pre><h2 id="updating-records" class="section-heading">
│ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="4972301692-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="4972301692-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="4972301692-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="4972301692-4">)</span><span class="p">.</span></code></pre><h2 id="updating-records" class="section-heading">
│ │ │    <a href="#updating-records" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Updating Records</span>
│ │ │  </h2>
│ │ │  <pre><code class="text">Expr#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p><code class="inline">Expr</code> is to evaluate to a <code class="inline">Name</code> record. A copy of this record is returned,
│ │ │  with the value of each specified field <code class="inline">FieldI</code> changed to the value of
│ │ │ @@ -178,51 +178,51 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Records in Guards</span>
│ │ │  </h2>
│ │ │  <p>Since record expressions are expanded to tuple expressions, creating
│ │ │  records and accessing record fields are allowed in guards. However,
│ │ │  all subexpressions (for initializing fields), must be valid guard
│ │ │ -expressions as well.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="1106461426-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1106461426-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Msg</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">#</span><span class="ss">msg</span><span class="p" data-group-id="1106461426-2">{</span><span class="ss">to</span><span class="o">=</span><span class="ss">void</span><span class="p">,</span><span class="w"> </span><span class="ss">no</span><span class="o">=</span><span class="mi">3</span><span class="p" data-group-id="1106461426-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +expressions as well.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="7902508965-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7902508965-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Msg</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">#</span><span class="ss">msg</span><span class="p" data-group-id="7902508965-2">{</span><span class="ss">to</span><span class="o">=</span><span class="ss">void</span><span class="p">,</span><span class="w"> </span><span class="ss">no</span><span class="o">=</span><span class="mi">3</span><span class="p" data-group-id="7902508965-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle</span><span class="p" data-group-id="1106461426-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1106461426-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">running</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>There is also a type test BIF <a href="../../erts-15.2.7/doc/html/erlang.html#is_record/2"><code class="inline">is_record(Term, RecordTag)</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_person</span><span class="p" data-group-id="5417859802-1">(</span><span class="n">P</span><span class="p" data-group-id="5417859802-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="5417859802-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="5417859802-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle</span><span class="p" data-group-id="7902508965-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7902508965-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">running</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>There is also a type test BIF <a href="../../erts-15.2.7/doc/html/erlang.html#is_record/2"><code class="inline">is_record(Term, RecordTag)</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_person</span><span class="p" data-group-id="2427608258-1">(</span><span class="n">P</span><span class="p" data-group-id="2427608258-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="2427608258-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="2427608258-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">is_person</span><span class="p" data-group-id="5417859802-3">(</span><span class="p">_</span><span class="n">P</span><span class="p" data-group-id="5417859802-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">is_person</span><span class="p" data-group-id="2427608258-3">(</span><span class="p">_</span><span class="n">P</span><span class="p" data-group-id="2427608258-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">false</span><span class="p">.</span></code></pre><h2 id="records-in-patterns" class="section-heading">
│ │ │    <a href="#records-in-patterns" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Records in Patterns</span>
│ │ │  </h2>
│ │ │  <p>A pattern that matches a certain record is created in the same way as a record
│ │ │  is created:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p>In this case, one or more of <code class="inline">Expr1</code> ... <code class="inline">ExprK</code> can be unbound variables.</p><h2 id="nested-records" class="section-heading">
│ │ │    <a href="#nested-records" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Nested Records</span>
│ │ │  </h2>
│ │ │ -<p>Assume the following record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8745397601-1">(</span><span class="ss">nrec0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8745397601-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested0&quot;</span><span class="p" data-group-id="8745397601-2">}</span><span class="p" data-group-id="8745397601-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8745397601-3">(</span><span class="ss">nrec1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8745397601-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec0</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec0</span><span class="p" data-group-id="8745397601-5">{</span><span class="p" data-group-id="8745397601-5">}</span><span class="p" data-group-id="8745397601-4">}</span><span class="p" data-group-id="8745397601-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8745397601-6">(</span><span class="ss">nrec2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8745397601-7">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested2&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec1</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec1</span><span class="p" data-group-id="8745397601-8">{</span><span class="p" data-group-id="8745397601-8">}</span><span class="p" data-group-id="8745397601-7">}</span><span class="p" data-group-id="8745397601-6">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Assume the following record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6071360381-1">(</span><span class="ss">nrec0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6071360381-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested0&quot;</span><span class="p" data-group-id="6071360381-2">}</span><span class="p" data-group-id="6071360381-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6071360381-3">(</span><span class="ss">nrec1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6071360381-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec0</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec0</span><span class="p" data-group-id="6071360381-5">{</span><span class="p" data-group-id="6071360381-5">}</span><span class="p" data-group-id="6071360381-4">}</span><span class="p" data-group-id="6071360381-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6071360381-6">(</span><span class="ss">nrec2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6071360381-7">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested2&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec1</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec1</span><span class="p" data-group-id="6071360381-8">{</span><span class="p" data-group-id="6071360381-8">}</span><span class="p" data-group-id="6071360381-7">}</span><span class="p" data-group-id="6071360381-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">N2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">nrec2</span><span class="p" data-group-id="8745397601-9">{</span><span class="p" data-group-id="8745397601-9">}</span><span class="p">,</span></code></pre><p>Accessing or updating nested records can be written without parentheses:</p><pre><code class="text">&quot;nested0&quot; = N2#nrec2.nrec1#nrec1.nrec0#nrec0.name,
│ │ │ +</span><span class="n">N2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">nrec2</span><span class="p" data-group-id="6071360381-9">{</span><span class="p" data-group-id="6071360381-9">}</span><span class="p">,</span></code></pre><p>Accessing or updating nested records can be written without parentheses:</p><pre><code class="text">&quot;nested0&quot; = N2#nrec2.nrec1#nrec1.nrec0#nrec0.name,
│ │ │      N0n = N2#nrec2.nrec1#nrec1.nrec0#nrec0{name = &quot;nested0a&quot;},</code></pre><p>which is equivalent to:</p><pre><code class="text">&quot;nested0&quot; = ((N2#nrec2.nrec1)#nrec1.nrec0)#nrec0.name,
│ │ │  N0n = ((N2#nrec2.nrec1)#nrec1.nrec0)#nrec0{name = &quot;nested0a&quot;},</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R14, parentheses were necessary when accessing or updating
│ │ │  nested records.</p></section><h2 id="internal-representation-of-records" class="section-heading">
│ │ │    <a href="#internal-representation-of-records" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Internal Representation of Records</span>
│ │ │  </h2>
│ │ │  <p>Record expressions are translated to tuple expressions during compilation. A
│ │ │ -record defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5596442042-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5596442042-2">{</span><span class="n">Field1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">FieldN</span><span class="p" data-group-id="5596442042-2">}</span><span class="p" data-group-id="5596442042-1">)</span><span class="p">.</span></code></pre><p>is internally represented by the tuple:</p><pre><code class="text">{Name, Value1, ..., ValueN}</code></pre><p>Here each <code class="inline">ValueI</code> is the default value for <code class="inline">FieldI</code>.</p><p>To each module using records, a pseudo function is added during compilation to
│ │ │ -obtain information about records:</p><pre><code class="makeup erlang" translate="no"><span class="nf">record_info</span><span class="p" data-group-id="8649510987-1">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="8649510987-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8649510987-2">[</span><span class="n">Field</span><span class="p" data-group-id="8649510987-2">]</span><span class="w">
│ │ │ -</span><span class="nf">record_info</span><span class="p" data-group-id="8649510987-3">(</span><span class="nb">size</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="8649510987-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Size</span></code></pre><p><code class="inline">Size</code> is the size of the tuple representation, that is, one more than the
│ │ │ +record defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1849260745-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1849260745-2">{</span><span class="n">Field1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">FieldN</span><span class="p" data-group-id="1849260745-2">}</span><span class="p" data-group-id="1849260745-1">)</span><span class="p">.</span></code></pre><p>is internally represented by the tuple:</p><pre><code class="text">{Name, Value1, ..., ValueN}</code></pre><p>Here each <code class="inline">ValueI</code> is the default value for <code class="inline">FieldI</code>.</p><p>To each module using records, a pseudo function is added during compilation to
│ │ │ +obtain information about records:</p><pre><code class="makeup erlang" translate="no"><span class="nf">record_info</span><span class="p" data-group-id="2417658686-1">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="2417658686-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2417658686-2">[</span><span class="n">Field</span><span class="p" data-group-id="2417658686-2">]</span><span class="w">
│ │ │ +</span><span class="nf">record_info</span><span class="p" data-group-id="2417658686-3">(</span><span class="nb">size</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="2417658686-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Size</span></code></pre><p><code class="inline">Size</code> is the size of the tuple representation, that is, one more than the
│ │ │  number of fields.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="macros.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/release_handling.html
│ │ │ @@ -223,38 +223,38 @@
│ │ │    <span class="text">update</span>
│ │ │  </h3>
│ │ │  <p>If a more complex change has been made, for example, a change to the format of
│ │ │  the internal state of a <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html"><code class="inline">gen_server</code></a>, simple code replacement is not sufficient.
│ │ │  Instead, it is necessary to:</p><ul><li>Suspend the processes using the module (to avoid that they try to handle any
│ │ │  requests before the code replacement is completed).</li><li>Ask them to transform the internal state format and switch to the new version
│ │ │  of the module.</li><li>Remove the old version.</li><li>Resume the processes.</li></ul><p>This is called <em>synchronized code replacement</em> and for this the following
│ │ │ -instructions are used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1557234453-1">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1557234453-2">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="1557234453-2">}</span><span class="p" data-group-id="1557234453-1">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1557234453-3">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="1557234453-3">}</span></code></pre><p><code class="inline">update</code> with argument <code class="inline">{advanced,Extra}</code> is used when changing the internal
│ │ │ +instructions are used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7501676836-1">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7501676836-2">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="7501676836-2">}</span><span class="p" data-group-id="7501676836-1">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7501676836-3">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7501676836-3">}</span></code></pre><p><code class="inline">update</code> with argument <code class="inline">{advanced,Extra}</code> is used when changing the internal
│ │ │  state of a behaviour as described above. It causes behaviour processes to call
│ │ │  the callback function <code class="inline">code_change/3</code>, passing the term <code class="inline">Extra</code> and some other
│ │ │  information as arguments. See the manual pages for the respective behaviours and
│ │ │  <a href="appup_cookbook.html#int_state">Appup Cookbook</a>.</p><p><code class="inline">update</code> with argument <code class="inline">supervisor</code> is used when changing the start
│ │ │  specification of a supervisor. See <a href="appup_cookbook.html#sup">Appup Cookbook</a>.</p><p>When a module is to be updated, the release handler finds which processes that
│ │ │  are <em>using</em> the module by traversing the supervision tree of each running
│ │ │ -application and checking all the child specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9866849145-1">{</span><span class="n">Id</span><span class="p">,</span><span class="w"> </span><span class="n">StartFunc</span><span class="p">,</span><span class="w"> </span><span class="n">Restart</span><span class="p">,</span><span class="w"> </span><span class="n">Shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Modules</span><span class="p" data-group-id="9866849145-1">}</span></code></pre><p>A process uses a module if the name is listed in <code class="inline">Modules</code> in the child
│ │ │ +application and checking all the child specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8184684487-1">{</span><span class="n">Id</span><span class="p">,</span><span class="w"> </span><span class="n">StartFunc</span><span class="p">,</span><span class="w"> </span><span class="n">Restart</span><span class="p">,</span><span class="w"> </span><span class="n">Shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Modules</span><span class="p" data-group-id="8184684487-1">}</span></code></pre><p>A process uses a module if the name is listed in <code class="inline">Modules</code> in the child
│ │ │  specification for the process.</p><p>If <code class="inline">Modules=dynamic</code>, which is the case for event managers, the event manager
│ │ │  process informs the release handler about the list of currently installed event
│ │ │  handlers (<code class="inline">gen_event</code>), and it is checked if the module name is in this list
│ │ │  instead.</p><p>The release handler suspends, asks for code change, and resumes processes by
│ │ │  calling the functions <code class="inline">sys:suspend/1,2</code>, <code class="inline">sys:change_code/4,5</code>, and
│ │ │  <code class="inline">sys:resume/1,2</code>, respectively.</p><h3 id="add_module-and-delete_module" class="section-heading">
│ │ │    <a href="#add_module-and-delete_module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">add_module and delete_module</span>
│ │ │  </h3>
│ │ │ -<p>If a new module is introduced, the following instruction is used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4769803714-1">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="4769803714-1">}</span></code></pre><p>This instruction loads module <code class="inline">Module</code>. When running Erlang in
│ │ │ +<p>If a new module is introduced, the following instruction is used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2857120277-1">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2857120277-1">}</span></code></pre><p>This instruction loads module <code class="inline">Module</code>. When running Erlang in
│ │ │  embedded mode it is necessary to use this this instruction. It is not
│ │ │  strictly required when running Erlang in interactive mode, since the
│ │ │ -code server automatically searches for and loads unloaded modules.</p><p>The opposite of <code class="inline">add_module</code> is <code class="inline">delete_module</code>, which unloads a module:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6725814316-1">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="6725814316-1">}</span></code></pre><p>Any process, in any application, with <code class="inline">Module</code> as residence module, is
│ │ │ +code server automatically searches for and loads unloaded modules.</p><p>The opposite of <code class="inline">add_module</code> is <code class="inline">delete_module</code>, which unloads a module:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9897033439-1">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="9897033439-1">}</span></code></pre><p>Any process, in any application, with <code class="inline">Module</code> as residence module, is
│ │ │  killed when the instruction is evaluated. Therefore, the user must
│ │ │  ensure that all such processes are terminated before deleting module
│ │ │  <code class="inline">Module</code> to avoid a situation with failing supervisor restarts.</p><h3 id="application-instructions" class="section-heading">
│ │ │    <a href="#application-instructions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Application Instructions</span>
│ │ │ @@ -341,60 +341,60 @@
│ │ │  <code class="inline">.app</code> file.</li><li>Each <code class="inline">UpFromVsn</code> is a previous version of the application to upgrade from.</li><li>Each <code class="inline">DownToVsn</code> is a previous version of the application to downgrade to.</li><li>Each <code class="inline">Instructions</code> is a list of release handling instructions.</li></ul><p><code class="inline">UpFromVsn</code> and <code class="inline">DownToVsn</code> can also be specified as regular expressions. For
│ │ │  more information about the syntax and contents of the <code class="inline">.appup</code> file, see
│ │ │  <a href="../../lib/sasl-4.2.2/doc/html/appup.html"><code class="inline">appup</code></a> in SASL.</p><p><a href="appup_cookbook.html">Appup Cookbook</a> includes examples of <code class="inline">.appup</code> files for
│ │ │  typical upgrade/downgrade cases.</p><p><em>Example:</em> Consider the release <code class="inline">ch_rel-1</code> from
│ │ │  <a href="release_structure.html#ch_rel">Releases</a>. Assume you want to add a function
│ │ │  <code class="inline">available/0</code> to server <code class="inline">ch3</code>, which returns the number of available channels
│ │ │  (when trying out the example, make the change in a copy of the original
│ │ │ -directory, to ensure that the first version is still available):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7785181626-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="7785181626-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="7785181626-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="7785181626-2">)</span><span class="p">.</span><span class="w">
│ │ │ +directory, to ensure that the first version is still available):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8901207272-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="8901207272-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8901207272-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="8901207272-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7785181626-3">(</span><span class="p" data-group-id="7785181626-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7785181626-4">]</span><span class="p" data-group-id="7785181626-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7785181626-5">(</span><span class="p" data-group-id="7785181626-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7785181626-6">]</span><span class="p" data-group-id="7785181626-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7785181626-7">(</span><span class="p" data-group-id="7785181626-8">[</span><span class="ss">available</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7785181626-8">]</span><span class="p" data-group-id="7785181626-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7785181626-9">(</span><span class="p" data-group-id="7785181626-10">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7785181626-10">]</span><span class="p" data-group-id="7785181626-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8901207272-3">(</span><span class="p" data-group-id="8901207272-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8901207272-4">]</span><span class="p" data-group-id="8901207272-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8901207272-5">(</span><span class="p" data-group-id="8901207272-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8901207272-6">]</span><span class="p" data-group-id="8901207272-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8901207272-7">(</span><span class="p" data-group-id="8901207272-8">[</span><span class="ss">available</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8901207272-8">]</span><span class="p" data-group-id="8901207272-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8901207272-9">(</span><span class="p" data-group-id="8901207272-10">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8901207272-10">]</span><span class="p" data-group-id="8901207272-9">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="7785181626-11">(</span><span class="p" data-group-id="7785181626-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="7785181626-12">(</span><span class="p" data-group-id="7785181626-13">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7785181626-13">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7785181626-14">[</span><span class="p" data-group-id="7785181626-14">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7785181626-15">[</span><span class="p" data-group-id="7785181626-15">]</span><span class="p" data-group-id="7785181626-12">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="8901207272-11">(</span><span class="p" data-group-id="8901207272-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8901207272-12">(</span><span class="p" data-group-id="8901207272-13">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8901207272-13">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8901207272-14">[</span><span class="p" data-group-id="8901207272-14">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8901207272-15">[</span><span class="p" data-group-id="8901207272-15">]</span><span class="p" data-group-id="8901207272-12">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="7785181626-16">(</span><span class="p" data-group-id="7785181626-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="7785181626-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="7785181626-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="8901207272-16">(</span><span class="p" data-group-id="8901207272-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="8901207272-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="8901207272-17">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="7785181626-18">(</span><span class="n">Ch</span><span class="p" data-group-id="7785181626-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="7785181626-19">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7785181626-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7785181626-20">}</span><span class="p" data-group-id="7785181626-19">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="8901207272-18">(</span><span class="n">Ch</span><span class="p" data-group-id="8901207272-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8901207272-19">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8901207272-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8901207272-20">}</span><span class="p" data-group-id="8901207272-19">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">available</span><span class="p" data-group-id="7785181626-21">(</span><span class="p" data-group-id="7785181626-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="7785181626-22">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">available</span><span class="p" data-group-id="7785181626-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">available</span><span class="p" data-group-id="8901207272-21">(</span><span class="p" data-group-id="8901207272-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="8901207272-22">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">available</span><span class="p" data-group-id="8901207272-22">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="7785181626-23">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="7785181626-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7785181626-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="7785181626-25">(</span><span class="p" data-group-id="7785181626-25">)</span><span class="p" data-group-id="7785181626-24">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8901207272-23">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="8901207272-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8901207272-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="8901207272-25">(</span><span class="p" data-group-id="8901207272-25">)</span><span class="p" data-group-id="8901207272-24">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="7785181626-26">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7785181626-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7785181626-27">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="7785181626-27">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="7785181626-28">(</span><span class="n">Chs</span><span class="p" data-group-id="7785181626-28">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7785181626-29">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="7785181626-29">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="7785181626-30">(</span><span class="ss">available</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7785181626-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">available</span><span class="p" data-group-id="7785181626-31">(</span><span class="n">Chs</span><span class="p" data-group-id="7785181626-31">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7785181626-32">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7785181626-32">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="8901207272-26">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8901207272-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8901207272-27">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="8901207272-27">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="8901207272-28">(</span><span class="n">Chs</span><span class="p" data-group-id="8901207272-28">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8901207272-29">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="8901207272-29">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="8901207272-30">(</span><span class="ss">available</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8901207272-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">available</span><span class="p" data-group-id="8901207272-31">(</span><span class="n">Chs</span><span class="p" data-group-id="8901207272-31">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8901207272-32">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8901207272-32">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="7785181626-33">(</span><span class="p" data-group-id="7785181626-34">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7785181626-34">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7785181626-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="7785181626-35">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7785181626-35">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7785181626-36">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="7785181626-36">}</span><span class="p">.</span></code></pre><p>A new version of the <code class="inline">ch_app.app</code> file must now be created, where the version is
│ │ │ -updated:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8598079989-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8598079989-2">[</span><span class="p" data-group-id="8598079989-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="8598079989-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8598079989-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="8598079989-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8598079989-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598079989-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8598079989-6">]</span><span class="p" data-group-id="8598079989-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8598079989-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598079989-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="8598079989-8">]</span><span class="p" data-group-id="8598079989-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8598079989-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598079989-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="8598079989-10">]</span><span class="p" data-group-id="8598079989-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8598079989-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598079989-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="8598079989-13">[</span><span class="p" data-group-id="8598079989-13">]</span><span class="p" data-group-id="8598079989-12">}</span><span class="p" data-group-id="8598079989-11">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8598079989-2">]</span><span class="p" data-group-id="8598079989-1">}</span><span class="p">.</span></code></pre><p>To upgrade <code class="inline">ch_app</code> from <code class="inline">&quot;1&quot;</code> to <code class="inline">&quot;2&quot;</code> (and to downgrade from <code class="inline">&quot;2&quot;</code> to <code class="inline">&quot;1&quot;</code>),
│ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="8901207272-33">(</span><span class="p" data-group-id="8901207272-34">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8901207272-34">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8901207272-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="8901207272-35">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8901207272-35">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8901207272-36">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="8901207272-36">}</span><span class="p">.</span></code></pre><p>A new version of the <code class="inline">ch_app.app</code> file must now be created, where the version is
│ │ │ +updated:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4560684867-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4560684867-2">[</span><span class="p" data-group-id="4560684867-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="4560684867-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4560684867-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="4560684867-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4560684867-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4560684867-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="4560684867-6">]</span><span class="p" data-group-id="4560684867-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4560684867-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4560684867-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="4560684867-8">]</span><span class="p" data-group-id="4560684867-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4560684867-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4560684867-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="4560684867-10">]</span><span class="p" data-group-id="4560684867-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4560684867-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4560684867-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="4560684867-13">[</span><span class="p" data-group-id="4560684867-13">]</span><span class="p" data-group-id="4560684867-12">}</span><span class="p" data-group-id="4560684867-11">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4560684867-2">]</span><span class="p" data-group-id="4560684867-1">}</span><span class="p">.</span></code></pre><p>To upgrade <code class="inline">ch_app</code> from <code class="inline">&quot;1&quot;</code> to <code class="inline">&quot;2&quot;</code> (and to downgrade from <code class="inline">&quot;2&quot;</code> to <code class="inline">&quot;1&quot;</code>),
│ │ │  you only need to load the new (old) version of the <code class="inline">ch3</code> callback module. Create
│ │ │ -the application upgrade file <code class="inline">ch_app.appup</code> in the <code class="inline">ebin</code> directory:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0784404099-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0784404099-2">[</span><span class="p" data-group-id="0784404099-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0784404099-4">[</span><span class="p" data-group-id="0784404099-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0784404099-5">}</span><span class="p" data-group-id="0784404099-4">]</span><span class="p" data-group-id="0784404099-3">}</span><span class="p" data-group-id="0784404099-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0784404099-6">[</span><span class="p" data-group-id="0784404099-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0784404099-8">[</span><span class="p" data-group-id="0784404099-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0784404099-9">}</span><span class="p" data-group-id="0784404099-8">]</span><span class="p" data-group-id="0784404099-7">}</span><span class="p" data-group-id="0784404099-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0784404099-1">}</span><span class="p">.</span></code></pre><p><a href="" id="relup"></a></p><h2 id="release-upgrade-file" class="section-heading">
│ │ │ +the application upgrade file <code class="inline">ch_app.appup</code> in the <code class="inline">ebin</code> directory:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7671308979-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7671308979-2">[</span><span class="p" data-group-id="7671308979-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7671308979-4">[</span><span class="p" data-group-id="7671308979-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7671308979-5">}</span><span class="p" data-group-id="7671308979-4">]</span><span class="p" data-group-id="7671308979-3">}</span><span class="p" data-group-id="7671308979-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7671308979-6">[</span><span class="p" data-group-id="7671308979-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7671308979-8">[</span><span class="p" data-group-id="7671308979-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7671308979-9">}</span><span class="p" data-group-id="7671308979-8">]</span><span class="p" data-group-id="7671308979-7">}</span><span class="p" data-group-id="7671308979-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7671308979-1">}</span><span class="p">.</span></code></pre><p><a href="" id="relup"></a></p><h2 id="release-upgrade-file" class="section-heading">
│ │ │    <a href="#release-upgrade-file" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Release Upgrade File</span>
│ │ │  </h2>
│ │ │  <p>To define how to upgrade/downgrade between the new version and previous versions
│ │ │  of a release, a <em>release upgrade file</em>, or in short <code class="inline">.relup</code> file, is to be
│ │ │ @@ -405,22 +405,22 @@
│ │ │  are to be added and deleted, and which applications that must be upgraded and/or
│ │ │  downgraded. The instructions for this are fetched from the <code class="inline">.appup</code> files and
│ │ │  transformed into a single list of low-level instructions in the right order.</p><p>If the <code class="inline">relup</code> file is relatively simple, it can be created manually. It is only
│ │ │  to contain low-level instructions.</p><p>For details about the syntax and contents of the release upgrade file, see
│ │ │  <a href="../../lib/sasl-4.2.2/doc/html/relup.html"><code class="inline">relup</code></a> in SASL.</p><p><em>Example, continued from the previous section:</em> You have a new version &quot;2&quot; of
│ │ │  <code class="inline">ch_app</code> and an <code class="inline">.appup</code> file. A new version of the <code class="inline">.rel</code> file is also needed.
│ │ │  This time the file is called <code class="inline">ch_rel-2.rel</code> and the release version string is
│ │ │ -changed from &quot;A&quot; to &quot;B&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4165320226-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4165320226-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="4165320226-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4165320226-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="4165320226-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4165320226-4">[</span><span class="p" data-group-id="4165320226-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="4165320226-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4165320226-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="4165320226-6">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4165320226-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="4165320226-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4165320226-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="4165320226-8">}</span><span class="p" data-group-id="4165320226-4">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4165320226-1">}</span><span class="p">.</span></code></pre><p>Now the <code class="inline">relup</code> file can be generated:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;]).
│ │ │ +changed from &quot;A&quot; to &quot;B&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1540440681-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1540440681-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="1540440681-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1540440681-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="1540440681-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1540440681-4">[</span><span class="p" data-group-id="1540440681-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="1540440681-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1540440681-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="1540440681-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1540440681-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="1540440681-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1540440681-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="1540440681-8">}</span><span class="p" data-group-id="1540440681-4">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1540440681-1">}</span><span class="p">.</span></code></pre><p>Now the <code class="inline">relup</code> file can be generated:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;]).
│ │ │  ok</code></pre><p>This generates a <code class="inline">relup</code> file with instructions for how to upgrade from version
│ │ │  &quot;A&quot; (&quot;ch_rel-1&quot;) to version &quot;B&quot; (&quot;ch_rel-2&quot;) and how to downgrade from version
│ │ │  &quot;B&quot; to version &quot;A&quot;.</p><p>Both the old and new versions of the <code class="inline">.app</code> and <code class="inline">.rel</code> files must be in the code
│ │ │  path, as well as the <code class="inline">.appup</code> and (new) <code class="inline">.beam</code> files. The code path can be
│ │ │  extended by using the option <code class="inline">path</code>:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;],
│ │ │  [{path,[&quot;../ch_rel-1&quot;,
│ │ │  &quot;../ch_rel-1/lib/ch_app-1/ebin&quot;]}]).
│ │ │ @@ -433,25 +433,25 @@
│ │ │  <p>When you have made a new version of a release, a release package can be created
│ │ │  with this new version and transferred to the target environment.</p><p>To install the new version of the release in runtime, the <em>release
│ │ │  handler</em> is used. This is a process belonging to the SASL application,
│ │ │  which handles unpacking, installation, and removal of release
│ │ │  packages. The <a href="../../lib/sasl-4.2.2/doc/html/release_handler.html"><code class="inline">release_handler</code></a> module communicates with this process.</p><p>Assuming there is an operational target system with installation root directory
│ │ │  <code class="inline">$ROOT</code>, the release package with the new version of the release is to be copied
│ │ │  to <code class="inline">$ROOT/releases</code>.</p><p>First, <em>unpack</em> the release package. The files are then extracted from the
│ │ │ -package:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="0307929895-1">(</span><span class="n">ReleaseName</span><span class="p" data-group-id="0307929895-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0307929895-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p" data-group-id="0307929895-2">}</span></code></pre><ul><li><code class="inline">ReleaseName</code> is the name of the release package except the <code class="inline">.tar.gz</code>
│ │ │ +package:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="9162897045-1">(</span><span class="n">ReleaseName</span><span class="p" data-group-id="9162897045-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9162897045-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p" data-group-id="9162897045-2">}</span></code></pre><ul><li><code class="inline">ReleaseName</code> is the name of the release package except the <code class="inline">.tar.gz</code>
│ │ │  extension.</li><li><code class="inline">Vsn</code> is the version of the unpacked release, as defined in its <code class="inline">.rel</code> file.</li></ul><p>A directory <code class="inline">$ROOT/lib/releases/Vsn</code> is created, where the <code class="inline">.rel</code> file, the boot
│ │ │  script <code class="inline">start.boot</code>, the system configuration file <code class="inline">sys.config</code>, and <code class="inline">relup</code> are
│ │ │  placed. For applications with new version numbers, the application directories
│ │ │  are placed under <code class="inline">$ROOT/lib</code>. Unchanged applications are not affected.</p><p>An unpacked release can be <em>installed</em>. The release handler then evaluates the
│ │ │ -instructions in <code class="inline">relup</code>, step by step:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="4802653560-1">(</span><span class="n">Vsn</span><span class="p" data-group-id="4802653560-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4802653560-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FromVsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4802653560-3">[</span><span class="p" data-group-id="4802653560-3">]</span><span class="p" data-group-id="4802653560-2">}</span></code></pre><p>If an error occurs during the installation, the system is rebooted using the old
│ │ │ +instructions in <code class="inline">relup</code>, step by step:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="8448665207-1">(</span><span class="n">Vsn</span><span class="p" data-group-id="8448665207-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8448665207-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FromVsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8448665207-3">[</span><span class="p" data-group-id="8448665207-3">]</span><span class="p" data-group-id="8448665207-2">}</span></code></pre><p>If an error occurs during the installation, the system is rebooted using the old
│ │ │  version of the release. If installation succeeds, the system is afterwards using
│ │ │  the new version of the release, but if anything happens and the system is
│ │ │  rebooted, it starts using the previous version again.</p><p>To be made the default version, the newly installed release must be made
│ │ │  <em>permanent</em>, which means the previous version becomes <em>old</em>:</p><pre><code class="text">release_handler:make_permanent(Vsn) =&gt; ok</code></pre><p>The system keeps information about which versions are old and permanent in the
│ │ │ -files <code class="inline">$ROOT/releases/RELEASES</code> and <code class="inline">$ROOT/releases/start_erl.data</code>.</p><p>To downgrade from <code class="inline">Vsn</code> to <code class="inline">FromVsn</code>, <code class="inline">install_release</code> must be called again:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="9544255489-1">(</span><span class="n">FromVsn</span><span class="p" data-group-id="9544255489-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9544255489-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9544255489-3">[</span><span class="p" data-group-id="9544255489-3">]</span><span class="p" data-group-id="9544255489-2">}</span></code></pre><p>An installed, but not permanent, release can be <em>removed</em>. Information about the
│ │ │ +files <code class="inline">$ROOT/releases/RELEASES</code> and <code class="inline">$ROOT/releases/start_erl.data</code>.</p><p>To downgrade from <code class="inline">Vsn</code> to <code class="inline">FromVsn</code>, <code class="inline">install_release</code> must be called again:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="8514794271-1">(</span><span class="n">FromVsn</span><span class="p" data-group-id="8514794271-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8514794271-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8514794271-3">[</span><span class="p" data-group-id="8514794271-3">]</span><span class="p" data-group-id="8514794271-2">}</span></code></pre><p>An installed, but not permanent, release can be <em>removed</em>. Information about the
│ │ │  release is then deleted from <code class="inline">$ROOT/releases/RELEASES</code> and the release-specific
│ │ │  code, that is, the new application directories and the <code class="inline">$ROOT/releases/Vsn</code>
│ │ │  directory, are removed.</p><pre><code class="text">release_handler:remove_release(Vsn) =&gt; ok</code></pre><h3 id="example-continued-from-the-previous-sections" class="section-heading">
│ │ │    <a href="#example-continued-from-the-previous-sections" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example (continued from the previous sections)</span>
│ │ │ @@ -462,17 +462,17 @@
│ │ │  is needed, the file is to contain the empty list:</p><pre><code class="text">[].</code></pre><p><em>Step 2)</em> Start the system as a simple target system. In reality, it is to be
│ │ │  started as an embedded system. However, using <code class="inline">erl</code> with the correct boot script
│ │ │  and config file is enough for illustration purposes:</p><pre><code class="text">% cd $ROOT
│ │ │  % bin/erl -boot $ROOT/releases/A/start -config $ROOT/releases/A/sys
│ │ │  ...</code></pre><p><code class="inline">$ROOT</code> is the installation directory of the target system.</p><p><em>Step 3)</em> In another Erlang shell, generate start scripts and create a release
│ │ │  package for the new version <code class="inline">&quot;B&quot;</code>. Remember to include (a possible updated)
│ │ │  <code class="inline">sys.config</code> and the <code class="inline">relup</code> file. For more information, see
│ │ │ -<a href="release_handling.html#relup">Release Upgrade File</a>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="0140416921-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="0140416921-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="release_handling.html#relup">Release Upgrade File</a>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="7392387850-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="7392387850-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="0140416921-2">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="0140416921-2">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="7392387850-2">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="7392387850-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>The new release package now also contains version &quot;2&quot; of <code class="inline">ch_app</code> and the
│ │ │  <code class="inline">relup</code> file:</p><pre><code class="text">% tar tf ch_rel-2.tar
│ │ │  lib/kernel-9.2.4/ebin/kernel.app
│ │ │  lib/kernel-9.2.4/ebin/application.beam
│ │ │  ...
│ │ │  lib/stdlib-5.2.3/ebin/stdlib.app
│ │ │  lib/stdlib-5.2.3/ebin/argparse.beam
│ │ │ @@ -485,31 +485,31 @@
│ │ │  lib/ch_app-2/ebin/ch_sup.beam
│ │ │  lib/ch_app-2/ebin/ch3.beam
│ │ │  releases/B/start.boot
│ │ │  releases/B/relup
│ │ │  releases/B/sys.config
│ │ │  releases/B/ch_rel-2.rel
│ │ │  releases/ch_rel-2.rel</code></pre><p><em>Step 4)</em> Copy the release package <code class="inline">ch_rel-2.tar.gz</code> to the <code class="inline">$ROOT/releases</code>
│ │ │ -directory.</p><p><em>Step 5)</em> In the running target system, unpack the release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="8997841246-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="8997841246-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8997841246-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="8997841246-2">}</span></code></pre><p>The new application version <code class="inline">ch_app-2</code> is installed under <code class="inline">$ROOT/lib</code> next to
│ │ │ +directory.</p><p><em>Step 5)</em> In the running target system, unpack the release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="7198681545-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="7198681545-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7198681545-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="7198681545-2">}</span></code></pre><p>The new application version <code class="inline">ch_app-2</code> is installed under <code class="inline">$ROOT/lib</code> next to
│ │ │  <code class="inline">ch_app-1</code>. The <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code> directories are not affected, as
│ │ │  they have not changed.</p><p>Under <code class="inline">$ROOT/releases</code>, a new directory <code class="inline">B</code> is created, containing
│ │ │ -<code class="inline">ch_rel-2.rel</code>, <code class="inline">start.boot</code>, <code class="inline">sys.config</code>, and <code class="inline">relup</code>.</p><p><em>Step 6)</em> Check if the function <code class="inline">ch3:available/0</code> is available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="9330937227-1">(</span><span class="p" data-group-id="9330937227-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">ch_rel-2.rel</code>, <code class="inline">start.boot</code>, <code class="inline">sys.config</code>, and <code class="inline">relup</code>.</p><p><em>Step 6)</em> Check if the function <code class="inline">ch3:available/0</code> is available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="7004203323-1">(</span><span class="p" data-group-id="7004203323-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: undefined function ch3:available/0</span></code></pre><p><em>Step 7)</em> Install the new release. The instructions in <code class="inline">$ROOT/releases/B/relup</code>
│ │ │  are executed one by one, resulting in the new version of <code class="inline">ch3</code> being loaded. The
│ │ │ -function <code class="inline">ch3:available/0</code> is now available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="2521829793-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="2521829793-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2521829793-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="p" data-group-id="2521829793-3">[</span><span class="p" data-group-id="2521829793-3">]</span><span class="p" data-group-id="2521829793-2">}</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="2521829793-4">(</span><span class="p" data-group-id="2521829793-4">)</span><span class="p">.</span><span class="w">
│ │ │ +function <code class="inline">ch3:available/0</code> is now available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="1410454275-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="1410454275-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1410454275-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="p" data-group-id="1410454275-3">[</span><span class="p" data-group-id="1410454275-3">]</span><span class="p" data-group-id="1410454275-2">}</span><span class="gp unselectable">
│ │ │ +4&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="1410454275-4">(</span><span class="p" data-group-id="1410454275-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="2521829793-5">(</span><span class="ss">ch3</span><span class="p" data-group-id="2521829793-5">)</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="1410454275-5">(</span><span class="ss">ch3</span><span class="p" data-group-id="1410454275-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;.../lib/ch_app-2/ebin/ch3.beam&quot;</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="2521829793-6">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="2521829793-6">)</span><span class="p">.</span><span class="w">
│ │ │ +6&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="1410454275-6">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="1410454275-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;.../lib/ch_app-1/ebin/ch_sup.beam&quot;</span></code></pre><p>Processes in <code class="inline">ch_app</code> for which code have not been updated, for example, the
│ │ │  supervisor, are still evaluating code from <code class="inline">ch_app-1</code>.</p><p><em>Step 8)</em> If the target system is now rebooted, it uses version &quot;A&quot; again. The
│ │ │ -&quot;B&quot; version must be made permanent, to be used when the system is rebooted.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">make_permanent</span><span class="p" data-group-id="3609575848-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="3609575848-1">)</span><span class="p">.</span><span class="w">
│ │ │ +&quot;B&quot; version must be made permanent, to be used when the system is rebooted.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">make_permanent</span><span class="p" data-group-id="0301046531-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="0301046531-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p><a href="" id="sys"></a></p><h2 id="updating-application-specifications" class="section-heading">
│ │ │    <a href="#updating-application-specifications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Updating Application Specifications</span>
│ │ │  </h2>
│ │ │  <p>When a new version of a release is installed, the application specifications are
│ │ │ @@ -518,15 +518,15 @@
│ │ │  boot script is generated from the same <code class="inline">.rel</code> file as is used to build the
│ │ │  release package itself.</p></section><p>Specifically, the application configuration parameters are automatically updated
│ │ │  according to (in increasing priority order):</p><ul><li>The data in the boot script, fetched from the new application resource file
│ │ │  <code class="inline">App.app</code></li><li>The new <code class="inline">sys.config</code></li><li>Command-line arguments <code class="inline">-App Par Val</code></li></ul><p>This means that parameter values set in the other system configuration files and
│ │ │  values set using <a href="../../lib/kernel-10.2.7.1/doc/html/application.html#set_env/3"><code class="inline">application:set_env/3</code></a> are disregarded.</p><p>When an installed release is made permanent, the system process <code class="inline">init</code> is set to
│ │ │  point out the new <code class="inline">sys.config</code>.</p><p>After the installation, the application controller compares the old and new
│ │ │  configuration parameters for all running applications and call the callback
│ │ │ -function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">config_change</span><span class="p" data-group-id="9936216615-1">(</span><span class="n">Changed</span><span class="p">,</span><span class="w"> </span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">Removed</span><span class="p" data-group-id="9936216615-1">)</span></code></pre><ul><li><code class="inline">Module</code> is the application callback module as defined by the <code class="inline">mod</code> key in the
│ │ │ +function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">config_change</span><span class="p" data-group-id="3635393213-1">(</span><span class="n">Changed</span><span class="p">,</span><span class="w"> </span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">Removed</span><span class="p" data-group-id="3635393213-1">)</span></code></pre><ul><li><code class="inline">Module</code> is the application callback module as defined by the <code class="inline">mod</code> key in the
│ │ │  <code class="inline">.app</code> file.</li><li><code class="inline">Changed</code> and <code class="inline">New</code> are lists of <code class="inline">{Par,Val}</code> for all changed and added
│ │ │  configuration parameters, respectively.</li><li><code class="inline">Removed</code> is a list of all parameters <code class="inline">Par</code> that have been removed.</li></ul><p>The function is optional and can be omitted when implementing an application
│ │ │  callback module.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/release_structure.html
│ │ │ @@ -136,37 +136,37 @@
│ │ │    <a href="#release-resource-file" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Release Resource File</span>
│ │ │  </h2>
│ │ │  <p>To define a release, create a <em>release resource file</em>, or in short a <code class="inline">.rel</code>
│ │ │  file. In the file, specify the name and version of the release, which ERTS
│ │ │ -version it is based on, and which applications it consists of:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0359115878-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0359115878-2">{</span><span class="n">Name</span><span class="p">,</span><span class="n">Vsn</span><span class="p" data-group-id="0359115878-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0359115878-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">EVsn</span><span class="p" data-group-id="0359115878-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0359115878-4">[</span><span class="p" data-group-id="0359115878-5">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsn1</span><span class="p" data-group-id="0359115878-5">}</span><span class="p">,</span><span class="w">
│ │ │ +version it is based on, and which applications it consists of:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2516056264-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2516056264-2">{</span><span class="n">Name</span><span class="p">,</span><span class="n">Vsn</span><span class="p" data-group-id="2516056264-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2516056264-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">EVsn</span><span class="p" data-group-id="2516056264-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2516056264-4">[</span><span class="p" data-group-id="2516056264-5">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsn1</span><span class="p" data-group-id="2516056264-5">}</span><span class="p">,</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0359115878-6">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsnN</span><span class="p" data-group-id="0359115878-6">}</span><span class="p" data-group-id="0359115878-4">]</span><span class="p" data-group-id="0359115878-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Name</code>, <code class="inline">Vsn</code>, <code class="inline">EVsn</code>, and <code class="inline">AppVsn</code> are strings.</p><p>The file must be named <code class="inline">Rel.rel</code>, where <code class="inline">Rel</code> is a unique name.</p><p>Each <code class="inline">Application</code> (atom) and <code class="inline">AppVsn</code> is the name and version of an application
│ │ │ +  </span><span class="p" data-group-id="2516056264-6">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsnN</span><span class="p" data-group-id="2516056264-6">}</span><span class="p" data-group-id="2516056264-4">]</span><span class="p" data-group-id="2516056264-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Name</code>, <code class="inline">Vsn</code>, <code class="inline">EVsn</code>, and <code class="inline">AppVsn</code> are strings.</p><p>The file must be named <code class="inline">Rel.rel</code>, where <code class="inline">Rel</code> is a unique name.</p><p>Each <code class="inline">Application</code> (atom) and <code class="inline">AppVsn</code> is the name and version of an application
│ │ │  included in the release. The minimal release based on Erlang/OTP consists of the
│ │ │  Kernel and STDLIB applications, so these applications must be included in the
│ │ │  list.</p><p>If the release is to be upgraded, it must also include the SASL application.</p><p><a href="" id="ch_rel"></a></p><p>Here is an example showing the <code class="inline">.app</code> file for a release of <code class="inline">ch_app</code> from
│ │ │ -the <a href="applications.html#ch_app">Applications</a> section:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6195681505-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6195681505-2">[</span><span class="p" data-group-id="6195681505-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="6195681505-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6195681505-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6195681505-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6195681505-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6195681505-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6195681505-6">]</span><span class="p" data-group-id="6195681505-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6195681505-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6195681505-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="6195681505-8">]</span><span class="p" data-group-id="6195681505-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6195681505-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6195681505-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="6195681505-10">]</span><span class="p" data-group-id="6195681505-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6195681505-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6195681505-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="6195681505-13">[</span><span class="p" data-group-id="6195681505-13">]</span><span class="p" data-group-id="6195681505-12">}</span><span class="p" data-group-id="6195681505-11">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6195681505-2">]</span><span class="p" data-group-id="6195681505-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">.rel</code> file must also contain <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code>, as these
│ │ │ -applications are required by <code class="inline">ch_app</code>. The file is called <code class="inline">ch_rel-1.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5476802437-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5476802437-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;A&quot;</span><span class="p" data-group-id="5476802437-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5476802437-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="5476802437-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5476802437-4">[</span><span class="p" data-group-id="5476802437-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="5476802437-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5476802437-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="5476802437-6">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5476802437-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="5476802437-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5476802437-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="5476802437-8">}</span><span class="p" data-group-id="5476802437-4">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5476802437-1">}</span><span class="p">.</span></code></pre><p><a href="" id="boot"></a></p><h2 id="generating-boot-scripts" class="section-heading">
│ │ │ +the <a href="applications.html#ch_app">Applications</a> section:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2058964082-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2058964082-2">[</span><span class="p" data-group-id="2058964082-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="2058964082-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2058964082-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="2058964082-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2058964082-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2058964082-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2058964082-6">]</span><span class="p" data-group-id="2058964082-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2058964082-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2058964082-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="2058964082-8">]</span><span class="p" data-group-id="2058964082-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2058964082-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2058964082-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="2058964082-10">]</span><span class="p" data-group-id="2058964082-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2058964082-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2058964082-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="2058964082-13">[</span><span class="p" data-group-id="2058964082-13">]</span><span class="p" data-group-id="2058964082-12">}</span><span class="p" data-group-id="2058964082-11">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2058964082-2">]</span><span class="p" data-group-id="2058964082-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">.rel</code> file must also contain <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code>, as these
│ │ │ +applications are required by <code class="inline">ch_app</code>. The file is called <code class="inline">ch_rel-1.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5903230927-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5903230927-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;A&quot;</span><span class="p" data-group-id="5903230927-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5903230927-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="5903230927-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5903230927-4">[</span><span class="p" data-group-id="5903230927-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="5903230927-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5903230927-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="5903230927-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5903230927-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="5903230927-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5903230927-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="5903230927-8">}</span><span class="p" data-group-id="5903230927-4">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5903230927-1">}</span><span class="p">.</span></code></pre><p><a href="" id="boot"></a></p><h2 id="generating-boot-scripts" class="section-heading">
│ │ │    <a href="#generating-boot-scripts" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Generating Boot Scripts</span>
│ │ │  </h2>
│ │ │  <p><a href="../../lib/sasl-4.2.2/doc/html/systools.html"><code class="inline">systools</code></a> in the SASL application includes tools to build and check
│ │ │  releases. The functions read the <code class="inline">.rel</code> and <code class="inline">.app</code> files and perform
│ │ │ @@ -190,17 +190,17 @@
│ │ │    <a href="#creating-a-release-package" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating a Release Package</span>
│ │ │  </h2>
│ │ │  <p>The <a href="../../lib/sasl-4.2.2/doc/html/systools.html#make_tar/2"><code class="inline">systools:make_tar/1,2</code></a> function takes a
│ │ │  <code class="inline">.rel</code> file as input and creates a zipped tar file with the code for
│ │ │ -the specified applications, a <em>release package</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="9977659496-1">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="9977659496-1">)</span><span class="p">.</span><span class="w">
│ │ │ +the specified applications, a <em>release package</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="8519911398-1">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="8519911398-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="9977659496-2">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="9977659496-2">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="8519911398-2">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="8519911398-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>The release package by default contains:</p><ul><li>The <code class="inline">.app</code> files</li><li>The <code class="inline">.rel</code> file</li><li>The object code for all applications, structured according to the
│ │ │  <a href="applications.html#app_dir">application directory structure</a></li><li>The binary boot script renamed to <code class="inline">start.boot</code></li></ul><pre><code class="text">% tar tf ch_rel-1.tar
│ │ │  lib/kernel-9.2.4/ebin/kernel.app
│ │ │  lib/kernel-9.2.4/ebin/application.beam
│ │ │  ...
│ │ │  lib/stdlib-5.2.3/ebin/stdlib.app
│ │ │  lib/stdlib-5.2.3/ebin/argparse.beam
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/robustness.html
│ │ │ @@ -128,68 +128,68 @@
│ │ │  </h2>
│ │ │  <p>Before improving the messenger program, let us look at some general principles,
│ │ │  using the ping pong program as an example. Recall that when &quot;ping&quot; finishes, it
│ │ │  tells &quot;pong&quot; that it has done so by sending the atom <code class="inline">finished</code> as a message to
│ │ │  &quot;pong&quot; so that &quot;pong&quot; can also finish. Another way to let &quot;pong&quot; finish is to
│ │ │  make &quot;pong&quot; exit if it does not receive a message from ping within a certain
│ │ │  time. This can be done by adding a <em>time-out</em> to <code class="inline">pong</code> as shown in the
│ │ │ -following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8893539877-1">(</span><span class="ss">tut19</span><span class="p" data-group-id="8893539877-1">)</span><span class="p">.</span><span class="w">
│ │ │ +following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7591947958-1">(</span><span class="ss">tut19</span><span class="p" data-group-id="7591947958-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8893539877-2">(</span><span class="p" data-group-id="8893539877-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8893539877-3">]</span><span class="p" data-group-id="8893539877-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7591947958-2">(</span><span class="p" data-group-id="7591947958-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7591947958-3">]</span><span class="p" data-group-id="7591947958-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="8893539877-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8893539877-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8893539877-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8893539877-6">[</span><span class="p" data-group-id="8893539877-6">]</span><span class="p" data-group-id="8893539877-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="7591947958-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7591947958-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7591947958-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7591947958-6">[</span><span class="p" data-group-id="7591947958-6">]</span><span class="p" data-group-id="7591947958-5">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="8893539877-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8893539877-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8893539877-8">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8893539877-8">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8893539877-9">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8893539877-10">(</span><span class="p" data-group-id="8893539877-10">)</span><span class="p" data-group-id="8893539877-9">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="7591947958-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7591947958-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7591947958-8">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7591947958-8">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7591947958-9">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7591947958-10">(</span><span class="p" data-group-id="7591947958-10">)</span><span class="p" data-group-id="7591947958-9">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8893539877-11">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8893539877-12">[</span><span class="p" data-group-id="8893539877-12">]</span><span class="p" data-group-id="8893539877-11">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7591947958-11">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7591947958-12">[</span><span class="p" data-group-id="7591947958-12">]</span><span class="p" data-group-id="7591947958-11">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="8893539877-13">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8893539877-13">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="7591947958-13">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7591947958-13">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="8893539877-14">(</span><span class="p" data-group-id="8893539877-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="7591947958-14">(</span><span class="p" data-group-id="7591947958-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8893539877-15">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="8893539877-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8893539877-16">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8893539877-17">[</span><span class="p" data-group-id="8893539877-17">]</span><span class="p" data-group-id="8893539877-16">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7591947958-15">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="7591947958-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7591947958-16">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7591947958-17">[</span><span class="p" data-group-id="7591947958-17">]</span><span class="p" data-group-id="7591947958-16">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="8893539877-18">(</span><span class="p" data-group-id="8893539877-18">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="7591947958-18">(</span><span class="p" data-group-id="7591947958-18">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8893539877-19">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8893539877-20">[</span><span class="p" data-group-id="8893539877-20">]</span><span class="p" data-group-id="8893539877-19">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7591947958-19">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7591947958-20">[</span><span class="p" data-group-id="7591947958-20">]</span><span class="p" data-group-id="7591947958-19">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_pong</span><span class="p" data-group-id="8893539877-21">(</span><span class="p" data-group-id="8893539877-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="8893539877-22">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="8893539877-23">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8893539877-24">[</span><span class="p" data-group-id="8893539877-24">]</span><span class="p" data-group-id="8893539877-23">)</span><span class="p" data-group-id="8893539877-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_pong</span><span class="p" data-group-id="7591947958-21">(</span><span class="p" data-group-id="7591947958-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="7591947958-22">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7591947958-23">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7591947958-24">[</span><span class="p" data-group-id="7591947958-24">]</span><span class="p" data-group-id="7591947958-23">)</span><span class="p" data-group-id="7591947958-22">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_ping</span><span class="p" data-group-id="8893539877-25">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="8893539877-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="8893539877-26">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8893539877-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="8893539877-27">]</span><span class="p" data-group-id="8893539877-26">)</span><span class="p">.</span></code></pre><p>After this is compiled and the file <code class="inline">tut19.beam</code> is copied to the necessary
│ │ │ +</span><span class="nf">start_ping</span><span class="p" data-group-id="7591947958-25">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="7591947958-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="7591947958-26">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7591947958-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7591947958-27">]</span><span class="p" data-group-id="7591947958-26">)</span><span class="p">.</span></code></pre><p>After this is compiled and the file <code class="inline">tut19.beam</code> is copied to the necessary
│ │ │  directories, the following is seen on (pong@kosken):</p><pre><code class="text">(pong@kosken)1&gt; tut19:start_pong().
│ │ │  true
│ │ │  Pong received ping
│ │ │  Pong received ping
│ │ │  Pong received ping
│ │ │  Pong timed out</code></pre><p>And the following is seen on (ping@gollum):</p><pre><code class="text">(ping@gollum)1&gt; tut19:start_ping(pong@kosken).
│ │ │  &lt;0.36.0&gt;
│ │ │  Ping received pong
│ │ │  Ping received pong
│ │ │  Ping received pong
│ │ │ -ping finished</code></pre><p>The time-out is set in:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pong</span><span class="p" data-group-id="2521661305-1">(</span><span class="p" data-group-id="2521661305-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +ping finished</code></pre><p>The time-out is set in:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pong</span><span class="p" data-group-id="9782124568-1">(</span><span class="p" data-group-id="9782124568-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2521661305-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2521661305-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2521661305-3">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2521661305-4">[</span><span class="p" data-group-id="2521661305-4">]</span><span class="p" data-group-id="2521661305-3">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="9782124568-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9782124568-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9782124568-3">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9782124568-4">[</span><span class="p" data-group-id="9782124568-4">]</span><span class="p" data-group-id="9782124568-3">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="2521661305-5">(</span><span class="p" data-group-id="2521661305-5">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="9782124568-5">(</span><span class="p" data-group-id="9782124568-5">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2521661305-6">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2521661305-7">[</span><span class="p" data-group-id="2521661305-7">]</span><span class="p" data-group-id="2521661305-6">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9782124568-6">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9782124568-7">[</span><span class="p" data-group-id="9782124568-7">]</span><span class="p" data-group-id="9782124568-6">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The time-out (<code class="inline">after 5000</code>) is started when <code class="inline">receive</code> is entered. The time-out
│ │ │  is canceled if <code class="inline">{ping,Ping_PID}</code> is received. If <code class="inline">{ping,Ping_PID}</code> is not
│ │ │  received, the actions following the time-out are done after 5000 milliseconds.
│ │ │  <code class="inline">after</code> must be last in the <code class="inline">receive</code>, that is, preceded by all other message
│ │ │  reception specifications in the <code class="inline">receive</code>. It is also possible to call a
│ │ │ -function that returned an integer for the time-out:</p><pre><code class="makeup erlang" translate="no"><span class="k">after</span><span class="w"> </span><span class="nf">pong_timeout</span><span class="p" data-group-id="5258597245-1">(</span><span class="p" data-group-id="5258597245-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>In general, there are better ways than using time-outs to supervise parts of a
│ │ │ +function that returned an integer for the time-out:</p><pre><code class="makeup erlang" translate="no"><span class="k">after</span><span class="w"> </span><span class="nf">pong_timeout</span><span class="p" data-group-id="0132336064-1">(</span><span class="p" data-group-id="0132336064-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>In general, there are better ways than using time-outs to supervise parts of a
│ │ │  distributed Erlang system. Time-outs are usually appropriate to supervise
│ │ │  external events, for example, if you have expected a message from some external
│ │ │  system within a specified time. For example, a time-out can be used to log a
│ │ │  user out of the messenger system if they have not accessed it for, say, ten
│ │ │  minutes.</p><h2 id="error-handling" class="section-heading">
│ │ │    <a href="#error-handling" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -209,96 +209,96 @@
│ │ │  something called a <em>signal</em> to all the processes it has links to.</p><p>The signal carries information about the pid it was sent from and the exit
│ │ │  reason.</p><p>The default behaviour of a process that receives a normal exit is to ignore the
│ │ │  signal.</p><p>The default behaviour in the two other cases (that is, abnormal exit) above is
│ │ │  to:</p><ul><li>Bypass all messages to the receiving process.</li><li>Kill the receiving process.</li><li>Propagate the same error signal to the links of the killed process.</li></ul><p>In this way you can connect all processes in a transaction together using links.
│ │ │  If one of the processes exits abnormally, all the processes in the transaction
│ │ │  are killed. As it is often wanted to create a process and link to it at the same
│ │ │  time, there is a special BIF, <a href="../../erts-15.2.7/doc/html/erlang.html#spawn_link/1">spawn_link</a> that does the
│ │ │ -same as <code class="inline">spawn</code>, but also creates a link to the spawned process.</p><p>Now an example of the ping pong example using links to terminate &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0763916612-1">(</span><span class="ss">tut20</span><span class="p" data-group-id="0763916612-1">)</span><span class="p">.</span><span class="w">
│ │ │ +same as <code class="inline">spawn</code>, but also creates a link to the spawned process.</p><p>Now an example of the ping pong example using links to terminate &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8633576453-1">(</span><span class="ss">tut20</span><span class="p" data-group-id="8633576453-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0763916612-2">(</span><span class="p" data-group-id="0763916612-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0763916612-3">]</span><span class="p" data-group-id="0763916612-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8633576453-2">(</span><span class="p" data-group-id="8633576453-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8633576453-3">]</span><span class="p" data-group-id="8633576453-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="0763916612-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="0763916612-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">link</span><span class="p" data-group-id="0763916612-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="0763916612-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="0763916612-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="0763916612-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="8633576453-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="8633576453-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">link</span><span class="p" data-group-id="8633576453-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="8633576453-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="8633576453-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="8633576453-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="0763916612-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="0763916612-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="0763916612-8">(</span><span class="ss">ping</span><span class="p" data-group-id="0763916612-8">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="8633576453-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="8633576453-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="8633576453-8">(</span><span class="ss">ping</span><span class="p" data-group-id="8633576453-8">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="0763916612-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="0763916612-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0763916612-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0763916612-11">(</span><span class="p" data-group-id="0763916612-11">)</span><span class="p" data-group-id="0763916612-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="8633576453-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="8633576453-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8633576453-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8633576453-11">(</span><span class="p" data-group-id="8633576453-11">)</span><span class="p" data-group-id="8633576453-10">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0763916612-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0763916612-13">[</span><span class="p" data-group-id="0763916612-13">]</span><span class="p" data-group-id="0763916612-12">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8633576453-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8633576453-13">[</span><span class="p" data-group-id="8633576453-13">]</span><span class="p" data-group-id="8633576453-12">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="0763916612-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="0763916612-14">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="8633576453-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="8633576453-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="0763916612-15">(</span><span class="p" data-group-id="0763916612-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="8633576453-15">(</span><span class="p" data-group-id="8633576453-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0763916612-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="0763916612-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0763916612-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0763916612-18">[</span><span class="p" data-group-id="0763916612-18">]</span><span class="p" data-group-id="0763916612-17">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8633576453-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="8633576453-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8633576453-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8633576453-18">[</span><span class="p" data-group-id="8633576453-18">]</span><span class="p" data-group-id="8633576453-17">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="0763916612-19">(</span><span class="p" data-group-id="0763916612-19">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="8633576453-19">(</span><span class="p" data-group-id="8633576453-19">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="0763916612-20">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="0763916612-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0763916612-21">(</span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0763916612-22">[</span><span class="p" data-group-id="0763916612-22">]</span><span class="p" data-group-id="0763916612-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="0763916612-23">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0763916612-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="0763916612-24">]</span><span class="p" data-group-id="0763916612-23">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)3&gt; tut20:start(s2@kosken).
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8633576453-20">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="8633576453-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="8633576453-21">(</span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8633576453-22">[</span><span class="p" data-group-id="8633576453-22">]</span><span class="p" data-group-id="8633576453-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="8633576453-23">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8633576453-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="8633576453-24">]</span><span class="p" data-group-id="8633576453-23">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)3&gt; tut20:start(s2@kosken).
│ │ │  Pong received ping
│ │ │  &lt;3820.41.0&gt;
│ │ │  Ping received pong
│ │ │  Pong received ping
│ │ │  Ping received pong
│ │ │  Pong received ping
│ │ │  Ping received pong</code></pre><p>This is a slight modification of the ping pong program where both processes are
│ │ │  spawned from the same <code class="inline">start/1</code> function, and the &quot;ping&quot; process can be spawned
│ │ │  on a separate node. Notice the use of the <code class="inline">link</code> BIF. &quot;Ping&quot; calls
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#exit/1"><code class="inline">exit(ping)</code></a> when it finishes and this causes an exit signal to be
│ │ │  sent to &quot;pong&quot;, which also terminates.</p><p>It is possible to modify the default behaviour of a process so that it does not
│ │ │  get killed when it receives abnormal exit signals. Instead, all signals are
│ │ │  turned into normal messages on the format <code class="inline">{'EXIT',FromPID,Reason}</code> and added to
│ │ │ -the end of the receiving process' message queue. This behaviour is set by:</p><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="9224783045-1">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9224783045-1">)</span></code></pre><p>There are several other process flags, see <a href="../../erts-15.2.7/doc/html/erlang.html#process_flag/2">erlang(3)</a>.
│ │ │ +the end of the receiving process' message queue. This behaviour is set by:</p><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="7789305272-1">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7789305272-1">)</span></code></pre><p>There are several other process flags, see <a href="../../erts-15.2.7/doc/html/erlang.html#process_flag/2">erlang(3)</a>.
│ │ │  Changing the default behaviour of a process in this way is usually not done in
│ │ │  standard user programs, but is left to the supervisory programs in OTP. However,
│ │ │ -the ping pong program is modified to illustrate exit trapping.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6547562155-1">(</span><span class="ss">tut21</span><span class="p" data-group-id="6547562155-1">)</span><span class="p">.</span><span class="w">
│ │ │ +the ping pong program is modified to illustrate exit trapping.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7519061907-1">(</span><span class="ss">tut21</span><span class="p" data-group-id="7519061907-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6547562155-2">(</span><span class="p" data-group-id="6547562155-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6547562155-3">]</span><span class="p" data-group-id="6547562155-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7519061907-2">(</span><span class="p" data-group-id="7519061907-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7519061907-3">]</span><span class="p" data-group-id="7519061907-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="6547562155-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="6547562155-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">link</span><span class="p" data-group-id="6547562155-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="6547562155-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="6547562155-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="6547562155-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="7519061907-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="7519061907-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">link</span><span class="p" data-group-id="7519061907-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="7519061907-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="7519061907-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="7519061907-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="6547562155-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6547562155-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="6547562155-8">(</span><span class="ss">ping</span><span class="p" data-group-id="6547562155-8">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="7519061907-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7519061907-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="7519061907-8">(</span><span class="ss">ping</span><span class="p" data-group-id="7519061907-8">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="6547562155-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="6547562155-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6547562155-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6547562155-11">(</span><span class="p" data-group-id="6547562155-11">)</span><span class="p" data-group-id="6547562155-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="7519061907-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="7519061907-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7519061907-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7519061907-11">(</span><span class="p" data-group-id="7519061907-11">)</span><span class="p" data-group-id="7519061907-10">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6547562155-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6547562155-13">[</span><span class="p" data-group-id="6547562155-13">]</span><span class="p" data-group-id="6547562155-12">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7519061907-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7519061907-13">[</span><span class="p" data-group-id="7519061907-13">]</span><span class="p" data-group-id="7519061907-12">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="6547562155-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="6547562155-14">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="7519061907-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="7519061907-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="6547562155-15">(</span><span class="p" data-group-id="6547562155-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="6547562155-16">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6547562155-16">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">pong1</span><span class="p" data-group-id="6547562155-17">(</span><span class="p" data-group-id="6547562155-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="7519061907-15">(</span><span class="p" data-group-id="7519061907-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="7519061907-16">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7519061907-16">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">pong1</span><span class="p" data-group-id="7519061907-17">(</span><span class="p" data-group-id="7519061907-17">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong1</span><span class="p" data-group-id="6547562155-18">(</span><span class="p" data-group-id="6547562155-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong1</span><span class="p" data-group-id="7519061907-18">(</span><span class="p" data-group-id="7519061907-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6547562155-19">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="6547562155-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6547562155-20">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6547562155-21">[</span><span class="p" data-group-id="6547562155-21">]</span><span class="p" data-group-id="6547562155-20">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7519061907-19">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="7519061907-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7519061907-20">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7519061907-21">[</span><span class="p" data-group-id="7519061907-21">]</span><span class="p" data-group-id="7519061907-20">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong1</span><span class="p" data-group-id="6547562155-22">(</span><span class="p" data-group-id="6547562155-22">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6547562155-23">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="6547562155-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6547562155-24">(</span><span class="s">&quot;pong exiting, got </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6547562155-25">[</span><span class="p" data-group-id="6547562155-26">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="6547562155-26">}</span><span class="p" data-group-id="6547562155-25">]</span><span class="p" data-group-id="6547562155-24">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong1</span><span class="p" data-group-id="7519061907-22">(</span><span class="p" data-group-id="7519061907-22">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7519061907-23">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="7519061907-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7519061907-24">(</span><span class="s">&quot;pong exiting, got </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7519061907-25">[</span><span class="p" data-group-id="7519061907-26">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="7519061907-26">}</span><span class="p" data-group-id="7519061907-25">]</span><span class="p" data-group-id="7519061907-24">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="6547562155-27">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="6547562155-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="6547562155-28">(</span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6547562155-29">[</span><span class="p" data-group-id="6547562155-29">]</span><span class="p" data-group-id="6547562155-28">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="6547562155-30">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6547562155-31">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="6547562155-31">]</span><span class="p" data-group-id="6547562155-30">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)1&gt; tut21:start(s2@gollum).
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="7519061907-27">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="7519061907-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7519061907-28">(</span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7519061907-29">[</span><span class="p" data-group-id="7519061907-29">]</span><span class="p" data-group-id="7519061907-28">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="7519061907-30">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7519061907-31">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="7519061907-31">]</span><span class="p" data-group-id="7519061907-30">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)1&gt; tut21:start(s2@gollum).
│ │ │  &lt;3820.39.0&gt;
│ │ │  Pong received ping
│ │ │  Ping received pong
│ │ │  Pong received ping
│ │ │  Ping received pong
│ │ │  Pong received ping
│ │ │  Ping received pong
│ │ │ @@ -351,135 +351,135 @@
│ │ │  </span><span class="c1">%%% Started: messenger:client(Server_Node, Name)</span><span class="w">
│ │ │  </span><span class="c1">%%% To client: logoff</span><span class="w">
│ │ │  </span><span class="c1">%%% To client: {message_to, ToName, Message}</span><span class="w">
│ │ │  </span><span class="c1">%%%</span><span class="w">
│ │ │  </span><span class="c1">%%% Configuration: change the server_node() function to return the</span><span class="w">
│ │ │  </span><span class="c1">%%% name of the node where the messenger server runs</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9115754114-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="9115754114-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9115754114-2">(</span><span class="p" data-group-id="9115754114-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9115754114-3">]</span><span class="p" data-group-id="9115754114-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3144399967-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="3144399967-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3144399967-2">(</span><span class="p" data-group-id="3144399967-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3144399967-3">]</span><span class="p" data-group-id="3144399967-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Change the function below to return the name of the node where the</span><span class="w">
│ │ │  </span><span class="c1">%%% messenger server runs</span><span class="w">
│ │ │ -</span><span class="nf">server_node</span><span class="p" data-group-id="9115754114-4">(</span><span class="p" data-group-id="9115754114-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_node</span><span class="p" data-group-id="3144399967-4">(</span><span class="p" data-group-id="3144399967-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">messenger@super</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% This is the server process for the &quot;messenger&quot;</span><span class="w">
│ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="9115754114-5">(</span><span class="p" data-group-id="9115754114-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9115754114-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9115754114-6">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="9115754114-7">(</span><span class="p" data-group-id="9115754114-8">[</span><span class="p" data-group-id="9115754114-8">]</span><span class="p" data-group-id="9115754114-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="3144399967-5">(</span><span class="p" data-group-id="3144399967-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="3144399967-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="3144399967-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="3144399967-7">(</span><span class="p" data-group-id="3144399967-8">[</span><span class="p" data-group-id="3144399967-8">]</span><span class="p" data-group-id="3144399967-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="9115754114-9">(</span><span class="n">User_List</span><span class="p" data-group-id="9115754114-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="3144399967-9">(</span><span class="n">User_List</span><span class="p" data-group-id="3144399967-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9115754114-10">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9115754114-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="9115754114-11">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-11">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9115754114-12">(</span><span class="n">New_User_List</span><span class="p" data-group-id="9115754114-12">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9115754114-13">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9115754114-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="9115754114-14">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-14">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9115754114-15">(</span><span class="n">New_User_List</span><span class="p" data-group-id="9115754114-15">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9115754114-16">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9115754114-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="9115754114-17">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-17">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9115754114-18">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9115754114-19">[</span><span class="n">User_List</span><span class="p" data-group-id="9115754114-19">]</span><span class="p" data-group-id="9115754114-18">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9115754114-20">(</span><span class="n">User_List</span><span class="p" data-group-id="9115754114-20">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3144399967-10">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3144399967-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="3144399967-11">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-11">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="3144399967-12">(</span><span class="n">New_User_List</span><span class="p" data-group-id="3144399967-12">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3144399967-13">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3144399967-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="3144399967-14">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-14">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="3144399967-15">(</span><span class="n">New_User_List</span><span class="p" data-group-id="3144399967-15">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3144399967-16">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3144399967-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="3144399967-17">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-17">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3144399967-18">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3144399967-19">[</span><span class="n">User_List</span><span class="p" data-group-id="3144399967-19">]</span><span class="p" data-group-id="3144399967-18">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="3144399967-20">(</span><span class="n">User_List</span><span class="p" data-group-id="3144399967-20">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="9115754114-21">(</span><span class="p" data-group-id="9115754114-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9115754114-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9115754114-23">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9115754114-24">[</span><span class="p" data-group-id="9115754114-24">]</span><span class="p" data-group-id="9115754114-23">)</span><span class="p" data-group-id="9115754114-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="3144399967-21">(</span><span class="p" data-group-id="3144399967-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="3144399967-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="3144399967-23">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3144399967-24">[</span><span class="p" data-group-id="3144399967-24">]</span><span class="p" data-group-id="3144399967-23">)</span><span class="p" data-group-id="3144399967-22">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="9115754114-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="3144399967-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="9115754114-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="3144399967-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9115754114-27">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="9115754114-27">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3144399967-27">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="3144399967-27">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9115754114-28">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="9115754114-28">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">link</span><span class="p" data-group-id="9115754114-29">(</span><span class="n">From</span><span class="p" data-group-id="9115754114-29">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9115754114-30">[</span><span class="p" data-group-id="9115754114-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9115754114-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3144399967-28">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="3144399967-28">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">link</span><span class="p" data-group-id="3144399967-29">(</span><span class="n">From</span><span class="p" data-group-id="3144399967-29">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="3144399967-30">[</span><span class="p" data-group-id="3144399967-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3144399967-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="9115754114-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="9115754114-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-33">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="3144399967-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="3144399967-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-33">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="9115754114-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="3144399967-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9115754114-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3144399967-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9115754114-36">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="9115754114-36">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9115754114-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9115754114-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9115754114-38">}</span><span class="p" data-group-id="9115754114-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="9115754114-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-39">)</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3144399967-36">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="3144399967-36">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3144399967-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3144399967-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3144399967-38">}</span><span class="p" data-group-id="3144399967-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="3144399967-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-39">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="9115754114-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="3144399967-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9115754114-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9115754114-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3144399967-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3144399967-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9115754114-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="9115754114-42">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9115754114-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9115754114-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="9115754114-44">}</span><span class="p" data-group-id="9115754114-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9115754114-45">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9115754114-45">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9115754114-46">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="9115754114-46">}</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3144399967-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="3144399967-42">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3144399967-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3144399967-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="3144399967-44">}</span><span class="p" data-group-id="3144399967-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3144399967-45">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3144399967-45">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3144399967-46">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="3144399967-46">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% User Commands</span><span class="w">
│ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="9115754114-47">(</span><span class="n">Name</span><span class="p" data-group-id="9115754114-47">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="9115754114-48">(</span><span class="ss">mess_client</span><span class="p" data-group-id="9115754114-48">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="3144399967-47">(</span><span class="n">Name</span><span class="p" data-group-id="3144399967-47">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="3144399967-48">(</span><span class="ss">mess_client</span><span class="p" data-group-id="3144399967-48">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="9115754114-49">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="9115754114-50">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9115754114-51">[</span><span class="nf">server_node</span><span class="p" data-group-id="9115754114-52">(</span><span class="p" data-group-id="9115754114-52">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9115754114-51">]</span><span class="p" data-group-id="9115754114-50">)</span><span class="p" data-group-id="9115754114-49">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="3144399967-49">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="3144399967-50">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3144399967-51">[</span><span class="nf">server_node</span><span class="p" data-group-id="3144399967-52">(</span><span class="p" data-group-id="3144399967-52">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3144399967-51">]</span><span class="p" data-group-id="3144399967-50">)</span><span class="p" data-group-id="3144399967-49">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="9115754114-53">(</span><span class="p" data-group-id="9115754114-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="3144399967-53">(</span><span class="p" data-group-id="3144399967-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="9115754114-54">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9115754114-54">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="9115754114-55">(</span><span class="ss">mess_client</span><span class="p" data-group-id="9115754114-55">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="3144399967-54">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3144399967-54">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="3144399967-55">(</span><span class="ss">mess_client</span><span class="p" data-group-id="3144399967-55">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9115754114-56">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9115754114-56">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3144399967-56">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3144399967-56">}</span><span class="p">,</span><span class="w">
│ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% The client process which runs on each user node</span><span class="w">
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="9115754114-57">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9115754114-57">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9115754114-58">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="9115754114-58">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9115754114-59">{</span><span class="nf">self</span><span class="p" data-group-id="9115754114-60">(</span><span class="p" data-group-id="9115754114-60">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9115754114-59">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="9115754114-61">(</span><span class="p" data-group-id="9115754114-61">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="9115754114-62">(</span><span class="n">Server_Node</span><span class="p" data-group-id="9115754114-62">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="3144399967-57">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3144399967-57">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3144399967-58">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="3144399967-58">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3144399967-59">{</span><span class="nf">self</span><span class="p" data-group-id="3144399967-60">(</span><span class="p" data-group-id="3144399967-60">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="3144399967-59">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="3144399967-61">(</span><span class="p" data-group-id="3144399967-61">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="3144399967-62">(</span><span class="n">Server_Node</span><span class="p" data-group-id="3144399967-62">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="9115754114-63">(</span><span class="n">Server_Node</span><span class="p" data-group-id="9115754114-63">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="3144399967-63">(</span><span class="n">Server_Node</span><span class="p" data-group-id="3144399967-63">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="9115754114-64">(</span><span class="ss">normal</span><span class="p" data-group-id="9115754114-64">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9115754114-65">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9115754114-65">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9115754114-66">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="9115754114-66">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9115754114-67">{</span><span class="nf">self</span><span class="p" data-group-id="9115754114-68">(</span><span class="p" data-group-id="9115754114-68">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9115754114-67">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="9115754114-69">(</span><span class="p" data-group-id="9115754114-69">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9115754114-70">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9115754114-70">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9115754114-71">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9115754114-72">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9115754114-72">]</span><span class="p" data-group-id="9115754114-71">)</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="3144399967-64">(</span><span class="ss">normal</span><span class="p" data-group-id="3144399967-64">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3144399967-65">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3144399967-65">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="3144399967-66">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="3144399967-66">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3144399967-67">{</span><span class="nf">self</span><span class="p" data-group-id="3144399967-68">(</span><span class="p" data-group-id="3144399967-68">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3144399967-67">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="3144399967-69">(</span><span class="p" data-group-id="3144399967-69">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3144399967-70">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3144399967-70">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3144399967-71">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3144399967-72">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="3144399967-72">]</span><span class="p" data-group-id="3144399967-71">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="9115754114-73">(</span><span class="n">Server_Node</span><span class="p" data-group-id="9115754114-73">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="3144399967-73">(</span><span class="n">Server_Node</span><span class="p" data-group-id="3144399967-73">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="9115754114-74">(</span><span class="p" data-group-id="9115754114-74">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="3144399967-74">(</span><span class="p" data-group-id="3144399967-74">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9115754114-75">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="9115754114-75">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9115754114-76">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9115754114-77">[</span><span class="n">Why</span><span class="p" data-group-id="9115754114-77">]</span><span class="p" data-group-id="9115754114-76">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="9115754114-78">(</span><span class="ss">normal</span><span class="p" data-group-id="9115754114-78">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9115754114-79">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="9115754114-79">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9115754114-80">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9115754114-81">[</span><span class="n">What</span><span class="p" data-group-id="9115754114-81">]</span><span class="p" data-group-id="9115754114-80">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3144399967-75">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="3144399967-75">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3144399967-76">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3144399967-77">[</span><span class="n">Why</span><span class="p" data-group-id="3144399967-77">]</span><span class="p" data-group-id="3144399967-76">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="3144399967-78">(</span><span class="ss">normal</span><span class="p" data-group-id="3144399967-78">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3144399967-79">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="3144399967-79">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3144399967-80">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3144399967-81">[</span><span class="n">What</span><span class="p" data-group-id="3144399967-81">]</span><span class="p" data-group-id="3144399967-80">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9115754114-82">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9115754114-83">[</span><span class="p" data-group-id="9115754114-83">]</span><span class="p" data-group-id="9115754114-82">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="9115754114-84">(</span><span class="ss">timeout</span><span class="p" data-group-id="9115754114-84">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3144399967-82">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3144399967-83">[</span><span class="p" data-group-id="3144399967-83">]</span><span class="p" data-group-id="3144399967-82">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="3144399967-84">(</span><span class="ss">timeout</span><span class="p" data-group-id="3144399967-84">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The following changes are added:</p><p>The messenger server traps exits. If it receives an exit signal,
│ │ │  <code class="inline">{'EXIT',From,Reason}</code>, this means that a client process has terminated or is
│ │ │  unreachable for one of the following reasons:</p><ul><li>The user has logged off (the &quot;logoff&quot; message is removed).</li><li>The network connection to the client is broken.</li><li>The node on which the client process resides has gone down.</li><li>The client processes has done some illegal operation.</li></ul><p>If an exit signal is received as above, the tuple <code class="inline">{From,Name}</code> is deleted from
│ │ │  the servers <code class="inline">User_List</code> using the <code class="inline">server_logoff</code> function. If the node on which
│ │ │  the server runs goes down, an exit signal (automatically generated by the
│ │ │  system) is sent to all of the client processes:
│ │ │  <code class="inline">{'EXIT',MessengerPID,noconnection}</code> causing all the client processes to
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/search.html
│ │ │ @@ -108,15 +108,15 @@
│ │ │  <div id="search">
│ │ │    <h1>
│ │ │      <span></span>
│ │ │    </h1>
│ │ │  
│ │ │    <div class="loading"><div></div><div></div><div></div><div></div></div>
│ │ │  </div>
│ │ │ -<script src="dist/search_data-D62CB992.js"></script>
│ │ │ +<script src="dist/search_data-CC135E6A.js"></script>
│ │ │      <footer class="footer">
│ │ │        <p>
│ │ │  
│ │ │          <span class="line">
│ │ │            <button class="a-main footer-button display-quick-switch" title="Search HexDocs packages">
│ │ │              Search HexDocs
│ │ │            </button>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/seq_prog.html
│ │ │ @@ -136,293 +136,293 @@
│ │ │  </span><span class="mi">7</span><span class="gp unselectable">
│ │ │  2&gt; </span></code></pre><p>As shown, the Erlang shell numbers the lines that can be entered, (as 1&gt; 2&gt;) and
│ │ │  that it correctly says that 2 + 5 is 7. If you make writing mistakes in the
│ │ │  shell, you can delete with the backspace key, as in most shells. There are many
│ │ │  more editing commands in the shell (see
│ │ │  <a href="../../erts-15.2.7/doc/html/tty.html">tty - A command line interface</a> in ERTS User's Guide).</p><p>(Notice that many line numbers given by the shell in the following examples are
│ │ │  out of sequence. This is because this tutorial was written and code-tested in
│ │ │ -separate sessions).</p><p>Here is a bit more complex calculation:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="6790381664-1">(</span><span class="mi">42</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">77</span><span class="p" data-group-id="6790381664-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">66</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ +separate sessions).</p><p>Here is a bit more complex calculation:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="7731909415-1">(</span><span class="mi">42</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">77</span><span class="p" data-group-id="7731909415-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">66</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">2618.0</span></code></pre><p>Notice the use of brackets, the multiplication operator <code class="inline">*</code>, and the division
│ │ │  operator <code class="inline">/</code>, as in normal arithmetic (see
│ │ │  <a href="../../doc/system/expressions.html">Expressions</a>).</p><p>Press Control-C to shut down the Erlang system and the Erlang shell.</p><p>The following output is shown:</p><pre><code class="text">BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
│ │ │         (v)ersion (k)ill (D)b-tables (d)istribution
│ │ │  a
│ │ │ -$</code></pre><p>Type <code class="inline">a</code> to leave the Erlang system.</p><p>Another way to shut down the Erlang system is by entering <a href="../../erts-15.2.7/doc/html/erlang.html#halt/0"><code class="inline">halt/0</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">halt</span><span class="p" data-group-id="4981726697-1">(</span><span class="p" data-group-id="4981726697-1">)</span><span class="p">.</span><span class="w">
│ │ │ +$</code></pre><p>Type <code class="inline">a</code> to leave the Erlang system.</p><p>Another way to shut down the Erlang system is by entering <a href="../../erts-15.2.7/doc/html/erlang.html#halt/0"><code class="inline">halt/0</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">halt</span><span class="p" data-group-id="5594149523-1">(</span><span class="p" data-group-id="5594149523-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="err">$</span></code></pre><h2 id="modules-and-functions" class="section-heading">
│ │ │    <a href="#modules-and-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Modules and Functions</span>
│ │ │  </h2>
│ │ │  <p>A programming language is not much use if you only can run code from the shell.
│ │ │  So here is a small Erlang program. Enter it into a file named <code class="inline">tut.erl</code> using a
│ │ │  suitable text editor. The file name <code class="inline">tut.erl</code> is important, and also that it is
│ │ │  in the same directory as the one where you started <code class="inline">erl</code>). If you are lucky your
│ │ │  editor has an Erlang mode that makes it easier for you to enter and format your
│ │ │  code nicely (see <a href="../../lib/tools-4.1.1/doc/html/erlang_mode_chapter.html">The Erlang mode for Emacs</a>
│ │ │  in Tools User's Guide), but you can manage perfectly well without. Here is the
│ │ │ -code to enter:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6764664983-1">(</span><span class="ss">tut</span><span class="p" data-group-id="6764664983-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6764664983-2">(</span><span class="p" data-group-id="6764664983-3">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6764664983-3">]</span><span class="p" data-group-id="6764664983-2">)</span><span class="p">.</span><span class="w">
│ │ │ +code to enter:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8248694306-1">(</span><span class="ss">tut</span><span class="p" data-group-id="8248694306-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8248694306-2">(</span><span class="p" data-group-id="8248694306-3">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8248694306-3">]</span><span class="p" data-group-id="8248694306-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="6764664983-4">(</span><span class="n">X</span><span class="p" data-group-id="6764664983-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="8248694306-4">(</span><span class="n">X</span><span class="p" data-group-id="8248694306-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="p">.</span></code></pre><p>It is not hard to guess that this program doubles the value of numbers. The
│ │ │  first two lines of the code are described later. Let us compile the program.
│ │ │ -This can be done in an Erlang shell as follows, where <code class="inline">c</code> means compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">c</span><span class="p" data-group-id="7351675779-1">(</span><span class="ss">tut</span><span class="p" data-group-id="7351675779-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7351675779-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut</span><span class="p" data-group-id="7351675779-2">}</span></code></pre><p>The <code class="inline">{ok,tut}</code> means that the compilation is OK. If it says <code class="inline">error</code> it means
│ │ │ +This can be done in an Erlang shell as follows, where <code class="inline">c</code> means compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">c</span><span class="p" data-group-id="6189586887-1">(</span><span class="ss">tut</span><span class="p" data-group-id="6189586887-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6189586887-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut</span><span class="p" data-group-id="6189586887-2">}</span></code></pre><p>The <code class="inline">{ok,tut}</code> means that the compilation is OK. If it says <code class="inline">error</code> it means
│ │ │  that there is some mistake in the text that you entered. Additional error
│ │ │  messages gives an idea to what is wrong so you can modify the text and then try
│ │ │ -to compile the program again.</p><p>Now run the program:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="9129765409-1">(</span><span class="mi">10</span><span class="p" data-group-id="9129765409-1">)</span><span class="p">.</span><span class="w">
│ │ │ +to compile the program again.</p><p>Now run the program:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="2734025605-1">(</span><span class="mi">10</span><span class="p" data-group-id="2734025605-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">20</span></code></pre><p>As expected, double of 10 is 20.</p><p>Now let us get back to the first two lines of the code. Erlang programs are
│ │ │  written in files. Each file contains an Erlang <em>module</em>. The first line of code
│ │ │ -in the module is the module name (see <a href="../../doc/system/modules.html">Modules</a>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9800284457-1">(</span><span class="ss">tut</span><span class="p" data-group-id="9800284457-1">)</span><span class="p">.</span></code></pre><p>Thus, the module is called <em>tut</em>. Notice the full stop <code class="inline">.</code> at the end of the
│ │ │ +in the module is the module name (see <a href="../../doc/system/modules.html">Modules</a>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9462200858-1">(</span><span class="ss">tut</span><span class="p" data-group-id="9462200858-1">)</span><span class="p">.</span></code></pre><p>Thus, the module is called <em>tut</em>. Notice the full stop <code class="inline">.</code> at the end of the
│ │ │  line. The files which are used to store the module must have the same name as
│ │ │  the module but with the extension <code class="inline">.erl</code>. In this case the file name is
│ │ │  <code class="inline">tut.erl</code>. When using a function in another module, the syntax
│ │ │  <code class="inline">module_name:function_name(arguments)</code> is used. So the following means call
│ │ │ -function <code class="inline">double</code> in module <code class="inline">tut</code> with argument <code class="inline">10</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="0341732942-1">(</span><span class="mi">10</span><span class="p" data-group-id="0341732942-1">)</span><span class="p">.</span></code></pre><p>The second line says that the module <code class="inline">tut</code> contains a function called <code class="inline">double</code>,
│ │ │ -which takes one argument (<code class="inline">X</code> in our example):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4956258249-1">(</span><span class="p" data-group-id="4956258249-2">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4956258249-2">]</span><span class="p" data-group-id="4956258249-1">)</span><span class="p">.</span></code></pre><p>The second line also says that this function can be called from outside the
│ │ │ +function <code class="inline">double</code> in module <code class="inline">tut</code> with argument <code class="inline">10</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="7834087414-1">(</span><span class="mi">10</span><span class="p" data-group-id="7834087414-1">)</span><span class="p">.</span></code></pre><p>The second line says that the module <code class="inline">tut</code> contains a function called <code class="inline">double</code>,
│ │ │ +which takes one argument (<code class="inline">X</code> in our example):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6458212768-1">(</span><span class="p" data-group-id="6458212768-2">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6458212768-2">]</span><span class="p" data-group-id="6458212768-1">)</span><span class="p">.</span></code></pre><p>The second line also says that this function can be called from outside the
│ │ │  module <code class="inline">tut</code>. More about this later. Again, notice the <code class="inline">.</code> at the end of the
│ │ │  line.</p><p>Now for a more complicated example, the factorial of a number. For example, the
│ │ │ -factorial of 4 is 4 <em> 3 </em> 2 * 1, which equals 24.</p><p>Enter the following code in a file named <code class="inline">tut1.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6147494208-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="6147494208-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6147494208-2">(</span><span class="p" data-group-id="6147494208-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6147494208-3">]</span><span class="p" data-group-id="6147494208-2">)</span><span class="p">.</span><span class="w">
│ │ │ +factorial of 4 is 4 <em> 3 </em> 2 * 1, which equals 24.</p><p>Enter the following code in a file named <code class="inline">tut1.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6171077333-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="6171077333-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6171077333-2">(</span><span class="p" data-group-id="6171077333-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6171077333-3">]</span><span class="p" data-group-id="6171077333-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="6147494208-4">(</span><span class="mi">1</span><span class="p" data-group-id="6147494208-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="6171077333-4">(</span><span class="mi">1</span><span class="p" data-group-id="6171077333-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="6147494208-5">(</span><span class="n">N</span><span class="p" data-group-id="6147494208-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="6147494208-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6147494208-6">)</span><span class="p">.</span></code></pre><p>So this is a module, called <code class="inline">tut1</code> that contains a function called <code class="inline">fac&gt;</code>, which
│ │ │ -takes one argument, <code class="inline">N</code>.</p><p>The first part says that the factorial of 1 is 1.:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="1415600959-1">(</span><span class="mi">1</span><span class="p" data-group-id="1415600959-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="6171077333-5">(</span><span class="n">N</span><span class="p" data-group-id="6171077333-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="6171077333-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6171077333-6">)</span><span class="p">.</span></code></pre><p>So this is a module, called <code class="inline">tut1</code> that contains a function called <code class="inline">fac&gt;</code>, which
│ │ │ +takes one argument, <code class="inline">N</code>.</p><p>The first part says that the factorial of 1 is 1.:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="5821294816-1">(</span><span class="mi">1</span><span class="p" data-group-id="5821294816-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">;</span></code></pre><p>Notice that this part ends with a semicolon <code class="inline">;</code> that indicates that there is
│ │ │  more of the function <code class="inline">fac&gt;</code> to come.</p><p>The second part says that the factorial of N is N multiplied by the factorial of
│ │ │ -N - 1:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="7056651191-1">(</span><span class="n">N</span><span class="p" data-group-id="7056651191-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="7056651191-2">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7056651191-2">)</span><span class="p">.</span></code></pre><p>Notice that this part ends with a <code class="inline">.</code> saying that there are no more parts of
│ │ │ -this function.</p><p>Compile the file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="2661149876-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="2661149876-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2661149876-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="2661149876-2">}</span></code></pre><p>And now calculate the factorial of 4.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">6&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">fac</span><span class="p" data-group-id="6412038617-1">(</span><span class="mi">4</span><span class="p" data-group-id="6412038617-1">)</span><span class="p">.</span><span class="w">
│ │ │ +N - 1:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="6437296164-1">(</span><span class="n">N</span><span class="p" data-group-id="6437296164-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="6437296164-2">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6437296164-2">)</span><span class="p">.</span></code></pre><p>Notice that this part ends with a <code class="inline">.</code> saying that there are no more parts of
│ │ │ +this function.</p><p>Compile the file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="8487554677-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="8487554677-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8487554677-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="8487554677-2">}</span></code></pre><p>And now calculate the factorial of 4.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">6&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">fac</span><span class="p" data-group-id="4436905257-1">(</span><span class="mi">4</span><span class="p" data-group-id="4436905257-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">24</span></code></pre><p>Here the function <code class="inline">fac&gt;</code> in module <code class="inline">tut1</code> is called with argument <code class="inline">4</code>.</p><p>A function can have many arguments. Let us expand the module <code class="inline">tut1</code> with the
│ │ │ -function to multiply two numbers:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2621368601-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="2621368601-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2621368601-2">(</span><span class="p" data-group-id="2621368601-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">mult</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2621368601-3">]</span><span class="p" data-group-id="2621368601-2">)</span><span class="p">.</span><span class="w">
│ │ │ +function to multiply two numbers:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6758304391-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="6758304391-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6758304391-2">(</span><span class="p" data-group-id="6758304391-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">mult</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6758304391-3">]</span><span class="p" data-group-id="6758304391-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="2621368601-4">(</span><span class="mi">1</span><span class="p" data-group-id="2621368601-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="6758304391-4">(</span><span class="mi">1</span><span class="p" data-group-id="6758304391-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="2621368601-5">(</span><span class="n">N</span><span class="p" data-group-id="2621368601-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="2621368601-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2621368601-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="6758304391-5">(</span><span class="n">N</span><span class="p" data-group-id="6758304391-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="6758304391-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6758304391-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">mult</span><span class="p" data-group-id="2621368601-7">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2621368601-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">mult</span><span class="p" data-group-id="6758304391-7">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6758304391-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>Notice that it is also required to expand the <code class="inline">-export</code> line with the
│ │ │ -information that there is another function <code class="inline">mult</code> with two arguments.</p><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nf">c</span><span class="p" data-group-id="1336350688-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="1336350688-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1336350688-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="1336350688-2">}</span></code></pre><p>Try out the new function <code class="inline">mult</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">8&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">mult</span><span class="p" data-group-id="7695274857-1">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7695274857-1">)</span><span class="p">.</span><span class="w">
│ │ │ +information that there is another function <code class="inline">mult</code> with two arguments.</p><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nf">c</span><span class="p" data-group-id="4901219667-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="4901219667-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4901219667-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="4901219667-2">}</span></code></pre><p>Try out the new function <code class="inline">mult</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">8&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">mult</span><span class="p" data-group-id="3972562674-1">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3972562674-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">12</span></code></pre><p>In this example the numbers are integers and the arguments in the functions in
│ │ │  the code <code class="inline">N</code>, <code class="inline">X</code>, and <code class="inline">Y</code> are called variables. Variables must start with a
│ │ │  capital letter (see <a href="../../doc/system/expressions.html">Variables</a>). Examples of
│ │ │  variables are <code class="inline">Number</code>, <code class="inline">ShoeSize</code>, and <code class="inline">Age</code>.</p><h2 id="atoms" class="section-heading">
│ │ │    <a href="#atoms" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Atoms</span>
│ │ │  </h2>
│ │ │  <p>Atom is another data type in Erlang. Atoms start with a small letter (see
│ │ │  <a href="../../doc/system/data_types.html">Atom</a>), for example, <code class="inline">charles</code>, <code class="inline">centimeter</code>, and
│ │ │  <code class="inline">inch</code>. Atoms are simply names, nothing else. They are not like variables, which
│ │ │  can have a value.</p><p>Enter the next program in a file named <code class="inline">tut2.erl</code>). It can be useful for
│ │ │ -converting from inches to centimeters and conversely:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4545577921-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="4545577921-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4545577921-2">(</span><span class="p" data-group-id="4545577921-3">[</span><span class="ss">convert</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4545577921-3">]</span><span class="p" data-group-id="4545577921-2">)</span><span class="p">.</span><span class="w">
│ │ │ +converting from inches to centimeters and conversely:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7860881849-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="7860881849-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7860881849-2">(</span><span class="p" data-group-id="7860881849-3">[</span><span class="ss">convert</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7860881849-3">]</span><span class="p" data-group-id="7860881849-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert</span><span class="p" data-group-id="4545577921-4">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="4545577921-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">convert</span><span class="p" data-group-id="7860881849-4">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="7860881849-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">M</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert</span><span class="p" data-group-id="4545577921-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="4545577921-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p">.</span></code></pre><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nf">c</span><span class="p" data-group-id="1291827906-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="1291827906-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1291827906-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut2</span><span class="p" data-group-id="1291827906-2">}</span></code></pre><p>Test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">10&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="9046097397-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="9046097397-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">convert</span><span class="p" data-group-id="7860881849-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="7860881849-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p">.</span></code></pre><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nf">c</span><span class="p" data-group-id="0709589308-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="0709589308-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0709589308-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut2</span><span class="p" data-group-id="0709589308-2">}</span></code></pre><p>Test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">10&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="7478027095-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="7478027095-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">1.1811023622047243</span><span class="gp unselectable">
│ │ │ -11&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="9046097397-2">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="9046097397-2">)</span><span class="p">.</span><span class="w">
│ │ │ +11&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="7478027095-2">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="7478027095-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">17.78</span></code></pre><p>Notice the introduction of decimals (floating point numbers) without any
│ │ │  explanation. Hopefully you can cope with that.</p><p>Let us see what happens if something other than <code class="inline">centimeter</code> or <code class="inline">inch</code> is
│ │ │ -entered in the <code class="inline">convert</code> function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">12&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="3501125549-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">miles</span><span class="p" data-group-id="3501125549-1">)</span><span class="p">.</span><span class="w">
│ │ │ +entered in the <code class="inline">convert</code> function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">12&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="5393990282-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">miles</span><span class="p" data-group-id="5393990282-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no function clause matching tut2:convert(3,miles) (tut2.erl, line 4)</span></code></pre><p>The two parts of the <code class="inline">convert</code> function are called its clauses. As shown,
│ │ │  <code class="inline">miles</code> is not part of either of the clauses. The Erlang system cannot <em>match</em>
│ │ │  either of the clauses so an error message <code class="inline">function_clause</code> is returned. The
│ │ │  shell formats the error message nicely, but the error tuple is saved in the
│ │ │ -shell's history list and can be output by the shell command <code class="inline">v/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">13&gt; </span><span class="nf">v</span><span class="p" data-group-id="7608095551-1">(</span><span class="mi">12</span><span class="p" data-group-id="7608095551-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7608095551-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="7608095551-3">{</span><span class="ss">function_clause</span><span class="p">,</span><span class="p" data-group-id="7608095551-4">[</span><span class="p" data-group-id="7608095551-5">{</span><span class="ss">tut2</span><span class="p">,</span><span class="ss">convert</span><span class="p">,</span><span class="w">
│ │ │ -                                </span><span class="p" data-group-id="7608095551-6">[</span><span class="mi">3</span><span class="p">,</span><span class="ss">miles</span><span class="p" data-group-id="7608095551-6">]</span><span class="p">,</span><span class="w">
│ │ │ -                                </span><span class="p" data-group-id="7608095551-7">[</span><span class="p" data-group-id="7608095551-8">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;tut2.erl&quot;</span><span class="p" data-group-id="7608095551-8">}</span><span class="p">,</span><span class="p" data-group-id="7608095551-9">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7608095551-9">}</span><span class="p" data-group-id="7608095551-7">]</span><span class="p" data-group-id="7608095551-5">}</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="p" data-group-id="7608095551-10">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="p" data-group-id="7608095551-11">[</span><span class="p" data-group-id="7608095551-12">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="7608095551-12">}</span><span class="p">,</span><span class="p" data-group-id="7608095551-13">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">677</span><span class="p" data-group-id="7608095551-13">}</span><span class="p" data-group-id="7608095551-11">]</span><span class="p" data-group-id="7608095551-10">}</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="p" data-group-id="7608095551-14">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="7608095551-15">[</span><span class="p" data-group-id="7608095551-16">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="7608095551-16">}</span><span class="p">,</span><span class="p" data-group-id="7608095551-17">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">687</span><span class="p" data-group-id="7608095551-17">}</span><span class="p" data-group-id="7608095551-15">]</span><span class="p" data-group-id="7608095551-14">}</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="p" data-group-id="7608095551-18">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="7608095551-19">[</span><span class="p" data-group-id="7608095551-20">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="7608095551-20">}</span><span class="p">,</span><span class="p" data-group-id="7608095551-21">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">642</span><span class="p" data-group-id="7608095551-21">}</span><span class="p" data-group-id="7608095551-19">]</span><span class="p" data-group-id="7608095551-18">}</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="p" data-group-id="7608095551-22">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_loop</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                 </span><span class="p" data-group-id="7608095551-23">[</span><span class="p" data-group-id="7608095551-24">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="7608095551-24">}</span><span class="p">,</span><span class="p" data-group-id="7608095551-25">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">627</span><span class="p" data-group-id="7608095551-25">}</span><span class="p" data-group-id="7608095551-23">]</span><span class="p" data-group-id="7608095551-22">}</span><span class="p" data-group-id="7608095551-4">]</span><span class="p" data-group-id="7608095551-3">}</span><span class="p" data-group-id="7608095551-2">}</span></code></pre><h2 id="tuples" class="section-heading">
│ │ │ +shell's history list and can be output by the shell command <code class="inline">v/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">13&gt; </span><span class="nf">v</span><span class="p" data-group-id="4355753015-1">(</span><span class="mi">12</span><span class="p" data-group-id="4355753015-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4355753015-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="4355753015-3">{</span><span class="ss">function_clause</span><span class="p">,</span><span class="p" data-group-id="4355753015-4">[</span><span class="p" data-group-id="4355753015-5">{</span><span class="ss">tut2</span><span class="p">,</span><span class="ss">convert</span><span class="p">,</span><span class="w">
│ │ │ +                                </span><span class="p" data-group-id="4355753015-6">[</span><span class="mi">3</span><span class="p">,</span><span class="ss">miles</span><span class="p" data-group-id="4355753015-6">]</span><span class="p">,</span><span class="w">
│ │ │ +                                </span><span class="p" data-group-id="4355753015-7">[</span><span class="p" data-group-id="4355753015-8">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;tut2.erl&quot;</span><span class="p" data-group-id="4355753015-8">}</span><span class="p">,</span><span class="p" data-group-id="4355753015-9">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4355753015-9">}</span><span class="p" data-group-id="4355753015-7">]</span><span class="p" data-group-id="4355753015-5">}</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="4355753015-10">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="p" data-group-id="4355753015-11">[</span><span class="p" data-group-id="4355753015-12">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="4355753015-12">}</span><span class="p">,</span><span class="p" data-group-id="4355753015-13">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">677</span><span class="p" data-group-id="4355753015-13">}</span><span class="p" data-group-id="4355753015-11">]</span><span class="p" data-group-id="4355753015-10">}</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="4355753015-14">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="4355753015-15">[</span><span class="p" data-group-id="4355753015-16">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="4355753015-16">}</span><span class="p">,</span><span class="p" data-group-id="4355753015-17">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">687</span><span class="p" data-group-id="4355753015-17">}</span><span class="p" data-group-id="4355753015-15">]</span><span class="p" data-group-id="4355753015-14">}</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="4355753015-18">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="4355753015-19">[</span><span class="p" data-group-id="4355753015-20">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="4355753015-20">}</span><span class="p">,</span><span class="p" data-group-id="4355753015-21">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">642</span><span class="p" data-group-id="4355753015-21">}</span><span class="p" data-group-id="4355753015-19">]</span><span class="p" data-group-id="4355753015-18">}</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="4355753015-22">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_loop</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                 </span><span class="p" data-group-id="4355753015-23">[</span><span class="p" data-group-id="4355753015-24">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="4355753015-24">}</span><span class="p">,</span><span class="p" data-group-id="4355753015-25">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">627</span><span class="p" data-group-id="4355753015-25">}</span><span class="p" data-group-id="4355753015-23">]</span><span class="p" data-group-id="4355753015-22">}</span><span class="p" data-group-id="4355753015-4">]</span><span class="p" data-group-id="4355753015-3">}</span><span class="p" data-group-id="4355753015-2">}</span></code></pre><h2 id="tuples" class="section-heading">
│ │ │    <a href="#tuples" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Tuples</span>
│ │ │  </h2>
│ │ │ -<p>Now the <code class="inline">tut2</code> program is hardly good programming style. Consider:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="7808103292-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="7808103292-1">)</span><span class="p">.</span></code></pre><p>Does this mean that 3 is in inches? Or does it mean that 3 is in centimeters and
│ │ │ +<p>Now the <code class="inline">tut2</code> program is hardly good programming style. Consider:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="3785308616-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="3785308616-1">)</span><span class="p">.</span></code></pre><p>Does this mean that 3 is in inches? Or does it mean that 3 is in centimeters and
│ │ │  is to be converted to inches? Erlang has a way to group things together to make
│ │ │  things more understandable. These are called <em>tuples</em> and are surrounded by
│ │ │  curly brackets, <code class="inline">{</code> and <code class="inline">}</code>.</p><p>So, <code class="inline">{inch,3}</code> denotes 3 inches and <code class="inline">{centimeter,5}</code> denotes 5 centimeters. Now
│ │ │  let us write a new program that converts centimeters to inches and conversely.
│ │ │ -Enter the following code in a file called <code class="inline">tut3.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1539134609-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="1539134609-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1539134609-2">(</span><span class="p" data-group-id="1539134609-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1539134609-3">]</span><span class="p" data-group-id="1539134609-2">)</span><span class="p">.</span><span class="w">
│ │ │ +Enter the following code in a file called <code class="inline">tut3.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4554927183-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="4554927183-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4554927183-2">(</span><span class="p" data-group-id="4554927183-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4554927183-3">]</span><span class="p" data-group-id="4554927183-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="1539134609-4">(</span><span class="p" data-group-id="1539134609-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1539134609-5">}</span><span class="p" data-group-id="1539134609-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1539134609-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="1539134609-6">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="1539134609-7">(</span><span class="p" data-group-id="1539134609-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1539134609-8">}</span><span class="p" data-group-id="1539134609-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1539134609-9">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="1539134609-9">}</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">14&gt; </span><span class="nf">c</span><span class="p" data-group-id="8304967954-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="8304967954-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8304967954-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut3</span><span class="p" data-group-id="8304967954-2">}</span><span class="gp unselectable">
│ │ │ -15&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="8304967954-3">(</span><span class="p" data-group-id="8304967954-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="8304967954-4">}</span><span class="p" data-group-id="8304967954-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8304967954-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">12.7</span><span class="p" data-group-id="8304967954-5">}</span><span class="gp unselectable">
│ │ │ -16&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="8304967954-6">(</span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="8304967954-7">(</span><span class="p" data-group-id="8304967954-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="8304967954-8">}</span><span class="p" data-group-id="8304967954-7">)</span><span class="p" data-group-id="8304967954-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8304967954-9">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">5.0</span><span class="p" data-group-id="8304967954-9">}</span></code></pre><p>Notice on line 16 that 5 inches is converted to centimeters and back again and
│ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="4554927183-4">(</span><span class="p" data-group-id="4554927183-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4554927183-5">}</span><span class="p" data-group-id="4554927183-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4554927183-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="4554927183-6">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="4554927183-7">(</span><span class="p" data-group-id="4554927183-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4554927183-8">}</span><span class="p" data-group-id="4554927183-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4554927183-9">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="4554927183-9">}</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">14&gt; </span><span class="nf">c</span><span class="p" data-group-id="9243407977-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="9243407977-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9243407977-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut3</span><span class="p" data-group-id="9243407977-2">}</span><span class="gp unselectable">
│ │ │ +15&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="9243407977-3">(</span><span class="p" data-group-id="9243407977-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="9243407977-4">}</span><span class="p" data-group-id="9243407977-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9243407977-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">12.7</span><span class="p" data-group-id="9243407977-5">}</span><span class="gp unselectable">
│ │ │ +16&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="9243407977-6">(</span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="9243407977-7">(</span><span class="p" data-group-id="9243407977-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="9243407977-8">}</span><span class="p" data-group-id="9243407977-7">)</span><span class="p" data-group-id="9243407977-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9243407977-9">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">5.0</span><span class="p" data-group-id="9243407977-9">}</span></code></pre><p>Notice on line 16 that 5 inches is converted to centimeters and back again and
│ │ │  reassuringly get back to the original value. That is, the argument to a function
│ │ │  can be the result of another function. Consider how line 16 (above) works. The
│ │ │  argument given to the function <code class="inline">{inch,5}</code> is first matched against the first
│ │ │  head clause of <code class="inline">convert_length</code>, that is, <code class="inline">convert_length({centimeter,X})</code>. It
│ │ │  can be seen that <code class="inline">{centimeter,X}</code> does not match <code class="inline">{inch,5}</code> (the head is the bit
│ │ │  before the <code class="inline">-&gt;</code>). This having failed, let us try the head of the next clause
│ │ │  that is, <code class="inline">convert_length({inch,Y})</code>. This matches, and <code class="inline">Y</code> gets the value 5.</p><p>Tuples can have more than two parts, in fact as many parts as you want, and
│ │ │  contain any valid Erlang <em>term</em>. For example, to represent the temperature of
│ │ │ -various cities of the world:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8589928435-1">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8589928435-2">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8589928435-2">}</span><span class="p" data-group-id="8589928435-1">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8589928435-3">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8589928435-4">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="8589928435-4">}</span><span class="p" data-group-id="8589928435-3">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8589928435-5">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8589928435-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8589928435-6">}</span><span class="p" data-group-id="8589928435-5">}</span></code></pre><p>Tuples have a fixed number of items in them. Each item in a tuple is called an
│ │ │ +various cities of the world:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7266724192-1">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7266724192-2">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="7266724192-2">}</span><span class="p" data-group-id="7266724192-1">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7266724192-3">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7266724192-4">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="7266724192-4">}</span><span class="p" data-group-id="7266724192-3">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7266724192-5">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7266724192-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="7266724192-6">}</span><span class="p" data-group-id="7266724192-5">}</span></code></pre><p>Tuples have a fixed number of items in them. Each item in a tuple is called an
│ │ │  <em>element</em>. In the tuple <code class="inline">{moscow,{c,-10}}</code>, element 1 is <code class="inline">moscow</code> and element 2
│ │ │  is <code class="inline">{c,-10}</code>. Here <code class="inline">c</code> represents Celsius and <code class="inline">f</code> Fahrenheit.</p><h2 id="lists" class="section-heading">
│ │ │    <a href="#lists" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Lists</span>
│ │ │  </h2>
│ │ │  <p>Whereas tuples group things together, it is also needed to represent lists of
│ │ │  things. Lists in Erlang are surrounded by square brackets, <code class="inline">[</code> and <code class="inline">]</code>. For
│ │ │ -example, a list of the temperatures of various cities in the world can be:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9521967119-1">[</span><span class="p" data-group-id="9521967119-2">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9521967119-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="9521967119-3">}</span><span class="p" data-group-id="9521967119-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9521967119-4">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9521967119-5">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="9521967119-5">}</span><span class="p" data-group-id="9521967119-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9521967119-6">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9521967119-7">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="9521967119-7">}</span><span class="p" data-group-id="9521967119-6">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9521967119-8">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9521967119-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="9521967119-9">}</span><span class="p" data-group-id="9521967119-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9521967119-10">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9521967119-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="9521967119-11">}</span><span class="p" data-group-id="9521967119-10">}</span><span class="p" data-group-id="9521967119-1">]</span></code></pre><p>Notice that this list was so long that it did not fit on one line. This does not
│ │ │ +example, a list of the temperatures of various cities in the world can be:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0808223326-1">[</span><span class="p" data-group-id="0808223326-2">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808223326-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="0808223326-3">}</span><span class="p" data-group-id="0808223326-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808223326-4">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808223326-5">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="0808223326-5">}</span><span class="p" data-group-id="0808223326-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808223326-6">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808223326-7">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="0808223326-7">}</span><span class="p" data-group-id="0808223326-6">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0808223326-8">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808223326-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="0808223326-9">}</span><span class="p" data-group-id="0808223326-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808223326-10">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808223326-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="0808223326-11">}</span><span class="p" data-group-id="0808223326-10">}</span><span class="p" data-group-id="0808223326-1">]</span></code></pre><p>Notice that this list was so long that it did not fit on one line. This does not
│ │ │  matter, Erlang allows line breaks at all &quot;sensible places&quot; but not, for example,
│ │ │  in the middle of atoms, integers, and others.</p><p>A useful way of looking at parts of lists, is by using <code class="inline">|</code>. This is best
│ │ │ -explained by an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">17&gt; </span><span class="p" data-group-id="1873702488-1">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="n">TheRest</span><span class="p" data-group-id="1873702488-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1873702488-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1873702488-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1873702488-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1873702488-3">]</span><span class="gp unselectable">
│ │ │ +explained by an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">17&gt; </span><span class="p" data-group-id="5269808160-1">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="n">TheRest</span><span class="p" data-group-id="5269808160-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5269808160-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5269808160-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5269808160-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5269808160-3">]</span><span class="gp unselectable">
│ │ │  18&gt; </span><span class="n">First</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="gp unselectable">
│ │ │  19&gt; </span><span class="n">TheRest</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1873702488-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1873702488-4">]</span></code></pre><p>To separate the first elements of the list from the rest of the list, <code class="inline">|</code> is
│ │ │ -used. <code class="inline">First</code> has got value <code class="inline">1</code> and <code class="inline">TheRest</code> has got the value <code class="inline">[2,3,4,5]</code>.</p><p>Another example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">20&gt; </span><span class="p" data-group-id="3088098029-1">[</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">R</span><span class="p" data-group-id="3088098029-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3088098029-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3088098029-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3088098029-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3088098029-3">]</span><span class="gp unselectable">
│ │ │ +</span><span class="p" data-group-id="5269808160-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5269808160-4">]</span></code></pre><p>To separate the first elements of the list from the rest of the list, <code class="inline">|</code> is
│ │ │ +used. <code class="inline">First</code> has got value <code class="inline">1</code> and <code class="inline">TheRest</code> has got the value <code class="inline">[2,3,4,5]</code>.</p><p>Another example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">20&gt; </span><span class="p" data-group-id="9054245540-1">[</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">R</span><span class="p" data-group-id="9054245540-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9054245540-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="9054245540-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9054245540-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="9054245540-3">]</span><span class="gp unselectable">
│ │ │  21&gt; </span><span class="n">E1</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="gp unselectable">
│ │ │  22&gt; </span><span class="n">E2</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">2</span><span class="gp unselectable">
│ │ │  23&gt; </span><span class="n">R</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3088098029-4">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3088098029-4">]</span></code></pre><p>Here you see the use of <code class="inline">|</code> to get the first two elements from the list. If you
│ │ │ +</span><span class="p" data-group-id="9054245540-4">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="9054245540-4">]</span></code></pre><p>Here you see the use of <code class="inline">|</code> to get the first two elements from the list. If you
│ │ │  try to get more elements from the list than there are elements in the list, an
│ │ │  error is returned. Notice also the special case of the list with no elements,
│ │ │ -<code class="inline">[]</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">24&gt; </span><span class="p" data-group-id="6744002850-1">[</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="6744002850-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6744002850-2">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6744002850-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6744002850-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6744002850-3">]</span><span class="gp unselectable">
│ │ │ +<code class="inline">[]</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">24&gt; </span><span class="p" data-group-id="0860216347-1">[</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="0860216347-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0860216347-2">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0860216347-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0860216347-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0860216347-3">]</span><span class="gp unselectable">
│ │ │  25&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="gp unselectable">
│ │ │  26&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">2</span><span class="gp unselectable">
│ │ │  27&gt; </span><span class="n">C</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6744002850-4">[</span><span class="p" data-group-id="6744002850-4">]</span></code></pre><p>In the previous examples, new variable names are used, instead of reusing the
│ │ │ +</span><span class="p" data-group-id="0860216347-4">[</span><span class="p" data-group-id="0860216347-4">]</span></code></pre><p>In the previous examples, new variable names are used, instead of reusing the
│ │ │  old ones: <code class="inline">First</code>, <code class="inline">TheRest</code>, <code class="inline">E1</code>, <code class="inline">E2</code>, <code class="inline">R</code>, <code class="inline">A</code>, <code class="inline">B</code>, and <code class="inline">C</code>. The reason for
│ │ │  this is that a variable can only be given a value once in its context (scope).
│ │ │  More about this later.</p><p>The following example shows how to find the length of a list. Enter the
│ │ │ -following code in a file named <code class="inline">tut4.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6142227922-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="6142227922-1">)</span><span class="p">.</span><span class="w">
│ │ │ +following code in a file named <code class="inline">tut4.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6798011271-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="6798011271-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6142227922-2">(</span><span class="p" data-group-id="6142227922-3">[</span><span class="ss">list_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6142227922-3">]</span><span class="p" data-group-id="6142227922-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6798011271-2">(</span><span class="p" data-group-id="6798011271-3">[</span><span class="ss">list_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6798011271-3">]</span><span class="p" data-group-id="6798011271-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">list_length</span><span class="p" data-group-id="6142227922-4">(</span><span class="p" data-group-id="6142227922-5">[</span><span class="p" data-group-id="6142227922-5">]</span><span class="p" data-group-id="6142227922-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">list_length</span><span class="p" data-group-id="6798011271-4">(</span><span class="p" data-group-id="6798011271-5">[</span><span class="p" data-group-id="6798011271-5">]</span><span class="p" data-group-id="6798011271-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">list_length</span><span class="p" data-group-id="6142227922-6">(</span><span class="p" data-group-id="6142227922-7">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6142227922-7">]</span><span class="p" data-group-id="6142227922-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="6142227922-8">(</span><span class="n">Rest</span><span class="p" data-group-id="6142227922-8">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">28&gt; </span><span class="nf">c</span><span class="p" data-group-id="1610751637-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="1610751637-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1610751637-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut4</span><span class="p" data-group-id="1610751637-2">}</span><span class="gp unselectable">
│ │ │ -29&gt; </span><span class="nc">tut4</span><span class="p">:</span><span class="nf">list_length</span><span class="p" data-group-id="1610751637-3">(</span><span class="p" data-group-id="1610751637-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="1610751637-4">]</span><span class="p" data-group-id="1610751637-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">7</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="5928204873-1">(</span><span class="p" data-group-id="5928204873-2">[</span><span class="p" data-group-id="5928204873-2">]</span><span class="p" data-group-id="5928204873-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="mi">0</span><span class="p">;</span></code></pre><p>The length of an empty list is obviously 0.</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="5856666313-1">(</span><span class="p" data-group-id="5856666313-2">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="5856666313-2">]</span><span class="p" data-group-id="5856666313-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="5856666313-3">(</span><span class="n">Rest</span><span class="p" data-group-id="5856666313-3">)</span><span class="p">.</span></code></pre><p>The length of a list with the first element <code class="inline">First</code> and the remaining elements
│ │ │ +</span><span class="nf">list_length</span><span class="p" data-group-id="6798011271-6">(</span><span class="p" data-group-id="6798011271-7">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6798011271-7">]</span><span class="p" data-group-id="6798011271-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="6798011271-8">(</span><span class="n">Rest</span><span class="p" data-group-id="6798011271-8">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">28&gt; </span><span class="nf">c</span><span class="p" data-group-id="5765371278-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="5765371278-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5765371278-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut4</span><span class="p" data-group-id="5765371278-2">}</span><span class="gp unselectable">
│ │ │ +29&gt; </span><span class="nc">tut4</span><span class="p">:</span><span class="nf">list_length</span><span class="p" data-group-id="5765371278-3">(</span><span class="p" data-group-id="5765371278-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="5765371278-4">]</span><span class="p" data-group-id="5765371278-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">7</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="6414117038-1">(</span><span class="p" data-group-id="6414117038-2">[</span><span class="p" data-group-id="6414117038-2">]</span><span class="p" data-group-id="6414117038-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="mi">0</span><span class="p">;</span></code></pre><p>The length of an empty list is obviously 0.</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="4538228283-1">(</span><span class="p" data-group-id="4538228283-2">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4538228283-2">]</span><span class="p" data-group-id="4538228283-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="4538228283-3">(</span><span class="n">Rest</span><span class="p" data-group-id="4538228283-3">)</span><span class="p">.</span></code></pre><p>The length of a list with the first element <code class="inline">First</code> and the remaining elements
│ │ │  <code class="inline">Rest</code> is 1 + the length of <code class="inline">Rest</code>.</p><p>(Advanced readers only: This is not tail recursive, there is a better way to
│ │ │  write this function.)</p><p>In general, tuples are used where &quot;records&quot; or &quot;structs&quot; are used in other
│ │ │  languages. Also, lists are used when representing things with varying sizes,
│ │ │  that is, where linked lists are used in other languages.</p><p>Erlang does not have a string data type. Instead, strings can be represented by
│ │ │  lists of Unicode characters. This implies for example that the list <code class="inline">[97,98,99]</code>
│ │ │  is equivalent to <code class="inline">&quot;abc&quot;</code>. The Erlang shell is &quot;clever&quot; and guesses what list you
│ │ │ -mean and outputs it in what it thinks is the most appropriate form, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">30&gt; </span><span class="p" data-group-id="3393949152-1">[</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="3393949152-1">]</span><span class="p">.</span><span class="w">
│ │ │ +mean and outputs it in what it thinks is the most appropriate form, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">30&gt; </span><span class="p" data-group-id="6858162701-1">[</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="6858162701-1">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;abc&quot;</span></code></pre><h2 id="maps" class="section-heading">
│ │ │    <a href="#maps" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Maps</span>
│ │ │  </h2>
│ │ │  <p>Maps are a set of key to value associations. These associations are encapsulated
│ │ │ -with <code class="inline">#{</code> and <code class="inline">}</code>. To create an association from <code class="inline">&quot;key&quot;</code> to value <code class="inline">42</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="1709888192-1">#{</span><span class="w"> </span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p" data-group-id="1709888192-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1709888192-2">#{</span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="1709888192-2">}</span></code></pre><p>Let us jump straight into the deep end with an example using some interesting
│ │ │ +with <code class="inline">#{</code> and <code class="inline">}</code>. To create an association from <code class="inline">&quot;key&quot;</code> to value <code class="inline">42</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="6377264321-1">#{</span><span class="w"> </span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p" data-group-id="6377264321-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6377264321-2">#{</span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="6377264321-2">}</span></code></pre><p>Let us jump straight into the deep end with an example using some interesting
│ │ │  features.</p><p>The following example shows how to calculate alpha blending using maps to
│ │ │ -reference color and alpha channels. Enter the code in a file named <code class="inline">color.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0210811635-1">(</span><span class="ss">color</span><span class="p" data-group-id="0210811635-1">)</span><span class="p">.</span><span class="w">
│ │ │ +reference color and alpha channels. Enter the code in a file named <code class="inline">color.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6306242233-1">(</span><span class="ss">color</span><span class="p" data-group-id="6306242233-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0210811635-2">(</span><span class="p" data-group-id="0210811635-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="ss">blend</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0210811635-3">]</span><span class="p" data-group-id="0210811635-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6306242233-2">(</span><span class="p" data-group-id="6306242233-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="ss">blend</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6306242233-3">]</span><span class="p" data-group-id="6306242233-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0210811635-4">(</span><span class="nf">is_channel</span><span class="p" data-group-id="0210811635-5">(</span><span class="n">V</span><span class="p" data-group-id="0210811635-5">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0210811635-6">(</span><span class="nf">is_float</span><span class="p" data-group-id="0210811635-7">(</span><span class="n">V</span><span class="p" data-group-id="0210811635-7">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="0210811635-6">)</span><span class="p" data-group-id="0210811635-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6306242233-4">(</span><span class="nf">is_channel</span><span class="p" data-group-id="6306242233-5">(</span><span class="n">V</span><span class="p" data-group-id="6306242233-5">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6306242233-6">(</span><span class="nf">is_float</span><span class="p" data-group-id="6306242233-7">(</span><span class="n">V</span><span class="p" data-group-id="6306242233-7">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="6306242233-6">)</span><span class="p" data-group-id="6306242233-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">new</span><span class="p" data-group-id="0210811635-8">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="0210811635-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0210811635-9">(</span><span class="n">R</span><span class="p" data-group-id="0210811635-9">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0210811635-10">(</span><span class="n">G</span><span class="p" data-group-id="0210811635-10">)</span><span class="p">,</span><span class="w">
│ │ │ -                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0210811635-11">(</span><span class="n">B</span><span class="p" data-group-id="0210811635-11">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0210811635-12">(</span><span class="n">A</span><span class="p" data-group-id="0210811635-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0210811635-13">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="0210811635-13">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="0210811635-14">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0210811635-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">blend</span><span class="p" data-group-id="0210811635-15">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="nf">alpha</span><span class="p" data-group-id="0210811635-16">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0210811635-16">)</span><span class="p" data-group-id="0210811635-15">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="0210811635-17">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="0210811635-17">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="0210811635-18">#{</span><span class="w">
│ │ │ -        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="0210811635-19">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0210811635-19">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="0210811635-20">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0210811635-20">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="0210811635-21">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0210811635-21">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">new</span><span class="p" data-group-id="6306242233-8">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="6306242233-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="6306242233-9">(</span><span class="n">R</span><span class="p" data-group-id="6306242233-9">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="6306242233-10">(</span><span class="n">G</span><span class="p" data-group-id="6306242233-10">)</span><span class="p">,</span><span class="w">
│ │ │ +                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="6306242233-11">(</span><span class="n">B</span><span class="p" data-group-id="6306242233-11">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="6306242233-12">(</span><span class="n">A</span><span class="p" data-group-id="6306242233-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6306242233-13">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="6306242233-13">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="6306242233-14">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="6306242233-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">blend</span><span class="p" data-group-id="6306242233-15">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="nf">alpha</span><span class="p" data-group-id="6306242233-16">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="6306242233-16">)</span><span class="p" data-group-id="6306242233-15">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="6306242233-17">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="6306242233-17">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="6306242233-18">#{</span><span class="w">
│ │ │ +        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="6306242233-19">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="6306242233-19">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="6306242233-20">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="6306242233-20">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="6306242233-21">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="6306242233-21">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Alpha</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0210811635-18">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="0210811635-22">(</span><span class="p">_</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0210811635-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="0210811635-23">#{</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6306242233-18">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="6306242233-22">(</span><span class="p">_</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6306242233-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="6306242233-23">#{</span><span class="w">
│ │ │          </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0210811635-23">}</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6306242233-23">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alpha</span><span class="p" data-group-id="0210811635-24">(</span><span class="p" data-group-id="0210811635-25">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0210811635-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0210811635-26">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0210811635-26">}</span><span class="p" data-group-id="0210811635-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0210811635-27">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0210811635-27">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">alpha</span><span class="p" data-group-id="6306242233-24">(</span><span class="p" data-group-id="6306242233-25">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="6306242233-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6306242233-26">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="6306242233-26">}</span><span class="p" data-group-id="6306242233-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="6306242233-27">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="6306242233-27">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">red</span><span class="p" data-group-id="0210811635-28">(</span><span class="p" data-group-id="0210811635-29">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0210811635-29">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0210811635-30">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0210811635-30">}</span><span class="p" data-group-id="0210811635-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0210811635-31">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0210811635-31">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">green</span><span class="p" data-group-id="0210811635-32">(</span><span class="p" data-group-id="0210811635-33">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0210811635-33">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0210811635-34">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0210811635-34">}</span><span class="p" data-group-id="0210811635-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0210811635-35">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0210811635-35">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">blue</span><span class="p" data-group-id="0210811635-36">(</span><span class="p" data-group-id="0210811635-37">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0210811635-37">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0210811635-38">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0210811635-38">}</span><span class="p" data-group-id="0210811635-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0210811635-39">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0210811635-39">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">c</span><span class="p" data-group-id="2202311028-1">(</span><span class="ss">color</span><span class="p" data-group-id="2202311028-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2202311028-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">color</span><span class="p" data-group-id="2202311028-2">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">C1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="2202311028-3">(</span><span class="mf">0.3</span><span class="p">,</span><span class="mf">0.4</span><span class="p">,</span><span class="mf">0.5</span><span class="p">,</span><span class="mf">1.0</span><span class="p" data-group-id="2202311028-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2202311028-4">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="2202311028-4">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">C2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="2202311028-5">(</span><span class="mf">1.0</span><span class="p">,</span><span class="mf">0.8</span><span class="p">,</span><span class="mf">0.1</span><span class="p">,</span><span class="mf">0.3</span><span class="p" data-group-id="2202311028-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2202311028-6">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.1</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.8</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="2202311028-6">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="2202311028-7">(</span><span class="n">C1</span><span class="p">,</span><span class="n">C2</span><span class="p" data-group-id="2202311028-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2202311028-8">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="2202311028-8">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="2202311028-9">(</span><span class="n">C2</span><span class="p">,</span><span class="n">C1</span><span class="p" data-group-id="2202311028-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2202311028-10">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.38</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.52</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.51</span><span class="p" data-group-id="2202311028-10">}</span></code></pre><p>This example warrants some explanation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3048013488-1">(</span><span class="nf">is_channel</span><span class="p" data-group-id="3048013488-2">(</span><span class="n">V</span><span class="p" data-group-id="3048013488-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3048013488-3">(</span><span class="nf">is_float</span><span class="p" data-group-id="3048013488-4">(</span><span class="n">V</span><span class="p" data-group-id="3048013488-4">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="3048013488-3">)</span><span class="p" data-group-id="3048013488-1">)</span><span class="p">.</span></code></pre><p>First a macro <code class="inline">is_channel</code> is defined to help with the guard tests. This is only
│ │ │ +</span><span class="nf">red</span><span class="p" data-group-id="6306242233-28">(</span><span class="p" data-group-id="6306242233-29">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="6306242233-29">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6306242233-30">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="6306242233-30">}</span><span class="p" data-group-id="6306242233-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="6306242233-31">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="6306242233-31">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">green</span><span class="p" data-group-id="6306242233-32">(</span><span class="p" data-group-id="6306242233-33">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="6306242233-33">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6306242233-34">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="6306242233-34">}</span><span class="p" data-group-id="6306242233-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="6306242233-35">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="6306242233-35">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">blue</span><span class="p" data-group-id="6306242233-36">(</span><span class="p" data-group-id="6306242233-37">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="6306242233-37">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6306242233-38">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="6306242233-38">}</span><span class="p" data-group-id="6306242233-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="6306242233-39">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="6306242233-39">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">c</span><span class="p" data-group-id="0449003102-1">(</span><span class="ss">color</span><span class="p" data-group-id="0449003102-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0449003102-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">color</span><span class="p" data-group-id="0449003102-2">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">C1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="0449003102-3">(</span><span class="mf">0.3</span><span class="p">,</span><span class="mf">0.4</span><span class="p">,</span><span class="mf">0.5</span><span class="p">,</span><span class="mf">1.0</span><span class="p" data-group-id="0449003102-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0449003102-4">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="0449003102-4">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">C2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="0449003102-5">(</span><span class="mf">1.0</span><span class="p">,</span><span class="mf">0.8</span><span class="p">,</span><span class="mf">0.1</span><span class="p">,</span><span class="mf">0.3</span><span class="p" data-group-id="0449003102-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0449003102-6">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.1</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.8</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="0449003102-6">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="0449003102-7">(</span><span class="n">C1</span><span class="p">,</span><span class="n">C2</span><span class="p" data-group-id="0449003102-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0449003102-8">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="0449003102-8">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="0449003102-9">(</span><span class="n">C2</span><span class="p">,</span><span class="n">C1</span><span class="p" data-group-id="0449003102-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0449003102-10">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.38</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.52</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.51</span><span class="p" data-group-id="0449003102-10">}</span></code></pre><p>This example warrants some explanation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2026097987-1">(</span><span class="nf">is_channel</span><span class="p" data-group-id="2026097987-2">(</span><span class="n">V</span><span class="p" data-group-id="2026097987-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2026097987-3">(</span><span class="nf">is_float</span><span class="p" data-group-id="2026097987-4">(</span><span class="n">V</span><span class="p" data-group-id="2026097987-4">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="2026097987-3">)</span><span class="p" data-group-id="2026097987-1">)</span><span class="p">.</span></code></pre><p>First a macro <code class="inline">is_channel</code> is defined to help with the guard tests. This is only
│ │ │  here for convenience and to reduce syntax cluttering. For more information about
│ │ │ -macros, see <a href="../../doc/system/macros.html">The Preprocessor</a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="0242048240-1">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="0242048240-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0242048240-2">(</span><span class="n">R</span><span class="p" data-group-id="0242048240-2">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0242048240-3">(</span><span class="n">G</span><span class="p" data-group-id="0242048240-3">)</span><span class="p">,</span><span class="w">
│ │ │ -                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0242048240-4">(</span><span class="n">B</span><span class="p" data-group-id="0242048240-4">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0242048240-5">(</span><span class="n">A</span><span class="p" data-group-id="0242048240-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0242048240-6">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="0242048240-6">}</span><span class="p">.</span></code></pre><p>The function <code class="inline">new/4</code> creates a new map term and lets the keys <code class="inline">red</code>, <code class="inline">green</code>,
│ │ │ +macros, see <a href="../../doc/system/macros.html">The Preprocessor</a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="1639145149-1">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="1639145149-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="1639145149-2">(</span><span class="n">R</span><span class="p" data-group-id="1639145149-2">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="1639145149-3">(</span><span class="n">G</span><span class="p" data-group-id="1639145149-3">)</span><span class="p">,</span><span class="w">
│ │ │ +                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="1639145149-4">(</span><span class="n">B</span><span class="p" data-group-id="1639145149-4">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="1639145149-5">(</span><span class="n">A</span><span class="p" data-group-id="1639145149-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1639145149-6">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="1639145149-6">}</span><span class="p">.</span></code></pre><p>The function <code class="inline">new/4</code> creates a new map term and lets the keys <code class="inline">red</code>, <code class="inline">green</code>,
│ │ │  <code class="inline">blue</code>, and <code class="inline">alpha</code> be associated with an initial value. In this case, only
│ │ │  float values between and including 0.0 and 1.0 are allowed, as ensured by the
│ │ │  <code class="inline">?is_channel/1</code> macro for each argument. Only the <code class="inline">=&gt;</code> operator is allowed when
│ │ │  creating a new map.</p><p>By calling <code class="inline">blend/2</code> on any color term created by <code class="inline">new/4</code>, the resulting color
│ │ │ -can be calculated as determined by the two map terms.</p><p>The first thing <code class="inline">blend/2</code> does is to calculate the resulting alpha channel:</p><pre><code class="makeup erlang" translate="no"><span class="nf">alpha</span><span class="p" data-group-id="0386053602-1">(</span><span class="p" data-group-id="0386053602-2">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0386053602-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0386053602-3">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0386053602-3">}</span><span class="p" data-group-id="0386053602-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0386053602-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0386053602-4">)</span><span class="p">.</span></code></pre><p>The value associated with key <code class="inline">alpha</code> is fetched for both arguments using the
│ │ │ +can be calculated as determined by the two map terms.</p><p>The first thing <code class="inline">blend/2</code> does is to calculate the resulting alpha channel:</p><pre><code class="makeup erlang" translate="no"><span class="nf">alpha</span><span class="p" data-group-id="2495333976-1">(</span><span class="p" data-group-id="2495333976-2">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2495333976-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2495333976-3">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="2495333976-3">}</span><span class="p" data-group-id="2495333976-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="2495333976-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2495333976-4">)</span><span class="p">.</span></code></pre><p>The value associated with key <code class="inline">alpha</code> is fetched for both arguments using the
│ │ │  <code class="inline">:=</code> operator. The other keys in the map are ignored, only the key <code class="inline">alpha</code> is
│ │ │ -required and checked for.</p><p>This is also the case for functions <code class="inline">red/2</code>, <code class="inline">blue/2</code>, and <code class="inline">green/2</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">red</span><span class="p" data-group-id="2480813908-1">(</span><span class="p" data-group-id="2480813908-2">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2480813908-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2480813908-3">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="2480813908-3">}</span><span class="p" data-group-id="2480813908-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="2480813908-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2480813908-4">)</span><span class="p">.</span></code></pre><p>The difference here is that a check is made for two keys in each map argument.
│ │ │ -The other keys are ignored.</p><p>Finally, let us return the resulting color in <code class="inline">blend/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">blend</span><span class="p" data-group-id="9713130054-1">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="9713130054-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="9713130054-2">#{</span><span class="w">
│ │ │ -        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="9713130054-3">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="9713130054-3">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="9713130054-4">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="9713130054-4">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="9713130054-5">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="9713130054-5">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +required and checked for.</p><p>This is also the case for functions <code class="inline">red/2</code>, <code class="inline">blue/2</code>, and <code class="inline">green/2</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">red</span><span class="p" data-group-id="8092617489-1">(</span><span class="p" data-group-id="8092617489-2">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="8092617489-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8092617489-3">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="8092617489-3">}</span><span class="p" data-group-id="8092617489-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="8092617489-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="8092617489-4">)</span><span class="p">.</span></code></pre><p>The difference here is that a check is made for two keys in each map argument.
│ │ │ +The other keys are ignored.</p><p>Finally, let us return the resulting color in <code class="inline">blend/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">blend</span><span class="p" data-group-id="8679746970-1">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="8679746970-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="8679746970-2">#{</span><span class="w">
│ │ │ +        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="8679746970-3">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="8679746970-3">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="8679746970-4">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="8679746970-4">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="8679746970-5">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="8679746970-5">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Alpha</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9713130054-2">}</span><span class="p">;</span></code></pre><p>The <code class="inline">Dst</code> map is updated with new channel values. The syntax for updating an
│ │ │ +    </span><span class="p" data-group-id="8679746970-2">}</span><span class="p">;</span></code></pre><p>The <code class="inline">Dst</code> map is updated with new channel values. The syntax for updating an
│ │ │  existing key with a new value is with the <code class="inline">:=</code> operator.</p><h2 id="standard-modules-and-manual-pages" class="section-heading">
│ │ │    <a href="#standard-modules-and-manual-pages" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Standard Modules and Manual Pages</span>
│ │ │  </h2>
│ │ │  <p>Erlang has many standard modules to help you do things. For example, the module
│ │ │ @@ -442,24 +442,24 @@
│ │ │    <a href="#writing-output-to-a-terminal" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Writing Output to a Terminal</span>
│ │ │  </h2>
│ │ │  <p>It is nice to be able to do formatted output in examples, so the next example
│ │ │  shows a simple way to use the <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function. Like all other exported
│ │ │ -functions, you can test the <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">31&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7026661290-1">(</span><span class="s">&quot;hello world</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7026661290-2">[</span><span class="p" data-group-id="7026661290-2">]</span><span class="p" data-group-id="7026661290-1">)</span><span class="p">.</span><span class="w">
│ │ │ +functions, you can test the <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">31&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7579866114-1">(</span><span class="s">&quot;hello world</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7579866114-2">[</span><span class="p" data-group-id="7579866114-2">]</span><span class="p" data-group-id="7579866114-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w"> </span><span class="ss">world</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -32&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7026661290-3">(</span><span class="s">&quot;this outputs one Erlang term: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7026661290-4">[</span><span class="ss">hello</span><span class="p" data-group-id="7026661290-4">]</span><span class="p" data-group-id="7026661290-3">)</span><span class="p">.</span><span class="w">
│ │ │ +32&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7579866114-3">(</span><span class="s">&quot;this outputs one Erlang term: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7579866114-4">[</span><span class="ss">hello</span><span class="p" data-group-id="7579866114-4">]</span><span class="p" data-group-id="7579866114-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">one</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">term</span><span class="p">:</span><span class="w"> </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -33&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7026661290-5">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7026661290-6">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="7026661290-6">]</span><span class="p" data-group-id="7026661290-5">)</span><span class="p">.</span><span class="w">
│ │ │ +33&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7579866114-5">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7579866114-6">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="7579866114-6">]</span><span class="p" data-group-id="7579866114-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">two</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">terms</span><span class="p">:</span><span class="w"> </span><span class="ss">helloworld</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -34&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7026661290-7">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7026661290-8">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="7026661290-8">]</span><span class="p" data-group-id="7026661290-7">)</span><span class="p">.</span><span class="w">
│ │ │ +34&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7579866114-7">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7579866114-8">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="7579866114-8">]</span><span class="p" data-group-id="7579866114-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">two</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">terms</span><span class="p">:</span><span class="w"> </span><span class="ss">hello</span><span class="w"> </span><span class="ss">world</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>The function <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> (that is, <code class="inline">format</code> with two arguments) takes two lists.
│ │ │  The first one is nearly always a list written between <code class="inline">&quot; &quot;</code>. This list is printed
│ │ │  out as it is, except that each <code class="inline">~w</code> is replaced by a term taken in order from the
│ │ │  second list. Each ~n is replaced by a new line. The <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function
│ │ │  itself returns the atom <code class="inline">ok</code> if everything goes as planned. Like other functions
│ │ │  in Erlang, it crashes if an error occurs. This is not a fault in Erlang, it is a
│ │ │ @@ -473,34 +473,34 @@
│ │ │    <span class="text">A Larger Example</span>
│ │ │  </h2>
│ │ │  <p>Now for a larger example to consolidate what you have learnt so far. Assume that
│ │ │  you have a list of temperature readings from a number of cities in the world.
│ │ │  Some of them are in Celsius and some in Fahrenheit (as in the previous list).
│ │ │  First let us convert them all to Celsius, then let us print the data neatly.</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% This module is in file tut5.erl</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7050256794-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="7050256794-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7050256794-2">(</span><span class="p" data-group-id="7050256794-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7050256794-3">]</span><span class="p" data-group-id="7050256794-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2555353487-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="2555353487-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2555353487-2">(</span><span class="p" data-group-id="2555353487-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2555353487-3">]</span><span class="p" data-group-id="2555353487-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% Only this function is exported</span><span class="w">
│ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="7050256794-4">(</span><span class="p" data-group-id="7050256794-5">[</span><span class="p" data-group-id="7050256794-5">]</span><span class="p" data-group-id="7050256794-4">)</span><span class="p">-&gt;</span><span class="w">                        </span><span class="c1">% No output for an empty list</span><span class="w">
│ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="2555353487-4">(</span><span class="p" data-group-id="2555353487-5">[</span><span class="p" data-group-id="2555353487-5">]</span><span class="p" data-group-id="2555353487-4">)</span><span class="p">-&gt;</span><span class="w">                        </span><span class="c1">% No output for an empty list</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="7050256794-6">(</span><span class="p" data-group-id="7050256794-7">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7050256794-7">]</span><span class="p" data-group-id="7050256794-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="7050256794-8">(</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="7050256794-9">(</span><span class="n">City</span><span class="p" data-group-id="7050256794-9">)</span><span class="p" data-group-id="7050256794-8">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">format_temps</span><span class="p" data-group-id="7050256794-10">(</span><span class="n">Rest</span><span class="p" data-group-id="7050256794-10">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="7050256794-11">(</span><span class="p" data-group-id="7050256794-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7050256794-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7050256794-13">}</span><span class="p" data-group-id="7050256794-12">}</span><span class="p" data-group-id="7050256794-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% No conversion needed</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7050256794-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7050256794-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7050256794-15">}</span><span class="p" data-group-id="7050256794-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="7050256794-16">(</span><span class="p" data-group-id="7050256794-17">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7050256794-18">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7050256794-18">}</span><span class="p" data-group-id="7050256794-17">}</span><span class="p" data-group-id="7050256794-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Do the conversion</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7050256794-19">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7050256794-20">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7050256794-21">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="7050256794-21">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="7050256794-20">}</span><span class="p" data-group-id="7050256794-19">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="7050256794-22">(</span><span class="p" data-group-id="7050256794-23">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7050256794-24">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7050256794-24">}</span><span class="p" data-group-id="7050256794-23">}</span><span class="p" data-group-id="7050256794-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7050256794-25">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7050256794-26">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7050256794-26">]</span><span class="p" data-group-id="7050256794-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">35&gt; </span><span class="nf">c</span><span class="p" data-group-id="2993662893-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="2993662893-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2993662893-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut5</span><span class="p" data-group-id="2993662893-2">}</span><span class="gp unselectable">
│ │ │ -36&gt; </span><span class="nc">tut5</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="2993662893-3">(</span><span class="p" data-group-id="2993662893-4">[</span><span class="p" data-group-id="2993662893-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2993662893-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2993662893-6">}</span><span class="p" data-group-id="2993662893-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2993662893-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2993662893-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="2993662893-8">}</span><span class="p" data-group-id="2993662893-7">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2993662893-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2993662893-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2993662893-10">}</span><span class="p" data-group-id="2993662893-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2993662893-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2993662893-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="2993662893-12">}</span><span class="p" data-group-id="2993662893-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2993662893-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2993662893-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="2993662893-14">}</span><span class="p" data-group-id="2993662893-13">}</span><span class="p" data-group-id="2993662893-4">]</span><span class="p" data-group-id="2993662893-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="2555353487-6">(</span><span class="p" data-group-id="2555353487-7">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2555353487-7">]</span><span class="p" data-group-id="2555353487-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="2555353487-8">(</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="2555353487-9">(</span><span class="n">City</span><span class="p" data-group-id="2555353487-9">)</span><span class="p" data-group-id="2555353487-8">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">format_temps</span><span class="p" data-group-id="2555353487-10">(</span><span class="n">Rest</span><span class="p" data-group-id="2555353487-10">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="2555353487-11">(</span><span class="p" data-group-id="2555353487-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2555353487-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2555353487-13">}</span><span class="p" data-group-id="2555353487-12">}</span><span class="p" data-group-id="2555353487-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% No conversion needed</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2555353487-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2555353487-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2555353487-15">}</span><span class="p" data-group-id="2555353487-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="2555353487-16">(</span><span class="p" data-group-id="2555353487-17">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2555353487-18">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2555353487-18">}</span><span class="p" data-group-id="2555353487-17">}</span><span class="p" data-group-id="2555353487-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Do the conversion</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2555353487-19">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2555353487-20">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2555353487-21">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="2555353487-21">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="2555353487-20">}</span><span class="p" data-group-id="2555353487-19">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="2555353487-22">(</span><span class="p" data-group-id="2555353487-23">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2555353487-24">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2555353487-24">}</span><span class="p" data-group-id="2555353487-23">}</span><span class="p" data-group-id="2555353487-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2555353487-25">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2555353487-26">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2555353487-26">]</span><span class="p" data-group-id="2555353487-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">35&gt; </span><span class="nf">c</span><span class="p" data-group-id="7743372588-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="7743372588-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7743372588-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut5</span><span class="p" data-group-id="7743372588-2">}</span><span class="gp unselectable">
│ │ │ +36&gt; </span><span class="nc">tut5</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="7743372588-3">(</span><span class="p" data-group-id="7743372588-4">[</span><span class="p" data-group-id="7743372588-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7743372588-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="7743372588-6">}</span><span class="p" data-group-id="7743372588-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7743372588-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7743372588-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="7743372588-8">}</span><span class="p" data-group-id="7743372588-7">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7743372588-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7743372588-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="7743372588-10">}</span><span class="p" data-group-id="7743372588-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7743372588-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7743372588-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="7743372588-12">}</span><span class="p" data-group-id="7743372588-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7743372588-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7743372588-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="7743372588-14">}</span><span class="p" data-group-id="7743372588-13">}</span><span class="p" data-group-id="7743372588-4">]</span><span class="p" data-group-id="7743372588-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>Before looking at how this program works, notice that a few comments are added
│ │ │  to the code. A comment starts with a %-character and goes on to the end of the
│ │ │ @@ -528,28 +528,28 @@
│ │ │    <a href="#matching-guards-and-scope-of-variables" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Matching, Guards, and Scope of Variables</span>
│ │ │  </h2>
│ │ │  <p>It can be useful to find the maximum and minimum temperature in lists like this.
│ │ │  Before extending the program to do this, let us look at functions for finding
│ │ │ -the maximum value of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4781958680-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="4781958680-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4781958680-2">(</span><span class="p" data-group-id="4781958680-3">[</span><span class="ss">list_max</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4781958680-3">]</span><span class="p" data-group-id="4781958680-2">)</span><span class="p">.</span><span class="w">
│ │ │ +the maximum value of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0756272594-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="0756272594-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0756272594-2">(</span><span class="p" data-group-id="0756272594-3">[</span><span class="ss">list_max</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0756272594-3">]</span><span class="p" data-group-id="0756272594-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="4781958680-4">(</span><span class="p" data-group-id="4781958680-5">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="4781958680-5">]</span><span class="p" data-group-id="4781958680-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="nf">list_max</span><span class="p" data-group-id="4781958680-6">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="4781958680-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="0756272594-4">(</span><span class="p" data-group-id="0756272594-5">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0756272594-5">]</span><span class="p" data-group-id="0756272594-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="nf">list_max</span><span class="p" data-group-id="0756272594-6">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="0756272594-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="4781958680-7">(</span><span class="p" data-group-id="4781958680-8">[</span><span class="p" data-group-id="4781958680-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="4781958680-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="0756272594-7">(</span><span class="p" data-group-id="0756272594-8">[</span><span class="p" data-group-id="0756272594-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="0756272594-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Res</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="4781958680-9">(</span><span class="p" data-group-id="4781958680-10">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="4781958680-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="4781958680-9">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="4781958680-11">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="4781958680-11">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="4781958680-12">(</span><span class="p" data-group-id="4781958680-13">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="4781958680-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="4781958680-12">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="4781958680-14">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="4781958680-14">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">37&gt; </span><span class="nf">c</span><span class="p" data-group-id="3021776668-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="3021776668-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3021776668-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut6</span><span class="p" data-group-id="3021776668-2">}</span><span class="gp unselectable">
│ │ │ -38&gt; </span><span class="nc">tut6</span><span class="p">:</span><span class="nf">list_max</span><span class="p" data-group-id="3021776668-3">(</span><span class="p" data-group-id="3021776668-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3021776668-4">]</span><span class="p" data-group-id="3021776668-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="0756272594-9">(</span><span class="p" data-group-id="0756272594-10">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0756272594-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="0756272594-9">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="0756272594-11">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="0756272594-11">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="0756272594-12">(</span><span class="p" data-group-id="0756272594-13">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0756272594-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="0756272594-12">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="0756272594-14">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="0756272594-14">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">37&gt; </span><span class="nf">c</span><span class="p" data-group-id="2569835330-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="2569835330-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2569835330-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut6</span><span class="p" data-group-id="2569835330-2">}</span><span class="gp unselectable">
│ │ │ +38&gt; </span><span class="nc">tut6</span><span class="p">:</span><span class="nf">list_max</span><span class="p" data-group-id="2569835330-3">(</span><span class="p" data-group-id="2569835330-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2569835330-4">]</span><span class="p" data-group-id="2569835330-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">7</span></code></pre><p>First notice that two functions have the same name, <code class="inline">list_max</code>. However, each of
│ │ │  these takes a different number of arguments (parameters). In Erlang these are
│ │ │  regarded as completely different functions. Where you need to distinguish
│ │ │  between these functions, you write Name/Arity, where Name is the function name
│ │ │  and Arity is the number of arguments, in this case <code class="inline">list_max/1</code> and
│ │ │  <code class="inline">list_max/2</code>.</p><p>In this example you walk through a list &quot;carrying&quot; a value, in this case
│ │ │  <code class="inline">Result_so_far</code>. <code class="inline">list_max/1</code> simply assumes that the max value of the list is
│ │ │ @@ -578,180 +578,180 @@
│ │ │  </span><span class="mi">5</span><span class="gp unselectable">
│ │ │  40&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value 6</span><span class="gp unselectable">
│ │ │  41&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value 6</span><span class="gp unselectable">
│ │ │  42&gt; </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">6</span></code></pre><p>The use of the match operator is particularly useful for pulling apart Erlang
│ │ │ -terms and creating new ones.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">43&gt; </span><span class="p" data-group-id="0417589654-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0417589654-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0417589654-2">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0417589654-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="0417589654-3">}</span><span class="p" data-group-id="0417589654-2">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0417589654-4">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="0417589654-5">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="0417589654-5">}</span><span class="p" data-group-id="0417589654-4">}</span><span class="gp unselectable">
│ │ │ +terms and creating new ones.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">43&gt; </span><span class="p" data-group-id="0012544565-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0012544565-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0012544565-2">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0012544565-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="0012544565-3">}</span><span class="p" data-group-id="0012544565-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0012544565-4">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="0012544565-5">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="0012544565-5">}</span><span class="p" data-group-id="0012544565-4">}</span><span class="gp unselectable">
│ │ │  44&gt; </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="gp unselectable">
│ │ │  45&gt; </span><span class="n">Y</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0417589654-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="0417589654-6">}</span></code></pre><p>Here <code class="inline">X</code> gets the value <code class="inline">paris</code> and <code class="inline">Y</code> the value <code class="inline">{f,28}</code>.</p><p>If you try to do the same again with another city, an error is returned:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">46&gt; </span><span class="p" data-group-id="1216980211-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1216980211-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1216980211-2">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1216980211-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="1216980211-3">}</span><span class="p" data-group-id="1216980211-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0012544565-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="0012544565-6">}</span></code></pre><p>Here <code class="inline">X</code> gets the value <code class="inline">paris</code> and <code class="inline">Y</code> the value <code class="inline">{f,28}</code>.</p><p>If you try to do the same again with another city, an error is returned:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">46&gt; </span><span class="p" data-group-id="0070841034-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0070841034-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0070841034-2">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0070841034-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="0070841034-3">}</span><span class="p" data-group-id="0070841034-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value {london,{f,36}}</span></code></pre><p>Variables can also be used to improve the readability of programs. For example,
│ │ │ -in function <code class="inline">list_max/2</code> above, you can write:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_max</span><span class="p" data-group-id="1061612434-1">(</span><span class="p" data-group-id="1061612434-2">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="1061612434-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="1061612434-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +in function <code class="inline">list_max/2</code> above, you can write:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_max</span><span class="p" data-group-id="4023750793-1">(</span><span class="p" data-group-id="4023750793-2">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="4023750793-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="4023750793-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">New_result_far</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Head</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="1061612434-3">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">New_result_far</span><span class="p" data-group-id="1061612434-3">)</span><span class="p">;</span></code></pre><p>This is possibly a little clearer.</p><h2 id="more-about-lists" class="section-heading">
│ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="4023750793-3">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">New_result_far</span><span class="p" data-group-id="4023750793-3">)</span><span class="p">;</span></code></pre><p>This is possibly a little clearer.</p><h2 id="more-about-lists" class="section-heading">
│ │ │    <a href="#more-about-lists" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">More About Lists</span>
│ │ │  </h2>
│ │ │ -<p>Remember that the <code class="inline">|</code> operator can be used to get the head of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">47&gt; </span><span class="p" data-group-id="5396541381-1">[</span><span class="n">M1</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="5396541381-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5396541381-2">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="ss">rome</span><span class="p" data-group-id="5396541381-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5396541381-3">[</span><span class="ss">paris</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="5396541381-3">]</span><span class="gp unselectable">
│ │ │ +<p>Remember that the <code class="inline">|</code> operator can be used to get the head of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">47&gt; </span><span class="p" data-group-id="7882889888-1">[</span><span class="n">M1</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="7882889888-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7882889888-2">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="ss">rome</span><span class="p" data-group-id="7882889888-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7882889888-3">[</span><span class="ss">paris</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="7882889888-3">]</span><span class="gp unselectable">
│ │ │  48&gt; </span><span class="n">M1</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="gp unselectable">
│ │ │  49&gt; </span><span class="n">T1</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5396541381-4">[</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="5396541381-4">]</span></code></pre><p>The <code class="inline">|</code> operator can also be used to add a head to a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">50&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0987288690-1">[</span><span class="ss">madrid</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="0987288690-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0987288690-2">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="0987288690-2">]</span><span class="gp unselectable">
│ │ │ +</span><span class="p" data-group-id="7882889888-4">[</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="7882889888-4">]</span></code></pre><p>The <code class="inline">|</code> operator can also be used to add a head to a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">50&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6929404379-1">[</span><span class="ss">madrid</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="6929404379-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6929404379-2">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="6929404379-2">]</span><span class="gp unselectable">
│ │ │  51&gt; </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0987288690-3">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="0987288690-3">]</span></code></pre><p>Now an example of this when working with lists - reversing the order of a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9289332088-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="9289332088-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6929404379-3">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="6929404379-3">]</span></code></pre><p>Now an example of this when working with lists - reversing the order of a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3912778225-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="3912778225-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9289332088-2">(</span><span class="p" data-group-id="9289332088-3">[</span><span class="ss">reverse</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9289332088-3">]</span><span class="p" data-group-id="9289332088-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3912778225-2">(</span><span class="p" data-group-id="3912778225-3">[</span><span class="ss">reverse</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3912778225-3">]</span><span class="p" data-group-id="3912778225-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="9289332088-4">(</span><span class="n">List</span><span class="p" data-group-id="9289332088-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="9289332088-5">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9289332088-6">[</span><span class="p" data-group-id="9289332088-6">]</span><span class="p" data-group-id="9289332088-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="3912778225-4">(</span><span class="n">List</span><span class="p" data-group-id="3912778225-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="3912778225-5">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3912778225-6">[</span><span class="p" data-group-id="3912778225-6">]</span><span class="p" data-group-id="3912778225-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="9289332088-7">(</span><span class="p" data-group-id="9289332088-8">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9289332088-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="9289332088-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="9289332088-9">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9289332088-10">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="9289332088-10">]</span><span class="p" data-group-id="9289332088-9">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="9289332088-11">(</span><span class="p" data-group-id="9289332088-12">[</span><span class="p" data-group-id="9289332088-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="9289332088-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Reversed_List</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">52&gt; </span><span class="nf">c</span><span class="p" data-group-id="8174412754-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="8174412754-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8174412754-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut8</span><span class="p" data-group-id="8174412754-2">}</span><span class="gp unselectable">
│ │ │ -53&gt; </span><span class="nc">tut8</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="8174412754-3">(</span><span class="p" data-group-id="8174412754-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8174412754-4">]</span><span class="p" data-group-id="8174412754-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8174412754-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8174412754-5">]</span></code></pre><p>Consider how <code class="inline">Reversed_List</code> is built. It starts as [], then successively the
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="3912778225-7">(</span><span class="p" data-group-id="3912778225-8">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3912778225-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="3912778225-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="3912778225-9">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3912778225-10">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="3912778225-10">]</span><span class="p" data-group-id="3912778225-9">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="3912778225-11">(</span><span class="p" data-group-id="3912778225-12">[</span><span class="p" data-group-id="3912778225-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="3912778225-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Reversed_List</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">52&gt; </span><span class="nf">c</span><span class="p" data-group-id="0860158702-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="0860158702-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0860158702-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut8</span><span class="p" data-group-id="0860158702-2">}</span><span class="gp unselectable">
│ │ │ +53&gt; </span><span class="nc">tut8</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="0860158702-3">(</span><span class="p" data-group-id="0860158702-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0860158702-4">]</span><span class="p" data-group-id="0860158702-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0860158702-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0860158702-5">]</span></code></pre><p>Consider how <code class="inline">Reversed_List</code> is built. It starts as [], then successively the
│ │ │  heads are taken off of the list to be reversed and added to the the
│ │ │ -<code class="inline">Reversed_List</code>, as shown in the following:</p><pre><code class="makeup erlang" translate="no"><span class="nf">reverse</span><span class="p" data-group-id="6064479426-1">(</span><span class="p" data-group-id="6064479426-2">[</span><span class="mi">1</span><span class="p">|</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6064479426-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6064479426-3">[</span><span class="p" data-group-id="6064479426-3">]</span><span class="p" data-group-id="6064479426-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="6064479426-4">(</span><span class="p" data-group-id="6064479426-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6064479426-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6064479426-6">[</span><span class="mi">1</span><span class="p">|</span><span class="p" data-group-id="6064479426-7">[</span><span class="p" data-group-id="6064479426-7">]</span><span class="p" data-group-id="6064479426-6">]</span><span class="p" data-group-id="6064479426-4">)</span><span class="w">
│ │ │ +<code class="inline">Reversed_List</code>, as shown in the following:</p><pre><code class="makeup erlang" translate="no"><span class="nf">reverse</span><span class="p" data-group-id="0868608698-1">(</span><span class="p" data-group-id="0868608698-2">[</span><span class="mi">1</span><span class="p">|</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0868608698-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0868608698-3">[</span><span class="p" data-group-id="0868608698-3">]</span><span class="p" data-group-id="0868608698-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="0868608698-4">(</span><span class="p" data-group-id="0868608698-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0868608698-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0868608698-6">[</span><span class="mi">1</span><span class="p">|</span><span class="p" data-group-id="0868608698-7">[</span><span class="p" data-group-id="0868608698-7">]</span><span class="p" data-group-id="0868608698-6">]</span><span class="p" data-group-id="0868608698-4">)</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="6064479426-8">(</span><span class="p" data-group-id="6064479426-9">[</span><span class="mi">2</span><span class="p">|</span><span class="mi">3</span><span class="p" data-group-id="6064479426-9">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6064479426-10">[</span><span class="mi">1</span><span class="p" data-group-id="6064479426-10">]</span><span class="p" data-group-id="6064479426-8">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="6064479426-11">(</span><span class="p" data-group-id="6064479426-12">[</span><span class="mi">3</span><span class="p" data-group-id="6064479426-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6064479426-13">[</span><span class="mi">2</span><span class="p">|</span><span class="p" data-group-id="6064479426-14">[</span><span class="mi">1</span><span class="p" data-group-id="6064479426-14">]</span><span class="p">)</span><span class="w">
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="0868608698-8">(</span><span class="p" data-group-id="0868608698-9">[</span><span class="mi">2</span><span class="p">|</span><span class="mi">3</span><span class="p" data-group-id="0868608698-9">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0868608698-10">[</span><span class="mi">1</span><span class="p" data-group-id="0868608698-10">]</span><span class="p" data-group-id="0868608698-8">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="0868608698-11">(</span><span class="p" data-group-id="0868608698-12">[</span><span class="mi">3</span><span class="p" data-group-id="0868608698-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0868608698-13">[</span><span class="mi">2</span><span class="p">|</span><span class="p" data-group-id="0868608698-14">[</span><span class="mi">1</span><span class="p" data-group-id="0868608698-14">]</span><span class="p">)</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="6064479426-15">(</span><span class="p" data-group-id="6064479426-16">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="6064479426-17">[</span><span class="p" data-group-id="6064479426-17">]</span><span class="p" data-group-id="6064479426-16">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6064479426-18">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6064479426-18">]</span><span class="p" data-group-id="6064479426-15">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="6064479426-19">(</span><span class="p" data-group-id="6064479426-20">[</span><span class="p" data-group-id="6064479426-20">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6064479426-21">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="6064479426-22">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6064479426-22">]</span><span class="p" data-group-id="6064479426-21">]</span><span class="p" data-group-id="6064479426-19">)</span><span class="w">
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="0868608698-15">(</span><span class="p" data-group-id="0868608698-16">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="0868608698-17">[</span><span class="p" data-group-id="0868608698-17">]</span><span class="p" data-group-id="0868608698-16">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0868608698-18">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0868608698-18">]</span><span class="p" data-group-id="0868608698-15">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="0868608698-19">(</span><span class="p" data-group-id="0868608698-20">[</span><span class="p" data-group-id="0868608698-20">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0868608698-21">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="0868608698-22">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0868608698-22">]</span><span class="p" data-group-id="0868608698-21">]</span><span class="p" data-group-id="0868608698-19">)</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="6064479426-23">(</span><span class="p" data-group-id="6064479426-24">[</span><span class="p" data-group-id="6064479426-24">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6064479426-25">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6064479426-25">]</span><span class="p" data-group-id="6064479426-23">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6064479426-26">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6064479426-26">]</span></code></pre><p>The module <code class="inline">lists</code> contains many functions for manipulating lists, for example,
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="0868608698-23">(</span><span class="p" data-group-id="0868608698-24">[</span><span class="p" data-group-id="0868608698-24">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0868608698-25">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0868608698-25">]</span><span class="p" data-group-id="0868608698-23">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0868608698-26">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0868608698-26">]</span></code></pre><p>The module <code class="inline">lists</code> contains many functions for manipulating lists, for example,
│ │ │  for reversing them. So before writing a list-manipulating function it is a good
│ │ │  idea to check if one not already is written for you (see the <a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html"><code class="inline">lists</code></a> manual
│ │ │  page in STDLIB).</p><p>Now let us get back to the cities and temperatures, but take a more structured
│ │ │ -approach this time. First let us convert the whole list to Celsius as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5339170578-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="5339170578-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5339170578-2">(</span><span class="p" data-group-id="5339170578-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5339170578-3">]</span><span class="p" data-group-id="5339170578-2">)</span><span class="p">.</span><span class="w">
│ │ │ +approach this time. First let us convert the whole list to Celsius as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1660905823-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="1660905823-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1660905823-2">(</span><span class="p" data-group-id="1660905823-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1660905823-3">]</span><span class="p" data-group-id="1660905823-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="5339170578-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="5339170578-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="5339170578-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="5339170578-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="1660905823-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="1660905823-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1660905823-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="1660905823-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="5339170578-6">(</span><span class="p" data-group-id="5339170578-7">[</span><span class="p" data-group-id="5339170578-8">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5339170578-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="5339170578-9">}</span><span class="p" data-group-id="5339170578-8">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="5339170578-7">]</span><span class="p" data-group-id="5339170578-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5339170578-10">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5339170578-11">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5339170578-12">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="5339170578-12">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="5339170578-11">}</span><span class="p" data-group-id="5339170578-10">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5339170578-13">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="5339170578-14">(</span><span class="n">Rest</span><span class="p" data-group-id="5339170578-14">)</span><span class="p" data-group-id="5339170578-13">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="5339170578-15">(</span><span class="p" data-group-id="5339170578-16">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="5339170578-16">]</span><span class="p" data-group-id="5339170578-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5339170578-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="5339170578-18">(</span><span class="n">Rest</span><span class="p" data-group-id="5339170578-18">)</span><span class="p" data-group-id="5339170578-17">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="5339170578-19">(</span><span class="p" data-group-id="5339170578-20">[</span><span class="p" data-group-id="5339170578-20">]</span><span class="p" data-group-id="5339170578-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5339170578-21">[</span><span class="p" data-group-id="5339170578-21">]</span><span class="p">.</span></code></pre><p>Test the function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">54&gt; </span><span class="nf">c</span><span class="p" data-group-id="7541050323-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="7541050323-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7541050323-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="7541050323-2">}</span><span class="p">.</span><span class="gp unselectable">
│ │ │ -55&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="7541050323-3">(</span><span class="p" data-group-id="7541050323-4">[</span><span class="p" data-group-id="7541050323-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7541050323-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="7541050323-6">}</span><span class="p" data-group-id="7541050323-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7541050323-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7541050323-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="7541050323-8">}</span><span class="p" data-group-id="7541050323-7">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7541050323-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7541050323-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="7541050323-10">}</span><span class="p" data-group-id="7541050323-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7541050323-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7541050323-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="7541050323-12">}</span><span class="p" data-group-id="7541050323-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7541050323-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7541050323-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="7541050323-14">}</span><span class="p" data-group-id="7541050323-13">}</span><span class="p" data-group-id="7541050323-4">]</span><span class="p" data-group-id="7541050323-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7541050323-15">[</span><span class="p" data-group-id="7541050323-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="7541050323-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="7541050323-17">}</span><span class="p" data-group-id="7541050323-16">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7541050323-18">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="7541050323-19">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">21.11111111111111</span><span class="p" data-group-id="7541050323-19">}</span><span class="p" data-group-id="7541050323-18">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7541050323-20">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="7541050323-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="7541050323-21">}</span><span class="p" data-group-id="7541050323-20">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7541050323-22">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="7541050323-23">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="7541050323-23">}</span><span class="p" data-group-id="7541050323-22">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7541050323-24">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="7541050323-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="7541050323-25">}</span><span class="p" data-group-id="7541050323-24">}</span><span class="p" data-group-id="7541050323-15">]</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">format_temps</span><span class="p" data-group-id="6355111333-1">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="6355111333-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6355111333-2">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="6355111333-2">)</span><span class="p">.</span></code></pre><p>Here <code class="inline">format_temps/1</code> calls <code class="inline">convert_list_to_c/1</code>. <code class="inline">convert_list_to_c/1</code> takes
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1660905823-6">(</span><span class="p" data-group-id="1660905823-7">[</span><span class="p" data-group-id="1660905823-8">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1660905823-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="1660905823-9">}</span><span class="p" data-group-id="1660905823-8">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1660905823-7">]</span><span class="p" data-group-id="1660905823-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1660905823-10">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1660905823-11">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1660905823-12">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="1660905823-12">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1660905823-11">}</span><span class="p" data-group-id="1660905823-10">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1660905823-13">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1660905823-14">(</span><span class="n">Rest</span><span class="p" data-group-id="1660905823-14">)</span><span class="p" data-group-id="1660905823-13">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1660905823-15">(</span><span class="p" data-group-id="1660905823-16">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1660905823-16">]</span><span class="p" data-group-id="1660905823-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1660905823-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1660905823-18">(</span><span class="n">Rest</span><span class="p" data-group-id="1660905823-18">)</span><span class="p" data-group-id="1660905823-17">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1660905823-19">(</span><span class="p" data-group-id="1660905823-20">[</span><span class="p" data-group-id="1660905823-20">]</span><span class="p" data-group-id="1660905823-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1660905823-21">[</span><span class="p" data-group-id="1660905823-21">]</span><span class="p">.</span></code></pre><p>Test the function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">54&gt; </span><span class="nf">c</span><span class="p" data-group-id="2185238686-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="2185238686-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2185238686-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="2185238686-2">}</span><span class="p">.</span><span class="gp unselectable">
│ │ │ +55&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="2185238686-3">(</span><span class="p" data-group-id="2185238686-4">[</span><span class="p" data-group-id="2185238686-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2185238686-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2185238686-6">}</span><span class="p" data-group-id="2185238686-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2185238686-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2185238686-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="2185238686-8">}</span><span class="p" data-group-id="2185238686-7">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2185238686-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2185238686-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2185238686-10">}</span><span class="p" data-group-id="2185238686-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2185238686-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2185238686-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="2185238686-12">}</span><span class="p" data-group-id="2185238686-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2185238686-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2185238686-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="2185238686-14">}</span><span class="p" data-group-id="2185238686-13">}</span><span class="p" data-group-id="2185238686-4">]</span><span class="p" data-group-id="2185238686-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2185238686-15">[</span><span class="p" data-group-id="2185238686-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="2185238686-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2185238686-17">}</span><span class="p" data-group-id="2185238686-16">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2185238686-18">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="2185238686-19">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">21.11111111111111</span><span class="p" data-group-id="2185238686-19">}</span><span class="p" data-group-id="2185238686-18">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2185238686-20">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="2185238686-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2185238686-21">}</span><span class="p" data-group-id="2185238686-20">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2185238686-22">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="2185238686-23">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="2185238686-23">}</span><span class="p" data-group-id="2185238686-22">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2185238686-24">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="2185238686-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="2185238686-25">}</span><span class="p" data-group-id="2185238686-24">}</span><span class="p" data-group-id="2185238686-15">]</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">format_temps</span><span class="p" data-group-id="2255337012-1">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="2255337012-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2255337012-2">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="2255337012-2">)</span><span class="p">.</span></code></pre><p>Here <code class="inline">format_temps/1</code> calls <code class="inline">convert_list_to_c/1</code>. <code class="inline">convert_list_to_c/1</code> takes
│ │ │  off the head of the <code class="inline">List_of_cities</code>, converts it to Celsius if needed. The <code class="inline">|</code>
│ │ │ -operator is used to add the (maybe) converted to the converted rest of the list:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3298058709-1">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3298058709-2">(</span><span class="n">Rest</span><span class="p" data-group-id="3298058709-2">)</span><span class="p" data-group-id="3298058709-1">]</span><span class="p">;</span></code></pre><p>or:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0592268315-1">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="0592268315-2">(</span><span class="n">Rest</span><span class="p" data-group-id="0592268315-2">)</span><span class="p" data-group-id="0592268315-1">]</span><span class="p">;</span></code></pre><p>This is done until the end of the list is reached, that is, the list is empty:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7464848595-1">(</span><span class="p" data-group-id="7464848595-2">[</span><span class="p" data-group-id="7464848595-2">]</span><span class="p" data-group-id="7464848595-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7464848595-3">[</span><span class="p" data-group-id="7464848595-3">]</span><span class="p">.</span></code></pre><p>Now when the list is converted, a function to print it is added:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1450311740-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="1450311740-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1450311740-2">(</span><span class="p" data-group-id="1450311740-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1450311740-3">]</span><span class="p" data-group-id="1450311740-2">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="1450311740-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="1450311740-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1450311740-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="1450311740-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="1450311740-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="1450311740-6">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1450311740-7">(</span><span class="p" data-group-id="1450311740-8">[</span><span class="p" data-group-id="1450311740-9">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1450311740-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="1450311740-10">}</span><span class="p" data-group-id="1450311740-9">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1450311740-8">]</span><span class="p" data-group-id="1450311740-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1450311740-11">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1450311740-12">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1450311740-13">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="1450311740-13">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1450311740-12">}</span><span class="p" data-group-id="1450311740-11">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1450311740-14">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1450311740-15">(</span><span class="n">Rest</span><span class="p" data-group-id="1450311740-15">)</span><span class="p" data-group-id="1450311740-14">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1450311740-16">(</span><span class="p" data-group-id="1450311740-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1450311740-17">]</span><span class="p" data-group-id="1450311740-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1450311740-18">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1450311740-19">(</span><span class="n">Rest</span><span class="p" data-group-id="1450311740-19">)</span><span class="p" data-group-id="1450311740-18">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1450311740-20">(</span><span class="p" data-group-id="1450311740-21">[</span><span class="p" data-group-id="1450311740-21">]</span><span class="p" data-group-id="1450311740-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1450311740-22">[</span><span class="p" data-group-id="1450311740-22">]</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="1450311740-23">(</span><span class="p" data-group-id="1450311740-24">[</span><span class="p" data-group-id="1450311740-25">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1450311740-26">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1450311740-26">}</span><span class="p" data-group-id="1450311740-25">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1450311740-24">]</span><span class="p" data-group-id="1450311740-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1450311740-27">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1450311740-28">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1450311740-28">]</span><span class="p" data-group-id="1450311740-27">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="1450311740-29">(</span><span class="n">Rest</span><span class="p" data-group-id="1450311740-29">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="1450311740-30">(</span><span class="p" data-group-id="1450311740-31">[</span><span class="p" data-group-id="1450311740-31">]</span><span class="p" data-group-id="1450311740-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">56&gt; </span><span class="nf">c</span><span class="p" data-group-id="6778978555-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="6778978555-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6778978555-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut7</span><span class="p" data-group-id="6778978555-2">}</span><span class="gp unselectable">
│ │ │ -57&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="6778978555-3">(</span><span class="p" data-group-id="6778978555-4">[</span><span class="p" data-group-id="6778978555-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6778978555-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6778978555-6">}</span><span class="p" data-group-id="6778978555-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6778978555-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6778978555-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6778978555-8">}</span><span class="p" data-group-id="6778978555-7">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6778978555-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6778978555-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6778978555-10">}</span><span class="p" data-group-id="6778978555-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6778978555-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6778978555-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6778978555-12">}</span><span class="p" data-group-id="6778978555-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6778978555-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6778978555-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="6778978555-14">}</span><span class="p" data-group-id="6778978555-13">}</span><span class="p" data-group-id="6778978555-4">]</span><span class="p" data-group-id="6778978555-3">)</span><span class="p">.</span><span class="w">
│ │ │ +operator is used to add the (maybe) converted to the converted rest of the list:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3833584434-1">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3833584434-2">(</span><span class="n">Rest</span><span class="p" data-group-id="3833584434-2">)</span><span class="p" data-group-id="3833584434-1">]</span><span class="p">;</span></code></pre><p>or:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2450071677-1">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2450071677-2">(</span><span class="n">Rest</span><span class="p" data-group-id="2450071677-2">)</span><span class="p" data-group-id="2450071677-1">]</span><span class="p">;</span></code></pre><p>This is done until the end of the list is reached, that is, the list is empty:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7989277342-1">(</span><span class="p" data-group-id="7989277342-2">[</span><span class="p" data-group-id="7989277342-2">]</span><span class="p" data-group-id="7989277342-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7989277342-3">[</span><span class="p" data-group-id="7989277342-3">]</span><span class="p">.</span></code></pre><p>Now when the list is converted, a function to print it is added:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2302454104-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="2302454104-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2302454104-2">(</span><span class="p" data-group-id="2302454104-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2302454104-3">]</span><span class="p" data-group-id="2302454104-2">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="2302454104-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="2302454104-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2302454104-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="2302454104-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="2302454104-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="2302454104-6">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2302454104-7">(</span><span class="p" data-group-id="2302454104-8">[</span><span class="p" data-group-id="2302454104-9">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2302454104-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="2302454104-10">}</span><span class="p" data-group-id="2302454104-9">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2302454104-8">]</span><span class="p" data-group-id="2302454104-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2302454104-11">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2302454104-12">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2302454104-13">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="2302454104-13">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="2302454104-12">}</span><span class="p" data-group-id="2302454104-11">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2302454104-14">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2302454104-15">(</span><span class="n">Rest</span><span class="p" data-group-id="2302454104-15">)</span><span class="p" data-group-id="2302454104-14">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2302454104-16">(</span><span class="p" data-group-id="2302454104-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2302454104-17">]</span><span class="p" data-group-id="2302454104-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2302454104-18">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2302454104-19">(</span><span class="n">Rest</span><span class="p" data-group-id="2302454104-19">)</span><span class="p" data-group-id="2302454104-18">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2302454104-20">(</span><span class="p" data-group-id="2302454104-21">[</span><span class="p" data-group-id="2302454104-21">]</span><span class="p" data-group-id="2302454104-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2302454104-22">[</span><span class="p" data-group-id="2302454104-22">]</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="2302454104-23">(</span><span class="p" data-group-id="2302454104-24">[</span><span class="p" data-group-id="2302454104-25">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2302454104-26">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2302454104-26">}</span><span class="p" data-group-id="2302454104-25">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2302454104-24">]</span><span class="p" data-group-id="2302454104-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2302454104-27">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2302454104-28">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2302454104-28">]</span><span class="p" data-group-id="2302454104-27">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="2302454104-29">(</span><span class="n">Rest</span><span class="p" data-group-id="2302454104-29">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="2302454104-30">(</span><span class="p" data-group-id="2302454104-31">[</span><span class="p" data-group-id="2302454104-31">]</span><span class="p" data-group-id="2302454104-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">56&gt; </span><span class="nf">c</span><span class="p" data-group-id="6985520128-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="6985520128-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6985520128-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut7</span><span class="p" data-group-id="6985520128-2">}</span><span class="gp unselectable">
│ │ │ +57&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="6985520128-3">(</span><span class="p" data-group-id="6985520128-4">[</span><span class="p" data-group-id="6985520128-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6985520128-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6985520128-6">}</span><span class="p" data-group-id="6985520128-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6985520128-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6985520128-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6985520128-8">}</span><span class="p" data-group-id="6985520128-7">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6985520128-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6985520128-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6985520128-10">}</span><span class="p" data-group-id="6985520128-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6985520128-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6985520128-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6985520128-12">}</span><span class="p" data-group-id="6985520128-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6985520128-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6985520128-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="6985520128-14">}</span><span class="p" data-group-id="6985520128-13">}</span><span class="p" data-group-id="6985520128-4">]</span><span class="p" data-group-id="6985520128-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>Now a function has to be added to find the cities with the maximum and minimum
│ │ │  temperatures. The following program is not the most efficient way of doing this
│ │ │  as you walk through the list of cities four times. But it is better to first
│ │ │  strive for clarity and correctness and to make programs efficient only if
│ │ │ -needed.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6380473384-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="6380473384-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6380473384-2">(</span><span class="p" data-group-id="6380473384-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6380473384-3">]</span><span class="p" data-group-id="6380473384-2">)</span><span class="p">.</span><span class="w">
│ │ │ +needed.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8298084975-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="8298084975-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8298084975-2">(</span><span class="p" data-group-id="8298084975-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8298084975-3">]</span><span class="p" data-group-id="8298084975-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="6380473384-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="6380473384-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6380473384-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="6380473384-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="6380473384-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="6380473384-6">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6380473384-7">{</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="6380473384-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="6380473384-8">(</span><span class="n">Converted_List</span><span class="p" data-group-id="6380473384-8">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_max_and_min</span><span class="p" data-group-id="6380473384-9">(</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="6380473384-9">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6380473384-10">(</span><span class="p" data-group-id="6380473384-11">[</span><span class="p" data-group-id="6380473384-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-13">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6380473384-13">}</span><span class="p" data-group-id="6380473384-12">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6380473384-11">]</span><span class="p" data-group-id="6380473384-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6380473384-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-16">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="6380473384-16">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="6380473384-15">}</span><span class="p" data-group-id="6380473384-14">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6380473384-17">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6380473384-18">(</span><span class="n">Rest</span><span class="p" data-group-id="6380473384-18">)</span><span class="p" data-group-id="6380473384-17">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6380473384-19">(</span><span class="p" data-group-id="6380473384-20">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6380473384-20">]</span><span class="p" data-group-id="6380473384-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6380473384-21">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6380473384-22">(</span><span class="n">Rest</span><span class="p" data-group-id="6380473384-22">)</span><span class="p" data-group-id="6380473384-21">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6380473384-23">(</span><span class="p" data-group-id="6380473384-24">[</span><span class="p" data-group-id="6380473384-24">]</span><span class="p" data-group-id="6380473384-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6380473384-25">[</span><span class="p" data-group-id="6380473384-25">]</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="6380473384-26">(</span><span class="p" data-group-id="6380473384-27">[</span><span class="p" data-group-id="6380473384-28">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-29">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6380473384-29">}</span><span class="p" data-group-id="6380473384-28">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6380473384-27">]</span><span class="p" data-group-id="6380473384-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6380473384-30">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-31">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6380473384-31">]</span><span class="p" data-group-id="6380473384-30">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="6380473384-32">(</span><span class="n">Rest</span><span class="p" data-group-id="6380473384-32">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="6380473384-33">(</span><span class="p" data-group-id="6380473384-34">[</span><span class="p" data-group-id="6380473384-34">]</span><span class="p" data-group-id="6380473384-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="8298084975-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="8298084975-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8298084975-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="8298084975-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="8298084975-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="8298084975-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8298084975-7">{</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="8298084975-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8298084975-8">(</span><span class="n">Converted_List</span><span class="p" data-group-id="8298084975-8">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_max_and_min</span><span class="p" data-group-id="8298084975-9">(</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="8298084975-9">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8298084975-10">(</span><span class="p" data-group-id="8298084975-11">[</span><span class="p" data-group-id="8298084975-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-13">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8298084975-13">}</span><span class="p" data-group-id="8298084975-12">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8298084975-11">]</span><span class="p" data-group-id="8298084975-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8298084975-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-16">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="8298084975-16">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="8298084975-15">}</span><span class="p" data-group-id="8298084975-14">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8298084975-17">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8298084975-18">(</span><span class="n">Rest</span><span class="p" data-group-id="8298084975-18">)</span><span class="p" data-group-id="8298084975-17">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8298084975-19">(</span><span class="p" data-group-id="8298084975-20">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8298084975-20">]</span><span class="p" data-group-id="8298084975-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8298084975-21">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8298084975-22">(</span><span class="n">Rest</span><span class="p" data-group-id="8298084975-22">)</span><span class="p" data-group-id="8298084975-21">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8298084975-23">(</span><span class="p" data-group-id="8298084975-24">[</span><span class="p" data-group-id="8298084975-24">]</span><span class="p" data-group-id="8298084975-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8298084975-25">[</span><span class="p" data-group-id="8298084975-25">]</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="8298084975-26">(</span><span class="p" data-group-id="8298084975-27">[</span><span class="p" data-group-id="8298084975-28">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-29">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8298084975-29">}</span><span class="p" data-group-id="8298084975-28">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8298084975-27">]</span><span class="p" data-group-id="8298084975-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8298084975-30">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-31">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8298084975-31">]</span><span class="p" data-group-id="8298084975-30">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="8298084975-32">(</span><span class="n">Rest</span><span class="p" data-group-id="8298084975-32">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="8298084975-33">(</span><span class="p" data-group-id="8298084975-34">[</span><span class="p" data-group-id="8298084975-34">]</span><span class="p" data-group-id="8298084975-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="6380473384-35">(</span><span class="p" data-group-id="6380473384-36">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6380473384-36">]</span><span class="p" data-group-id="6380473384-35">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="6380473384-37">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p" data-group-id="6380473384-37">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8298084975-35">(</span><span class="p" data-group-id="8298084975-36">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8298084975-36">]</span><span class="p" data-group-id="8298084975-35">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8298084975-37">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p" data-group-id="8298084975-37">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="6380473384-38">(</span><span class="p" data-group-id="6380473384-39">[</span><span class="p" data-group-id="6380473384-40">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-41">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6380473384-41">}</span><span class="p" data-group-id="6380473384-40">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6380473384-39">]</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="6380473384-42">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-43">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="6380473384-43">}</span><span class="p" data-group-id="6380473384-42">}</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="6380473384-44">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-45">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="6380473384-45">}</span><span class="p" data-group-id="6380473384-44">}</span><span class="p" data-group-id="6380473384-38">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8298084975-38">(</span><span class="p" data-group-id="8298084975-39">[</span><span class="p" data-group-id="8298084975-40">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-41">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8298084975-41">}</span><span class="p" data-group-id="8298084975-40">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8298084975-39">]</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="8298084975-42">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-43">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="8298084975-43">}</span><span class="p" data-group-id="8298084975-42">}</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="8298084975-44">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-45">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="8298084975-45">}</span><span class="p" data-group-id="8298084975-44">}</span><span class="p" data-group-id="8298084975-38">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">Temp</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Max_Temp</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6380473384-46">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-47">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6380473384-47">}</span><span class="p" data-group-id="6380473384-46">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ +            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8298084975-46">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-47">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8298084975-47">}</span><span class="p" data-group-id="8298084975-46">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6380473384-48">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-49">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="6380473384-49">}</span><span class="p" data-group-id="6380473384-48">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ +            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8298084975-48">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-49">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="8298084975-49">}</span><span class="p" data-group-id="8298084975-48">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │           </span><span class="n">Temp</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Min_Temp</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6380473384-50">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-51">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6380473384-51">}</span><span class="p" data-group-id="6380473384-50">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ +            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8298084975-50">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-51">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8298084975-51">}</span><span class="p" data-group-id="8298084975-50">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6380473384-52">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-53">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="6380473384-53">}</span><span class="p" data-group-id="6380473384-52">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ +            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8298084975-52">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-53">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="8298084975-53">}</span><span class="p" data-group-id="8298084975-52">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="6380473384-54">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="6380473384-54">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8298084975-54">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="8298084975-54">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="6380473384-55">(</span><span class="p" data-group-id="6380473384-56">[</span><span class="p" data-group-id="6380473384-56">]</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="6380473384-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6380473384-57">{</span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="6380473384-57">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8298084975-55">(</span><span class="p" data-group-id="8298084975-56">[</span><span class="p" data-group-id="8298084975-56">]</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="8298084975-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8298084975-57">{</span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="8298084975-57">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">print_max_and_min</span><span class="p" data-group-id="6380473384-58">(</span><span class="p" data-group-id="6380473384-59">{</span><span class="n">Max_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-60">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_temp</span><span class="p" data-group-id="6380473384-60">}</span><span class="p" data-group-id="6380473384-59">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-61">{</span><span class="n">Min_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-62">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_temp</span><span class="p" data-group-id="6380473384-62">}</span><span class="p" data-group-id="6380473384-61">}</span><span class="p" data-group-id="6380473384-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6380473384-63">(</span><span class="s">&quot;Max temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-64">[</span><span class="n">Max_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Max_name</span><span class="p" data-group-id="6380473384-64">]</span><span class="p" data-group-id="6380473384-63">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6380473384-65">(</span><span class="s">&quot;Min temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6380473384-66">[</span><span class="n">Min_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Min_name</span><span class="p" data-group-id="6380473384-66">]</span><span class="p" data-group-id="6380473384-65">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">58&gt; </span><span class="nf">c</span><span class="p" data-group-id="1363925318-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="1363925318-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1363925318-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="1363925318-2">}</span><span class="gp unselectable">
│ │ │ -59&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="1363925318-3">(</span><span class="p" data-group-id="1363925318-4">[</span><span class="p" data-group-id="1363925318-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1363925318-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="1363925318-6">}</span><span class="p" data-group-id="1363925318-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1363925318-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1363925318-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="1363925318-8">}</span><span class="p" data-group-id="1363925318-7">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1363925318-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1363925318-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="1363925318-10">}</span><span class="p" data-group-id="1363925318-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1363925318-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1363925318-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="1363925318-12">}</span><span class="p" data-group-id="1363925318-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1363925318-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1363925318-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="1363925318-14">}</span><span class="p" data-group-id="1363925318-13">}</span><span class="p" data-group-id="1363925318-4">]</span><span class="p" data-group-id="1363925318-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">print_max_and_min</span><span class="p" data-group-id="8298084975-58">(</span><span class="p" data-group-id="8298084975-59">{</span><span class="n">Max_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-60">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_temp</span><span class="p" data-group-id="8298084975-60">}</span><span class="p" data-group-id="8298084975-59">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-61">{</span><span class="n">Min_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-62">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_temp</span><span class="p" data-group-id="8298084975-62">}</span><span class="p" data-group-id="8298084975-61">}</span><span class="p" data-group-id="8298084975-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8298084975-63">(</span><span class="s">&quot;Max temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-64">[</span><span class="n">Max_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Max_name</span><span class="p" data-group-id="8298084975-64">]</span><span class="p" data-group-id="8298084975-63">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8298084975-65">(</span><span class="s">&quot;Min temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8298084975-66">[</span><span class="n">Min_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Min_name</span><span class="p" data-group-id="8298084975-66">]</span><span class="p" data-group-id="8298084975-65">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">58&gt; </span><span class="nf">c</span><span class="p" data-group-id="1055283835-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="1055283835-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1055283835-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="1055283835-2">}</span><span class="gp unselectable">
│ │ │ +59&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="1055283835-3">(</span><span class="p" data-group-id="1055283835-4">[</span><span class="p" data-group-id="1055283835-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1055283835-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="1055283835-6">}</span><span class="p" data-group-id="1055283835-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1055283835-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1055283835-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="1055283835-8">}</span><span class="p" data-group-id="1055283835-7">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1055283835-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1055283835-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="1055283835-10">}</span><span class="p" data-group-id="1055283835-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1055283835-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1055283835-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="1055283835-12">}</span><span class="p" data-group-id="1055283835-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1055283835-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1055283835-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="1055283835-14">}</span><span class="p" data-group-id="1055283835-13">}</span><span class="p" data-group-id="1055283835-4">]</span><span class="p" data-group-id="1055283835-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="n">Max</span><span class="w"> </span><span class="ss">temperature</span><span class="w"> </span><span class="ss">was</span><span class="w"> </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">cape_town</span><span class="w">
│ │ │  </span><span class="n">Min</span><span class="w"> </span><span class="ss">temperature</span><span class="w"> </span><span class="ss">was</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">moscow</span><span class="w">
│ │ │ @@ -773,88 +773,88 @@
│ │ │          Action 4
│ │ │  end</code></pre><p>Notice that there is no <code class="inline">;</code> before <code class="inline">end</code>. Conditions do the same as guards, that
│ │ │  is, tests that succeed or fail. Erlang starts at the top and tests until it
│ │ │  finds a condition that succeeds. Then it evaluates (performs) the action
│ │ │  following the condition and ignores all other conditions and actions before the
│ │ │  <code class="inline">end</code>. If no condition matches, a run-time failure occurs. A condition that
│ │ │  always succeeds is the atom <code class="inline">true</code>. This is often used last in an <code class="inline">if</code>, meaning,
│ │ │ -do the action following the <code class="inline">true</code> if all other conditions have failed.</p><p>The following is a short program to show the workings of <code class="inline">if</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4111607742-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="4111607742-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4111607742-2">(</span><span class="p" data-group-id="4111607742-3">[</span><span class="ss">test_if</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4111607742-3">]</span><span class="p" data-group-id="4111607742-2">)</span><span class="p">.</span><span class="w">
│ │ │ +do the action following the <code class="inline">true</code> if all other conditions have failed.</p><p>The following is a short program to show the workings of <code class="inline">if</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6501471446-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="6501471446-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6501471446-2">(</span><span class="p" data-group-id="6501471446-3">[</span><span class="ss">test_if</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6501471446-3">]</span><span class="p" data-group-id="6501471446-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">test_if</span><span class="p" data-group-id="4111607742-4">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4111607742-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">test_if</span><span class="p" data-group-id="6501471446-4">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="6501471446-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4111607742-5">(</span><span class="s">&quot;A == 5</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4111607742-6">[</span><span class="p" data-group-id="4111607742-6">]</span><span class="p" data-group-id="4111607742-5">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6501471446-5">(</span><span class="s">&quot;A == 5</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6501471446-6">[</span><span class="p" data-group-id="6501471446-6">]</span><span class="p" data-group-id="6501471446-5">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="ss">a_equals_5</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4111607742-7">(</span><span class="s">&quot;B == 6</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4111607742-8">[</span><span class="p" data-group-id="4111607742-8">]</span><span class="p" data-group-id="4111607742-7">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6501471446-7">(</span><span class="s">&quot;B == 6</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6501471446-8">[</span><span class="p" data-group-id="6501471446-8">]</span><span class="p" data-group-id="6501471446-7">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="ss">b_equals_6</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">                      </span><span class="c1">%That is A equals 2 and B equals 3</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4111607742-9">(</span><span class="s">&quot;A == 2, B == 3</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4111607742-10">[</span><span class="p" data-group-id="4111607742-10">]</span><span class="p" data-group-id="4111607742-9">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6501471446-9">(</span><span class="s">&quot;A == 2, B == 3</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6501471446-10">[</span><span class="p" data-group-id="6501471446-10">]</span><span class="p" data-group-id="6501471446-9">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="ss">a_equals_2_b_equals_3</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">                     </span><span class="c1">%That is A equals 1 or B equals 7</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4111607742-11">(</span><span class="s">&quot;A == 1 ; B == 7</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4111607742-12">[</span><span class="p" data-group-id="4111607742-12">]</span><span class="p" data-group-id="4111607742-11">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6501471446-11">(</span><span class="s">&quot;A == 1 ; B == 7</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6501471446-12">[</span><span class="p" data-group-id="6501471446-12">]</span><span class="p" data-group-id="6501471446-11">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Testing this program gives:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">60&gt; </span><span class="nf">c</span><span class="p" data-group-id="9194824187-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="9194824187-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9194824187-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut9</span><span class="p" data-group-id="9194824187-2">}</span><span class="gp unselectable">
│ │ │ -61&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9194824187-3">(</span><span class="mi">5</span><span class="p">,</span><span class="mi">33</span><span class="p" data-group-id="9194824187-3">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Testing this program gives:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">60&gt; </span><span class="nf">c</span><span class="p" data-group-id="9061593139-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="9061593139-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9061593139-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut9</span><span class="p" data-group-id="9061593139-2">}</span><span class="gp unselectable">
│ │ │ +61&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9061593139-3">(</span><span class="mi">5</span><span class="p">,</span><span class="mi">33</span><span class="p" data-group-id="9061593139-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │  </span><span class="ss">a_equals_5</span><span class="gp unselectable">
│ │ │ -62&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9194824187-4">(</span><span class="mi">33</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9194824187-4">)</span><span class="p">.</span><span class="w">
│ │ │ +62&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9061593139-4">(</span><span class="mi">33</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9061593139-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">6</span><span class="w">
│ │ │  </span><span class="ss">b_equals_6</span><span class="gp unselectable">
│ │ │ -63&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9194824187-5">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="9194824187-5">)</span><span class="p">.</span><span class="w">
│ │ │ +63&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9061593139-5">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="9061593139-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="w">
│ │ │  </span><span class="ss">a_equals_2_b_equals_3</span><span class="gp unselectable">
│ │ │ -64&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9194824187-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="9194824187-6">)</span><span class="p">.</span><span class="w">
│ │ │ +64&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9061593139-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="9061593139-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w">
│ │ │  </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="gp unselectable">
│ │ │ -65&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9194824187-7">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="9194824187-7">)</span><span class="p">.</span><span class="w">
│ │ │ +65&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9061593139-7">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="9061593139-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w">
│ │ │  </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="gp unselectable">
│ │ │ -66&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9194824187-8">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="9194824187-8">)</span><span class="p">.</span><span class="w">
│ │ │ +66&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9061593139-8">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="9061593139-8">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no true branch found when evaluating an if expression
│ │ │       in function  tut9:test_if/2 (tut9.erl, line 5)</span></code></pre><p>Notice that <code class="inline">tut9:test_if(33,33)</code> does not cause any condition to succeed. This
│ │ │  leads to the run time error <code class="inline">if_clause</code>, here nicely formatted by the shell. See
│ │ │  <a href="../../doc/system/expressions.html">Guard Sequences</a> for details of the many guard tests
│ │ │  available.</p><p><code class="inline">case</code> is another construct in Erlang. Recall that the <code class="inline">convert_length</code> function
│ │ │ -was written as:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_length</span><span class="p" data-group-id="7388924433-1">(</span><span class="p" data-group-id="7388924433-2">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7388924433-2">}</span><span class="p" data-group-id="7388924433-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7388924433-3">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="7388924433-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="7388924433-4">(</span><span class="p" data-group-id="7388924433-5">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7388924433-5">}</span><span class="p" data-group-id="7388924433-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7388924433-6">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="7388924433-6">}</span><span class="p">.</span></code></pre><p>The same program can also be written as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9841841232-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="9841841232-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9841841232-2">(</span><span class="p" data-group-id="9841841232-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9841841232-3">]</span><span class="p" data-group-id="9841841232-2">)</span><span class="p">.</span><span class="w">
│ │ │ +was written as:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_length</span><span class="p" data-group-id="9271786110-1">(</span><span class="p" data-group-id="9271786110-2">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9271786110-2">}</span><span class="p" data-group-id="9271786110-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9271786110-3">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="9271786110-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="9271786110-4">(</span><span class="p" data-group-id="9271786110-5">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9271786110-5">}</span><span class="p" data-group-id="9271786110-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9271786110-6">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="9271786110-6">}</span><span class="p">.</span></code></pre><p>The same program can also be written as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8596648714-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="8596648714-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8596648714-2">(</span><span class="p" data-group-id="8596648714-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8596648714-3">]</span><span class="p" data-group-id="8596648714-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="9841841232-4">(</span><span class="n">Length</span><span class="p" data-group-id="9841841232-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="8596648714-4">(</span><span class="n">Length</span><span class="p" data-group-id="8596648714-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9841841232-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9841841232-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9841841232-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="9841841232-6">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9841841232-7">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9841841232-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9841841232-8">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="9841841232-8">}</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">67&gt; </span><span class="nf">c</span><span class="p" data-group-id="9079261556-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="9079261556-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9079261556-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut10</span><span class="p" data-group-id="9079261556-2">}</span><span class="gp unselectable">
│ │ │ -68&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="9079261556-3">(</span><span class="p" data-group-id="9079261556-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="9079261556-4">}</span><span class="p" data-group-id="9079261556-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9079261556-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">15.24</span><span class="p" data-group-id="9079261556-5">}</span><span class="gp unselectable">
│ │ │ -69&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="9079261556-6">(</span><span class="p" data-group-id="9079261556-7">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="mf">2.5</span><span class="p" data-group-id="9079261556-7">}</span><span class="p" data-group-id="9079261556-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9079261556-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">0.984251968503937</span><span class="p" data-group-id="9079261556-8">}</span></code></pre><p>Both <code class="inline">case</code> and <code class="inline">if</code> have <em>return values</em>, that is, in the above example <code class="inline">case</code>
│ │ │ +        </span><span class="p" data-group-id="8596648714-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8596648714-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8596648714-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="8596648714-6">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8596648714-7">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8596648714-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8596648714-8">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="8596648714-8">}</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">67&gt; </span><span class="nf">c</span><span class="p" data-group-id="4507624127-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="4507624127-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4507624127-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut10</span><span class="p" data-group-id="4507624127-2">}</span><span class="gp unselectable">
│ │ │ +68&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="4507624127-3">(</span><span class="p" data-group-id="4507624127-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="4507624127-4">}</span><span class="p" data-group-id="4507624127-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4507624127-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">15.24</span><span class="p" data-group-id="4507624127-5">}</span><span class="gp unselectable">
│ │ │ +69&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="4507624127-6">(</span><span class="p" data-group-id="4507624127-7">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="mf">2.5</span><span class="p" data-group-id="4507624127-7">}</span><span class="p" data-group-id="4507624127-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4507624127-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">0.984251968503937</span><span class="p" data-group-id="4507624127-8">}</span></code></pre><p>Both <code class="inline">case</code> and <code class="inline">if</code> have <em>return values</em>, that is, in the above example <code class="inline">case</code>
│ │ │  returned either <code class="inline">{inch,X/2.54}</code> or <code class="inline">{centimeter,Y*2.54}</code>. The behaviour of
│ │ │  <code class="inline">case</code> can also be modified by using guards. The following example clarifies
│ │ │  this. It tells us the length of a month, given the year. The year must be known,
│ │ │ -since February has 29 days in a leap year.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3892707731-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="3892707731-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3892707731-2">(</span><span class="p" data-group-id="3892707731-3">[</span><span class="ss">month_length</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3892707731-3">]</span><span class="p" data-group-id="3892707731-2">)</span><span class="p">.</span><span class="w">
│ │ │ +since February has 29 days in a leap year.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9468282092-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="9468282092-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9468282092-2">(</span><span class="p" data-group-id="9468282092-3">[</span><span class="ss">month_length</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9468282092-3">]</span><span class="p" data-group-id="9468282092-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">month_length</span><span class="p" data-group-id="3892707731-4">(</span><span class="n">Year</span><span class="p">,</span><span class="w"> </span><span class="n">Month</span><span class="p" data-group-id="3892707731-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">month_length</span><span class="p" data-group-id="9468282092-4">(</span><span class="n">Year</span><span class="p">,</span><span class="w"> </span><span class="n">Month</span><span class="p" data-group-id="9468282092-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% All years divisible by 400 are leap</span><span class="w">
│ │ │      </span><span class="c1">%% Years divisible by 100 are not leap (except the 400 rule above)</span><span class="w">
│ │ │      </span><span class="c1">%% Years divisible by 4 are leap (except the 100 rule above)</span><span class="w">
│ │ │      </span><span class="n">Leap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">if</span><span class="w">
│ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="3892707731-5">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="3892707731-5">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="9468282092-5">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="9468282092-5">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">leap</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="3892707731-6">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="3892707731-6">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">100</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="9468282092-6">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="9468282092-6">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">100</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">not_leap</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="3892707731-7">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="3892707731-7">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="9468282092-7">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="9468282092-7">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">leap</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">not_leap</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Month</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">sep</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">30</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">apr</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">30</span><span class="p">;</span><span class="w">
│ │ │ @@ -865,152 +865,152 @@
│ │ │          </span><span class="ss">jan</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">mar</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">may</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">jul</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">aug</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">oct</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">dec</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">70&gt; </span><span class="nf">c</span><span class="p" data-group-id="4287841114-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="4287841114-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4287841114-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut11</span><span class="p" data-group-id="4287841114-2">}</span><span class="gp unselectable">
│ │ │ -71&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="4287841114-3">(</span><span class="mi">2004</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="4287841114-3">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">70&gt; </span><span class="nf">c</span><span class="p" data-group-id="1669846041-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="1669846041-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1669846041-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut11</span><span class="p" data-group-id="1669846041-2">}</span><span class="gp unselectable">
│ │ │ +71&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="1669846041-3">(</span><span class="mi">2004</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="1669846041-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">29</span><span class="gp unselectable">
│ │ │ -72&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="4287841114-4">(</span><span class="mi">2003</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="4287841114-4">)</span><span class="p">.</span><span class="w">
│ │ │ +72&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="1669846041-4">(</span><span class="mi">2003</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="1669846041-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">28</span><span class="gp unselectable">
│ │ │ -73&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="4287841114-5">(</span><span class="mi">1947</span><span class="p">,</span><span class="w"> </span><span class="ss">aug</span><span class="p" data-group-id="4287841114-5">)</span><span class="p">.</span><span class="w">
│ │ │ +73&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="1669846041-5">(</span><span class="mi">1947</span><span class="p">,</span><span class="w"> </span><span class="ss">aug</span><span class="p" data-group-id="1669846041-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">31</span></code></pre><h2 id="built-in-functions-bifs" class="section-heading">
│ │ │    <a href="#built-in-functions-bifs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Built-In Functions (BIFs)</span>
│ │ │  </h2>
│ │ │  <p>BIFs are functions that for some reason are built-in to the Erlang virtual
│ │ │  machine. BIFs often implement functionality that is impossible or is too
│ │ │  inefficient to implement in Erlang. Some BIFs can be called using the function
│ │ │  name only but they are by default belonging to the <code class="inline">erlang</code> module. For example,
│ │ │  the call to the BIF <code class="inline">trunc</code> below is equivalent to a call to <code class="inline">erlang:trunc</code>.</p><p>As shown, first it is checked if a year is leap. If a year is divisible by 400,
│ │ │  it is a leap year. To determine this, first divide the year by 400 and use the
│ │ │  BIF <code class="inline">trunc</code> (more about this later) to cut off any decimals. Then multiply by
│ │ │  400 again and see if the same value is returned again. For example, year 2004:</p><pre><code class="makeup erlang" translate="no"><span class="mi">2004</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">5.01</span><span class="w">
│ │ │ -</span><span class="nf">trunc</span><span class="p" data-group-id="6630194509-1">(</span><span class="mf">5.01</span><span class="p" data-group-id="6630194509-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ +</span><span class="nf">trunc</span><span class="p" data-group-id="0364756202-1">(</span><span class="mf">5.01</span><span class="p" data-group-id="0364756202-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │  </span><span class="mi">5</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2000</span></code></pre><p>2000 is not the same as 2004, so 2004 is not divisible by 400. Year 2000:</p><pre><code class="makeup erlang" translate="no"><span class="mi">2000</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">5.0</span><span class="w">
│ │ │ -</span><span class="nf">trunc</span><span class="p" data-group-id="8409805986-1">(</span><span class="mf">5.0</span><span class="p" data-group-id="8409805986-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ +</span><span class="nf">trunc</span><span class="p" data-group-id="5503535542-1">(</span><span class="mf">5.0</span><span class="p" data-group-id="5503535542-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │  </span><span class="mi">5</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2000</span></code></pre><p>That is, a leap year. The next two <code class="inline">trunc</code>-tests evaluate if the year is
│ │ │  divisible by 100 or 4 in the same way. The first <code class="inline">if</code> returns <code class="inline">leap</code> or
│ │ │  <code class="inline">not_leap</code>, which lands up in the variable <code class="inline">Leap</code>. This variable is used in the
│ │ │  guard for <code class="inline">feb</code> in the following <code class="inline">case</code> that tells us how long the month is.</p><p>This example showed the use of <code class="inline">trunc</code>. It is easier to use the Erlang operator
│ │ │  <code class="inline">rem</code> that gives the remainder after division, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">74&gt; </span><span class="mi">2004</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">400</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">4</span></code></pre><p>So instead of writing:</p><pre><code class="makeup erlang" translate="no"><span class="nf">trunc</span><span class="p" data-group-id="2511848486-1">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="2511848486-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="mi">4</span></code></pre><p>So instead of writing:</p><pre><code class="makeup erlang" translate="no"><span class="nf">trunc</span><span class="p" data-group-id="4055914706-1">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="4055914706-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">leap</span><span class="p">;</span></code></pre><p>it can be written:</p><pre><code class="makeup erlang" translate="no"><span class="n">Year</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">leap</span><span class="p">;</span></code></pre><p>There are many other BIFs such as <code class="inline">trunc</code>. Only a few BIFs can be used in
│ │ │  guards, and you cannot use functions you have defined yourself in guards. (see
│ │ │  <a href="../../doc/system/expressions.html">Guard Sequences</a>) (For advanced readers: This is to
│ │ │  ensure that guards do not have side effects.) Let us play with a few of these
│ │ │ -functions in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">75&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="5386740266-1">(</span><span class="mf">5.6</span><span class="p" data-group-id="5386740266-1">)</span><span class="p">.</span><span class="w">
│ │ │ +functions in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">75&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="3513660429-1">(</span><span class="mf">5.6</span><span class="p" data-group-id="3513660429-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">5</span><span class="gp unselectable">
│ │ │ -76&gt; </span><span class="nf">round</span><span class="p" data-group-id="5386740266-2">(</span><span class="mf">5.6</span><span class="p" data-group-id="5386740266-2">)</span><span class="p">.</span><span class="w">
│ │ │ +76&gt; </span><span class="nf">round</span><span class="p" data-group-id="3513660429-2">(</span><span class="mf">5.6</span><span class="p" data-group-id="3513660429-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">6</span><span class="gp unselectable">
│ │ │ -77&gt; </span><span class="nf">length</span><span class="p" data-group-id="5386740266-3">(</span><span class="p" data-group-id="5386740266-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="5386740266-4">]</span><span class="p" data-group-id="5386740266-3">)</span><span class="p">.</span><span class="w">
│ │ │ +77&gt; </span><span class="nf">length</span><span class="p" data-group-id="3513660429-3">(</span><span class="p" data-group-id="3513660429-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="3513660429-4">]</span><span class="p" data-group-id="3513660429-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="gp unselectable">
│ │ │ -78&gt; </span><span class="nf">float</span><span class="p" data-group-id="5386740266-5">(</span><span class="mi">5</span><span class="p" data-group-id="5386740266-5">)</span><span class="p">.</span><span class="w">
│ │ │ +78&gt; </span><span class="nf">float</span><span class="p" data-group-id="3513660429-5">(</span><span class="mi">5</span><span class="p" data-group-id="3513660429-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">5.0</span><span class="gp unselectable">
│ │ │ -79&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="5386740266-6">(</span><span class="ss">hello</span><span class="p" data-group-id="5386740266-6">)</span><span class="p">.</span><span class="w">
│ │ │ +79&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="3513660429-6">(</span><span class="ss">hello</span><span class="p" data-group-id="3513660429-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -80&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="5386740266-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5386740266-7">)</span><span class="p">.</span><span class="w">
│ │ │ +80&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="3513660429-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="3513660429-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ -81&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="5386740266-8">(</span><span class="p" data-group-id="5386740266-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5386740266-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="5386740266-10">}</span><span class="p" data-group-id="5386740266-9">}</span><span class="p" data-group-id="5386740266-8">)</span><span class="p">.</span><span class="w">
│ │ │ +81&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="3513660429-8">(</span><span class="p" data-group-id="3513660429-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3513660429-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="3513660429-10">}</span><span class="p" data-group-id="3513660429-9">}</span><span class="p" data-group-id="3513660429-8">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -82&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="5386740266-11">(</span><span class="p" data-group-id="5386740266-12">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5386740266-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="5386740266-13">}</span><span class="p" data-group-id="5386740266-12">]</span><span class="p" data-group-id="5386740266-11">)</span><span class="p">.</span><span class="w">
│ │ │ +82&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="3513660429-11">(</span><span class="p" data-group-id="3513660429-12">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3513660429-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="3513660429-13">}</span><span class="p" data-group-id="3513660429-12">]</span><span class="p" data-group-id="3513660429-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre><p>All of these can be used in guards. Now for some BIFs that cannot be used in
│ │ │ -guards:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">83&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="2752703805-1">(</span><span class="ss">hello</span><span class="p" data-group-id="2752703805-1">)</span><span class="p">.</span><span class="w">
│ │ │ +guards:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">83&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="8449507841-1">(</span><span class="ss">hello</span><span class="p" data-group-id="8449507841-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;hello&quot;</span><span class="gp unselectable">
│ │ │ -84&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="2752703805-2">(</span><span class="s">&quot;goodbye&quot;</span><span class="p" data-group-id="2752703805-2">)</span><span class="p">.</span><span class="w">
│ │ │ +84&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="8449507841-2">(</span><span class="s">&quot;goodbye&quot;</span><span class="p" data-group-id="8449507841-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">goodbye</span><span class="gp unselectable">
│ │ │ -85&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="2752703805-3">(</span><span class="mi">22</span><span class="p" data-group-id="2752703805-3">)</span><span class="p">.</span><span class="w">
│ │ │ +85&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="8449507841-3">(</span><span class="mi">22</span><span class="p" data-group-id="8449507841-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;22&quot;</span></code></pre><p>These three BIFs do conversions that would be difficult (or impossible) to do in
│ │ │  Erlang.</p><h2 id="higher-order-functions-funs" class="section-heading">
│ │ │    <a href="#higher-order-functions-funs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Higher-Order Functions (Funs)</span>
│ │ │  </h2>
│ │ │  <p>Erlang, like most modern functional programming languages, has higher-order
│ │ │ -functions. Here is an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">86&gt; </span><span class="n">Xf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0021191110-1">(</span><span class="n">X</span><span class="p" data-group-id="0021191110-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +functions. Here is an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">86&gt; </span><span class="n">Xf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4670176848-1">(</span><span class="n">X</span><span class="p" data-group-id="4670176848-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -87&gt; </span><span class="n">Xf</span><span class="p" data-group-id="0021191110-2">(</span><span class="mi">5</span><span class="p" data-group-id="0021191110-2">)</span><span class="p">.</span><span class="w">
│ │ │ +87&gt; </span><span class="n">Xf</span><span class="p" data-group-id="4670176848-2">(</span><span class="mi">5</span><span class="p" data-group-id="4670176848-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span></code></pre><p>Here is defined a function that doubles the value of a number and assigned this
│ │ │  function to a variable. Thus <code class="inline">Xf(5)</code> returns value 10. Two useful functions when
│ │ │ -working with lists are <code class="inline">foreach</code> and <code class="inline">map</code>, which are defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="2287603255-1">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2287603255-2">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="2287603255-2">]</span><span class="p" data-group-id="2287603255-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Fun</span><span class="p" data-group-id="2287603255-3">(</span><span class="n">First</span><span class="p" data-group-id="2287603255-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="2287603255-4">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2287603255-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="2287603255-5">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2287603255-6">[</span><span class="p" data-group-id="2287603255-6">]</span><span class="p" data-group-id="2287603255-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +working with lists are <code class="inline">foreach</code> and <code class="inline">map</code>, which are defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="0341558237-1">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0341558237-2">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0341558237-2">]</span><span class="p" data-group-id="0341558237-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Fun</span><span class="p" data-group-id="0341558237-3">(</span><span class="n">First</span><span class="p" data-group-id="0341558237-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="0341558237-4">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0341558237-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="0341558237-5">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0341558237-6">[</span><span class="p" data-group-id="0341558237-6">]</span><span class="p" data-group-id="0341558237-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="2287603255-7">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2287603255-8">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="2287603255-8">]</span><span class="p" data-group-id="2287603255-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2287603255-9">[</span><span class="n">Fun</span><span class="p" data-group-id="2287603255-10">(</span><span class="n">First</span><span class="p" data-group-id="2287603255-10">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="2287603255-11">(</span><span class="n">Fun</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="2287603255-11">)</span><span class="p" data-group-id="2287603255-9">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="2287603255-12">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2287603255-13">[</span><span class="p" data-group-id="2287603255-13">]</span><span class="p" data-group-id="2287603255-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2287603255-14">[</span><span class="p" data-group-id="2287603255-14">]</span><span class="p">.</span></code></pre><p>These two functions are provided in the standard module <code class="inline">lists</code>. <code class="inline">foreach</code> takes
│ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="0341558237-7">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0341558237-8">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0341558237-8">]</span><span class="p" data-group-id="0341558237-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0341558237-9">[</span><span class="n">Fun</span><span class="p" data-group-id="0341558237-10">(</span><span class="n">First</span><span class="p" data-group-id="0341558237-10">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="0341558237-11">(</span><span class="n">Fun</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="0341558237-11">)</span><span class="p" data-group-id="0341558237-9">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="0341558237-12">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0341558237-13">[</span><span class="p" data-group-id="0341558237-13">]</span><span class="p" data-group-id="0341558237-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0341558237-14">[</span><span class="p" data-group-id="0341558237-14">]</span><span class="p">.</span></code></pre><p>These two functions are provided in the standard module <code class="inline">lists</code>. <code class="inline">foreach</code> takes
│ │ │  a list and applies a fun to every element in the list. <code class="inline">map</code> creates a new list
│ │ │  by applying a fun to every element in a list. Going back to the shell, <code class="inline">map</code> is
│ │ │ -used and a fun to add 3 to every element of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">88&gt; </span><span class="n">Add_3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3857693595-1">(</span><span class="n">X</span><span class="p" data-group-id="3857693595-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +used and a fun to add 3 to every element of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">88&gt; </span><span class="n">Add_3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="8546096932-1">(</span><span class="n">X</span><span class="p" data-group-id="8546096932-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -89&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="3857693595-2">(</span><span class="n">Add_3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3857693595-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3857693595-3">]</span><span class="p" data-group-id="3857693595-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3857693595-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="3857693595-4">]</span></code></pre><p>Let us (again) print the temperatures in a list of cities:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">90&gt; </span><span class="n">Print_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="8332762571-1">(</span><span class="p" data-group-id="8332762571-2">{</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8332762571-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8332762571-3">}</span><span class="p" data-group-id="8332762571-2">}</span><span class="p" data-group-id="8332762571-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8332762571-4">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8332762571-5">[</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8332762571-5">]</span><span class="p" data-group-id="8332762571-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +89&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="8546096932-2">(</span><span class="n">Add_3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8546096932-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8546096932-3">]</span><span class="p" data-group-id="8546096932-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8546096932-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8546096932-4">]</span></code></pre><p>Let us (again) print the temperatures in a list of cities:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">90&gt; </span><span class="n">Print_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6163284629-1">(</span><span class="p" data-group-id="6163284629-2">{</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163284629-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6163284629-3">}</span><span class="p" data-group-id="6163284629-2">}</span><span class="p" data-group-id="6163284629-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6163284629-4">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6163284629-5">[</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6163284629-5">]</span><span class="p" data-group-id="6163284629-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -91&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="8332762571-6">(</span><span class="n">Print_City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8332762571-7">[</span><span class="p" data-group-id="8332762571-8">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8332762571-9">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8332762571-9">}</span><span class="p" data-group-id="8332762571-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8332762571-10">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8332762571-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="8332762571-11">}</span><span class="p" data-group-id="8332762571-10">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8332762571-12">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8332762571-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8332762571-13">}</span><span class="p" data-group-id="8332762571-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8332762571-14">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8332762571-15">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8332762571-15">}</span><span class="p" data-group-id="8332762571-14">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8332762571-16">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8332762571-17">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="8332762571-17">}</span><span class="p" data-group-id="8332762571-16">}</span><span class="p" data-group-id="8332762571-7">]</span><span class="p" data-group-id="8332762571-6">)</span><span class="p">.</span><span class="w">
│ │ │ +91&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="6163284629-6">(</span><span class="n">Print_City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163284629-7">[</span><span class="p" data-group-id="6163284629-8">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163284629-9">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6163284629-9">}</span><span class="p" data-group-id="6163284629-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163284629-10">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163284629-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6163284629-11">}</span><span class="p" data-group-id="6163284629-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6163284629-12">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163284629-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6163284629-13">}</span><span class="p" data-group-id="6163284629-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163284629-14">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163284629-15">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6163284629-15">}</span><span class="p" data-group-id="6163284629-14">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163284629-16">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163284629-17">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="6163284629-17">}</span><span class="p" data-group-id="6163284629-16">}</span><span class="p" data-group-id="6163284629-7">]</span><span class="p" data-group-id="6163284629-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="ss">c</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="w">
│ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="ss">f</span><span class="w"> </span><span class="mi">70</span><span class="w">
│ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="ss">c</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="ss">f</span><span class="w"> </span><span class="mi">28</span><span class="w">
│ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="ss">f</span><span class="w"> </span><span class="mi">36</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>Let us now define a fun that can be used to go through a list of cities and
│ │ │ -temperatures and transform them all to Celsius.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2447149977-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="2447149977-1">)</span><span class="p">.</span><span class="w">
│ │ │ +temperatures and transform them all to Celsius.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9453183431-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="9453183431-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2447149977-2">(</span><span class="p" data-group-id="2447149977-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2447149977-3">]</span><span class="p" data-group-id="2447149977-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9453183431-2">(</span><span class="p" data-group-id="9453183431-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9453183431-3">]</span><span class="p" data-group-id="9453183431-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="2447149977-4">(</span><span class="p" data-group-id="2447149977-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2447149977-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2447149977-6">}</span><span class="p" data-group-id="2447149977-5">}</span><span class="p" data-group-id="2447149977-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2447149977-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2447149977-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="2447149977-9">(</span><span class="p" data-group-id="2447149977-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="2447149977-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="2447149977-9">)</span><span class="p" data-group-id="2447149977-8">}</span><span class="p" data-group-id="2447149977-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="2447149977-11">(</span><span class="p" data-group-id="2447149977-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2447149977-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2447149977-13">}</span><span class="p" data-group-id="2447149977-12">}</span><span class="p" data-group-id="2447149977-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2447149977-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2447149977-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2447149977-15">}</span><span class="p" data-group-id="2447149977-14">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2447149977-16">(</span><span class="n">List</span><span class="p" data-group-id="2447149977-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="2447149977-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="2447149977-17">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">92&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9649693046-1">(</span><span class="p" data-group-id="9649693046-2">[</span><span class="p" data-group-id="9649693046-3">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9649693046-4">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="9649693046-4">}</span><span class="p" data-group-id="9649693046-3">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9649693046-5">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9649693046-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="9649693046-6">}</span><span class="p" data-group-id="9649693046-5">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9649693046-7">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9649693046-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="9649693046-8">}</span><span class="p" data-group-id="9649693046-7">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9649693046-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9649693046-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="9649693046-10">}</span><span class="p" data-group-id="9649693046-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9649693046-11">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9649693046-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="9649693046-12">}</span><span class="p" data-group-id="9649693046-11">}</span><span class="p" data-group-id="9649693046-2">]</span><span class="p" data-group-id="9649693046-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9649693046-13">[</span><span class="p" data-group-id="9649693046-14">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="9649693046-15">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="9649693046-15">}</span><span class="p" data-group-id="9649693046-14">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9649693046-16">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="9649693046-17">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="9649693046-17">}</span><span class="p" data-group-id="9649693046-16">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9649693046-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="9649693046-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="9649693046-19">}</span><span class="p" data-group-id="9649693046-18">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9649693046-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="9649693046-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="9649693046-21">}</span><span class="p" data-group-id="9649693046-20">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9649693046-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="9649693046-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9649693046-23">}</span><span class="p" data-group-id="9649693046-22">}</span><span class="p" data-group-id="9649693046-13">]</span></code></pre><p>The <code class="inline">convert_to_c</code> function is the same as before, but here it is used as a fun:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1547022007-1">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1547022007-1">)</span></code></pre><p>When a function defined elsewhere is used as a fun, it can be referred to as
│ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="9453183431-4">(</span><span class="p" data-group-id="9453183431-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9453183431-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9453183431-6">}</span><span class="p" data-group-id="9453183431-5">}</span><span class="p" data-group-id="9453183431-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9453183431-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9453183431-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="9453183431-9">(</span><span class="p" data-group-id="9453183431-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="9453183431-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="9453183431-9">)</span><span class="p" data-group-id="9453183431-8">}</span><span class="p" data-group-id="9453183431-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="9453183431-11">(</span><span class="p" data-group-id="9453183431-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9453183431-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9453183431-13">}</span><span class="p" data-group-id="9453183431-12">}</span><span class="p" data-group-id="9453183431-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9453183431-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9453183431-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9453183431-15">}</span><span class="p" data-group-id="9453183431-14">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9453183431-16">(</span><span class="n">List</span><span class="p" data-group-id="9453183431-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="9453183431-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9453183431-17">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">92&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8747903556-1">(</span><span class="p" data-group-id="8747903556-2">[</span><span class="p" data-group-id="8747903556-3">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8747903556-4">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8747903556-4">}</span><span class="p" data-group-id="8747903556-3">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8747903556-5">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8747903556-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="8747903556-6">}</span><span class="p" data-group-id="8747903556-5">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8747903556-7">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8747903556-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8747903556-8">}</span><span class="p" data-group-id="8747903556-7">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8747903556-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8747903556-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8747903556-10">}</span><span class="p" data-group-id="8747903556-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8747903556-11">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8747903556-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="8747903556-12">}</span><span class="p" data-group-id="8747903556-11">}</span><span class="p" data-group-id="8747903556-2">]</span><span class="p" data-group-id="8747903556-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8747903556-13">[</span><span class="p" data-group-id="8747903556-14">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="8747903556-15">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8747903556-15">}</span><span class="p" data-group-id="8747903556-14">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8747903556-16">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="8747903556-17">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="8747903556-17">}</span><span class="p" data-group-id="8747903556-16">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8747903556-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="8747903556-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8747903556-19">}</span><span class="p" data-group-id="8747903556-18">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8747903556-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="8747903556-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="8747903556-21">}</span><span class="p" data-group-id="8747903556-20">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8747903556-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="8747903556-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8747903556-23">}</span><span class="p" data-group-id="8747903556-22">}</span><span class="p" data-group-id="8747903556-13">]</span></code></pre><p>The <code class="inline">convert_to_c</code> function is the same as before, but here it is used as a fun:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="8131831520-1">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="8131831520-1">)</span></code></pre><p>When a function defined elsewhere is used as a fun, it can be referred to as
│ │ │  <code class="inline">Function/Arity</code> (remember that <code class="inline">Arity</code> = number of arguments). So in the
│ │ │  <code class="inline">map</code>-call <code class="inline">lists:map(fun convert_to_c/1, List)</code> is written. As shown,
│ │ │  <code class="inline">convert_list_to_c</code> becomes much shorter and easier to understand.</p><p>The standard module <code class="inline">lists</code> also contains a function <code class="inline">sort(Fun, List)</code> where
│ │ │  <code class="inline">Fun</code> is a fun with two arguments. This fun returns <code class="inline">true</code> if the first argument
│ │ │  is less than the second argument, or else <code class="inline">false</code>. Sorting is added to the
│ │ │ -<code class="inline">convert_list_to_c</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0166541818-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="0166541818-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">convert_list_to_c</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1747105461-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="1747105461-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0166541818-2">(</span><span class="p" data-group-id="0166541818-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0166541818-3">]</span><span class="p" data-group-id="0166541818-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1747105461-2">(</span><span class="p" data-group-id="1747105461-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1747105461-3">]</span><span class="p" data-group-id="1747105461-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="0166541818-4">(</span><span class="p" data-group-id="0166541818-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0166541818-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="0166541818-6">}</span><span class="p" data-group-id="0166541818-5">}</span><span class="p" data-group-id="0166541818-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0166541818-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0166541818-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="0166541818-9">(</span><span class="p" data-group-id="0166541818-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="0166541818-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="0166541818-9">)</span><span class="p" data-group-id="0166541818-8">}</span><span class="p" data-group-id="0166541818-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="0166541818-11">(</span><span class="p" data-group-id="0166541818-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0166541818-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="0166541818-13">}</span><span class="p" data-group-id="0166541818-12">}</span><span class="p" data-group-id="0166541818-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0166541818-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0166541818-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="0166541818-15">}</span><span class="p" data-group-id="0166541818-14">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="0166541818-16">(</span><span class="n">List</span><span class="p" data-group-id="0166541818-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">New_list</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0166541818-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="0166541818-17">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="0166541818-18">(</span><span class="nf">fun</span><span class="p" data-group-id="0166541818-19">(</span><span class="p" data-group-id="0166541818-20">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0166541818-21">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="0166541818-21">}</span><span class="p" data-group-id="0166541818-20">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0166541818-22">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0166541818-23">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="0166541818-23">}</span><span class="p" data-group-id="0166541818-22">}</span><span class="p" data-group-id="0166541818-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                       </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">New_list</span><span class="p" data-group-id="0166541818-18">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">93&gt; </span><span class="nf">c</span><span class="p" data-group-id="2540142376-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="2540142376-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2540142376-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut13</span><span class="p" data-group-id="2540142376-2">}</span><span class="gp unselectable">
│ │ │ -94&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2540142376-3">(</span><span class="p" data-group-id="2540142376-4">[</span><span class="p" data-group-id="2540142376-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2540142376-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2540142376-6">}</span><span class="p" data-group-id="2540142376-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2540142376-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2540142376-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="2540142376-8">}</span><span class="p" data-group-id="2540142376-7">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2540142376-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2540142376-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2540142376-10">}</span><span class="p" data-group-id="2540142376-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2540142376-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2540142376-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="2540142376-12">}</span><span class="p" data-group-id="2540142376-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2540142376-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2540142376-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="2540142376-14">}</span><span class="p" data-group-id="2540142376-13">}</span><span class="p" data-group-id="2540142376-4">]</span><span class="p" data-group-id="2540142376-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2540142376-15">[</span><span class="p" data-group-id="2540142376-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="2540142376-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2540142376-17">}</span><span class="p" data-group-id="2540142376-16">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2540142376-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="2540142376-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2540142376-19">}</span><span class="p" data-group-id="2540142376-18">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2540142376-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="2540142376-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="2540142376-21">}</span><span class="p" data-group-id="2540142376-20">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2540142376-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="2540142376-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2540142376-23">}</span><span class="p" data-group-id="2540142376-22">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2540142376-24">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="2540142376-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="2540142376-25">}</span><span class="p" data-group-id="2540142376-24">}</span><span class="p" data-group-id="2540142376-15">]</span></code></pre><p>In <code class="inline">sort</code> the fun is used:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="p" data-group-id="3603429351-1">(</span><span class="p" data-group-id="3603429351-2">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3603429351-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="3603429351-3">}</span><span class="p" data-group-id="3603429351-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3603429351-4">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3603429351-5">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="3603429351-5">}</span><span class="p" data-group-id="3603429351-4">}</span><span class="p" data-group-id="3603429351-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span></code></pre><p>Here the concept of an <em>anonymous variable</em> <code class="inline">_</code> is introduced. This is simply
│ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="1747105461-4">(</span><span class="p" data-group-id="1747105461-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1747105461-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1747105461-6">}</span><span class="p" data-group-id="1747105461-5">}</span><span class="p" data-group-id="1747105461-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1747105461-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1747105461-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="1747105461-9">(</span><span class="p" data-group-id="1747105461-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="1747105461-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1747105461-9">)</span><span class="p" data-group-id="1747105461-8">}</span><span class="p" data-group-id="1747105461-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="1747105461-11">(</span><span class="p" data-group-id="1747105461-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1747105461-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1747105461-13">}</span><span class="p" data-group-id="1747105461-12">}</span><span class="p" data-group-id="1747105461-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1747105461-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1747105461-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1747105461-15">}</span><span class="p" data-group-id="1747105461-14">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1747105461-16">(</span><span class="n">List</span><span class="p" data-group-id="1747105461-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">New_list</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1747105461-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1747105461-17">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="1747105461-18">(</span><span class="nf">fun</span><span class="p" data-group-id="1747105461-19">(</span><span class="p" data-group-id="1747105461-20">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1747105461-21">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="1747105461-21">}</span><span class="p" data-group-id="1747105461-20">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1747105461-22">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1747105461-23">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="1747105461-23">}</span><span class="p" data-group-id="1747105461-22">}</span><span class="p" data-group-id="1747105461-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                       </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">New_list</span><span class="p" data-group-id="1747105461-18">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">93&gt; </span><span class="nf">c</span><span class="p" data-group-id="4515310994-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="4515310994-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4515310994-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut13</span><span class="p" data-group-id="4515310994-2">}</span><span class="gp unselectable">
│ │ │ +94&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4515310994-3">(</span><span class="p" data-group-id="4515310994-4">[</span><span class="p" data-group-id="4515310994-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4515310994-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4515310994-6">}</span><span class="p" data-group-id="4515310994-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4515310994-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4515310994-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4515310994-8">}</span><span class="p" data-group-id="4515310994-7">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4515310994-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4515310994-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4515310994-10">}</span><span class="p" data-group-id="4515310994-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4515310994-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4515310994-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4515310994-12">}</span><span class="p" data-group-id="4515310994-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4515310994-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4515310994-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4515310994-14">}</span><span class="p" data-group-id="4515310994-13">}</span><span class="p" data-group-id="4515310994-4">]</span><span class="p" data-group-id="4515310994-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4515310994-15">[</span><span class="p" data-group-id="4515310994-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="4515310994-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4515310994-17">}</span><span class="p" data-group-id="4515310994-16">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4515310994-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="4515310994-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4515310994-19">}</span><span class="p" data-group-id="4515310994-18">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4515310994-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="4515310994-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="4515310994-21">}</span><span class="p" data-group-id="4515310994-20">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4515310994-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="4515310994-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4515310994-23">}</span><span class="p" data-group-id="4515310994-22">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4515310994-24">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="4515310994-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="4515310994-25">}</span><span class="p" data-group-id="4515310994-24">}</span><span class="p" data-group-id="4515310994-15">]</span></code></pre><p>In <code class="inline">sort</code> the fun is used:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="p" data-group-id="0629123998-1">(</span><span class="p" data-group-id="0629123998-2">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0629123998-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="0629123998-3">}</span><span class="p" data-group-id="0629123998-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0629123998-4">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0629123998-5">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="0629123998-5">}</span><span class="p" data-group-id="0629123998-4">}</span><span class="p" data-group-id="0629123998-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span></code></pre><p>Here the concept of an <em>anonymous variable</em> <code class="inline">_</code> is introduced. This is simply
│ │ │  shorthand for a variable that gets a value, but the value is ignored. This can
│ │ │  be used anywhere suitable, not just in funs. <code class="inline">Temp1 &lt; Temp2</code> returns <code class="inline">true</code> if
│ │ │  <code class="inline">Temp1</code> is less than <code class="inline">Temp2</code>.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/spec_proc.html
│ │ │ @@ -123,72 +123,72 @@
│ │ │    <a href="#simple-debugging" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Simple Debugging</span>
│ │ │  </h2>
│ │ │  <p>The <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html"><code class="inline">sys</code></a> module has functions for simple debugging of processes implemented
│ │ │  using behaviours. The <code class="inline">code_lock</code> example from
│ │ │ -<a href="statem.html#example">gen_statem Behaviour</a> is used to illustrate this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="4435000742-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="4435000742-1">]</span><span class="w"> </span><span class="p" data-group-id="4435000742-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4435000742-2">]</span><span class="w"> </span><span class="p" data-group-id="4435000742-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4435000742-3">]</span><span class="w"> </span><span class="p" data-group-id="4435000742-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4435000742-4">]</span><span class="w"> </span><span class="p" data-group-id="4435000742-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4435000742-5">]</span><span class="w"> </span><span class="p" data-group-id="4435000742-6">[</span><span class="ss">jit</span><span class="p" data-group-id="4435000742-6">]</span><span class="w">
│ │ │ +<a href="statem.html#example">gen_statem Behaviour</a> is used to illustrate this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="5719183700-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="5719183700-1">]</span><span class="w"> </span><span class="p" data-group-id="5719183700-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="5719183700-2">]</span><span class="w"> </span><span class="p" data-group-id="5719183700-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="5719183700-3">]</span><span class="w"> </span><span class="p" data-group-id="5719183700-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="5719183700-4">]</span><span class="w"> </span><span class="p" data-group-id="5719183700-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5719183700-5">]</span><span class="w"> </span><span class="p" data-group-id="5719183700-6">[</span><span class="ss">jit</span><span class="p" data-group-id="5719183700-6">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="4435000742-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="4435000742-8">(</span><span class="p" data-group-id="4435000742-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="4435000742-7">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4435000742-9">(</span><span class="p" data-group-id="4435000742-10">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4435000742-10">]</span><span class="p" data-group-id="4435000742-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="5719183700-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="5719183700-8">(</span><span class="p" data-group-id="5719183700-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="5719183700-7">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5719183700-9">(</span><span class="p" data-group-id="5719183700-10">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5719183700-10">]</span><span class="p" data-group-id="5719183700-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">Lock</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4435000742-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4435000742-11">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="4435000742-12">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4435000742-12">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5719183700-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5719183700-11">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5719183700-12">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5719183700-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="4435000742-13">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4435000742-13">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="5719183700-13">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5719183700-13">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="4435000742-14">(</span><span class="mi">1</span><span class="p" data-group-id="4435000742-14">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="4435000742-15">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4435000742-15">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5719183700-14">(</span><span class="mi">1</span><span class="p" data-group-id="5719183700-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5719183700-15">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5719183700-15">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="4435000742-16">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4435000742-16">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="4435000742-17">(</span><span class="mi">2</span><span class="p" data-group-id="4435000742-17">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="4435000742-18">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4435000742-18">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5719183700-16">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5719183700-16">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ +5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5719183700-17">(</span><span class="mi">2</span><span class="p" data-group-id="5719183700-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5719183700-18">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5719183700-18">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="4435000742-19">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4435000742-19">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="4435000742-20">(</span><span class="mi">3</span><span class="p" data-group-id="4435000742-20">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="4435000742-21">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4435000742-21">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5719183700-19">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5719183700-19">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ +6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5719183700-20">(</span><span class="mi">3</span><span class="p" data-group-id="5719183700-20">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5719183700-21">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5719183700-21">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="4435000742-22">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4435000742-22">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ -7&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="4435000742-23">(</span><span class="mi">4</span><span class="p" data-group-id="4435000742-23">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="4435000742-24">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4435000742-24">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5719183700-22">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5719183700-22">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ +7&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="5719183700-23">(</span><span class="mi">4</span><span class="p" data-group-id="5719183700-23">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5719183700-24">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5719183700-24">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="n">Unlock</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="4435000742-25">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4435000742-25">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="nb">start_timer</span><span class="w"> </span><span class="p" data-group-id="4435000742-26">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10000</span><span class="p">,</span><span class="ss">lock</span><span class="p">,</span><span class="p" data-group-id="4435000742-27">[</span><span class="p" data-group-id="4435000742-27">]</span><span class="p" data-group-id="4435000742-26">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="5719183700-25">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5719183700-25">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="nb">start_timer</span><span class="w"> </span><span class="p" data-group-id="5719183700-26">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10000</span><span class="p">,</span><span class="ss">lock</span><span class="p">,</span><span class="p" data-group-id="5719183700-27">[</span><span class="p" data-group-id="5719183700-27">]</span><span class="p" data-group-id="5719183700-26">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │  </span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">state_timeout</span><span class="w"> </span><span class="ss">lock</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │  </span><span class="n">Lock</span><span class="w">
│ │ │  </span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">state_timeout</span><span class="w"> </span><span class="ss">lock</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">locked</span><span class="gp unselectable">
│ │ │ -8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="4435000742-28">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="4435000742-28">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4435000742-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="4435000742-30">[</span><span class="p" data-group-id="4435000742-31">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="4435000742-32">{</span><span class="p" data-group-id="4435000742-33">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4435000742-33">}</span><span class="p">,</span><span class="p" data-group-id="4435000742-34">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4435000742-34">}</span><span class="p" data-group-id="4435000742-32">}</span><span class="p" data-group-id="4435000742-31">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="4435000742-35">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="4435000742-36">{</span><span class="p" data-group-id="4435000742-37">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4435000742-37">}</span><span class="p">,</span><span class="p" data-group-id="4435000742-38">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">48</span><span class="p" data-group-id="4435000742-38">}</span><span class="p" data-group-id="4435000742-36">}</span><span class="p" data-group-id="4435000742-35">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="4435000742-39">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">4098</span><span class="p" data-group-id="4435000742-39">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="4435000742-40">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4435000742-40">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="4435000742-41">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4435000742-41">}</span><span class="p" data-group-id="4435000742-30">]</span><span class="p" data-group-id="4435000742-29">}</span><span class="gp unselectable">
│ │ │ -9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="4435000742-42">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="4435000742-42">)</span><span class="p">.</span><span class="w">
│ │ │ +8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5719183700-28">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="5719183700-28">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5719183700-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="5719183700-30">[</span><span class="p" data-group-id="5719183700-31">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="5719183700-32">{</span><span class="p" data-group-id="5719183700-33">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5719183700-33">}</span><span class="p">,</span><span class="p" data-group-id="5719183700-34">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5719183700-34">}</span><span class="p" data-group-id="5719183700-32">}</span><span class="p" data-group-id="5719183700-31">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="5719183700-35">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="5719183700-36">{</span><span class="p" data-group-id="5719183700-37">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5719183700-37">}</span><span class="p">,</span><span class="p" data-group-id="5719183700-38">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">48</span><span class="p" data-group-id="5719183700-38">}</span><span class="p" data-group-id="5719183700-36">}</span><span class="p" data-group-id="5719183700-35">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="5719183700-39">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">4098</span><span class="p" data-group-id="5719183700-39">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="5719183700-40">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5719183700-40">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="5719183700-41">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="5719183700-41">}</span><span class="p" data-group-id="5719183700-30">]</span><span class="p" data-group-id="5719183700-29">}</span><span class="gp unselectable">
│ │ │ +9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5719183700-42">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="5719183700-42">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -10&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="4435000742-43">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="4435000742-43">)</span><span class="p">.</span><span class="w">
│ │ │ +10&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="5719183700-43">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="5719183700-43">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -11&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="4435000742-44">(</span><span class="ss">code_lock</span><span class="p" data-group-id="4435000742-44">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4435000742-45">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4435000742-46">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">gen_statem</span><span class="p" data-group-id="4435000742-46">}</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4435000742-47">[</span><span class="p" data-group-id="4435000742-48">[</span><span class="p" data-group-id="4435000742-49">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="4435000742-50">{</span><span class="ss">code_lock</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4435000742-50">}</span><span class="p" data-group-id="4435000742-49">}</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="4435000742-51">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="4435000742-52">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ -                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4435000742-52">]</span><span class="p" data-group-id="4435000742-51">}</span><span class="p" data-group-id="4435000742-48">]</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="4435000742-53">[</span><span class="p" data-group-id="4435000742-53">]</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="4435000742-54">[</span><span class="p" data-group-id="4435000742-55">{</span><span class="ss">header</span><span class="p">,</span><span class="s">&quot;Status for state machine code_lock&quot;</span><span class="p" data-group-id="4435000742-55">}</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="4435000742-56">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="4435000742-57">[</span><span class="p" data-group-id="4435000742-58">{</span><span class="s">&quot;Status&quot;</span><span class="p">,</span><span class="ss">running</span><span class="p" data-group-id="4435000742-58">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="4435000742-59">{</span><span class="s">&quot;Parent&quot;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4435000742-59">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="4435000742-60">{</span><span class="s">&quot;Modules&quot;</span><span class="p">,</span><span class="p" data-group-id="4435000742-61">[</span><span class="ss">code_lock</span><span class="p" data-group-id="4435000742-61">]</span><span class="p" data-group-id="4435000742-60">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="4435000742-62">{</span><span class="s">&quot;Time-outs&quot;</span><span class="p">,</span><span class="p" data-group-id="4435000742-63">{</span><span class="mi">0</span><span class="p">,</span><span class="p" data-group-id="4435000742-64">[</span><span class="p" data-group-id="4435000742-64">]</span><span class="p" data-group-id="4435000742-63">}</span><span class="p" data-group-id="4435000742-62">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="4435000742-65">{</span><span class="s">&quot;Logged Events&quot;</span><span class="p">,</span><span class="p" data-group-id="4435000742-66">[</span><span class="p" data-group-id="4435000742-66">]</span><span class="p" data-group-id="4435000742-65">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="4435000742-67">{</span><span class="s">&quot;Postponed&quot;</span><span class="p">,</span><span class="p" data-group-id="4435000742-68">[</span><span class="p" data-group-id="4435000742-68">]</span><span class="p" data-group-id="4435000742-67">}</span><span class="p" data-group-id="4435000742-57">]</span><span class="p" data-group-id="4435000742-56">}</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="4435000742-69">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="4435000742-70">[</span><span class="p" data-group-id="4435000742-71">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="w">
│ │ │ -                  </span><span class="p" data-group-id="4435000742-72">{</span><span class="ss">locked</span><span class="p">,</span><span class="p" data-group-id="4435000742-73">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4435000742-74">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4435000742-74">]</span><span class="p">,</span><span class="w">
│ │ │ -                            </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4435000742-75">[</span><span class="p" data-group-id="4435000742-75">]</span><span class="p" data-group-id="4435000742-73">}</span><span class="p" data-group-id="4435000742-72">}</span><span class="p" data-group-id="4435000742-71">}</span><span class="p" data-group-id="4435000742-70">]</span><span class="p" data-group-id="4435000742-69">}</span><span class="p" data-group-id="4435000742-54">]</span><span class="p" data-group-id="4435000742-47">]</span><span class="p" data-group-id="4435000742-45">}</span></code></pre><h2 id="special-processes" class="section-heading">
│ │ │ +11&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="5719183700-44">(</span><span class="ss">code_lock</span><span class="p" data-group-id="5719183700-44">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5719183700-45">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5719183700-46">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">gen_statem</span><span class="p" data-group-id="5719183700-46">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5719183700-47">[</span><span class="p" data-group-id="5719183700-48">[</span><span class="p" data-group-id="5719183700-49">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="5719183700-50">{</span><span class="ss">code_lock</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5719183700-50">}</span><span class="p" data-group-id="5719183700-49">}</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="5719183700-51">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="5719183700-52">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ +                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5719183700-52">]</span><span class="p" data-group-id="5719183700-51">}</span><span class="p" data-group-id="5719183700-48">]</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="5719183700-53">[</span><span class="p" data-group-id="5719183700-53">]</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="5719183700-54">[</span><span class="p" data-group-id="5719183700-55">{</span><span class="ss">header</span><span class="p">,</span><span class="s">&quot;Status for state machine code_lock&quot;</span><span class="p" data-group-id="5719183700-55">}</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="5719183700-56">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="5719183700-57">[</span><span class="p" data-group-id="5719183700-58">{</span><span class="s">&quot;Status&quot;</span><span class="p">,</span><span class="ss">running</span><span class="p" data-group-id="5719183700-58">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="5719183700-59">{</span><span class="s">&quot;Parent&quot;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5719183700-59">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="5719183700-60">{</span><span class="s">&quot;Modules&quot;</span><span class="p">,</span><span class="p" data-group-id="5719183700-61">[</span><span class="ss">code_lock</span><span class="p" data-group-id="5719183700-61">]</span><span class="p" data-group-id="5719183700-60">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="5719183700-62">{</span><span class="s">&quot;Time-outs&quot;</span><span class="p">,</span><span class="p" data-group-id="5719183700-63">{</span><span class="mi">0</span><span class="p">,</span><span class="p" data-group-id="5719183700-64">[</span><span class="p" data-group-id="5719183700-64">]</span><span class="p" data-group-id="5719183700-63">}</span><span class="p" data-group-id="5719183700-62">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="5719183700-65">{</span><span class="s">&quot;Logged Events&quot;</span><span class="p">,</span><span class="p" data-group-id="5719183700-66">[</span><span class="p" data-group-id="5719183700-66">]</span><span class="p" data-group-id="5719183700-65">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="5719183700-67">{</span><span class="s">&quot;Postponed&quot;</span><span class="p">,</span><span class="p" data-group-id="5719183700-68">[</span><span class="p" data-group-id="5719183700-68">]</span><span class="p" data-group-id="5719183700-67">}</span><span class="p" data-group-id="5719183700-57">]</span><span class="p" data-group-id="5719183700-56">}</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="5719183700-69">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="5719183700-70">[</span><span class="p" data-group-id="5719183700-71">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="w">
│ │ │ +                  </span><span class="p" data-group-id="5719183700-72">{</span><span class="ss">locked</span><span class="p">,</span><span class="p" data-group-id="5719183700-73">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5719183700-74">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5719183700-74">]</span><span class="p">,</span><span class="w">
│ │ │ +                            </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5719183700-75">[</span><span class="p" data-group-id="5719183700-75">]</span><span class="p" data-group-id="5719183700-73">}</span><span class="p" data-group-id="5719183700-72">}</span><span class="p" data-group-id="5719183700-71">}</span><span class="p" data-group-id="5719183700-70">]</span><span class="p" data-group-id="5719183700-69">}</span><span class="p" data-group-id="5719183700-54">]</span><span class="p" data-group-id="5719183700-47">]</span><span class="p" data-group-id="5719183700-45">}</span></code></pre><h2 id="special-processes" class="section-heading">
│ │ │    <a href="#special-processes" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Special Processes</span>
│ │ │  </h2>
│ │ │  <p>This section describes how to write a process that complies to the OTP design
│ │ │  principles, without using a standard behaviour. Such a process is to:</p><ul><li>Be started in a way that makes the process fit into a supervision tree</li><li>Support the <code class="inline">sys</code> <a href="spec_proc.html#debug">debug facilities</a></li><li>Take care of <a href="spec_proc.html#msg">system messages</a>.</li></ul><p>System messages are messages with a special meaning, used in the supervision
│ │ │ @@ -198,238 +198,238 @@
│ │ │    <a href="#example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example</span>
│ │ │  </h3>
│ │ │  <p>Here follows the simple server from
│ │ │  <a href="design_principles.html#ch1">Overview</a>,
│ │ │ -implemented using <code class="inline">sys</code> and <code class="inline">proc_lib</code> to fit into a supervision tree:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8377630245-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="8377630245-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8377630245-2">(</span><span class="p" data-group-id="8377630245-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8377630245-3">]</span><span class="p" data-group-id="8377630245-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8377630245-4">(</span><span class="p" data-group-id="8377630245-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8377630245-5">]</span><span class="p" data-group-id="8377630245-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8377630245-6">(</span><span class="p" data-group-id="8377630245-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8377630245-7">]</span><span class="p" data-group-id="8377630245-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8377630245-8">(</span><span class="p" data-group-id="8377630245-9">[</span><span class="ss">system_continue</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">system_terminate</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w">
│ │ │ +implemented using <code class="inline">sys</code> and <code class="inline">proc_lib</code> to fit into a supervision tree:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0455778317-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="0455778317-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0455778317-2">(</span><span class="p" data-group-id="0455778317-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0455778317-3">]</span><span class="p" data-group-id="0455778317-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0455778317-4">(</span><span class="p" data-group-id="0455778317-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0455778317-5">]</span><span class="p" data-group-id="0455778317-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0455778317-6">(</span><span class="p" data-group-id="0455778317-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0455778317-7">]</span><span class="p" data-group-id="0455778317-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0455778317-8">(</span><span class="p" data-group-id="0455778317-9">[</span><span class="ss">system_continue</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">system_terminate</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w">
│ │ │           </span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="ss">system_get_state</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">system_replace_state</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8377630245-9">]</span><span class="p" data-group-id="8377630245-8">)</span><span class="p">.</span><span class="w">
│ │ │ +         </span><span class="ss">system_get_state</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">system_replace_state</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0455778317-9">]</span><span class="p" data-group-id="0455778317-8">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="8377630245-10">(</span><span class="p" data-group-id="8377630245-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8377630245-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8377630245-12">[</span><span class="nf">self</span><span class="p" data-group-id="8377630245-13">(</span><span class="p" data-group-id="8377630245-13">)</span><span class="p" data-group-id="8377630245-12">]</span><span class="p" data-group-id="8377630245-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="0455778317-10">(</span><span class="p" data-group-id="0455778317-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0455778317-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0455778317-12">[</span><span class="nf">self</span><span class="p" data-group-id="0455778317-13">(</span><span class="p" data-group-id="0455778317-13">)</span><span class="p" data-group-id="0455778317-12">]</span><span class="p" data-group-id="0455778317-11">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="8377630245-14">(</span><span class="p" data-group-id="8377630245-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8377630245-15">{</span><span class="nf">self</span><span class="p" data-group-id="8377630245-16">(</span><span class="p" data-group-id="8377630245-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="8377630245-15">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="0455778317-14">(</span><span class="p" data-group-id="0455778317-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0455778317-15">{</span><span class="nf">self</span><span class="p" data-group-id="0455778317-16">(</span><span class="p" data-group-id="0455778317-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0455778317-15">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8377630245-17">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="8377630245-17">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0455778317-17">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="0455778317-17">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Res</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="8377630245-18">(</span><span class="n">Ch</span><span class="p" data-group-id="8377630245-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8377630245-19">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8377630245-19">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="0455778317-18">(</span><span class="n">Ch</span><span class="p" data-group-id="0455778317-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0455778317-19">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0455778317-19">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8377630245-20">(</span><span class="n">Parent</span><span class="p" data-group-id="8377630245-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="8377630245-21">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8377630245-22">(</span><span class="p" data-group-id="8377630245-22">)</span><span class="p" data-group-id="8377630245-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="8377630245-23">(</span><span class="p" data-group-id="8377630245-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="8377630245-24">(</span><span class="p" data-group-id="8377630245-25">[</span><span class="p" data-group-id="8377630245-25">]</span><span class="p" data-group-id="8377630245-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="8377630245-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8377630245-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8377630245-28">(</span><span class="p" data-group-id="8377630245-28">)</span><span class="p" data-group-id="8377630245-27">}</span><span class="p" data-group-id="8377630245-26">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="8377630245-29">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="8377630245-29">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="0455778317-20">(</span><span class="n">Parent</span><span class="p" data-group-id="0455778317-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="0455778317-21">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0455778317-22">(</span><span class="p" data-group-id="0455778317-22">)</span><span class="p" data-group-id="0455778317-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="0455778317-23">(</span><span class="p" data-group-id="0455778317-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="0455778317-24">(</span><span class="p" data-group-id="0455778317-25">[</span><span class="p" data-group-id="0455778317-25">]</span><span class="p" data-group-id="0455778317-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="0455778317-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0455778317-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0455778317-28">(</span><span class="p" data-group-id="0455778317-28">)</span><span class="p" data-group-id="0455778317-27">}</span><span class="p" data-group-id="0455778317-26">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="0455778317-29">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0455778317-29">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="8377630245-30">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="8377630245-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="0455778317-30">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0455778317-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8377630245-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="8377630245-31">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="8377630245-32">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8377630245-33">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="8377630245-33">}</span><span class="p" data-group-id="8377630245-32">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="8377630245-34">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="8377630245-34">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="8377630245-35">(</span><span class="n">Chs</span><span class="p" data-group-id="8377630245-35">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8377630245-36">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8377630245-36">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="8377630245-37">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8377630245-38">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8377630245-39">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8377630245-39">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="8377630245-38">}</span><span class="p" data-group-id="8377630245-37">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="8377630245-40">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="8377630245-40">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8377630245-41">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8377630245-41">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="8377630245-42">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8377630245-43">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8377630245-44">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8377630245-44">}</span><span class="p" data-group-id="8377630245-43">}</span><span class="p" data-group-id="8377630245-42">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="8377630245-45">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8377630245-45">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="8377630245-46">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="8377630245-46">)</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -        </span><span class="p" data-group-id="8377630245-47">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="8377630245-47">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="8377630245-48">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ -                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8377630245-48">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0455778317-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0455778317-31">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0455778317-32">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0455778317-33">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="0455778317-33">}</span><span class="p" data-group-id="0455778317-32">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="0455778317-34">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="0455778317-34">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="0455778317-35">(</span><span class="n">Chs</span><span class="p" data-group-id="0455778317-35">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0455778317-36">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0455778317-36">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0455778317-37">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0455778317-38">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0455778317-39">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0455778317-39">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="0455778317-38">}</span><span class="p" data-group-id="0455778317-37">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="0455778317-40">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="0455778317-40">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0455778317-41">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0455778317-41">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0455778317-42">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0455778317-43">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0455778317-44">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0455778317-44">}</span><span class="p" data-group-id="0455778317-43">}</span><span class="p" data-group-id="0455778317-42">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="0455778317-45">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0455778317-45">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="0455778317-46">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="0455778317-46">)</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +        </span><span class="p" data-group-id="0455778317-47">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0455778317-47">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="0455778317-48">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ +                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0455778317-48">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_continue</span><span class="p" data-group-id="8377630245-49">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8377630245-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="8377630245-50">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="8377630245-50">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_continue</span><span class="p" data-group-id="0455778317-49">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0455778317-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="0455778317-50">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0455778317-50">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_terminate</span><span class="p" data-group-id="8377630245-51">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Chs</span><span class="p" data-group-id="8377630245-51">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="8377630245-52">(</span><span class="n">Reason</span><span class="p" data-group-id="8377630245-52">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_terminate</span><span class="p" data-group-id="0455778317-51">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Chs</span><span class="p" data-group-id="0455778317-51">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="0455778317-52">(</span><span class="n">Reason</span><span class="p" data-group-id="0455778317-52">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_get_state</span><span class="p" data-group-id="8377630245-53">(</span><span class="n">Chs</span><span class="p" data-group-id="8377630245-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8377630245-54">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8377630245-54">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_get_state</span><span class="p" data-group-id="0455778317-53">(</span><span class="n">Chs</span><span class="p" data-group-id="0455778317-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0455778317-54">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0455778317-54">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_replace_state</span><span class="p" data-group-id="8377630245-55">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8377630245-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="8377630245-56">(</span><span class="n">Chs</span><span class="p" data-group-id="8377630245-56">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8377630245-57">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="8377630245-57">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_replace_state</span><span class="p" data-group-id="0455778317-55">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0455778317-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="0455778317-56">(</span><span class="n">Chs</span><span class="p" data-group-id="0455778317-56">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0455778317-57">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="0455778317-57">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">write_debug</span><span class="p" data-group-id="8377630245-58">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8377630245-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8377630245-59">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8377630245-60">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="8377630245-60">]</span><span class="p" data-group-id="8377630245-59">)</span><span class="p">.</span></code></pre><p id="ex">As it is not relevant to the example, the channel handling functions have been
│ │ │ +</span><span class="nf">write_debug</span><span class="p" data-group-id="0455778317-58">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0455778317-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0455778317-59">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0455778317-60">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="0455778317-60">]</span><span class="p" data-group-id="0455778317-59">)</span><span class="p">.</span></code></pre><p id="ex">As it is not relevant to the example, the channel handling functions have been
│ │ │  omitted. To compile this example, the
│ │ │  <a href="design_principles.html#channels-implementation">implementation of channel handling</a>
│ │ │  needs to be added to the module.</p><p>Here is an example showing how the debugging functions in the <code class="inline">sys</code>
│ │ │  module can be used for <code class="inline">ch4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="9721461364-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="9721461364-1">]</span><span class="w"> </span><span class="p" data-group-id="9721461364-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="9721461364-2">]</span><span class="w"> </span><span class="p" data-group-id="9721461364-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="9721461364-3">]</span><span class="w"> </span><span class="p" data-group-id="9721461364-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="9721461364-4">]</span><span class="w"> </span><span class="p" data-group-id="9721461364-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="9721461364-5">]</span><span class="w"> </span><span class="p" data-group-id="9721461364-6">[</span><span class="ss">jit</span><span class="p" data-group-id="9721461364-6">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="0878644317-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="0878644317-1">]</span><span class="w"> </span><span class="p" data-group-id="0878644317-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0878644317-2">]</span><span class="w"> </span><span class="p" data-group-id="0878644317-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0878644317-3">]</span><span class="w"> </span><span class="p" data-group-id="0878644317-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="0878644317-4">]</span><span class="w"> </span><span class="p" data-group-id="0878644317-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0878644317-5">]</span><span class="w"> </span><span class="p" data-group-id="0878644317-6">[</span><span class="ss">jit</span><span class="p" data-group-id="0878644317-6">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="9721461364-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="9721461364-8">(</span><span class="p" data-group-id="9721461364-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="9721461364-7">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="9721461364-9">(</span><span class="p" data-group-id="9721461364-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9721461364-10">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="9721461364-10">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="9721461364-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9721461364-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="0878644317-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="0878644317-8">(</span><span class="p" data-group-id="0878644317-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="0878644317-7">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0878644317-9">(</span><span class="p" data-group-id="0878644317-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0878644317-10">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0878644317-10">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0878644317-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0878644317-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="9721461364-12">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9721461364-12">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="0878644317-12">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0878644317-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">alloc</span><span class="p" data-group-id="9721461364-13">(</span><span class="p" data-group-id="9721461364-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9721461364-14">{</span><span class="ss">in</span><span class="p">,</span><span class="ss">alloc</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="9721461364-14">}</span><span class="w">
│ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9721461364-15">{</span><span class="ss">out</span><span class="p">,</span><span class="p" data-group-id="9721461364-16">{</span><span class="ss">ch4</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="9721461364-16">}</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="9721461364-15">}</span><span class="w">
│ │ │ +4&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">alloc</span><span class="p" data-group-id="0878644317-13">(</span><span class="p" data-group-id="0878644317-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0878644317-14">{</span><span class="ss">in</span><span class="p">,</span><span class="ss">alloc</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0878644317-14">}</span><span class="w">
│ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0878644317-15">{</span><span class="ss">out</span><span class="p">,</span><span class="p" data-group-id="0878644317-16">{</span><span class="ss">ch4</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0878644317-16">}</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0878644317-15">}</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">free</span><span class="p" data-group-id="9721461364-17">(</span><span class="ss">ch1</span><span class="p" data-group-id="9721461364-17">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9721461364-18">{</span><span class="ss">in</span><span class="p">,</span><span class="p" data-group-id="9721461364-19">{</span><span class="ss">free</span><span class="p">,</span><span class="ss">ch1</span><span class="p" data-group-id="9721461364-19">}</span><span class="p" data-group-id="9721461364-18">}</span><span class="w">
│ │ │ +5&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">free</span><span class="p" data-group-id="0878644317-17">(</span><span class="ss">ch1</span><span class="p" data-group-id="0878644317-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0878644317-18">{</span><span class="ss">in</span><span class="p">,</span><span class="p" data-group-id="0878644317-19">{</span><span class="ss">free</span><span class="p">,</span><span class="ss">ch1</span><span class="p" data-group-id="0878644317-19">}</span><span class="p" data-group-id="0878644317-18">}</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="9721461364-20">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="9721461364-20">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9721461364-21">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="9721461364-22">[</span><span class="p" data-group-id="9721461364-23">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="9721461364-24">{</span><span class="p" data-group-id="9721461364-25">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9721461364-25">}</span><span class="p">,</span><span class="p" data-group-id="9721461364-26">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="9721461364-26">}</span><span class="p" data-group-id="9721461364-24">}</span><span class="p" data-group-id="9721461364-23">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="9721461364-27">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="9721461364-28">{</span><span class="p" data-group-id="9721461364-29">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9721461364-29">}</span><span class="p">,</span><span class="p" data-group-id="9721461364-30">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">49</span><span class="p" data-group-id="9721461364-30">}</span><span class="p" data-group-id="9721461364-28">}</span><span class="p" data-group-id="9721461364-27">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="9721461364-31">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">202</span><span class="p" data-group-id="9721461364-31">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="9721461364-32">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9721461364-32">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="9721461364-33">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="9721461364-33">}</span><span class="p" data-group-id="9721461364-22">]</span><span class="p" data-group-id="9721461364-21">}</span><span class="gp unselectable">
│ │ │ -7&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="9721461364-34">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="9721461364-34">)</span><span class="p">.</span><span class="w">
│ │ │ +6&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0878644317-20">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="0878644317-20">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0878644317-21">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="0878644317-22">[</span><span class="p" data-group-id="0878644317-23">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="0878644317-24">{</span><span class="p" data-group-id="0878644317-25">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0878644317-25">}</span><span class="p">,</span><span class="p" data-group-id="0878644317-26">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="0878644317-26">}</span><span class="p" data-group-id="0878644317-24">}</span><span class="p" data-group-id="0878644317-23">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0878644317-27">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="0878644317-28">{</span><span class="p" data-group-id="0878644317-29">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0878644317-29">}</span><span class="p">,</span><span class="p" data-group-id="0878644317-30">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">49</span><span class="p" data-group-id="0878644317-30">}</span><span class="p" data-group-id="0878644317-28">}</span><span class="p" data-group-id="0878644317-27">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0878644317-31">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">202</span><span class="p" data-group-id="0878644317-31">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0878644317-32">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0878644317-32">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0878644317-33">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0878644317-33">}</span><span class="p" data-group-id="0878644317-22">]</span><span class="p" data-group-id="0878644317-21">}</span><span class="gp unselectable">
│ │ │ +7&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0878644317-34">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="0878644317-34">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="9721461364-35">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="9721461364-35">)</span><span class="p">.</span><span class="w">
│ │ │ +8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="0878644317-35">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="0878644317-35">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="9721461364-36">(</span><span class="ss">ch4</span><span class="p" data-group-id="9721461364-36">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9721461364-37">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9721461364-38">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">ch4</span><span class="p" data-group-id="9721461364-38">}</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9721461364-39">[</span><span class="p" data-group-id="9721461364-40">[</span><span class="p" data-group-id="9721461364-41">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="9721461364-42">{</span><span class="ss">ch4</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="9721461364-42">}</span><span class="p" data-group-id="9721461364-41">}</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="9721461364-43">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="9721461364-44">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ -                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="9721461364-44">]</span><span class="p" data-group-id="9721461364-43">}</span><span class="p" data-group-id="9721461364-40">]</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="9721461364-45">[</span><span class="p" data-group-id="9721461364-45">]</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="9721461364-46">{</span><span class="p" data-group-id="9721461364-47">[</span><span class="mi">1</span><span class="p" data-group-id="9721461364-47">]</span><span class="p">,</span><span class="p" data-group-id="9721461364-48">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">18</span><span class="p">,</span><span class="mi">19</span><span class="p">|</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9721461364-48">]</span><span class="p" data-group-id="9721461364-46">}</span><span class="p" data-group-id="9721461364-39">]</span><span class="p" data-group-id="9721461364-37">}</span></code></pre><h3 id="starting-the-process" class="section-heading">
│ │ │ +9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="0878644317-36">(</span><span class="ss">ch4</span><span class="p" data-group-id="0878644317-36">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0878644317-37">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0878644317-38">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">ch4</span><span class="p" data-group-id="0878644317-38">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0878644317-39">[</span><span class="p" data-group-id="0878644317-40">[</span><span class="p" data-group-id="0878644317-41">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="0878644317-42">{</span><span class="ss">ch4</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0878644317-42">}</span><span class="p" data-group-id="0878644317-41">}</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="0878644317-43">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="0878644317-44">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ +                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0878644317-44">]</span><span class="p" data-group-id="0878644317-43">}</span><span class="p" data-group-id="0878644317-40">]</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="0878644317-45">[</span><span class="p" data-group-id="0878644317-45">]</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="0878644317-46">{</span><span class="p" data-group-id="0878644317-47">[</span><span class="mi">1</span><span class="p" data-group-id="0878644317-47">]</span><span class="p">,</span><span class="p" data-group-id="0878644317-48">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">18</span><span class="p">,</span><span class="mi">19</span><span class="p">|</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0878644317-48">]</span><span class="p" data-group-id="0878644317-46">}</span><span class="p" data-group-id="0878644317-39">]</span><span class="p" data-group-id="0878644317-37">}</span></code></pre><h3 id="starting-the-process" class="section-heading">
│ │ │    <a href="#starting-the-process" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting the Process</span>
│ │ │  </h3>
│ │ │  <p>A function in the <a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html"><code class="inline">proc_lib</code></a> module is to be used to start the process. Several
│ │ │  functions are available, for example,
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html#spawn_link/4"><code class="inline">proc_lib:spawn_link/3,4</code></a>
│ │ │  for asynchronous start and
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html#start_link/5"><code class="inline">proc_lib:start_link/3,4,5</code></a> for synchronous start.</p><p>Information necessary for a process within a supervision tree, such as
│ │ │  details on ancestors and the initial call, is stored when a process
│ │ │  is started through one of these functions.</p><p>If the process terminates with a reason other than <code class="inline">normal</code> or <code class="inline">shutdown</code>, a
│ │ │  crash report is generated. For more information about the crash report, see
│ │ │  <a href="../../lib/kernel-10.2.7.1/doc/html/logger_chapter.html">Logging</a> in Kernel User's Guide.</p><p>In the example, synchronous start is used. The process starts by calling
│ │ │ -<code class="inline">ch4:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="2390503634-1">(</span><span class="p" data-group-id="2390503634-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2390503634-2">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2390503634-3">[</span><span class="nf">self</span><span class="p" data-group-id="2390503634-4">(</span><span class="p" data-group-id="2390503634-4">)</span><span class="p" data-group-id="2390503634-3">]</span><span class="p" data-group-id="2390503634-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch4:start_link/0</code> calls <a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>, which takes a module
│ │ │ +<code class="inline">ch4:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="9019564766-1">(</span><span class="p" data-group-id="9019564766-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="9019564766-2">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9019564766-3">[</span><span class="nf">self</span><span class="p" data-group-id="9019564766-4">(</span><span class="p" data-group-id="9019564766-4">)</span><span class="p" data-group-id="9019564766-3">]</span><span class="p" data-group-id="9019564766-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch4:start_link/0</code> calls <a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>, which takes a module
│ │ │  name, a function name, and an argument list as arguments. It then
│ │ │  spawns a new process and establishes a link. The new process starts
│ │ │  by executing the given function, here <code class="inline">ch4:init(Pid)</code>, where <code class="inline">Pid</code> is
│ │ │  the pid of the parent process (obtained by the call to
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#self/0"><code class="inline">self()</code></a> in the call to <a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>).</p><p>All initialization, including name registration, is done in <code class="inline">init/1</code>. The new
│ │ │ -process has to acknowledge that it has been started to the parent:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1040647361-1">(</span><span class="n">Parent</span><span class="p" data-group-id="1040647361-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +process has to acknowledge that it has been started to the parent:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8513259582-1">(</span><span class="n">Parent</span><span class="p" data-group-id="8513259582-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="1040647361-2">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1040647361-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1040647361-4">(</span><span class="p" data-group-id="1040647361-4">)</span><span class="p" data-group-id="1040647361-3">}</span><span class="p" data-group-id="1040647361-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="1040647361-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1040647361-5">)</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a> is synchronous and does not return until
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="8513259582-2">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8513259582-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8513259582-4">(</span><span class="p" data-group-id="8513259582-4">)</span><span class="p" data-group-id="8513259582-3">}</span><span class="p" data-group-id="8513259582-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="8513259582-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8513259582-5">)</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a> is synchronous and does not return until
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html#init_ack/2"><code class="inline">proc_lib:init_ack/1,2</code></a> or
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html#init_fail/3"><code class="inline">proc_lib:init_fail/2,3</code></a> has been called,
│ │ │  or the process has exited.</p><p><a href="" id="debug"></a></p><h3 id="debugging" class="section-heading">
│ │ │    <a href="#debugging" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Debugging</span>
│ │ │  </h3>
│ │ │  <p>To support the debug facilities in <code class="inline">sys</code>, a <em>debug structure</em> is needed. The
│ │ │ -<code class="inline">Deb</code> term is initialized using <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4498430276-1">(</span><span class="n">Parent</span><span class="p" data-group-id="4498430276-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<code class="inline">Deb</code> term is initialized using <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="0765920451-1">(</span><span class="n">Parent</span><span class="p" data-group-id="0765920451-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="4498430276-2">(</span><span class="p" data-group-id="4498430276-3">[</span><span class="p" data-group-id="4498430276-3">]</span><span class="p" data-group-id="4498430276-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="0765920451-2">(</span><span class="p" data-group-id="0765920451-3">[</span><span class="p" data-group-id="0765920451-3">]</span><span class="p" data-group-id="0765920451-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="4498430276-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="4498430276-4">)</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a> takes a list of options. Given an empty list as in this
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="0765920451-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0765920451-4">)</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a> takes a list of options. Given an empty list as in this
│ │ │  example means that debugging is initially disabled. For information about the
│ │ │  possible options, see <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html"><code class="inline">sys</code></a> in STDLIB.</p><p>For each <em>system event</em> to be logged or traced, the following function
│ │ │ -is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="1638696934-1">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Func</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="1638696934-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Deb1</span></code></pre><p>The arguments have the follow meaning:</p><ul><li><code class="inline">Deb</code> is the debug structure as returned from <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>.</li><li><code class="inline">Func</code> is a fun specifying a (user-defined) function used to format trace
│ │ │ +is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="8443228052-1">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Func</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="8443228052-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Deb1</span></code></pre><p>The arguments have the follow meaning:</p><ul><li><code class="inline">Deb</code> is the debug structure as returned from <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>.</li><li><code class="inline">Func</code> is a fun specifying a (user-defined) function used to format trace
│ │ │  output. For each system event, the format function is called as
│ │ │  <code class="inline">Func(Dev, Event, Info)</code>, where:<ul><li><code class="inline">Dev</code> is the I/O device to which the output is to be printed. See <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html"><code class="inline">io</code></a>
│ │ │  in STDLIB.</li><li><code class="inline">Event</code> and <code class="inline">Info</code> are passed as-is from the call to <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a>.</li></ul></li><li><code class="inline">Info</code> is used to pass more information to <code class="inline">Func</code>. It can be any term, and it
│ │ │  is passed as-is.</li><li><code class="inline">Event</code> is the system event. It is up to the user to define what a system
│ │ │  event is and how it is to be represented. Typically, at least incoming and
│ │ │  outgoing messages are considered system events and represented by the tuples
│ │ │  <code class="inline">{in,Msg[,From]}</code> and <code class="inline">{out,Msg,To[,State]}</code>, respectively.</li></ul><p><a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a> returns an updated debug structure <code class="inline">Deb1</code>.</p><p>In the example, <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a> is called for each incoming and
│ │ │  outgoing message. The format function <code class="inline">Func</code> is the function
│ │ │ -<code class="inline">ch4:write_debug/3</code>, which prints the message using <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/3"><code class="inline">io:format/3</code></a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="7744711823-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="7744711823-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<code class="inline">ch4:write_debug/3</code>, which prints the message using <a href="../../lib/stdlib-6.2.2.1/doc/html/io.html#format/3"><code class="inline">io:format/3</code></a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="5590761662-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="5590761662-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7744711823-2">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="7744711823-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="7744711823-3">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7744711823-4">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="7744711823-4">}</span><span class="p" data-group-id="7744711823-3">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="7744711823-5">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="7744711823-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="7744711823-6">(</span><span class="n">Chs</span><span class="p" data-group-id="7744711823-6">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7744711823-7">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7744711823-7">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="7744711823-8">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7744711823-9">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7744711823-10">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7744711823-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="7744711823-9">}</span><span class="p" data-group-id="7744711823-8">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="7744711823-11">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="7744711823-11">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7744711823-12">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7744711823-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="7744711823-13">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7744711823-14">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7744711823-15">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7744711823-15">}</span><span class="p" data-group-id="7744711823-14">}</span><span class="p" data-group-id="7744711823-13">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="7744711823-16">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7744711823-16">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="7744711823-17">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="7744711823-17">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5590761662-2">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="5590761662-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="5590761662-3">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5590761662-4">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="5590761662-4">}</span><span class="p" data-group-id="5590761662-3">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="5590761662-5">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="5590761662-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="5590761662-6">(</span><span class="n">Chs</span><span class="p" data-group-id="5590761662-6">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5590761662-7">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5590761662-7">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="5590761662-8">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5590761662-9">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5590761662-10">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5590761662-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="5590761662-9">}</span><span class="p" data-group-id="5590761662-8">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="5590761662-11">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="5590761662-11">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5590761662-12">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5590761662-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="5590761662-13">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5590761662-14">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5590761662-15">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5590761662-15">}</span><span class="p" data-group-id="5590761662-14">}</span><span class="p" data-group-id="5590761662-13">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="5590761662-16">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5590761662-16">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="5590761662-17">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="5590761662-17">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">write_debug</span><span class="p" data-group-id="7744711823-18">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7744711823-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7744711823-19">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7744711823-20">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="7744711823-20">]</span><span class="p" data-group-id="7744711823-19">)</span><span class="p">.</span></code></pre><p><a href="" id="msg"></a></p><h3 id="handling-system-messages" class="section-heading">
│ │ │ +</span><span class="nf">write_debug</span><span class="p" data-group-id="5590761662-18">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="5590761662-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5590761662-19">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5590761662-20">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="5590761662-20">]</span><span class="p" data-group-id="5590761662-19">)</span><span class="p">.</span></code></pre><p><a href="" id="msg"></a></p><h3 id="handling-system-messages" class="section-heading">
│ │ │    <a href="#handling-system-messages" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Handling System Messages</span>
│ │ │  </h3>
│ │ │  <p><em>System messages</em> are received as:</p><pre><code class="text">{system, From, Request}</code></pre><p>The content and meaning of these messages are not to be interpreted by the
│ │ │ -process. Instead the following function is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="7815177255-1">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7815177255-1">)</span></code></pre><p>The arguments have the following meaning:</p><ul><li><code class="inline">Request</code> and <code class="inline">From</code> from the received system message are to be
│ │ │ +process. Instead the following function is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="2471278591-1">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="2471278591-1">)</span></code></pre><p>The arguments have the following meaning:</p><ul><li><code class="inline">Request</code> and <code class="inline">From</code> from the received system message are to be
│ │ │  passed as-is to the call to <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a>.</li><li><code class="inline">Parent</code> is the pid of the parent process.</li><li><code class="inline">Module</code> is the name of the module implementing the speciall process.</li><li><code class="inline">Deb</code> is the debug structure.</li><li><code class="inline">State</code> is a term describing the internal state and is passed on to
│ │ │  <code class="inline">Module:system_continue/3</code>, <code class="inline">Module:system_terminate/4</code>/
│ │ │  <code class="inline">Module:system_get_state/1</code>, and <code class="inline">Module:system_replace_state/2</code>.</li></ul><p><a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a> does not return. It handles the system
│ │ │  message and <em>eventually</em> calls either of the following functions:</p><ul><li><p><code class="inline">Module:system_continue(Parent, Deb, State)</code> - if process execution is to
│ │ │  continue.</p></li><li><p><code class="inline">Module:system_terminate(Reason, Parent, Deb, State)</code> - if the
│ │ │  process is to terminate.</p></li></ul><p>While handling the system message, <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a> can call
│ │ │  one of the following functions:</p><ul><li><p><code class="inline">Module:system_get_state(State)</code> - if the process is to return its state.</p></li><li><p><code class="inline">Module:system_replace_state(StateFun, State)</code> - if the process is
│ │ │  to replace its state using the fun <code class="inline">StateFun</code> fun. See <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#replace_state/3"><code class="inline">sys:replace_state/3</code></a>
│ │ │  for more information.</p></li><li><p><code class="inline">system_code_change(Misc, Module, OldVsn, Extra)</code> - if the process is to
│ │ │  perform a code change.</p></li></ul><p>A process in a supervision tree is expected to terminate with the same reason as
│ │ │ -its parent.</p><p>In the example, system messages are handed by the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="6973428624-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="6973428624-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +its parent.</p><p>In the example, system messages are handed by the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="8997705178-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="8997705178-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -        </span><span class="p" data-group-id="6973428624-2">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="6973428624-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="6973428624-3">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ -                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6973428624-3">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8997705178-2">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="8997705178-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="8997705178-3">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ +                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8997705178-3">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_continue</span><span class="p" data-group-id="6973428624-4">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6973428624-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="6973428624-5">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="6973428624-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_continue</span><span class="p" data-group-id="8997705178-4">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8997705178-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="8997705178-5">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="8997705178-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_terminate</span><span class="p" data-group-id="6973428624-6">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6973428624-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="6973428624-7">(</span><span class="n">Reason</span><span class="p" data-group-id="6973428624-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_terminate</span><span class="p" data-group-id="8997705178-6">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8997705178-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="8997705178-7">(</span><span class="n">Reason</span><span class="p" data-group-id="8997705178-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_get_state</span><span class="p" data-group-id="6973428624-8">(</span><span class="n">Chs</span><span class="p" data-group-id="6973428624-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6973428624-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6973428624-9">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_get_state</span><span class="p" data-group-id="8997705178-8">(</span><span class="n">Chs</span><span class="p" data-group-id="8997705178-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8997705178-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8997705178-9">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_replace_state</span><span class="p" data-group-id="6973428624-10">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6973428624-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="6973428624-11">(</span><span class="n">Chs</span><span class="p" data-group-id="6973428624-11">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6973428624-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="6973428624-12">}</span><span class="p">.</span></code></pre><p>If a special process is configured to trap exits, it must take notice
│ │ │ +</span><span class="nf">system_replace_state</span><span class="p" data-group-id="8997705178-10">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8997705178-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="8997705178-11">(</span><span class="n">Chs</span><span class="p" data-group-id="8997705178-11">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8997705178-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="8997705178-12">}</span><span class="p">.</span></code></pre><p>If a special process is configured to trap exits, it must take notice
│ │ │  of 'EXIT' messages from its parent process and terminate using the
│ │ │ -same exit reason once the parent process has terminated.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="0391627082-1">(</span><span class="n">Parent</span><span class="p" data-group-id="0391627082-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +same exit reason once the parent process has terminated.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1780507256-1">(</span><span class="n">Parent</span><span class="p" data-group-id="1780507256-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="0391627082-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0391627082-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="1780507256-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1780507256-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="0391627082-3">(</span><span class="n">Parent</span><span class="p" data-group-id="0391627082-3">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="1780507256-3">(</span><span class="n">Parent</span><span class="p" data-group-id="1780507256-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="0391627082-4">(</span><span class="n">Parent</span><span class="p" data-group-id="0391627082-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="1780507256-4">(</span><span class="n">Parent</span><span class="p" data-group-id="1780507256-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0391627082-5">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="0391627082-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="1780507256-5">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1780507256-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="c1">%% Clean up here, if needed.</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="0391627082-6">(</span><span class="n">Reason</span><span class="p" data-group-id="0391627082-6">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="1780507256-6">(</span><span class="n">Reason</span><span class="p" data-group-id="1780507256-6">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="user-defined-behaviours" class="section-heading">
│ │ │    <a href="#user-defined-behaviours" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">User-Defined Behaviours</span>
│ │ │  </h2>
│ │ │ @@ -448,71 +448,71 @@
│ │ │  function. Note that the <code class="inline">-optional_callbacks</code> attribute is to be used together
│ │ │  with the <code class="inline">-callback</code> attribute; it cannot be combined with the
│ │ │  <code class="inline">behaviour_info()</code> function described below.</p><p>Tools that need to know about optional callback functions can call
│ │ │  <code class="inline">Behaviour:behaviour_info(optional_callbacks)</code> to get a list of all optional
│ │ │  callback functions.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>We recommend using the <code class="inline">-callback</code> attribute rather than the
│ │ │  <code class="inline">behaviour_info()</code> function. The reason is that the extra type information can
│ │ │  be used by tools to produce documentation or find discrepancies.</p></section><p>As an alternative to the <code class="inline">-callback</code> and <code class="inline">-optional_callbacks</code> attributes you
│ │ │ -may directly implement and export <code class="inline">behaviour_info()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="3950366071-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="3950366071-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3950366071-2">[</span><span class="p" data-group-id="3950366071-3">{</span><span class="n">Name1</span><span class="p">,</span><span class="w"> </span><span class="n">Arity1</span><span class="p" data-group-id="3950366071-3">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="p" data-group-id="3950366071-4">{</span><span class="n">NameN</span><span class="p">,</span><span class="w"> </span><span class="n">ArityN</span><span class="p" data-group-id="3950366071-4">}</span><span class="p" data-group-id="3950366071-2">]</span><span class="p">.</span></code></pre><p>where each <code class="inline">{Name, Arity}</code> specifies the name and arity of a callback function.
│ │ │ +may directly implement and export <code class="inline">behaviour_info()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="3888833351-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="3888833351-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3888833351-2">[</span><span class="p" data-group-id="3888833351-3">{</span><span class="n">Name1</span><span class="p">,</span><span class="w"> </span><span class="n">Arity1</span><span class="p" data-group-id="3888833351-3">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="p" data-group-id="3888833351-4">{</span><span class="n">NameN</span><span class="p">,</span><span class="w"> </span><span class="n">ArityN</span><span class="p" data-group-id="3888833351-4">}</span><span class="p" data-group-id="3888833351-2">]</span><span class="p">.</span></code></pre><p>where each <code class="inline">{Name, Arity}</code> specifies the name and arity of a callback function.
│ │ │  This function is otherwise automatically generated by the compiler using the
│ │ │  <code class="inline">-callback</code> attributes.</p><p>When the compiler encounters the module attribute <code class="inline">-behaviour(Behaviour).</code> in a
│ │ │  module <code class="inline">Mod</code>, it calls <code class="inline">Behaviour:behaviour_info(callbacks)</code> and compares the
│ │ │  result with the set of functions actually exported from <code class="inline">Mod</code>, and issues a
│ │ │  warning if any callback function is missing.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">%% User-defined behaviour module</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9367395474-1">(</span><span class="ss">simple_server</span><span class="p" data-group-id="9367395474-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9367395474-2">(</span><span class="p" data-group-id="9367395474-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9367395474-3">]</span><span class="p" data-group-id="9367395474-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3007088945-1">(</span><span class="ss">simple_server</span><span class="p" data-group-id="3007088945-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3007088945-2">(</span><span class="p" data-group-id="3007088945-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3007088945-3">]</span><span class="p" data-group-id="3007088945-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">init</span><span class="p" data-group-id="9367395474-4">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="9367395474-5">(</span><span class="p" data-group-id="9367395474-5">)</span><span class="p" data-group-id="9367395474-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="9367395474-6">(</span><span class="n">Req</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="9367395474-7">(</span><span class="p" data-group-id="9367395474-7">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="9367395474-8">(</span><span class="p" data-group-id="9367395474-8">)</span><span class="p" data-group-id="9367395474-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9367395474-9">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="9367395474-10">(</span><span class="p" data-group-id="9367395474-10">)</span><span class="p" data-group-id="9367395474-9">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">terminate</span><span class="p" data-group-id="9367395474-11">(</span><span class="p" data-group-id="9367395474-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">format_state</span><span class="p" data-group-id="9367395474-12">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="9367395474-13">(</span><span class="p" data-group-id="9367395474-13">)</span><span class="p" data-group-id="9367395474-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="9367395474-14">(</span><span class="p" data-group-id="9367395474-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">init</span><span class="p" data-group-id="3007088945-4">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3007088945-5">(</span><span class="p" data-group-id="3007088945-5">)</span><span class="p" data-group-id="3007088945-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="3007088945-6">(</span><span class="n">Req</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3007088945-7">(</span><span class="p" data-group-id="3007088945-7">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3007088945-8">(</span><span class="p" data-group-id="3007088945-8">)</span><span class="p" data-group-id="3007088945-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3007088945-9">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3007088945-10">(</span><span class="p" data-group-id="3007088945-10">)</span><span class="p" data-group-id="3007088945-9">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">terminate</span><span class="p" data-group-id="3007088945-11">(</span><span class="p" data-group-id="3007088945-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">format_state</span><span class="p" data-group-id="3007088945-12">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3007088945-13">(</span><span class="p" data-group-id="3007088945-13">)</span><span class="p" data-group-id="3007088945-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3007088945-14">(</span><span class="p" data-group-id="3007088945-14">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">optional_callbacks</span><span class="p" data-group-id="9367395474-15">(</span><span class="p" data-group-id="9367395474-16">[</span><span class="ss">format_state</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9367395474-16">]</span><span class="p" data-group-id="9367395474-15">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">optional_callbacks</span><span class="p" data-group-id="3007088945-15">(</span><span class="p" data-group-id="3007088945-16">[</span><span class="ss">format_state</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3007088945-16">]</span><span class="p" data-group-id="3007088945-15">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% Alternatively you may define:</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% -export([behaviour_info/1]).</span><span class="w">
│ │ │  </span><span class="c1">%% behaviour_info(callbacks) -&gt;</span><span class="w">
│ │ │  </span><span class="c1">%%     [{init,1},</span><span class="w">
│ │ │  </span><span class="c1">%%      {handle_req,2},</span><span class="w">
│ │ │  </span><span class="c1">%%      {terminate,0}].</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="9367395474-17">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="9367395474-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="9367395474-18">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9367395474-19">[</span><span class="nf">self</span><span class="p" data-group-id="9367395474-20">(</span><span class="p" data-group-id="9367395474-20">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="9367395474-19">]</span><span class="p" data-group-id="9367395474-18">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="3007088945-17">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="3007088945-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3007088945-18">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3007088945-19">[</span><span class="nf">self</span><span class="p" data-group-id="3007088945-20">(</span><span class="p" data-group-id="3007088945-20">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="3007088945-19">]</span><span class="p" data-group-id="3007088945-18">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="9367395474-21">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="9367395474-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9367395474-22">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9367395474-23">(</span><span class="p" data-group-id="9367395474-23">)</span><span class="p" data-group-id="9367395474-22">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="3007088945-21">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="3007088945-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="3007088945-22">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3007088945-23">(</span><span class="p" data-group-id="3007088945-23">)</span><span class="p" data-group-id="3007088945-22">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Dbg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="9367395474-24">(</span><span class="p" data-group-id="9367395474-25">[</span><span class="p" data-group-id="9367395474-25">]</span><span class="p" data-group-id="9367395474-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="9367395474-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9367395474-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9367395474-28">(</span><span class="p" data-group-id="9367395474-28">)</span><span class="p" data-group-id="9367395474-27">}</span><span class="p" data-group-id="9367395474-26">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="9367395474-29">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9367395474-29">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="n">Dbg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="3007088945-24">(</span><span class="p" data-group-id="3007088945-25">[</span><span class="p" data-group-id="3007088945-25">]</span><span class="p" data-group-id="3007088945-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="3007088945-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3007088945-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3007088945-28">(</span><span class="p" data-group-id="3007088945-28">)</span><span class="p" data-group-id="3007088945-27">}</span><span class="p" data-group-id="3007088945-26">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="3007088945-29">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3007088945-29">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>In a callback module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3125293330-1">(</span><span class="ss">db</span><span class="p" data-group-id="3125293330-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3125293330-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="3125293330-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>In a callback module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7314434627-1">(</span><span class="ss">db</span><span class="p" data-group-id="7314434627-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="7314434627-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="7314434627-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3125293330-3">(</span><span class="p" data-group-id="3125293330-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3125293330-4">]</span><span class="p" data-group-id="3125293330-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7314434627-3">(</span><span class="p" data-group-id="7314434627-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7314434627-4">]</span><span class="p" data-group-id="7314434627-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The contracts specified with <code class="inline">-callback</code> attributes in behaviour modules can be
│ │ │  further refined by adding <code class="inline">-spec</code> attributes in callback modules. This can be
│ │ │  useful as <code class="inline">-callback</code> contracts are usually generic. The same callback module
│ │ │ -with contracts for the callbacks:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0409861128-1">(</span><span class="ss">db</span><span class="p" data-group-id="0409861128-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="0409861128-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="0409861128-2">)</span><span class="p">.</span><span class="w">
│ │ │ +with contracts for the callbacks:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2082892686-1">(</span><span class="ss">db</span><span class="p" data-group-id="2082892686-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="2082892686-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="2082892686-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0409861128-3">(</span><span class="p" data-group-id="0409861128-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0409861128-4">]</span><span class="p" data-group-id="0409861128-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2082892686-3">(</span><span class="p" data-group-id="2082892686-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2082892686-4">]</span><span class="p" data-group-id="2082892686-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0409861128-5">(</span><span class="ss">state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0409861128-6">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0409861128-7">[</span><span class="nf">atom</span><span class="p" data-group-id="0409861128-8">(</span><span class="p" data-group-id="0409861128-8">)</span><span class="p" data-group-id="0409861128-7">]</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0409861128-9">(</span><span class="p" data-group-id="0409861128-9">)</span><span class="p" data-group-id="0409861128-6">}</span><span class="p" data-group-id="0409861128-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2082892686-5">(</span><span class="ss">state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2082892686-6">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="2082892686-7">[</span><span class="nf">atom</span><span class="p" data-group-id="2082892686-8">(</span><span class="p" data-group-id="2082892686-8">)</span><span class="p" data-group-id="2082892686-7">]</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="2082892686-9">(</span><span class="p" data-group-id="2082892686-9">)</span><span class="p" data-group-id="2082892686-6">}</span><span class="p" data-group-id="2082892686-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="0409861128-10">(</span><span class="p" data-group-id="0409861128-10">)</span><span class="w">   </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="0409861128-11">{</span><span class="p" data-group-id="0409861128-11">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">request</span><span class="p" data-group-id="0409861128-12">(</span><span class="p" data-group-id="0409861128-12">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0409861128-13">{</span><span class="ss">&#39;store&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0409861128-14">(</span><span class="p" data-group-id="0409861128-14">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0409861128-15">(</span><span class="p" data-group-id="0409861128-15">)</span><span class="p" data-group-id="0409861128-13">}</span><span class="p">;</span><span class="w">
│ │ │ -                   </span><span class="p" data-group-id="0409861128-16">{</span><span class="ss">&#39;lookup&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0409861128-17">(</span><span class="p" data-group-id="0409861128-17">)</span><span class="p" data-group-id="0409861128-16">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="2082892686-10">(</span><span class="p" data-group-id="2082892686-10">)</span><span class="w">   </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="2082892686-11">{</span><span class="p" data-group-id="2082892686-11">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">request</span><span class="p" data-group-id="2082892686-12">(</span><span class="p" data-group-id="2082892686-12">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="2082892686-13">{</span><span class="ss">&#39;store&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2082892686-14">(</span><span class="p" data-group-id="2082892686-14">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2082892686-15">(</span><span class="p" data-group-id="2082892686-15">)</span><span class="p" data-group-id="2082892686-13">}</span><span class="p">;</span><span class="w">
│ │ │ +                   </span><span class="p" data-group-id="2082892686-16">{</span><span class="ss">&#39;lookup&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2082892686-17">(</span><span class="p" data-group-id="2082892686-17">)</span><span class="p" data-group-id="2082892686-16">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="0409861128-18">(</span><span class="nf">request</span><span class="p" data-group-id="0409861128-19">(</span><span class="p" data-group-id="0409861128-19">)</span><span class="p">,</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="0409861128-20">(</span><span class="p" data-group-id="0409861128-20">)</span><span class="p" data-group-id="0409861128-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0409861128-21">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0409861128-22">(</span><span class="p" data-group-id="0409861128-22">)</span><span class="p" data-group-id="0409861128-21">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="2082892686-18">(</span><span class="nf">request</span><span class="p" data-group-id="2082892686-19">(</span><span class="p" data-group-id="2082892686-19">)</span><span class="p">,</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="2082892686-20">(</span><span class="p" data-group-id="2082892686-20">)</span><span class="p" data-group-id="2082892686-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2082892686-21">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2082892686-22">(</span><span class="p" data-group-id="2082892686-22">)</span><span class="p" data-group-id="2082892686-21">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Each <code class="inline">-spec</code> contract is to be a subtype of the respective <code class="inline">-callback</code> contract.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/statem.html
│ │ │ @@ -124,15 +124,15 @@
│ │ │  </h2>
│ │ │  <p>Established Automata Theory does not deal much with how a <em>state transition</em>
│ │ │  is triggered, but assumes that the output is a function of the input
│ │ │  (and the state) and that they are some kind of values.</p><p>For an Event-Driven State Machine, the input is an <em>event</em> that triggers
│ │ │  a <em>state transition</em> and the output is actions executed during
│ │ │  the <em>state transition</em>.  Analogously to the mathematical model
│ │ │  of a Finite State Machine, it can be described as a set of relations
│ │ │ -of the following form:</p><pre><code class="makeup erlang" translate="no"><span class="n">State</span><span class="p" data-group-id="6741000356-1">(</span><span class="n">S</span><span class="p" data-group-id="6741000356-1">)</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="6741000356-2">(</span><span class="n">E</span><span class="p" data-group-id="6741000356-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Actions</span><span class="p" data-group-id="6741000356-3">(</span><span class="n">A</span><span class="p" data-group-id="6741000356-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6741000356-4">(</span><span class="n">S</span><span class="err">&#39;</span><span class="p" data-group-id="6741000356-4">)</span></code></pre><p>These relations are interpreted as follows: if we are in state <code class="inline">S</code>,
│ │ │ +of the following form:</p><pre><code class="makeup erlang" translate="no"><span class="n">State</span><span class="p" data-group-id="2858891211-1">(</span><span class="n">S</span><span class="p" data-group-id="2858891211-1">)</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="2858891211-2">(</span><span class="n">E</span><span class="p" data-group-id="2858891211-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Actions</span><span class="p" data-group-id="2858891211-3">(</span><span class="n">A</span><span class="p" data-group-id="2858891211-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="2858891211-4">(</span><span class="n">S</span><span class="err">&#39;</span><span class="p" data-group-id="2858891211-4">)</span></code></pre><p>These relations are interpreted as follows: if we are in state <code class="inline">S</code>,
│ │ │  and event <code class="inline">E</code> occurs, we are to perform actions <code class="inline">A</code>, and make a transition
│ │ │  to state <code class="inline">S'</code>.  Notice that <code class="inline">S'</code> can be equal to <code class="inline">S</code>,
│ │ │  and that <code class="inline">A</code> can be empty.</p><p>In <code class="inline">gen_statem</code> we define a <em>state change</em> as a <em>state transition</em> in which the
│ │ │  new state <code class="inline">S'</code> is different from the current state <code class="inline">S</code>, where &quot;different&quot; means
│ │ │  Erlang's strict inequality: <code class="inline">=/=</code> also known as &quot;does not match&quot;. <code class="inline">gen_statem</code>
│ │ │  does more things during <em>state changes</em> than during other <em>state transitions</em>.</p><p>As <code class="inline">A</code> and <code class="inline">S'</code> depend only on <code class="inline">S</code> and <code class="inline">E</code>, the kind of state machine described
│ │ │  here is a Mealy machine (see, for example, the Wikipedia article
│ │ │ @@ -405,20 +405,20 @@
│ │ │    </a>
│ │ │    <span class="text">State Enter Calls</span>
│ │ │  </h2>
│ │ │  <p>The <code class="inline">gen_statem</code> behaviour can, if this is enabled, regardless of <em>callback
│ │ │  mode</em>, automatically call the <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#t:state_enter/0"><em>state callback</em></a>
│ │ │  with special arguments whenever the state changes, so you can write
│ │ │  state enter actions near the rest of the <em>state transition</em> rules.
│ │ │ -It typically looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">StateName</span><span class="p" data-group-id="9941941479-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9941941479-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +It typically looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">StateName</span><span class="p" data-group-id="7438301391-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7438301391-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">enter</span><span class="w"> </span><span class="ss">actions</span><span class="w"> </span><span class="ss">here</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9941941479-2">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="9941941479-2">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="n">StateName</span><span class="p" data-group-id="9941941479-3">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9941941479-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7438301391-2">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="7438301391-2">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="n">StateName</span><span class="p" data-group-id="7438301391-3">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7438301391-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">actions</span><span class="w"> </span><span class="ss">here</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9941941479-4">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewStateName</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="9941941479-4">}</span><span class="p">.</span></code></pre><p>Since the <em>state enter call</em> is not an event there are restrictions on the
│ │ │ +    </span><span class="p" data-group-id="7438301391-4">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewStateName</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="7438301391-4">}</span><span class="p">.</span></code></pre><p>Since the <em>state enter call</em> is not an event there are restrictions on the
│ │ │  allowed return value and state <a href="#transition-actions"><em>transition actions</em></a>.
│ │ │  You must not change the state, <a href="#postponing-events">postpone</a> this non-event,
│ │ │  <a href="#inserted-events">insert any events</a>, or change the
│ │ │  <a href="#callback-module"><em>callback module</em></a>.</p><p>The first state that is entered after <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#c:init/1"><code class="inline">gen_statem:init/1</code></a> will get
│ │ │  a <em>state enter call</em> with <code class="inline">OldState</code> equal to the current state.</p><p>You may repeat the <em>state enter call</em> using the <code class="inline">{repeat_state,...}</code> return
│ │ │  value from the <a href="#state-callback"><em>state callback</em></a>. In this case
│ │ │  <code class="inline">OldState</code> will also be equal to the current state.</p><p>Depending on how your state machine is specified, this can be a very useful
│ │ │ @@ -499,72 +499,72 @@
│ │ │  
│ │ │      locked      --&gt; check_code : {button, Button}\n* Collect Buttons
│ │ │      check_code  --&gt; locked     : Incorrect code
│ │ │      check_code  --&gt; open       : Correct code\n* do_unlock()\n* Clear Buttons\n* Set state_timeout 10 s
│ │ │  
│ │ │      open        --&gt; open   : {button, Digit}
│ │ │      open        --&gt; locked : state_timeout\n* do_lock()</code></pre><p>This code lock state machine can be implemented using <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html"><code class="inline">gen_statem</code></a> with
│ │ │ -the following <em>callback module</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8404283142-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="8404283142-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8404283142-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="8404283142-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8404283142-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock</span><span class="p" data-group-id="8404283142-3">)</span><span class="p">.</span><span class="w">
│ │ │ +the following <em>callback module</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1237050357-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="1237050357-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1237050357-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="1237050357-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1237050357-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock</span><span class="p" data-group-id="1237050357-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8404283142-4">(</span><span class="p" data-group-id="8404283142-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8404283142-5">]</span><span class="p" data-group-id="8404283142-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8404283142-6">(</span><span class="p" data-group-id="8404283142-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8404283142-7">]</span><span class="p" data-group-id="8404283142-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8404283142-8">(</span><span class="p" data-group-id="8404283142-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="8404283142-9">]</span><span class="p" data-group-id="8404283142-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8404283142-10">(</span><span class="p" data-group-id="8404283142-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="8404283142-11">]</span><span class="p" data-group-id="8404283142-10">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="8404283142-12">(</span><span class="n">Code</span><span class="p" data-group-id="8404283142-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8404283142-13">(</span><span class="p" data-group-id="8404283142-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="8404283142-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8404283142-15">[</span><span class="p" data-group-id="8404283142-15">]</span><span class="p" data-group-id="8404283142-13">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="8404283142-16">(</span><span class="n">Button</span><span class="p" data-group-id="8404283142-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8404283142-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8404283142-18">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8404283142-18">}</span><span class="p" data-group-id="8404283142-17">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8404283142-19">(</span><span class="n">Code</span><span class="p" data-group-id="8404283142-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="8404283142-20">(</span><span class="p" data-group-id="8404283142-20">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8404283142-21">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8404283142-22">(</span><span class="n">Code</span><span class="p" data-group-id="8404283142-22">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8404283142-23">[</span><span class="p" data-group-id="8404283142-23">]</span><span class="p" data-group-id="8404283142-21">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8404283142-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8404283142-24">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="8404283142-25">(</span><span class="p" data-group-id="8404283142-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="3326796688-1">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3326796688-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3326796688-2">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="3326796688-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="3326796688-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3326796688-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1237050357-4">(</span><span class="p" data-group-id="1237050357-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1237050357-5">]</span><span class="p" data-group-id="1237050357-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1237050357-6">(</span><span class="p" data-group-id="1237050357-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1237050357-7">]</span><span class="p" data-group-id="1237050357-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1237050357-8">(</span><span class="p" data-group-id="1237050357-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="1237050357-9">]</span><span class="p" data-group-id="1237050357-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1237050357-10">(</span><span class="p" data-group-id="1237050357-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="1237050357-11">]</span><span class="p" data-group-id="1237050357-10">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="1237050357-12">(</span><span class="n">Code</span><span class="p" data-group-id="1237050357-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1237050357-13">(</span><span class="p" data-group-id="1237050357-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="1237050357-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1237050357-15">[</span><span class="p" data-group-id="1237050357-15">]</span><span class="p" data-group-id="1237050357-13">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="1237050357-16">(</span><span class="n">Button</span><span class="p" data-group-id="1237050357-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1237050357-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1237050357-18">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1237050357-18">}</span><span class="p" data-group-id="1237050357-17">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="1237050357-19">(</span><span class="n">Code</span><span class="p" data-group-id="1237050357-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="1237050357-20">(</span><span class="p" data-group-id="1237050357-20">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1237050357-21">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="1237050357-22">(</span><span class="n">Code</span><span class="p" data-group-id="1237050357-22">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1237050357-23">[</span><span class="p" data-group-id="1237050357-23">]</span><span class="p" data-group-id="1237050357-21">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1237050357-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1237050357-24">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="1237050357-25">(</span><span class="p" data-group-id="1237050357-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="3012389539-1">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3012389539-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3012389539-2">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3012389539-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="3012389539-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3012389539-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │          </span><span class="k">if</span><span class="w">
│ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="3326796688-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="3326796688-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="3012389539-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="3012389539-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="3326796688-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="3326796688-5">)</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="3326796688-6">[</span><span class="n">Button</span><span class="p" data-group-id="3326796688-6">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="3012389539-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="3012389539-5">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="3012389539-6">[</span><span class="n">Button</span><span class="p" data-group-id="3012389539-6">]</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3326796688-7">(</span><span class="p" data-group-id="3326796688-7">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3326796688-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3326796688-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3326796688-10">[</span><span class="p" data-group-id="3326796688-10">]</span><span class="p" data-group-id="3326796688-9">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="3326796688-11">[</span><span class="p" data-group-id="3326796688-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3326796688-12">}</span><span class="p" data-group-id="3326796688-11">]</span><span class="p" data-group-id="3326796688-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3012389539-7">(</span><span class="p" data-group-id="3012389539-7">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="3012389539-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3012389539-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3012389539-10">[</span><span class="p" data-group-id="3012389539-10">]</span><span class="p" data-group-id="3012389539-9">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="3012389539-11">[</span><span class="p" data-group-id="3012389539-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3012389539-12">}</span><span class="p" data-group-id="3012389539-11">]</span><span class="p" data-group-id="3012389539-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3326796688-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3326796688-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="3326796688-14">}</span><span class="p" data-group-id="3326796688-13">}</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="8706215178-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="8706215178-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="8706215178-2">(</span><span class="p" data-group-id="8706215178-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8706215178-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8706215178-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8706215178-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8706215178-5">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8706215178-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8706215178-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8706215178-6">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8706215178-6">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="4232077546-1">(</span><span class="p" data-group-id="4232077546-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4232077546-2">(</span><span class="s">&quot;Lock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4232077546-3">[</span><span class="p" data-group-id="4232077546-3">]</span><span class="p" data-group-id="4232077546-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="4232077546-4">(</span><span class="p" data-group-id="4232077546-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4232077546-5">(</span><span class="s">&quot;Unlock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4232077546-6">[</span><span class="p" data-group-id="4232077546-6">]</span><span class="p" data-group-id="4232077546-5">)</span><span class="p">.</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="3012389539-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3012389539-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="3012389539-14">}</span><span class="p" data-group-id="3012389539-13">}</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="2451882188-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="2451882188-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="2451882188-2">(</span><span class="p" data-group-id="2451882188-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2451882188-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2451882188-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="2451882188-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2451882188-5">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2451882188-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2451882188-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2451882188-6">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2451882188-6">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="7995423862-1">(</span><span class="p" data-group-id="7995423862-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7995423862-2">(</span><span class="s">&quot;Lock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7995423862-3">[</span><span class="p" data-group-id="7995423862-3">]</span><span class="p" data-group-id="7995423862-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="7995423862-4">(</span><span class="p" data-group-id="7995423862-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7995423862-5">(</span><span class="s">&quot;Unlock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7995423862-6">[</span><span class="p" data-group-id="7995423862-6">]</span><span class="p" data-group-id="7995423862-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="4232077546-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="4232077546-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="4232077546-8">(</span><span class="p" data-group-id="4232077546-8">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="7995423862-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="7995423862-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="7995423862-8">(</span><span class="p" data-group-id="7995423862-8">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-gen_statem" class="section-heading">
│ │ │    <a href="#starting-gen_statem" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting gen_statem</span>
│ │ │  </h2>
│ │ │  <p>In the example in the previous section, <code class="inline">gen_statem</code> is started by calling
│ │ │ -<code class="inline">code_lock:start_link(Code)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="1762209062-1">(</span><span class="n">Code</span><span class="p" data-group-id="1762209062-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1762209062-2">(</span><span class="p" data-group-id="1762209062-3">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="1762209062-3">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1762209062-4">[</span><span class="p" data-group-id="1762209062-4">]</span><span class="p" data-group-id="1762209062-2">)</span><span class="p">.</span></code></pre><p><code class="inline">start_link/1</code> calls function <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/4</code></a>,
│ │ │ +<code class="inline">code_lock:start_link(Code)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="9883704844-1">(</span><span class="n">Code</span><span class="p" data-group-id="9883704844-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="9883704844-2">(</span><span class="p" data-group-id="9883704844-3">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="9883704844-3">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9883704844-4">[</span><span class="p" data-group-id="9883704844-4">]</span><span class="p" data-group-id="9883704844-2">)</span><span class="p">.</span></code></pre><p><code class="inline">start_link/1</code> calls function <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/4</code></a>,
│ │ │  which spawns and links to a new process, a <code class="inline">gen_statem</code>.</p><ul><li><p>The first argument, <code class="inline">{local,?NAME}</code>, specifies the name. In this case, the
│ │ │  <code class="inline">gen_statem</code> is locally registered as <code class="inline">code_lock</code> through the macro <code class="inline">?NAME</code>.</p><p>If the name is omitted, the <code class="inline">gen_statem</code> is not registered. Instead its pid
│ │ │  must be used. The name can also be specified as <code class="inline">{global, Name}</code>, then the
│ │ │  <code class="inline">gen_statem</code> is registered using <a href="../../lib/kernel-10.2.7.1/doc/html/global.html#register_name/2"><code class="inline">global:register_name/2</code></a> in Kernel.</p></li><li><p>The second argument, <code class="inline">?MODULE</code>, is the name of the <em>callback module</em>,
│ │ │  that is, the module where the callback functions are located,
│ │ │  which is this module.</p><p>The interface functions (<code class="inline">start_link/1</code> and <code class="inline">button/1</code>) are located in the
│ │ │  same module as the callback functions (<code class="inline">init/1</code>, <code class="inline">locked/3</code>, and <code class="inline">open/3</code>).
│ │ │ @@ -574,184 +574,184 @@
│ │ │  see <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3</code></a>.</p></li></ul><p>If name registration succeeds, the new <code class="inline">gen_statem</code> process calls callback
│ │ │  function <code class="inline">code_lock:init(Code)</code>. This function is expected to return
│ │ │  <code class="inline">{ok, State, Data}</code>, where <code class="inline">State</code> is the initial state of the <code class="inline">gen_statem</code>,
│ │ │  in this case <code class="inline">locked</code>; assuming that the door is locked to begin with.
│ │ │  <code class="inline">Data</code> is the internal server data of the <code class="inline">gen_statem</code>. Here the server data
│ │ │  is a <a href="../../lib/stdlib-6.2.2.1/doc/html/maps.html"><code class="inline">map()</code></a> with key <code class="inline">code</code> that stores the correct
│ │ │  button sequence, key <code class="inline">length</code> store its length, and key <code class="inline">buttons</code>
│ │ │ -that stores the collected buttons up to the same length.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7173206948-1">(</span><span class="n">Code</span><span class="p" data-group-id="7173206948-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="7173206948-2">(</span><span class="p" data-group-id="7173206948-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7173206948-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7173206948-4">(</span><span class="n">Code</span><span class="p" data-group-id="7173206948-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7173206948-5">[</span><span class="p" data-group-id="7173206948-5">]</span><span class="p" data-group-id="7173206948-3">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7173206948-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7173206948-6">}</span><span class="p">.</span></code></pre><p>Function <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │ +that stores the collected buttons up to the same length.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7499135765-1">(</span><span class="n">Code</span><span class="p" data-group-id="7499135765-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="7499135765-2">(</span><span class="p" data-group-id="7499135765-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7499135765-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7499135765-4">(</span><span class="n">Code</span><span class="p" data-group-id="7499135765-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7499135765-5">[</span><span class="p" data-group-id="7499135765-5">]</span><span class="p" data-group-id="7499135765-3">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7499135765-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7499135765-6">}</span><span class="p">.</span></code></pre><p>Function <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │  is synchronous. It does not return until the <code class="inline">gen_statem</code> is initialized
│ │ │  and is ready to receive events.</p><p>Function <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │  must be used if the <code class="inline">gen_statem</code> is part of a supervision tree, that is,
│ │ │  started by a supervisor.  Function,
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#start/3"><code class="inline">gen_statem:start/3,4</code></a> can be used to start
│ │ │  a standalone <code class="inline">gen_statem</code>, meaning it is not part of a supervision tree.</p><p>Function <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#c:callback_mode/0"><code class="inline">Module:callback_mode/0</code></a> selects
│ │ │  the <a href="#callback-modes"><code class="inline">CallbackMode</code></a> for the <em>callback module</em>,
│ │ │  in this case <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#t:callback_mode/0"><code class="inline">state_functions</code></a>.
│ │ │ -That is, each state has its own handler function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="9237216126-1">(</span><span class="p" data-group-id="9237216126-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +That is, each state has its own handler function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="8743627655-1">(</span><span class="p" data-group-id="8743627655-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><h2 id="handling-events" class="section-heading">
│ │ │    <a href="#handling-events" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Handling Events</span>
│ │ │  </h2>
│ │ │  <p>The function notifying the code lock about a button event is implemented using
│ │ │ -<a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#cast/2"><code class="inline">gen_statem:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">button</span><span class="p" data-group-id="0603079745-1">(</span><span class="n">Button</span><span class="p" data-group-id="0603079745-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="0603079745-2">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0603079745-3">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0603079745-3">}</span><span class="p" data-group-id="0603079745-2">)</span><span class="p">.</span></code></pre><p>The first argument is the name of the <code class="inline">gen_statem</code> and must agree with
│ │ │ +<a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#cast/2"><code class="inline">gen_statem:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">button</span><span class="p" data-group-id="1627213227-1">(</span><span class="n">Button</span><span class="p" data-group-id="1627213227-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1627213227-2">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1627213227-3">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1627213227-3">}</span><span class="p" data-group-id="1627213227-2">)</span><span class="p">.</span></code></pre><p>The first argument is the name of the <code class="inline">gen_statem</code> and must agree with
│ │ │  the name used to start it. So, we use the same macro <code class="inline">?NAME</code> as when starting.
│ │ │  <code class="inline">{button, Button}</code> is the event content.</p><p>The event is sent to the <code class="inline">gen_statem</code>. When the event is received, the
│ │ │  <code class="inline">gen_statem</code> calls <code class="inline">StateName(cast, Event, Data)</code>, which is expected
│ │ │  to return a tuple <code class="inline">{next_state, NewStateName, NewData}</code>, or
│ │ │  <code class="inline">{next_state, NewStateName, NewData, Actions}</code>. <code class="inline">StateName</code> is the name
│ │ │  of the current state and <code class="inline">NewStateName</code> is the name of the next state.
│ │ │  <code class="inline">NewData</code> is a new value for the server data of the <code class="inline">gen_statem</code>,
│ │ │ -and <code class="inline">Actions</code> is a list of actions to be performed by the <code class="inline">gen_statem</code> engine.</p><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="2262661711-1">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2262661711-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2262661711-2">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="2262661711-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="2262661711-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2262661711-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +and <code class="inline">Actions</code> is a list of actions to be performed by the <code class="inline">gen_statem</code> engine.</p><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="2863538144-1">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2863538144-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2863538144-2">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2863538144-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="2863538144-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2863538144-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │          </span><span class="k">if</span><span class="w">
│ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="2262661711-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="2262661711-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="2863538144-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="2863538144-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="2262661711-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="2262661711-5">)</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2262661711-6">[</span><span class="n">Button</span><span class="p" data-group-id="2262661711-6">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="2863538144-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="2863538144-5">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2863538144-6">[</span><span class="n">Button</span><span class="p" data-group-id="2863538144-6">]</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="2262661711-7">(</span><span class="p" data-group-id="2262661711-7">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="2262661711-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2262661711-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="2262661711-10">[</span><span class="p" data-group-id="2262661711-10">]</span><span class="p" data-group-id="2262661711-9">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="2262661711-11">[</span><span class="p" data-group-id="2262661711-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="2262661711-12">}</span><span class="p" data-group-id="2262661711-11">]</span><span class="p" data-group-id="2262661711-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="2863538144-7">(</span><span class="p" data-group-id="2863538144-7">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2863538144-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2863538144-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="2863538144-10">[</span><span class="p" data-group-id="2863538144-10">]</span><span class="p" data-group-id="2863538144-9">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="2863538144-11">[</span><span class="p" data-group-id="2863538144-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="2863538144-12">}</span><span class="p" data-group-id="2863538144-11">]</span><span class="p" data-group-id="2863538144-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="2262661711-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2262661711-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="2262661711-14">}</span><span class="p" data-group-id="2262661711-13">}</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2863538144-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2863538144-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="2863538144-14">}</span><span class="p" data-group-id="2863538144-13">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>In state <code class="inline">locked</code>, when a button is pressed, it is collected with the
│ │ │  previously pressed buttons up to the length of the correct code, then
│ │ │  compared with the correct code. Depending on the result, the door is
│ │ │  either unlocked and the <code class="inline">gen_statem</code> goes to state <code class="inline">open</code>, or the door
│ │ │  remains in state <code class="inline">locked</code>.</p><p>When changing to state <code class="inline">open</code>, the collected buttons are reset, the lock
│ │ │ -unlocked, and a <em>state time-out</em> for 10 seconds is started.</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="5773336525-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5773336525-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5773336525-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5773336525-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5773336525-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5773336525-3">}</span><span class="p">.</span></code></pre><p>In state <code class="inline">open</code>, a button event is ignored by staying in the same state.
│ │ │ +unlocked, and a <em>state time-out</em> for 10 seconds is started.</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="4007648586-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4007648586-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4007648586-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4007648586-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4007648586-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4007648586-3">}</span><span class="p">.</span></code></pre><p>In state <code class="inline">open</code>, a button event is ignored by staying in the same state.
│ │ │  This can also be done by returning <code class="inline">{keep_state, Data}</code>, or in this case
│ │ │  since <code class="inline">Data</code> is unchanged, by returning <code class="inline">keep_state_and_data</code>.</p><h2 id="state-time-outs" class="section-heading">
│ │ │    <a href="#state-time-outs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">State Time-Outs</span>
│ │ │  </h2>
│ │ │  <p>When a correct code has been given, the door is unlocked and the following
│ │ │ -tuple is returned from <code class="inline">locked/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4274721140-1">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4274721140-2">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4274721140-3">[</span><span class="p" data-group-id="4274721140-3">]</span><span class="p" data-group-id="4274721140-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4274721140-4">[</span><span class="p" data-group-id="4274721140-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="4274721140-5">}</span><span class="p" data-group-id="4274721140-4">]</span><span class="p" data-group-id="4274721140-1">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span></code></pre><p>10,000 is a time-out value in milliseconds. After this time (10 seconds),
│ │ │ +tuple is returned from <code class="inline">locked/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1098202465-1">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1098202465-2">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1098202465-3">[</span><span class="p" data-group-id="1098202465-3">]</span><span class="p" data-group-id="1098202465-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1098202465-4">[</span><span class="p" data-group-id="1098202465-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="1098202465-5">}</span><span class="p" data-group-id="1098202465-4">]</span><span class="p" data-group-id="1098202465-1">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span></code></pre><p>10,000 is a time-out value in milliseconds. After this time (10 seconds),
│ │ │  a time-out occurs. Then, <code class="inline">StateName(state_timeout, lock, Data)</code> is called.
│ │ │  The time-out occurs when the door has been in state <code class="inline">open</code> for 10 seconds.
│ │ │ -After that the door is locked again:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="6166821127-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="6166821127-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="6166821127-2">(</span><span class="p" data-group-id="6166821127-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6166821127-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6166821127-3">}</span><span class="p">;</span></code></pre><p>The timer for a <em>state time-out</em> is automatically canceled when
│ │ │ +After that the door is locked again:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="0885303930-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="0885303930-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="0885303930-2">(</span><span class="p" data-group-id="0885303930-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0885303930-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0885303930-3">}</span><span class="p">;</span></code></pre><p>The timer for a <em>state time-out</em> is automatically canceled when
│ │ │  the state machine does a <em>state change</em>.</p><p>You can restart, cancel, or update a <em>state time-out</em>. See section
│ │ │  <a href="#time-outs"><em>Time-Outs</em></a> for details.</p><h2 id="all-state-events" class="section-heading">
│ │ │    <a href="#all-state-events" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">All State Events</span>
│ │ │  </h2>
│ │ │  <p>Sometimes events can arrive in any state of the <code class="inline">gen_statem</code>. It is convenient
│ │ │  to handle these in a common state handler function that all state functions
│ │ │  call for events not specific to the state.</p><p>Consider a <code class="inline">code_length/0</code> function that returns the length
│ │ │  of the correct code.  We dispatch all events that are not state-specific
│ │ │  to the common function <code class="inline">handle_common/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5771046257-1">(</span><span class="p" data-group-id="5771046257-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5771046257-2">]</span><span class="p" data-group-id="5771046257-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7898868321-1">(</span><span class="p" data-group-id="7898868321-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7898868321-2">]</span><span class="p" data-group-id="7898868321-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="5771046257-3">(</span><span class="p" data-group-id="5771046257-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="5771046257-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="5771046257-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="7898868321-3">(</span><span class="p" data-group-id="7898868321-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="7898868321-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="7898868321-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="5771046257-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5771046257-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="5771046257-6">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5771046257-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">handle_common</span><span class="p" data-group-id="5771046257-7">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5771046257-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="7898868321-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7898868321-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="7898868321-6">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7898868321-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">handle_common</span><span class="p" data-group-id="7898868321-7">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7898868321-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="5771046257-8">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5771046257-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="5771046257-9">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5771046257-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">handle_common</span><span class="p" data-group-id="5771046257-10">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5771046257-10">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="5771046257-11">(</span><span class="p" data-group-id="5771046257-12">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="5771046257-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5771046257-13">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="5771046257-13">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5771046257-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5771046257-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="5771046257-15">[</span><span class="p" data-group-id="5771046257-16">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="5771046257-17">(</span><span class="n">Code</span><span class="p" data-group-id="5771046257-17">)</span><span class="p" data-group-id="5771046257-16">}</span><span class="p" data-group-id="5771046257-15">]</span><span class="p" data-group-id="5771046257-14">}</span><span class="p">.</span></code></pre><p>Another way to do it is through a convenience macro <code class="inline">?HANDLE_COMMON/0</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1278742355-1">(</span><span class="p" data-group-id="1278742355-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1278742355-2">]</span><span class="p" data-group-id="1278742355-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="7898868321-8">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7898868321-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="7898868321-9">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7898868321-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">handle_common</span><span class="p" data-group-id="7898868321-10">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7898868321-10">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="7898868321-11">(</span><span class="p" data-group-id="7898868321-12">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="7898868321-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7898868321-13">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="7898868321-13">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7898868321-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7898868321-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="7898868321-15">[</span><span class="p" data-group-id="7898868321-16">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="7898868321-17">(</span><span class="n">Code</span><span class="p" data-group-id="7898868321-17">)</span><span class="p" data-group-id="7898868321-16">}</span><span class="p" data-group-id="7898868321-15">]</span><span class="p" data-group-id="7898868321-14">}</span><span class="p">.</span></code></pre><p>Another way to do it is through a convenience macro <code class="inline">?HANDLE_COMMON/0</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0281361510-1">(</span><span class="p" data-group-id="0281361510-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0281361510-2">]</span><span class="p" data-group-id="0281361510-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="1278742355-3">(</span><span class="p" data-group-id="1278742355-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="1278742355-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="1278742355-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="0281361510-3">(</span><span class="p" data-group-id="0281361510-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="0281361510-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="0281361510-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1278742355-5">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="1278742355-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="1278742355-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="1278742355-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="1278742355-7">)</span><span class="p" data-group-id="1278742355-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0281361510-5">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="0281361510-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="0281361510-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="0281361510-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="0281361510-7">)</span><span class="p" data-group-id="0281361510-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="1278742355-8">(</span><span class="p" data-group-id="1278742355-9">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="1278742355-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1278742355-10">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="1278742355-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1278742355-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1278742355-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="1278742355-12">[</span><span class="p" data-group-id="1278742355-13">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="1278742355-14">(</span><span class="n">Code</span><span class="p" data-group-id="1278742355-14">)</span><span class="p" data-group-id="1278742355-13">}</span><span class="p" data-group-id="1278742355-12">]</span><span class="p" data-group-id="1278742355-11">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="0281361510-8">(</span><span class="p" data-group-id="0281361510-9">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="0281361510-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0281361510-10">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="0281361510-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0281361510-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0281361510-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0281361510-12">[</span><span class="p" data-group-id="0281361510-13">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="0281361510-14">(</span><span class="n">Code</span><span class="p" data-group-id="0281361510-14">)</span><span class="p" data-group-id="0281361510-13">}</span><span class="p" data-group-id="0281361510-12">]</span><span class="p" data-group-id="0281361510-11">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="1278742355-15">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1278742355-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="0281361510-15">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0281361510-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="1278742355-16">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1278742355-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="0281361510-16">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0281361510-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><p>This example uses <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#call/2"><code class="inline">gen_statem:call/2</code></a>, which waits for a reply from the server.
│ │ │  The reply is sent with a <code class="inline">{reply, From, Reply}</code> tuple in an action list in the
│ │ │  <code class="inline">{keep_state, ...}</code> tuple that retains the current state. This return form is
│ │ │  convenient when you want to stay in the current state but do not know or care
│ │ │  about what it is.</p><p>If the common <em>state callback</em> needs to know the current state a function
│ │ │ -<code class="inline">handle_common/4</code> can be used instead:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2712973820-1">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="2712973820-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="2712973820-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="2712973820-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="2712973820-3">)</span><span class="p" data-group-id="2712973820-1">)</span><span class="p">.</span></code></pre><h2 id="one-state-callback" class="section-heading">
│ │ │ +<code class="inline">handle_common/4</code> can be used instead:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2761757477-1">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="2761757477-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="2761757477-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="2761757477-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="2761757477-3">)</span><span class="p" data-group-id="2761757477-1">)</span><span class="p">.</span></code></pre><h2 id="one-state-callback" class="section-heading">
│ │ │    <a href="#one-state-callback" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">One State Callback</span>
│ │ │  </h2>
│ │ │  <p>If <a href="#callback-modes"><em>callback mode</em></a> <code class="inline">handle_event_function</code> is used,
│ │ │  all events are handled in
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#c:handle_event/4"><code class="inline">Module:handle_event/4</code></a> and we can
│ │ │  (but do not have to) use an event-centered approach where we first branch
│ │ │  depending on event and then depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4964946258-1">(</span><span class="p" data-group-id="4964946258-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="4964946258-2">]</span><span class="p" data-group-id="4964946258-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8035829150-1">(</span><span class="p" data-group-id="8035829150-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="8035829150-2">]</span><span class="p" data-group-id="8035829150-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="4964946258-3">(</span><span class="p" data-group-id="4964946258-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="8035829150-3">(</span><span class="p" data-group-id="8035829150-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">handle_event_function</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4964946258-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4964946258-5">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4964946258-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4964946258-6">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="4964946258-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4964946258-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="8035829150-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8035829150-5">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8035829150-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8035829150-6">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="8035829150-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8035829150-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │  	</span><span class="ss">locked</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4964946258-7">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="4964946258-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8035829150-7">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="8035829150-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │                  </span><span class="k">if</span><span class="w">
│ │ │ -                    </span><span class="nf">length</span><span class="p" data-group-id="4964946258-8">(</span><span class="n">Buttons</span><span class="p" data-group-id="4964946258-8">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                    </span><span class="nf">length</span><span class="p" data-group-id="8035829150-8">(</span><span class="n">Buttons</span><span class="p" data-group-id="8035829150-8">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                          </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │                      </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                        </span><span class="nf">tl</span><span class="p" data-group-id="4964946258-9">(</span><span class="n">Buttons</span><span class="p" data-group-id="4964946258-9">)</span><span class="w">
│ │ │ -                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4964946258-10">[</span><span class="n">Button</span><span class="p" data-group-id="4964946258-10">]</span><span class="p">,</span><span class="w">
│ │ │ +                        </span><span class="nf">tl</span><span class="p" data-group-id="8035829150-9">(</span><span class="n">Buttons</span><span class="p" data-group-id="8035829150-9">)</span><span class="w">
│ │ │ +                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="8035829150-10">[</span><span class="n">Button</span><span class="p" data-group-id="8035829150-10">]</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="k">if</span><span class="w">
│ │ │                  </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="4964946258-11">(</span><span class="p" data-group-id="4964946258-11">)</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="4964946258-12">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4964946258-13">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4964946258-14">[</span><span class="p" data-group-id="4964946258-14">]</span><span class="p" data-group-id="4964946258-13">}</span><span class="p">,</span><span class="w">
│ │ │ -                     </span><span class="p" data-group-id="4964946258-15">[</span><span class="p" data-group-id="4964946258-16">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="4964946258-16">}</span><span class="p" data-group-id="4964946258-15">]</span><span class="p" data-group-id="4964946258-12">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="8035829150-11">(</span><span class="p" data-group-id="8035829150-11">)</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="8035829150-12">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8035829150-13">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8035829150-14">[</span><span class="p" data-group-id="8035829150-14">]</span><span class="p" data-group-id="8035829150-13">}</span><span class="p">,</span><span class="w">
│ │ │ +                     </span><span class="p" data-group-id="8035829150-15">[</span><span class="p" data-group-id="8035829150-16">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8035829150-16">}</span><span class="p" data-group-id="8035829150-15">]</span><span class="p" data-group-id="8035829150-12">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │                  </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="4964946258-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4964946258-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="4964946258-18">}</span><span class="p" data-group-id="4964946258-17">}</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="8035829150-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8035829150-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="8035829150-18">}</span><span class="p" data-group-id="8035829150-17">}</span><span class="w">
│ │ │              </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">open</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4964946258-19">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4964946258-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="4964946258-20">(</span><span class="p" data-group-id="4964946258-20">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4964946258-21">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4964946258-21">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4964946258-22">(</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4964946258-23">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="4964946258-23">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4964946258-24">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="4964946258-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4964946258-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4964946258-25">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="4964946258-26">[</span><span class="p" data-group-id="4964946258-27">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="4964946258-28">(</span><span class="n">Code</span><span class="p" data-group-id="4964946258-28">)</span><span class="p" data-group-id="4964946258-27">}</span><span class="p" data-group-id="4964946258-26">]</span><span class="p" data-group-id="4964946258-25">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="8035829150-19">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8035829150-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="8035829150-20">(</span><span class="p" data-group-id="8035829150-20">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8035829150-21">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8035829150-21">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="8035829150-22">(</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8035829150-23">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="8035829150-23">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8035829150-24">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="8035829150-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8035829150-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8035829150-25">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="8035829150-26">[</span><span class="p" data-group-id="8035829150-27">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="8035829150-28">(</span><span class="n">Code</span><span class="p" data-group-id="8035829150-28">)</span><span class="p" data-group-id="8035829150-27">}</span><span class="p" data-group-id="8035829150-26">]</span><span class="p" data-group-id="8035829150-25">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │    <a href="#stopping" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Stopping</span>
│ │ │  </h2>
│ │ │ @@ -763,59 +763,59 @@
│ │ │  </h3>
│ │ │  <p>If the <code class="inline">gen_statem</code> is part of a supervision tree, no stop function is needed.
│ │ │  The <code class="inline">gen_statem</code> is automatically terminated by its supervisor. Exactly how
│ │ │  this is done is defined by a <a href="sup_princ.html#shutdown">shutdown strategy</a>
│ │ │  set in the supervisor.</p><p>If it is necessary to clean up before termination, the shutdown strategy
│ │ │  must be a time-out value and the <code class="inline">gen_statem</code> must in function <code class="inline">init/1</code>
│ │ │  set itself to trap exit signals by calling
│ │ │ -<a href="../../erts-15.2.7/doc/html/erlang.html#process_flag/2"><code class="inline">process_flag(trap_exit, true)</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6714063540-1">(</span><span class="n">Args</span><span class="p" data-group-id="6714063540-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="6714063540-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6714063540-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="6714063540-3">(</span><span class="p" data-group-id="6714063540-3">)</span><span class="p">,</span><span class="w">
│ │ │ +<a href="../../erts-15.2.7/doc/html/erlang.html#process_flag/2"><code class="inline">process_flag(trap_exit, true)</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4500712915-1">(</span><span class="n">Args</span><span class="p" data-group-id="4500712915-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="4500712915-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4500712915-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="4500712915-3">(</span><span class="p" data-group-id="4500712915-3">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>When ordered to shut down, the <code class="inline">gen_statem</code> then calls callback function
│ │ │  <code class="inline">terminate(shutdown, State, Data)</code>.</p><p>In this example, function <code class="inline">terminate/3</code> locks the door if it is open,
│ │ │  so we do not accidentally leave the door open
│ │ │ -when the supervision tree terminates:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="0127512831-1">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0127512831-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="0127512831-2">(</span><span class="p" data-group-id="0127512831-2">)</span><span class="p">,</span><span class="w">
│ │ │ +when the supervision tree terminates:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="3352236181-1">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="3352236181-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="3352236181-2">(</span><span class="p" data-group-id="3352236181-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="standalone-gen_statem" class="section-heading">
│ │ │    <a href="#standalone-gen_statem" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Standalone gen_statem</span>
│ │ │  </h3>
│ │ │  <p>If the <code class="inline">gen_statem</code> is not part of a supervision tree, it can be stopped
│ │ │  using <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#stop/1"><code class="inline">gen_statem:stop/1</code></a>, preferably through
│ │ │  an API function:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0564702072-1">(</span><span class="p" data-group-id="0564702072-2">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0564702072-2">]</span><span class="p" data-group-id="0564702072-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7933835264-1">(</span><span class="p" data-group-id="7933835264-2">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7933835264-2">]</span><span class="p" data-group-id="7933835264-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="0564702072-3">(</span><span class="p" data-group-id="0564702072-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="0564702072-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="0564702072-4">)</span><span class="p">.</span></code></pre><p>This makes the <code class="inline">gen_statem</code> call callback function <code class="inline">terminate/3</code> just like
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="7933835264-3">(</span><span class="p" data-group-id="7933835264-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="7933835264-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="7933835264-4">)</span><span class="p">.</span></code></pre><p>This makes the <code class="inline">gen_statem</code> call callback function <code class="inline">terminate/3</code> just like
│ │ │  for a supervised server and waits for the process to terminate.</p><h2 id="event-time-outs" class="section-heading">
│ │ │    <a href="#event-time-outs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Event Time-Outs</span>
│ │ │  </h2>
│ │ │  <p>A time-out feature inherited from <code class="inline">gen_statem</code>'s predecessor <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_fsm.html"><code class="inline">gen_fsm</code></a>,
│ │ │  is an <em>event time-out</em>, that is, if an event arrives the timer is canceled.
│ │ │  You get either an event or a time-out, but not both.</p><p>It is ordered by the
│ │ │  <a href="#transition-actions"><em>transition action</em></a> <code class="inline">{timeout, Time, EventContent}</code>,
│ │ │  or just an integer <code class="inline">Time</code>, even without the enclosing actions list (the latter
│ │ │  is a form inherited from <code class="inline">gen_fsm</code>).</p><p>This type of time-out is useful, for example, to act on inactivity.
│ │ │  Let's restart the code sequence if no button is pressed for say 30 seconds:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="6891399776-1">(</span><span class="ss">timeout</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6891399776-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6891399776-2">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6891399776-3">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="6891399776-4">[</span><span class="p" data-group-id="6891399776-4">]</span><span class="p" data-group-id="6891399776-3">}</span><span class="p" data-group-id="6891399776-2">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="6891399776-5">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6891399776-6">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6891399776-6">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6891399776-7">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="6891399776-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6891399776-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="1317445521-1">(</span><span class="ss">timeout</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1317445521-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1317445521-2">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1317445521-3">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1317445521-4">[</span><span class="p" data-group-id="1317445521-4">]</span><span class="p" data-group-id="1317445521-3">}</span><span class="p" data-group-id="1317445521-2">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="1317445521-5">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1317445521-6">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1317445521-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1317445521-7">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="1317445521-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1317445521-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="6891399776-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6891399776-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="6891399776-9">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p" data-group-id="6891399776-8">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="1317445521-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1317445521-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="1317445521-9">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p" data-group-id="1317445521-8">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Whenever we receive a button event we start an <em>event time-out</em> of 30 seconds,
│ │ │  and if we get an <em>event type</em> of <code class="inline">timeout</code> we reset the remaining
│ │ │  code sequence.</p><p>An <em>event time-out</em> is canceled by any other event so you either get
│ │ │  some other event or the time-out event. Therefore, canceling,
│ │ │  restarting, or updating an <em>event time-out</em> is neither possible nor
│ │ │  necessary. Whatever event you act on has already canceled
│ │ │  the <em>event time-out</em>, so there is never a running <em>event time-out</em>
│ │ │ @@ -834,30 +834,30 @@
│ │ │  another, maybe cancel the time-out without changing states, or perhaps run
│ │ │  multiple time-outs in parallel. All this can be accomplished with
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#t:generic_timeout/0"><em>generic time-outs</em></a>. They may look a little
│ │ │  bit like <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#t:event_timeout/0"><em>event time-outs</em></a> but contain
│ │ │  a name to allow for any number of them simultaneously and they are
│ │ │  not automatically canceled.</p><p>Here is how to accomplish the <em>state time-out</em> in the previous example
│ │ │  by instead using a <em>generic time-out</em> named for example <code class="inline">open</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="8982480316-1">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8982480316-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8982480316-2">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8982480316-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="8982480316-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8982480316-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="6102001590-1">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6102001590-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6102001590-2">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6102001590-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="6102001590-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6102001590-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="8982480316-4">(</span><span class="p" data-group-id="8982480316-4">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="8982480316-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8982480316-6">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8982480316-7">[</span><span class="p" data-group-id="8982480316-7">]</span><span class="p" data-group-id="8982480316-6">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="8982480316-8">[</span><span class="p" data-group-id="8982480316-9">{</span><span class="p" data-group-id="8982480316-10">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="8982480316-10">}</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8982480316-9">}</span><span class="p" data-group-id="8982480316-8">]</span><span class="p" data-group-id="8982480316-5">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="6102001590-4">(</span><span class="p" data-group-id="6102001590-4">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="6102001590-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6102001590-6">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="6102001590-7">[</span><span class="p" data-group-id="6102001590-7">]</span><span class="p" data-group-id="6102001590-6">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="6102001590-8">[</span><span class="p" data-group-id="6102001590-9">{</span><span class="p" data-group-id="6102001590-10">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="6102001590-10">}</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="6102001590-9">}</span><span class="p" data-group-id="6102001590-8">]</span><span class="p" data-group-id="6102001590-5">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8982480316-11">(</span><span class="p" data-group-id="8982480316-12">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="8982480316-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8982480316-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="8982480316-13">(</span><span class="p" data-group-id="8982480316-13">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8982480316-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="8982480316-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8982480316-15">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8982480316-16">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8982480316-16">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8982480316-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8982480316-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="8982480316-17">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="6102001590-11">(</span><span class="p" data-group-id="6102001590-12">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="6102001590-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6102001590-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="6102001590-13">(</span><span class="p" data-group-id="6102001590-13">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6102001590-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="6102001590-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="6102001590-15">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6102001590-16">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6102001590-16">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6102001590-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6102001590-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="6102001590-17">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Specific <em>generic time-outs</em> can just as <a href="#state-time-outs"><em>state time-outs</em></a>
│ │ │  be restarted or canceled by setting it to a new time or <code class="inline">infinity</code>.</p><p>In this particular case we do not need to cancel the time-out since
│ │ │  the time-out event is the only possible reason to do a <em>state change</em>
│ │ │  from <code class="inline">open</code> to <code class="inline">locked</code>.</p><p>Instead of bothering with when to cancel a time-out, a late time-out event
│ │ │  can be handled by ignoring it if it arrives in a state
│ │ │  where it is known to be late.</p><p>You can restart, cancel, or update a <em>generic time-out</em>.
│ │ │  See section <a href="#time-outs"><em>Time-Outs</em></a> for details.</p><h2 id="erlang-timers" class="section-heading">
│ │ │ @@ -869,32 +869,32 @@
│ │ │  <p>The most versatile way to handle time-outs is to use Erlang Timers; see
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#start_timer/4"><code class="inline">erlang:start_timer/3,4</code></a>. Most time-out tasks
│ │ │  can be performed with the time-out features in <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html"><code class="inline">gen_statem</code></a>,
│ │ │  but an example of one that cannot is if you should need the return value
│ │ │  from <a href="../../erts-15.2.7/doc/html/erlang.html#cancel_timer/2"><code class="inline">erlang:cancel_timer(Tref)</code></a>, that is,
│ │ │  the remaining time of the timer.</p><p>Here is how to accomplish the <em>state time-out</em> in the previous example
│ │ │  by instead using an Erlang Timer:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="3401505957-1">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3401505957-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3401505957-2">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="3401505957-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="3401505957-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3401505957-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="7214990167-1">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7214990167-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7214990167-2">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="7214990167-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="7214990167-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7214990167-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3401505957-4">(</span><span class="p" data-group-id="3401505957-4">)</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="7214990167-4">(</span><span class="p" data-group-id="7214990167-4">)</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="n">Tref</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ -                 </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">start_timer</span><span class="p" data-group-id="3401505957-5">(</span><span class="w">
│ │ │ -                     </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3401505957-6">(</span><span class="p" data-group-id="3401505957-6">)</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p" data-group-id="3401505957-5">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3401505957-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3401505957-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3401505957-9">[</span><span class="p" data-group-id="3401505957-9">]</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="3401505957-8">}</span><span class="p" data-group-id="3401505957-7">}</span><span class="p">;</span><span class="w">
│ │ │ +                 </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">start_timer</span><span class="p" data-group-id="7214990167-5">(</span><span class="w">
│ │ │ +                     </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7214990167-6">(</span><span class="p" data-group-id="7214990167-6">)</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p" data-group-id="7214990167-5">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="7214990167-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7214990167-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="7214990167-9">[</span><span class="p" data-group-id="7214990167-9">]</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="7214990167-8">}</span><span class="p" data-group-id="7214990167-7">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="3401505957-10">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3401505957-11">{</span><span class="ss">timeout</span><span class="p">,</span><span class="n">Tref</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3401505957-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3401505957-12">#{</span><span class="ss">timer</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="3401505957-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3401505957-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="3401505957-13">(</span><span class="p" data-group-id="3401505957-13">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3401505957-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="3401505957-15">(</span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3401505957-15">)</span><span class="p" data-group-id="3401505957-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="3401505957-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3401505957-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3401505957-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3401505957-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3401505957-18">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="3401505957-18">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="7214990167-10">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7214990167-11">{</span><span class="ss">timeout</span><span class="p">,</span><span class="n">Tref</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="7214990167-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7214990167-12">#{</span><span class="ss">timer</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="7214990167-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7214990167-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="7214990167-13">(</span><span class="p" data-group-id="7214990167-13">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7214990167-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="7214990167-15">(</span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7214990167-15">)</span><span class="p" data-group-id="7214990167-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="7214990167-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7214990167-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7214990167-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7214990167-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7214990167-18">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="7214990167-18">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Removing the <code class="inline">timer</code> key from the map when we do a <em>state change</em> to <code class="inline">locked</code>
│ │ │  is not strictly necessary since we can only get into state <code class="inline">open</code>
│ │ │  with an updated <code class="inline">timer</code> map value. But it can be nice to not have
│ │ │  outdated values in the state <code class="inline">Data</code>.</p><p>If you need to cancel a timer because of some other event, you can use
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#cancel_timer/2"><code class="inline">erlang:cancel_timer(Tref)</code></a>. Note that no time-out
│ │ │  message will arrive after this (because the timer has been
│ │ │  explicitly canceled), unless you have already postponed one earlier
│ │ │ @@ -910,16 +910,16 @@
│ │ │    <span class="text">Postponing Events</span>
│ │ │  </h2>
│ │ │  <p>If you want to ignore a particular event in the current state and handle it
│ │ │  in a future state, you can postpone the event. A postponed event
│ │ │  is retried after a <em>state change</em>, that is, <code class="inline">OldState =/= NewState</code>.</p><p>Postponing is ordered by the
│ │ │  <a href="#transition-actions"><em>transition action</em></a> <code class="inline">postpone</code>.</p><p>In this example, instead of ignoring button events while in the <code class="inline">open</code> state,
│ │ │  we can postpone them handle them later in the <code class="inline">locked</code> state:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="3684291173-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3684291173-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3684291173-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3684291173-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3684291173-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="3684291173-4">[</span><span class="ss">postpone</span><span class="p" data-group-id="3684291173-4">]</span><span class="p" data-group-id="3684291173-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="3834975143-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3834975143-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3834975143-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3834975143-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3834975143-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="3834975143-4">[</span><span class="ss">postpone</span><span class="p" data-group-id="3834975143-4">]</span><span class="p" data-group-id="3834975143-3">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Since a postponed event is only retried after a <em>state change</em>, you have to
│ │ │  think about where to keep a state data item. You can keep it in the server
│ │ │  <code class="inline">Data</code> or in the <code class="inline">State</code> itself, for example by having two more or less
│ │ │  identical states to keep a boolean value, or by using a complex state (see
│ │ │  section <a href="#complex-state"><em>Complex State</em></a>) with
│ │ │  <a href="#callback-modes"><em>callback mode</em></a>
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#t:callback_mode/0"><code class="inline">handle_event_function</code></a>. If a change
│ │ │ @@ -940,55 +940,55 @@
│ │ │    <a href="#selective-receive" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Selective Receive</span>
│ │ │  </h3>
│ │ │  <p>Erlang's selective <code class="inline">receive</code> statement is often used to describe simple state
│ │ │  machine examples in straightforward Erlang code. The following is a possible
│ │ │ -implementation of the first example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5859854074-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="5859854074-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5859854074-2">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_1</span><span class="p" data-group-id="5859854074-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5859854074-3">(</span><span class="p" data-group-id="5859854074-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5859854074-4">]</span><span class="p" data-group-id="5859854074-3">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="5859854074-5">(</span><span class="n">Code</span><span class="p" data-group-id="5859854074-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="5859854074-6">(</span><span class="w">
│ │ │ -      </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5859854074-7">(</span><span class="p" data-group-id="5859854074-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">register</span><span class="p" data-group-id="5859854074-8">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5859854074-9">(</span><span class="p" data-group-id="5859854074-9">)</span><span class="p" data-group-id="5859854074-8">)</span><span class="p">,</span><span class="w">
│ │ │ -	      </span><span class="nf">do_lock</span><span class="p" data-group-id="5859854074-10">(</span><span class="p" data-group-id="5859854074-10">)</span><span class="p">,</span><span class="w">
│ │ │ -	      </span><span class="nf">locked</span><span class="p" data-group-id="5859854074-11">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="5859854074-12">(</span><span class="n">Code</span><span class="p" data-group-id="5859854074-12">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5859854074-13">[</span><span class="p" data-group-id="5859854074-13">]</span><span class="p" data-group-id="5859854074-11">)</span><span class="w">
│ │ │ -      </span><span class="k">end</span><span class="p" data-group-id="5859854074-6">)</span><span class="p">.</span><span class="w">
│ │ │ +implementation of the first example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7209600606-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="7209600606-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="7209600606-2">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_1</span><span class="p" data-group-id="7209600606-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7209600606-3">(</span><span class="p" data-group-id="7209600606-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7209600606-4">]</span><span class="p" data-group-id="7209600606-3">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="7209600606-5">(</span><span class="n">Code</span><span class="p" data-group-id="7209600606-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="7209600606-6">(</span><span class="w">
│ │ │ +      </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7209600606-7">(</span><span class="p" data-group-id="7209600606-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">register</span><span class="p" data-group-id="7209600606-8">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7209600606-9">(</span><span class="p" data-group-id="7209600606-9">)</span><span class="p" data-group-id="7209600606-8">)</span><span class="p">,</span><span class="w">
│ │ │ +	      </span><span class="nf">do_lock</span><span class="p" data-group-id="7209600606-10">(</span><span class="p" data-group-id="7209600606-10">)</span><span class="p">,</span><span class="w">
│ │ │ +	      </span><span class="nf">locked</span><span class="p" data-group-id="7209600606-11">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7209600606-12">(</span><span class="n">Code</span><span class="p" data-group-id="7209600606-12">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7209600606-13">[</span><span class="p" data-group-id="7209600606-13">]</span><span class="p" data-group-id="7209600606-11">)</span><span class="w">
│ │ │ +      </span><span class="k">end</span><span class="p" data-group-id="7209600606-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="5859854074-14">(</span><span class="n">Button</span><span class="p" data-group-id="5859854074-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">NAME</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5859854074-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5859854074-15">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="6862817000-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="6862817000-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="7209600606-14">(</span><span class="n">Button</span><span class="p" data-group-id="7209600606-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">NAME</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7209600606-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7209600606-15">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="0118958191-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="0118958191-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6862817000-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6862817000-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0118958191-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0118958191-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │                  </span><span class="k">if</span><span class="w">
│ │ │ -                    </span><span class="nf">length</span><span class="p" data-group-id="6862817000-3">(</span><span class="n">Buttons</span><span class="p" data-group-id="6862817000-3">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                    </span><span class="nf">length</span><span class="p" data-group-id="0118958191-3">(</span><span class="n">Buttons</span><span class="p" data-group-id="0118958191-3">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                          </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │                      </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                        </span><span class="nf">tl</span><span class="p" data-group-id="6862817000-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="6862817000-4">)</span><span class="w">
│ │ │ -                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6862817000-5">[</span><span class="n">Button</span><span class="p" data-group-id="6862817000-5">]</span><span class="p">,</span><span class="w">
│ │ │ +                        </span><span class="nf">tl</span><span class="p" data-group-id="0118958191-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="0118958191-4">)</span><span class="w">
│ │ │ +                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0118958191-5">[</span><span class="n">Button</span><span class="p" data-group-id="0118958191-5">]</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="k">if</span><span class="w">
│ │ │                  </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="6862817000-6">(</span><span class="p" data-group-id="6862817000-6">)</span><span class="p">,</span><span class="w">
│ │ │ -		    </span><span class="nf">open</span><span class="p" data-group-id="6862817000-7">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="6862817000-7">)</span><span class="p">;</span><span class="w">
│ │ │ +                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="0118958191-6">(</span><span class="p" data-group-id="0118958191-6">)</span><span class="p">,</span><span class="w">
│ │ │ +		    </span><span class="nf">open</span><span class="p" data-group-id="0118958191-7">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="0118958191-7">)</span><span class="p">;</span><span class="w">
│ │ │                  </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -                    </span><span class="nf">locked</span><span class="p" data-group-id="6862817000-8">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="6862817000-8">)</span><span class="w">
│ │ │ +                    </span><span class="nf">locked</span><span class="p" data-group-id="0118958191-8">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="0118958191-8">)</span><span class="w">
│ │ │              </span><span class="k">end</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="7835551840-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="7835551840-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="5401099998-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="5401099998-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -	    </span><span class="nf">do_lock</span><span class="p" data-group-id="7835551840-2">(</span><span class="p" data-group-id="7835551840-2">)</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">locked</span><span class="p" data-group-id="7835551840-3">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7835551840-4">[</span><span class="p" data-group-id="7835551840-4">]</span><span class="p" data-group-id="7835551840-3">)</span><span class="w">
│ │ │ +	    </span><span class="nf">do_lock</span><span class="p" data-group-id="5401099998-2">(</span><span class="p" data-group-id="5401099998-2">)</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="nf">locked</span><span class="p" data-group-id="5401099998-3">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5401099998-4">[</span><span class="p" data-group-id="5401099998-4">]</span><span class="p" data-group-id="5401099998-3">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">do_lock</span><span class="p" data-group-id="7835551840-5">(</span><span class="p" data-group-id="7835551840-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7835551840-6">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7835551840-7">[</span><span class="p" data-group-id="7835551840-7">]</span><span class="p" data-group-id="7835551840-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="7835551840-8">(</span><span class="p" data-group-id="7835551840-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7835551840-9">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7835551840-10">[</span><span class="p" data-group-id="7835551840-10">]</span><span class="p" data-group-id="7835551840-9">)</span><span class="p">.</span></code></pre><p>The selective receive in this case causes <code class="inline">open</code> to implicitly postpone any
│ │ │ +</span><span class="nf">do_lock</span><span class="p" data-group-id="5401099998-5">(</span><span class="p" data-group-id="5401099998-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5401099998-6">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5401099998-7">[</span><span class="p" data-group-id="5401099998-7">]</span><span class="p" data-group-id="5401099998-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="5401099998-8">(</span><span class="p" data-group-id="5401099998-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5401099998-9">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5401099998-10">[</span><span class="p" data-group-id="5401099998-10">]</span><span class="p" data-group-id="5401099998-9">)</span><span class="p">.</span></code></pre><p>The selective receive in this case causes <code class="inline">open</code> to implicitly postpone any
│ │ │  events to the <code class="inline">locked</code> state.</p><p>A catch-all receive should never be used from a <code class="inline">gen_statem</code> behaviour
│ │ │  (or from any <code class="inline">gen_*</code> behaviour), as the receive statement is within
│ │ │  the <code class="inline">gen_*</code> engine itself. <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html"><code class="inline">sys</code></a>-compatible behaviours must respond to
│ │ │  system messages and therefore do that in their engine receive loop,
│ │ │  passing non-system messages to the <em>callback module</em>. Using a catch-all
│ │ │  receive can result in system messages being discarded, which in turn
│ │ │  can lead to unexpected behaviour. If a selective receive must be used,
│ │ │ @@ -1011,40 +1011,40 @@
│ │ │  section), especially if only one or a few states have state enter actions,
│ │ │  this is a perfect use case for the built in
│ │ │  <a href="#state-enter-calls"><em>state enter calls</em></a>.</p><p>You return a list containing <code class="inline">state_enter</code> from your
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#c:callback_mode/0"><code class="inline">callback_mode/0</code></a> function and the
│ │ │  <code class="inline">gen_statem</code> engine will call your <em>state callback</em> once with an event
│ │ │  <code class="inline">(enter, OldState, ...)</code> whenever it does a <em>state change</em>. Then you
│ │ │  just need to handle these event-like calls in all states.</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8942827085-1">(</span><span class="n">Code</span><span class="p" data-group-id="8942827085-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="8942827085-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8942827085-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8942827085-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8942827085-4">(</span><span class="n">Code</span><span class="p" data-group-id="8942827085-4">)</span><span class="p" data-group-id="8942827085-3">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8942827085-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8942827085-5">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="8942827085-6">(</span><span class="p" data-group-id="8942827085-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8942827085-7">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="8942827085-7">]</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="8942827085-8">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8942827085-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="8942827085-9">(</span><span class="p" data-group-id="8942827085-9">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8942827085-10">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="8942827085-11">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8942827085-12">[</span><span class="p" data-group-id="8942827085-12">]</span><span class="p" data-group-id="8942827085-11">}</span><span class="p" data-group-id="8942827085-10">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="8942827085-13">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8942827085-14">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8942827085-14">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8942827085-15">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="8942827085-15">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8942827085-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8858088704-1">(</span><span class="n">Code</span><span class="p" data-group-id="8858088704-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="8858088704-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8858088704-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8858088704-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8858088704-4">(</span><span class="n">Code</span><span class="p" data-group-id="8858088704-4">)</span><span class="p" data-group-id="8858088704-3">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8858088704-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8858088704-5">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="8858088704-6">(</span><span class="p" data-group-id="8858088704-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8858088704-7">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="8858088704-7">]</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="8858088704-8">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8858088704-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="8858088704-9">(</span><span class="p" data-group-id="8858088704-9">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8858088704-10">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="8858088704-11">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8858088704-12">[</span><span class="p" data-group-id="8858088704-12">]</span><span class="p" data-group-id="8858088704-11">}</span><span class="p" data-group-id="8858088704-10">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="8858088704-13">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8858088704-14">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8858088704-14">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8858088704-15">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="8858088704-15">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8858088704-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="8942827085-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8942827085-16">}</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8858088704-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8858088704-16">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8942827085-17">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="8942827085-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="8942827085-18">(</span><span class="p" data-group-id="8942827085-18">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8942827085-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="8942827085-20">[</span><span class="p" data-group-id="8942827085-21">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8942827085-21">}</span><span class="p" data-group-id="8942827085-20">]</span><span class="p" data-group-id="8942827085-19">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8942827085-22">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8942827085-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8942827085-23">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8942827085-23">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="8858088704-17">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="8858088704-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="8858088704-18">(</span><span class="p" data-group-id="8858088704-18">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8858088704-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="8858088704-20">[</span><span class="p" data-group-id="8858088704-21">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8858088704-21">}</span><span class="p" data-group-id="8858088704-20">]</span><span class="p" data-group-id="8858088704-19">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="8858088704-22">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8858088704-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8858088704-23">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8858088704-23">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>You can repeat the state enter code by returning one of
│ │ │  <code class="inline">{repeat_state, ...}</code>,<code class="inline">{repeat_state_and_data, _}</code>,
│ │ │  or <code class="inline">repeat_state_and_data</code> that otherwise behaves exactly like their
│ │ │  <code class="inline">keep_state</code> siblings.  See the type
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#t:state_callback_result/2"><code class="inline">state_callback_result()</code></a>
│ │ │  in the Reference Manual.</p><h2 id="inserted-events" class="section-heading">
│ │ │    <a href="#inserted-events" class="hover-link">
│ │ │ @@ -1066,44 +1066,44 @@
│ │ │  to dispatch pre-processed events as internal events to the main state
│ │ │  machine.</p><p>Using internal events also can make it easier to synchronize the state
│ │ │  machines.</p><p>A variant of this is to use a <a href="#complex-state">complex state</a> with
│ │ │  <a href="#one-state-callback">one state callback</a>, modeling the state
│ │ │  with, for example, a tuple <code class="inline">{MainFSMState, SubFSMState}</code>.</p><p>To illustrate this we make up an example where the buttons instead generate
│ │ │  down and up (press and release) events, and the lock responds
│ │ │  to an up event only after the corresponding down event.</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5540623151-1">(</span><span class="p" data-group-id="5540623151-2">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5540623151-2">]</span><span class="p" data-group-id="5540623151-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1058389264-1">(</span><span class="p" data-group-id="1058389264-2">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1058389264-2">]</span><span class="p" data-group-id="1058389264-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">down</span><span class="p" data-group-id="5540623151-3">(</span><span class="n">Button</span><span class="p" data-group-id="5540623151-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="5540623151-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5540623151-5">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5540623151-5">}</span><span class="p" data-group-id="5540623151-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">down</span><span class="p" data-group-id="1058389264-3">(</span><span class="n">Button</span><span class="p" data-group-id="1058389264-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1058389264-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1058389264-5">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1058389264-5">}</span><span class="p" data-group-id="1058389264-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">up</span><span class="p" data-group-id="5540623151-6">(</span><span class="n">Button</span><span class="p" data-group-id="5540623151-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="5540623151-7">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5540623151-8">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5540623151-8">}</span><span class="p" data-group-id="5540623151-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">up</span><span class="p" data-group-id="1058389264-6">(</span><span class="n">Button</span><span class="p" data-group-id="1058389264-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1058389264-7">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1058389264-8">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1058389264-8">}</span><span class="p" data-group-id="1058389264-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="5540623151-9">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5540623151-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="5540623151-10">(</span><span class="p" data-group-id="5540623151-10">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5540623151-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="5540623151-12">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5540623151-13">[</span><span class="p" data-group-id="5540623151-13">]</span><span class="p" data-group-id="5540623151-12">}</span><span class="p" data-group-id="5540623151-11">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="5540623151-14">(</span><span class="w">
│ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5540623151-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5540623151-15">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5540623151-16">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="5540623151-16">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5540623151-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">handle_common</span><span class="p" data-group-id="7114698243-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7114698243-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7114698243-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7114698243-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7114698243-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7114698243-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="7114698243-4">}</span><span class="p" data-group-id="7114698243-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="7114698243-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7114698243-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7114698243-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7114698243-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="1058389264-9">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1058389264-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="1058389264-10">(</span><span class="p" data-group-id="1058389264-10">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1058389264-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="1058389264-12">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1058389264-13">[</span><span class="p" data-group-id="1058389264-13">]</span><span class="p" data-group-id="1058389264-12">}</span><span class="p" data-group-id="1058389264-11">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="1058389264-14">(</span><span class="w">
│ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1058389264-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1058389264-15">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1058389264-16">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="1058389264-16">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1058389264-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">handle_common</span><span class="p" data-group-id="3689069995-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3689069995-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3689069995-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3689069995-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3689069995-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3689069995-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="3689069995-4">}</span><span class="p" data-group-id="3689069995-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="3689069995-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3689069995-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3689069995-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3689069995-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7114698243-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="7114698243-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="7114698243-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="7114698243-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7114698243-9">)</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="7114698243-10">[</span><span class="p" data-group-id="7114698243-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="7114698243-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7114698243-12">}</span><span class="p" data-group-id="7114698243-11">}</span><span class="p" data-group-id="7114698243-10">]</span><span class="p" data-group-id="7114698243-8">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7114698243-13">#{</span><span class="p" data-group-id="7114698243-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3689069995-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="3689069995-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="3689069995-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="3689069995-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3689069995-9">)</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="3689069995-10">[</span><span class="p" data-group-id="3689069995-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="3689069995-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3689069995-12">}</span><span class="p" data-group-id="3689069995-11">}</span><span class="p" data-group-id="3689069995-10">]</span><span class="p" data-group-id="3689069995-8">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3689069995-13">#{</span><span class="p" data-group-id="3689069995-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="7114698243-14">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7114698243-15">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7114698243-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7114698243-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7114698243-16">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="7114698243-17">[</span><span class="ss">postpone</span><span class="p" data-group-id="7114698243-17">]</span><span class="p" data-group-id="7114698243-16">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="3689069995-14">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3689069995-15">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3689069995-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3689069995-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3689069995-16">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="3689069995-17">[</span><span class="ss">postpone</span><span class="p" data-group-id="3689069995-17">]</span><span class="p" data-group-id="3689069995-16">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>If you start this program with <code class="inline">code_lock:start([17])</code> you can unlock with
│ │ │  <code class="inline">code_lock:down(17), code_lock:up(17).</code></p><h2 id="example-revisited" class="section-heading">
│ │ │    <a href="#example-revisited" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example Revisited</span>
│ │ │  </h2>
│ │ │ @@ -1131,152 +1131,152 @@
│ │ │  Also, the state diagram does not show that the <code class="inline">code_length/0</code> call
│ │ │  must be handled in every state.</p><h3 id="callback-mode-state_functions" class="section-heading">
│ │ │    <a href="#callback-mode-state_functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Callback Mode: state_functions</span>
│ │ │  </h3>
│ │ │ -<p>Using state functions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4875723700-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="4875723700-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4875723700-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="4875723700-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4875723700-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_2</span><span class="p" data-group-id="4875723700-3">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Using state functions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4958731217-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="4958731217-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4958731217-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="4958731217-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4958731217-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_2</span><span class="p" data-group-id="4958731217-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4875723700-4">(</span><span class="p" data-group-id="4875723700-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4875723700-5">]</span><span class="p" data-group-id="4875723700-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4875723700-6">(</span><span class="p" data-group-id="4875723700-7">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4875723700-7">]</span><span class="p" data-group-id="4875723700-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4875723700-8">(</span><span class="p" data-group-id="4875723700-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4875723700-9">]</span><span class="p" data-group-id="4875723700-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4875723700-10">(</span><span class="p" data-group-id="4875723700-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4875723700-11">]</span><span class="p" data-group-id="4875723700-10">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="4875723700-12">(</span><span class="n">Code</span><span class="p" data-group-id="4875723700-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4875723700-13">(</span><span class="p" data-group-id="4875723700-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4875723700-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4875723700-15">[</span><span class="p" data-group-id="4875723700-15">]</span><span class="p" data-group-id="4875723700-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="4875723700-16">(</span><span class="p" data-group-id="4875723700-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="4875723700-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4875723700-17">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">down</span><span class="p" data-group-id="4875723700-18">(</span><span class="n">Button</span><span class="p" data-group-id="4875723700-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4875723700-19">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4875723700-20">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4875723700-20">}</span><span class="p" data-group-id="4875723700-19">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">up</span><span class="p" data-group-id="4875723700-21">(</span><span class="n">Button</span><span class="p" data-group-id="4875723700-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4875723700-22">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4875723700-23">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4875723700-23">}</span><span class="p" data-group-id="4875723700-22">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="4875723700-24">(</span><span class="p" data-group-id="4875723700-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4875723700-25">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="4875723700-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9654301007-1">(</span><span class="n">Code</span><span class="p" data-group-id="9654301007-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9654301007-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9654301007-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9654301007-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9654301007-4">(</span><span class="n">Code</span><span class="p" data-group-id="9654301007-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9654301007-5">[</span><span class="p" data-group-id="9654301007-5">]</span><span class="p" data-group-id="9654301007-3">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9654301007-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9654301007-6">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4958731217-4">(</span><span class="p" data-group-id="4958731217-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4958731217-5">]</span><span class="p" data-group-id="4958731217-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4958731217-6">(</span><span class="p" data-group-id="4958731217-7">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4958731217-7">]</span><span class="p" data-group-id="4958731217-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4958731217-8">(</span><span class="p" data-group-id="4958731217-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4958731217-9">]</span><span class="p" data-group-id="4958731217-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4958731217-10">(</span><span class="p" data-group-id="4958731217-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4958731217-11">]</span><span class="p" data-group-id="4958731217-10">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="4958731217-12">(</span><span class="n">Code</span><span class="p" data-group-id="4958731217-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4958731217-13">(</span><span class="p" data-group-id="4958731217-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4958731217-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4958731217-15">[</span><span class="p" data-group-id="4958731217-15">]</span><span class="p" data-group-id="4958731217-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="4958731217-16">(</span><span class="p" data-group-id="4958731217-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="4958731217-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4958731217-17">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">down</span><span class="p" data-group-id="4958731217-18">(</span><span class="n">Button</span><span class="p" data-group-id="4958731217-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4958731217-19">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4958731217-20">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4958731217-20">}</span><span class="p" data-group-id="4958731217-19">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">up</span><span class="p" data-group-id="4958731217-21">(</span><span class="n">Button</span><span class="p" data-group-id="4958731217-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4958731217-22">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4958731217-23">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4958731217-23">}</span><span class="p" data-group-id="4958731217-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="4958731217-24">(</span><span class="p" data-group-id="4958731217-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4958731217-25">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="4958731217-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="2650439969-1">(</span><span class="n">Code</span><span class="p" data-group-id="2650439969-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="2650439969-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2650439969-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2650439969-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="2650439969-4">(</span><span class="n">Code</span><span class="p" data-group-id="2650439969-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2650439969-5">[</span><span class="p" data-group-id="2650439969-5">]</span><span class="p" data-group-id="2650439969-3">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2650439969-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2650439969-6">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="9654301007-7">(</span><span class="p" data-group-id="9654301007-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9654301007-8">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="9654301007-8">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="2650439969-7">(</span><span class="p" data-group-id="2650439969-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2650439969-8">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="2650439969-8">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9654301007-9">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="9654301007-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9654301007-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="9654301007-11">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9654301007-11">)</span><span class="p" data-group-id="9654301007-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2650439969-9">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="2650439969-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="2650439969-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="2650439969-11">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="2650439969-11">)</span><span class="p" data-group-id="2650439969-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="9654301007-12">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9654301007-13">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9654301007-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9654301007-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9654301007-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9654301007-15">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="9654301007-15">}</span><span class="p" data-group-id="9654301007-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="9654301007-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9654301007-17">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9654301007-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9654301007-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="2650439969-12">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2650439969-13">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2650439969-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2650439969-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2650439969-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2650439969-15">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="2650439969-15">}</span><span class="p" data-group-id="2650439969-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="2650439969-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2650439969-17">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2650439969-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2650439969-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9654301007-18">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="9654301007-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9654301007-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="9654301007-20">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9654301007-20">)</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="9654301007-21">[</span><span class="p" data-group-id="9654301007-22">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="9654301007-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9654301007-23">}</span><span class="p" data-group-id="9654301007-22">}</span><span class="p" data-group-id="9654301007-21">]</span><span class="p" data-group-id="9654301007-19">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9654301007-24">#{</span><span class="p" data-group-id="9654301007-24">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2650439969-18">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="2650439969-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2650439969-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="2650439969-20">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2650439969-20">)</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="2650439969-21">[</span><span class="p" data-group-id="2650439969-22">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="2650439969-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2650439969-23">}</span><span class="p" data-group-id="2650439969-22">}</span><span class="p" data-group-id="2650439969-21">]</span><span class="p" data-group-id="2650439969-19">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2650439969-24">#{</span><span class="p" data-group-id="2650439969-24">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="9654301007-25">(</span><span class="p" data-group-id="9654301007-26">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="9654301007-26">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9654301007-27">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="9654301007-27">}</span><span class="p" data-group-id="9654301007-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9654301007-28">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="9654301007-29">[</span><span class="p" data-group-id="9654301007-30">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="9654301007-31">(</span><span class="n">Code</span><span class="p" data-group-id="9654301007-31">)</span><span class="p" data-group-id="9654301007-30">}</span><span class="p" data-group-id="9654301007-29">]</span><span class="p" data-group-id="9654301007-28">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="3658995796-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3658995796-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="3658995796-2">(</span><span class="p" data-group-id="3658995796-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3658995796-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3658995796-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3658995796-5">[</span><span class="p" data-group-id="3658995796-5">]</span><span class="p" data-group-id="3658995796-4">}</span><span class="p" data-group-id="3658995796-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="3658995796-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3658995796-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3658995796-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3658995796-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3658995796-9">[</span><span class="p" data-group-id="3658995796-9">]</span><span class="p" data-group-id="3658995796-8">}</span><span class="p" data-group-id="3658995796-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="3658995796-10">(</span><span class="w">
│ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3658995796-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3658995796-11">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="3658995796-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="3658995796-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3658995796-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="2650439969-25">(</span><span class="p" data-group-id="2650439969-26">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="2650439969-26">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2650439969-27">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="2650439969-27">}</span><span class="p" data-group-id="2650439969-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2650439969-28">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="2650439969-29">[</span><span class="p" data-group-id="2650439969-30">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="2650439969-31">(</span><span class="n">Code</span><span class="p" data-group-id="2650439969-31">)</span><span class="p" data-group-id="2650439969-30">}</span><span class="p" data-group-id="2650439969-29">]</span><span class="p" data-group-id="2650439969-28">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="0541184175-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0541184175-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="0541184175-2">(</span><span class="p" data-group-id="0541184175-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0541184175-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0541184175-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="0541184175-5">[</span><span class="p" data-group-id="0541184175-5">]</span><span class="p" data-group-id="0541184175-4">}</span><span class="p" data-group-id="0541184175-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="0541184175-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0541184175-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0541184175-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0541184175-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="0541184175-9">[</span><span class="p" data-group-id="0541184175-9">]</span><span class="p" data-group-id="0541184175-8">}</span><span class="p" data-group-id="0541184175-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="0541184175-10">(</span><span class="w">
│ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0541184175-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0541184175-11">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="0541184175-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="0541184175-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0541184175-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │          </span><span class="k">if</span><span class="w">
│ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="3658995796-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="3658995796-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="0541184175-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="0541184175-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="3658995796-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="3658995796-14">)</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="3658995796-15">[</span><span class="n">Button</span><span class="p" data-group-id="3658995796-15">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="0541184175-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="0541184175-14">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0541184175-15">[</span><span class="n">Button</span><span class="p" data-group-id="0541184175-15">]</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3658995796-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3658995796-16">}</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="0541184175-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0541184175-16">}</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3658995796-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3658995796-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="3658995796-18">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="3658995796-19">[</span><span class="p" data-group-id="3658995796-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="3658995796-20">}</span><span class="p" data-group-id="3658995796-19">]</span><span class="p" data-group-id="3658995796-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="0541184175-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0541184175-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="0541184175-18">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="0541184175-19">[</span><span class="p" data-group-id="0541184175-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="0541184175-20">}</span><span class="p" data-group-id="0541184175-19">]</span><span class="p" data-group-id="0541184175-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="8937953535-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="8937953535-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="8937953535-2">(</span><span class="p" data-group-id="8937953535-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8937953535-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="8937953535-4">[</span><span class="p" data-group-id="8937953535-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8937953535-5">}</span><span class="p" data-group-id="8937953535-4">]</span><span class="p" data-group-id="8937953535-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8937953535-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8937953535-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8937953535-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8937953535-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8937953535-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8937953535-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8937953535-9">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="8937953535-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8937953535-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8937953535-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="8937953535-11">]</span><span class="p" data-group-id="8937953535-10">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="2007862914-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2007862914-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="2007862914-2">(</span><span class="p" data-group-id="2007862914-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2007862914-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="2007862914-4">[</span><span class="p" data-group-id="2007862914-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="2007862914-5">}</span><span class="p" data-group-id="2007862914-4">]</span><span class="p" data-group-id="2007862914-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="2007862914-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2007862914-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2007862914-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2007862914-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="2007862914-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2007862914-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2007862914-9">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2007862914-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2007862914-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2007862914-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="2007862914-11">]</span><span class="p" data-group-id="2007862914-10">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">do_lock</span><span class="p" data-group-id="8937953535-12">(</span><span class="p" data-group-id="8937953535-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8937953535-13">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8937953535-14">[</span><span class="p" data-group-id="8937953535-14">]</span><span class="p" data-group-id="8937953535-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="8937953535-15">(</span><span class="p" data-group-id="8937953535-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8937953535-16">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8937953535-17">[</span><span class="p" data-group-id="8937953535-17">]</span><span class="p" data-group-id="8937953535-16">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">do_lock</span><span class="p" data-group-id="2007862914-12">(</span><span class="p" data-group-id="2007862914-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2007862914-13">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2007862914-14">[</span><span class="p" data-group-id="2007862914-14">]</span><span class="p" data-group-id="2007862914-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="2007862914-15">(</span><span class="p" data-group-id="2007862914-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2007862914-16">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2007862914-17">[</span><span class="p" data-group-id="2007862914-17">]</span><span class="p" data-group-id="2007862914-16">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="8937953535-18">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="8937953535-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="8937953535-19">(</span><span class="p" data-group-id="8937953535-19">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="2007862914-18">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2007862914-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="2007862914-19">(</span><span class="p" data-group-id="2007862914-19">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="callback-mode-handle_event_function" class="section-heading">
│ │ │    <a href="#callback-mode-handle_event_function" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Callback Mode: handle_event_function</span>
│ │ │  </h3>
│ │ │  <p>This section describes what to change in the example to use one
│ │ │  <code class="inline">handle_event/4</code> function.  The previously used approach to first branch
│ │ │  depending on event does not work that well here because of
│ │ │ -the <em>state enter calls</em>, so this example first branches depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7536547561-1">(</span><span class="p" data-group-id="7536547561-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="7536547561-2">]</span><span class="p" data-group-id="7536547561-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="2032882576-1">(</span><span class="p" data-group-id="2032882576-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2032882576-2">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="2032882576-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ +the <em>state enter calls</em>, so this example first branches depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8761883100-1">(</span><span class="p" data-group-id="8761883100-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="8761883100-2">]</span><span class="p" data-group-id="8761883100-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="6736910360-1">(</span><span class="p" data-group-id="6736910360-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6736910360-2">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="6736910360-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% State: locked</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9470719939-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9470719939-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="9470719939-2">(</span><span class="p" data-group-id="9470719939-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9470719939-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9470719939-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9470719939-5">[</span><span class="p" data-group-id="9470719939-5">]</span><span class="p" data-group-id="9470719939-4">}</span><span class="p" data-group-id="9470719939-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9470719939-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9470719939-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9470719939-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9470719939-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9470719939-9">[</span><span class="p" data-group-id="9470719939-9">]</span><span class="p" data-group-id="9470719939-8">}</span><span class="p" data-group-id="9470719939-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9470719939-10">(</span><span class="w">
│ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9470719939-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9470719939-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9470719939-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9470719939-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9470719939-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3843744745-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3843744745-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="3843744745-2">(</span><span class="p" data-group-id="3843744745-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3843744745-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3843744745-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3843744745-5">[</span><span class="p" data-group-id="3843744745-5">]</span><span class="p" data-group-id="3843744745-4">}</span><span class="p" data-group-id="3843744745-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3843744745-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3843744745-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3843744745-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3843744745-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3843744745-9">[</span><span class="p" data-group-id="3843744745-9">]</span><span class="p" data-group-id="3843744745-8">}</span><span class="p" data-group-id="3843744745-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3843744745-10">(</span><span class="w">
│ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3843744745-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3843744745-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3843744745-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="3843744745-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3843744745-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │          </span><span class="k">if</span><span class="w">
│ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="9470719939-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="9470719939-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="3843744745-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="3843744745-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="9470719939-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="9470719939-14">)</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9470719939-15">[</span><span class="n">Button</span><span class="p" data-group-id="9470719939-15">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="3843744745-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="3843744745-14">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="3843744745-15">[</span><span class="n">Button</span><span class="p" data-group-id="3843744745-15">]</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9470719939-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9470719939-16">}</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="3843744745-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3843744745-16">}</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9470719939-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9470719939-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="9470719939-18">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="9470719939-19">[</span><span class="p" data-group-id="9470719939-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="9470719939-20">}</span><span class="p" data-group-id="9470719939-19">]</span><span class="p" data-group-id="9470719939-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="3843744745-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3843744745-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="3843744745-18">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="3843744745-19">[</span><span class="p" data-group-id="3843744745-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="3843744745-20">}</span><span class="p" data-group-id="3843744745-19">]</span><span class="p" data-group-id="3843744745-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9083547839-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="9083547839-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="9083547839-2">(</span><span class="p" data-group-id="9083547839-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9083547839-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="9083547839-4">[</span><span class="p" data-group-id="9083547839-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="9083547839-5">}</span><span class="p" data-group-id="9083547839-4">]</span><span class="p" data-group-id="9083547839-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9083547839-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9083547839-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9083547839-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9083547839-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9083547839-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9083547839-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9083547839-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9083547839-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9083547839-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="9083547839-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="9083547839-11">]</span><span class="p" data-group-id="9083547839-10">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%% Common events</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="0006030824-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0006030824-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0006030824-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0006030824-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0006030824-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0006030824-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="0006030824-4">}</span><span class="p" data-group-id="0006030824-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="0006030824-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0006030824-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0006030824-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0006030824-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="4621476987-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="4621476987-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="4621476987-2">(</span><span class="p" data-group-id="4621476987-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4621476987-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="4621476987-4">[</span><span class="p" data-group-id="4621476987-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="4621476987-5">}</span><span class="p" data-group-id="4621476987-4">]</span><span class="p" data-group-id="4621476987-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="4621476987-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4621476987-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4621476987-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4621476987-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="4621476987-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4621476987-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4621476987-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="4621476987-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4621476987-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="4621476987-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="4621476987-11">]</span><span class="p" data-group-id="4621476987-10">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%% Common events</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="0870358043-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0870358043-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0870358043-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0870358043-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0870358043-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0870358043-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="0870358043-4">}</span><span class="p" data-group-id="0870358043-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="0870358043-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0870358043-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0870358043-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0870358043-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0006030824-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="0006030824-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="0006030824-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="0006030824-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0006030824-9">)</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="0006030824-10">[</span><span class="p" data-group-id="0006030824-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="0006030824-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0006030824-12">}</span><span class="p" data-group-id="0006030824-11">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="0006030824-13">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="0006030824-13">}</span><span class="p" data-group-id="0006030824-10">]</span><span class="p" data-group-id="0006030824-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0006030824-14">#{</span><span class="p" data-group-id="0006030824-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0870358043-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="0870358043-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="0870358043-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="0870358043-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0870358043-9">)</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="0870358043-10">[</span><span class="p" data-group-id="0870358043-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="0870358043-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0870358043-12">}</span><span class="p" data-group-id="0870358043-11">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="0870358043-13">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="0870358043-13">}</span><span class="p" data-group-id="0870358043-10">]</span><span class="p" data-group-id="0870358043-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0870358043-14">#{</span><span class="p" data-group-id="0870358043-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="0006030824-15">(</span><span class="p" data-group-id="0006030824-16">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="0006030824-16">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0006030824-17">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="0006030824-17">}</span><span class="p" data-group-id="0006030824-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0006030824-18">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="0006030824-19">[</span><span class="p" data-group-id="0006030824-20">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">Length</span><span class="p" data-group-id="0006030824-20">}</span><span class="p" data-group-id="0006030824-19">]</span><span class="p" data-group-id="0006030824-18">}</span><span class="p">.</span></code></pre><p>Notice that postponing buttons from the <code class="inline">open</code> state to the <code class="inline">locked</code> state
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="0870358043-15">(</span><span class="p" data-group-id="0870358043-16">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="0870358043-16">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0870358043-17">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="0870358043-17">}</span><span class="p" data-group-id="0870358043-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0870358043-18">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0870358043-19">[</span><span class="p" data-group-id="0870358043-20">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">Length</span><span class="p" data-group-id="0870358043-20">}</span><span class="p" data-group-id="0870358043-19">]</span><span class="p" data-group-id="0870358043-18">}</span><span class="p">.</span></code></pre><p>Notice that postponing buttons from the <code class="inline">open</code> state to the <code class="inline">locked</code> state
│ │ │  seems like a strange thing to do for a code lock, but it at least
│ │ │  illustrates event postponing.</p><h2 id="filter-the-state" class="section-heading">
│ │ │    <a href="#filter-the-state" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Filter the State</span>
│ │ │  </h2>
│ │ │ @@ -1286,30 +1286,30 @@
│ │ │  and which digits that remain to unlock.</p><p>This state data can be regarded as sensitive, and maybe not what you want
│ │ │  in the error log because of some unpredictable event.</p><p>Another reason to filter the state can be that the state is too large to print,
│ │ │  as it fills the error log with uninteresting details.</p><p>To avoid this, you can format the internal state that gets in the error log
│ │ │  and gets returned from <a href="../../lib/stdlib-6.2.2.1/doc/html/sys.html#get_status/1"><code class="inline">sys:get_status/1,2</code></a>
│ │ │  by implementing function
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#c:format_status/2"><code class="inline">Module:format_status/2</code></a>,
│ │ │  for example like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1495755670-1">(</span><span class="p" data-group-id="1495755670-2">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">format_status</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1495755670-2">]</span><span class="p" data-group-id="1495755670-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5494894636-1">(</span><span class="p" data-group-id="5494894636-2">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">format_status</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5494894636-2">]</span><span class="p" data-group-id="5494894636-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">format_status</span><span class="p" data-group-id="1495755670-3">(</span><span class="n">Opt</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1495755670-4">[</span><span class="p">_</span><span class="n">PDict</span><span class="p">,</span><span class="n">State</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="1495755670-4">]</span><span class="p" data-group-id="1495755670-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">format_status</span><span class="p" data-group-id="5494894636-3">(</span><span class="n">Opt</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5494894636-4">[</span><span class="p">_</span><span class="n">PDict</span><span class="p">,</span><span class="n">State</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="5494894636-4">]</span><span class="p" data-group-id="5494894636-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">StateData</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="1495755670-5">{</span><span class="n">State</span><span class="p">,</span><span class="w">
│ │ │ -	 </span><span class="nc">maps</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="1495755670-6">(</span><span class="w">
│ │ │ -	   </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1495755670-7">(</span><span class="ss">code</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1495755670-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="p">;</span><span class="w">
│ │ │ -	       </span><span class="p" data-group-id="1495755670-8">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1495755670-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="5494894636-5">{</span><span class="n">State</span><span class="p">,</span><span class="w">
│ │ │ +	 </span><span class="nc">maps</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="5494894636-6">(</span><span class="w">
│ │ │ +	   </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5494894636-7">(</span><span class="ss">code</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="5494894636-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="p">;</span><span class="w">
│ │ │ +	       </span><span class="p" data-group-id="5494894636-8">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="5494894636-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="w">
│ │ │  	   </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -	   </span><span class="n">Data</span><span class="p" data-group-id="1495755670-6">)</span><span class="p" data-group-id="1495755670-5">}</span><span class="p">,</span><span class="w">
│ │ │ +	   </span><span class="n">Data</span><span class="p" data-group-id="5494894636-6">)</span><span class="p" data-group-id="5494894636-5">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Opt</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │  	</span><span class="ss">terminate</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">StateData</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">normal</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="p" data-group-id="1495755670-9">[</span><span class="p" data-group-id="1495755670-10">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="1495755670-11">[</span><span class="p" data-group-id="1495755670-12">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="n">StateData</span><span class="p" data-group-id="1495755670-12">}</span><span class="p" data-group-id="1495755670-11">]</span><span class="p" data-group-id="1495755670-10">}</span><span class="p" data-group-id="1495755670-9">]</span><span class="w">
│ │ │ +	    </span><span class="p" data-group-id="5494894636-9">[</span><span class="p" data-group-id="5494894636-10">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="5494894636-11">[</span><span class="p" data-group-id="5494894636-12">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="n">StateData</span><span class="p" data-group-id="5494894636-12">}</span><span class="p" data-group-id="5494894636-11">]</span><span class="p" data-group-id="5494894636-10">}</span><span class="p" data-group-id="5494894636-9">]</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>It is not mandatory to implement a
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#c:format_status/2"><code class="inline">Module:format_status/2</code></a> function.
│ │ │  If you do not, a default implementation is used that does the same
│ │ │  as this example function without filtering the <code class="inline">Data</code> term, that is,
│ │ │  <code class="inline">StateData = {State, Data}</code>, in this example containing sensitive information.</p><h2 id="complex-state" class="section-heading">
│ │ │    <a href="#complex-state" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -1322,104 +1322,104 @@
│ │ │  like a tuple.</p><p>One reason to use this is when you have a state item that when changed
│ │ │  should cancel the <a href="#state-time-outs"><em>state time-out</em></a>, or one that affects
│ │ │  the event handling in combination with postponing events. We will go for
│ │ │  the latter and complicate the previous example by introducing
│ │ │  a configurable lock button (this is the state item in question),
│ │ │  which in the <code class="inline">open</code> state immediately locks the door, and an API function
│ │ │  <code class="inline">set_lock_button/1</code> to set the lock button.</p><p>Suppose now that we call <code class="inline">set_lock_button</code> while the door is open,
│ │ │ -and we have already postponed a button event that was the new lock button:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6574562205-1">(</span><span class="p" data-group-id="6574562205-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6574562205-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">x</span><span class="p" data-group-id="6574562205-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6574562205-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.666</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6574562205-3">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="6574562205-4">(</span><span class="ss">a</span><span class="p" data-group-id="6574562205-4">)</span><span class="p">.</span><span class="w">
│ │ │ +and we have already postponed a button event that was the new lock button:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1828074368-1">(</span><span class="p" data-group-id="1828074368-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1828074368-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">x</span><span class="p" data-group-id="1828074368-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1828074368-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.666</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="1828074368-3">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1828074368-4">(</span><span class="ss">a</span><span class="p" data-group-id="1828074368-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="6574562205-5">(</span><span class="ss">b</span><span class="p" data-group-id="6574562205-5">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1828074368-5">(</span><span class="ss">b</span><span class="p" data-group-id="1828074368-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="6574562205-6">(</span><span class="ss">c</span><span class="p" data-group-id="6574562205-6">)</span><span class="p">.</span><span class="w">
│ │ │ +4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1828074368-6">(</span><span class="ss">c</span><span class="p" data-group-id="1828074368-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="n">Open</span><span class="gp unselectable">
│ │ │ -5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="6574562205-7">(</span><span class="ss">y</span><span class="p" data-group-id="6574562205-7">)</span><span class="p">.</span><span class="w">
│ │ │ +5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1828074368-7">(</span><span class="ss">y</span><span class="p" data-group-id="1828074368-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">set_lock_button</span><span class="p" data-group-id="6574562205-8">(</span><span class="ss">y</span><span class="p" data-group-id="6574562205-8">)</span><span class="p">.</span><span class="w">
│ │ │ +6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">set_lock_button</span><span class="p" data-group-id="1828074368-8">(</span><span class="ss">y</span><span class="p" data-group-id="1828074368-8">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">x</span><span class="w">
│ │ │  </span><span class="c1">% What should happen here?  Immediate lock or nothing?</span></code></pre><p>We could say that the button was pressed too early so it should not be
│ │ │  recognized as the lock button. Or we can make the lock button part of
│ │ │  the state so when we then change the lock button in the locked state,
│ │ │  the change becomes a <em>state change</em> and all postponed events are retried,
│ │ │  therefore the lock is immediately locked!</p><p>We define the state as <code class="inline">{StateName, LockButton}</code>, where <code class="inline">StateName</code>
│ │ │ -is as before and <code class="inline">LockButton</code> is the current lock button:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6190870161-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="6190870161-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="6190870161-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="6190870161-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6190870161-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_3</span><span class="p" data-group-id="6190870161-3">)</span><span class="p">.</span><span class="w">
│ │ │ +is as before and <code class="inline">LockButton</code> is the current lock button:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7194590453-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="7194590453-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="7194590453-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="7194590453-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="7194590453-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_3</span><span class="p" data-group-id="7194590453-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6190870161-4">(</span><span class="p" data-group-id="6190870161-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6190870161-5">]</span><span class="p" data-group-id="6190870161-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6190870161-6">(</span><span class="p" data-group-id="6190870161-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">set_lock_button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6190870161-7">]</span><span class="p" data-group-id="6190870161-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6190870161-8">(</span><span class="p" data-group-id="6190870161-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="6190870161-9">]</span><span class="p" data-group-id="6190870161-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6190870161-10">(</span><span class="p" data-group-id="6190870161-11">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="6190870161-11">]</span><span class="p" data-group-id="6190870161-10">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="6190870161-12">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">LockButton</span><span class="p" data-group-id="6190870161-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6190870161-13">(</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6190870161-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="6190870161-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6190870161-15">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6190870161-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6190870161-16">[</span><span class="p" data-group-id="6190870161-16">]</span><span class="p" data-group-id="6190870161-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="6190870161-17">(</span><span class="p" data-group-id="6190870161-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="6190870161-18">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="6190870161-18">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="6190870161-19">(</span><span class="n">Button</span><span class="p" data-group-id="6190870161-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6190870161-20">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6190870161-21">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6190870161-21">}</span><span class="p" data-group-id="6190870161-20">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">set_lock_button</span><span class="p" data-group-id="6190870161-22">(</span><span class="n">LockButton</span><span class="p" data-group-id="6190870161-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="6190870161-23">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6190870161-24">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6190870161-24">}</span><span class="p" data-group-id="6190870161-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6847079376-1">(</span><span class="p" data-group-id="6847079376-2">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6847079376-2">}</span><span class="p" data-group-id="6847079376-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="6847079376-3">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6847079376-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6847079376-4">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="6847079376-5">(</span><span class="n">Code</span><span class="p" data-group-id="6847079376-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6847079376-6">[</span><span class="p" data-group-id="6847079376-6">]</span><span class="p" data-group-id="6847079376-4">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6847079376-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6847079376-8">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6847079376-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6847079376-7">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7194590453-4">(</span><span class="p" data-group-id="7194590453-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7194590453-5">]</span><span class="p" data-group-id="7194590453-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7194590453-6">(</span><span class="p" data-group-id="7194590453-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">set_lock_button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7194590453-7">]</span><span class="p" data-group-id="7194590453-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7194590453-8">(</span><span class="p" data-group-id="7194590453-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="7194590453-9">]</span><span class="p" data-group-id="7194590453-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7194590453-10">(</span><span class="p" data-group-id="7194590453-11">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="7194590453-11">]</span><span class="p" data-group-id="7194590453-10">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="7194590453-12">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">LockButton</span><span class="p" data-group-id="7194590453-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="7194590453-13">(</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7194590453-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="7194590453-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7194590453-15">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="7194590453-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7194590453-16">[</span><span class="p" data-group-id="7194590453-16">]</span><span class="p" data-group-id="7194590453-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="7194590453-17">(</span><span class="p" data-group-id="7194590453-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="7194590453-18">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="7194590453-18">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="7194590453-19">(</span><span class="n">Button</span><span class="p" data-group-id="7194590453-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="7194590453-20">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7194590453-21">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7194590453-21">}</span><span class="p" data-group-id="7194590453-20">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">set_lock_button</span><span class="p" data-group-id="7194590453-22">(</span><span class="n">LockButton</span><span class="p" data-group-id="7194590453-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="7194590453-23">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7194590453-24">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="7194590453-24">}</span><span class="p" data-group-id="7194590453-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1204635741-1">(</span><span class="p" data-group-id="1204635741-2">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1204635741-2">}</span><span class="p" data-group-id="1204635741-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="1204635741-3">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1204635741-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1204635741-4">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="1204635741-5">(</span><span class="n">Code</span><span class="p" data-group-id="1204635741-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1204635741-6">[</span><span class="p" data-group-id="1204635741-6">]</span><span class="p" data-group-id="1204635741-4">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1204635741-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1204635741-8">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1204635741-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1204635741-7">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="6847079376-9">(</span><span class="p" data-group-id="6847079376-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6847079376-10">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="6847079376-10">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="1204635741-9">(</span><span class="p" data-group-id="1204635741-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1204635741-10">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="1204635741-10">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% State: locked</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="6847079376-11">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6847079376-12">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6847079376-12">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6847079376-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="6847079376-13">(</span><span class="p" data-group-id="6847079376-13">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6847079376-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6847079376-15">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="6847079376-16">[</span><span class="p" data-group-id="6847079376-16">]</span><span class="p" data-group-id="6847079376-15">}</span><span class="p" data-group-id="6847079376-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="6847079376-17">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6847079376-18">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6847079376-18">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6847079376-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6847079376-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6847079376-20">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="6847079376-21">[</span><span class="p" data-group-id="6847079376-21">]</span><span class="p" data-group-id="6847079376-20">}</span><span class="p" data-group-id="6847079376-19">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="6847079376-22">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6847079376-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6847079376-23">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6847079376-24">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6847079376-24">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6847079376-25">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="6847079376-25">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6847079376-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="1204635741-11">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1204635741-12">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1204635741-12">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1204635741-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="1204635741-13">(</span><span class="p" data-group-id="1204635741-13">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1204635741-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1204635741-15">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1204635741-16">[</span><span class="p" data-group-id="1204635741-16">]</span><span class="p" data-group-id="1204635741-15">}</span><span class="p" data-group-id="1204635741-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="1204635741-17">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1204635741-18">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1204635741-18">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1204635741-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1204635741-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1204635741-20">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1204635741-21">[</span><span class="p" data-group-id="1204635741-21">]</span><span class="p" data-group-id="1204635741-20">}</span><span class="p" data-group-id="1204635741-19">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="1204635741-22">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1204635741-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1204635741-23">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1204635741-24">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1204635741-24">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1204635741-25">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="1204635741-25">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1204635741-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │          </span><span class="k">if</span><span class="w">
│ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="6847079376-26">(</span><span class="n">Buttons</span><span class="p" data-group-id="6847079376-26">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="1204635741-26">(</span><span class="n">Buttons</span><span class="p" data-group-id="1204635741-26">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="6847079376-27">(</span><span class="n">Buttons</span><span class="p" data-group-id="6847079376-27">)</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6847079376-28">[</span><span class="n">Button</span><span class="p" data-group-id="6847079376-28">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="1204635741-27">(</span><span class="n">Buttons</span><span class="p" data-group-id="1204635741-27">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1204635741-28">[</span><span class="n">Button</span><span class="p" data-group-id="1204635741-28">]</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="6847079376-29">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6847079376-30">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6847079376-30">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6847079376-29">}</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="1204635741-29">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1204635741-30">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1204635741-30">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1204635741-29">}</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="6847079376-31">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6847079376-32">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="6847079376-32">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="6847079376-33">[</span><span class="p" data-group-id="6847079376-34">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="6847079376-34">}</span><span class="p" data-group-id="6847079376-33">]</span><span class="p" data-group-id="6847079376-31">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="1204635741-31">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1204635741-32">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="1204635741-32">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="1204635741-33">[</span><span class="p" data-group-id="1204635741-34">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="1204635741-34">}</span><span class="p" data-group-id="1204635741-33">]</span><span class="p" data-group-id="1204635741-31">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1510847735-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1510847735-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1510847735-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="1510847735-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="1510847735-3">(</span><span class="p" data-group-id="1510847735-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1510847735-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="1510847735-5">[</span><span class="p" data-group-id="1510847735-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="1510847735-6">}</span><span class="p" data-group-id="1510847735-5">]</span><span class="p" data-group-id="1510847735-4">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1510847735-7">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1510847735-8">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1510847735-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1510847735-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1510847735-9">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1510847735-10">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1510847735-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1510847735-9">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1510847735-11">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1510847735-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1510847735-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1510847735-13">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1510847735-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1510847735-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1510847735-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1510847735-15">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1510847735-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1510847735-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1510847735-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1510847735-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1510847735-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1510847735-18">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1510847735-18">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="1510847735-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1510847735-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="1510847735-20">[</span><span class="ss">postpone</span><span class="p" data-group-id="1510847735-20">]</span><span class="p" data-group-id="1510847735-19">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2172056899-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2172056899-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2172056899-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2172056899-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="2172056899-3">(</span><span class="p" data-group-id="2172056899-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2172056899-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="2172056899-5">[</span><span class="p" data-group-id="2172056899-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="2172056899-6">}</span><span class="p" data-group-id="2172056899-5">]</span><span class="p" data-group-id="2172056899-4">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2172056899-7">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2172056899-8">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2172056899-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2172056899-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2172056899-9">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2172056899-10">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2172056899-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2172056899-9">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2172056899-11">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2172056899-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2172056899-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2172056899-13">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2172056899-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2172056899-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2172056899-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2172056899-15">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2172056899-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2172056899-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2172056899-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2172056899-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2172056899-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2172056899-18">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2172056899-18">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2172056899-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2172056899-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="2172056899-20">[</span><span class="ss">postpone</span><span class="p" data-group-id="2172056899-20">]</span><span class="p" data-group-id="2172056899-19">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% Common events</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4990956895-1">(</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4990956895-2">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="4990956895-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990956895-3">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="4990956895-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4990956895-4">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="4990956895-4">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4990956895-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4990956895-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990956895-6">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="4990956895-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="4990956895-7">[</span><span class="p" data-group-id="4990956895-8">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="4990956895-8">}</span><span class="p" data-group-id="4990956895-7">]</span><span class="p" data-group-id="4990956895-5">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="8425361347-1">(</span><span class="p" data-group-id="8425361347-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8425361347-2">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8425361347-3">[</span><span class="p" data-group-id="8425361347-3">]</span><span class="p" data-group-id="8425361347-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="8425361347-4">(</span><span class="p" data-group-id="8425361347-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8425361347-5">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8425361347-6">[</span><span class="p" data-group-id="8425361347-6">]</span><span class="p" data-group-id="8425361347-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="9428593517-1">(</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9428593517-2">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="9428593517-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9428593517-3">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="9428593517-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9428593517-4">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="9428593517-4">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9428593517-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9428593517-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9428593517-6">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="9428593517-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="9428593517-7">[</span><span class="p" data-group-id="9428593517-8">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="9428593517-8">}</span><span class="p" data-group-id="9428593517-7">]</span><span class="p" data-group-id="9428593517-5">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="7579116487-1">(</span><span class="p" data-group-id="7579116487-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7579116487-2">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7579116487-3">[</span><span class="p" data-group-id="7579116487-3">]</span><span class="p" data-group-id="7579116487-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="7579116487-4">(</span><span class="p" data-group-id="7579116487-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7579116487-5">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7579116487-6">[</span><span class="p" data-group-id="7579116487-6">]</span><span class="p" data-group-id="7579116487-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="8425361347-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="8425361347-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="8425361347-8">(</span><span class="p" data-group-id="8425361347-8">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="7579116487-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="7579116487-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="7579116487-8">(</span><span class="p" data-group-id="7579116487-8">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h2 id="hibernation" class="section-heading">
│ │ │    <a href="#hibernation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Hibernation</span>
│ │ │  </h2>
│ │ │  <p>If you have many servers in one node and they have some state(s) in their
│ │ │ @@ -1428,19 +1428,19 @@
│ │ │  footprint of a server can be minimized by hibernating it through
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/proc_lib.html#hibernate/3"><code class="inline">proc_lib:hibernate/3</code></a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>It is rather costly to hibernate a process; see <a href="../../erts-15.2.7/doc/html/erlang.html#hibernate/3"><code class="inline">erlang:hibernate/3</code></a>. It is
│ │ │  not something you want to do after every event.</p></section><p>We can in this example hibernate in the <code class="inline">{open, _}</code> state,
│ │ │  because what normally occurs in that state is that the <em>state time-out</em>
│ │ │  after a while triggers a transition to <code class="inline">{locked, _}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5581829120-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5581829120-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5581829120-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="5581829120-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="5581829120-3">(</span><span class="p" data-group-id="5581829120-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5581829120-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="5581829120-5">[</span><span class="p" data-group-id="5581829120-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="5581829120-6">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -      </span><span class="ss">hibernate</span><span class="p" data-group-id="5581829120-5">]</span><span class="p" data-group-id="5581829120-4">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="8359332953-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8359332953-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8359332953-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="8359332953-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="8359332953-3">(</span><span class="p" data-group-id="8359332953-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8359332953-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="8359332953-5">[</span><span class="p" data-group-id="8359332953-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8359332953-6">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +      </span><span class="ss">hibernate</span><span class="p" data-group-id="8359332953-5">]</span><span class="p" data-group-id="8359332953-4">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The atom <a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#t:hibernate/0"><code class="inline">hibernate</code></a> in the action list on the
│ │ │  last line when entering the <code class="inline">{open, _}</code> state is the only change. If any event
│ │ │  arrives in the <code class="inline">{open, _},</code> state, we do not bother to rehibernate,
│ │ │  so the server stays awake after any event.</p><p>To change that we would need to insert action <code class="inline">hibernate</code> in more places.
│ │ │  For example, the state-independent <code class="inline">set_lock_button</code> operation
│ │ │  would have to use <code class="inline">hibernate</code> but only in the <code class="inline">{open, _}</code> state,
│ │ │  which would clutter the code.</p><p>Another not uncommon scenario is to use the
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/sup_princ.html
│ │ │ @@ -128,48 +128,48 @@
│ │ │  the order specified by this list, and are terminated in the reverse order.</p><h2 id="example" class="section-heading">
│ │ │    <a href="#example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example</span>
│ │ │  </h2>
│ │ │  <p>The callback module for a supervisor starting the server from
│ │ │ -<a href="gen_server_concepts.html#ex">gen_server Behaviour</a> can look as follows:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8078176245-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="8078176245-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8078176245-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="8078176245-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="gen_server_concepts.html#ex">gen_server Behaviour</a> can look as follows:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2123826097-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="2123826097-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="2123826097-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="2123826097-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8078176245-3">(</span><span class="p" data-group-id="8078176245-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8078176245-4">]</span><span class="p" data-group-id="8078176245-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8078176245-5">(</span><span class="p" data-group-id="8078176245-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8078176245-6">]</span><span class="p" data-group-id="8078176245-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2123826097-3">(</span><span class="p" data-group-id="2123826097-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2123826097-4">]</span><span class="p" data-group-id="2123826097-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2123826097-5">(</span><span class="p" data-group-id="2123826097-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2123826097-6">]</span><span class="p" data-group-id="2123826097-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="8078176245-7">(</span><span class="p" data-group-id="8078176245-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8078176245-8">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8078176245-9">[</span><span class="p" data-group-id="8078176245-9">]</span><span class="p" data-group-id="8078176245-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="2123826097-7">(</span><span class="p" data-group-id="2123826097-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2123826097-8">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2123826097-9">[</span><span class="p" data-group-id="2123826097-9">]</span><span class="p" data-group-id="2123826097-8">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8078176245-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="8078176245-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8078176245-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_one</span><span class="p">,</span><span class="w"> </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="8078176245-11">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8078176245-12">[</span><span class="p" data-group-id="8078176245-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8078176245-14">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8078176245-15">[</span><span class="p" data-group-id="8078176245-15">]</span><span class="p" data-group-id="8078176245-14">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="2123826097-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="2123826097-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2123826097-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_one</span><span class="p">,</span><span class="w"> </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="2123826097-11">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2123826097-12">[</span><span class="p" data-group-id="2123826097-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2123826097-14">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2123826097-15">[</span><span class="p" data-group-id="2123826097-15">]</span><span class="p" data-group-id="2123826097-14">}</span><span class="p">,</span><span class="w">
│ │ │                      </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">permanent</span><span class="p">,</span><span class="w">
│ │ │                      </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w">
│ │ │                      </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8078176245-16">[</span><span class="ss">ch3</span><span class="p" data-group-id="8078176245-16">]</span><span class="p" data-group-id="8078176245-13">}</span><span class="p" data-group-id="8078176245-12">]</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8078176245-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8078176245-18">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="8078176245-18">}</span><span class="p" data-group-id="8078176245-17">}</span><span class="p">.</span></code></pre><p>The <code class="inline">SupFlags</code> variable in the return value from <code class="inline">init/1</code> represents the
│ │ │ +                    </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2123826097-16">[</span><span class="ss">ch3</span><span class="p" data-group-id="2123826097-16">]</span><span class="p" data-group-id="2123826097-13">}</span><span class="p" data-group-id="2123826097-12">]</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2123826097-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2123826097-18">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="2123826097-18">}</span><span class="p" data-group-id="2123826097-17">}</span><span class="p">.</span></code></pre><p>The <code class="inline">SupFlags</code> variable in the return value from <code class="inline">init/1</code> represents the
│ │ │  <a href="sup_princ.html#flags">supervisor flags</a>.</p><p>The <code class="inline">ChildSpecs</code> variable in the return value from <code class="inline">init/1</code> is a list of
│ │ │  <a href="sup_princ.html#spec">child specifications</a>.</p><p><a href="" id="flags"></a></p><h2 id="supervisor-flags" class="section-heading">
│ │ │    <a href="#supervisor-flags" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Supervisor Flags</span>
│ │ │  </h2>
│ │ │ -<p>This is the type definition for the supervisor flags:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sup_flags</span><span class="p" data-group-id="3485518225-1">(</span><span class="p" data-group-id="3485518225-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3485518225-2">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">strategy</span><span class="p" data-group-id="3485518225-3">(</span><span class="p" data-group-id="3485518225-3">)</span><span class="p">,</span><span class="w">           </span><span class="c1">% optional</span><span class="w">
│ │ │ -                </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="3485518225-4">(</span><span class="p" data-group-id="3485518225-4">)</span><span class="p">,</span><span class="w">   </span><span class="c1">% optional</span><span class="w">
│ │ │ -                </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="3485518225-5">(</span><span class="p" data-group-id="3485518225-5">)</span><span class="p">,</span><span class="w">          </span><span class="c1">% optional</span><span class="w">
│ │ │ -                </span><span class="ss">auto_shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="3485518225-6">(</span><span class="p" data-group-id="3485518225-6">)</span><span class="p" data-group-id="3485518225-2">}</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ -    </span><span class="nf">strategy</span><span class="p" data-group-id="3485518225-7">(</span><span class="p" data-group-id="3485518225-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">one_for_all</span><span class="w">
│ │ │ +<p>This is the type definition for the supervisor flags:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sup_flags</span><span class="p" data-group-id="7979184792-1">(</span><span class="p" data-group-id="7979184792-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7979184792-2">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">strategy</span><span class="p" data-group-id="7979184792-3">(</span><span class="p" data-group-id="7979184792-3">)</span><span class="p">,</span><span class="w">           </span><span class="c1">% optional</span><span class="w">
│ │ │ +                </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="7979184792-4">(</span><span class="p" data-group-id="7979184792-4">)</span><span class="p">,</span><span class="w">   </span><span class="c1">% optional</span><span class="w">
│ │ │ +                </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="7979184792-5">(</span><span class="p" data-group-id="7979184792-5">)</span><span class="p">,</span><span class="w">          </span><span class="c1">% optional</span><span class="w">
│ │ │ +                </span><span class="ss">auto_shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="7979184792-6">(</span><span class="p" data-group-id="7979184792-6">)</span><span class="p" data-group-id="7979184792-2">}</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ +    </span><span class="nf">strategy</span><span class="p" data-group-id="7979184792-7">(</span><span class="p" data-group-id="7979184792-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">one_for_all</span><span class="w">
│ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">one_for_one</span><span class="w">
│ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">rest_for_one</span><span class="w">
│ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="w">
│ │ │ -    </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="3485518225-8">(</span><span class="p" data-group-id="3485518225-8">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">never</span><span class="w">
│ │ │ +    </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="7979184792-8">(</span><span class="p" data-group-id="7979184792-8">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">never</span><span class="w">
│ │ │                      </span><span class="p">|</span><span class="w"> </span><span class="ss">any_significant</span><span class="w">
│ │ │                      </span><span class="p">|</span><span class="w"> </span><span class="ss">all_significant</span></code></pre><ul><li><code class="inline">strategy</code> specifies the <a href="sup_princ.html#strategy">restart strategy</a>.</li><li><code class="inline">intensity</code> and <code class="inline">period</code> specify the
│ │ │  <a href="sup_princ.html#max_intensity">maximum restart intensity</a>.</li><li><code class="inline">auto_shutdown</code> specifies whether and when a supervisor should
│ │ │  <a href="sup_princ.html#automatic-shutdown">automatically shut itself down</a>.</li></ul><p><a href="" id="strategy"></a></p><h2 id="restart-strategy" class="section-heading">
│ │ │    <a href="#restart-strategy" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -408,28 +408,28 @@
│ │ │  exhaust the <a href="sup_princ.html#max_intensity">Maximum Restart Intensity</a> of the
│ │ │  parent supervisor.</p></section><p><a href="" id="spec"></a></p><h2 id="child-specification" class="section-heading">
│ │ │    <a href="#child-specification" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Child Specification</span>
│ │ │  </h2>
│ │ │ -<p>The type definition for a child specification is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">child_spec</span><span class="p" data-group-id="7356481453-1">(</span><span class="p" data-group-id="7356481453-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7356481453-2">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">child_id</span><span class="p" data-group-id="7356481453-3">(</span><span class="p" data-group-id="7356481453-3">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% mandatory</span><span class="w">
│ │ │ -                 </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">mfargs</span><span class="p" data-group-id="7356481453-4">(</span><span class="p" data-group-id="7356481453-4">)</span><span class="p">,</span><span class="w">            </span><span class="c1">% mandatory</span><span class="w">
│ │ │ -                 </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">restart</span><span class="p" data-group-id="7356481453-5">(</span><span class="p" data-group-id="7356481453-5">)</span><span class="p">,</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ -                 </span><span class="ss">significant</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">significant</span><span class="p" data-group-id="7356481453-6">(</span><span class="p" data-group-id="7356481453-6">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ -                 </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">shutdown</span><span class="p" data-group-id="7356481453-7">(</span><span class="p" data-group-id="7356481453-7">)</span><span class="p">,</span><span class="w">       </span><span class="c1">% optional</span><span class="w">
│ │ │ -                 </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">worker</span><span class="p" data-group-id="7356481453-8">(</span><span class="p" data-group-id="7356481453-8">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% optional</span><span class="w">
│ │ │ -                 </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">modules</span><span class="p" data-group-id="7356481453-9">(</span><span class="p" data-group-id="7356481453-9">)</span><span class="p" data-group-id="7356481453-2">}</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ -    </span><span class="nf">child_id</span><span class="p" data-group-id="7356481453-10">(</span><span class="p" data-group-id="7356481453-10">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7356481453-11">(</span><span class="p" data-group-id="7356481453-11">)</span><span class="w">
│ │ │ -    </span><span class="nf">mfargs</span><span class="p" data-group-id="7356481453-12">(</span><span class="p" data-group-id="7356481453-12">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7356481453-13">{</span><span class="n">M</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">module</span><span class="p" data-group-id="7356481453-14">(</span><span class="p" data-group-id="7356481453-14">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="7356481453-15">(</span><span class="p" data-group-id="7356481453-15">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="7356481453-16">[</span><span class="nf">term</span><span class="p" data-group-id="7356481453-17">(</span><span class="p" data-group-id="7356481453-17">)</span><span class="p" data-group-id="7356481453-16">]</span><span class="p" data-group-id="7356481453-13">}</span><span class="w">
│ │ │ -    </span><span class="nf">modules</span><span class="p" data-group-id="7356481453-18">(</span><span class="p" data-group-id="7356481453-18">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7356481453-19">[</span><span class="nf">module</span><span class="p" data-group-id="7356481453-20">(</span><span class="p" data-group-id="7356481453-20">)</span><span class="p" data-group-id="7356481453-19">]</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">dynamic</span><span class="w">
│ │ │ -    </span><span class="nf">restart</span><span class="p" data-group-id="7356481453-21">(</span><span class="p" data-group-id="7356481453-21">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">permanent</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">transient</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">temporary</span><span class="w">
│ │ │ -    </span><span class="nf">significant</span><span class="p" data-group-id="7356481453-22">(</span><span class="p" data-group-id="7356481453-22">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="7356481453-23">(</span><span class="p" data-group-id="7356481453-23">)</span><span class="w">
│ │ │ -    </span><span class="nf">shutdown</span><span class="p" data-group-id="7356481453-24">(</span><span class="p" data-group-id="7356481453-24">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">timeout</span><span class="p" data-group-id="7356481453-25">(</span><span class="p" data-group-id="7356481453-25">)</span><span class="w">
│ │ │ -    </span><span class="nf">worker</span><span class="p" data-group-id="7356481453-26">(</span><span class="p" data-group-id="7356481453-26">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">worker</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">supervisor</span></code></pre><ul><li><p><code class="inline">id</code> is used to identify the child specification internally by the supervisor.</p><p>The <code class="inline">id</code> key is mandatory.</p><p>Note that this identifier occasionally has been called &quot;name&quot;. As far as
│ │ │ +<p>The type definition for a child specification is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">child_spec</span><span class="p" data-group-id="1119867249-1">(</span><span class="p" data-group-id="1119867249-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1119867249-2">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">child_id</span><span class="p" data-group-id="1119867249-3">(</span><span class="p" data-group-id="1119867249-3">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% mandatory</span><span class="w">
│ │ │ +                 </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">mfargs</span><span class="p" data-group-id="1119867249-4">(</span><span class="p" data-group-id="1119867249-4">)</span><span class="p">,</span><span class="w">            </span><span class="c1">% mandatory</span><span class="w">
│ │ │ +                 </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">restart</span><span class="p" data-group-id="1119867249-5">(</span><span class="p" data-group-id="1119867249-5">)</span><span class="p">,</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ +                 </span><span class="ss">significant</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">significant</span><span class="p" data-group-id="1119867249-6">(</span><span class="p" data-group-id="1119867249-6">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ +                 </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">shutdown</span><span class="p" data-group-id="1119867249-7">(</span><span class="p" data-group-id="1119867249-7">)</span><span class="p">,</span><span class="w">       </span><span class="c1">% optional</span><span class="w">
│ │ │ +                 </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">worker</span><span class="p" data-group-id="1119867249-8">(</span><span class="p" data-group-id="1119867249-8">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% optional</span><span class="w">
│ │ │ +                 </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">modules</span><span class="p" data-group-id="1119867249-9">(</span><span class="p" data-group-id="1119867249-9">)</span><span class="p" data-group-id="1119867249-2">}</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ +    </span><span class="nf">child_id</span><span class="p" data-group-id="1119867249-10">(</span><span class="p" data-group-id="1119867249-10">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="1119867249-11">(</span><span class="p" data-group-id="1119867249-11">)</span><span class="w">
│ │ │ +    </span><span class="nf">mfargs</span><span class="p" data-group-id="1119867249-12">(</span><span class="p" data-group-id="1119867249-12">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1119867249-13">{</span><span class="n">M</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">module</span><span class="p" data-group-id="1119867249-14">(</span><span class="p" data-group-id="1119867249-14">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="1119867249-15">(</span><span class="p" data-group-id="1119867249-15">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1119867249-16">[</span><span class="nf">term</span><span class="p" data-group-id="1119867249-17">(</span><span class="p" data-group-id="1119867249-17">)</span><span class="p" data-group-id="1119867249-16">]</span><span class="p" data-group-id="1119867249-13">}</span><span class="w">
│ │ │ +    </span><span class="nf">modules</span><span class="p" data-group-id="1119867249-18">(</span><span class="p" data-group-id="1119867249-18">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1119867249-19">[</span><span class="nf">module</span><span class="p" data-group-id="1119867249-20">(</span><span class="p" data-group-id="1119867249-20">)</span><span class="p" data-group-id="1119867249-19">]</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">dynamic</span><span class="w">
│ │ │ +    </span><span class="nf">restart</span><span class="p" data-group-id="1119867249-21">(</span><span class="p" data-group-id="1119867249-21">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">permanent</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">transient</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">temporary</span><span class="w">
│ │ │ +    </span><span class="nf">significant</span><span class="p" data-group-id="1119867249-22">(</span><span class="p" data-group-id="1119867249-22">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="1119867249-23">(</span><span class="p" data-group-id="1119867249-23">)</span><span class="w">
│ │ │ +    </span><span class="nf">shutdown</span><span class="p" data-group-id="1119867249-24">(</span><span class="p" data-group-id="1119867249-24">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">timeout</span><span class="p" data-group-id="1119867249-25">(</span><span class="p" data-group-id="1119867249-25">)</span><span class="w">
│ │ │ +    </span><span class="nf">worker</span><span class="p" data-group-id="1119867249-26">(</span><span class="p" data-group-id="1119867249-26">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">worker</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">supervisor</span></code></pre><ul><li><p><code class="inline">id</code> is used to identify the child specification internally by the supervisor.</p><p>The <code class="inline">id</code> key is mandatory.</p><p>Note that this identifier occasionally has been called &quot;name&quot;. As far as
│ │ │  possible, the terms &quot;identifier&quot; or &quot;id&quot; are now used but in order to keep
│ │ │  backwards compatibility, some occurrences of &quot;name&quot; can still be found, for
│ │ │  example in error messages.</p></li><li><p><code class="inline">start</code> defines the function call used to start the child process. It is a
│ │ │  module-function-arguments tuple used as <a href="../../erts-15.2.7/doc/html/erlang.html#apply/3"><code class="inline">apply(M, F, A)</code></a>.</p><p>It is to be (or result in) a call to any of the following:</p><ul><li><a href="../../lib/stdlib-6.2.2.1/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link/2,3</code></a></li><li><a href="../../lib/stdlib-6.2.2.1/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/3,4</code></a></li><li><a href="../../lib/stdlib-6.2.2.1/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/3,4</code></a></li><li><a href="../../lib/stdlib-6.2.2.1/doc/html/gen_event.html#start_link/2"><code class="inline">gen_event:start_link/0,1,2</code></a></li><li>A function compliant with these functions. For details, see
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/supervisor.html"><code class="inline">supervisor</code></a>.</li></ul><p>The <code class="inline">start</code> key is mandatory.</p></li><li><p><a href="" id="restart"></a> <code class="inline">restart</code> defines when a terminated child process is to be
│ │ │  restarted.</p><ul><li>A <code class="inline">permanent</code> child process is always restarted.</li><li>A <code class="inline">temporary</code> child process is never restarted (not even when the supervisor
│ │ │  restart strategy is <code class="inline">rest_for_one</code> or <code class="inline">one_for_all</code> and a sibling death
│ │ │ @@ -457,53 +457,53 @@
│ │ │  <code class="inline">supervisor</code>, the default value <code class="inline">infinity</code> will be used.</p></li><li><p><code class="inline">type</code> specifies whether the child process is a supervisor or a worker.</p><p>The <code class="inline">type</code> key is optional. If it is not given, the default value <code class="inline">worker</code>
│ │ │  will be used.</p></li><li><p><code class="inline">modules</code> has to be a list consisting of a single element. The value
│ │ │  of that element depends on the behaviour of the process:</p><ul><li>If the child process is a <code class="inline">gen_event</code>, the element has to be the atom
│ │ │  <code class="inline">dynamic</code>.</li><li>Otherwise, the element should be <code class="inline">Module</code>, where <code class="inline">Module</code> is the
│ │ │  name of the callback module.</li></ul><p>This information is used by the release handler during upgrades and
│ │ │  downgrades; see <a href="release_handling.html">Release Handling</a>.</p><p>The <code class="inline">modules</code> key is optional. If it is not given, it defaults to <code class="inline">[M]</code>, where
│ │ │  <code class="inline">M</code> comes from the child's start <code class="inline">{M,F,A}</code>.</p></li></ul><p><em>Example:</em> The child specification to start the server <code class="inline">ch3</code> in the previous
│ │ │ -example look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2018736246-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2018736246-2">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2018736246-3">[</span><span class="p" data-group-id="2018736246-3">]</span><span class="p" data-group-id="2018736246-2">}</span><span class="p">,</span><span class="w">
│ │ │ +example look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1953061421-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1953061421-2">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1953061421-3">[</span><span class="p" data-group-id="1953061421-3">]</span><span class="p" data-group-id="1953061421-2">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">permanent</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2018736246-4">[</span><span class="ss">ch3</span><span class="p" data-group-id="2018736246-4">]</span><span class="p" data-group-id="2018736246-1">}</span></code></pre><p>or simplified, relying on the default values:</p><pre><code class="text">#{id =&gt; ch3,
│ │ │ +  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1953061421-4">[</span><span class="ss">ch3</span><span class="p" data-group-id="1953061421-4">]</span><span class="p" data-group-id="1953061421-1">}</span></code></pre><p>or simplified, relying on the default values:</p><pre><code class="text">#{id =&gt; ch3,
│ │ │    start =&gt; {ch3, start_link, []},
│ │ │    shutdown =&gt; brutal_kill}</code></pre><p>Example: A child specification to start the event manager from the chapter about
│ │ │ -<a href="events.html#mgr">gen_event</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7725438806-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">error_man</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7725438806-2">{</span><span class="ss">gen_event</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7725438806-3">[</span><span class="p" data-group-id="7725438806-4">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="7725438806-4">}</span><span class="p" data-group-id="7725438806-3">]</span><span class="p" data-group-id="7725438806-2">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">dynamic</span><span class="p" data-group-id="7725438806-1">}</span></code></pre><p>Both server and event manager are registered processes which can be expected to
│ │ │ +<a href="events.html#mgr">gen_event</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7581264394-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">error_man</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7581264394-2">{</span><span class="ss">gen_event</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7581264394-3">[</span><span class="p" data-group-id="7581264394-4">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="7581264394-4">}</span><span class="p" data-group-id="7581264394-3">]</span><span class="p" data-group-id="7581264394-2">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">dynamic</span><span class="p" data-group-id="7581264394-1">}</span></code></pre><p>Both server and event manager are registered processes which can be expected to
│ │ │  be always accessible. Thus they are specified to be <code class="inline">permanent</code>.</p><p><code class="inline">ch3</code> does not need to do any cleaning up before termination. Thus, no shutdown
│ │ │  time is needed, but <code class="inline">brutal_kill</code> is sufficient. <code class="inline">error_man</code> can need some time
│ │ │  for the event handlers to clean up, thus the shutdown time is set to 5000 ms
│ │ │ -(which is the default value).</p><p>Example: A child specification to start another supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7749992753-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">sup</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7749992753-2">{</span><span class="ss">sup</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7749992753-3">[</span><span class="p" data-group-id="7749992753-3">]</span><span class="p" data-group-id="7749992753-2">}</span><span class="p">,</span><span class="w">
│ │ │ +(which is the default value).</p><p>Example: A child specification to start another supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5664700269-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">sup</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5664700269-2">{</span><span class="ss">sup</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5664700269-3">[</span><span class="p" data-group-id="5664700269-3">]</span><span class="p" data-group-id="5664700269-2">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">transient</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7749992753-1">}</span><span class="w"> </span><span class="c1">% will cause default shutdown=&gt;infinity</span></code></pre><p><a href="" id="super_tree"></a></p><h2 id="starting-a-supervisor" class="section-heading">
│ │ │ +  </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="5664700269-1">}</span><span class="w"> </span><span class="c1">% will cause default shutdown=&gt;infinity</span></code></pre><p><a href="" id="super_tree"></a></p><h2 id="starting-a-supervisor" class="section-heading">
│ │ │    <a href="#starting-a-supervisor" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting a Supervisor</span>
│ │ │  </h2>
│ │ │  <p>In the previous example, the supervisor is started by calling
│ │ │ -<code class="inline">ch_sup:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="1692576754-1">(</span><span class="p" data-group-id="1692576754-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1692576754-2">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1692576754-3">[</span><span class="p" data-group-id="1692576754-3">]</span><span class="p" data-group-id="1692576754-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch_sup:start_link</code> calls function <a href="../../lib/stdlib-6.2.2.1/doc/html/supervisor.html#start_link/2"><code class="inline">supervisor:start_link/2</code></a>, which spawns and
│ │ │ +<code class="inline">ch_sup:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="9286938166-1">(</span><span class="p" data-group-id="9286938166-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="9286938166-2">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9286938166-3">[</span><span class="p" data-group-id="9286938166-3">]</span><span class="p" data-group-id="9286938166-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch_sup:start_link</code> calls function <a href="../../lib/stdlib-6.2.2.1/doc/html/supervisor.html#start_link/2"><code class="inline">supervisor:start_link/2</code></a>, which spawns and
│ │ │  links to a new process, a supervisor.</p><ul><li>The first argument, <code class="inline">ch_sup</code>, is the name of the callback module, that is, the
│ │ │  module where the <code class="inline">init</code> callback function is located.</li><li>The second argument, <code class="inline">[]</code>, is a term that is passed as is to the callback
│ │ │  function <code class="inline">init</code>. Here, <code class="inline">init</code> does not need any data and ignores the argument.</li></ul><p>In this case, the supervisor is not registered. Instead its pid must be used. A
│ │ │  name can be specified by calling
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link({local, Name}, Module, Args)</code></a>
│ │ │  or
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link({global, Name}, Module, Args)</code></a>.</p><p>The new supervisor process calls the callback function <code class="inline">ch_sup:init([])</code>. <code class="inline">init</code>
│ │ │ -has to return <code class="inline">{ok, {SupFlags, ChildSpecs}}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4468558556-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="4468558556-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4468558556-2">#{</span><span class="p" data-group-id="4468558556-2">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4468558556-3">[</span><span class="p" data-group-id="4468558556-4">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4468558556-5">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4468558556-6">[</span><span class="p" data-group-id="4468558556-6">]</span><span class="p" data-group-id="4468558556-5">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="4468558556-4">}</span><span class="p" data-group-id="4468558556-3">]</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4468558556-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4468558556-8">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="4468558556-8">}</span><span class="p" data-group-id="4468558556-7">}</span><span class="p">.</span></code></pre><p>Subsequently, the supervisor starts its child processes according to the child
│ │ │ +has to return <code class="inline">{ok, {SupFlags, ChildSpecs}}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="3620058225-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="3620058225-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3620058225-2">#{</span><span class="p" data-group-id="3620058225-2">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3620058225-3">[</span><span class="p" data-group-id="3620058225-4">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3620058225-5">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3620058225-6">[</span><span class="p" data-group-id="3620058225-6">]</span><span class="p" data-group-id="3620058225-5">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="3620058225-4">}</span><span class="p" data-group-id="3620058225-3">]</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3620058225-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3620058225-8">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="3620058225-8">}</span><span class="p" data-group-id="3620058225-7">}</span><span class="p">.</span></code></pre><p>Subsequently, the supervisor starts its child processes according to the child
│ │ │  specifications in the start specification. In this case there is a single child
│ │ │  process, called <code class="inline">ch3</code>.</p><p><a href="../../lib/stdlib-6.2.2.1/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link/3</code></a> is synchronous. It does not return until all child
│ │ │  processes have been started.</p><h2 id="adding-a-child-process" class="section-heading">
│ │ │    <a href="#adding-a-child-process" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Adding a Child Process</span>
│ │ │ @@ -532,31 +532,31 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Simplified one_for_one Supervisors</span>
│ │ │  </h2>
│ │ │  <p>A supervisor with restart strategy <code class="inline">simple_one_for_one</code> is a simplified
│ │ │  <code class="inline">one_for_one</code> supervisor, where all child processes are dynamically added
│ │ │  instances of the same process.</p><p>The following is an example of a callback module for a <code class="inline">simple_one_for_one</code>
│ │ │ -supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1199927964-1">(</span><span class="ss">simple_sup</span><span class="p" data-group-id="1199927964-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1199927964-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="1199927964-2">)</span><span class="p">.</span><span class="w">
│ │ │ +supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8544608097-1">(</span><span class="ss">simple_sup</span><span class="p" data-group-id="8544608097-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8544608097-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="8544608097-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1199927964-3">(</span><span class="p" data-group-id="1199927964-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1199927964-4">]</span><span class="p" data-group-id="1199927964-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1199927964-5">(</span><span class="p" data-group-id="1199927964-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1199927964-6">]</span><span class="p" data-group-id="1199927964-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8544608097-3">(</span><span class="p" data-group-id="8544608097-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8544608097-4">]</span><span class="p" data-group-id="8544608097-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8544608097-5">(</span><span class="p" data-group-id="8544608097-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8544608097-6">]</span><span class="p" data-group-id="8544608097-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="1199927964-7">(</span><span class="p" data-group-id="1199927964-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1199927964-8">(</span><span class="ss">simple_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1199927964-9">[</span><span class="p" data-group-id="1199927964-9">]</span><span class="p" data-group-id="1199927964-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="8544608097-7">(</span><span class="p" data-group-id="8544608097-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8544608097-8">(</span><span class="ss">simple_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8544608097-9">[</span><span class="p" data-group-id="8544608097-9">]</span><span class="p" data-group-id="8544608097-8">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1199927964-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="1199927964-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1199927964-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8544608097-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="8544608097-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8544608097-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="p">,</span><span class="w">
│ │ │                   </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1199927964-11">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1199927964-12">[</span><span class="p" data-group-id="1199927964-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">call</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1199927964-14">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1199927964-15">[</span><span class="p" data-group-id="1199927964-15">]</span><span class="p" data-group-id="1199927964-14">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="1199927964-13">}</span><span class="p" data-group-id="1199927964-12">]</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1199927964-16">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1199927964-17">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="1199927964-17">}</span><span class="p" data-group-id="1199927964-16">}</span><span class="p">.</span></code></pre><p>When started, the supervisor does not start any child
│ │ │ +                 </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8544608097-11">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8544608097-12">[</span><span class="p" data-group-id="8544608097-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">call</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8544608097-14">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8544608097-15">[</span><span class="p" data-group-id="8544608097-15">]</span><span class="p" data-group-id="8544608097-14">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="8544608097-13">}</span><span class="p" data-group-id="8544608097-12">]</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8544608097-16">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8544608097-17">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="8544608097-17">}</span><span class="p" data-group-id="8544608097-16">}</span><span class="p">.</span></code></pre><p>When started, the supervisor does not start any child
│ │ │  processes. Instead, all child processes need to be added dynamically by
│ │ │  calling <a href="../../lib/stdlib-6.2.2.1/doc/html/supervisor.html#start_child/2"><code class="inline">supervisor:start_child(Sup, List)</code></a>.</p><p><code class="inline">Sup</code> is the pid, or name, of the supervisor. <code class="inline">List</code> is an arbitrary list of
│ │ │  terms, which are added to the list of arguments specified in the child
│ │ │  specification. If the start function is specified as <code class="inline">{M, F, A}</code>, the child
│ │ │  process is started by calling <a href="../../erts-15.2.7/doc/html/erlang.html#apply/3"><code class="inline">apply(M, F, A++List)</code></a>.</p><p>For example, adding a child to <code class="inline">simple_sup</code> above:</p><pre><code class="text">supervisor:start_child(Pid, [id1])</code></pre><p>The result is that the child process is started by calling
│ │ │  <a href="../../erts-15.2.7/doc/html/erlang.html#apply/3"><code class="inline">apply(call, start_link, []++[id1])</code></a>, or actually:</p><pre><code class="text">call:start_link(id1)</code></pre><p>A child under a <code class="inline">simple_one_for_one</code> supervisor can be terminated with the
│ │ │  following:</p><pre><code class="text">supervisor:terminate_child(Sup, Pid)</code></pre><p><code class="inline">Sup</code> is the pid, or name, of the supervisor and <code class="inline">Pid</code> is the pid of the child.</p><p>Because a <code class="inline">simple_one_for_one</code> supervisor can have many children, it shuts them
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/tablesdatabases.html
│ │ │ @@ -146,73 +146,73 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Deleting an Element</span>
│ │ │  </h3>
│ │ │  <p>The <code class="inline">delete</code> operation is considered successful if the element was not present
│ │ │  in the table. Hence all attempts to check that the element is present in the
│ │ │  Ets/Mnesia table before deletion are unnecessary. Here follows an example for
│ │ │ -Ets tables:</p><p><strong>DO</strong></p><pre><code class="text">ets:delete(Tab, Key),</code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="4450512051-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="4450512051-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4450512051-2">[</span><span class="p" data-group-id="4450512051-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +Ets tables:</p><p><strong>DO</strong></p><pre><code class="text">ets:delete(Tab, Key),</code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="1430011663-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="1430011663-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1430011663-2">[</span><span class="p" data-group-id="1430011663-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4450512051-3">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="4450512051-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">ets</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="4450512051-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="4450512051-4">)</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1430011663-3">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="1430011663-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">ets</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="1430011663-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="1430011663-4">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre><h3 id="fetching-data" class="section-heading">
│ │ │    <a href="#fetching-data" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Fetching Data</span>
│ │ │  </h3>
│ │ │  <p>Do not fetch data that you already have.</p><p>Consider that you have a module that handles the abstract data type <code class="inline">Person</code>.
│ │ │  You export the interface function <code class="inline">print_person/1</code>, which uses the internal
│ │ │  functions <code class="inline">print_name/1</code>, <code class="inline">print_age/1</code>, and <code class="inline">print_occupation/1</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>If the function <code class="inline">print_name/1</code>, and so on, had been interface functions, the
│ │ │  situation would have been different, as you do not want the user of the
│ │ │  interface to know about the internal data representation.</p></section><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ -</span><span class="nf">print_person</span><span class="p" data-group-id="5621805802-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="5621805802-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">print_person</span><span class="p" data-group-id="0429364595-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="0429364595-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Look up the person in the named table person,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="5621805802-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="5621805802-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5621805802-3">[</span><span class="n">Person</span><span class="p" data-group-id="5621805802-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">print_name</span><span class="p" data-group-id="5621805802-4">(</span><span class="n">Person</span><span class="p" data-group-id="5621805802-4">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">print_age</span><span class="p" data-group-id="5621805802-5">(</span><span class="n">Person</span><span class="p" data-group-id="5621805802-5">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">print_occupation</span><span class="p" data-group-id="5621805802-6">(</span><span class="n">Person</span><span class="p" data-group-id="5621805802-6">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5621805802-7">[</span><span class="p" data-group-id="5621805802-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5621805802-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5621805802-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="5621805802-9">]</span><span class="p" data-group-id="5621805802-8">)</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="0429364595-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="0429364595-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0429364595-3">[</span><span class="n">Person</span><span class="p" data-group-id="0429364595-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">print_name</span><span class="p" data-group-id="0429364595-4">(</span><span class="n">Person</span><span class="p" data-group-id="0429364595-4">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">print_age</span><span class="p" data-group-id="0429364595-5">(</span><span class="n">Person</span><span class="p" data-group-id="0429364595-5">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">print_occupation</span><span class="p" data-group-id="0429364595-6">(</span><span class="n">Person</span><span class="p" data-group-id="0429364595-6">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0429364595-7">[</span><span class="p" data-group-id="0429364595-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0429364595-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0429364595-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="0429364595-9">]</span><span class="p" data-group-id="0429364595-8">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Internal functions</span><span class="w">
│ │ │ -</span><span class="nf">print_name</span><span class="p" data-group-id="5621805802-10">(</span><span class="n">Person</span><span class="p" data-group-id="5621805802-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5621805802-11">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5621805802-12">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="5621805802-12">]</span><span class="p" data-group-id="5621805802-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">print_name</span><span class="p" data-group-id="0429364595-10">(</span><span class="n">Person</span><span class="p" data-group-id="0429364595-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0429364595-11">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0429364595-12">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="0429364595-12">]</span><span class="p" data-group-id="0429364595-11">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">print_age</span><span class="p" data-group-id="5621805802-13">(</span><span class="n">Person</span><span class="p" data-group-id="5621805802-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5621805802-14">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5621805802-15">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="5621805802-15">]</span><span class="p" data-group-id="5621805802-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">print_age</span><span class="p" data-group-id="0429364595-13">(</span><span class="n">Person</span><span class="p" data-group-id="0429364595-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0429364595-14">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0429364595-15">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="0429364595-15">]</span><span class="p" data-group-id="0429364595-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">print_occupation</span><span class="p" data-group-id="5621805802-16">(</span><span class="n">Person</span><span class="p" data-group-id="5621805802-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5621805802-17">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5621805802-18">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="5621805802-18">]</span><span class="p" data-group-id="5621805802-17">)</span><span class="p">.</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ -</span><span class="nf">print_person</span><span class="p" data-group-id="9417550137-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="9417550137-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">print_occupation</span><span class="p" data-group-id="0429364595-16">(</span><span class="n">Person</span><span class="p" data-group-id="0429364595-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0429364595-17">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0429364595-18">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="0429364595-18">]</span><span class="p" data-group-id="0429364595-17">)</span><span class="p">.</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ +</span><span class="nf">print_person</span><span class="p" data-group-id="5306979407-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="5306979407-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Look up the person in the named table person,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="9417550137-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="9417550137-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9417550137-3">[</span><span class="n">Person</span><span class="p" data-group-id="9417550137-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">print_name</span><span class="p" data-group-id="9417550137-4">(</span><span class="n">PersonID</span><span class="p" data-group-id="9417550137-4">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">print_age</span><span class="p" data-group-id="9417550137-5">(</span><span class="n">PersonID</span><span class="p" data-group-id="9417550137-5">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">print_occupation</span><span class="p" data-group-id="9417550137-6">(</span><span class="n">PersonID</span><span class="p" data-group-id="9417550137-6">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9417550137-7">[</span><span class="p" data-group-id="9417550137-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9417550137-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9417550137-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="9417550137-9">]</span><span class="p" data-group-id="9417550137-8">)</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="5306979407-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="5306979407-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5306979407-3">[</span><span class="n">Person</span><span class="p" data-group-id="5306979407-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">print_name</span><span class="p" data-group-id="5306979407-4">(</span><span class="n">PersonID</span><span class="p" data-group-id="5306979407-4">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">print_age</span><span class="p" data-group-id="5306979407-5">(</span><span class="n">PersonID</span><span class="p" data-group-id="5306979407-5">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">print_occupation</span><span class="p" data-group-id="5306979407-6">(</span><span class="n">PersonID</span><span class="p" data-group-id="5306979407-6">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5306979407-7">[</span><span class="p" data-group-id="5306979407-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5306979407-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5306979407-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="5306979407-9">]</span><span class="p" data-group-id="5306979407-8">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Internal functions</span><span class="w">
│ │ │ -</span><span class="nf">print_name</span><span class="p" data-group-id="9417550137-10">(</span><span class="n">PersonID</span><span class="p" data-group-id="9417550137-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9417550137-11">[</span><span class="n">Person</span><span class="p" data-group-id="9417550137-11">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="9417550137-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="9417550137-12">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9417550137-13">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9417550137-14">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="9417550137-14">]</span><span class="p" data-group-id="9417550137-13">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">print_age</span><span class="p" data-group-id="9417550137-15">(</span><span class="n">PersonID</span><span class="p" data-group-id="9417550137-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9417550137-16">[</span><span class="n">Person</span><span class="p" data-group-id="9417550137-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="9417550137-17">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="9417550137-17">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9417550137-18">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9417550137-19">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="9417550137-19">]</span><span class="p" data-group-id="9417550137-18">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">print_occupation</span><span class="p" data-group-id="9417550137-20">(</span><span class="n">PersonID</span><span class="p" data-group-id="9417550137-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9417550137-21">[</span><span class="n">Person</span><span class="p" data-group-id="9417550137-21">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="9417550137-22">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="9417550137-22">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9417550137-23">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9417550137-24">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="9417550137-24">]</span><span class="p" data-group-id="9417550137-23">)</span><span class="p">.</span></code></pre><h3 id="non-persistent-database-storage" class="section-heading">
│ │ │ +</span><span class="nf">print_name</span><span class="p" data-group-id="5306979407-10">(</span><span class="n">PersonID</span><span class="p" data-group-id="5306979407-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5306979407-11">[</span><span class="n">Person</span><span class="p" data-group-id="5306979407-11">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="5306979407-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="5306979407-12">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5306979407-13">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5306979407-14">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="5306979407-14">]</span><span class="p" data-group-id="5306979407-13">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">print_age</span><span class="p" data-group-id="5306979407-15">(</span><span class="n">PersonID</span><span class="p" data-group-id="5306979407-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5306979407-16">[</span><span class="n">Person</span><span class="p" data-group-id="5306979407-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="5306979407-17">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="5306979407-17">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5306979407-18">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5306979407-19">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="5306979407-19">]</span><span class="p" data-group-id="5306979407-18">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">print_occupation</span><span class="p" data-group-id="5306979407-20">(</span><span class="n">PersonID</span><span class="p" data-group-id="5306979407-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5306979407-21">[</span><span class="n">Person</span><span class="p" data-group-id="5306979407-21">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="5306979407-22">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="5306979407-22">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5306979407-23">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5306979407-24">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="5306979407-24">]</span><span class="p" data-group-id="5306979407-23">)</span><span class="p">.</span></code></pre><h3 id="non-persistent-database-storage" class="section-heading">
│ │ │    <a href="#non-persistent-database-storage" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Non-Persistent Database Storage</span>
│ │ │  </h3>
│ │ │  <p>For non-persistent database storage, prefer Ets tables over Mnesia
│ │ │  <code class="inline">local_content</code> tables. Even the Mnesia <code class="inline">dirty_write</code> operations carry a fixed
│ │ │ @@ -226,38 +226,38 @@
│ │ │  </h3>
│ │ │  <p>Assuming an Ets table that uses <code class="inline">idno</code> as key and contains the following:</p><pre><code class="text">[#person{idno = 1, name = &quot;Adam&quot;,  age = 31, occupation = &quot;mailman&quot;},
│ │ │   #person{idno = 2, name = &quot;Bryan&quot;, age = 31, occupation = &quot;cashier&quot;},
│ │ │   #person{idno = 3, name = &quot;Bryan&quot;, age = 35, occupation = &quot;banker&quot;},
│ │ │   #person{idno = 4, name = &quot;Carl&quot;,  age = 25, occupation = &quot;mailman&quot;}]</code></pre><p>If you <em>must</em> return all data stored in the Ets table, you can use
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/ets.html#tab2list/1"><code class="inline">ets:tab2list/1</code></a>. However, usually you are only interested in a subset of the
│ │ │  information in which case <a href="../../lib/stdlib-6.2.2.1/doc/html/ets.html#tab2list/1"><code class="inline">ets:tab2list/1</code></a> is expensive. If you only want to
│ │ │ -extract one field from each record, for example, the age of every person, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="7026296619-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7026296619-2">[</span><span class="p" data-group-id="7026296619-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7026296619-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ +extract one field from each record, for example, the age of every person, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="9154314478-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9154314478-2">[</span><span class="p" data-group-id="9154314478-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9154314478-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;$1&#39;</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="7026296619-4">}</span><span class="p">,</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="7026296619-5">[</span><span class="p" data-group-id="7026296619-5">]</span><span class="p">,</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="7026296619-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="7026296619-6">]</span><span class="p" data-group-id="7026296619-3">}</span><span class="p" data-group-id="7026296619-2">]</span><span class="p" data-group-id="7026296619-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="3789249656-1">(</span><span class="n">Tab</span><span class="p" data-group-id="3789249656-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="3789249656-2">(</span><span class="nf">fun</span><span class="p" data-group-id="3789249656-3">(</span><span class="n">X</span><span class="p" data-group-id="3789249656-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="3789249656-2">)</span><span class="p">,</span></code></pre><p>If you are only interested in the age of all persons named &quot;Bryan&quot;, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="3175177987-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3175177987-2">[</span><span class="p" data-group-id="3175177987-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3175177987-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="9154314478-4">}</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="9154314478-5">[</span><span class="p" data-group-id="9154314478-5">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="9154314478-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="9154314478-6">]</span><span class="p" data-group-id="9154314478-3">}</span><span class="p" data-group-id="9154314478-2">]</span><span class="p" data-group-id="9154314478-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="3195932263-1">(</span><span class="n">Tab</span><span class="p" data-group-id="3195932263-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="3195932263-2">(</span><span class="nf">fun</span><span class="p" data-group-id="3195932263-3">(</span><span class="n">X</span><span class="p" data-group-id="3195932263-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="3195932263-2">)</span><span class="p">,</span></code></pre><p>If you are only interested in the age of all persons named &quot;Bryan&quot;, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="0918256171-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0918256171-2">[</span><span class="p" data-group-id="0918256171-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0918256171-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Bryan&quot;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;$1&#39;</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="3175177987-4">}</span><span class="p">,</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="3175177987-5">[</span><span class="p" data-group-id="3175177987-5">]</span><span class="p">,</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="3175177987-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="3175177987-6">]</span><span class="p" data-group-id="3175177987-3">}</span><span class="p" data-group-id="3175177987-2">]</span><span class="p" data-group-id="3175177987-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="8181621575-1">(</span><span class="n">Tab</span><span class="p" data-group-id="8181621575-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="8181621575-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8181621575-3">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8181621575-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="0918256171-4">}</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="0918256171-5">[</span><span class="p" data-group-id="0918256171-5">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="0918256171-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="0918256171-6">]</span><span class="p" data-group-id="0918256171-3">}</span><span class="p" data-group-id="0918256171-2">]</span><span class="p" data-group-id="0918256171-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="8035246614-1">(</span><span class="n">Tab</span><span class="p" data-group-id="8035246614-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="8035246614-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8035246614-3">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8035246614-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │                                  </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                                    </span><span class="p" data-group-id="8181621575-4">[</span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="8181621575-4">]</span><span class="p">;</span><span class="w">
│ │ │ +                                    </span><span class="p" data-group-id="8035246614-4">[</span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="8035246614-4">]</span><span class="p">;</span><span class="w">
│ │ │                                   </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                                       </span><span class="n">Acc</span><span class="w">
│ │ │                             </span><span class="k">end</span><span class="w">
│ │ │ -             </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8181621575-5">[</span><span class="p" data-group-id="8181621575-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="8181621575-2">)</span></code></pre><p>If you need all information stored in the Ets table about persons named &quot;Bryan&quot;,
│ │ │ -then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="1146309868-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1146309868-2">[</span><span class="p" data-group-id="1146309868-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1146309868-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8035246614-5">[</span><span class="p" data-group-id="8035246614-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="8035246614-2">)</span></code></pre><p>If you need all information stored in the Ets table about persons named &quot;Bryan&quot;,
│ │ │ +then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="5342367658-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5342367658-2">[</span><span class="p" data-group-id="5342367658-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5342367658-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Bryan&quot;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="1146309868-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1146309868-5">[</span><span class="p" data-group-id="1146309868-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1146309868-6">[</span><span class="ss">&#39;$_&#39;</span><span class="p" data-group-id="1146309868-6">]</span><span class="p" data-group-id="1146309868-3">}</span><span class="p" data-group-id="1146309868-2">]</span><span class="p" data-group-id="1146309868-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="1899642544-1">(</span><span class="n">Tab</span><span class="p" data-group-id="1899642544-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="1899642544-2">(</span><span class="nf">fun</span><span class="p" data-group-id="1899642544-3">(</span><span class="n">X</span><span class="p" data-group-id="1899642544-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="1899642544-2">)</span><span class="p">,</span></code></pre><h3 id="ordered_set-tables" class="section-heading">
│ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="5342367658-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5342367658-5">[</span><span class="p" data-group-id="5342367658-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5342367658-6">[</span><span class="ss">&#39;$_&#39;</span><span class="p" data-group-id="5342367658-6">]</span><span class="p" data-group-id="5342367658-3">}</span><span class="p" data-group-id="5342367658-2">]</span><span class="p" data-group-id="5342367658-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="3717337478-1">(</span><span class="n">Tab</span><span class="p" data-group-id="3717337478-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="3717337478-2">(</span><span class="nf">fun</span><span class="p" data-group-id="3717337478-3">(</span><span class="n">X</span><span class="p" data-group-id="3717337478-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="3717337478-2">)</span><span class="p">,</span></code></pre><h3 id="ordered_set-tables" class="section-heading">
│ │ │    <a href="#ordered_set-tables" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text"><code class="inline">ordered_set</code> Tables</span>
│ │ │  </h3>
│ │ │  <p>If the data in the table is to be accessed so that the order of the keys in the
│ │ │  table is significant, the table type <code class="inline">ordered_set</code> can be used instead of the
│ │ │ @@ -293,20 +293,20 @@
│ │ │  Clearly, the second table would have to be kept consistent with the master
│ │ │  table. Mnesia can do this for you, but a home-brew index table can be very
│ │ │  efficient compared to the overhead involved in using Mnesia.</p><p>An index table for the table in the previous examples would have to be a bag (as
│ │ │  keys would appear more than once) and can have the following contents:</p><pre><code class="text">[#index_entry{name=&quot;Adam&quot;, idno=1},
│ │ │   #index_entry{name=&quot;Bryan&quot;, idno=2},
│ │ │   #index_entry{name=&quot;Bryan&quot;, idno=3},
│ │ │   #index_entry{name=&quot;Carl&quot;, idno=4}]</code></pre><p>Given this index table, a lookup of the <code class="inline">age</code> fields for all persons named
│ │ │ -&quot;Bryan&quot; can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">MatchingIDs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="0579370526-1">(</span><span class="n">IndexTable</span><span class="p">,</span><span class="s">&quot;Bryan&quot;</span><span class="p" data-group-id="0579370526-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0579370526-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0579370526-3">(</span><span class="o">#</span><span class="ss">index_entry</span><span class="p" data-group-id="0579370526-4">{</span><span class="ss">idno</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="0579370526-4">}</span><span class="p" data-group-id="0579370526-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="0579370526-5">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0579370526-6">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="0579370526-6">}</span><span class="p" data-group-id="0579370526-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="0579370526-7">(</span><span class="n">PersonTable</span><span class="p">,</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="0579370526-7">)</span><span class="p">,</span><span class="w">
│ │ │ +&quot;Bryan&quot; can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">MatchingIDs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="4636580683-1">(</span><span class="n">IndexTable</span><span class="p">,</span><span class="s">&quot;Bryan&quot;</span><span class="p" data-group-id="4636580683-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="4636580683-2">(</span><span class="nf">fun</span><span class="p" data-group-id="4636580683-3">(</span><span class="o">#</span><span class="ss">index_entry</span><span class="p" data-group-id="4636580683-4">{</span><span class="ss">idno</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="4636580683-4">}</span><span class="p" data-group-id="4636580683-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="4636580683-5">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4636580683-6">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="4636580683-6">}</span><span class="p" data-group-id="4636580683-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="4636580683-7">(</span><span class="n">PersonTable</span><span class="p">,</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="4636580683-7">)</span><span class="p">,</span><span class="w">
│ │ │                   </span><span class="n">Age</span><span class="w">
│ │ │            </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="n">MatchingIDs</span><span class="p" data-group-id="0579370526-2">)</span><span class="p">,</span></code></pre><p>Notice that this code does not use <a href="../../lib/stdlib-6.2.2.1/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>, but instead uses the
│ │ │ +          </span><span class="n">MatchingIDs</span><span class="p" data-group-id="4636580683-2">)</span><span class="p">,</span></code></pre><p>Notice that this code does not use <a href="../../lib/stdlib-6.2.2.1/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>, but instead uses the
│ │ │  <a href="../../lib/stdlib-6.2.2.1/doc/html/ets.html#lookup/2"><code class="inline">ets:lookup/2</code></a> call. The <a href="../../lib/stdlib-6.2.2.1/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> call is only used to traverse the <code class="inline">idno</code>s
│ │ │  matching the name &quot;Bryan&quot; in the table; thus the number of lookups in the master
│ │ │  table is minimized.</p><p>Keeping an index table introduces some overhead when inserting records in the
│ │ │  table. The number of operations gained from the table must therefore be compared
│ │ │  against the number of operations inserting objects in the table. However, notice
│ │ │  that the gain is significant when the key can be used to lookup elements.</p><h2 id="mnesia" class="section-heading">
│ │ │    <a href="#mnesia" class="hover-link">
│ │ │ @@ -321,51 +321,51 @@
│ │ │    <span class="text">Secondary Index</span>
│ │ │  </h3>
│ │ │  <p>If you frequently do lookups on a field that is not the key of the table, you
│ │ │  lose performance using <a href="../../lib/mnesia-4.23.5/doc/html/mnesia.html#select/3">mnesia:select()</a> or
│ │ │  <a href="../../lib/mnesia-4.23.5/doc/html/mnesia.html#match_object/1"><code class="inline">mnesia:match_object()</code></a> as these function traverse
│ │ │  the whole table. Instead, you can create a secondary index and use
│ │ │  <a href="../../lib/mnesia-4.23.5/doc/html/mnesia.html#index_read/3"><code class="inline">mnesia:index_read/3</code></a> to get faster access at the expense of using more
│ │ │ -memory.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3806980960-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3806980960-2">{</span><span class="ss">idno</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">occupation</span><span class="p" data-group-id="3806980960-2">}</span><span class="p" data-group-id="3806980960-1">)</span><span class="p">.</span><span class="w">
│ │ │ +memory.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1987938931-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1987938931-2">{</span><span class="ss">idno</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">occupation</span><span class="p" data-group-id="1987938931-2">}</span><span class="p" data-group-id="1987938931-1">)</span><span class="p">.</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3806980960-3">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="3806980960-3">}</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ -</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">create_table</span><span class="p" data-group-id="3806980960-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3806980960-5">[</span><span class="p" data-group-id="3806980960-6">{</span><span class="ss">index</span><span class="p">,</span><span class="p" data-group-id="3806980960-7">[</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="3806980960-7">]</span><span class="p" data-group-id="3806980960-6">}</span><span class="p">,</span><span class="w">
│ │ │ -                              </span><span class="p" data-group-id="3806980960-8">{</span><span class="ss">attributes</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="nf">record_info</span><span class="p" data-group-id="3806980960-9">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="3806980960-9">)</span><span class="p" data-group-id="3806980960-8">}</span><span class="p" data-group-id="3806980960-5">]</span><span class="p" data-group-id="3806980960-4">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3806980960-10">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="3806980960-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">add_table_index</span><span class="p" data-group-id="3806980960-11">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="3806980960-11">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1987938931-3">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="1987938931-3">}</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ +</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">create_table</span><span class="p" data-group-id="1987938931-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1987938931-5">[</span><span class="p" data-group-id="1987938931-6">{</span><span class="ss">index</span><span class="p">,</span><span class="p" data-group-id="1987938931-7">[</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="1987938931-7">]</span><span class="p" data-group-id="1987938931-6">}</span><span class="p">,</span><span class="w">
│ │ │ +                              </span><span class="p" data-group-id="1987938931-8">{</span><span class="ss">attributes</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="nf">record_info</span><span class="p" data-group-id="1987938931-9">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="1987938931-9">)</span><span class="p" data-group-id="1987938931-8">}</span><span class="p" data-group-id="1987938931-5">]</span><span class="p" data-group-id="1987938931-4">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1987938931-10">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="1987938931-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">add_table_index</span><span class="p" data-group-id="1987938931-11">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="1987938931-11">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="n">PersonsAge42</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ -     </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_index_read</span><span class="p" data-group-id="3806980960-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="3806980960-12">)</span><span class="p">,</span></code></pre><h3 id="transactions" class="section-heading">
│ │ │ +     </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_index_read</span><span class="p" data-group-id="1987938931-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="1987938931-12">)</span><span class="p">,</span></code></pre><h3 id="transactions" class="section-heading">
│ │ │    <a href="#transactions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Transactions</span>
│ │ │  </h3>
│ │ │  <p>Using transactions is a way to guarantee that the distributed Mnesia database
│ │ │  remains consistent, even when many different processes update it in parallel.
│ │ │  However, if you have real-time requirements it is recommended to use dirtry
│ │ │  operations instead of transactions. When using dirty operations, you lose the
│ │ │  consistency guarantee; this is usually solved by only letting one process update
│ │ │  the table. Other processes must send update requests to that process.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Using transaction</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5613137056-1">(</span><span class="p" data-group-id="5613137056-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="5613137056-2">[</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="5613137056-3">(</span><span class="p" data-group-id="5613137056-4">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="5613137056-4">}</span><span class="p" data-group-id="5613137056-3">)</span><span class="p">,</span><span class="w">
│ │ │ -           </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="5613137056-5">(</span><span class="p" data-group-id="5613137056-6">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="5613137056-6">}</span><span class="p" data-group-id="5613137056-5">)</span><span class="p" data-group-id="5613137056-2">]</span><span class="w">
│ │ │ +</span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0528882992-1">(</span><span class="p" data-group-id="0528882992-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="0528882992-2">[</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="0528882992-3">(</span><span class="p" data-group-id="0528882992-4">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="0528882992-4">}</span><span class="p" data-group-id="0528882992-3">)</span><span class="p">,</span><span class="w">
│ │ │ +           </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="0528882992-5">(</span><span class="p" data-group-id="0528882992-6">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="0528882992-6">}</span><span class="p" data-group-id="0528882992-5">)</span><span class="p" data-group-id="0528882992-2">]</span><span class="w">
│ │ │        </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="5613137056-7">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5613137056-8">[</span><span class="n">Result1</span><span class="p">,</span><span class="w"> </span><span class="n">Result2</span><span class="p" data-group-id="5613137056-8">]</span><span class="p" data-group-id="5613137056-7">}</span><span class="w">  </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">transaction</span><span class="p" data-group-id="5613137056-9">(</span><span class="n">Fun</span><span class="p" data-group-id="5613137056-9">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0528882992-7">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0528882992-8">[</span><span class="n">Result1</span><span class="p">,</span><span class="w"> </span><span class="n">Result2</span><span class="p" data-group-id="0528882992-8">]</span><span class="p" data-group-id="0528882992-7">}</span><span class="w">  </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">transaction</span><span class="p" data-group-id="0528882992-9">(</span><span class="n">Fun</span><span class="p" data-group-id="0528882992-9">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% Same thing using dirty operations</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Result1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="5613137056-10">(</span><span class="p" data-group-id="5613137056-11">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="5613137056-11">}</span><span class="p" data-group-id="5613137056-10">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Result2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="5613137056-12">(</span><span class="p" data-group-id="5613137056-13">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="5613137056-13">}</span><span class="p" data-group-id="5613137056-12">)</span><span class="p">,</span></code></pre>
│ │ │ +</span><span class="n">Result1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="0528882992-10">(</span><span class="p" data-group-id="0528882992-11">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="0528882992-11">}</span><span class="p" data-group-id="0528882992-10">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Result2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="0528882992-12">(</span><span class="p" data-group-id="0528882992-13">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="0528882992-13">}</span><span class="p" data-group-id="0528882992-12">)</span><span class="p">,</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="eff_guide_functions.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/typespec.html
│ │ │ @@ -238,124 +238,124 @@
│ │ │  and optional <code class="inline">(=&gt;)</code> association types. If an association type is mandatory, an
│ │ │  association with that type needs to be present. In the case of an optional
│ │ │  association type it is not required for the key type to be present.</p><p>The notation <code class="inline">#{}</code> specifies the singleton type for the empty map. Note that
│ │ │  this notation is not a shorthand for the <a href="../../erts-15.2.7/doc/html/erlang.html#t:map/0"><code class="inline">map/0</code></a> type.</p><p>For convenience, the following types are also built-in. They can be thought as
│ │ │  predefined aliases for the type unions also shown in the table.</p><p><a href="" id="builtin_types"></a></p><table><thead><tr><th style="text-align: left;"><em>Built-in type</em></th><th style="text-align: left;"><em>Defined as</em></th></tr></thead><tbody><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:term/0"><code class="inline">term/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:any/0"><code class="inline">any/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:binary/0"><code class="inline">binary/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:_*8&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:nonempty_binary/0"><code class="inline">nonempty_binary/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:8, _:_*8&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:bitstring/0"><code class="inline">bitstring/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:_*1&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:nonempty_bitstring/0"><code class="inline">nonempty_bitstring/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:1, _:_*1&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:boolean/0"><code class="inline">boolean/0</code></a></td><td style="text-align: left;"><code class="inline">'false'</code> | <code class="inline">'true'</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:byte/0"><code class="inline">byte/0</code></a></td><td style="text-align: left;"><code class="inline">0..255</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:char/0"><code class="inline">char/0</code></a></td><td style="text-align: left;"><code class="inline">0..16#10ffff</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:nil/0"><code class="inline">nil/0</code></a></td><td style="text-align: left;"><code class="inline">[]</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:number/0"><code class="inline">number/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:integer/0"><code class="inline">integer/0</code></a> | <a href="../../erts-15.2.7/doc/html/erlang.html#t:float/0"><code class="inline">float/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:list/0"><code class="inline">list/0</code></a></td><td style="text-align: left;"><code class="inline">[any()]</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:maybe_improper_list/0"><code class="inline">maybe_improper_list/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:maybe_improper_list/2"><code class="inline">maybe_improper_list(any(), any())</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:nonempty_list/0"><code class="inline">nonempty_list/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:nonempty_list/1"><code class="inline">nonempty_list(any())</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:string/0"><code class="inline">string/0</code></a></td><td style="text-align: left;"><code class="inline">[char()]</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:nonempty_string/0"><code class="inline">nonempty_string/0</code></a></td><td style="text-align: left;"><code class="inline">[char(),...]</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:iodata/0"><code class="inline">iodata/0</code></a></td><td style="text-align: left;"><code class="inline">iolist()</code> | <code class="inline">binary()</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:iolist/0"><code class="inline">iolist/0</code></a></td><td style="text-align: left;"><code class="inline">maybe_improper_list(byte()</code> | <code class="inline">binary()</code> | <code class="inline">iolist(), binary()</code> | <code class="inline">[])</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:map/0"><code class="inline">map/0</code></a></td><td style="text-align: left;"><code class="inline">#{any() =&gt; any()}</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:function/0"><code class="inline">function/0</code></a></td><td style="text-align: left;"><code class="inline">fun()</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:module/0"><code class="inline">module/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:atom/0"><code class="inline">atom/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:mfa/0"><code class="inline">mfa/0</code></a></td><td style="text-align: left;"><code class="inline">{module(),atom(),arity()}</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:arity/0"><code class="inline">arity/0</code></a></td><td style="text-align: left;"><code class="inline">0..255</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:identifier/0"><code class="inline">identifier/0</code></a></td><td style="text-align: left;"><code class="inline">pid()</code> | <code class="inline">port()</code> | <code class="inline">reference()</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#node/0"><code class="inline">node/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:atom/0"><code class="inline">atom/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:timeout/0"><code class="inline">timeout/0</code></a></td><td style="text-align: left;"><code class="inline">'infinity'</code> | <code class="inline">non_neg_integer()</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:none/0"><code class="inline">none/0</code></a></td></tr></tbody></table><p><em>Table: Built-in types, predefined aliases</em></p><p>In addition, the following three built-in types exist and can be thought as
│ │ │  defined below, though strictly their &quot;type definition&quot; is not valid syntax
│ │ │  according to the type language defined above.</p><table><thead><tr><th style="text-align: left;"><em>Built-in type</em></th><th style="text-align: left;"><em>Can be thought defined by the syntax</em></th></tr></thead><tbody><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:non_neg_integer/0"><code class="inline">non_neg_integer/0</code></a></td><td style="text-align: left;"><code class="inline">0..</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:pos_integer/0"><code class="inline">pos_integer/0</code></a></td><td style="text-align: left;"><code class="inline">1..</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7/doc/html/erlang.html#t:neg_integer/0"><code class="inline">neg_integer/0</code></a></td><td style="text-align: left;"><code class="inline">..-1</code></td></tr></tbody></table><p><em>Table: Additional built-in types</em></p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The following built-in list types also exist, but they are expected to be
│ │ │ -rarely used. Hence, they have long names:</p></section><pre><code class="makeup erlang" translate="no"><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="9317975773-1">(</span><span class="p" data-group-id="9317975773-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="9317975773-2">(</span><span class="nf">any</span><span class="p" data-group-id="9317975773-3">(</span><span class="p" data-group-id="9317975773-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="9317975773-4">(</span><span class="p" data-group-id="9317975773-4">)</span><span class="p" data-group-id="9317975773-2">)</span><span class="w">
│ │ │ -</span><span class="nf">nonempty_improper_list</span><span class="p" data-group-id="9317975773-5">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="9317975773-5">)</span><span class="w">
│ │ │ -</span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="9317975773-6">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="9317975773-6">)</span></code></pre><p>where the last two types define the set of Erlang terms one would expect.</p><p>Also for convenience, record notation is allowed to be used. Records are
│ │ │ -shorthands for the corresponding tuples:</p><pre><code class="makeup erlang" translate="no"><span class="n">Record</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="6601612269-1">{</span><span class="p" data-group-id="6601612269-1">}</span><span class="w">
│ │ │ -        </span><span class="p">|</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="6601612269-2">{</span><span class="n">Fields</span><span class="p" data-group-id="6601612269-2">}</span></code></pre><p>Records are extended to possibly contain type information. This is described in
│ │ │ +rarely used. Hence, they have long names:</p></section><pre><code class="makeup erlang" translate="no"><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="4448939603-1">(</span><span class="p" data-group-id="4448939603-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="4448939603-2">(</span><span class="nf">any</span><span class="p" data-group-id="4448939603-3">(</span><span class="p" data-group-id="4448939603-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="4448939603-4">(</span><span class="p" data-group-id="4448939603-4">)</span><span class="p" data-group-id="4448939603-2">)</span><span class="w">
│ │ │ +</span><span class="nf">nonempty_improper_list</span><span class="p" data-group-id="4448939603-5">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="4448939603-5">)</span><span class="w">
│ │ │ +</span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="4448939603-6">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="4448939603-6">)</span></code></pre><p>where the last two types define the set of Erlang terms one would expect.</p><p>Also for convenience, record notation is allowed to be used. Records are
│ │ │ +shorthands for the corresponding tuples:</p><pre><code class="makeup erlang" translate="no"><span class="n">Record</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="5031922563-1">{</span><span class="p" data-group-id="5031922563-1">}</span><span class="w">
│ │ │ +        </span><span class="p">|</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="5031922563-2">{</span><span class="n">Fields</span><span class="p" data-group-id="5031922563-2">}</span></code></pre><p>Records are extended to possibly contain type information. This is described in
│ │ │  <a href="typespec.html#typeinrecords">Type Information in Record Declarations</a>.</p><h3 id="redefining-built-in-types" class="section-heading">
│ │ │    <a href="#redefining-built-in-types" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Redefining built-in types</span>
│ │ │  </h3>
│ │ │  <section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Starting from Erlang/OTP 26, it is permitted to define a type having the same
│ │ │  name as a built-in type.</p></section><p>It is recommended to avoid deliberately reusing built-in names because it can be
│ │ │  confusing. However, when an Erlang/OTP release introduces a new type, code that
│ │ │  happened to define its own type having the same name will continue to work.</p><p>As an example, imagine that the Erlang/OTP 42 release introduces a new type
│ │ │ -<code class="inline">gadget()</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="3862458693-1">(</span><span class="p" data-group-id="3862458693-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="3862458693-2">{</span><span class="ss">&#39;gadget&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">reference</span><span class="p" data-group-id="3862458693-3">(</span><span class="p" data-group-id="3862458693-3">)</span><span class="p" data-group-id="3862458693-2">}</span><span class="p">.</span></code></pre><p>Further imagine that some code has its own (different) definition of <code class="inline">gadget()</code>,
│ │ │ -for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="7229207332-1">(</span><span class="p" data-group-id="7229207332-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="7229207332-2">#{</span><span class="p" data-group-id="7229207332-2">}</span><span class="p">.</span></code></pre><p>Since redefinitions are allowed, the code will still compile (but with a
│ │ │ +<code class="inline">gadget()</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="5545731129-1">(</span><span class="p" data-group-id="5545731129-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="5545731129-2">{</span><span class="ss">&#39;gadget&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">reference</span><span class="p" data-group-id="5545731129-3">(</span><span class="p" data-group-id="5545731129-3">)</span><span class="p" data-group-id="5545731129-2">}</span><span class="p">.</span></code></pre><p>Further imagine that some code has its own (different) definition of <code class="inline">gadget()</code>,
│ │ │ +for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="8507075176-1">(</span><span class="p" data-group-id="8507075176-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="8507075176-2">#{</span><span class="p" data-group-id="8507075176-2">}</span><span class="p">.</span></code></pre><p>Since redefinitions are allowed, the code will still compile (but with a
│ │ │  warning), and Dialyzer will not emit any additional warnings.</p><h2 id="type-declarations-of-user-defined-types" class="section-heading">
│ │ │    <a href="#type-declarations-of-user-defined-types" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Type Declarations of User-Defined Types</span>
│ │ │  </h2>
│ │ │  <p>As seen, the basic syntax of a type is an atom followed by closed parentheses.
│ │ │  New types are declared using <code class="inline">-type</code> and <code class="inline">-opaque</code> attributes as in the
│ │ │ -following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_struct_type</span><span class="p" data-group-id="8002498445-1">(</span><span class="p" data-group-id="8002498445-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">my_opaq_type</span><span class="p" data-group-id="8002498445-2">(</span><span class="p" data-group-id="8002498445-2">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span></code></pre><p>The type name is the atom <code class="inline">my_struct_type</code>, followed by parentheses. <code class="inline">Type</code> is a
│ │ │ +following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_struct_type</span><span class="p" data-group-id="9998248639-1">(</span><span class="p" data-group-id="9998248639-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">my_opaq_type</span><span class="p" data-group-id="9998248639-2">(</span><span class="p" data-group-id="9998248639-2">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span></code></pre><p>The type name is the atom <code class="inline">my_struct_type</code>, followed by parentheses. <code class="inline">Type</code> is a
│ │ │  type as defined in the previous section. A current restriction is that <code class="inline">Type</code>
│ │ │  can contain only predefined types, or user-defined types which are either of the
│ │ │  following:</p><ul><li>Module-local type, that is, with a definition that is present in the code of
│ │ │  the module</li><li>Remote type, that is, type defined in, and exported by, other modules; more
│ │ │  about this soon.</li></ul><p>For module-local types, the restriction that their definition exists in the
│ │ │  module is enforced by the compiler and results in a compilation error. (A
│ │ │  similar restriction currently exists for records.)</p><p>Type declarations can also be parameterized by including type variables between
│ │ │  the parentheses. The syntax of type variables is the same as Erlang variables,
│ │ │  that is, starts with an upper-case letter. These variables is to
│ │ │ -appear on the RHS of the definition. A concrete example follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">orddict</span><span class="p" data-group-id="7486699138-1">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="7486699138-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="7486699138-2">[</span><span class="p" data-group-id="7486699138-3">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="7486699138-3">}</span><span class="p" data-group-id="7486699138-2">]</span><span class="p">.</span></code></pre><p>A module can export some types to declare that other modules are allowed to
│ │ │ -refer to them as <em>remote types</em>. This declaration has the following form:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="9836692454-1">(</span><span class="p" data-group-id="9836692454-2">[</span><span class="n">T1</span><span class="o">/</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Tk</span><span class="o">/</span><span class="n">Ak</span><span class="p" data-group-id="9836692454-2">]</span><span class="p" data-group-id="9836692454-1">)</span><span class="p">.</span></code></pre><p>Here the <code class="inline">Ti</code>s are atoms (the name of the type) and the <code class="inline">Ai</code>s are their arguments.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="8327859271-1">(</span><span class="p" data-group-id="8327859271-2">[</span><span class="ss">my_struct_type</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">orddict</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8327859271-2">]</span><span class="p" data-group-id="8327859271-1">)</span><span class="p">.</span></code></pre><p>Assuming that these types are exported from module <code class="inline">'mod'</code>, you can refer to
│ │ │ -them from other modules using remote type expressions like the following:</p><pre><code class="makeup erlang" translate="no"><span class="nc">mod</span><span class="p">:</span><span class="nf">my_struct_type</span><span class="p" data-group-id="9677044187-1">(</span><span class="p" data-group-id="9677044187-1">)</span><span class="w">
│ │ │ -</span><span class="nc">mod</span><span class="p">:</span><span class="nf">orddict</span><span class="p" data-group-id="9677044187-2">(</span><span class="nf">atom</span><span class="p" data-group-id="9677044187-3">(</span><span class="p" data-group-id="9677044187-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="9677044187-4">(</span><span class="p" data-group-id="9677044187-4">)</span><span class="p" data-group-id="9677044187-2">)</span></code></pre><p>It is not allowed to refer to types that are not declared as exported.</p><p>Types declared as <code class="inline">opaque</code> represent sets of terms whose structure is not
│ │ │ +appear on the RHS of the definition. A concrete example follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">orddict</span><span class="p" data-group-id="6293635033-1">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="6293635033-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6293635033-2">[</span><span class="p" data-group-id="6293635033-3">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="6293635033-3">}</span><span class="p" data-group-id="6293635033-2">]</span><span class="p">.</span></code></pre><p>A module can export some types to declare that other modules are allowed to
│ │ │ +refer to them as <em>remote types</em>. This declaration has the following form:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="4235979525-1">(</span><span class="p" data-group-id="4235979525-2">[</span><span class="n">T1</span><span class="o">/</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Tk</span><span class="o">/</span><span class="n">Ak</span><span class="p" data-group-id="4235979525-2">]</span><span class="p" data-group-id="4235979525-1">)</span><span class="p">.</span></code></pre><p>Here the <code class="inline">Ti</code>s are atoms (the name of the type) and the <code class="inline">Ai</code>s are their arguments.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="9562351850-1">(</span><span class="p" data-group-id="9562351850-2">[</span><span class="ss">my_struct_type</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">orddict</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9562351850-2">]</span><span class="p" data-group-id="9562351850-1">)</span><span class="p">.</span></code></pre><p>Assuming that these types are exported from module <code class="inline">'mod'</code>, you can refer to
│ │ │ +them from other modules using remote type expressions like the following:</p><pre><code class="makeup erlang" translate="no"><span class="nc">mod</span><span class="p">:</span><span class="nf">my_struct_type</span><span class="p" data-group-id="8888406121-1">(</span><span class="p" data-group-id="8888406121-1">)</span><span class="w">
│ │ │ +</span><span class="nc">mod</span><span class="p">:</span><span class="nf">orddict</span><span class="p" data-group-id="8888406121-2">(</span><span class="nf">atom</span><span class="p" data-group-id="8888406121-3">(</span><span class="p" data-group-id="8888406121-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="8888406121-4">(</span><span class="p" data-group-id="8888406121-4">)</span><span class="p" data-group-id="8888406121-2">)</span></code></pre><p>It is not allowed to refer to types that are not declared as exported.</p><p>Types declared as <code class="inline">opaque</code> represent sets of terms whose structure is not
│ │ │  supposed to be visible from outside of their defining module. That is, only the
│ │ │  module defining them is allowed to depend on their term structure. Consequently,
│ │ │  such types do not make much sense as module local - module local types are not
│ │ │  accessible by other modules anyway - and is always to be exported.</p><p>Read more on <a href="opaques.html">Opaques</a></p><p><a href="" id="typeinrecords"></a></p><h2 id="type-information-in-record-declarations" class="section-heading">
│ │ │    <a href="#type-information-in-record-declarations" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Type Information in Record Declarations</span>
│ │ │  </h2>
│ │ │  <p>The types of record fields can be specified in the declaration of the record.
│ │ │ -The syntax for this is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0965686886-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0965686886-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="0965686886-2">}</span><span class="p" data-group-id="0965686886-1">)</span><span class="p">.</span></code></pre><p>For fields without type annotations, their type defaults to <code class="inline">any()</code>. That is, the
│ │ │ -previous example is a shorthand for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5371953677-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5371953677-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="5371953677-3">(</span><span class="p" data-group-id="5371953677-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="5371953677-2">}</span><span class="p" data-group-id="5371953677-1">)</span><span class="p">.</span></code></pre><p>In the presence of initial values for fields, the type must be declared after
│ │ │ -the initialization, as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2272188577-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2272188577-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2272188577-3">[</span><span class="p" data-group-id="2272188577-3">]</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="2272188577-2">}</span><span class="p" data-group-id="2272188577-1">)</span><span class="p">.</span></code></pre><p>The initial values for fields are to be compatible with (that is, a member of)
│ │ │ +The syntax for this is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4084134121-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4084134121-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="4084134121-2">}</span><span class="p" data-group-id="4084134121-1">)</span><span class="p">.</span></code></pre><p>For fields without type annotations, their type defaults to <code class="inline">any()</code>. That is, the
│ │ │ +previous example is a shorthand for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2684840246-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2684840246-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="2684840246-3">(</span><span class="p" data-group-id="2684840246-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="2684840246-2">}</span><span class="p" data-group-id="2684840246-1">)</span><span class="p">.</span></code></pre><p>In the presence of initial values for fields, the type must be declared after
│ │ │ +the initialization, as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5327096909-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5327096909-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5327096909-3">[</span><span class="p" data-group-id="5327096909-3">]</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="5327096909-2">}</span><span class="p" data-group-id="5327096909-1">)</span><span class="p">.</span></code></pre><p>The initial values for fields are to be compatible with (that is, a member of)
│ │ │  the corresponding types. This is checked by the compiler and results in a
│ │ │  compilation error if a violation is detected.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 19, for fields without initial values, the singleton type
│ │ │  <code class="inline">'undefined'</code> was added to all declared types. In other words, the following
│ │ │ -two record declarations had identical effects:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8918860948-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8918860948-2">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="8918860948-3">(</span><span class="p" data-group-id="8918860948-3">)</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="8918860948-4">(</span><span class="p" data-group-id="8918860948-4">)</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="8918860948-2">}</span><span class="p" data-group-id="8918860948-1">)</span><span class="p">.</span><span class="w">
│ │ │ +two record declarations had identical effects:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7916521329-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7916521329-2">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="7916521329-3">(</span><span class="p" data-group-id="7916521329-3">)</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="7916521329-4">(</span><span class="p" data-group-id="7916521329-4">)</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="7916521329-2">}</span><span class="p" data-group-id="7916521329-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8918860948-5">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8918860948-6">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="8918860948-7">(</span><span class="p" data-group-id="8918860948-7">)</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="8918860948-8">(</span><span class="p" data-group-id="8918860948-8">)</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="8918860948-6">}</span><span class="p" data-group-id="8918860948-5">)</span><span class="p">.</span></code></pre><p>This is no longer the case. If you require <code class="inline">'undefined'</code> in your record field
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7916521329-5">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7916521329-6">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="7916521329-7">(</span><span class="p" data-group-id="7916521329-7">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="7916521329-8">(</span><span class="p" data-group-id="7916521329-8">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="7916521329-6">}</span><span class="p" data-group-id="7916521329-5">)</span><span class="p">.</span></code></pre><p>This is no longer the case. If you require <code class="inline">'undefined'</code> in your record field
│ │ │  type, you must explicitly add it to the typespec, as in the 2nd example.</p></section><p>Any record, containing type information or not, once defined, can be used as a
│ │ │  type using the following syntax:</p><pre><code class="text">#rec{}</code></pre><p>In addition, the record fields can be further specified when using a record type
│ │ │  by adding type information about the field as follows:</p><pre><code class="text">#rec{some_field :: Type}</code></pre><p>Any unspecified fields are assumed to have the type in the original record
│ │ │  declaration.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>When records are used to create patterns for ETS and Mnesia match functions,
│ │ │ -Dialyzer may need some help not to emit bad warnings. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="5658151181-1">(</span><span class="p" data-group-id="5658151181-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="5658151181-2">(</span><span class="p" data-group-id="5658151181-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5658151181-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5658151181-4">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="5658151181-5">(</span><span class="p" data-group-id="5658151181-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="5658151181-6">(</span><span class="p" data-group-id="5658151181-6">)</span><span class="p" data-group-id="5658151181-4">}</span><span class="p" data-group-id="5658151181-3">)</span><span class="p">.</span><span class="w">
│ │ │ +Dialyzer may need some help not to emit bad warnings. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="4568076204-1">(</span><span class="p" data-group-id="4568076204-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="4568076204-2">(</span><span class="p" data-group-id="4568076204-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4568076204-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4568076204-4">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="4568076204-5">(</span><span class="p" data-group-id="4568076204-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="4568076204-6">(</span><span class="p" data-group-id="4568076204-6">)</span><span class="p" data-group-id="4568076204-4">}</span><span class="p" data-group-id="4568076204-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="5658151181-7">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="5658151181-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="5658151181-8">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5658151181-9">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="5658151181-9">}</span><span class="p" data-group-id="5658151181-8">)</span><span class="p">.</span></code></pre><p>Dialyzer will emit a warning since <code class="inline">'_'</code> is not in the type of record field
│ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="4568076204-7">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="4568076204-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="4568076204-8">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4568076204-9">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="4568076204-9">}</span><span class="p" data-group-id="4568076204-8">)</span><span class="p">.</span></code></pre><p>Dialyzer will emit a warning since <code class="inline">'_'</code> is not in the type of record field
│ │ │  <code class="inline">height</code>.</p><p>The recommended way of dealing with this is to declare the smallest record
│ │ │  field types to accommodate all your needs, and then create refinements as
│ │ │ -needed. The modified example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5820805658-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5820805658-2">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="5820805658-3">(</span><span class="p" data-group-id="5820805658-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="5820805658-4">(</span><span class="p" data-group-id="5820805658-4">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="5820805658-2">}</span><span class="p" data-group-id="5820805658-1">)</span><span class="p">.</span><span class="w">
│ │ │ +needed. The modified example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4571648885-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4571648885-2">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="4571648885-3">(</span><span class="p" data-group-id="4571648885-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="4571648885-4">(</span><span class="p" data-group-id="4571648885-4">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="4571648885-2">}</span><span class="p" data-group-id="4571648885-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">person</span><span class="p" data-group-id="5820805658-5">(</span><span class="p" data-group-id="5820805658-5">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5820805658-6">{</span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="5820805658-7">(</span><span class="p" data-group-id="5820805658-7">)</span><span class="p" data-group-id="5820805658-6">}</span><span class="p">.</span></code></pre><p>In specifications and type declarations the type <code class="inline">person()</code> is to be preferred
│ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">person</span><span class="p" data-group-id="4571648885-5">(</span><span class="p" data-group-id="4571648885-5">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4571648885-6">{</span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="4571648885-7">(</span><span class="p" data-group-id="4571648885-7">)</span><span class="p" data-group-id="4571648885-6">}</span><span class="p">.</span></code></pre><p>In specifications and type declarations the type <code class="inline">person()</code> is to be preferred
│ │ │  before <code class="inline">#person{}</code>.</p></section><h2 id="specifications-for-functions" class="section-heading">
│ │ │    <a href="#specifications-for-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Specifications for Functions</span>
│ │ │  </h2>
│ │ │  <p>A specification (or contract) for a function is given using the <code class="inline">-spec</code>
│ │ │  attribute. The general format is as follows:</p><pre><code class="text">-spec Function(ArgType1, ..., ArgTypeN) -&gt; ReturnType.</code></pre><p>An implementation of the function with the same name <code class="inline">Function</code> must exist in
│ │ │  the current module, and the arity of the function must match the number of
│ │ │  arguments, otherwise the compilation fails.</p><p>The following longer format with module name is also valid as long as <code class="inline">Module</code>
│ │ │  is the name of the current module. This can be useful for documentation
│ │ │  purposes.</p><pre><code class="text">-spec Module:Function(ArgType1, ..., ArgTypeN) -&gt; ReturnType.</code></pre><p>Also, for documentation purposes, argument names can be given:</p><pre><code class="text">-spec Function(ArgName1 :: Type1, ..., ArgNameN :: TypeN) -&gt; RT.</code></pre><p>A function specification can be overloaded. That is, it can have several types,
│ │ │ -separated by a semicolon (<code class="inline">;</code>). For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="3860538327-1">(</span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="3860538327-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T3</span><span class="p">;</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="3860538327-2">(</span><span class="n">T4</span><span class="p">,</span><span class="w"> </span><span class="n">T5</span><span class="p" data-group-id="3860538327-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T6</span><span class="p">.</span></code></pre><p>A current restriction, which currently results in a warning by Dialyzer, is that
│ │ │ +separated by a semicolon (<code class="inline">;</code>). For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="5751431901-1">(</span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="5751431901-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T3</span><span class="p">;</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="5751431901-2">(</span><span class="n">T4</span><span class="p">,</span><span class="w"> </span><span class="n">T5</span><span class="p" data-group-id="5751431901-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T6</span><span class="p">.</span></code></pre><p>A current restriction, which currently results in a warning by Dialyzer, is that
│ │ │  the domains of the argument types cannot overlap. For example, the following
│ │ │ -specification results in a warning:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="0793258488-1">(</span><span class="nf">pos_integer</span><span class="p" data-group-id="0793258488-2">(</span><span class="p" data-group-id="0793258488-2">)</span><span class="p" data-group-id="0793258488-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="0793258488-3">(</span><span class="p" data-group-id="0793258488-3">)</span><span class="p">;</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="0793258488-4">(</span><span class="nf">integer</span><span class="p" data-group-id="0793258488-5">(</span><span class="p" data-group-id="0793258488-5">)</span><span class="p" data-group-id="0793258488-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0793258488-6">(</span><span class="p" data-group-id="0793258488-6">)</span><span class="p">.</span></code></pre><p>Type variables can be used in specifications to specify relations for the input
│ │ │ +specification results in a warning:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="1839979873-1">(</span><span class="nf">pos_integer</span><span class="p" data-group-id="1839979873-2">(</span><span class="p" data-group-id="1839979873-2">)</span><span class="p" data-group-id="1839979873-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="1839979873-3">(</span><span class="p" data-group-id="1839979873-3">)</span><span class="p">;</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="1839979873-4">(</span><span class="nf">integer</span><span class="p" data-group-id="1839979873-5">(</span><span class="p" data-group-id="1839979873-5">)</span><span class="p" data-group-id="1839979873-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1839979873-6">(</span><span class="p" data-group-id="1839979873-6">)</span><span class="p">.</span></code></pre><p>Type variables can be used in specifications to specify relations for the input
│ │ │  and output arguments of a function. For example, the following specification
│ │ │  defines the type of a polymorphic identity function:</p><pre><code class="text">-spec id(X) -&gt; X.</code></pre><p>Notice that the above specification does not restrict the input and output type
│ │ │  in any way. These types can be constrained by guard-like subtype constraints and
│ │ │ -provide bounded quantification:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="5578378701-1">(</span><span class="n">X</span><span class="p" data-group-id="5578378701-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="5578378701-2">(</span><span class="p" data-group-id="5578378701-2">)</span><span class="p">.</span></code></pre><p>Currently, the <code class="inline">::</code> constraint (read as &quot;is a subtype of&quot;) is the only guard
│ │ │ +provide bounded quantification:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="8387620154-1">(</span><span class="n">X</span><span class="p" data-group-id="8387620154-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="8387620154-2">(</span><span class="p" data-group-id="8387620154-2">)</span><span class="p">.</span></code></pre><p>Currently, the <code class="inline">::</code> constraint (read as &quot;is a subtype of&quot;) is the only guard
│ │ │  constraint that can be used in the <code class="inline">when</code> part of a <code class="inline">-spec</code> attribute.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The above function specification uses multiple occurrences of the same type
│ │ │  variable. That provides more type information than the following function
│ │ │ -specification, where the type variables are missing:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="6313957575-1">(</span><span class="nf">tuple</span><span class="p" data-group-id="6313957575-2">(</span><span class="p" data-group-id="6313957575-2">)</span><span class="p" data-group-id="6313957575-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="6313957575-3">(</span><span class="p" data-group-id="6313957575-3">)</span><span class="p">.</span></code></pre><p>The latter specification says that the function takes some tuple and returns
│ │ │ +specification, where the type variables are missing:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="6695766189-1">(</span><span class="nf">tuple</span><span class="p" data-group-id="6695766189-2">(</span><span class="p" data-group-id="6695766189-2">)</span><span class="p" data-group-id="6695766189-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="6695766189-3">(</span><span class="p" data-group-id="6695766189-3">)</span><span class="p">.</span></code></pre><p>The latter specification says that the function takes some tuple and returns
│ │ │  some tuple. The specification with the <code class="inline">X</code> type variable specifies that the
│ │ │  function takes a tuple and returns <em>the same</em> tuple.</p><p>However, it is up to the tools that process the specifications to choose
│ │ │  whether to take this extra information into account or not.</p></section><p>The scope of a <code class="inline">::</code> constraint is the <code class="inline">(...) -&gt; RetType</code> specification after
│ │ │  which it appears. To avoid confusion, it is suggested that different variables
│ │ │  are used in different constituents of an overloaded contract, as shown in the
│ │ │ -following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="2192501541-1">(</span><span class="p" data-group-id="2192501541-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="2192501541-3">(</span><span class="p" data-group-id="2192501541-3">)</span><span class="p" data-group-id="2192501541-2">}</span><span class="p" data-group-id="2192501541-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="2192501541-4">(</span><span class="p" data-group-id="2192501541-4">)</span><span class="p">;</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="2192501541-5">(</span><span class="p" data-group-id="2192501541-6">[</span><span class="n">Y</span><span class="p" data-group-id="2192501541-6">]</span><span class="p" data-group-id="2192501541-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="2192501541-7">(</span><span class="p" data-group-id="2192501541-7">)</span><span class="p">.</span></code></pre><p>Some functions in Erlang are not meant to return; either because they define
│ │ │ +following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="4782721703-1">(</span><span class="p" data-group-id="4782721703-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4782721703-3">(</span><span class="p" data-group-id="4782721703-3">)</span><span class="p" data-group-id="4782721703-2">}</span><span class="p" data-group-id="4782721703-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="4782721703-4">(</span><span class="p" data-group-id="4782721703-4">)</span><span class="p">;</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="4782721703-5">(</span><span class="p" data-group-id="4782721703-6">[</span><span class="n">Y</span><span class="p" data-group-id="4782721703-6">]</span><span class="p" data-group-id="4782721703-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4782721703-7">(</span><span class="p" data-group-id="4782721703-7">)</span><span class="p">.</span></code></pre><p>Some functions in Erlang are not meant to return; either because they define
│ │ │  servers or because they are used to throw exceptions, as in the following
│ │ │ -function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_error</span><span class="p" data-group-id="5365593090-1">(</span><span class="n">Err</span><span class="p" data-group-id="5365593090-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="5365593090-2">(</span><span class="p" data-group-id="5365593090-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Err</span><span class="p" data-group-id="5365593090-3">}</span><span class="p" data-group-id="5365593090-2">)</span><span class="p">.</span></code></pre><p>For such functions, it is recommended to use the special <a href="../../erts-15.2.7/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a> type
│ │ │ +function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_error</span><span class="p" data-group-id="5636184311-1">(</span><span class="n">Err</span><span class="p" data-group-id="5636184311-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="5636184311-2">(</span><span class="p" data-group-id="5636184311-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Err</span><span class="p" data-group-id="5636184311-3">}</span><span class="p" data-group-id="5636184311-2">)</span><span class="p">.</span></code></pre><p>For such functions, it is recommended to use the special <a href="../../erts-15.2.7/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a> type
│ │ │  for their &quot;return&quot;, through a contract of the following form:</p><pre><code class="text">-spec my_error(term()) -&gt; no_return().</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Erlang uses the shorthand version <code class="inline">_</code> as an anonymous type variable equivalent
│ │ │  to <a href="../../erts-15.2.7/doc/html/erlang.html#t:term/0"><code class="inline">term/0</code></a> or <a href="../../erts-15.2.7/doc/html/erlang.html#t:any/0"><code class="inline">any/0</code></a>. For example, the following function</p><pre><code class="text">-spec Function(string(), _) -&gt; string().</code></pre><p>is equivalent to:</p><pre><code class="text">-spec Function(string(), any()) -&gt; string().</code></pre></section>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/upcoming_incompatibilities.html
│ │ │ @@ -149,45 +149,45 @@
│ │ │  occurrences of <code class="inline">maybe</code> without quotes.</p><p><a href="" id="float_matching"></a></p><h3 id="0-0-and-0-0-will-no-longer-be-exactly-equal" class="section-heading">
│ │ │    <a href="#0-0-and-0-0-will-no-longer-be-exactly-equal" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">0.0 and -0.0 will no longer be exactly equal</span>
│ │ │  </h3>
│ │ │  <p>Currently, the floating point numbers <code class="inline">0.0</code> and <code class="inline">-0.0</code> have distinct internal
│ │ │ -representations. That can be seen if they are converted to binaries:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4145370951-1">&lt;&lt;</span><span class="mf">0.0</span><span class="o">/</span><span class="nb">float</span><span class="p" data-group-id="4145370951-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4145370951-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4145370951-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="p" data-group-id="4145370951-3">&lt;&lt;</span><span class="o">-</span><span class="mf">0.0</span><span class="o">/</span><span class="nb">float</span><span class="p" data-group-id="4145370951-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4145370951-4">&lt;&lt;</span><span class="mi">128</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4145370951-4">&gt;&gt;</span></code></pre><p>However, when they are matched against each other or compared using the <code class="inline">=:=</code>
│ │ │ +representations. That can be seen if they are converted to binaries:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0830158417-1">&lt;&lt;</span><span class="mf">0.0</span><span class="o">/</span><span class="nb">float</span><span class="p" data-group-id="0830158417-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0830158417-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="0830158417-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="p" data-group-id="0830158417-3">&lt;&lt;</span><span class="o">-</span><span class="mf">0.0</span><span class="o">/</span><span class="nb">float</span><span class="p" data-group-id="0830158417-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0830158417-4">&lt;&lt;</span><span class="mi">128</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="0830158417-4">&gt;&gt;</span></code></pre><p>However, when they are matched against each other or compared using the <code class="inline">=:=</code>
│ │ │  operator, they are considered to be equal. Thus, <code class="inline">0.0 =:= -0.0</code> currently
│ │ │  returns <code class="inline">true</code>.</p><p>In Erlang/OTP 27, <code class="inline">0.0 =:= -0.0</code> will return <code class="inline">false</code>, and matching <code class="inline">0.0</code> against
│ │ │  <code class="inline">-0.0</code> will fail. When used as map keys, <code class="inline">0.0</code> and <code class="inline">-0.0</code> will be considered to
│ │ │  be distinct.</p><p>The <code class="inline">==</code> operator will continue to return <code class="inline">true</code> for <code class="inline">0.0 == -0.0</code>.</p><p>To help to find code that might need to be revised, in OTP 27 there will be a
│ │ │  new compiler warning when matching against <code class="inline">0.0</code> or comparing to that value
│ │ │  using the <code class="inline">=:=</code> operator. The warning can be suppressed by matching against
│ │ │  <code class="inline">+0.0</code> instead of <code class="inline">0.0</code>.</p><p>We plan to introduce the same warning in OTP 26.1, but by default it will be
│ │ │  disabled.</p><p><a href="" id="singleton_typevars"></a></p><h3 id="singleton-type-variables-will-become-a-compile-time-error" class="section-heading">
│ │ │    <a href="#singleton-type-variables-will-become-a-compile-time-error" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Singleton type variables will become a compile-time error</span>
│ │ │  </h3>
│ │ │ -<p>Before Erlang/OTP 26, the compiler would silenty accept the following spec:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="3376172849-1">(</span><span class="n">Opts</span><span class="p" data-group-id="3376172849-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3376172849-2">(</span><span class="p" data-group-id="3376172849-2">)</span><span class="w"> </span><span class="k">when</span><span class="w">
│ │ │ -    </span><span class="n">Opts</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="3376172849-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Unknown</span><span class="p" data-group-id="3376172849-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="3376172849-4">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Unknown</span><span class="p" data-group-id="3376172849-4">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="3376172849-5">(</span><span class="p">_</span><span class="p" data-group-id="3376172849-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="p">.</span></code></pre><p>In OTP 26, the compiler emits a warning pointing out that the type variable
│ │ │ -<code class="inline">Unknown</code> is unbound:</p><pre><code class="makeup erlang" translate="no"><span class="ss">t</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">6</span><span class="p">:</span><span class="mi">18</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="ss">variable</span><span class="w"> </span><span class="ss">&#39;Unknown&#39;</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">only</span><span class="w"> </span><span class="ss">used</span><span class="w"> </span><span class="nf">once</span><span class="w"> </span><span class="p" data-group-id="9519516429-1">(</span><span class="ss">is</span><span class="w"> </span><span class="ss">unbound</span><span class="p" data-group-id="9519516429-1">)</span><span class="w">
│ │ │ +<p>Before Erlang/OTP 26, the compiler would silenty accept the following spec:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="9032603022-1">(</span><span class="n">Opts</span><span class="p" data-group-id="9032603022-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="9032603022-2">(</span><span class="p" data-group-id="9032603022-2">)</span><span class="w"> </span><span class="k">when</span><span class="w">
│ │ │ +    </span><span class="n">Opts</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="9032603022-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Unknown</span><span class="p" data-group-id="9032603022-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="9032603022-4">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Unknown</span><span class="p" data-group-id="9032603022-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="9032603022-5">(</span><span class="p">_</span><span class="p" data-group-id="9032603022-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="p">.</span></code></pre><p>In OTP 26, the compiler emits a warning pointing out that the type variable
│ │ │ +<code class="inline">Unknown</code> is unbound:</p><pre><code class="makeup erlang" translate="no"><span class="ss">t</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">6</span><span class="p">:</span><span class="mi">18</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="ss">variable</span><span class="w"> </span><span class="ss">&#39;Unknown&#39;</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">only</span><span class="w"> </span><span class="ss">used</span><span class="w"> </span><span class="nf">once</span><span class="w"> </span><span class="p" data-group-id="6171595952-1">(</span><span class="ss">is</span><span class="w"> </span><span class="ss">unbound</span><span class="p" data-group-id="6171595952-1">)</span><span class="w">
│ │ │  </span><span class="c1">%    6|     Opts :: {ok, Unknown} | {error, Unknown}.</span><span class="w">
│ │ │  </span><span class="c1">%     |                  ^</span></code></pre><p>In OTP 27, that warning will become an error.</p><p><a href="" id="escripts_will_be_compiled"></a></p><h3 id="escripts-will-be-compiled-by-default" class="section-heading">
│ │ │    <a href="#escripts-will-be-compiled-by-default" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Escripts will be compiled by default</span>
│ │ │  </h3>
│ │ │  <p>Escripts will be compiled by default instead of interpreted. That means that the
│ │ │  <code class="inline">compiler</code> application must be available.</p><p>The old behavior of interpreting escripts can be restored by adding the
│ │ │ -following line to the script file:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">mode</span><span class="p" data-group-id="2629488597-1">(</span><span class="ss">interpret</span><span class="p" data-group-id="2629488597-1">)</span><span class="p">.</span></code></pre><p>In OTP 28, support for interpreting an escript will be removed.</p><h3 id="code_path_choice-will-default-to-strict" class="section-heading">
│ │ │ +following line to the script file:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">mode</span><span class="p" data-group-id="1506145809-1">(</span><span class="ss">interpret</span><span class="p" data-group-id="1506145809-1">)</span><span class="p">.</span></code></pre><p>In OTP 28, support for interpreting an escript will be removed.</p><h3 id="code_path_choice-will-default-to-strict" class="section-heading">
│ │ │    <a href="#code_path_choice-will-default-to-strict" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">-code_path_choice will default to strict</span>
│ │ │  </h3>
│ │ │  <p>This command line option controls if paths given in the command line, boot
│ │ │  scripts, and the code server should be interpreted as is strict or relaxed.</p><p>OTP 26 and earlier defaults to <code class="inline">relaxed</code>, which means <code class="inline">-pa myapp/ebin</code> would
│ │ │ @@ -231,18 +231,18 @@
│ │ │  &quot;
│ │ │  String Content
│ │ │  &quot;
│ │ │  %%
│ │ │  %% In OTP 27 it is instead interpreted as a
│ │ │  %% Triple-Quoted String equivalent to
│ │ │  &quot;String Content&quot;</code></pre><pre><code class="makeup erlang" translate="no"><span class="s">&quot;&quot;</span><span class="s">&quot;&quot;</span><span class="w">
│ │ │ -</span><span class="o">++</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="6347127826-1">(</span><span class="p" data-group-id="6347127826-1">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ +</span><span class="o">++</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="4719360052-1">(</span><span class="p" data-group-id="4719360052-1">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │  </span><span class="s">&quot;&quot;</span><span class="s">&quot;&quot;</span><span class="w">
│ │ │  </span><span class="c1">%% Became</span><span class="w">
│ │ │ -</span><span class="s">&quot;&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="6347127826-2">(</span><span class="p" data-group-id="6347127826-2">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="w">
│ │ │ +</span><span class="s">&quot;&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="4719360052-2">(</span><span class="p" data-group-id="4719360052-2">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% In OTP 27 it is instead interpreted as a</span><span class="w">
│ │ │  </span><span class="c1">%% Triple-Quoted String (triple-or-more) equivalent to</span><span class="w">
│ │ │  </span><span class="s">&quot;++ foo() ++&quot;</span></code></pre><p>From Erlang/OTP 26.1 up to 27.0 the compiler issues a warning for a sequence of
│ │ │  3 or more double-quote characters since that is almost certainly a mistake or
│ │ │  something like a result of bad automatic code generation. If a users gets that
│ │ │  warning, the code should be corrected for example by inserting appropriate
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/.build
│ │ │ @@ -42,15 +42,15 @@
│ │ │  dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │  dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │  dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │  dist/lato-latin-ext-300-normal-VPGGJKJL.woff2
│ │ │  dist/lato-latin-ext-400-normal-N27NCBWW.woff2
│ │ │  dist/lato-latin-ext-700-normal-Q2L5DVMW.woff2
│ │ │  dist/remixicon-NKANDIL5.woff2
│ │ │ -dist/search_data-2EF91EE2.js
│ │ │ +dist/search_data-A22E82DE.js
│ │ │  dist/sidebar_items-EAF8F760.js
│ │ │  driver.html
│ │ │  driver_entry.html
│ │ │  epmd_cmd.html
│ │ │  erl_cmd.html
│ │ │  erl_dist_protocol.html
│ │ │  erl_driver.html
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/alt_dist.html
│ │ │ @@ -237,50 +237,50 @@
│ │ │  <code class="inline">uds_dist</code> example using a port driver written in C, <code class="inline">erl_uds_dist</code> is written
│ │ │  entirely in Erlang.</p><h3 id="exported-callback-functions" class="section-heading">
│ │ │    <a href="#exported-callback-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Exported Callback Functions</span>
│ │ │  </h3>
│ │ │ -<p>The following functions are mandatory:</p><ul><li><pre id="listen"><code class="makeup erlang" translate="no"><span class="nf">listen</span><span class="p" data-group-id="8047921334-1">(</span><span class="n">Name</span><span class="p" data-group-id="8047921334-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="8047921334-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8047921334-3">{</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p">,</span><span class="w"> </span><span class="n">Creation</span><span class="p" data-group-id="8047921334-3">}</span><span class="p" data-group-id="8047921334-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8047921334-4">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8047921334-4">}</span><span class="w">
│ │ │ -</span><span class="nf">listen</span><span class="p" data-group-id="8047921334-5">(</span><span class="n">Name</span><span class="p">,</span><span class="n">Host</span><span class="p" data-group-id="8047921334-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="8047921334-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8047921334-7">{</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p">,</span><span class="w"> </span><span class="n">Creation</span><span class="p" data-group-id="8047921334-7">}</span><span class="p" data-group-id="8047921334-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8047921334-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8047921334-8">}</span></code></pre><p><code class="inline">listen/2</code> is called once in order to listen for incoming connection requests.
│ │ │ +<p>The following functions are mandatory:</p><ul><li><pre id="listen"><code class="makeup erlang" translate="no"><span class="nf">listen</span><span class="p" data-group-id="1687235929-1">(</span><span class="n">Name</span><span class="p" data-group-id="1687235929-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="1687235929-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1687235929-3">{</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p">,</span><span class="w"> </span><span class="n">Creation</span><span class="p" data-group-id="1687235929-3">}</span><span class="p" data-group-id="1687235929-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="1687235929-4">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="1687235929-4">}</span><span class="w">
│ │ │ +</span><span class="nf">listen</span><span class="p" data-group-id="1687235929-5">(</span><span class="n">Name</span><span class="p">,</span><span class="n">Host</span><span class="p" data-group-id="1687235929-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="1687235929-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1687235929-7">{</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p">,</span><span class="w"> </span><span class="n">Creation</span><span class="p" data-group-id="1687235929-7">}</span><span class="p" data-group-id="1687235929-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="1687235929-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="1687235929-8">}</span></code></pre><p><code class="inline">listen/2</code> is called once in order to listen for incoming connection requests.
│ │ │  The call is made when the distribution is brought up. The argument <code class="inline">Name</code> is
│ │ │  the part of the node name before the <code class="inline">@</code> sign in the full node name. It can be
│ │ │  either an atom or a string. The argument <code class="inline">Host</code> is the part of the node name
│ │ │  after the <code class="inline">@</code> sign in the full node name. It is always a string.</p><p>The return value consists of a <code class="inline">Listen</code> handle (which is later passed to the
│ │ │  <a href="alt_dist.html#accept"><code class="inline">accept/1</code></a> callback), <code class="inline">Address</code> which is a
│ │ │  <code class="inline">#net_address{}</code> record with information about the address for the node (the
│ │ │  <code class="inline">#net_address{}</code> record is defined in <code class="inline">kernel/include/net_address.hrl</code>), and
│ │ │  <code class="inline">Creation</code> which (currently) is an integer <code class="inline">1</code>, <code class="inline">2</code>, or <code class="inline">3</code>.</p><p>If <a href="epmd_cmd.html"><code class="inline">epmd</code></a> is to be used for node discovery, you typically want
│ │ │  to use the <code class="inline">erl_epmd</code> module (part of the <code class="inline">kernel</code> application) in order to
│ │ │ -register the listen port with <code class="inline">epmd</code> and retrieve <code class="inline">Creation</code> to use.</p></li><li><pre id="address"><code class="makeup erlang" translate="no"><span class="nf">address</span><span class="p" data-group-id="9549958497-1">(</span><span class="p" data-group-id="9549958497-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +register the listen port with <code class="inline">epmd</code> and retrieve <code class="inline">Creation</code> to use.</p></li><li><pre id="address"><code class="makeup erlang" translate="no"><span class="nf">address</span><span class="p" data-group-id="0618697670-1">(</span><span class="p" data-group-id="0618697670-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="err"> </span><span class="err"> </span><span class="n">Address</span></code></pre><p><code class="inline">address/0</code> is called in order to get the <code class="inline">Address</code> part of the
│ │ │  <a href="alt_dist.html#listen"><code class="inline">listen/2</code></a> function without creating a listen socket.
│ │ │ -All fields except <code class="inline">address</code> have to be set in the returned record</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">address</span><span class="p" data-group-id="3266265115-1">(</span><span class="p" data-group-id="3266265115-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3266265115-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Host</span><span class="p" data-group-id="3266265115-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">inet</span><span class="p">:</span><span class="nf">gethostname</span><span class="p" data-group-id="3266265115-3">(</span><span class="p" data-group-id="3266265115-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">#</span><span class="ss">net_address</span><span class="p" data-group-id="3266265115-4">{</span><span class="w"> </span><span class="ss">host</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Host</span><span class="p">,</span><span class="w"> </span><span class="ss">protocol</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">tcp</span><span class="p">,</span><span class="w"> </span><span class="ss">family</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">inet6</span><span class="w"> </span><span class="p" data-group-id="3266265115-4">}</span><span class="p">.</span></code></pre></li><li><pre id="accept"><code class="makeup erlang" translate="no"><span class="nf">accept</span><span class="p" data-group-id="2865611110-1">(</span><span class="n">Listen</span><span class="p" data-group-id="2865611110-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +All fields except <code class="inline">address</code> have to be set in the returned record</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">address</span><span class="p" data-group-id="7656036843-1">(</span><span class="p" data-group-id="7656036843-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7656036843-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Host</span><span class="p" data-group-id="7656036843-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">inet</span><span class="p">:</span><span class="nf">gethostname</span><span class="p" data-group-id="7656036843-3">(</span><span class="p" data-group-id="7656036843-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">#</span><span class="ss">net_address</span><span class="p" data-group-id="7656036843-4">{</span><span class="w"> </span><span class="ss">host</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Host</span><span class="p">,</span><span class="w"> </span><span class="ss">protocol</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">tcp</span><span class="p">,</span><span class="w"> </span><span class="ss">family</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">inet6</span><span class="w"> </span><span class="p" data-group-id="7656036843-4">}</span><span class="p">.</span></code></pre></li><li><pre id="accept"><code class="makeup erlang" translate="no"><span class="nf">accept</span><span class="p" data-group-id="2055715051-1">(</span><span class="n">Listen</span><span class="p" data-group-id="2055715051-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="err"> </span><span class="err"> </span><span class="n">AcceptorPid</span></code></pre><p><code class="inline">accept/1</code> should spawn a process that accepts connections. This process
│ │ │  should preferably execute on <code class="inline">max</code> priority. The process identifier of this
│ │ │  process should be returned.</p><p>The <code class="inline">Listen</code> argument will be the same as the <code class="inline">Listen</code> handle part of the
│ │ │  return value of the <a href="alt_dist.html#listen"><code class="inline">listen/1</code></a> callback above.
│ │ │  <code class="inline">accept/1</code> is called only once when the distribution protocol is started.</p><p>The caller of this function is a representative for <code class="inline">net_kernel</code> (this may or
│ │ │  may not be the process registered as <code class="inline">net_kernel</code>) and is in this document
│ │ │  identified as <code class="inline">Kernel</code>. When a connection has been accepted by the acceptor
│ │ │  process, it needs to inform <code class="inline">Kernel</code> about the accepted connection. This is
│ │ │ -done by passing a message on the form:</p><pre><code class="makeup erlang" translate="no"><span class="n">Kernel</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6375415583-1">{</span><span class="ss">accept</span><span class="p">,</span><span class="w"> </span><span class="n">AcceptorPid</span><span class="p">,</span><span class="w"> </span><span class="n">DistController</span><span class="p">,</span><span class="w"> </span><span class="n">Family</span><span class="p">,</span><span class="w"> </span><span class="n">Proto</span><span class="p" data-group-id="6375415583-1">}</span></code></pre><p><code class="inline">DistController</code> is either the process or port identifier of the distribution
│ │ │ +done by passing a message on the form:</p><pre><code class="makeup erlang" translate="no"><span class="n">Kernel</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6719020167-1">{</span><span class="ss">accept</span><span class="p">,</span><span class="w"> </span><span class="n">AcceptorPid</span><span class="p">,</span><span class="w"> </span><span class="n">DistController</span><span class="p">,</span><span class="w"> </span><span class="n">Family</span><span class="p">,</span><span class="w"> </span><span class="n">Proto</span><span class="p" data-group-id="6719020167-1">}</span></code></pre><p><code class="inline">DistController</code> is either the process or port identifier of the distribution
│ │ │  controller for the connection. The distribution controller should be created
│ │ │  by the acceptor processes when a new connection is accepted. Its job is to
│ │ │  dispatch traffic on the connection.</p><p><code class="inline">Kernel</code> responds with one of the following messages:</p><ul><li><p><strong><code class="inline">{Kernel, controller, SupervisorPid}</code></strong> - The request was accepted and
│ │ │  <code class="inline">SupervisorPid</code> is the process identifier of the connection supervisor
│ │ │  process (which is created in the
│ │ │  <a href="alt_dist.html#accept_connection"><code class="inline">accept_connection/5</code></a> callback).</p></li><li><p><strong><code class="inline">{Kernel, unsupported_protocol}</code></strong> - The request was rejected. This is a
│ │ │  fatal error. The acceptor process should terminate.</p></li></ul><p>When an accept sequence has been completed the acceptor process is expected to
│ │ │ -continue accepting further requests.</p></li><li><pre id="accept_connection"><code class="makeup erlang" translate="no"><span class="nf">accept_connection</span><span class="p" data-group-id="4300355142-1">(</span><span class="n">AcceptorPid</span><span class="p">,</span><span class="w"> </span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">MyNode</span><span class="p">,</span><span class="w"> </span><span class="n">Allowed</span><span class="p">,</span><span class="w"> </span><span class="n">SetupTime</span><span class="p" data-group-id="4300355142-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +continue accepting further requests.</p></li><li><pre id="accept_connection"><code class="makeup erlang" translate="no"><span class="nf">accept_connection</span><span class="p" data-group-id="7734705126-1">(</span><span class="n">AcceptorPid</span><span class="p">,</span><span class="w"> </span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">MyNode</span><span class="p">,</span><span class="w"> </span><span class="n">Allowed</span><span class="p">,</span><span class="w"> </span><span class="n">SetupTime</span><span class="p" data-group-id="7734705126-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="err"> </span><span class="err"> </span><span class="n">ConnectionSupervisorPid</span></code></pre><p><code class="inline">accept_connection/5</code> should spawn a process that will perform the Erlang
│ │ │  distribution handshake for the connection. If the handshake successfully
│ │ │  completes it should continue to function as a connection supervisor. This
│ │ │  process should preferably execute on <code class="inline">max</code> priority and should be linked to
│ │ │  the caller. The <code class="inline">dist_util:net_ticker_spawn_options()</code> function can be called
│ │ │  to get spawn options suitable for this process which can be passed directly to
│ │ │  <a href="erlang.html#spawn_opt/4"><code class="inline">erlang:spawn_opt/4</code></a>. <code class="inline">dist_util:net_ticker_spawn_options()</code> will by default
│ │ │ @@ -294,15 +294,15 @@
│ │ │  <code class="inline">dist_util:handshake_other_started(HsData)</code>.</p></li><li><p><strong><code class="inline">Allowed</code></strong> - To be passed along to
│ │ │  <code class="inline">dist_util:handshake_other_started(HsData)</code>.</p></li><li><p><strong><code class="inline">SetupTime</code></strong> - Time used for creating a setup timer by a call to
│ │ │  <code class="inline">dist_util:start_timer(SetupTime)</code>. The timer should be passed along to
│ │ │  <code class="inline">dist_util:handshake_other_started(HsData)</code>.</p></li></ul><p>The created process should provide callbacks and other information needed for
│ │ │  the handshake in a <a href="alt_dist.html#hs_data_record"><code class="inline">#hs_data{}</code></a> record and call
│ │ │  <code class="inline">dist_util:handshake_other_started(HsData)</code> with this record.</p><p><code class="inline">dist_util:handshake_other_started(HsData)</code> will perform the handshake and if
│ │ │  the handshake successfully completes this process will then continue in a
│ │ │ -connection supervisor loop as long as the connection is up.</p></li><li><pre id="setup"><code class="makeup erlang" translate="no"><span class="nf">setup</span><span class="p" data-group-id="3227333453-1">(</span><span class="n">Node</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">MyNode</span><span class="p">,</span><span class="w"> </span><span class="n">LongOrShortNames</span><span class="p">,</span><span class="w"> </span><span class="n">SetupTime</span><span class="p" data-group-id="3227333453-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +connection supervisor loop as long as the connection is up.</p></li><li><pre id="setup"><code class="makeup erlang" translate="no"><span class="nf">setup</span><span class="p" data-group-id="0643809436-1">(</span><span class="n">Node</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">MyNode</span><span class="p">,</span><span class="w"> </span><span class="n">LongOrShortNames</span><span class="p">,</span><span class="w"> </span><span class="n">SetupTime</span><span class="p" data-group-id="0643809436-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="err"> </span><span class="err"> </span><span class="n">ConnectionSupervisorPid</span></code></pre><p><code class="inline">setup/5</code> should spawn a process that connects to <code class="inline">Node</code>. When connection has
│ │ │  been established it should perform the Erlang distribution handshake for the
│ │ │  connection. If the handshake successfully completes it should continue to
│ │ │  function as a connection supervisor. This process should preferably execute on
│ │ │  <code class="inline">max</code> priority and should be linked to the caller. The
│ │ │  <code class="inline">dist_util:net_ticker_spawn_options()</code> function can be called to get spawn
│ │ │  options suitable for this process which can be passed directly to
│ │ │ @@ -320,23 +320,23 @@
│ │ │  may not be the process registered as <code class="inline">net_kernel</code>) and is in this document
│ │ │  identified as <code class="inline">Kernel</code>.</p><p>This function should, besides spawning the connection supervisor, also create
│ │ │  a distribution controller. The distribution controller is either a process or
│ │ │  a port which is responsible for dispatching traffic.</p><p>The created process should provide callbacks and other information needed for
│ │ │  the handshake in a <a href="alt_dist.html#hs_data_record"><code class="inline">#hs_data{}</code></a> record and call
│ │ │  <code class="inline">dist_util:handshake_we_started(HsData)</code> with this record.</p><p><code class="inline">dist_util:handshake_we_started(HsData)</code> will perform the handshake and the
│ │ │  handshake successfully completes this process will then continue in a
│ │ │ -connection supervisor loop as long as the connection is up.</p></li><li><pre id="close"><code class="makeup erlang" translate="no"><span class="nf">close</span><span class="p" data-group-id="8707447674-1">(</span><span class="n">Listen</span><span class="p" data-group-id="8707447674-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="nf">void</span><span class="p" data-group-id="8707447674-2">(</span><span class="p" data-group-id="8707447674-2">)</span></code></pre><p>Called in order to close the <code class="inline">Listen</code> handle that originally was passed from
│ │ │ -the <a href="alt_dist.html#listen"><code class="inline">listen/1</code></a> callback.</p></li><li><pre id="select"><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="8015849343-1">(</span><span class="n">NodeName</span><span class="p" data-group-id="8015849343-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="nf">boolean</span><span class="p" data-group-id="8015849343-2">(</span><span class="p" data-group-id="8015849343-2">)</span></code></pre><p>Return <code class="inline">true</code> if the host name part of the <code class="inline">NodeName</code> is valid for use with
│ │ │ -this protocol; otherwise, <code class="inline">false</code>.</p></li></ul><p>There are also two optional functions that may be exported:</p><ul><li><pre id="setopts"><code class="makeup erlang" translate="no"><span class="nf">setopts</span><span class="p" data-group-id="8575120403-1">(</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="8575120403-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8575120403-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8575120403-2">}</span></code></pre><p>The argument <code class="inline">Listen</code> is the handle originally passed from the
│ │ │ +connection supervisor loop as long as the connection is up.</p></li><li><pre id="close"><code class="makeup erlang" translate="no"><span class="nf">close</span><span class="p" data-group-id="5285356706-1">(</span><span class="n">Listen</span><span class="p" data-group-id="5285356706-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="nf">void</span><span class="p" data-group-id="5285356706-2">(</span><span class="p" data-group-id="5285356706-2">)</span></code></pre><p>Called in order to close the <code class="inline">Listen</code> handle that originally was passed from
│ │ │ +the <a href="alt_dist.html#listen"><code class="inline">listen/1</code></a> callback.</p></li><li><pre id="select"><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="2934167796-1">(</span><span class="n">NodeName</span><span class="p" data-group-id="2934167796-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="nf">boolean</span><span class="p" data-group-id="2934167796-2">(</span><span class="p" data-group-id="2934167796-2">)</span></code></pre><p>Return <code class="inline">true</code> if the host name part of the <code class="inline">NodeName</code> is valid for use with
│ │ │ +this protocol; otherwise, <code class="inline">false</code>.</p></li></ul><p>There are also two optional functions that may be exported:</p><ul><li><pre id="setopts"><code class="makeup erlang" translate="no"><span class="nf">setopts</span><span class="p" data-group-id="4859230656-1">(</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="4859230656-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="4859230656-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="4859230656-2">}</span></code></pre><p>The argument <code class="inline">Listen</code> is the handle originally passed from the
│ │ │  <a href="alt_dist.html#listen"><code class="inline">listen/1</code></a> callback. The argument <code class="inline">Opts</code> is a list of
│ │ │ -options to set on future connections.</p></li><li><pre id="getopts"><code class="makeup erlang" translate="no"><span class="nf">getopts</span><span class="p" data-group-id="8904240224-1">(</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="8904240224-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="8904240224-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">OptionValues</span><span class="p" data-group-id="8904240224-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8904240224-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8904240224-3">}</span></code></pre><p>The argument <code class="inline">Listen</code> is the handle originally passed from the
│ │ │ +options to set on future connections.</p></li><li><pre id="getopts"><code class="makeup erlang" translate="no"><span class="nf">getopts</span><span class="p" data-group-id="0720833087-1">(</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="0720833087-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="0720833087-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">OptionValues</span><span class="p" data-group-id="0720833087-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="0720833087-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="0720833087-3">}</span></code></pre><p>The argument <code class="inline">Listen</code> is the handle originally passed from the
│ │ │  <a href="alt_dist.html#listen"><code class="inline">listen/1</code></a> callback. The argument <code class="inline">Opts</code> is a list of
│ │ │  options to read for future connections.</p></li></ul><p><a href="" id="hs_data_record"></a></p><h3 id="the-hs_data-record" class="section-heading">
│ │ │    <a href="#the-hs_data-record" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">The #hs_data{} Record</span>
│ │ │  </h3>
│ │ │ @@ -350,44 +350,44 @@
│ │ │  <a href="alt_dist.html#accept_connection"><code class="inline">accept_connection/5</code></a>.</p></li><li><p><strong><code class="inline" id="hs_data_other_node">other_node</code></strong> - Name of the other node. This field
│ │ │  is only mandatory when this node initiates the connection. That is, when
│ │ │  connection is set up via <a href="alt_dist.html#setup"><code class="inline">setup/5</code></a>.</p></li><li><p><strong><code class="inline" id="hs_data_this_node">this_node</code></strong> - The node name of this node.</p></li><li><p><strong><code class="inline" id="hs_data_socket">socket</code></strong> - The identifier of the distribution
│ │ │  controller.</p></li><li><p><strong><code class="inline" id="hs_data_timer">timer</code></strong> - The timer created using
│ │ │  <code class="inline">dist_util:start_timer/1</code>.</p></li><li><p><strong><code class="inline" id="hs_data_allowed">allowed</code></strong> - Information passed as <code class="inline">Allowed</code> to
│ │ │  <code class="inline">accept_connection/5</code>. This field is only mandatory when the remote node
│ │ │  initiated the connection. That is, when the connection is set up via
│ │ │ -<a href="alt_dist.html#accept_connection"><code class="inline">accept_connection/5</code></a>.</p></li><li><p><strong><code class="inline" id="hs_data_f_send">f_send</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3835500804-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3835500804-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="3835500804-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="3835500804-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Data</code>
│ │ │ -is io data to pass to the other side.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_recv">f_recv</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2599689871-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="2599689871-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2599689871-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Packet</span><span class="p" data-group-id="2599689871-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="2599689871-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="2599689871-3">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. If
│ │ │ +<a href="alt_dist.html#accept_connection"><code class="inline">accept_connection/5</code></a>.</p></li><li><p><strong><code class="inline" id="hs_data_f_send">f_send</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2581577419-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2581577419-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="2581577419-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="2581577419-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Data</code>
│ │ │ +is io data to pass to the other side.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_recv">f_recv</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0537365152-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="0537365152-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0537365152-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Packet</span><span class="p" data-group-id="0537365152-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="0537365152-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="0537365152-3">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. If
│ │ │  <code class="inline">Length</code> is <code class="inline">0</code>, all available bytes should be returned. If <code class="inline">Length &gt; 0</code>,
│ │ │  exactly <code class="inline">Length</code> bytes should be returned, or an error; possibly discarding
│ │ │  less than <code class="inline">Length</code> bytes of data when the connection is closed from the other
│ │ │  side. It is used for passive receive of data from the other end.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_setopts_pre_nodeup">f_setopts_pre_nodeup</code></strong> - A fun with the
│ │ │ -following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8794127626-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="8794127626-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8794127626-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8794127626-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. Called
│ │ │ +following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5111419560-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="5111419560-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="5111419560-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="5111419560-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. Called
│ │ │  just before the distribution channel is taken up for normal traffic.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_setopts_post_nodeup">f_setopts_post_nodeup</code></strong> - A fun with
│ │ │ -the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="9235359107-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="9235359107-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="9235359107-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="9235359107-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. Called
│ │ │ -just after distribution channel has been taken up for normal traffic.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_getll">f_getll</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="9135839497-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="9135839497-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">ID</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">ID</code> is
│ │ │ +the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8922436958-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="8922436958-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8922436958-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8922436958-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. Called
│ │ │ +just after distribution channel has been taken up for normal traffic.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_getll">f_getll</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0260507694-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="0260507694-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">ID</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">ID</code> is
│ │ │  the identifier of the low level entity that handles the connection (often
│ │ │ -<code class="inline">DistCtrlr</code> itself).</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_address">f_address</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7574975662-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="7574975662-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">NetAddress</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Node</code> is
│ │ │ +<code class="inline">DistCtrlr</code> itself).</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_address">f_address</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7253445309-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="7253445309-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">NetAddress</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Node</code> is
│ │ │  the node name of the node on the other end, and <code class="inline">NetAddress</code> is a
│ │ │  <code class="inline">#net_address{}</code> record with information about the address for the <code class="inline">Node</code> on
│ │ │  the other end of the connection. The <code class="inline">#net_address{}</code> record is defined in
│ │ │ -<code class="inline">kernel/include/net_address.hrl</code>.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_mf_tick">mf_tick</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7195983620-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="7195983620-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">void</span><span class="p" data-group-id="7195983620-2">(</span><span class="p" data-group-id="7195983620-2">)</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. This
│ │ │ +<code class="inline">kernel/include/net_address.hrl</code>.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_mf_tick">mf_tick</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3125523116-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="3125523116-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">void</span><span class="p" data-group-id="3125523116-2">(</span><span class="p" data-group-id="3125523116-2">)</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. This
│ │ │  function should send information over the connection that is not interpreted
│ │ │  by the other end while increasing the statistics of received packets on the
│ │ │  other end. This is usually implemented by sending an empty packet.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>It is of vital importance that this operation does not block the caller for
│ │ │ -a long time. This since it is called from the connection supervisor.</p></section><p>Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_mf_getstat">mf_getstat</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4171777304-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="4171777304-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4171777304-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Received</span><span class="p">,</span><span class="w"> </span><span class="n">Sent</span><span class="p">,</span><span class="w"> </span><span class="n">PendSend</span><span class="p" data-group-id="4171777304-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Received</code>
│ │ │ +a long time. This since it is called from the connection supervisor.</p></section><p>Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_mf_getstat">mf_getstat</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="9156044864-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="9156044864-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9156044864-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Received</span><span class="p">,</span><span class="w"> </span><span class="n">Sent</span><span class="p">,</span><span class="w"> </span><span class="n">PendSend</span><span class="p" data-group-id="9156044864-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Received</code>
│ │ │  is received packets, <code class="inline">Sent</code> is sent packets, and <code class="inline">PendSend</code> is amount of data
│ │ │  in queue to be sent (typically in bytes, but <code class="inline">dist_util</code> only checks whether
│ │ │  the value is non-zero to know there is data in queue) or a <a href="erlang.html#t:boolean/0"><code class="inline">boolean/0</code></a>
│ │ │  indicating whether there are packets in queue to be sent.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>It is of vital importance that this operation does not block the caller for
│ │ │  a long time. This since it is called from the connection supervisor.</p></section><p>Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_request_type">request_type</code></strong> - The request <code class="inline">Type</code> as passed to
│ │ │  <a href="alt_dist.html#setup"><code class="inline">setup/5</code></a>. This is only mandatory when the connection has
│ │ │ -been initiated by this node. That is, the connection is set up via <code class="inline">setup/5</code>.</p></li><li><p><strong><code class="inline" id="hs_data_mf_setopts">mf_setopts</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7279341194-1">(</span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7279341194-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="7279341194-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="7279341194-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Opts</code>
│ │ │ -is a list of options to set on the connection.</p><p>This function is optional. Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_mf_getopts">mf_getopts</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4430166915-1">(</span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="4430166915-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4430166915-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">OptionValues</span><span class="p" data-group-id="4430166915-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="4430166915-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="4430166915-3">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Opts</code>
│ │ │ +been initiated by this node. That is, the connection is set up via <code class="inline">setup/5</code>.</p></li><li><p><strong><code class="inline" id="hs_data_mf_setopts">mf_setopts</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7312866407-1">(</span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7312866407-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="7312866407-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="7312866407-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Opts</code>
│ │ │ +is a list of options to set on the connection.</p><p>This function is optional. Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_mf_getopts">mf_getopts</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="6119602104-1">(</span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="6119602104-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6119602104-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">OptionValues</span><span class="p" data-group-id="6119602104-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="6119602104-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="6119602104-3">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Opts</code>
│ │ │  is a list of options to read for the connection.</p><p>This function is optional. Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_f_handshake_complete">f_handshake_complete</code></strong> - A fun with the
│ │ │ -following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8089230610-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p">,</span><span class="w"> </span><span class="n">DHandle</span><span class="p" data-group-id="8089230610-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">void</span><span class="p" data-group-id="8089230610-2">(</span><span class="p" data-group-id="8089230610-2">)</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Node</code> is
│ │ │ +following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0226603965-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p">,</span><span class="w"> </span><span class="n">DHandle</span><span class="p" data-group-id="0226603965-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">void</span><span class="p" data-group-id="0226603965-2">(</span><span class="p" data-group-id="0226603965-2">)</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Node</code> is
│ │ │  the node name of the node connected at the other end, and <code class="inline">DHandle</code> is a
│ │ │  distribution handle needed by a distribution controller process when calling
│ │ │  the following BIFs:</p><ul><li><a href="erlang.html#dist_ctrl_get_data/1"><code class="inline">erlang:dist_ctrl_get_data/1</code></a></li><li><a href="erlang.html#dist_ctrl_get_data_notification/1"><code class="inline">erlang:dist_ctrl_get_data_notification/1</code></a></li><li><a href="erlang.html#dist_ctrl_input_handler/2"><code class="inline">erlang:dist_ctrl_input_handler/2</code></a></li><li><a href="erlang.html#dist_ctrl_put_data/2"><code class="inline">erlang:dist_ctrl_put_data/2</code></a></li></ul><p>This function is called when the handshake has completed and the distribution
│ │ │  channel is up. The distribution controller can begin dispatching traffic over
│ │ │  the channel. This function is optional.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_add_flags">add_flags</code></strong> -
│ │ │  <a href="erl_dist_protocol.html#dflags">Distribution flags</a> to add to the connection.
│ │ │  Currently all (non obsolete) flags will automatically be enabled.</p><p>This flag field is optional.</p></li><li><p><strong><code class="inline" id="hs_data_reject_flags">reject_flags</code></strong> -
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/automaticyieldingofccode.html
│ │ │ @@ -209,17 +209,17 @@
│ │ │  they have to follow certain restrictions. The convention for making
│ │ │  this clear is to have a comment above the function that explains that
│ │ │  the function is transformed by YCF (see <code class="inline">maps_values_1_helper</code> in
│ │ │  <code class="inline">erl_map.c</code> for an example). If only the transformed version of the
│ │ │  function is used, the convention is to &quot;comment out&quot; the source for the
│ │ │  function by surrounding it with the following <code class="inline">#ifdef</code> (this way, one
│ │ │  will not get warnings about unused functions):</p><pre><code class="makeup erlang" translate="no"><span class="p">#</span><span class="ss">ifdef</span><span class="w"> </span><span class="n">INCLUDE_YCF_TRANSFORMED_ONLY_FUNCTIONS</span><span class="w">
│ │ │ -</span><span class="ss">void</span><span class="w"> </span><span class="nf">my_fun</span><span class="p" data-group-id="0918089235-1">(</span><span class="p" data-group-id="0918089235-1">)</span><span class="w"> </span><span class="p" data-group-id="0918089235-2">{</span><span class="w">
│ │ │ +</span><span class="ss">void</span><span class="w"> </span><span class="nf">my_fun</span><span class="p" data-group-id="8066241034-1">(</span><span class="p" data-group-id="8066241034-1">)</span><span class="w"> </span><span class="p" data-group-id="8066241034-2">{</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0918089235-2">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8066241034-2">}</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="ss">endif</span><span class="w"> </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">INCLUDE_YCF_TRANSFORMED_ONLY_FUNCTIONS</span><span class="w"> </span><span class="o">*</span><span class="o">/</span></code></pre><p>While editing the function one can define
│ │ │  <code class="inline">INCLUDE_YCF_TRANSFORMED_ONLY_FUNCTIONS</code> so that one can see errors
│ │ │  and warnings in the non-transformed source.</p><h3 id="where-to-place-ycf-transformed-functions" class="section-heading">
│ │ │    <a href="#where-to-place-ycf-transformed-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Where to Place YCF Transformed Functions</span>
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/beam_makeops.html
│ │ │ @@ -151,17 +151,17 @@
│ │ │  The loader translates generic instructions to specific instructions.
│ │ │  In general, for each generic instruction, there exists a family of
│ │ │  specific instructions.  The OTP 20 release has 389 specific
│ │ │  instructions.</p></li><li><p>The implementation of specific instructions for the traditional
│ │ │  BEAM interpreter. For the <a href="beamasm.html">BeamAsm JIT</a> introduced
│ │ │  in OTP 24, the implementation of instructions are defined in emitter
│ │ │  functions written in C++.</p></li></ul><p>Generic instructions have typed operands. Here are a few examples of
│ │ │ -operands for <code class="inline">move/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1508880715-1">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="1508880715-2">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">id</span><span class="p" data-group-id="1508880715-2">}</span><span class="p">,</span><span class="p" data-group-id="1508880715-3">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1508880715-3">}</span><span class="p" data-group-id="1508880715-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1508880715-4">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="1508880715-5">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1508880715-5">}</span><span class="p">,</span><span class="p" data-group-id="1508880715-6">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="1508880715-6">}</span><span class="p" data-group-id="1508880715-4">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1508880715-7">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="1508880715-8">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1508880715-8">}</span><span class="p">,</span><span class="p" data-group-id="1508880715-9">{</span><span class="ss">y</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1508880715-9">}</span><span class="p" data-group-id="1508880715-7">}</span><span class="p">.</span></code></pre><p>When those instructions are loaded, the loader rewrites them
│ │ │ +operands for <code class="inline">move/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1203597290-1">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="1203597290-2">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">id</span><span class="p" data-group-id="1203597290-2">}</span><span class="p">,</span><span class="p" data-group-id="1203597290-3">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1203597290-3">}</span><span class="p" data-group-id="1203597290-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1203597290-4">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="1203597290-5">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1203597290-5">}</span><span class="p">,</span><span class="p" data-group-id="1203597290-6">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="1203597290-6">}</span><span class="p" data-group-id="1203597290-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1203597290-7">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="1203597290-8">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1203597290-8">}</span><span class="p">,</span><span class="p" data-group-id="1203597290-9">{</span><span class="ss">y</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1203597290-9">}</span><span class="p" data-group-id="1203597290-7">}</span><span class="p">.</span></code></pre><p>When those instructions are loaded, the loader rewrites them
│ │ │  to specific instructions:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move_cx</span><span class="w"> </span><span class="ss">id</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │  </span><span class="ss">move_xx</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="mi">0</span><span class="w">
│ │ │  </span><span class="ss">move_xy</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="mi">1</span></code></pre><p>Corresponding to each generic instruction, there is a family of
│ │ │  specific instructions.  The types that an instance of a specific
│ │ │  instruction can handle are encoded in the instruction names.  For
│ │ │  example, <code class="inline">move_xy</code> takes an X register number as the first operand and
│ │ │  a Y register number as the second operand.  <code class="inline">move_cx</code> takes a tagged
│ │ │ @@ -185,17 +185,17 @@
│ │ │  </span><span class="ss">move</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="ss">x</span></code></pre><p>Each specific instructions is defined by following the name of the
│ │ │  instruction with the types for each operand.  An operand type is a
│ │ │  single letter.  For example, <code class="inline">x</code> means an X register, <code class="inline">y</code>
│ │ │  means a Y register, and <code class="inline">c</code> is a &quot;constant&quot; (a tagged term such as
│ │ │  an integer, an atom, or a literal).</p><p>Now let's look at the implementation of the <code class="inline">move</code> instruction.  There
│ │ │  are multiple files containing implementations of instructions in the
│ │ │  <code class="inline">erts/emulator/beam/emu</code> directory.  The <code class="inline">move</code> instruction is defined
│ │ │ -in <code class="inline">instrs.tab</code>.  It looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="5542471676-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="5542471676-1">)</span><span class="w"> </span><span class="p" data-group-id="5542471676-2">{</span><span class="w">
│ │ │ +in <code class="inline">instrs.tab</code>.  It looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="9795177940-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="9795177940-1">)</span><span class="w"> </span><span class="p" data-group-id="9795177940-2">{</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5542471676-2">}</span></code></pre><p>The implementation for an instruction largely follows the C syntax,
│ │ │ +</span><span class="p" data-group-id="9795177940-2">}</span></code></pre><p>The implementation for an instruction largely follows the C syntax,
│ │ │  except that the variables in the function head don't have any types.
│ │ │  The <code class="inline">$</code> before an identifier denotes a macro expansion.  Thus,
│ │ │  <code class="inline">$Src</code> will expand to the code to pick up the source operand for
│ │ │  the instruction and <code class="inline">$Dst</code> to the code for the destination register.</p><p>We will look at the code for each specific instruction in turn.  To
│ │ │  make the code easier to understand, let's first look at the memory
│ │ │  layout for the instruction <code class="inline">{move,{atom,id},{x,5}}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="w">     </span><span class="o">+</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">+</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">+</span><span class="w">
│ │ │  </span><span class="n">I</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">|</span><span class="w">                 </span><span class="mi">40</span><span class="w"> </span><span class="p">|</span><span class="w">       </span><span class="p">&amp;&amp;</span><span class="ss">lb_move_cx</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │ @@ -204,61 +204,61 @@
│ │ │       </span><span class="o">+</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">+</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">+</span></code></pre><p>This example and all other examples in the document assumes a 64-bit
│ │ │  architecture, and furthermore that pointers to C code fit in 32 bits.</p><p><code class="inline">I</code> in the BEAM virtual machine is the instruction pointer.  When BEAM
│ │ │  executes an instruction, <code class="inline">I</code> points to the first word of the
│ │ │  instruction.</p><p><code class="inline">&amp;&amp;lb_move_cx</code> is the address to C code that implements <code class="inline">move_cx</code>.  It
│ │ │  is stored in the lower 32 bits of the word.  In the upper 32 bits is
│ │ │  the byte offset to the X register; the register number 5 has been
│ │ │  multiplied by the word size size 8.</p><p>In the next word the tagged atom <code class="inline">id</code> is stored.</p><p>With that background, we can look at the generated code for <code class="inline">move_cx</code>
│ │ │ -in <code class="inline">beam_hot.h</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="3137283872-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="3137283872-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3137283872-2">{</span><span class="w">
│ │ │ -  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="3137283872-3">(</span><span class="n">I</span><span class="p" data-group-id="3137283872-4">[</span><span class="mi">2</span><span class="p" data-group-id="3137283872-4">]</span><span class="p" data-group-id="3137283872-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">xb</span><span class="p" data-group-id="3137283872-5">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="3137283872-6">(</span><span class="n">I</span><span class="p" data-group-id="3137283872-7">[</span><span class="mi">0</span><span class="p" data-group-id="3137283872-7">]</span><span class="p" data-group-id="3137283872-6">)</span><span class="p" data-group-id="3137283872-5">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="3137283872-8">[</span><span class="mi">1</span><span class="p" data-group-id="3137283872-8">]</span><span class="p">;</span><span class="w">
│ │ │ +in <code class="inline">beam_hot.h</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="6537102763-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="6537102763-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6537102763-2">{</span><span class="w">
│ │ │ +  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="6537102763-3">(</span><span class="n">I</span><span class="p" data-group-id="6537102763-4">[</span><span class="mi">2</span><span class="p" data-group-id="6537102763-4">]</span><span class="p" data-group-id="6537102763-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">xb</span><span class="p" data-group-id="6537102763-5">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="6537102763-6">(</span><span class="n">I</span><span class="p" data-group-id="6537102763-7">[</span><span class="mi">0</span><span class="p" data-group-id="6537102763-7">]</span><span class="p" data-group-id="6537102763-6">)</span><span class="p" data-group-id="6537102763-5">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="6537102763-8">[</span><span class="mi">1</span><span class="p" data-group-id="6537102763-8">]</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="3137283872-9">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="3137283872-10">(</span><span class="ss">next_pf</span><span class="p" data-group-id="3137283872-10">)</span><span class="p" data-group-id="3137283872-9">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">GotoPF</span><span class="p" data-group-id="3137283872-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="3137283872-11">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3137283872-2">}</span></code></pre><p>We will go through each line in turn.</p><ul><li><p><code class="inline">OpCase(move_cx):</code> defines a label for the instruction.  The
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="6537102763-9">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="6537102763-10">(</span><span class="ss">next_pf</span><span class="p" data-group-id="6537102763-10">)</span><span class="p" data-group-id="6537102763-9">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">GotoPF</span><span class="p" data-group-id="6537102763-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="6537102763-11">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6537102763-2">}</span></code></pre><p>We will go through each line in turn.</p><ul><li><p><code class="inline">OpCase(move_cx):</code> defines a label for the instruction.  The
│ │ │  <code class="inline">OpCase()</code> macro is defined in <code class="inline">beam_emu.c</code>.  It will expand this line
│ │ │  to <code class="inline">lb_move_cx:</code>.</p></li><li><p><code class="inline">BeamInstr next_pf = BeamCodeAddr(I[2]);</code> fetches the pointer to
│ │ │  code for the next instruction to be executed.  The <code class="inline">BeamCodeAddr()</code>
│ │ │  macro extracts the pointer from the lower 32 bits of the instruction
│ │ │  word.</p></li><li><p><code class="inline">xb(BeamExtraData(I[0])) = I[1];</code> is the expansion of <code class="inline">$Dst = $Src</code>.
│ │ │  <code class="inline">BeamExtraData()</code> is a macro that will extract the upper 32 bits from
│ │ │  the instruction word.  In this example, it will return 40 which is the
│ │ │  byte offset for X register 5.  The <code class="inline">xb()</code> macro will cast a byte
│ │ │  pointer to an <code class="inline">Eterm</code> pointer and dereference it.  The <code class="inline">I[1]</code> on
│ │ │  the right-hand side of the <code class="inline">=</code> fetches an Erlang term (the atom <code class="inline">id</code> in
│ │ │  this case).</p></li><li><p><code class="inline">I += 2</code> advances the instruction pointer to the next
│ │ │  instruction.</p></li><li><p>In a debug-compiled emulator, <code class="inline">ASSERT(VALID_INSTR(next_pf));</code> makes
│ │ │  sure that <code class="inline">next_pf</code> is a valid instruction (that is, that it points
│ │ │ -within the <code class="inline">process_main()</code> function in <code class="inline">beam_emu.c</code>).</p></li><li><p><code class="inline">GotoPF(next_pf);</code> transfers control to the next instruction.</p></li></ul><p>Now let's look at the implementation of <code class="inline">move_xx</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="1256518430-1">(</span><span class="ss">move_xx</span><span class="p" data-group-id="1256518430-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1256518430-2">{</span><span class="w">
│ │ │ -  </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">tmp_packed1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamExtraData</span><span class="p" data-group-id="1256518430-3">(</span><span class="n">I</span><span class="p" data-group-id="1256518430-4">[</span><span class="mi">0</span><span class="p" data-group-id="1256518430-4">]</span><span class="p" data-group-id="1256518430-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="1256518430-5">(</span><span class="n">I</span><span class="p" data-group-id="1256518430-6">[</span><span class="mi">1</span><span class="p" data-group-id="1256518430-6">]</span><span class="p" data-group-id="1256518430-5">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">xb</span><span class="p" data-group-id="1256518430-7">(</span><span class="p" data-group-id="1256518430-8">(</span><span class="ss">tmp_packed1</span><span class="p">&gt;&gt;</span><span class="n">BEAM_TIGHT_SHIFT</span><span class="p" data-group-id="1256518430-8">)</span><span class="p" data-group-id="1256518430-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="1256518430-9">(</span><span class="ss">tmp_packed1</span><span class="err">&amp;</span><span class="n">BEAM_TIGHT_MASK</span><span class="p" data-group-id="1256518430-9">)</span><span class="p">;</span><span class="w">
│ │ │ +within the <code class="inline">process_main()</code> function in <code class="inline">beam_emu.c</code>).</p></li><li><p><code class="inline">GotoPF(next_pf);</code> transfers control to the next instruction.</p></li></ul><p>Now let's look at the implementation of <code class="inline">move_xx</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="5855116543-1">(</span><span class="ss">move_xx</span><span class="p" data-group-id="5855116543-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5855116543-2">{</span><span class="w">
│ │ │ +  </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">tmp_packed1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamExtraData</span><span class="p" data-group-id="5855116543-3">(</span><span class="n">I</span><span class="p" data-group-id="5855116543-4">[</span><span class="mi">0</span><span class="p" data-group-id="5855116543-4">]</span><span class="p" data-group-id="5855116543-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="5855116543-5">(</span><span class="n">I</span><span class="p" data-group-id="5855116543-6">[</span><span class="mi">1</span><span class="p" data-group-id="5855116543-6">]</span><span class="p" data-group-id="5855116543-5">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">xb</span><span class="p" data-group-id="5855116543-7">(</span><span class="p" data-group-id="5855116543-8">(</span><span class="ss">tmp_packed1</span><span class="p">&gt;&gt;</span><span class="n">BEAM_TIGHT_SHIFT</span><span class="p" data-group-id="5855116543-8">)</span><span class="p" data-group-id="5855116543-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="5855116543-9">(</span><span class="ss">tmp_packed1</span><span class="err">&amp;</span><span class="n">BEAM_TIGHT_MASK</span><span class="p" data-group-id="5855116543-9">)</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="1256518430-10">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="1256518430-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="1256518430-11">)</span><span class="p" data-group-id="1256518430-10">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">GotoPF</span><span class="p" data-group-id="1256518430-12">(</span><span class="ss">next_pf</span><span class="p" data-group-id="1256518430-12">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1256518430-2">}</span></code></pre><p>We will go through the lines that are new or have changed compared to
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="5855116543-10">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="5855116543-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="5855116543-11">)</span><span class="p" data-group-id="5855116543-10">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">GotoPF</span><span class="p" data-group-id="5855116543-12">(</span><span class="ss">next_pf</span><span class="p" data-group-id="5855116543-12">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5855116543-2">}</span></code></pre><p>We will go through the lines that are new or have changed compared to
│ │ │  <code class="inline">move_cx</code>.</p><ul><li><p><code class="inline">Eterm tmp_packed1 = BeamExtraData(I[0]);</code> picks up both X register
│ │ │  numbers packed into the upper 32 bits of the instruction word.</p></li><li><p><code class="inline">BeamInstr next_pf = BeamCodeAddr(I[1]);</code> pre-fetches the address of
│ │ │  the next instruction. Note that because both X registers operands fits
│ │ │  into the instruction word, the next instruction is in the very next
│ │ │  word.</p></li><li><p><code class="inline">xb((tmp_packed1&gt;&gt;BEAM_TIGHT_SHIFT)) = xb(tmp_packed1&amp;BEAM_TIGHT_MASK);</code>
│ │ │  copies the source to the destination.  (For a 64-bit architecture,
│ │ │  <code class="inline">BEAM_TIGHT_SHIFT</code> is 16 and <code class="inline">BEAM_TIGHT_MASK</code> is <code class="inline">0xFFFF</code>.)</p></li><li><p><code class="inline">I += 1;</code> advances the instruction pointer to the next instruction.</p></li></ul><p><code class="inline">move_xy</code> is almost identical to <code class="inline">move_xx</code>.  The only difference is
│ │ │  the use of the <code class="inline">yb()</code> macro instead of <code class="inline">xb()</code> to reference the
│ │ │ -destination register:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="9282615285-1">(</span><span class="ss">move_xy</span><span class="p" data-group-id="9282615285-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9282615285-2">{</span><span class="w">
│ │ │ -  </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">tmp_packed1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamExtraData</span><span class="p" data-group-id="9282615285-3">(</span><span class="n">I</span><span class="p" data-group-id="9282615285-4">[</span><span class="mi">0</span><span class="p" data-group-id="9282615285-4">]</span><span class="p" data-group-id="9282615285-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="9282615285-5">(</span><span class="n">I</span><span class="p" data-group-id="9282615285-6">[</span><span class="mi">1</span><span class="p" data-group-id="9282615285-6">]</span><span class="p" data-group-id="9282615285-5">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">yb</span><span class="p" data-group-id="9282615285-7">(</span><span class="p" data-group-id="9282615285-8">(</span><span class="ss">tmp_packed1</span><span class="p">&gt;&gt;</span><span class="n">BEAM_TIGHT_SHIFT</span><span class="p" data-group-id="9282615285-8">)</span><span class="p" data-group-id="9282615285-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="9282615285-9">(</span><span class="ss">tmp_packed1</span><span class="err">&amp;</span><span class="n">BEAM_TIGHT_MASK</span><span class="p" data-group-id="9282615285-9">)</span><span class="p">;</span><span class="w">
│ │ │ +destination register:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="2851071054-1">(</span><span class="ss">move_xy</span><span class="p" data-group-id="2851071054-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2851071054-2">{</span><span class="w">
│ │ │ +  </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">tmp_packed1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamExtraData</span><span class="p" data-group-id="2851071054-3">(</span><span class="n">I</span><span class="p" data-group-id="2851071054-4">[</span><span class="mi">0</span><span class="p" data-group-id="2851071054-4">]</span><span class="p" data-group-id="2851071054-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="2851071054-5">(</span><span class="n">I</span><span class="p" data-group-id="2851071054-6">[</span><span class="mi">1</span><span class="p" data-group-id="2851071054-6">]</span><span class="p" data-group-id="2851071054-5">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">yb</span><span class="p" data-group-id="2851071054-7">(</span><span class="p" data-group-id="2851071054-8">(</span><span class="ss">tmp_packed1</span><span class="p">&gt;&gt;</span><span class="n">BEAM_TIGHT_SHIFT</span><span class="p" data-group-id="2851071054-8">)</span><span class="p" data-group-id="2851071054-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="2851071054-9">(</span><span class="ss">tmp_packed1</span><span class="err">&amp;</span><span class="n">BEAM_TIGHT_MASK</span><span class="p" data-group-id="2851071054-9">)</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="9282615285-10">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="9282615285-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="9282615285-11">)</span><span class="p" data-group-id="9282615285-10">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">GotoPF</span><span class="p" data-group-id="9282615285-12">(</span><span class="ss">next_pf</span><span class="p" data-group-id="9282615285-12">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9282615285-2">}</span></code></pre><h3 id="transformation-rules" class="section-heading">
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="2851071054-10">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="2851071054-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="2851071054-11">)</span><span class="p" data-group-id="2851071054-10">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">GotoPF</span><span class="p" data-group-id="2851071054-12">(</span><span class="ss">next_pf</span><span class="p" data-group-id="2851071054-12">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2851071054-2">}</span></code></pre><h3 id="transformation-rules" class="section-heading">
│ │ │    <a href="#transformation-rules" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Transformation rules</span>
│ │ │  </h3>
│ │ │  <p>Next let's look at how we can do some optimizations using transformation
│ │ │  rules.  For simple instructions such as <code class="inline">move/2</code>, the instruction dispatch
│ │ │ @@ -271,21 +271,21 @@
│ │ │  with an uppercase letter just as in Erlang.  A pattern variable may be
│ │ │  followed <code class="inline">=</code> and one or more type letters to constrain the match to
│ │ │  one of those types.  The variables that are bound on the left-hand side can
│ │ │  be used on the right-hand side.</p><p>We will also need to define a specific instruction and an implementation:</p><pre><code class="makeup erlang" translate="no"><span class="p">#</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="ss">ops</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │  </span><span class="ss">move2</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">y</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="ss">instrs</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │ -</span><span class="nf">move2</span><span class="p" data-group-id="9560453890-1">(</span><span class="n">S1</span><span class="p">,</span><span class="w"> </span><span class="n">D1</span><span class="p">,</span><span class="w"> </span><span class="n">S2</span><span class="p">,</span><span class="w"> </span><span class="n">D2</span><span class="p" data-group-id="9560453890-1">)</span><span class="w"> </span><span class="p" data-group-id="9560453890-2">{</span><span class="w">
│ │ │ +</span><span class="nf">move2</span><span class="p" data-group-id="6543597984-1">(</span><span class="n">S1</span><span class="p">,</span><span class="w"> </span><span class="n">D1</span><span class="p">,</span><span class="w"> </span><span class="n">S2</span><span class="p">,</span><span class="w"> </span><span class="n">D2</span><span class="p" data-group-id="6543597984-1">)</span><span class="w"> </span><span class="p" data-group-id="6543597984-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="n">V2</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">V1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">V2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="mi">1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">V1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="mi">2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">V2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9560453890-2">}</span></code></pre><p>When the loader has found a match and replaced the matched instructions,
│ │ │ +</span><span class="p" data-group-id="6543597984-2">}</span></code></pre><p>When the loader has found a match and replaced the matched instructions,
│ │ │  it will match the new instructions against the transformation rules.
│ │ │  Because of that, we can define the rule for a <code class="inline">move3/6</code> instruction
│ │ │  as follows:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move2</span><span class="w"> </span><span class="n">X1</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y1</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="n">X2</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y2</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">move</span><span class="w"> </span><span class="n">X3</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y3</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │        </span><span class="ss">move3</span><span class="w"> </span><span class="n">X1</span><span class="w"> </span><span class="n">Y1</span><span class="w"> </span><span class="n">X2</span><span class="w"> </span><span class="n">Y2</span><span class="w"> </span><span class="n">X3</span><span class="w"> </span><span class="n">Y3</span></code></pre><p>(For readability, a long transformation line can be broken after <code class="inline">|</code>
│ │ │  and <code class="inline">=&gt;</code> operators.)</p><p>It would also be possible to define it like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move</span><span class="w"> </span><span class="n">X1</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y1</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">move</span><span class="w"> </span><span class="n">X2</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y2</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">move</span><span class="w"> </span><span class="n">X3</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y3</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │       </span><span class="ss">move3</span><span class="w"> </span><span class="n">X1</span><span class="w"> </span><span class="n">Y1</span><span class="w"> </span><span class="n">X2</span><span class="w"> </span><span class="n">Y2</span><span class="w"> </span><span class="n">X3</span><span class="w"> </span><span class="n">Y3</span></code></pre><p>but in that case it must be defined before the rule for <code class="inline">move2/4</code>
│ │ │  because the first matching rule will be applied.</p><p>One must be careful not to create infinite loops.  For example, if we
│ │ │ @@ -433,29 +433,29 @@
│ │ │  </span><span class="ss">i_bs_get_integer_32</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">f</span><span class="o">?</span><span class="w"> </span><span class="ss">x</span><span class="w">
│ │ │  </span><span class="c1">%endif</span></code></pre><p>The specific instruction <code class="inline">i_bs_get_integer_32</code> will only be defined
│ │ │  on a 64-bit machine.</p><p>The condition can be inverted by using <code class="inline">%unless</code> instead of <code class="inline">%if</code>:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%unless NO_FPE_SIGNALS</span><span class="w">
│ │ │  </span><span class="ss">fcheckerror</span><span class="w"> </span><span class="ss">p</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">i_fcheckerror</span><span class="w">
│ │ │  </span><span class="ss">i_fcheckerror</span><span class="w">
│ │ │  </span><span class="ss">fclearerror</span><span class="w">
│ │ │  </span><span class="c1">%endif</span></code></pre><p>It is also possible to add an <code class="inline">%else</code> clause:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%if ARCH_64</span><span class="w">
│ │ │ -</span><span class="n">BS_SAFE_MUL</span><span class="p" data-group-id="7329882331-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="7329882331-1">)</span><span class="w"> </span><span class="p" data-group-id="7329882331-2">{</span><span class="w">
│ │ │ -    </span><span class="n">Uint64</span><span class="w"> </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7329882331-3">(</span><span class="sc">$A</span><span class="p" data-group-id="7329882331-3">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="7329882331-4">(</span><span class="sc">$B</span><span class="p" data-group-id="7329882331-4">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="7329882331-5">(</span><span class="ss">res</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="sc">$B</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="sc">$A</span><span class="p" data-group-id="7329882331-5">)</span><span class="w"> </span><span class="p" data-group-id="7329882331-6">{</span><span class="w">
│ │ │ +</span><span class="n">BS_SAFE_MUL</span><span class="p" data-group-id="4880621363-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="4880621363-1">)</span><span class="w"> </span><span class="p" data-group-id="4880621363-2">{</span><span class="w">
│ │ │ +    </span><span class="n">Uint64</span><span class="w"> </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4880621363-3">(</span><span class="sc">$A</span><span class="p" data-group-id="4880621363-3">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="4880621363-4">(</span><span class="sc">$B</span><span class="p" data-group-id="4880621363-4">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="4880621363-5">(</span><span class="ss">res</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="sc">$B</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="sc">$A</span><span class="p" data-group-id="4880621363-5">)</span><span class="w"> </span><span class="p" data-group-id="4880621363-6">{</span><span class="w">
│ │ │          </span><span class="sc">$F</span><span class="ss">ail</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7329882331-6">}</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4880621363-6">}</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">res</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7329882331-2">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4880621363-2">}</span><span class="w">
│ │ │  </span><span class="c1">%else</span><span class="w">
│ │ │ -</span><span class="n">BS_SAFE_MUL</span><span class="p" data-group-id="7329882331-7">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="7329882331-7">)</span><span class="w"> </span><span class="p" data-group-id="7329882331-8">{</span><span class="w">
│ │ │ -    </span><span class="n">Uint64</span><span class="w"> </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7329882331-9">(</span><span class="n">Uint64</span><span class="p" data-group-id="7329882331-9">)</span><span class="p" data-group-id="7329882331-10">(</span><span class="sc">$A</span><span class="p" data-group-id="7329882331-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="7329882331-11">(</span><span class="n">Uint64</span><span class="p" data-group-id="7329882331-11">)</span><span class="p" data-group-id="7329882331-12">(</span><span class="sc">$B</span><span class="p" data-group-id="7329882331-12">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="7329882331-13">(</span><span class="p" data-group-id="7329882331-14">(</span><span class="ss">res</span><span class="w"> </span><span class="p">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="7329882331-15">(</span><span class="mi">8</span><span class="o">*</span><span class="nf">sizeof</span><span class="p" data-group-id="7329882331-16">(</span><span class="n">Uint</span><span class="p" data-group-id="7329882331-16">)</span><span class="p" data-group-id="7329882331-15">)</span><span class="p" data-group-id="7329882331-14">)</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7329882331-13">)</span><span class="w"> </span><span class="p" data-group-id="7329882331-17">{</span><span class="w">
│ │ │ +</span><span class="n">BS_SAFE_MUL</span><span class="p" data-group-id="4880621363-7">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="4880621363-7">)</span><span class="w"> </span><span class="p" data-group-id="4880621363-8">{</span><span class="w">
│ │ │ +    </span><span class="n">Uint64</span><span class="w"> </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4880621363-9">(</span><span class="n">Uint64</span><span class="p" data-group-id="4880621363-9">)</span><span class="p" data-group-id="4880621363-10">(</span><span class="sc">$A</span><span class="p" data-group-id="4880621363-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="4880621363-11">(</span><span class="n">Uint64</span><span class="p" data-group-id="4880621363-11">)</span><span class="p" data-group-id="4880621363-12">(</span><span class="sc">$B</span><span class="p" data-group-id="4880621363-12">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="4880621363-13">(</span><span class="p" data-group-id="4880621363-14">(</span><span class="ss">res</span><span class="w"> </span><span class="p">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="4880621363-15">(</span><span class="mi">8</span><span class="o">*</span><span class="nf">sizeof</span><span class="p" data-group-id="4880621363-16">(</span><span class="n">Uint</span><span class="p" data-group-id="4880621363-16">)</span><span class="p" data-group-id="4880621363-15">)</span><span class="p" data-group-id="4880621363-14">)</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4880621363-13">)</span><span class="w"> </span><span class="p" data-group-id="4880621363-17">{</span><span class="w">
│ │ │          </span><span class="sc">$F</span><span class="ss">ail</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7329882331-17">}</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4880621363-17">}</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">res</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7329882331-8">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4880621363-8">}</span><span class="w">
│ │ │  </span><span class="c1">%endif</span></code></pre><h4>Symbols that are defined in directives</h4><p>The following symbols are always defined.</p><ul><li><code class="inline">ARCH_64</code> - is 1 for a 64-bit machine, and 0 otherwise.</li><li><code class="inline">ARCH_32</code> - is 1 for 32-bit machine, and 0 otherwise.</li></ul><p>The <code class="inline">Makefile</code> for building the emulator currently defines the
│ │ │  following symbols by using the <code class="inline">-D</code> option on the command line for
│ │ │  <strong>beam_makeops</strong>.</p><ul><li><code class="inline">USE_VM_PROBES</code> - 1 if the runtime system is compiled to use VM
│ │ │  probes (support for dtrace or systemtap), 0 otherwise.</li></ul><h3 id="defining-external-generic-instructions" class="section-heading">
│ │ │    <a href="#defining-external-generic-instructions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -676,15 +676,15 @@
│ │ │  match both source and destination registers.  As an operand in a specific
│ │ │  instruction, it must only be used for a destination register.)</p></li><li><p><code class="inline">o</code> - Overflow.  An untagged integer that does not fit in a machine word.</p></li></ul><h4>Predicates</h4><p>If the constraints described so far is not enough, additional
│ │ │  constraints can be implemented in C and be called as a guard function
│ │ │  on the left-hand side of the transformation.  If the guard function returns
│ │ │  a non-zero value, the matching of the rule will continue, otherwise
│ │ │  the match will fail.  Such guard functions are hereafter called
│ │ │  <em>predicates</em>.</p><p>The most commonly used guard constraints is <code class="inline">equal()</code>. It can be used
│ │ │ -to remove a redundant <code class="inline">move</code> instructio like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move</span><span class="w"> </span><span class="n">R1</span><span class="w"> </span><span class="n">R2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">equal</span><span class="p" data-group-id="1382340822-1">(</span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="1382340822-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">_</span></code></pre><p>or remove a redundant <code class="inline">is_eq_exact</code> instruction like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">is_eq_exact</span><span class="w"> </span><span class="n">Lbl</span><span class="w"> </span><span class="n">Src1</span><span class="w"> </span><span class="n">Src2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">equal</span><span class="p" data-group-id="4652231428-1">(</span><span class="n">Src1</span><span class="p">,</span><span class="w"> </span><span class="n">Src2</span><span class="p" data-group-id="4652231428-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">_</span></code></pre><p>At the time of writing, all predicates are defined in files named
│ │ │ +to remove a redundant <code class="inline">move</code> instructio like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move</span><span class="w"> </span><span class="n">R1</span><span class="w"> </span><span class="n">R2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">equal</span><span class="p" data-group-id="3102717058-1">(</span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="3102717058-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">_</span></code></pre><p>or remove a redundant <code class="inline">is_eq_exact</code> instruction like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">is_eq_exact</span><span class="w"> </span><span class="n">Lbl</span><span class="w"> </span><span class="n">Src1</span><span class="w"> </span><span class="n">Src2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">equal</span><span class="p" data-group-id="4708425004-1">(</span><span class="n">Src1</span><span class="p">,</span><span class="w"> </span><span class="n">Src2</span><span class="p" data-group-id="4708425004-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">_</span></code></pre><p>At the time of writing, all predicates are defined in files named
│ │ │  <code class="inline">predicates.tab</code> in several directories.  In <code class="inline">predicates.tab</code> directly
│ │ │  in <code class="inline">$ERL_TOP/erts/emulator/beam</code>, predicates that are used by both the
│ │ │  traditinal emulator and the JIT implementations are contained.
│ │ │  Predicates only used by the emulator can be found in
│ │ │  <code class="inline">emu/predicates.tab</code>.</p><h3 id="a-very-brief-note-on-implementation-of-predicates" class="section-heading">
│ │ │    <a href="#a-very-brief-note-on-implementation-of-predicates" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -692,41 +692,41 @@
│ │ │    <span class="text">A very brief note on implementation of predicates</span>
│ │ │  </h3>
│ │ │  <p>It is outside the scope for this document to describe in detail how
│ │ │  predicates are implemented because it requires knowledge of the
│ │ │  internal loader data structures, but here is quick look at the
│ │ │  implementation of a simple predicate called <code class="inline">literal_is_map()</code>.</p><p>Here is first an example how it is used:</p><p>   is<em>map Fail Lit=q | literal_is_map(Lit) =&gt; </em></p><p>If the <code class="inline">Lit</code> operand is a literal, then the <code class="inline">literal_is_map()</code>
│ │ │  predicate is called to determine whether it is a map literal.
│ │ │ -If it is, the instruction is not needed and can be removed.</p><p><code class="inline">literal_is_map()</code> is implemented like this (in <code class="inline">emu/predicates.tab</code>):</p><pre><code class="makeup erlang" translate="no"><span class="ss">pred</span><span class="p">.</span><span class="nf">literal_is_map</span><span class="p" data-group-id="3602610885-1">(</span><span class="n">Lit</span><span class="p" data-group-id="3602610885-1">)</span><span class="w"> </span><span class="p" data-group-id="3602610885-2">{</span><span class="w">
│ │ │ +If it is, the instruction is not needed and can be removed.</p><p><code class="inline">literal_is_map()</code> is implemented like this (in <code class="inline">emu/predicates.tab</code>):</p><pre><code class="makeup erlang" translate="no"><span class="ss">pred</span><span class="p">.</span><span class="nf">literal_is_map</span><span class="p" data-group-id="3784905483-1">(</span><span class="n">Lit</span><span class="p" data-group-id="3784905483-1">)</span><span class="w"> </span><span class="p" data-group-id="3784905483-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">term</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="3602610885-3">(</span><span class="n">Lit</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_q</span><span class="p" data-group-id="3602610885-3">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">beamfile_get_literal</span><span class="p" data-group-id="3602610885-4">(</span><span class="err">&amp;</span><span class="n">S</span><span class="p">-&gt;</span><span class="ss">beam</span><span class="p">,</span><span class="w"> </span><span class="n">Lit</span><span class="p">.</span><span class="ss">val</span><span class="p" data-group-id="3602610885-4">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">return</span><span class="w"> </span><span class="nf">is_map</span><span class="p" data-group-id="3602610885-5">(</span><span class="ss">term</span><span class="p" data-group-id="3602610885-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3602610885-2">}</span></code></pre><p>The <code class="inline">pred.</code> prefix tells <strong>beam_makeops</strong> that this function is a
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="3784905483-3">(</span><span class="n">Lit</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_q</span><span class="p" data-group-id="3784905483-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">beamfile_get_literal</span><span class="p" data-group-id="3784905483-4">(</span><span class="err">&amp;</span><span class="n">S</span><span class="p">-&gt;</span><span class="ss">beam</span><span class="p">,</span><span class="w"> </span><span class="n">Lit</span><span class="p">.</span><span class="ss">val</span><span class="p" data-group-id="3784905483-4">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">return</span><span class="w"> </span><span class="nf">is_map</span><span class="p" data-group-id="3784905483-5">(</span><span class="ss">term</span><span class="p" data-group-id="3784905483-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3784905483-2">}</span></code></pre><p>The <code class="inline">pred.</code> prefix tells <strong>beam_makeops</strong> that this function is a
│ │ │  predicate.  Without the prefix, it would have been interpreted as the
│ │ │  implementation of an instruction (described in <strong>Defining the
│ │ │  implementation</strong>).</p><p>Predicate functions have a magic variabled called <code class="inline">S</code>, which is a
│ │ │  pointer to a state struct. In the example,
│ │ │  <code class="inline">beamfile_get_literal(&amp;S-&gt;beam, Lit.val);</code> is used to retrieve the actual term
│ │ │  for the literal.</p><p>At the time of writing, the expanded C code generated by
│ │ │ -<strong>beam_makeops</strong> looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">static</span><span class="w"> </span><span class="ss">int</span><span class="w"> </span><span class="nf">literal_is_map</span><span class="p" data-group-id="7903492133-1">(</span><span class="n">LoaderState</span><span class="o">*</span><span class="w"> </span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="n">BeamOpArg</span><span class="w"> </span><span class="n">Lit</span><span class="p" data-group-id="7903492133-1">)</span><span class="w"> </span><span class="p" data-group-id="7903492133-2">{</span><span class="w">
│ │ │ +<strong>beam_makeops</strong> looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">static</span><span class="w"> </span><span class="ss">int</span><span class="w"> </span><span class="nf">literal_is_map</span><span class="p" data-group-id="8573815552-1">(</span><span class="n">LoaderState</span><span class="o">*</span><span class="w"> </span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="n">BeamOpArg</span><span class="w"> </span><span class="n">Lit</span><span class="p" data-group-id="8573815552-1">)</span><span class="w"> </span><span class="p" data-group-id="8573815552-2">{</span><span class="w">
│ │ │    </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">term</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="7903492133-3">(</span><span class="n">Lit</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_q</span><span class="p" data-group-id="7903492133-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="ss">term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p">-&gt;</span><span class="ss">literals</span><span class="p" data-group-id="7903492133-4">[</span><span class="n">Lit</span><span class="p">.</span><span class="ss">val</span><span class="p" data-group-id="7903492133-4">]</span><span class="p">.</span><span class="ss">term</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="ss">return</span><span class="w"> </span><span class="nf">is_map</span><span class="p" data-group-id="7903492133-5">(</span><span class="ss">term</span><span class="p" data-group-id="7903492133-5">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7903492133-2">}</span></code></pre><h4>Handling instructions with variable number of operands</h4><p>Some instructions, such as <code class="inline">select_val/3</code>, essentially has a variable
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="8573815552-3">(</span><span class="n">Lit</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_q</span><span class="p" data-group-id="8573815552-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="ss">term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p">-&gt;</span><span class="ss">literals</span><span class="p" data-group-id="8573815552-4">[</span><span class="n">Lit</span><span class="p">.</span><span class="ss">val</span><span class="p" data-group-id="8573815552-4">]</span><span class="p">.</span><span class="ss">term</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="ss">return</span><span class="w"> </span><span class="nf">is_map</span><span class="p" data-group-id="8573815552-5">(</span><span class="ss">term</span><span class="p" data-group-id="8573815552-5">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8573815552-2">}</span></code></pre><h4>Handling instructions with variable number of operands</h4><p>Some instructions, such as <code class="inline">select_val/3</code>, essentially has a variable
│ │ │  number of operands.  Such instructions have a <code class="inline">{list,[...]}</code> operand
│ │ │ -as their last operand in the BEAM assembly code.  For example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4802240515-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="4802240515-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4802240515-2">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4802240515-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4802240515-3">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4802240515-4">{</span><span class="ss">list</span><span class="p">,</span><span class="p" data-group-id="4802240515-5">[</span><span class="p" data-group-id="4802240515-6">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4802240515-6">}</span><span class="p">,</span><span class="p" data-group-id="4802240515-7">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4802240515-7">}</span><span class="p">,</span><span class="p" data-group-id="4802240515-8">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4802240515-8">}</span><span class="p">,</span><span class="p" data-group-id="4802240515-9">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4802240515-9">}</span><span class="p" data-group-id="4802240515-5">]</span><span class="p" data-group-id="4802240515-4">}</span><span class="p" data-group-id="4802240515-1">}</span><span class="p">.</span></code></pre><p>The loader will convert a <code class="inline">{list,[...]}</code> operand to an <code class="inline">u</code> operand whose
│ │ │ +as their last operand in the BEAM assembly code.  For example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9620154430-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="9620154430-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="9620154430-2">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="9620154430-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="9620154430-3">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="9620154430-4">{</span><span class="ss">list</span><span class="p">,</span><span class="p" data-group-id="9620154430-5">[</span><span class="p" data-group-id="9620154430-6">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9620154430-6">}</span><span class="p">,</span><span class="p" data-group-id="9620154430-7">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="9620154430-7">}</span><span class="p">,</span><span class="p" data-group-id="9620154430-8">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="9620154430-8">}</span><span class="p">,</span><span class="p" data-group-id="9620154430-9">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9620154430-9">}</span><span class="p" data-group-id="9620154430-5">]</span><span class="p" data-group-id="9620154430-4">}</span><span class="p" data-group-id="9620154430-1">}</span><span class="p">.</span></code></pre><p>The loader will convert a <code class="inline">{list,[...]}</code> operand to an <code class="inline">u</code> operand whose
│ │ │  value is the number of elements in the list, followed by each element in
│ │ │  the list.  The instruction above would be translated to the following
│ │ │ -generic instruction:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0928008162-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="0928008162-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="0928008162-2">}</span><span class="p">,</span><span class="p" data-group-id="0928008162-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0928008162-3">}</span><span class="p">,</span><span class="p" data-group-id="0928008162-4">{</span><span class="ss">u</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0928008162-4">}</span><span class="p">,</span><span class="p" data-group-id="0928008162-5">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="0928008162-5">}</span><span class="p">,</span><span class="p" data-group-id="0928008162-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0928008162-6">}</span><span class="p">,</span><span class="p" data-group-id="0928008162-7">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="0928008162-7">}</span><span class="p">,</span><span class="p" data-group-id="0928008162-8">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0928008162-8">}</span><span class="p" data-group-id="0928008162-1">}</span></code></pre><p>To match a variable number of arguments we need to use the special
│ │ │ +generic instruction:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2984475208-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="2984475208-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="2984475208-2">}</span><span class="p">,</span><span class="p" data-group-id="2984475208-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2984475208-3">}</span><span class="p">,</span><span class="p" data-group-id="2984475208-4">{</span><span class="ss">u</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2984475208-4">}</span><span class="p">,</span><span class="p" data-group-id="2984475208-5">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2984475208-5">}</span><span class="p">,</span><span class="p" data-group-id="2984475208-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2984475208-6">}</span><span class="p">,</span><span class="p" data-group-id="2984475208-7">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="2984475208-7">}</span><span class="p">,</span><span class="p" data-group-id="2984475208-8">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2984475208-8">}</span><span class="p" data-group-id="2984475208-1">}</span></code></pre><p>To match a variable number of arguments we need to use the special
│ │ │  operand type <code class="inline">*</code> like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">select_val</span><span class="w"> </span><span class="n">Src</span><span class="o">=</span><span class="ss">aiq</span><span class="w"> </span><span class="n">Fail</span><span class="o">=</span><span class="ss">f</span><span class="w"> </span><span class="n">Size</span><span class="o">=</span><span class="ss">u</span><span class="w"> </span><span class="n">List</span><span class="o">=</span><span class="o">*</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │      </span><span class="ss">i_const_select_val</span><span class="w"> </span><span class="n">Src</span><span class="w"> </span><span class="n">Fail</span><span class="w"> </span><span class="n">Size</span><span class="w"> </span><span class="n">List</span></code></pre><p>This transformation renames a <code class="inline">select_val/3</code> instruction
│ │ │  with a constant source operand to <code class="inline">i_const_select_val/3</code>.</p><h4>Constructing new instructions on the right-hand side</h4><p>The most common operand on the right-hand side is a variable that was
│ │ │  bound while matching the pattern on the left-hand side.  For example:</p><pre><code class="makeup erlang" translate="no"><span class="ss">trim</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="n">Remaining</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">i_trim</span><span class="w"> </span><span class="n">N</span></code></pre><p>An operand can also be a type letter to construct an operand of that
│ │ │  type.  Each type has a default value.  For example, the type <code class="inline">x</code> has
│ │ │  the default value 1023, which is the highest X register.  That makes
│ │ │  <code class="inline">x</code> on the right-hand side a convenient shortcut for a temporary X
│ │ │ @@ -746,53 +746,53 @@
│ │ │  transformation rule.</p><ul><li><p><code class="inline">u</code> - Construct an untagged integer.  The default value is 0.</p></li><li><p><code class="inline">x</code> - X register.  The default value is 1023.  That makes <code class="inline">x</code> convenient to
│ │ │  use as a temporary X register.</p></li><li><p><code class="inline">y</code> - Y register.  The default value is 0.</p></li><li><p><code class="inline">l</code> - Floating point register number.  The default value is 0.</p></li><li><p><code class="inline">i</code> - Tagged literal integer.  The default value is 0.</p></li><li><p><code class="inline">a</code> - Tagged atom.  The default value is the empty atom (<code class="inline">am_Empty</code>).</p></li><li><p><code class="inline">p</code> - Zero failure label.</p></li><li><p><code class="inline">n</code> - NIL (<code class="inline">[]</code>, the empty list).</p></li></ul><h4>Function call on the right-hand side</h4><p>Transformations that are not possible to describe with the rule
│ │ │  language as described here can be implemented as a generator function
│ │ │  in C and called from the right-hand side of a transformation.  The left-hand
│ │ │  side of the transformation will perform the match and bind operands to
│ │ │  variables.  The variables can then be passed to a generator function
│ │ │  on the right-hand side.  For example:</p><pre><code class="makeup erlang" translate="no"><span class="ss">bif2</span><span class="w"> </span><span class="n">Fail</span><span class="o">=</span><span class="ss">j</span><span class="w"> </span><span class="ss">u</span><span class="sc">$b</span><span class="nc">if</span><span class="p">:</span><span class="nc">erlang</span><span class="p">:</span><span class="nb">element</span><span class="p">/</span><span class="mi">2</span><span class="w"> </span><span class="n">Index</span><span class="o">=</span><span class="ss">s</span><span class="w"> </span><span class="n">Tuple</span><span class="o">=</span><span class="ss">xy</span><span class="w"> </span><span class="n">Dst</span><span class="o">=</span><span class="ss">d</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">element</span><span class="p" data-group-id="6336225919-1">(</span><span class="n">Jump</span><span class="p">,</span><span class="w"> </span><span class="n">Index</span><span class="p">,</span><span class="w"> </span><span class="n">Tuple</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="6336225919-1">)</span></code></pre><p>This transformation rule matches a call to the BIF <a href="erlang.html#element/2"><code class="inline">element/2</code></a>.
│ │ │ +    </span><span class="nf">element</span><span class="p" data-group-id="8725791157-1">(</span><span class="n">Jump</span><span class="p">,</span><span class="w"> </span><span class="n">Index</span><span class="p">,</span><span class="w"> </span><span class="n">Tuple</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="8725791157-1">)</span></code></pre><p>This transformation rule matches a call to the BIF <a href="erlang.html#element/2"><code class="inline">element/2</code></a>.
│ │ │  The operands will be captured and the generator function <code class="inline">element()</code> will
│ │ │  be called.</p><p>The <code class="inline">element()</code> generator will produce one of two instructions
│ │ │  depending on <code class="inline">Index</code>.  If <code class="inline">Index</code> is an integer in the range from 1 up
│ │ │  to the maximum tuple size, the instruction <code class="inline">i_fast_element/2</code> will be
│ │ │  produced, otherwise the instruction <code class="inline">i_element/4</code> will be produced.
│ │ │  The corresponding specific instructions are:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_fast_element</span><span class="w"> </span><span class="ss">xy</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_element</span><span class="w"> </span><span class="ss">xy</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">d</span></code></pre><p>The <code class="inline">i_fast_element/2</code> instruction is faster because the tuple is
│ │ │  already an untagged integer.  It also knows that the index is at least
│ │ │  1, so it does not have to test for that.  The <code class="inline">i_element/4</code>
│ │ │  instruction will have to fetch the index from a register, test that it
│ │ │  is an integer, and untag the integer.</p><p>At the time of writing, all generators functions were defined in files
│ │ │  named <code class="inline">generators.tab</code> in several directories (in the same directories
│ │ │  as the <code class="inline">predicates.tab</code> files).</p><p>It is outside the scope of this document to describe in detail how
│ │ │  generator functions are written, but here is the implementation of
│ │ │ -<code class="inline">element()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">gen</span><span class="p">.</span><span class="nf">element</span><span class="p" data-group-id="4720998570-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Index</span><span class="p">,</span><span class="w"> </span><span class="n">Tuple</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="4720998570-1">)</span><span class="w"> </span><span class="p" data-group-id="4720998570-2">{</span><span class="w">
│ │ │ +<code class="inline">element()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">gen</span><span class="p">.</span><span class="nf">element</span><span class="p" data-group-id="1837812723-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Index</span><span class="p">,</span><span class="w"> </span><span class="n">Tuple</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="1837812723-1">)</span><span class="w"> </span><span class="p" data-group-id="1837812723-2">{</span><span class="w">
│ │ │      </span><span class="n">BeamOp</span><span class="o">*</span><span class="w"> </span><span class="ss">op</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="sc">$N</span><span class="nf">ewBeamOp</span><span class="p" data-group-id="4720998570-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="ss">op</span><span class="p" data-group-id="4720998570-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="sc">$N</span><span class="nf">ewBeamOp</span><span class="p" data-group-id="1837812723-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="ss">op</span><span class="p" data-group-id="1837812723-3">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="4720998570-4">(</span><span class="n">Index</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_i</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w"> </span><span class="n">Index</span><span class="p">.</span><span class="ss">val</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="1837812723-4">(</span><span class="n">Index</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_i</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w"> </span><span class="n">Index</span><span class="p">.</span><span class="ss">val</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w">
│ │ │          </span><span class="n">Index</span><span class="p">.</span><span class="ss">val</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="n">ERTS_MAX_TUPLE_SIZE</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4720998570-5">(</span><span class="n">Tuple</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Tuple</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_y</span><span class="p" data-group-id="4720998570-5">)</span><span class="p" data-group-id="4720998570-4">)</span><span class="w"> </span><span class="p" data-group-id="4720998570-6">{</span><span class="w">
│ │ │ -        </span><span class="sc">$B</span><span class="nf">eamOpNameArity</span><span class="p" data-group-id="4720998570-7">(</span><span class="ss">op</span><span class="p">,</span><span class="w"> </span><span class="ss">i_fast_element</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="4720998570-7">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="4720998570-8">[</span><span class="mi">0</span><span class="p" data-group-id="4720998570-8">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Tuple</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="4720998570-9">[</span><span class="mi">1</span><span class="p" data-group-id="4720998570-9">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Fail</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="4720998570-10">[</span><span class="mi">2</span><span class="p" data-group-id="4720998570-10">]</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">TAG_u</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="4720998570-11">[</span><span class="mi">2</span><span class="p" data-group-id="4720998570-11">]</span><span class="p">.</span><span class="ss">val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Index</span><span class="p">.</span><span class="ss">val</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="4720998570-12">[</span><span class="mi">3</span><span class="p" data-group-id="4720998570-12">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dst</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4720998570-6">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="4720998570-13">{</span><span class="w">
│ │ │ -        </span><span class="sc">$B</span><span class="nf">eamOpNameArity</span><span class="p" data-group-id="4720998570-14">(</span><span class="ss">op</span><span class="p">,</span><span class="w"> </span><span class="ss">i_element</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="4720998570-14">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="4720998570-15">[</span><span class="mi">0</span><span class="p" data-group-id="4720998570-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Tuple</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="4720998570-16">[</span><span class="mi">1</span><span class="p" data-group-id="4720998570-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Fail</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="4720998570-17">[</span><span class="mi">2</span><span class="p" data-group-id="4720998570-17">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Index</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="4720998570-18">[</span><span class="mi">3</span><span class="p" data-group-id="4720998570-18">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dst</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4720998570-13">}</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="1837812723-5">(</span><span class="n">Tuple</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Tuple</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_y</span><span class="p" data-group-id="1837812723-5">)</span><span class="p" data-group-id="1837812723-4">)</span><span class="w"> </span><span class="p" data-group-id="1837812723-6">{</span><span class="w">
│ │ │ +        </span><span class="sc">$B</span><span class="nf">eamOpNameArity</span><span class="p" data-group-id="1837812723-7">(</span><span class="ss">op</span><span class="p">,</span><span class="w"> </span><span class="ss">i_fast_element</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1837812723-7">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1837812723-8">[</span><span class="mi">0</span><span class="p" data-group-id="1837812723-8">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Tuple</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1837812723-9">[</span><span class="mi">1</span><span class="p" data-group-id="1837812723-9">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Fail</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1837812723-10">[</span><span class="mi">2</span><span class="p" data-group-id="1837812723-10">]</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">TAG_u</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1837812723-11">[</span><span class="mi">2</span><span class="p" data-group-id="1837812723-11">]</span><span class="p">.</span><span class="ss">val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Index</span><span class="p">.</span><span class="ss">val</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1837812723-12">[</span><span class="mi">3</span><span class="p" data-group-id="1837812723-12">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dst</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1837812723-6">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="1837812723-13">{</span><span class="w">
│ │ │ +        </span><span class="sc">$B</span><span class="nf">eamOpNameArity</span><span class="p" data-group-id="1837812723-14">(</span><span class="ss">op</span><span class="p">,</span><span class="w"> </span><span class="ss">i_element</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1837812723-14">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1837812723-15">[</span><span class="mi">0</span><span class="p" data-group-id="1837812723-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Tuple</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1837812723-16">[</span><span class="mi">1</span><span class="p" data-group-id="1837812723-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Fail</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1837812723-17">[</span><span class="mi">2</span><span class="p" data-group-id="1837812723-17">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Index</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1837812723-18">[</span><span class="mi">3</span><span class="p" data-group-id="1837812723-18">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dst</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1837812723-13">}</span><span class="w">
│ │ │  
│ │ │      </span><span class="ss">return</span><span class="w"> </span><span class="ss">op</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4720998570-2">}</span></code></pre><p>The <code class="inline">gen.</code> prefix tells <strong>beam_makeops</strong> that this function is a
│ │ │ +</span><span class="p" data-group-id="1837812723-2">}</span></code></pre><p>The <code class="inline">gen.</code> prefix tells <strong>beam_makeops</strong> that this function is a
│ │ │  generator.  Without the prefix, it would have been interpreted as the
│ │ │  implementation of an instruction (described in <strong>Defining the
│ │ │  implementation</strong>).</p><p>Generator functions have a magic variabled called <code class="inline">S</code>, which is a
│ │ │  pointer to a state struct.  In the example, <code class="inline">S</code> is used in the invocation
│ │ │  of the <code class="inline">NewBeamOp</code> macro.</p><h3 id="defining-the-implementation" class="section-heading">
│ │ │    <a href="#defining-the-implementation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -814,473 +814,473 @@
│ │ │  </span><span class="ss">msg_instrs</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │  </span><span class="ss">select_instrs</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │  </span><span class="ss">trace_instrs</span><span class="p">.</span><span class="ss">tab</span></code></pre><p>There is also a file that only contains macro definitions:</p><pre><code class="makeup erlang" translate="no"><span class="ss">macros</span><span class="p">.</span><span class="ss">tab</span></code></pre><p>The syntax of each file is similar to C code.  In fact, most of
│ │ │  the contents <em>is</em> C code, interspersed with macro invocations.</p><p>To allow Emacs to auto-indent the code, each file starts with the
│ │ │  following line:</p><pre><code class="makeup erlang" translate="no"><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="o">-</span><span class="o">*</span><span class="o">-</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="o">-</span><span class="o">*</span><span class="o">-</span></code></pre><p>To avoid messing up the indentation, all comments are written
│ │ │  as C++ style comments (<code class="inline">//</code>) instead of <code class="inline">#</code>.  Note that a comment
│ │ │  must start at the beginning of a line.</p><p>The meat of an instruction definition file are macro definitions.
│ │ │ -We have seen this macro definition before:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="7192671746-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="7192671746-1">)</span><span class="w"> </span><span class="p" data-group-id="7192671746-2">{</span><span class="w">
│ │ │ +We have seen this macro definition before:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="6067408596-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="6067408596-1">)</span><span class="w"> </span><span class="p" data-group-id="6067408596-2">{</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7192671746-2">}</span></code></pre><p>A macro definitions must start at the beginning of the line (no spaces
│ │ │ +</span><span class="p" data-group-id="6067408596-2">}</span></code></pre><p>A macro definitions must start at the beginning of the line (no spaces
│ │ │  allowed), the opening curly bracket must be on the same line, and the
│ │ │  finishing curly bracket must be at the beginning of a line.  It is
│ │ │  recommended that the macro body is properly indented.</p><p>As a convention, the macro arguments in the head all start with an
│ │ │  uppercase letter.  In the body, the macro arguments can be expanded
│ │ │  by preceding them with <code class="inline">$</code>.</p><p>A macro definition whose name and arity matches a family of
│ │ │  specific instructions is assumed to be the implementation of that
│ │ │  instruction.</p><p>A macro can also be invoked from within another macro.  For example,
│ │ │  <code class="inline">move_deallocate_return/2</code> avoids repeating code by invoking
│ │ │ -<code class="inline">$deallocate_return()</code> as a macro:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move_deallocate_return</span><span class="p" data-group-id="3714358672-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Deallocate</span><span class="p" data-group-id="3714358672-1">)</span><span class="w"> </span><span class="p" data-group-id="3714358672-2">{</span><span class="w">
│ │ │ -    </span><span class="nf">x</span><span class="p" data-group-id="3714358672-3">(</span><span class="mi">0</span><span class="p" data-group-id="3714358672-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="sc">$d</span><span class="nf">eallocate_return</span><span class="p" data-group-id="3714358672-4">(</span><span class="sc">$D</span><span class="ss">eallocate</span><span class="p" data-group-id="3714358672-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3714358672-2">}</span></code></pre><p>Here is the definition of <code class="inline">deallocate_return/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">deallocate_return</span><span class="p" data-group-id="4573747687-1">(</span><span class="n">Deallocate</span><span class="p" data-group-id="4573747687-1">)</span><span class="w"> </span><span class="p" data-group-id="4573747687-2">{</span><span class="w">
│ │ │ +<code class="inline">$deallocate_return()</code> as a macro:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move_deallocate_return</span><span class="p" data-group-id="7776107964-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Deallocate</span><span class="p" data-group-id="7776107964-1">)</span><span class="w"> </span><span class="p" data-group-id="7776107964-2">{</span><span class="w">
│ │ │ +    </span><span class="nf">x</span><span class="p" data-group-id="7776107964-3">(</span><span class="mi">0</span><span class="p" data-group-id="7776107964-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="sc">$d</span><span class="nf">eallocate_return</span><span class="p" data-group-id="7776107964-4">(</span><span class="sc">$D</span><span class="ss">eallocate</span><span class="p" data-group-id="7776107964-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7776107964-2">}</span></code></pre><p>Here is the definition of <code class="inline">deallocate_return/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">deallocate_return</span><span class="p" data-group-id="7833315030-1">(</span><span class="n">Deallocate</span><span class="p" data-group-id="7833315030-1">)</span><span class="w"> </span><span class="p" data-group-id="7833315030-2">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_next</span><span class="w">
│ │ │      </span><span class="ss">int</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$D</span><span class="ss">eallocate</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">SET_I</span><span class="p" data-group-id="4573747687-3">(</span><span class="p" data-group-id="4573747687-4">(</span><span class="n">BeamInstr</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="4573747687-4">)</span><span class="w"> </span><span class="nf">cp_val</span><span class="p" data-group-id="4573747687-5">(</span><span class="o">*</span><span class="n">E</span><span class="p" data-group-id="4573747687-5">)</span><span class="p" data-group-id="4573747687-3">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ADD_BYTE_OFFSET</span><span class="p" data-group-id="4573747687-6">(</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="p" data-group-id="4573747687-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">CHECK_TERM</span><span class="p" data-group-id="4573747687-7">(</span><span class="nf">x</span><span class="p" data-group-id="4573747687-8">(</span><span class="mi">0</span><span class="p" data-group-id="4573747687-8">)</span><span class="p" data-group-id="4573747687-7">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">SET_I</span><span class="p" data-group-id="7833315030-3">(</span><span class="p" data-group-id="7833315030-4">(</span><span class="n">BeamInstr</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="7833315030-4">)</span><span class="w"> </span><span class="nf">cp_val</span><span class="p" data-group-id="7833315030-5">(</span><span class="o">*</span><span class="n">E</span><span class="p" data-group-id="7833315030-5">)</span><span class="p" data-group-id="7833315030-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ADD_BYTE_OFFSET</span><span class="p" data-group-id="7833315030-6">(</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="p" data-group-id="7833315030-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">CHECK_TERM</span><span class="p" data-group-id="7833315030-7">(</span><span class="nf">x</span><span class="p" data-group-id="7833315030-8">(</span><span class="mi">0</span><span class="p" data-group-id="7833315030-8">)</span><span class="p" data-group-id="7833315030-7">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">DispatchReturn</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4573747687-2">}</span></code></pre><p>The expanded code for <code class="inline">move_deallocate_return</code> will look this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="0791103470-1">(</span><span class="ss">move_deallocate_return_cQ</span><span class="p" data-group-id="0791103470-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0791103470-2">{</span><span class="w">
│ │ │ -  </span><span class="nf">x</span><span class="p" data-group-id="0791103470-3">(</span><span class="mi">0</span><span class="p" data-group-id="0791103470-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="0791103470-4">[</span><span class="mi">1</span><span class="p" data-group-id="0791103470-4">]</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="ss">do</span><span class="w"> </span><span class="p" data-group-id="0791103470-5">{</span><span class="w">
│ │ │ -    </span><span class="ss">int</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Qb</span><span class="p" data-group-id="0791103470-6">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="0791103470-7">(</span><span class="n">I</span><span class="p" data-group-id="0791103470-8">[</span><span class="mi">0</span><span class="p" data-group-id="0791103470-8">]</span><span class="p" data-group-id="0791103470-7">)</span><span class="p" data-group-id="0791103470-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">SET_I</span><span class="p" data-group-id="0791103470-9">(</span><span class="p" data-group-id="0791103470-10">(</span><span class="n">BeamInstr</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="0791103470-10">)</span><span class="w"> </span><span class="nf">cp_val</span><span class="p" data-group-id="0791103470-11">(</span><span class="o">*</span><span class="n">E</span><span class="p" data-group-id="0791103470-11">)</span><span class="p" data-group-id="0791103470-9">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ADD_BYTE_OFFSET</span><span class="p" data-group-id="0791103470-12">(</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="p" data-group-id="0791103470-12">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">CHECK_TERM</span><span class="p" data-group-id="0791103470-13">(</span><span class="nf">x</span><span class="p" data-group-id="0791103470-14">(</span><span class="mi">0</span><span class="p" data-group-id="0791103470-14">)</span><span class="p" data-group-id="0791103470-13">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7833315030-2">}</span></code></pre><p>The expanded code for <code class="inline">move_deallocate_return</code> will look this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="4445785333-1">(</span><span class="ss">move_deallocate_return_cQ</span><span class="p" data-group-id="4445785333-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4445785333-2">{</span><span class="w">
│ │ │ +  </span><span class="nf">x</span><span class="p" data-group-id="4445785333-3">(</span><span class="mi">0</span><span class="p" data-group-id="4445785333-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="4445785333-4">[</span><span class="mi">1</span><span class="p" data-group-id="4445785333-4">]</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="ss">do</span><span class="w"> </span><span class="p" data-group-id="4445785333-5">{</span><span class="w">
│ │ │ +    </span><span class="ss">int</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Qb</span><span class="p" data-group-id="4445785333-6">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="4445785333-7">(</span><span class="n">I</span><span class="p" data-group-id="4445785333-8">[</span><span class="mi">0</span><span class="p" data-group-id="4445785333-8">]</span><span class="p" data-group-id="4445785333-7">)</span><span class="p" data-group-id="4445785333-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">SET_I</span><span class="p" data-group-id="4445785333-9">(</span><span class="p" data-group-id="4445785333-10">(</span><span class="n">BeamInstr</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="4445785333-10">)</span><span class="w"> </span><span class="nf">cp_val</span><span class="p" data-group-id="4445785333-11">(</span><span class="o">*</span><span class="n">E</span><span class="p" data-group-id="4445785333-11">)</span><span class="p" data-group-id="4445785333-9">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ADD_BYTE_OFFSET</span><span class="p" data-group-id="4445785333-12">(</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="p" data-group-id="4445785333-12">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">CHECK_TERM</span><span class="p" data-group-id="4445785333-13">(</span><span class="nf">x</span><span class="p" data-group-id="4445785333-14">(</span><span class="mi">0</span><span class="p" data-group-id="4445785333-14">)</span><span class="p" data-group-id="4445785333-13">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">DispatchReturn</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0791103470-5">}</span><span class="w"> </span><span class="nf">while</span><span class="w"> </span><span class="p" data-group-id="0791103470-15">(</span><span class="mi">0</span><span class="p" data-group-id="0791103470-15">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0791103470-2">}</span></code></pre><p>When expanding macros, <strong>beam_makeops</strong> wraps the expansion in a
│ │ │ +  </span><span class="p" data-group-id="4445785333-5">}</span><span class="w"> </span><span class="nf">while</span><span class="w"> </span><span class="p" data-group-id="4445785333-15">(</span><span class="mi">0</span><span class="p" data-group-id="4445785333-15">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4445785333-2">}</span></code></pre><p>When expanding macros, <strong>beam_makeops</strong> wraps the expansion in a
│ │ │  <code class="inline">do</code>/<code class="inline">while</code> wrapper unless <strong>beam_makeops</strong> can clearly see that no
│ │ │  wrapper is needed.  In this case, the wrapper is needed.</p><p>Note that arguments for macros cannot be complex expressions, because
│ │ │  the arguments are split on <code class="inline">,</code>.  For example, the following would
│ │ │  not work because <strong>beam_makeops</strong> would split the expression into
│ │ │ -two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$d</span><span class="nf">eallocate_return</span><span class="p" data-group-id="7626496168-1">(</span><span class="nf">get_deallocation</span><span class="p" data-group-id="7626496168-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="sc">$D</span><span class="ss">eallocate</span><span class="p" data-group-id="7626496168-2">)</span><span class="p" data-group-id="7626496168-1">)</span><span class="p">;</span></code></pre><h4>Code generation directives</h4><p>Within macro definitions, <code class="inline">//</code> comments are in general not treated
│ │ │ +two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$d</span><span class="nf">eallocate_return</span><span class="p" data-group-id="3257699516-1">(</span><span class="nf">get_deallocation</span><span class="p" data-group-id="3257699516-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="sc">$D</span><span class="ss">eallocate</span><span class="p" data-group-id="3257699516-2">)</span><span class="p" data-group-id="3257699516-1">)</span><span class="p">;</span></code></pre><h4>Code generation directives</h4><p>Within macro definitions, <code class="inline">//</code> comments are in general not treated
│ │ │  specially.  They will be copied to the file with the generated code
│ │ │  along with the rest of code in the body.</p><p>However, there is an exception. Within a macro definition, a line that
│ │ │  starts with whitespace followed by <code class="inline">//|</code> is treated specially.  The
│ │ │  rest of the line is assumed to contain directives to control code
│ │ │  generation.</p><p>Currently, two code generation directives are recognized:</p><ul><li><code class="inline">-no_prefetch</code></li><li><code class="inline">-no_next</code></li></ul><h5>The -no_prefetch directive</h5><p>To see what <code class="inline">-no_prefetch</code> does, let's first look at the default code
│ │ │ -generation.  Here is the code generated for <code class="inline">move_cx</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="0161315528-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="0161315528-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0161315528-2">{</span><span class="w">
│ │ │ -  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="0161315528-3">(</span><span class="n">I</span><span class="p" data-group-id="0161315528-4">[</span><span class="mi">2</span><span class="p" data-group-id="0161315528-4">]</span><span class="p" data-group-id="0161315528-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">xb</span><span class="p" data-group-id="0161315528-5">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="0161315528-6">(</span><span class="n">I</span><span class="p" data-group-id="0161315528-7">[</span><span class="mi">0</span><span class="p" data-group-id="0161315528-7">]</span><span class="p" data-group-id="0161315528-6">)</span><span class="p" data-group-id="0161315528-5">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="0161315528-8">[</span><span class="mi">1</span><span class="p" data-group-id="0161315528-8">]</span><span class="p">;</span><span class="w">
│ │ │ +generation.  Here is the code generated for <code class="inline">move_cx</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="0067471298-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="0067471298-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0067471298-2">{</span><span class="w">
│ │ │ +  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="0067471298-3">(</span><span class="n">I</span><span class="p" data-group-id="0067471298-4">[</span><span class="mi">2</span><span class="p" data-group-id="0067471298-4">]</span><span class="p" data-group-id="0067471298-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">xb</span><span class="p" data-group-id="0067471298-5">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="0067471298-6">(</span><span class="n">I</span><span class="p" data-group-id="0067471298-7">[</span><span class="mi">0</span><span class="p" data-group-id="0067471298-7">]</span><span class="p" data-group-id="0067471298-6">)</span><span class="p" data-group-id="0067471298-5">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="0067471298-8">[</span><span class="mi">1</span><span class="p" data-group-id="0067471298-8">]</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="0161315528-9">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="0161315528-10">(</span><span class="ss">next_pf</span><span class="p" data-group-id="0161315528-10">)</span><span class="p" data-group-id="0161315528-9">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">GotoPF</span><span class="p" data-group-id="0161315528-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="0161315528-11">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0161315528-2">}</span></code></pre><p>Note that the very first thing done is to fetch the address to the
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="0067471298-9">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="0067471298-10">(</span><span class="ss">next_pf</span><span class="p" data-group-id="0067471298-10">)</span><span class="p" data-group-id="0067471298-9">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">GotoPF</span><span class="p" data-group-id="0067471298-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="0067471298-11">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0067471298-2">}</span></code></pre><p>Note that the very first thing done is to fetch the address to the
│ │ │  next instruction.  The reason is that it usually improves performance.</p><p>Just as a demonstration, we can add a <code class="inline">-no_prefetch</code> directive to
│ │ │ -the <code class="inline">move/2</code> instruction:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="8850200922-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="8850200922-1">)</span><span class="w"> </span><span class="p" data-group-id="8850200922-2">{</span><span class="w">
│ │ │ +the <code class="inline">move/2</code> instruction:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="4866981958-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="4866981958-1">)</span><span class="w"> </span><span class="p" data-group-id="4866981958-2">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_prefetch</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8850200922-2">}</span></code></pre><p>We can see that the prefetch is no longer done:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="8361552444-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="8361552444-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8361552444-2">{</span><span class="w">
│ │ │ -  </span><span class="nf">xb</span><span class="p" data-group-id="8361552444-3">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="8361552444-4">(</span><span class="n">I</span><span class="p" data-group-id="8361552444-5">[</span><span class="mi">0</span><span class="p" data-group-id="8361552444-5">]</span><span class="p" data-group-id="8361552444-4">)</span><span class="p" data-group-id="8361552444-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="8361552444-6">[</span><span class="mi">1</span><span class="p" data-group-id="8361552444-6">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4866981958-2">}</span></code></pre><p>We can see that the prefetch is no longer done:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="0241489272-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="0241489272-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0241489272-2">{</span><span class="w">
│ │ │ +  </span><span class="nf">xb</span><span class="p" data-group-id="0241489272-3">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="0241489272-4">(</span><span class="n">I</span><span class="p" data-group-id="0241489272-5">[</span><span class="mi">0</span><span class="p" data-group-id="0241489272-5">]</span><span class="p" data-group-id="0241489272-4">)</span><span class="p" data-group-id="0241489272-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="0241489272-6">[</span><span class="mi">1</span><span class="p" data-group-id="0241489272-6">]</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="8361552444-7">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="8361552444-8">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="8361552444-8">)</span><span class="p" data-group-id="8361552444-7">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">Goto</span><span class="p" data-group-id="8361552444-9">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="8361552444-9">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8361552444-2">}</span></code></pre><p>When would we want to turn off the prefetch in practice?</p><p>In instructions that will not always execute the next instruction.
│ │ │ -For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">is_atom</span><span class="p" data-group-id="9890555263-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="9890555263-1">)</span><span class="w"> </span><span class="p" data-group-id="9890555263-2">{</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="9890555263-3">(</span><span class="nf">is_not_atom</span><span class="p" data-group-id="9890555263-4">(</span><span class="sc">$S</span><span class="ss">rc</span><span class="p" data-group-id="9890555263-4">)</span><span class="p" data-group-id="9890555263-3">)</span><span class="w"> </span><span class="p" data-group-id="9890555263-5">{</span><span class="w">
│ │ │ -        </span><span class="sc">$F</span><span class="n">AIL</span><span class="p" data-group-id="9890555263-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="9890555263-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9890555263-5">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9890555263-2">}</span><span class="w">
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="0241489272-7">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="0241489272-8">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="0241489272-8">)</span><span class="p" data-group-id="0241489272-7">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">Goto</span><span class="p" data-group-id="0241489272-9">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="0241489272-9">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0241489272-2">}</span></code></pre><p>When would we want to turn off the prefetch in practice?</p><p>In instructions that will not always execute the next instruction.
│ │ │ +For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">is_atom</span><span class="p" data-group-id="9285910996-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="9285910996-1">)</span><span class="w"> </span><span class="p" data-group-id="9285910996-2">{</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="9285910996-3">(</span><span class="nf">is_not_atom</span><span class="p" data-group-id="9285910996-4">(</span><span class="sc">$S</span><span class="ss">rc</span><span class="p" data-group-id="9285910996-4">)</span><span class="p" data-group-id="9285910996-3">)</span><span class="w"> </span><span class="p" data-group-id="9285910996-5">{</span><span class="w">
│ │ │ +        </span><span class="sc">$F</span><span class="n">AIL</span><span class="p" data-group-id="9285910996-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="9285910996-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9285910996-5">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9285910996-2">}</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">From</span><span class="w"> </span><span class="ss">macros</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │ -</span><span class="n">FAIL</span><span class="p" data-group-id="9890555263-7">(</span><span class="n">Fail</span><span class="p" data-group-id="9890555263-7">)</span><span class="w"> </span><span class="p" data-group-id="9890555263-8">{</span><span class="w">
│ │ │ +</span><span class="n">FAIL</span><span class="p" data-group-id="9285910996-7">(</span><span class="n">Fail</span><span class="p" data-group-id="9285910996-7">)</span><span class="w"> </span><span class="p" data-group-id="9285910996-8">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_prefetch</span><span class="w">
│ │ │ -    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="9890555263-9">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="9890555263-9">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">Goto</span><span class="p" data-group-id="9890555263-10">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="9890555263-10">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9890555263-8">}</span></code></pre><p><code class="inline">is_atom/2</code> may either execute the next instruction (if the second
│ │ │ -operand is an atom) or branch to the failure label.</p><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="8635687434-1">(</span><span class="ss">is_atom_fx</span><span class="p" data-group-id="8635687434-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8635687434-2">{</span><span class="w">
│ │ │ -  </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="8635687434-3">(</span><span class="nf">is_not_atom</span><span class="p" data-group-id="8635687434-4">(</span><span class="nf">xb</span><span class="p" data-group-id="8635687434-5">(</span><span class="n">I</span><span class="p" data-group-id="8635687434-6">[</span><span class="mi">1</span><span class="p" data-group-id="8635687434-6">]</span><span class="p" data-group-id="8635687434-5">)</span><span class="p" data-group-id="8635687434-4">)</span><span class="p" data-group-id="8635687434-3">)</span><span class="w"> </span><span class="p" data-group-id="8635687434-7">{</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="8635687434-8">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="8635687434-9">(</span><span class="o">*</span><span class="p" data-group-id="8635687434-10">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="8635687434-11">(</span><span class="nf">fb</span><span class="p" data-group-id="8635687434-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="8635687434-13">(</span><span class="n">I</span><span class="p" data-group-id="8635687434-14">[</span><span class="mi">0</span><span class="p" data-group-id="8635687434-14">]</span><span class="p" data-group-id="8635687434-13">)</span><span class="p" data-group-id="8635687434-12">)</span><span class="p" data-group-id="8635687434-11">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8635687434-10">)</span><span class="p" data-group-id="8635687434-9">)</span><span class="p" data-group-id="8635687434-8">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="8635687434-15">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="8635687434-16">(</span><span class="n">I</span><span class="p" data-group-id="8635687434-17">[</span><span class="mi">0</span><span class="p" data-group-id="8635687434-17">]</span><span class="p" data-group-id="8635687434-16">)</span><span class="p" data-group-id="8635687434-15">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">Goto</span><span class="p" data-group-id="8635687434-18">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="8635687434-18">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8635687434-7">}</span><span class="w">
│ │ │ +    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="9285910996-9">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="9285910996-9">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">Goto</span><span class="p" data-group-id="9285910996-10">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="9285910996-10">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9285910996-8">}</span></code></pre><p><code class="inline">is_atom/2</code> may either execute the next instruction (if the second
│ │ │ +operand is an atom) or branch to the failure label.</p><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="7550372199-1">(</span><span class="ss">is_atom_fx</span><span class="p" data-group-id="7550372199-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7550372199-2">{</span><span class="w">
│ │ │ +  </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="7550372199-3">(</span><span class="nf">is_not_atom</span><span class="p" data-group-id="7550372199-4">(</span><span class="nf">xb</span><span class="p" data-group-id="7550372199-5">(</span><span class="n">I</span><span class="p" data-group-id="7550372199-6">[</span><span class="mi">1</span><span class="p" data-group-id="7550372199-6">]</span><span class="p" data-group-id="7550372199-5">)</span><span class="p" data-group-id="7550372199-4">)</span><span class="p" data-group-id="7550372199-3">)</span><span class="w"> </span><span class="p" data-group-id="7550372199-7">{</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="7550372199-8">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="7550372199-9">(</span><span class="o">*</span><span class="p" data-group-id="7550372199-10">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="7550372199-11">(</span><span class="nf">fb</span><span class="p" data-group-id="7550372199-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="7550372199-13">(</span><span class="n">I</span><span class="p" data-group-id="7550372199-14">[</span><span class="mi">0</span><span class="p" data-group-id="7550372199-14">]</span><span class="p" data-group-id="7550372199-13">)</span><span class="p" data-group-id="7550372199-12">)</span><span class="p" data-group-id="7550372199-11">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7550372199-10">)</span><span class="p" data-group-id="7550372199-9">)</span><span class="p" data-group-id="7550372199-8">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="7550372199-15">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="7550372199-16">(</span><span class="n">I</span><span class="p" data-group-id="7550372199-17">[</span><span class="mi">0</span><span class="p" data-group-id="7550372199-17">]</span><span class="p" data-group-id="7550372199-16">)</span><span class="p" data-group-id="7550372199-15">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">Goto</span><span class="p" data-group-id="7550372199-18">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="7550372199-18">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="7550372199-7">}</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="8635687434-19">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="8635687434-20">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="8635687434-20">)</span><span class="p" data-group-id="8635687434-19">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">Goto</span><span class="p" data-group-id="8635687434-21">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="8635687434-21">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8635687434-2">}</span></code></pre><h5>The -no_next directive</h5><p>Next we will look at when the <code class="inline">-no_next</code> directive can be used.  Here
│ │ │ -is the <code class="inline">jump/1</code> instruction:</p><pre><code class="makeup erlang" translate="no"><span class="nf">jump</span><span class="p" data-group-id="2203548699-1">(</span><span class="n">Fail</span><span class="p" data-group-id="2203548699-1">)</span><span class="w"> </span><span class="p" data-group-id="2203548699-2">{</span><span class="w">
│ │ │ -    </span><span class="sc">$J</span><span class="n">UMP</span><span class="p" data-group-id="2203548699-3">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="2203548699-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2203548699-2">}</span><span class="w">
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="7550372199-19">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="7550372199-20">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="7550372199-20">)</span><span class="p" data-group-id="7550372199-19">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">Goto</span><span class="p" data-group-id="7550372199-21">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="7550372199-21">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7550372199-2">}</span></code></pre><h5>The -no_next directive</h5><p>Next we will look at when the <code class="inline">-no_next</code> directive can be used.  Here
│ │ │ +is the <code class="inline">jump/1</code> instruction:</p><pre><code class="makeup erlang" translate="no"><span class="nf">jump</span><span class="p" data-group-id="5037422312-1">(</span><span class="n">Fail</span><span class="p" data-group-id="5037422312-1">)</span><span class="w"> </span><span class="p" data-group-id="5037422312-2">{</span><span class="w">
│ │ │ +    </span><span class="sc">$J</span><span class="n">UMP</span><span class="p" data-group-id="5037422312-3">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="5037422312-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037422312-2">}</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">From</span><span class="w"> </span><span class="ss">macros</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │ -</span><span class="n">JUMP</span><span class="p" data-group-id="2203548699-4">(</span><span class="n">Fail</span><span class="p" data-group-id="2203548699-4">)</span><span class="w"> </span><span class="p" data-group-id="2203548699-5">{</span><span class="w">
│ │ │ +</span><span class="n">JUMP</span><span class="p" data-group-id="5037422312-4">(</span><span class="n">Fail</span><span class="p" data-group-id="5037422312-4">)</span><span class="w"> </span><span class="p" data-group-id="5037422312-5">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_next</span><span class="w">
│ │ │ -    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="2203548699-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="2203548699-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">Goto</span><span class="p" data-group-id="2203548699-7">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="2203548699-7">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2203548699-5">}</span></code></pre><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="0378251380-1">(</span><span class="ss">jump_f</span><span class="p" data-group-id="0378251380-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0378251380-2">{</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="0378251380-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="0378251380-4">(</span><span class="o">*</span><span class="p" data-group-id="0378251380-5">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="0378251380-6">(</span><span class="nf">fb</span><span class="p" data-group-id="0378251380-7">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="0378251380-8">(</span><span class="n">I</span><span class="p" data-group-id="0378251380-9">[</span><span class="mi">0</span><span class="p" data-group-id="0378251380-9">]</span><span class="p" data-group-id="0378251380-8">)</span><span class="p" data-group-id="0378251380-7">)</span><span class="p" data-group-id="0378251380-6">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0378251380-5">)</span><span class="p" data-group-id="0378251380-4">)</span><span class="p" data-group-id="0378251380-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="0378251380-10">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="0378251380-11">(</span><span class="n">I</span><span class="p" data-group-id="0378251380-12">[</span><span class="mi">0</span><span class="p" data-group-id="0378251380-12">]</span><span class="p" data-group-id="0378251380-11">)</span><span class="p" data-group-id="0378251380-10">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">Goto</span><span class="p" data-group-id="0378251380-13">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="0378251380-13">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0378251380-2">}</span></code></pre><p>If we remove the <code class="inline">-no_next</code> directive, the code would look like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="2591769570-1">(</span><span class="ss">jump_f</span><span class="p" data-group-id="2591769570-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2591769570-2">{</span><span class="w">
│ │ │ -  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="2591769570-3">(</span><span class="n">I</span><span class="p" data-group-id="2591769570-4">[</span><span class="mi">1</span><span class="p" data-group-id="2591769570-4">]</span><span class="p" data-group-id="2591769570-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="2591769570-5">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="2591769570-6">(</span><span class="o">*</span><span class="p" data-group-id="2591769570-7">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="2591769570-8">(</span><span class="nf">fb</span><span class="p" data-group-id="2591769570-9">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="2591769570-10">(</span><span class="n">I</span><span class="p" data-group-id="2591769570-11">[</span><span class="mi">0</span><span class="p" data-group-id="2591769570-11">]</span><span class="p" data-group-id="2591769570-10">)</span><span class="p" data-group-id="2591769570-9">)</span><span class="p" data-group-id="2591769570-8">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2591769570-7">)</span><span class="p" data-group-id="2591769570-6">)</span><span class="p" data-group-id="2591769570-5">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="2591769570-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="2591769570-13">(</span><span class="n">I</span><span class="p" data-group-id="2591769570-14">[</span><span class="mi">0</span><span class="p" data-group-id="2591769570-14">]</span><span class="p" data-group-id="2591769570-13">)</span><span class="p" data-group-id="2591769570-12">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">Goto</span><span class="p" data-group-id="2591769570-15">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="2591769570-15">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="5037422312-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="5037422312-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">Goto</span><span class="p" data-group-id="5037422312-7">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="5037422312-7">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037422312-5">}</span></code></pre><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="7458995268-1">(</span><span class="ss">jump_f</span><span class="p" data-group-id="7458995268-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7458995268-2">{</span><span class="w">
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="7458995268-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="7458995268-4">(</span><span class="o">*</span><span class="p" data-group-id="7458995268-5">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="7458995268-6">(</span><span class="nf">fb</span><span class="p" data-group-id="7458995268-7">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="7458995268-8">(</span><span class="n">I</span><span class="p" data-group-id="7458995268-9">[</span><span class="mi">0</span><span class="p" data-group-id="7458995268-9">]</span><span class="p" data-group-id="7458995268-8">)</span><span class="p" data-group-id="7458995268-7">)</span><span class="p" data-group-id="7458995268-6">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7458995268-5">)</span><span class="p" data-group-id="7458995268-4">)</span><span class="p" data-group-id="7458995268-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="7458995268-10">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="7458995268-11">(</span><span class="n">I</span><span class="p" data-group-id="7458995268-12">[</span><span class="mi">0</span><span class="p" data-group-id="7458995268-12">]</span><span class="p" data-group-id="7458995268-11">)</span><span class="p" data-group-id="7458995268-10">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">Goto</span><span class="p" data-group-id="7458995268-13">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="7458995268-13">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7458995268-2">}</span></code></pre><p>If we remove the <code class="inline">-no_next</code> directive, the code would look like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="9468371719-1">(</span><span class="ss">jump_f</span><span class="p" data-group-id="9468371719-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9468371719-2">{</span><span class="w">
│ │ │ +  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="9468371719-3">(</span><span class="n">I</span><span class="p" data-group-id="9468371719-4">[</span><span class="mi">1</span><span class="p" data-group-id="9468371719-4">]</span><span class="p" data-group-id="9468371719-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="9468371719-5">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="9468371719-6">(</span><span class="o">*</span><span class="p" data-group-id="9468371719-7">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="9468371719-8">(</span><span class="nf">fb</span><span class="p" data-group-id="9468371719-9">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="9468371719-10">(</span><span class="n">I</span><span class="p" data-group-id="9468371719-11">[</span><span class="mi">0</span><span class="p" data-group-id="9468371719-11">]</span><span class="p" data-group-id="9468371719-10">)</span><span class="p" data-group-id="9468371719-9">)</span><span class="p" data-group-id="9468371719-8">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="9468371719-7">)</span><span class="p" data-group-id="9468371719-6">)</span><span class="p" data-group-id="9468371719-5">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="9468371719-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="9468371719-13">(</span><span class="n">I</span><span class="p" data-group-id="9468371719-14">[</span><span class="mi">0</span><span class="p" data-group-id="9468371719-14">]</span><span class="p" data-group-id="9468371719-13">)</span><span class="p" data-group-id="9468371719-12">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">Goto</span><span class="p" data-group-id="9468371719-15">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="9468371719-15">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="2591769570-16">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="2591769570-17">(</span><span class="ss">next_pf</span><span class="p" data-group-id="2591769570-17">)</span><span class="p" data-group-id="2591769570-16">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">GotoPF</span><span class="p" data-group-id="2591769570-18">(</span><span class="ss">next_pf</span><span class="p" data-group-id="2591769570-18">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2591769570-2">}</span></code></pre><p>In the end, the C compiler will probably optimize this code to the
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="9468371719-16">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="9468371719-17">(</span><span class="ss">next_pf</span><span class="p" data-group-id="9468371719-17">)</span><span class="p" data-group-id="9468371719-16">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">GotoPF</span><span class="p" data-group-id="9468371719-18">(</span><span class="ss">next_pf</span><span class="p" data-group-id="9468371719-18">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9468371719-2">}</span></code></pre><p>In the end, the C compiler will probably optimize this code to the
│ │ │  same native code as the first version, but the first version is certainly
│ │ │  much easier to read for human readers.</p><h4>Macros in the macros.tab file</h4><p>The file <code class="inline">macros.tab</code> contains many useful macros.  When implementing
│ │ │  new instructions it is good practice to look through <code class="inline">macros.tab</code> to
│ │ │  see if any of existing macros can be used rather than re-inventing
│ │ │  the wheel.</p><p>We will describe a few of the most useful macros here.</p><p><a href="" id="the-GC_REGEXP-definition"></a></p><h5>The GC_REGEXP definition</h5><p>The following line defines a regular expression that will recognize
│ │ │  a call to a function that does a garbage collection:</p><pre><code class="makeup erlang" translate="no"><span class="w"> </span><span class="n">GC_REGEXP</span><span class="o">=</span><span class="ss">erts_garbage_collect</span><span class="p">|</span><span class="ss">erts_gc</span><span class="p">|</span><span class="n">GcBifFunction</span><span class="p">;</span></code></pre><p>The purpose is that <strong>beam_makeops</strong> can verify that an instruction
│ │ │  that does a garbage collection and has an <code class="inline">d</code> operand uses the
│ │ │  <code class="inline">$REFRESH_GEN_DEST()</code> macro.</p><p>If you need to define a new function that does garbage collection,
│ │ │  you should give it the prefix <code class="inline">erts_gc_</code>.  If that is not possible
│ │ │  you should update the regular expression so that it will match your
│ │ │ -new function.</p><h5>FAIL(Fail)</h5><p>Branch to <code class="inline">$Fail</code>.  Will suppress prefetch (<code class="inline">-no_prefetch</code>).  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">is_nonempty_list</span><span class="p" data-group-id="7531802556-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="7531802556-1">)</span><span class="w"> </span><span class="p" data-group-id="7531802556-2">{</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="7531802556-3">(</span><span class="nf">is_not_list</span><span class="p" data-group-id="7531802556-4">(</span><span class="sc">$S</span><span class="ss">rc</span><span class="p" data-group-id="7531802556-4">)</span><span class="p" data-group-id="7531802556-3">)</span><span class="w"> </span><span class="p" data-group-id="7531802556-5">{</span><span class="w">
│ │ │ -        </span><span class="sc">$F</span><span class="n">AIL</span><span class="p" data-group-id="7531802556-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="7531802556-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7531802556-5">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7531802556-2">}</span></code></pre><h5>JUMP(Fail)</h5><p>Branch to <code class="inline">$Fail</code>.  Suppresses generation of dispatch of the next
│ │ │ -instruction (<code class="inline">-no_next</code>).  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">jump</span><span class="p" data-group-id="1107682664-1">(</span><span class="n">Fail</span><span class="p" data-group-id="1107682664-1">)</span><span class="w"> </span><span class="p" data-group-id="1107682664-2">{</span><span class="w">
│ │ │ -    </span><span class="sc">$J</span><span class="n">UMP</span><span class="p" data-group-id="1107682664-3">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="1107682664-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1107682664-2">}</span></code></pre><h5>GC_TEST(NeedStack, NeedHeap, Live)</h5><p><code class="inline">$GC_TEST(NeedStack, NeedHeap, Live)</code> tests that given amount of
│ │ │ +new function.</p><h5>FAIL(Fail)</h5><p>Branch to <code class="inline">$Fail</code>.  Will suppress prefetch (<code class="inline">-no_prefetch</code>).  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">is_nonempty_list</span><span class="p" data-group-id="6755724445-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="6755724445-1">)</span><span class="w"> </span><span class="p" data-group-id="6755724445-2">{</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="6755724445-3">(</span><span class="nf">is_not_list</span><span class="p" data-group-id="6755724445-4">(</span><span class="sc">$S</span><span class="ss">rc</span><span class="p" data-group-id="6755724445-4">)</span><span class="p" data-group-id="6755724445-3">)</span><span class="w"> </span><span class="p" data-group-id="6755724445-5">{</span><span class="w">
│ │ │ +        </span><span class="sc">$F</span><span class="n">AIL</span><span class="p" data-group-id="6755724445-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="6755724445-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6755724445-5">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6755724445-2">}</span></code></pre><h5>JUMP(Fail)</h5><p>Branch to <code class="inline">$Fail</code>.  Suppresses generation of dispatch of the next
│ │ │ +instruction (<code class="inline">-no_next</code>).  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">jump</span><span class="p" data-group-id="7329328618-1">(</span><span class="n">Fail</span><span class="p" data-group-id="7329328618-1">)</span><span class="w"> </span><span class="p" data-group-id="7329328618-2">{</span><span class="w">
│ │ │ +    </span><span class="sc">$J</span><span class="n">UMP</span><span class="p" data-group-id="7329328618-3">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="7329328618-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7329328618-2">}</span></code></pre><h5>GC_TEST(NeedStack, NeedHeap, Live)</h5><p><code class="inline">$GC_TEST(NeedStack, NeedHeap, Live)</code> tests that given amount of
│ │ │  stack space and heap space is available.  If not it will do a
│ │ │ -garbage collection.  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">test_heap</span><span class="p" data-group-id="3085742129-1">(</span><span class="n">Nh</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p" data-group-id="3085742129-1">)</span><span class="w"> </span><span class="p" data-group-id="3085742129-2">{</span><span class="w">
│ │ │ -    </span><span class="sc">$G</span><span class="n">C_TEST</span><span class="p" data-group-id="3085742129-3">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="ss">h</span><span class="p">,</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p" data-group-id="3085742129-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3085742129-2">}</span></code></pre><h5>AH(NeedStack, NeedHeap, Live)</h5><p><code class="inline">AH(NeedStack, NeedHeap, Live)</code> allocates a stack frame and
│ │ │ +garbage collection.  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">test_heap</span><span class="p" data-group-id="4270401893-1">(</span><span class="n">Nh</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p" data-group-id="4270401893-1">)</span><span class="w"> </span><span class="p" data-group-id="4270401893-2">{</span><span class="w">
│ │ │ +    </span><span class="sc">$G</span><span class="n">C_TEST</span><span class="p" data-group-id="4270401893-3">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="ss">h</span><span class="p">,</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p" data-group-id="4270401893-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4270401893-2">}</span></code></pre><h5>AH(NeedStack, NeedHeap, Live)</h5><p><code class="inline">AH(NeedStack, NeedHeap, Live)</code> allocates a stack frame and
│ │ │  optionally additional heap space.</p><h4>Pre-defined macros and variables</h4><p><strong>beam_makeops</strong> defines several built-in macros and pre-bound variables.</p><h5>The NEXT_INSTRUCTION pre-bound variable</h5><p>The NEXT_INSTRUCTION is a pre-bound variable that is available in
│ │ │ -all instructions.  It expands to the address of the next instruction.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">i_call</span><span class="p" data-group-id="3679646287-1">(</span><span class="n">CallDest</span><span class="p" data-group-id="3679646287-1">)</span><span class="w"> </span><span class="p" data-group-id="3679646287-2">{</span><span class="w">
│ │ │ +all instructions.  It expands to the address of the next instruction.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">i_call</span><span class="p" data-group-id="7111255976-1">(</span><span class="n">CallDest</span><span class="p" data-group-id="7111255976-1">)</span><span class="w"> </span><span class="p" data-group-id="7111255976-2">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_next</span><span class="w">
│ │ │ -    </span><span class="sc">$S</span><span class="n">AVE_CONTINUATION_POINTER</span><span class="p" data-group-id="3679646287-3">(</span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="p" data-group-id="3679646287-3">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="sc">$D</span><span class="n">ISPATCH_REL</span><span class="p" data-group-id="3679646287-4">(</span><span class="sc">$C</span><span class="ss">allDest</span><span class="p" data-group-id="3679646287-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3679646287-2">}</span></code></pre><p>When calling a function, the return address is first stored in <code class="inline">E[0]</code>
│ │ │ +    </span><span class="sc">$S</span><span class="n">AVE_CONTINUATION_POINTER</span><span class="p" data-group-id="7111255976-3">(</span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="p" data-group-id="7111255976-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="sc">$D</span><span class="n">ISPATCH_REL</span><span class="p" data-group-id="7111255976-4">(</span><span class="sc">$C</span><span class="ss">allDest</span><span class="p" data-group-id="7111255976-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7111255976-2">}</span></code></pre><p>When calling a function, the return address is first stored in <code class="inline">E[0]</code>
│ │ │  (using the <code class="inline">$SAVE_CONTINUATION_POINTER()</code> macro), and then control is
│ │ │ -transferred to the callee.  Here is the generated code:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="0478103211-1">(</span><span class="ss">i_call_f</span><span class="p" data-group-id="0478103211-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0478103211-2">{</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="0478103211-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="0478103211-4">(</span><span class="o">*</span><span class="p" data-group-id="0478103211-5">(</span><span class="n">I</span><span class="o">+</span><span class="mi">2</span><span class="p" data-group-id="0478103211-5">)</span><span class="p" data-group-id="0478103211-4">)</span><span class="p" data-group-id="0478103211-3">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="o">*</span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0478103211-6">(</span><span class="n">BeamInstr</span><span class="p" data-group-id="0478103211-6">)</span><span class="w"> </span><span class="p" data-group-id="0478103211-7">(</span><span class="n">I</span><span class="o">+</span><span class="mi">2</span><span class="p" data-group-id="0478103211-7">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +transferred to the callee.  Here is the generated code:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="7941912293-1">(</span><span class="ss">i_call_f</span><span class="p" data-group-id="7941912293-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7941912293-2">{</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="7941912293-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="7941912293-4">(</span><span class="o">*</span><span class="p" data-group-id="7941912293-5">(</span><span class="n">I</span><span class="o">+</span><span class="mi">2</span><span class="p" data-group-id="7941912293-5">)</span><span class="p" data-group-id="7941912293-4">)</span><span class="p" data-group-id="7941912293-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="o">*</span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7941912293-6">(</span><span class="n">BeamInstr</span><span class="p" data-group-id="7941912293-6">)</span><span class="w"> </span><span class="p" data-group-id="7941912293-7">(</span><span class="n">I</span><span class="o">+</span><span class="mi">2</span><span class="p" data-group-id="7941912293-7">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │      </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">dispatch</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">intentionally</span><span class="w"> </span><span class="ss">left</span><span class="w"> </span><span class="ss">out</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0478103211-2">}</span></code></pre><p>We can see that that <code class="inline">$NEXT_INSTRUCTION</code> has been expanded to <code class="inline">I+2</code>.
│ │ │ +</span><span class="p" data-group-id="7941912293-2">}</span></code></pre><p>We can see that that <code class="inline">$NEXT_INSTRUCTION</code> has been expanded to <code class="inline">I+2</code>.
│ │ │  That makes sense since the size of the <code class="inline">i_call_f/1</code> instruction is
│ │ │  two words.</p><h5>The IP_ADJUSTMENT pre-bound variable</h5><p><code class="inline">$IP_ADJUSTMENT</code> is usually 0.  In a few combined instructions
│ │ │  (described below) it can be non-zero.  It is used like this
│ │ │ -in <code class="inline">macros.tab</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">SET_I_REL</span><span class="p" data-group-id="7664995428-1">(</span><span class="n">Offset</span><span class="p" data-group-id="7664995428-1">)</span><span class="w"> </span><span class="p" data-group-id="7664995428-2">{</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="7664995428-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="7664995428-4">(</span><span class="o">*</span><span class="p" data-group-id="7664995428-5">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="7664995428-6">(</span><span class="sc">$O</span><span class="ss">ffset</span><span class="p" data-group-id="7664995428-6">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$I</span><span class="n">P_ADJUSTMENT</span><span class="p" data-group-id="7664995428-5">)</span><span class="p" data-group-id="7664995428-4">)</span><span class="p" data-group-id="7664995428-3">)</span><span class="p">;</span><span class="w">
│ │ │ +in <code class="inline">macros.tab</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">SET_I_REL</span><span class="p" data-group-id="5325545790-1">(</span><span class="n">Offset</span><span class="p" data-group-id="5325545790-1">)</span><span class="w"> </span><span class="p" data-group-id="5325545790-2">{</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="5325545790-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="5325545790-4">(</span><span class="o">*</span><span class="p" data-group-id="5325545790-5">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="5325545790-6">(</span><span class="sc">$O</span><span class="ss">ffset</span><span class="p" data-group-id="5325545790-6">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$I</span><span class="n">P_ADJUSTMENT</span><span class="p" data-group-id="5325545790-5">)</span><span class="p" data-group-id="5325545790-4">)</span><span class="p" data-group-id="5325545790-3">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="sc">$O</span><span class="ss">ffset</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$I</span><span class="n">P_ADJUSTMENT</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7664995428-2">}</span></code></pre><p>Avoid using <code class="inline">IP_ADJUSTMENT</code> directly.  Use <code class="inline">SET_I_REL()</code> or
│ │ │ +</span><span class="p" data-group-id="5325545790-2">}</span></code></pre><p>Avoid using <code class="inline">IP_ADJUSTMENT</code> directly.  Use <code class="inline">SET_I_REL()</code> or
│ │ │  one of the macros that invoke such as <code class="inline">FAIL()</code> or <code class="inline">JUMP()</code>
│ │ │  defined in <code class="inline">macros.tab</code>.</p><h4>Pre-defined macro functions</h4><h5>The IF() macro</h5><p><code class="inline">$IF(Expr, IfTrue, IfFalse)</code> evaluates <code class="inline">Expr</code>, which must be a valid
│ │ │  Perl expression (which for simple numeric expressions have the same
│ │ │  syntax as C).  If <code class="inline">Expr</code> evaluates to 0, the entire <code class="inline">IF()</code> expression will be
│ │ │  replaced with <code class="inline">IfFalse</code>, otherwise it will be replaced with <code class="inline">IfTrue</code>.</p><p>See the description of <code class="inline">OPERAND_POSITION()</code> for an example.</p><h5>The OPERAND_POSITION() macro</h5><p><code class="inline">$OPERAND_POSITION(Expr)</code> returns the position for <code class="inline">Expr</code>, if
│ │ │  <code class="inline">Expr</code> is an operand that is not packed.  The first operand is
│ │ │ -at position 1.</p><p>Returns 0 otherwise.</p><p>This macro could be used like this in order to share code:</p><pre><code class="makeup erlang" translate="no"><span class="n">FAIL</span><span class="p" data-group-id="4619168827-1">(</span><span class="n">Fail</span><span class="p" data-group-id="4619168827-1">)</span><span class="w"> </span><span class="p" data-group-id="4619168827-2">{</span><span class="w">
│ │ │ +at position 1.</p><p>Returns 0 otherwise.</p><p>This macro could be used like this in order to share code:</p><pre><code class="makeup erlang" translate="no"><span class="n">FAIL</span><span class="p" data-group-id="7692483499-1">(</span><span class="n">Fail</span><span class="p" data-group-id="7692483499-1">)</span><span class="w"> </span><span class="p" data-group-id="7692483499-2">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_prefetch</span><span class="w">
│ │ │ -    </span><span class="sc">$I</span><span class="n">F</span><span class="p" data-group-id="4619168827-3">(</span><span class="sc">$O</span><span class="n">PERAND_POSITION</span><span class="p" data-group-id="4619168827-4">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="4619168827-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w"> </span><span class="sc">$I</span><span class="n">P_ADJUSTMENT</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="sc">$I</span><span class="n">F</span><span class="p" data-group-id="7692483499-3">(</span><span class="sc">$O</span><span class="n">PERAND_POSITION</span><span class="p" data-group-id="7692483499-4">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="7692483499-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w"> </span><span class="sc">$I</span><span class="n">P_ADJUSTMENT</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">goto</span><span class="w"> </span><span class="ss">common_jump</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="sc">$D</span><span class="n">O_JUMP</span><span class="p" data-group-id="4619168827-5">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="4619168827-5">)</span><span class="p" data-group-id="4619168827-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4619168827-2">}</span><span class="w">
│ │ │ +        </span><span class="sc">$D</span><span class="n">O_JUMP</span><span class="p" data-group-id="7692483499-5">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="7692483499-5">)</span><span class="p" data-group-id="7692483499-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7692483499-2">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">DO_JUMP</span><span class="p" data-group-id="4619168827-6">(</span><span class="n">Fail</span><span class="p" data-group-id="4619168827-6">)</span><span class="w"> </span><span class="p" data-group-id="4619168827-7">{</span><span class="w">
│ │ │ -    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="4619168827-8">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="4619168827-8">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">Goto</span><span class="p" data-group-id="4619168827-9">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="4619168827-9">)</span><span class="p">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4619168827-7">}</span><span class="w">
│ │ │ +</span><span class="n">DO_JUMP</span><span class="p" data-group-id="7692483499-6">(</span><span class="n">Fail</span><span class="p" data-group-id="7692483499-6">)</span><span class="w"> </span><span class="p" data-group-id="7692483499-7">{</span><span class="w">
│ │ │ +    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="7692483499-8">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="7692483499-8">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">Goto</span><span class="p" data-group-id="7692483499-9">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="7692483499-9">)</span><span class="p">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7692483499-7">}</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="ss">beam_emu</span><span class="p">.</span><span class="nc">c</span><span class="p">:</span><span class="w">
│ │ │  </span><span class="nc">common_jump</span><span class="p">:</span><span class="w">
│ │ │ -   </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="4619168827-10">[</span><span class="mi">1</span><span class="p" data-group-id="4619168827-10">]</span><span class="p">;</span><span class="w">
│ │ │ -   </span><span class="n">Goto</span><span class="p" data-group-id="4619168827-11">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="4619168827-11">)</span><span class="p">)</span><span class="p">;</span></code></pre><h4>The $REFRESH_GEN_DEST() macro</h4><p>When a specific instruction has a <code class="inline">d</code> operand, early during execution
│ │ │ +   </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="7692483499-10">[</span><span class="mi">1</span><span class="p" data-group-id="7692483499-10">]</span><span class="p">;</span><span class="w">
│ │ │ +   </span><span class="n">Goto</span><span class="p" data-group-id="7692483499-11">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="7692483499-11">)</span><span class="p">)</span><span class="p">;</span></code></pre><h4>The $REFRESH_GEN_DEST() macro</h4><p>When a specific instruction has a <code class="inline">d</code> operand, early during execution
│ │ │  of the instruction, a pointer will be initialized to point to the X or
│ │ │  Y register in question.</p><p>If there is a garbage collection before the result is stored,
│ │ │  the stack will move and if the <code class="inline">d</code> operand referred to a Y
│ │ │  register, the pointer will no longer be valid.  (Y registers are
│ │ │  stored on the stack.)</p><p>In those circumstances, <code class="inline">$REFRESH_GEN_DEST()</code> must be invoked
│ │ │  to set up the pointer again. <strong>beam_makeops</strong> will notice
│ │ │  if there is a call to a function that does a garbage collection and
│ │ │  <code class="inline">$REFRESH_GEN_DEST()</code> is not called.</p><p>Here is a complete example.  The <code class="inline">new_map</code> instruction is defined
│ │ │ -like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">new_map</span><span class="w"> </span><span class="ss">d</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="n">I</span></code></pre><p>It is implemented like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new_map</span><span class="p" data-group-id="9868482246-1">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="9868482246-1">)</span><span class="w"> </span><span class="p" data-group-id="9868482246-2">{</span><span class="w">
│ │ │ +like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">new_map</span><span class="w"> </span><span class="ss">d</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="n">I</span></code></pre><p>It is implemented like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new_map</span><span class="p" data-group-id="5297294357-1">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="5297294357-1">)</span><span class="w"> </span><span class="p" data-group-id="5297294357-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">res</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │      </span><span class="n">HEAVY_SWAPOUT</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_new_map</span><span class="p" data-group-id="9868482246-3">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="p" data-group-id="9868482246-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_new_map</span><span class="p" data-group-id="5297294357-3">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="p" data-group-id="5297294357-3">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">HEAVY_SWAPIN</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="9868482246-4">(</span><span class="p" data-group-id="9868482246-4">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="5297294357-4">(</span><span class="p" data-group-id="5297294357-4">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">res</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="sc">$N</span><span class="n">EXT</span><span class="p" data-group-id="9868482246-5">(</span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="o">+</span><span class="sc">$N</span><span class="p" data-group-id="9868482246-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9868482246-2">}</span></code></pre><p>If we have forgotten the <code class="inline">$REFRESH_GEN_DEST()</code> there would be a message
│ │ │ -similar to this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pointer</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">destination</span><span class="w"> </span><span class="nb">register</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">invalid</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="n">GC</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="ss">use</span><span class="w"> </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="6939387184-1">(</span><span class="p" data-group-id="6939387184-1">)</span><span class="w">
│ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">body</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="ss">new_map</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">beam</span><span class="o">/</span><span class="ss">map_instrs</span><span class="p">.</span><span class="nf">tab</span><span class="p" data-group-id="6939387184-2">(</span><span class="mi">30</span><span class="p" data-group-id="6939387184-2">)</span></code></pre><h4>Variable number of operands</h4><p>Here follows an example of how to handle an instruction with a variable number
│ │ │ +    </span><span class="sc">$N</span><span class="n">EXT</span><span class="p" data-group-id="5297294357-5">(</span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="o">+</span><span class="sc">$N</span><span class="p" data-group-id="5297294357-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5297294357-2">}</span></code></pre><p>If we have forgotten the <code class="inline">$REFRESH_GEN_DEST()</code> there would be a message
│ │ │ +similar to this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pointer</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">destination</span><span class="w"> </span><span class="nb">register</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">invalid</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="n">GC</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="ss">use</span><span class="w"> </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="5821948143-1">(</span><span class="p" data-group-id="5821948143-1">)</span><span class="w">
│ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">body</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="ss">new_map</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">beam</span><span class="o">/</span><span class="ss">map_instrs</span><span class="p">.</span><span class="nf">tab</span><span class="p" data-group-id="5821948143-2">(</span><span class="mi">30</span><span class="p" data-group-id="5821948143-2">)</span></code></pre><h4>Variable number of operands</h4><p>Here follows an example of how to handle an instruction with a variable number
│ │ │  of operands for the interpreter.  Here is the instruction definition in <code class="inline">emu/ops.tab</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">put_tuple2</span><span class="w"> </span><span class="ss">xy</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">*</span></code></pre><p>For the interpreter, the <code class="inline">*</code> is optional, because it does not effect code generation
│ │ │  in any way. However, it is recommended to include it to make it clear for human readers
│ │ │  that there is a variable number of operands.</p><p>Use the <code class="inline">$NEXT_INSTRUCTION</code> macro to obtain a pointer to the first of the variable
│ │ │ -operands.</p><p>Here is the implementation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">put_tuple2</span><span class="p" data-group-id="3399591840-1">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Arity</span><span class="p" data-group-id="3399591840-1">)</span><span class="w"> </span><span class="p" data-group-id="3399591840-2">{</span><span class="w">
│ │ │ +operands.</p><p>Here is the implementation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">put_tuple2</span><span class="p" data-group-id="3031510537-1">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Arity</span><span class="p" data-group-id="3031510537-1">)</span><span class="w"> </span><span class="p" data-group-id="3031510537-2">{</span><span class="w">
│ │ │  </span><span class="n">Eterm</span><span class="o">*</span><span class="w"> </span><span class="ss">hp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">HTOP</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">arity</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$A</span><span class="ss">rity</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="n">Eterm</span><span class="o">*</span><span class="w"> </span><span class="ss">dst_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="err">&amp;</span><span class="p" data-group-id="3399591840-3">(</span><span class="sc">$D</span><span class="ss">st</span><span class="p" data-group-id="3399591840-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="n">Eterm</span><span class="o">*</span><span class="w"> </span><span class="ss">dst_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="err">&amp;</span><span class="p" data-group-id="3031510537-3">(</span><span class="sc">$D</span><span class="ss">st</span><span class="p" data-group-id="3031510537-3">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_next</span><span class="w">
│ │ │ -</span><span class="n">ASSERT</span><span class="p" data-group-id="3399591840-4">(</span><span class="ss">arity</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3399591840-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_arityval</span><span class="p" data-group-id="3399591840-5">(</span><span class="ss">arity</span><span class="p" data-group-id="3399591840-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="n">ASSERT</span><span class="p" data-group-id="3031510537-4">(</span><span class="ss">arity</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3031510537-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_arityval</span><span class="p" data-group-id="3031510537-5">(</span><span class="ss">arity</span><span class="p" data-group-id="3031510537-5">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="w"> </span><span class="n">The</span><span class="w"> </span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="w"> </span><span class="ss">macro</span><span class="w"> </span><span class="ss">points</span><span class="w"> </span><span class="ss">just</span><span class="w"> </span><span class="ss">beyond</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">fixed</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="w"> </span><span class="ss">operands</span><span class="p">.</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="ss">this</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="ss">it</span><span class="w"> </span><span class="ss">points</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">descriptor</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">first</span><span class="w"> </span><span class="nb">element</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">be</span><span class="w"> </span><span class="nb">put</span><span class="w"> </span><span class="ss">into</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">tuple</span><span class="p">.</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │  </span><span class="n">I</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="ss">do</span><span class="w"> </span><span class="p" data-group-id="3399591840-6">{</span><span class="w">
│ │ │ +</span><span class="ss">do</span><span class="w"> </span><span class="p" data-group-id="3031510537-6">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">*</span><span class="n">I</span><span class="o">++</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">switch</span><span class="w"> </span><span class="p" data-group-id="3399591840-7">(</span><span class="nf">loader_tag</span><span class="p" data-group-id="3399591840-8">(</span><span class="ss">term</span><span class="p" data-group-id="3399591840-8">)</span><span class="p" data-group-id="3399591840-7">)</span><span class="w"> </span><span class="p" data-group-id="3399591840-9">{</span><span class="w">
│ │ │ +    </span><span class="nf">switch</span><span class="w"> </span><span class="p" data-group-id="3031510537-7">(</span><span class="nf">loader_tag</span><span class="p" data-group-id="3031510537-8">(</span><span class="ss">term</span><span class="p" data-group-id="3031510537-8">)</span><span class="p" data-group-id="3031510537-7">)</span><span class="w"> </span><span class="p" data-group-id="3031510537-9">{</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">LOADER_X_REG</span><span class="p">:</span><span class="w">
│ │ │ -    </span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">x</span><span class="p" data-group-id="3399591840-10">(</span><span class="nf">loader_x_reg_index</span><span class="p" data-group-id="3399591840-11">(</span><span class="ss">term</span><span class="p" data-group-id="3399591840-11">)</span><span class="p" data-group-id="3399591840-10">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">x</span><span class="p" data-group-id="3031510537-10">(</span><span class="nf">loader_x_reg_index</span><span class="p" data-group-id="3031510537-11">(</span><span class="ss">term</span><span class="p" data-group-id="3031510537-11">)</span><span class="p" data-group-id="3031510537-10">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">break</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">LOADER_Y_REG</span><span class="p">:</span><span class="w">
│ │ │ -    </span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">y</span><span class="p" data-group-id="3399591840-12">(</span><span class="nf">loader_y_reg_index</span><span class="p" data-group-id="3399591840-13">(</span><span class="ss">term</span><span class="p" data-group-id="3399591840-13">)</span><span class="p" data-group-id="3399591840-12">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">y</span><span class="p" data-group-id="3031510537-12">(</span><span class="nf">loader_y_reg_index</span><span class="p" data-group-id="3031510537-13">(</span><span class="ss">term</span><span class="p" data-group-id="3031510537-13">)</span><span class="p" data-group-id="3031510537-12">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">break</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="nc">default</span><span class="p">:</span><span class="w">
│ │ │      </span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">term</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">break</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3399591840-9">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3399591840-6">}</span><span class="w"> </span><span class="nf">while</span><span class="w"> </span><span class="p" data-group-id="3399591840-14">(</span><span class="o">--</span><span class="ss">arity</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3399591840-14">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="ss">dst_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_tuple</span><span class="p" data-group-id="3399591840-15">(</span><span class="n">HTOP</span><span class="p" data-group-id="3399591840-15">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3031510537-9">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3031510537-6">}</span><span class="w"> </span><span class="nf">while</span><span class="w"> </span><span class="p" data-group-id="3031510537-14">(</span><span class="o">--</span><span class="ss">arity</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3031510537-14">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="ss">dst_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_tuple</span><span class="p" data-group-id="3031510537-15">(</span><span class="n">HTOP</span><span class="p" data-group-id="3031510537-15">)</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="n">HTOP</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">hp</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="n">ASSERT</span><span class="p" data-group-id="3399591840-16">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="3399591840-17">(</span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="3399591840-18">(</span><span class="n">Eterm</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="3399591840-18">)</span><span class="n">I</span><span class="p" data-group-id="3399591840-17">)</span><span class="p" data-group-id="3399591840-16">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="n">Goto</span><span class="p" data-group-id="3399591840-19">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="3399591840-19">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3399591840-2">}</span></code></pre><h4>Combined instructions</h4><p><strong>Problem</strong>: For frequently executed instructions we want to use
│ │ │ +</span><span class="n">ASSERT</span><span class="p" data-group-id="3031510537-16">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="3031510537-17">(</span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="3031510537-18">(</span><span class="n">Eterm</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="3031510537-18">)</span><span class="n">I</span><span class="p" data-group-id="3031510537-17">)</span><span class="p" data-group-id="3031510537-16">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="n">Goto</span><span class="p" data-group-id="3031510537-19">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="3031510537-19">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3031510537-2">}</span></code></pre><h4>Combined instructions</h4><p><strong>Problem</strong>: For frequently executed instructions we want to use
│ │ │  &quot;fast&quot; operands types such as <code class="inline">x</code> and <code class="inline">y</code>, as opposed to <code class="inline">s</code> or <code class="inline">S</code>.
│ │ │  To avoid an explosion in code size, we want to share most of the
│ │ │  implementation between the instructions.  Here are the specific
│ │ │  instructions for <code class="inline">i_increment/5</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_increment</span><span class="w"> </span><span class="ss">r</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_increment</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │ -</span><span class="ss">i_increment</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span></code></pre><p>The <code class="inline">i_increment</code> instruction is implemented like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">i_increment</span><span class="p" data-group-id="2285494945-1">(</span><span class="n">Source</span><span class="p">,</span><span class="w"> </span><span class="n">IncrementVal</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="2285494945-1">)</span><span class="w"> </span><span class="p" data-group-id="2285494945-2">{</span><span class="w">
│ │ │ +</span><span class="ss">i_increment</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span></code></pre><p>The <code class="inline">i_increment</code> instruction is implemented like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">i_increment</span><span class="p" data-group-id="0547307740-1">(</span><span class="n">Source</span><span class="p">,</span><span class="w"> </span><span class="n">IncrementVal</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="0547307740-1">)</span><span class="w"> </span><span class="p" data-group-id="0547307740-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">increment_reg_source</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">ource</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">increment_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$I</span><span class="ss">ncrementVal</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Uint</span><span class="w"> </span><span class="ss">live</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">result</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="2285494945-3">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="2285494945-4">(</span><span class="nf">is_small</span><span class="p" data-group-id="2285494945-5">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="2285494945-5">)</span><span class="p" data-group-id="2285494945-4">)</span><span class="p" data-group-id="2285494945-3">)</span><span class="w"> </span><span class="p" data-group-id="2285494945-6">{</span><span class="w">
│ │ │ -        </span><span class="n">Sint</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">signed_val</span><span class="p" data-group-id="2285494945-7">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="2285494945-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">increment_val</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="2285494945-8">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="2285494945-9">(</span><span class="n">IS_SSMALL</span><span class="p" data-group-id="2285494945-10">(</span><span class="ss">i</span><span class="p" data-group-id="2285494945-10">)</span><span class="p" data-group-id="2285494945-9">)</span><span class="p" data-group-id="2285494945-8">)</span><span class="w"> </span><span class="p" data-group-id="2285494945-11">{</span><span class="w">
│ │ │ -            </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="2285494945-12">(</span><span class="ss">i</span><span class="p" data-group-id="2285494945-12">)</span><span class="p">;</span><span class="w">
│ │ │ -            </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="2285494945-13">(</span><span class="p" data-group-id="2285494945-13">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2285494945-11">}</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2285494945-6">}</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="0547307740-3">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="0547307740-4">(</span><span class="nf">is_small</span><span class="p" data-group-id="0547307740-5">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="0547307740-5">)</span><span class="p" data-group-id="0547307740-4">)</span><span class="p" data-group-id="0547307740-3">)</span><span class="w"> </span><span class="p" data-group-id="0547307740-6">{</span><span class="w">
│ │ │ +        </span><span class="n">Sint</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">signed_val</span><span class="p" data-group-id="0547307740-7">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="0547307740-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">increment_val</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="0547307740-8">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="0547307740-9">(</span><span class="n">IS_SSMALL</span><span class="p" data-group-id="0547307740-10">(</span><span class="ss">i</span><span class="p" data-group-id="0547307740-10">)</span><span class="p" data-group-id="0547307740-9">)</span><span class="p" data-group-id="0547307740-8">)</span><span class="w"> </span><span class="p" data-group-id="0547307740-11">{</span><span class="w">
│ │ │ +            </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="0547307740-12">(</span><span class="ss">i</span><span class="p" data-group-id="0547307740-12">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="0547307740-13">(</span><span class="p" data-group-id="0547307740-13">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0547307740-11">}</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0547307740-6">}</span><span class="w">
│ │ │      </span><span class="ss">live</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">HEAVY_SWAPOUT</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">reg</span><span class="p" data-group-id="2285494945-14">[</span><span class="ss">live</span><span class="p" data-group-id="2285494945-14">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">reg</span><span class="p" data-group-id="2285494945-15">[</span><span class="ss">live</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="2285494945-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="2285494945-16">(</span><span class="ss">increment_val</span><span class="p" data-group-id="2285494945-16">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_mixed_plus</span><span class="p" data-group-id="2285494945-17">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="ss">live</span><span class="p" data-group-id="2285494945-17">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">reg</span><span class="p" data-group-id="0547307740-14">[</span><span class="ss">live</span><span class="p" data-group-id="0547307740-14">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">reg</span><span class="p" data-group-id="0547307740-15">[</span><span class="ss">live</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="0547307740-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="0547307740-16">(</span><span class="ss">increment_val</span><span class="p" data-group-id="0547307740-16">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_mixed_plus</span><span class="p" data-group-id="0547307740-17">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="ss">live</span><span class="p" data-group-id="0547307740-17">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">HEAVY_SWAPIN</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ERTS_HOLE_CHECK</span><span class="p" data-group-id="2285494945-18">(</span><span class="ss">c_p</span><span class="p" data-group-id="2285494945-18">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="2285494945-19">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="2285494945-20">(</span><span class="nf">is_value</span><span class="p" data-group-id="2285494945-21">(</span><span class="ss">result</span><span class="p" data-group-id="2285494945-21">)</span><span class="p" data-group-id="2285494945-20">)</span><span class="p" data-group-id="2285494945-19">)</span><span class="w"> </span><span class="p" data-group-id="2285494945-22">{</span><span class="w">
│ │ │ -        </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="2285494945-23">(</span><span class="p" data-group-id="2285494945-23">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">ERTS_HOLE_CHECK</span><span class="p" data-group-id="0547307740-18">(</span><span class="ss">c_p</span><span class="p" data-group-id="0547307740-18">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="0547307740-19">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="0547307740-20">(</span><span class="nf">is_value</span><span class="p" data-group-id="0547307740-21">(</span><span class="ss">result</span><span class="p" data-group-id="0547307740-21">)</span><span class="p" data-group-id="0547307740-20">)</span><span class="p" data-group-id="0547307740-19">)</span><span class="w"> </span><span class="p" data-group-id="0547307740-22">{</span><span class="w">
│ │ │ +        </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="0547307740-23">(</span><span class="p" data-group-id="0547307740-23">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">result</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="2285494945-24">(</span><span class="p" data-group-id="2285494945-24">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2285494945-22">}</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="2285494945-25">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">freason</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="n">BADMATCH</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_value</span><span class="p" data-group-id="2285494945-26">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">fvalue</span><span class="p" data-group-id="2285494945-26">)</span><span class="p" data-group-id="2285494945-25">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="0547307740-24">(</span><span class="p" data-group-id="0547307740-24">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0547307740-22">}</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="0547307740-25">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">freason</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="n">BADMATCH</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_value</span><span class="p" data-group-id="0547307740-26">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">fvalue</span><span class="p" data-group-id="0547307740-26">)</span><span class="p" data-group-id="0547307740-25">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">goto</span><span class="w"> </span><span class="ss">find_func_info</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2285494945-2">}</span></code></pre><p>There will be three almost identical copies of the code.  Given the
│ │ │ +</span><span class="p" data-group-id="0547307740-2">}</span></code></pre><p>There will be three almost identical copies of the code.  Given the
│ │ │  size of the code, that could be too high cost to pay.</p><p>To avoid the three copies of the code, we could use only one specific
│ │ │  instruction:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_increment</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span></code></pre><p>(The same implementation as above will work.)</p><p>That reduces the code size, but is slower because <code class="inline">S</code> means that
│ │ │  there will be extra code to test whether the operand refers to an X
│ │ │  register or a Y register.</p><p><strong>Solution</strong>: We can use &quot;combined instructions&quot;.  Combined
│ │ │  instructions are combined from instruction fragments.  The
│ │ │  bulk of the code can be shared.</p><p>Here we will show how <code class="inline">i_increment</code> can be implemented as a combined
│ │ │  instruction.  We will show each individual fragment first, and then
│ │ │  show how to connect them together.  First we will need a variable that
│ │ │ -we can store the value fetched from the register in:</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">head</span><span class="p" data-group-id="6151153514-1">(</span><span class="p" data-group-id="6151153514-1">)</span><span class="w"> </span><span class="p" data-group-id="6151153514-2">{</span><span class="w">
│ │ │ +we can store the value fetched from the register in:</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">head</span><span class="p" data-group-id="3296102775-1">(</span><span class="p" data-group-id="3296102775-1">)</span><span class="w"> </span><span class="p" data-group-id="3296102775-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6151153514-2">}</span></code></pre><p>The name <code class="inline">increment</code> is the name of the group that the fragment
│ │ │ +</span><span class="p" data-group-id="3296102775-2">}</span></code></pre><p>The name <code class="inline">increment</code> is the name of the group that the fragment
│ │ │  belongs to.  Note that it does not need to have the same
│ │ │  name as the instruction.  The group name is followed by <code class="inline">.</code> and
│ │ │  the name of the fragment.  The name <code class="inline">head</code> is pre-defined.
│ │ │  The code in it will be placed at the beginning of a block, so
│ │ │  that all fragments in the group can access it.</p><p>Next we define the fragment that will pick up the value from the
│ │ │ -register from the first operand:</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">fetch</span><span class="p" data-group-id="1512531892-1">(</span><span class="n">Src</span><span class="p" data-group-id="1512531892-1">)</span><span class="w"> </span><span class="p" data-group-id="1512531892-2">{</span><span class="w">
│ │ │ +register from the first operand:</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">fetch</span><span class="p" data-group-id="3947541743-1">(</span><span class="n">Src</span><span class="p" data-group-id="3947541743-1">)</span><span class="w"> </span><span class="p" data-group-id="3947541743-2">{</span><span class="w">
│ │ │      </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1512531892-2">}</span></code></pre><p>We call this fragment <code class="inline">fetch</code>.  This fragment will be duplicated three
│ │ │ -times, one for each value of the first operand (<code class="inline">r</code>, <code class="inline">x</code>, and <code class="inline">y</code>).</p><p>Next we define the main part of the code that do the actual incrementing.</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="8903912383-1">(</span><span class="n">IncrementVal</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="8903912383-1">)</span><span class="w"> </span><span class="p" data-group-id="8903912383-2">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3947541743-2">}</span></code></pre><p>We call this fragment <code class="inline">fetch</code>.  This fragment will be duplicated three
│ │ │ +times, one for each value of the first operand (<code class="inline">r</code>, <code class="inline">x</code>, and <code class="inline">y</code>).</p><p>Next we define the main part of the code that do the actual incrementing.</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="4670335612-1">(</span><span class="n">IncrementVal</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="4670335612-1">)</span><span class="w"> </span><span class="p" data-group-id="4670335612-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">increment_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$I</span><span class="ss">ncrementVal</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Uint</span><span class="w"> </span><span class="ss">live</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">result</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="8903912383-3">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="8903912383-4">(</span><span class="nf">is_small</span><span class="p" data-group-id="8903912383-5">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="8903912383-5">)</span><span class="p" data-group-id="8903912383-4">)</span><span class="p" data-group-id="8903912383-3">)</span><span class="w"> </span><span class="p" data-group-id="8903912383-6">{</span><span class="w">
│ │ │ -        </span><span class="n">Sint</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">signed_val</span><span class="p" data-group-id="8903912383-7">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="8903912383-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">increment_val</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="8903912383-8">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="8903912383-9">(</span><span class="n">IS_SSMALL</span><span class="p" data-group-id="8903912383-10">(</span><span class="ss">i</span><span class="p" data-group-id="8903912383-10">)</span><span class="p" data-group-id="8903912383-9">)</span><span class="p" data-group-id="8903912383-8">)</span><span class="w"> </span><span class="p" data-group-id="8903912383-11">{</span><span class="w">
│ │ │ -            </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="8903912383-12">(</span><span class="ss">i</span><span class="p" data-group-id="8903912383-12">)</span><span class="p">;</span><span class="w">
│ │ │ -            </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="8903912383-13">(</span><span class="p" data-group-id="8903912383-13">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8903912383-11">}</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8903912383-6">}</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="4670335612-3">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="4670335612-4">(</span><span class="nf">is_small</span><span class="p" data-group-id="4670335612-5">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="4670335612-5">)</span><span class="p" data-group-id="4670335612-4">)</span><span class="p" data-group-id="4670335612-3">)</span><span class="w"> </span><span class="p" data-group-id="4670335612-6">{</span><span class="w">
│ │ │ +        </span><span class="n">Sint</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">signed_val</span><span class="p" data-group-id="4670335612-7">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="4670335612-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">increment_val</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="4670335612-8">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="4670335612-9">(</span><span class="n">IS_SSMALL</span><span class="p" data-group-id="4670335612-10">(</span><span class="ss">i</span><span class="p" data-group-id="4670335612-10">)</span><span class="p" data-group-id="4670335612-9">)</span><span class="p" data-group-id="4670335612-8">)</span><span class="w"> </span><span class="p" data-group-id="4670335612-11">{</span><span class="w">
│ │ │ +            </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="4670335612-12">(</span><span class="ss">i</span><span class="p" data-group-id="4670335612-12">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="4670335612-13">(</span><span class="p" data-group-id="4670335612-13">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="4670335612-11">}</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4670335612-6">}</span><span class="w">
│ │ │      </span><span class="ss">live</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">HEAVY_SWAPOUT</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">reg</span><span class="p" data-group-id="8903912383-14">[</span><span class="ss">live</span><span class="p" data-group-id="8903912383-14">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">reg</span><span class="p" data-group-id="8903912383-15">[</span><span class="ss">live</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="8903912383-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="8903912383-16">(</span><span class="ss">increment_val</span><span class="p" data-group-id="8903912383-16">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_mixed_plus</span><span class="p" data-group-id="8903912383-17">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="ss">live</span><span class="p" data-group-id="8903912383-17">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">reg</span><span class="p" data-group-id="4670335612-14">[</span><span class="ss">live</span><span class="p" data-group-id="4670335612-14">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">reg</span><span class="p" data-group-id="4670335612-15">[</span><span class="ss">live</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="4670335612-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="4670335612-16">(</span><span class="ss">increment_val</span><span class="p" data-group-id="4670335612-16">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_mixed_plus</span><span class="p" data-group-id="4670335612-17">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="ss">live</span><span class="p" data-group-id="4670335612-17">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">HEAVY_SWAPIN</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ERTS_HOLE_CHECK</span><span class="p" data-group-id="8903912383-18">(</span><span class="ss">c_p</span><span class="p" data-group-id="8903912383-18">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="8903912383-19">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="8903912383-20">(</span><span class="nf">is_value</span><span class="p" data-group-id="8903912383-21">(</span><span class="ss">result</span><span class="p" data-group-id="8903912383-21">)</span><span class="p" data-group-id="8903912383-20">)</span><span class="p" data-group-id="8903912383-19">)</span><span class="w"> </span><span class="p" data-group-id="8903912383-22">{</span><span class="w">
│ │ │ -        </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="8903912383-23">(</span><span class="p" data-group-id="8903912383-23">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">ERTS_HOLE_CHECK</span><span class="p" data-group-id="4670335612-18">(</span><span class="ss">c_p</span><span class="p" data-group-id="4670335612-18">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="4670335612-19">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="4670335612-20">(</span><span class="nf">is_value</span><span class="p" data-group-id="4670335612-21">(</span><span class="ss">result</span><span class="p" data-group-id="4670335612-21">)</span><span class="p" data-group-id="4670335612-20">)</span><span class="p" data-group-id="4670335612-19">)</span><span class="w"> </span><span class="p" data-group-id="4670335612-22">{</span><span class="w">
│ │ │ +        </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="4670335612-23">(</span><span class="p" data-group-id="4670335612-23">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">result</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="8903912383-24">(</span><span class="p" data-group-id="8903912383-24">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8903912383-22">}</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="8903912383-25">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">freason</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="n">BADMATCH</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_value</span><span class="p" data-group-id="8903912383-26">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">fvalue</span><span class="p" data-group-id="8903912383-26">)</span><span class="p" data-group-id="8903912383-25">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="4670335612-24">(</span><span class="p" data-group-id="4670335612-24">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4670335612-22">}</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="4670335612-25">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">freason</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="n">BADMATCH</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_value</span><span class="p" data-group-id="4670335612-26">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">fvalue</span><span class="p" data-group-id="4670335612-26">)</span><span class="p" data-group-id="4670335612-25">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">goto</span><span class="w"> </span><span class="ss">find_func_info</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8903912383-2">}</span></code></pre><p>We call this fragment <code class="inline">execute</code>.  It will handle the three remaining
│ │ │ +</span><span class="p" data-group-id="4670335612-2">}</span></code></pre><p>We call this fragment <code class="inline">execute</code>.  It will handle the three remaining
│ │ │  operands (<code class="inline">W t d</code>).  There will only be one copy of this fragment.</p><p>Now that we have defined the fragments, we need to inform
│ │ │  <strong>beam_makeops</strong> how they should be connected:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_increment</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">increment</span><span class="p">.</span><span class="ss">fetch</span><span class="p">.</span><span class="ss">execute</span><span class="p">;</span></code></pre><p>To the left of the <code class="inline">:=</code> is the name of the specific instruction that
│ │ │  should be implemented by the fragments, in this case <code class="inline">i_increment</code>.
│ │ │  To the right of <code class="inline">:=</code> is the name of the group with the fragments,
│ │ │  followed by a <code class="inline">.</code>.  Then the name of the fragments in the group are
│ │ │  listed in the order they should be executed.  Note that the <code class="inline">head</code>
│ │ │  fragment is not listed.</p><p>The line ends in <code class="inline">;</code> (to avoid messing up the indentation in Emacs).</p><p>(Note that in practice the <code class="inline">:=</code> line is usually placed before the
│ │ │ -fragments.)</p><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6118003903-1">{</span><span class="w">
│ │ │ +fragments.)</p><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5042809152-1">{</span><span class="w">
│ │ │    </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">OpCase</span><span class="p" data-group-id="6118003903-2">(</span><span class="ss">i_increment_rWtd</span><span class="p" data-group-id="6118003903-2">)</span><span class="p">:</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6118003903-3">{</span><span class="w">
│ │ │ -    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">r</span><span class="p" data-group-id="6118003903-4">(</span><span class="mi">0</span><span class="p" data-group-id="6118003903-4">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6118003903-3">}</span><span class="w">
│ │ │ +  </span><span class="n">OpCase</span><span class="p" data-group-id="5042809152-2">(</span><span class="ss">i_increment_rWtd</span><span class="p" data-group-id="5042809152-2">)</span><span class="p">:</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5042809152-3">{</span><span class="w">
│ │ │ +    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">r</span><span class="p" data-group-id="5042809152-4">(</span><span class="mi">0</span><span class="p" data-group-id="5042809152-4">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5042809152-3">}</span><span class="w">
│ │ │    </span><span class="ss">goto</span><span class="w"> </span><span class="ss">increment__execute</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="n">OpCase</span><span class="p" data-group-id="6118003903-5">(</span><span class="ss">i_increment_xWtd</span><span class="p" data-group-id="6118003903-5">)</span><span class="p">:</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6118003903-6">{</span><span class="w">
│ │ │ -    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="6118003903-7">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="6118003903-8">(</span><span class="n">I</span><span class="p" data-group-id="6118003903-9">[</span><span class="mi">0</span><span class="p" data-group-id="6118003903-9">]</span><span class="p" data-group-id="6118003903-8">)</span><span class="p" data-group-id="6118003903-7">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6118003903-6">}</span><span class="w">
│ │ │ +  </span><span class="n">OpCase</span><span class="p" data-group-id="5042809152-5">(</span><span class="ss">i_increment_xWtd</span><span class="p" data-group-id="5042809152-5">)</span><span class="p">:</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5042809152-6">{</span><span class="w">
│ │ │ +    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="5042809152-7">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="5042809152-8">(</span><span class="n">I</span><span class="p" data-group-id="5042809152-9">[</span><span class="mi">0</span><span class="p" data-group-id="5042809152-9">]</span><span class="p" data-group-id="5042809152-8">)</span><span class="p" data-group-id="5042809152-7">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5042809152-6">}</span><span class="w">
│ │ │    </span><span class="ss">goto</span><span class="w"> </span><span class="ss">increment__execute</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="n">OpCase</span><span class="p" data-group-id="6118003903-10">(</span><span class="ss">i_increment_yWtd</span><span class="p" data-group-id="6118003903-10">)</span><span class="p">:</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6118003903-11">{</span><span class="w">
│ │ │ -    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">yb</span><span class="p" data-group-id="6118003903-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="6118003903-13">(</span><span class="n">I</span><span class="p" data-group-id="6118003903-14">[</span><span class="mi">0</span><span class="p" data-group-id="6118003903-14">]</span><span class="p" data-group-id="6118003903-13">)</span><span class="p" data-group-id="6118003903-12">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6118003903-11">}</span><span class="w">
│ │ │ +  </span><span class="n">OpCase</span><span class="p" data-group-id="5042809152-10">(</span><span class="ss">i_increment_yWtd</span><span class="p" data-group-id="5042809152-10">)</span><span class="p">:</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5042809152-11">{</span><span class="w">
│ │ │ +    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">yb</span><span class="p" data-group-id="5042809152-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="5042809152-13">(</span><span class="n">I</span><span class="p" data-group-id="5042809152-14">[</span><span class="mi">0</span><span class="p" data-group-id="5042809152-14">]</span><span class="p" data-group-id="5042809152-13">)</span><span class="p" data-group-id="5042809152-12">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5042809152-11">}</span><span class="w">
│ │ │    </span><span class="ss">goto</span><span class="w"> </span><span class="ss">increment__execute</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │    </span><span class="nc">increment__execute</span><span class="p">:</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="6118003903-15">{</span><span class="w">
│ │ │ -    </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">Here</span><span class="w"> </span><span class="ss">follows</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">increment</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="6118003903-16">(</span><span class="p" data-group-id="6118003903-16">)</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5042809152-15">{</span><span class="w">
│ │ │ +    </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">Here</span><span class="w"> </span><span class="ss">follows</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">increment</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="5042809152-16">(</span><span class="p" data-group-id="5042809152-16">)</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6118003903-15">}</span></code></pre><h5>Some notes about combined instructions</h5><p>The operands that are different must be at
│ │ │ +</span><span class="p" data-group-id="5042809152-15">}</span></code></pre><h5>Some notes about combined instructions</h5><p>The operands that are different must be at
│ │ │  the beginning of the instruction.  All operands in the last
│ │ │  fragment must have the same operands in all variants of
│ │ │  the specific instruction.</p><p>As an example, the following specific instructions cannot be
│ │ │  implemented as a combined instruction:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_times</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_times</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_times</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">d</span></code></pre><p>We would have to change the order of the operands so that the
│ │ │  two operands that are different are placed first:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_times</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_times</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_times</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span></code></pre><p>We can then define:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_times</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">times</span><span class="p">.</span><span class="ss">fetch</span><span class="p">.</span><span class="ss">execute</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">times</span><span class="p">.</span><span class="ss">head</span><span class="w"> </span><span class="p" data-group-id="1538842160-1">{</span><span class="w">
│ │ │ +</span><span class="ss">times</span><span class="p">.</span><span class="ss">head</span><span class="w"> </span><span class="p" data-group-id="4695153316-1">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">op1</span><span class="p">,</span><span class="w"> </span><span class="ss">op2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1538842160-1">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4695153316-1">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">times</span><span class="p">.</span><span class="nf">fetch</span><span class="p" data-group-id="1538842160-2">(</span><span class="n">Src1</span><span class="p">,</span><span class="w"> </span><span class="n">Src2</span><span class="p" data-group-id="1538842160-2">)</span><span class="w"> </span><span class="p" data-group-id="1538842160-3">{</span><span class="w">
│ │ │ +</span><span class="ss">times</span><span class="p">.</span><span class="nf">fetch</span><span class="p" data-group-id="4695153316-2">(</span><span class="n">Src1</span><span class="p">,</span><span class="w"> </span><span class="n">Src2</span><span class="p" data-group-id="4695153316-2">)</span><span class="w"> </span><span class="p" data-group-id="4695153316-3">{</span><span class="w">
│ │ │      </span><span class="ss">op1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">op2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1538842160-3">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4695153316-3">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">times</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="1538842160-4">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="1538842160-4">)</span><span class="w"> </span><span class="p" data-group-id="1538842160-5">{</span><span class="w">
│ │ │ +</span><span class="ss">times</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="4695153316-4">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="4695153316-4">)</span><span class="w"> </span><span class="p" data-group-id="4695153316-5">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">Multiply</span><span class="w"> </span><span class="ss">op1</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="ss">op2</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1538842160-5">}</span></code></pre><p>Several instructions can share a group.  As an example, the following
│ │ │ +</span><span class="p" data-group-id="4695153316-5">}</span></code></pre><p>Several instructions can share a group.  As an example, the following
│ │ │  instructions have different names, but in the end they all create a
│ │ │  binary.  The last two operands are common for all of them:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_bs_init_fail</span><span class="w">       </span><span class="ss">xy</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="o">?</span><span class="w"> </span><span class="ss">x</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init_fail_heap</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="o">?</span><span class="w"> </span><span class="ss">x</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init</span><span class="w">                </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="o">?</span><span class="w"> </span><span class="ss">x</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init_heap</span><span class="w">         </span><span class="n">W</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="ss">t</span><span class="o">?</span><span class="w"> </span><span class="ss">x</span></code></pre><p>The instructions are defined like this (formatted with extra
│ │ │  spaces for clarity):</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_bs_init_fail_heap</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">bs_init</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">fail_heap</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">verify</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">execute</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init_fail</span><span class="w">      </span><span class="p">:=</span><span class="w"> </span><span class="ss">bs_init</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">fail</span><span class="w">      </span><span class="p">.</span><span class="w"> </span><span class="ss">verify</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">execute</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init</span><span class="w">           </span><span class="p">:=</span><span class="w"> </span><span class="ss">bs_init</span><span class="w"> </span><span class="p">.</span><span class="w">           </span><span class="p">.</span><span class="w">  </span><span class="ss">plain</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">execute</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init_heap</span><span class="w">      </span><span class="p">:=</span><span class="w"> </span><span class="ss">bs_init</span><span class="w"> </span><span class="p">.</span><span class="w">               </span><span class="ss">heap</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">execute</span><span class="p">;</span></code></pre><p>Note that the first two instruction have three fragments, while the
│ │ │ -other two only have two fragments.  Here are the fragments:</p><pre><code class="makeup erlang" translate="no"><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">head</span><span class="p" data-group-id="9298605059-1">(</span><span class="p" data-group-id="9298605059-1">)</span><span class="w"> </span><span class="p" data-group-id="9298605059-2">{</span><span class="w">
│ │ │ +other two only have two fragments.  Here are the fragments:</p><pre><code class="makeup erlang" translate="no"><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">head</span><span class="p" data-group-id="1762697534-1">(</span><span class="p" data-group-id="1762697534-1">)</span><span class="w"> </span><span class="p" data-group-id="1762697534-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">num_bits_term</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Uint</span><span class="w"> </span><span class="ss">num_bits</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Uint</span><span class="w"> </span><span class="ss">alloc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9298605059-2">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1762697534-2">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">plain</span><span class="p" data-group-id="9298605059-3">(</span><span class="n">NumBits</span><span class="p" data-group-id="9298605059-3">)</span><span class="w"> </span><span class="p" data-group-id="9298605059-4">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">plain</span><span class="p" data-group-id="1762697534-3">(</span><span class="n">NumBits</span><span class="p" data-group-id="1762697534-3">)</span><span class="w"> </span><span class="p" data-group-id="1762697534-4">{</span><span class="w">
│ │ │      </span><span class="ss">num_bits</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$N</span><span class="ss">umBits</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">alloc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9298605059-4">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1762697534-4">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">heap</span><span class="p" data-group-id="9298605059-5">(</span><span class="n">NumBits</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="9298605059-5">)</span><span class="w"> </span><span class="p" data-group-id="9298605059-6">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">heap</span><span class="p" data-group-id="1762697534-5">(</span><span class="n">NumBits</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="1762697534-5">)</span><span class="w"> </span><span class="p" data-group-id="1762697534-6">{</span><span class="w">
│ │ │      </span><span class="ss">num_bits</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$N</span><span class="ss">umBits</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">alloc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$A</span><span class="ss">lloc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9298605059-6">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1762697534-6">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">fail</span><span class="p" data-group-id="9298605059-7">(</span><span class="n">NumBitsTerm</span><span class="p" data-group-id="9298605059-7">)</span><span class="w"> </span><span class="p" data-group-id="9298605059-8">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">fail</span><span class="p" data-group-id="1762697534-7">(</span><span class="n">NumBitsTerm</span><span class="p" data-group-id="1762697534-7">)</span><span class="w"> </span><span class="p" data-group-id="1762697534-8">{</span><span class="w">
│ │ │      </span><span class="ss">num_bits_term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$N</span><span class="ss">umBitsTerm</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">alloc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9298605059-8">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1762697534-8">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">fail_heap</span><span class="p" data-group-id="9298605059-9">(</span><span class="n">NumBitsTerm</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="9298605059-9">)</span><span class="w"> </span><span class="p" data-group-id="9298605059-10">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">fail_heap</span><span class="p" data-group-id="1762697534-9">(</span><span class="n">NumBitsTerm</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="1762697534-9">)</span><span class="w"> </span><span class="p" data-group-id="1762697534-10">{</span><span class="w">
│ │ │      </span><span class="ss">num_bits_term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$N</span><span class="ss">umBitsTerm</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">alloc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$A</span><span class="ss">lloc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9298605059-10">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1762697534-10">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">verify</span><span class="p" data-group-id="9298605059-11">(</span><span class="n">Fail</span><span class="p" data-group-id="9298605059-11">)</span><span class="w"> </span><span class="p" data-group-id="9298605059-12">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">verify</span><span class="p" data-group-id="1762697534-11">(</span><span class="n">Fail</span><span class="p" data-group-id="1762697534-11">)</span><span class="w"> </span><span class="p" data-group-id="1762697534-12">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">Verify</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">num_bits_term</span><span class="p">,</span><span class="w"> </span><span class="ss">fail</span><span class="w"> </span><span class="ss">using</span><span class="w"> </span><span class="sc">$F</span><span class="n">AIL</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="ss">there</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">problem</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9298605059-12">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1762697534-12">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="9298605059-13">(</span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="9298605059-13">)</span><span class="w"> </span><span class="p" data-group-id="9298605059-14">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="1762697534-13">(</span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="1762697534-13">)</span><span class="w"> </span><span class="p" data-group-id="1762697534-14">{</span><span class="w">
│ │ │     </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">Long</span><span class="w"> </span><span class="ss">complicated</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">create</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">binary</span><span class="p">.</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9298605059-14">}</span></code></pre><p>The full definitions of those instructions can be found in <code class="inline">bs_instrs.tab</code>.
│ │ │ +</span><span class="p" data-group-id="1762697534-14">}</span></code></pre><p>The full definitions of those instructions can be found in <code class="inline">bs_instrs.tab</code>.
│ │ │  The generated code can be found in <code class="inline">beam_warm.h</code>.</p><h3 id="code-generation-for-beamasm" class="section-heading">
│ │ │    <a href="#code-generation-for-beamasm" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Code generation for BeamAsm</span>
│ │ │  </h3>
│ │ │  <p>For the BeamAsm runtime system, the implementation of each instruction is defined
│ │ │  by emitter functions written in C++ that emit the assembly code for each instruction.
│ │ │  There is one emitter function for each family of specific instructions.</p><p>Take for example the <code class="inline">move</code> instruction. In <code class="inline">beam/asm/ops.tab</code> there is a
│ │ │ -single specific instruction for <code class="inline">move</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">d</span></code></pre><p>The implementation is found in <code class="inline">beam/asm/instr_common.cpp</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_move</span><span class="p" data-group-id="1101312048-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Dst</span><span class="p" data-group-id="1101312048-1">)</span><span class="w"> </span><span class="p" data-group-id="1101312048-2">{</span><span class="w">
│ │ │ -    </span><span class="nf">mov_arg</span><span class="p" data-group-id="1101312048-3">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="1101312048-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1101312048-2">}</span></code></pre><p>The <code class="inline">mov_arg()</code> helper function will handle all combinations of source and destination
│ │ │ -operands.  For example, the instruction <code class="inline">{move,{x,1},{y,1}}</code> will be translated like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mov</span><span class="w"> </span><span class="ss">rdi</span><span class="p">,</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="7363468922-1">[</span><span class="ss">rbx</span><span class="o">+</span><span class="mi">8</span><span class="p" data-group-id="7363468922-1">]</span><span class="w">
│ │ │ -</span><span class="ss">mov</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="7363468922-2">[</span><span class="ss">rsp</span><span class="o">+</span><span class="mi">8</span><span class="p" data-group-id="7363468922-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">rdi</span></code></pre><p>while <code class="inline">{move,{integer,42},{x,0}}</code> will be translated like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mov</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="6668340040-1">[</span><span class="ss">rbx</span><span class="p" data-group-id="6668340040-1">]</span><span class="p">,</span><span class="w"> </span><span class="mi">687</span></code></pre><p>It is possible to define more than one specific instruction, but there will still be
│ │ │ +single specific instruction for <code class="inline">move</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">d</span></code></pre><p>The implementation is found in <code class="inline">beam/asm/instr_common.cpp</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_move</span><span class="p" data-group-id="2784107262-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Dst</span><span class="p" data-group-id="2784107262-1">)</span><span class="w"> </span><span class="p" data-group-id="2784107262-2">{</span><span class="w">
│ │ │ +    </span><span class="nf">mov_arg</span><span class="p" data-group-id="2784107262-3">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="2784107262-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2784107262-2">}</span></code></pre><p>The <code class="inline">mov_arg()</code> helper function will handle all combinations of source and destination
│ │ │ +operands.  For example, the instruction <code class="inline">{move,{x,1},{y,1}}</code> will be translated like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mov</span><span class="w"> </span><span class="ss">rdi</span><span class="p">,</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="3263028310-1">[</span><span class="ss">rbx</span><span class="o">+</span><span class="mi">8</span><span class="p" data-group-id="3263028310-1">]</span><span class="w">
│ │ │ +</span><span class="ss">mov</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="3263028310-2">[</span><span class="ss">rsp</span><span class="o">+</span><span class="mi">8</span><span class="p" data-group-id="3263028310-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">rdi</span></code></pre><p>while <code class="inline">{move,{integer,42},{x,0}}</code> will be translated like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mov</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="9102452838-1">[</span><span class="ss">rbx</span><span class="p" data-group-id="9102452838-1">]</span><span class="p">,</span><span class="w"> </span><span class="mi">687</span></code></pre><p>It is possible to define more than one specific instruction, but there will still be
│ │ │  only one emitter function. For example:</p><pre><code class="makeup erlang" translate="no"><span class="ss">fload</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="ss">l</span><span class="w">
│ │ │  </span><span class="ss">fload</span><span class="w"> </span><span class="ss">q</span><span class="w"> </span><span class="ss">l</span></code></pre><p>By defining <code class="inline">fload</code> like this, the source operand must be a X register, Y register, or
│ │ │  a literal.  If not, the loading will be aborted.  If the instruction instead had been
│ │ │  defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">fload</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">l</span></code></pre><p>attempting to load an invalid instruction such as <code class="inline">{fload,{atom,clearly_bad},{fr,0}}</code>
│ │ │  would cause a crash (either at load time or when the instruction was executed).</p><p>Regardless on how many specific instructions there are in the family,
│ │ │ -only a single <code class="inline">emit_fload()</code> function is allowed:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_fload</span><span class="p" data-group-id="0585403646-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Dst</span><span class="p" data-group-id="0585403646-1">)</span><span class="w"> </span><span class="p" data-group-id="0585403646-2">{</span><span class="w">
│ │ │ +only a single <code class="inline">emit_fload()</code> function is allowed:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_fload</span><span class="p" data-group-id="8030049690-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Dst</span><span class="p" data-group-id="8030049690-1">)</span><span class="w"> </span><span class="p" data-group-id="8030049690-2">{</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0585403646-2">}</span></code></pre><p><a href="" id="handling-a-variable-number-of-operands"></a></p><h4>Handling a variable number of operands</h4><p>Here follows an example of how an instruction with a variable number
│ │ │ +</span><span class="p" data-group-id="8030049690-2">}</span></code></pre><p><a href="" id="handling-a-variable-number-of-operands"></a></p><h4>Handling a variable number of operands</h4><p>Here follows an example of how an instruction with a variable number
│ │ │  of operands could be handled.  One such instructions is
│ │ │ -<code class="inline">select_val/3</code>. Here is an example how it can look like in BEAM code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2264819642-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="2264819642-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="2264819642-2">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="2264819642-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2264819642-3">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="2264819642-4">{</span><span class="ss">list</span><span class="p">,</span><span class="p" data-group-id="2264819642-5">[</span><span class="p" data-group-id="2264819642-6">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2264819642-6">}</span><span class="p">,</span><span class="p" data-group-id="2264819642-7">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2264819642-7">}</span><span class="p">,</span><span class="p" data-group-id="2264819642-8">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="2264819642-8">}</span><span class="p">,</span><span class="p" data-group-id="2264819642-9">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2264819642-9">}</span><span class="p" data-group-id="2264819642-5">]</span><span class="p" data-group-id="2264819642-4">}</span><span class="p" data-group-id="2264819642-1">}</span><span class="p">.</span></code></pre><p>The loader will convert a <code class="inline">{list,[...]}</code> operand to an <code class="inline">u</code> operand whose
│ │ │ +<code class="inline">select_val/3</code>. Here is an example how it can look like in BEAM code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4148315167-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="4148315167-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4148315167-2">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="4148315167-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4148315167-3">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="4148315167-4">{</span><span class="ss">list</span><span class="p">,</span><span class="p" data-group-id="4148315167-5">[</span><span class="p" data-group-id="4148315167-6">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4148315167-6">}</span><span class="p">,</span><span class="p" data-group-id="4148315167-7">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4148315167-7">}</span><span class="p">,</span><span class="p" data-group-id="4148315167-8">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4148315167-8">}</span><span class="p">,</span><span class="p" data-group-id="4148315167-9">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4148315167-9">}</span><span class="p" data-group-id="4148315167-5">]</span><span class="p" data-group-id="4148315167-4">}</span><span class="p" data-group-id="4148315167-1">}</span><span class="p">.</span></code></pre><p>The loader will convert a <code class="inline">{list,[...]}</code> operand to an <code class="inline">u</code> operand whose
│ │ │  value is the number of elements in the list, followed by each element in
│ │ │  the list.  The instruction above would be translated to the following
│ │ │ -instruction:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2262515471-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="2262515471-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="2262515471-2">}</span><span class="p">,</span><span class="p" data-group-id="2262515471-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2262515471-3">}</span><span class="p">,</span><span class="p" data-group-id="2262515471-4">{</span><span class="ss">u</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2262515471-4">}</span><span class="p">,</span><span class="p" data-group-id="2262515471-5">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2262515471-5">}</span><span class="p">,</span><span class="p" data-group-id="2262515471-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2262515471-6">}</span><span class="p">,</span><span class="p" data-group-id="2262515471-7">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="2262515471-7">}</span><span class="p">,</span><span class="p" data-group-id="2262515471-8">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2262515471-8">}</span><span class="p" data-group-id="2262515471-1">}</span></code></pre><p>A definition of a specific instruction for that instruction would look
│ │ │ +instruction:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2497727879-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="2497727879-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="2497727879-2">}</span><span class="p">,</span><span class="p" data-group-id="2497727879-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2497727879-3">}</span><span class="p">,</span><span class="p" data-group-id="2497727879-4">{</span><span class="ss">u</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2497727879-4">}</span><span class="p">,</span><span class="p" data-group-id="2497727879-5">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2497727879-5">}</span><span class="p">,</span><span class="p" data-group-id="2497727879-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2497727879-6">}</span><span class="p">,</span><span class="p" data-group-id="2497727879-7">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="2497727879-7">}</span><span class="p">,</span><span class="p" data-group-id="2497727879-8">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2497727879-8">}</span><span class="p" data-group-id="2497727879-1">}</span></code></pre><p>A definition of a specific instruction for that instruction would look
│ │ │  like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">select_val</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">f</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">*</span></code></pre><p>The <code class="inline">*</code> as the last operand will make sure that the variable operands
│ │ │  are passed in as a <code class="inline">Span</code> of <code class="inline">ArgVal</code> (will be <code class="inline">std::span</code> in C++20 onwards).
│ │ │ -Here is the emitter function:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_select_val</span><span class="p" data-group-id="3811977745-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w">
│ │ │ +Here is the emitter function:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_select_val</span><span class="p" data-group-id="9631395343-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w">
│ │ │                                            </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Fail</span><span class="p">,</span><span class="w">
│ │ │                                            </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Size</span><span class="p">,</span><span class="w">
│ │ │ -                                          </span><span class="ss">const</span><span class="w"> </span><span class="n">Span</span><span class="o">&lt;</span><span class="n">ArgVal</span><span class="o">&gt;</span><span class="w"> </span><span class="err">&amp;</span><span class="ss">args</span><span class="p" data-group-id="3811977745-1">)</span><span class="w"> </span><span class="p" data-group-id="3811977745-2">{</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="3811977745-3">(</span><span class="n">Size</span><span class="p">.</span><span class="nf">getValue</span><span class="p" data-group-id="3811977745-4">(</span><span class="p" data-group-id="3811977745-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="ss">args</span><span class="p">.</span><span class="nf">size</span><span class="p" data-group-id="3811977745-5">(</span><span class="p" data-group-id="3811977745-5">)</span><span class="p" data-group-id="3811977745-3">)</span><span class="p">;</span><span class="w">
│ │ │ +                                          </span><span class="ss">const</span><span class="w"> </span><span class="n">Span</span><span class="o">&lt;</span><span class="n">ArgVal</span><span class="o">&gt;</span><span class="w"> </span><span class="err">&amp;</span><span class="ss">args</span><span class="p" data-group-id="9631395343-1">)</span><span class="w"> </span><span class="p" data-group-id="9631395343-2">{</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="9631395343-3">(</span><span class="n">Size</span><span class="p">.</span><span class="nf">getValue</span><span class="p" data-group-id="9631395343-4">(</span><span class="p" data-group-id="9631395343-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="ss">args</span><span class="p">.</span><span class="nf">size</span><span class="p" data-group-id="9631395343-5">(</span><span class="p" data-group-id="9631395343-5">)</span><span class="p" data-group-id="9631395343-3">)</span><span class="p">;</span><span class="w">
│ │ │         </span><span class="p">.</span><span class="w">
│ │ │         </span><span class="p">.</span><span class="w">
│ │ │         </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3811977745-2">}</span></code></pre>
│ │ │ +</span><span class="p" data-group-id="9631395343-2">}</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="tracing.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/beamasm.html
│ │ │ @@ -145,26 +145,26 @@
│ │ │  </h2>
│ │ │  <p>The code is loaded very similarly to how it is loaded for the interpreter. Each beam
│ │ │  file is parsed and then optimized through the transformations described in
│ │ │  <a href="beam_makeops.html#defining-transformation-rules">beam_makeops</a>. The transformations
│ │ │  used in BeamAsm are much simpler than the interpreter's, as most of the
│ │ │  transformations for the interpreter are done only to eliminate the instruction
│ │ │  dispatch overhead.</p><p>Then each instruction is encoded using the C++ functions in the
│ │ │ -<code class="inline">jit/$ARCH/instr_*.cpp</code> files. For example:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_is_nonempty_list</span><span class="p" data-group-id="8891023869-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p" data-group-id="8891023869-1">)</span><span class="w"> </span><span class="p" data-group-id="8891023869-2">{</span><span class="w">
│ │ │ -  </span><span class="ss">a</span><span class="p">.</span><span class="nf">test</span><span class="p" data-group-id="8891023869-3">(</span><span class="nf">getArgRef</span><span class="p" data-group-id="8891023869-4">(</span><span class="n">Src</span><span class="p" data-group-id="8891023869-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">imm</span><span class="p" data-group-id="8891023869-5">(</span><span class="p">_</span><span class="n">TAG_PRIMARY_MASK</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">TAG_PRIMARY_LIST</span><span class="p" data-group-id="8891023869-5">)</span><span class="p" data-group-id="8891023869-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="ss">a</span><span class="p">.</span><span class="nf">jne</span><span class="p" data-group-id="8891023869-6">(</span><span class="ss">labels</span><span class="p" data-group-id="8891023869-7">[</span><span class="n">Fail</span><span class="p">.</span><span class="nf">getLabel</span><span class="p" data-group-id="8891023869-8">(</span><span class="p" data-group-id="8891023869-8">)</span><span class="p" data-group-id="8891023869-7">]</span><span class="p" data-group-id="8891023869-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8891023869-2">}</span></code></pre><p><a href="https://github.com/asmjit/asmjit">asmjit</a> provides a fairly straightforward
│ │ │ +<code class="inline">jit/$ARCH/instr_*.cpp</code> files. For example:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_is_nonempty_list</span><span class="p" data-group-id="0619577180-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p" data-group-id="0619577180-1">)</span><span class="w"> </span><span class="p" data-group-id="0619577180-2">{</span><span class="w">
│ │ │ +  </span><span class="ss">a</span><span class="p">.</span><span class="nf">test</span><span class="p" data-group-id="0619577180-3">(</span><span class="nf">getArgRef</span><span class="p" data-group-id="0619577180-4">(</span><span class="n">Src</span><span class="p" data-group-id="0619577180-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">imm</span><span class="p" data-group-id="0619577180-5">(</span><span class="p">_</span><span class="n">TAG_PRIMARY_MASK</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">TAG_PRIMARY_LIST</span><span class="p" data-group-id="0619577180-5">)</span><span class="p" data-group-id="0619577180-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="ss">a</span><span class="p">.</span><span class="nf">jne</span><span class="p" data-group-id="0619577180-6">(</span><span class="ss">labels</span><span class="p" data-group-id="0619577180-7">[</span><span class="n">Fail</span><span class="p">.</span><span class="nf">getLabel</span><span class="p" data-group-id="0619577180-8">(</span><span class="p" data-group-id="0619577180-8">)</span><span class="p" data-group-id="0619577180-7">]</span><span class="p" data-group-id="0619577180-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0619577180-2">}</span></code></pre><p><a href="https://github.com/asmjit/asmjit">asmjit</a> provides a fairly straightforward
│ │ │  mapping from a C++ function call to the x86 assembly instruction. The above
│ │ │  instruction tests if the value in the <code class="inline">Src</code> register is a non-empty list and if
│ │ │  it is not then it jumps to the fail label.</p><p>For comparison, the interpreter has 8 combinations and specializations of
│ │ │  this implementation to minimize the instruction dispatch overhead for
│ │ │  common patterns.</p><p>The original register allocation done by the Erlang compiler is used to manage the
│ │ │  liveness of values and the physical registers are statically allocated to keep
│ │ │  the necessary process state. At the moment this is the static register
│ │ │ -allocation on x86-64:</p><pre><code class="makeup erlang" translate="no"><span class="nc">rbx</span><span class="p">:</span><span class="w"> </span><span class="n">ErtsSchedulerRegisters</span><span class="w"> </span><span class="nf">struct</span><span class="w"> </span><span class="p" data-group-id="1471664038-1">(</span><span class="ss">contains</span><span class="w"> </span><span class="ss">x</span><span class="o">/</span><span class="nb">float</span><span class="w"> </span><span class="ss">registers</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="ss">some</span><span class="w"> </span><span class="ss">metadata</span><span class="p" data-group-id="1471664038-1">)</span><span class="w">
│ │ │ +allocation on x86-64:</p><pre><code class="makeup erlang" translate="no"><span class="nc">rbx</span><span class="p">:</span><span class="w"> </span><span class="n">ErtsSchedulerRegisters</span><span class="w"> </span><span class="nf">struct</span><span class="w"> </span><span class="p" data-group-id="0240640111-1">(</span><span class="ss">contains</span><span class="w"> </span><span class="ss">x</span><span class="o">/</span><span class="nb">float</span><span class="w"> </span><span class="ss">registers</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="ss">some</span><span class="w"> </span><span class="ss">metadata</span><span class="p" data-group-id="0240640111-1">)</span><span class="w">
│ │ │  </span><span class="nc">rbp</span><span class="p">:</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="ss">frame</span><span class="w"> </span><span class="ss">pointer</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="err">`</span><span class="ss">perf</span><span class="err">`</span><span class="w"> </span><span class="ss">support</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">enabled</span><span class="p">,</span><span class="w"> </span><span class="ss">otherwise</span><span class="w"> </span><span class="ss">this</span><span class="w">
│ │ │       </span><span class="ss">is</span><span class="w"> </span><span class="ss">an</span><span class="w"> </span><span class="ss">optional</span><span class="w"> </span><span class="ss">save</span><span class="w"> </span><span class="ss">slot</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="ss">stack</span><span class="w"> </span><span class="ss">pointer</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="ss">executing</span><span class="w"> </span><span class="n">C</span><span class="w">
│ │ │       </span><span class="ss">code</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="nc">r12</span><span class="p">:</span><span class="w"> </span><span class="n">Active</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">index</span><span class="w">
│ │ │  </span><span class="nc">r13</span><span class="p">:</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="ss">running</span><span class="w"> </span><span class="ss">process</span><span class="w">
│ │ │  </span><span class="nc">r14</span><span class="p">:</span><span class="w"> </span><span class="n">Remaining</span><span class="w"> </span><span class="ss">reductions</span><span class="w">
│ │ │  </span><span class="nc">r15</span><span class="p">:</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="ss">heap</span><span class="w"> </span><span class="ss">pointer</span></code></pre><p>Note that all of these are callee save registers under the System V and Windows
│ │ │ @@ -183,21 +183,21 @@
│ │ │  shared and only the arguments to the instructions vary. Using as little memory as
│ │ │  possible has many advantages; less memory is used, loading time decreases,
│ │ │  higher cache hit-rate.</p><p>In BeamAsm we need to achieve something similar since the load-time of a module
│ │ │  scales almost linearly with the amount of memory it uses. Early BeamAsm prototypes
│ │ │  used about double the amount of memory for code as the interpreter, while current
│ │ │  versions use about 10% more. How was this achieved?</p><p>In BeamAsm we heavily use shared code fragments to try to emit as much code as
│ │ │  possible as global shared fragments instead of duplicating the code unnecessarily.
│ │ │ -For instance, the return instruction looks something like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Label</span><span class="w"> </span><span class="ss">yield</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">a</span><span class="p">.</span><span class="nf">newLabel</span><span class="p" data-group-id="5230345929-1">(</span><span class="p" data-group-id="5230345929-1">)</span><span class="p">;</span><span class="w">
│ │ │ +For instance, the return instruction looks something like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Label</span><span class="w"> </span><span class="ss">yield</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">a</span><span class="p">.</span><span class="nf">newLabel</span><span class="p" data-group-id="3385397881-1">(</span><span class="p" data-group-id="3385397881-1">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">Decrement</span><span class="w"> </span><span class="ss">reduction</span><span class="w"> </span><span class="ss">counter</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="ss">a</span><span class="p">.</span><span class="nf">dec</span><span class="p" data-group-id="5230345929-2">(</span><span class="n">FCALLS</span><span class="p" data-group-id="5230345929-2">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">a</span><span class="p">.</span><span class="nf">dec</span><span class="p" data-group-id="3385397881-2">(</span><span class="n">FCALLS</span><span class="p" data-group-id="3385397881-2">)</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">If</span><span class="w"> </span><span class="n">FCALLS</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">jump</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">yield</span><span class="o">-</span><span class="ss">on</span><span class="o">-</span><span class="ss">return</span><span class="w"> </span><span class="ss">fragment</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="ss">a</span><span class="p">.</span><span class="nf">jl</span><span class="p" data-group-id="5230345929-3">(</span><span class="nf">resolve_fragment</span><span class="p" data-group-id="5230345929-4">(</span><span class="ss">ga</span><span class="p">-&gt;</span><span class="nf">get_dispatch_return</span><span class="p" data-group-id="5230345929-5">(</span><span class="p" data-group-id="5230345929-5">)</span><span class="p" data-group-id="5230345929-4">)</span><span class="p" data-group-id="5230345929-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="ss">a</span><span class="p">.</span><span class="nf">ret</span><span class="p" data-group-id="5230345929-6">(</span><span class="p" data-group-id="5230345929-6">)</span><span class="p">;</span></code></pre><p>The code above is not exactly what is emitted, but close enough. The thing to note
│ │ │ +</span><span class="ss">a</span><span class="p">.</span><span class="nf">jl</span><span class="p" data-group-id="3385397881-3">(</span><span class="nf">resolve_fragment</span><span class="p" data-group-id="3385397881-4">(</span><span class="ss">ga</span><span class="p">-&gt;</span><span class="nf">get_dispatch_return</span><span class="p" data-group-id="3385397881-5">(</span><span class="p" data-group-id="3385397881-5">)</span><span class="p" data-group-id="3385397881-4">)</span><span class="p" data-group-id="3385397881-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">a</span><span class="p">.</span><span class="nf">ret</span><span class="p" data-group-id="3385397881-6">(</span><span class="p" data-group-id="3385397881-6">)</span><span class="p">;</span></code></pre><p>The code above is not exactly what is emitted, but close enough. The thing to note
│ │ │  is that the code for doing the context switch is never emitted. Instead, we jump
│ │ │  to a global fragment that all return instructions share. This greatly reduces
│ │ │  the amount of code that has to be emitted for each module.</p><h2 id="running-erlang-code" class="section-heading">
│ │ │    <a href="#running-erlang-code" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running Erlang code</span>
│ │ │ @@ -239,43 +239,43 @@
│ │ │    <a href="#running-c-code" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running C code</span>
│ │ │  </h2>
│ │ │  <p>As Erlang stacks can be very small, we have to switch over to a different stack
│ │ │  when we need to execute C code (which may expect a much larger stack). This is
│ │ │ -done through <code class="inline">emit_enter_runtime</code> and <code class="inline">emit_leave_runtime</code>, for example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mov_arg</span><span class="p" data-group-id="5813586697-1">(</span><span class="n">ARG4</span><span class="p">,</span><span class="w"> </span><span class="n">NumFree</span><span class="p" data-group-id="5813586697-1">)</span><span class="p">;</span><span class="w">
│ │ │ +done through <code class="inline">emit_enter_runtime</code> and <code class="inline">emit_leave_runtime</code>, for example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mov_arg</span><span class="p" data-group-id="0772390534-1">(</span><span class="n">ARG4</span><span class="p">,</span><span class="w"> </span><span class="n">NumFree</span><span class="p" data-group-id="0772390534-1">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">Move</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="ss">stack</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="ss">swap</span><span class="w"> </span><span class="ss">out</span><span class="w"> </span><span class="ss">our</span><span class="w"> </span><span class="ss">current</span><span class="w"> </span><span class="ss">reductions</span><span class="p">,</span><span class="w"> </span><span class="ss">stack</span><span class="o">-</span><span class="p">,</span><span class="w"> </span><span class="ow">and</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="w"> </span><span class="ss">heap</span><span class="w"> </span><span class="ss">pointer</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">process</span><span class="w"> </span><span class="ss">structure</span><span class="p">.</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="ss">emit_enter_runtime</span><span class="o">&lt;</span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eReductions</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eStack</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eHeap</span><span class="o">&gt;</span><span class="p" data-group-id="5813586697-2">(</span><span class="p" data-group-id="5813586697-2">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">emit_enter_runtime</span><span class="o">&lt;</span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eReductions</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eStack</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eHeap</span><span class="o">&gt;</span><span class="p" data-group-id="0772390534-2">(</span><span class="p" data-group-id="0772390534-2">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">a</span><span class="p">.</span><span class="nf">mov</span><span class="p" data-group-id="5813586697-3">(</span><span class="n">ARG1</span><span class="p">,</span><span class="w"> </span><span class="ss">c_p</span><span class="p" data-group-id="5813586697-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">load_x_reg_array</span><span class="p" data-group-id="5813586697-4">(</span><span class="n">ARG2</span><span class="p" data-group-id="5813586697-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">make_move_patch</span><span class="p" data-group-id="5813586697-5">(</span><span class="n">ARG3</span><span class="p">,</span><span class="w"> </span><span class="ss">lambdas</span><span class="p" data-group-id="5813586697-6">[</span><span class="n">Fun</span><span class="p">.</span><span class="nf">getValue</span><span class="p" data-group-id="5813586697-7">(</span><span class="p" data-group-id="5813586697-7">)</span><span class="p" data-group-id="5813586697-6">]</span><span class="p">.</span><span class="ss">patches</span><span class="p" data-group-id="5813586697-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">a</span><span class="p">.</span><span class="nf">mov</span><span class="p" data-group-id="0772390534-3">(</span><span class="n">ARG1</span><span class="p">,</span><span class="w"> </span><span class="ss">c_p</span><span class="p" data-group-id="0772390534-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">load_x_reg_array</span><span class="p" data-group-id="0772390534-4">(</span><span class="n">ARG2</span><span class="p" data-group-id="0772390534-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">make_move_patch</span><span class="p" data-group-id="0772390534-5">(</span><span class="n">ARG3</span><span class="p">,</span><span class="w"> </span><span class="ss">lambdas</span><span class="p" data-group-id="0772390534-6">[</span><span class="n">Fun</span><span class="p">.</span><span class="nf">getValue</span><span class="p" data-group-id="0772390534-7">(</span><span class="p" data-group-id="0772390534-7">)</span><span class="p" data-group-id="0772390534-6">]</span><span class="p">.</span><span class="ss">patches</span><span class="p" data-group-id="0772390534-5">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">Call</span><span class="w"> </span><span class="err">`</span><span class="ss">new_fun</span><span class="err">`</span><span class="p">,</span><span class="w"> </span><span class="ss">asserting</span><span class="w"> </span><span class="ss">that</span><span class="w"> </span><span class="ss">we</span><span class="err">&#39;</span><span class="ss">re</span><span class="w"> </span><span class="ss">on</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="ss">stack</span><span class="p">.</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="ss">runtime_call</span><span class="o">&lt;</span><span class="mi">4</span><span class="o">&gt;</span><span class="p" data-group-id="5813586697-8">(</span><span class="ss">new_fun</span><span class="p" data-group-id="5813586697-8">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">runtime_call</span><span class="o">&lt;</span><span class="mi">4</span><span class="o">&gt;</span><span class="p" data-group-id="0772390534-8">(</span><span class="ss">new_fun</span><span class="p" data-group-id="0772390534-8">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">Move</span><span class="w"> </span><span class="ss">back</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="ss">stack</span><span class="p">,</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="ss">read</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">updated</span><span class="w"> </span><span class="ss">values</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">process</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="w"> </span><span class="ss">structure</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="ss">emit_leave_runtime</span><span class="o">&lt;</span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eReductions</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eStack</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eHeap</span><span class="o">&gt;</span><span class="p" data-group-id="5813586697-9">(</span><span class="p" data-group-id="5813586697-9">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">emit_leave_runtime</span><span class="o">&lt;</span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eReductions</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eStack</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eHeap</span><span class="o">&gt;</span><span class="p" data-group-id="0772390534-9">(</span><span class="p" data-group-id="0772390534-9">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">a</span><span class="p">.</span><span class="nf">mov</span><span class="p" data-group-id="5813586697-10">(</span><span class="nf">getXRef</span><span class="p" data-group-id="5813586697-11">(</span><span class="mi">0</span><span class="p" data-group-id="5813586697-11">)</span><span class="p">,</span><span class="w"> </span><span class="n">RET</span><span class="p" data-group-id="5813586697-10">)</span><span class="p">;</span></code></pre><p>All combinations of the <code class="inline">Update</code> constants are legal, but the ones given to
│ │ │ +</span><span class="ss">a</span><span class="p">.</span><span class="nf">mov</span><span class="p" data-group-id="0772390534-10">(</span><span class="nf">getXRef</span><span class="p" data-group-id="0772390534-11">(</span><span class="mi">0</span><span class="p" data-group-id="0772390534-11">)</span><span class="p">,</span><span class="w"> </span><span class="n">RET</span><span class="p" data-group-id="0772390534-10">)</span><span class="p">;</span></code></pre><p>All combinations of the <code class="inline">Update</code> constants are legal, but the ones given to
│ │ │  <code class="inline">emit_leave_runtime</code> <em>must</em> be the same as those given to <code class="inline">emit_enter_runtime</code>.</p><h2 id="tracing-and-nif-loading" class="section-heading">
│ │ │    <a href="#tracing-and-nif-loading" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Tracing and NIF Loading</span>
│ │ │  </h2>
│ │ │  <p>To make tracing and NIF loading work there needs to be a way to intercept
│ │ │  any function call. In the interpreter, this is done by rewriting the loaded
│ │ │  BEAM code, but this is more complicated in BeamAsm as we want to have a fast
│ │ │  and compact way to do this. This is solved by emitting the code below at the
│ │ │ -start of each function (x86 variant below):</p><pre><code class="makeup erlang" translate="no"><span class="w">  </span><span class="mi">0</span><span class="nc">x0</span><span class="p">:</span><span class="w"> </span><span class="ss">short</span><span class="w"> </span><span class="ss">jmp</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="p" data-group-id="3023545542-1">(</span><span class="ss">address</span><span class="w"> </span><span class="mi">0</span><span class="ss">x8</span><span class="p" data-group-id="3023545542-1">)</span><span class="w">
│ │ │ +start of each function (x86 variant below):</p><pre><code class="makeup erlang" translate="no"><span class="w">  </span><span class="mi">0</span><span class="nc">x0</span><span class="p">:</span><span class="w"> </span><span class="ss">short</span><span class="w"> </span><span class="ss">jmp</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="p" data-group-id="7731451781-1">(</span><span class="ss">address</span><span class="w"> </span><span class="mi">0</span><span class="ss">x8</span><span class="p" data-group-id="7731451781-1">)</span><span class="w">
│ │ │    </span><span class="mi">0</span><span class="nc">x2</span><span class="p">:</span><span class="w"> </span><span class="ss">nop</span><span class="w">
│ │ │    </span><span class="mi">0</span><span class="nc">x3</span><span class="p">:</span><span class="w"> </span><span class="ss">relative</span><span class="w"> </span><span class="ss">near</span><span class="w"> </span><span class="ss">call</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">shared</span><span class="w"> </span><span class="ss">breakpoint</span><span class="w"> </span><span class="ss">fragment</span><span class="w">
│ │ │    </span><span class="mi">0</span><span class="nc">x8</span><span class="p">:</span><span class="w"> </span><span class="ss">actual</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">function</span></code></pre><p>When code starts to execute it will simply see the <code class="inline">short jmp 6</code> instruction
│ │ │  which skips the prologue and starts to execute the code directly.</p><p>When we want to enable a certain breakpoint we set the jmp target to be 1,
│ │ │  which means it will land on the call to the shared breakpoint fragment. This
│ │ │  fragment checks the current <code class="inline">breakpoint_flag</code> stored in the ErtsCodeInfo of
│ │ │  this function, and then calls <code class="inline">erts_call_nif_early</code> and
│ │ │ @@ -289,31 +289,31 @@
│ │ │    <span class="text">Updating code</span>
│ │ │  </h3>
│ │ │  <p>Because many environments enforce <a href="https://en.wikipedia.org/wiki/W%5EX" title="">W^X</a> it's not always possible to write
│ │ │  directly to the code pages. Because of this we map code twice: once with an
│ │ │  executable page and once with a writable page. Since they're backed by the
│ │ │  same memory, writes to the writable page appear magically in the executable
│ │ │  one.</p><p>The <code class="inline">erts_writable_code_ptr</code> function can be used to get writable pointers
│ │ │ -given a module instance, provided that it has been unsealed first:</p><pre><code class="makeup erlang" translate="no"><span class="nf">for</span><span class="w"> </span><span class="p" data-group-id="6880667276-1">(</span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="ss">n</span><span class="p">;</span><span class="w"> </span><span class="ss">i</span><span class="o">++</span><span class="p" data-group-id="6880667276-1">)</span><span class="w"> </span><span class="p" data-group-id="6880667276-2">{</span><span class="w">
│ │ │ +given a module instance, provided that it has been unsealed first:</p><pre><code class="makeup erlang" translate="no"><span class="nf">for</span><span class="w"> </span><span class="p" data-group-id="7416246050-1">(</span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="ss">n</span><span class="p">;</span><span class="w"> </span><span class="ss">i</span><span class="o">++</span><span class="p" data-group-id="7416246050-1">)</span><span class="w"> </span><span class="p" data-group-id="7416246050-2">{</span><span class="w">
│ │ │      </span><span class="ss">const</span><span class="w"> </span><span class="n">ErtsCodeInfo</span><span class="o">*</span><span class="w"> </span><span class="ss">ci_exec</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">ErtsCodeInfo</span><span class="o">*</span><span class="w"> </span><span class="ss">ci_rw</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">void</span><span class="w"> </span><span class="o">*</span><span class="ss">w_ptr</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">erts_unseal_module</span><span class="p" data-group-id="6880667276-3">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p" data-group-id="6880667276-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">erts_unseal_module</span><span class="p" data-group-id="7416246050-3">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p" data-group-id="7416246050-3">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="ss">ci_exec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">code_hdr</span><span class="p">-&gt;</span><span class="ss">functions</span><span class="p" data-group-id="6880667276-4">[</span><span class="ss">i</span><span class="p" data-group-id="6880667276-4">]</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">w_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_writable_code_ptr</span><span class="p" data-group-id="6880667276-5">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_exec</span><span class="p" data-group-id="6880667276-5">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">ci_rw</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6880667276-6">(</span><span class="n">ErtsCodeInfo</span><span class="o">*</span><span class="p" data-group-id="6880667276-6">)</span><span class="ss">w_ptr</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">ci_exec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">code_hdr</span><span class="p">-&gt;</span><span class="ss">functions</span><span class="p" data-group-id="7416246050-4">[</span><span class="ss">i</span><span class="p" data-group-id="7416246050-4">]</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">w_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_writable_code_ptr</span><span class="p" data-group-id="7416246050-5">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_exec</span><span class="p" data-group-id="7416246050-5">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">ci_rw</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7416246050-6">(</span><span class="n">ErtsCodeInfo</span><span class="o">*</span><span class="p" data-group-id="7416246050-6">)</span><span class="ss">w_ptr</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">uninstall_breakpoint</span><span class="p" data-group-id="6880667276-7">(</span><span class="ss">ci_rw</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_exec</span><span class="p" data-group-id="6880667276-7">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">consolidate_bp_data</span><span class="p" data-group-id="6880667276-8">(</span><span class="ss">modp</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_rw</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6880667276-8">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="6880667276-9">(</span><span class="ss">ci_rw</span><span class="p">-&gt;</span><span class="ss">gen_bp</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">NULL</span><span class="p" data-group-id="6880667276-9">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">uninstall_breakpoint</span><span class="p" data-group-id="7416246050-7">(</span><span class="ss">ci_rw</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_exec</span><span class="p" data-group-id="7416246050-7">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">consolidate_bp_data</span><span class="p" data-group-id="7416246050-8">(</span><span class="ss">modp</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_rw</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7416246050-8">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="7416246050-9">(</span><span class="ss">ci_rw</span><span class="p">-&gt;</span><span class="ss">gen_bp</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">NULL</span><span class="p" data-group-id="7416246050-9">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">erts_seal_module</span><span class="p" data-group-id="6880667276-10">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p" data-group-id="6880667276-10">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6880667276-2">}</span></code></pre><p>Without the module instance there's no reliable way to figure out the writable
│ │ │ +    </span><span class="nf">erts_seal_module</span><span class="p" data-group-id="7416246050-10">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p" data-group-id="7416246050-10">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7416246050-2">}</span></code></pre><p>Without the module instance there's no reliable way to figure out the writable
│ │ │  address of a code page, and we rely on <em>address space layout randomization</em>
│ │ │  (ASLR) to make it difficult to guess. On some platforms, security is further
│ │ │  enhanced by protecting the writable area from writes until the module has been
│ │ │  unsealed by <code class="inline">erts_unseal_module</code>.</p><h3 id="export-tracing" class="section-heading">
│ │ │    <a href="#export-tracing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -393,15 +393,15 @@
│ │ │  </span><span class="ss">perf</span><span class="w"> </span><span class="ss">script</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">perf</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="ss">run</span><span class="w"> </span><span class="ss">stackcollapse</span><span class="w">
│ │ │  </span><span class="ss">stackcollapse</span><span class="o">-</span><span class="ss">perf</span><span class="p">.</span><span class="ss">pl</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">perf</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">folded</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="n">Create</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">svg</span><span class="w">
│ │ │  </span><span class="ss">flamegraph</span><span class="p">.</span><span class="ss">pl</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">folded</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">svg</span></code></pre><p>We get a graph that would look something like this:</p><p><img src="assets/perf-beamasm.svg" alt="Linux Perf FlameGraph: dialyzer PLT build"/></p><p>You can view a larger version <a href="assets/perf-beamasm.svg">here</a>. It contains
│ │ │  the same information, but it is easier to share with others as it does
│ │ │  not need the symbols in the executable.</p><p>Using the same data we can also produce a graph where the scheduler profile data
│ │ │ -has been merged by using <code class="inline">sed</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="n">Strip</span><span class="w"> </span><span class="p" data-group-id="1663397631-1">[</span><span class="mi">0</span><span class="o">-</span><span class="mi">9</span><span class="p" data-group-id="1663397631-1">]</span><span class="o">+</span><span class="p">_</span><span class="w"> </span><span class="ow">and</span><span class="o">/</span><span class="ow">or</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1663397631-2">[</span><span class="mi">0</span><span class="o">-</span><span class="mi">9</span><span class="p" data-group-id="1663397631-2">]</span><span class="o">+</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">scheduler</span><span class="w"> </span><span class="ss">names</span><span class="w">
│ │ │ +has been merged by using <code class="inline">sed</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="n">Strip</span><span class="w"> </span><span class="p" data-group-id="3740646374-1">[</span><span class="mi">0</span><span class="o">-</span><span class="mi">9</span><span class="p" data-group-id="3740646374-1">]</span><span class="o">+</span><span class="p">_</span><span class="w"> </span><span class="ow">and</span><span class="o">/</span><span class="ow">or</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3740646374-2">[</span><span class="mi">0</span><span class="o">-</span><span class="mi">9</span><span class="p" data-group-id="3740646374-2">]</span><span class="o">+</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">scheduler</span><span class="w"> </span><span class="ss">names</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="ss">scheduler</span><span class="w"> </span><span class="ss">names</span><span class="w"> </span><span class="ss">changed</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="n">OTP26</span><span class="p">,</span><span class="w"> </span><span class="ss">hence</span><span class="w"> </span><span class="ss">two</span><span class="w"> </span><span class="ss">expressions</span><span class="w">
│ │ │  </span><span class="ss">sed</span><span class="w"> </span><span class="o">-</span><span class="ss">e</span><span class="w"> </span><span class="ss">&#39;s/^[0-9]\+_//&#39;</span><span class="w"> </span><span class="o">-</span><span class="ss">e</span><span class="w"> </span><span class="ss">&#39;s/^erts_\([^_]\+\)_[0-9]\+/erts_\1/&#39;</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">folded</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">folded_sched</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="n">Create</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">svg</span><span class="w">
│ │ │  </span><span class="ss">flamegraph</span><span class="p">.</span><span class="ss">pl</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">folded_sched</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">out_sched</span><span class="p">.</span><span class="ss">svg</span></code></pre><p><img src="assets/perf-beamasm-merged.svg" alt="Linux Perf FlameGraph: dialyzer PLT build"/></p><p>You can view a larger version <a href="assets/perf-beamasm-merged.svg">here</a>.
│ │ │  There are many different transformations that you can do to make the graph show
│ │ │  you what you want.</p><h3 id="annotate-perf-functions" class="section-heading">
│ │ │    <a href="#annotate-perf-functions" class="hover-link">
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/codeloading.html
│ │ │ @@ -163,16 +163,16 @@
│ │ │  only be done by one loader process at a time. A second loader process
│ │ │  trying to enter finishing phase will be suspended until the first
│ │ │  loader is done. This will only block the process, the scheduler is
│ │ │  free to schedule other work while the second loader is waiting. (See
│ │ │  <code class="inline">erts_try_seize_code_load_permission</code> and
│ │ │  <code class="inline">erts_release_code_load_permission</code>).</p><p>The ability to prepare several modules in parallel is not currently
│ │ │  used as almost all code loading is serialized by the code_server
│ │ │ -process. The BIF interface is however prepared for this.</p><pre><code class="makeup erlang" translate="no"><span class="w">  </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">prepare_loading</span><span class="p" data-group-id="2950924208-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="2950924208-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">LoaderState</span><span class="w">
│ │ │ -  </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">finish_loading</span><span class="p" data-group-id="2950924208-2">(</span><span class="p" data-group-id="2950924208-3">[</span><span class="n">LoaderState</span><span class="p" data-group-id="2950924208-3">]</span><span class="p" data-group-id="2950924208-2">)</span></code></pre><p>The idea is that <code class="inline">prepare_loading</code> could be called in parallel for
│ │ │ +process. The BIF interface is however prepared for this.</p><pre><code class="makeup erlang" translate="no"><span class="w">  </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">prepare_loading</span><span class="p" data-group-id="2895005484-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="2895005484-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">LoaderState</span><span class="w">
│ │ │ +  </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">finish_loading</span><span class="p" data-group-id="2895005484-2">(</span><span class="p" data-group-id="2895005484-3">[</span><span class="n">LoaderState</span><span class="p" data-group-id="2895005484-3">]</span><span class="p" data-group-id="2895005484-2">)</span></code></pre><p>The idea is that <code class="inline">prepare_loading</code> could be called in parallel for
│ │ │  different modules and returns a &quot;magic binary&quot; containing the internal
│ │ │  state of each prepared module. Function <code class="inline">finish_loading</code> could take a
│ │ │  list of such states and do the finishing of all of them in one go.</p><p>Currently we use the legacy BIF <code class="inline">erlang:load_module</code> which is now
│ │ │  implemented in Erlang by calling the above two functions in
│ │ │  sequence. Function <code class="inline">finish_loading</code> is limited to only accepts a list
│ │ │  with one module state as we do not yet use the multi module loading
│ │ │  feature.</p><h2 id="the-finishing-sequence" class="section-heading">
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/crash_dump.html
│ │ │ @@ -401,21 +401,21 @@
│ │ │  <a href="erlang.html#put/2"><code class="inline">put/2</code></a> and <a href="erlang.html#get/1"><code class="inline">get/1</code></a> thing) is non-empty.</p><p>The raw memory information can be decoded by the Crashdump Viewer tool. You can
│ │ │  then see the stack dump, the message queue (if any), and the dictionary (if
│ │ │  any).</p><p>The stack dump is a dump of the Erlang process stack. Most of the live data
│ │ │  (that is, variables currently in use) are placed on the stack; thus this can be
│ │ │  interesting. One has to &quot;guess&quot; what is what, but as the information is
│ │ │  symbolic, thorough reading of this information can be useful. As an example, we
│ │ │  can find the state variable of the Erlang primitive loader online <code class="inline">(5)</code> and
│ │ │ -<code class="inline">(6)</code> in the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8359085298-1">(</span><span class="mi">1</span><span class="p" data-group-id="8359085298-1">)</span><span class="w">  </span><span class="mi">3</span><span class="ss">cac44</span><span class="w">   </span><span class="n">Return</span><span class="w"> </span><span class="ss">addr</span><span class="w"> </span><span class="mi">0</span><span class="nf">x13BF58</span><span class="w"> </span><span class="p" data-group-id="8359085298-2">(</span><span class="o">&lt;</span><span class="ss">terminate</span><span class="w"> </span><span class="ss">process</span><span class="w"> </span><span class="ss">normally</span><span class="o">&gt;</span><span class="p" data-group-id="8359085298-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8359085298-3">(</span><span class="mi">2</span><span class="p" data-group-id="8359085298-3">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="8359085298-4">(</span><span class="mi">0</span><span class="p" data-group-id="8359085298-4">)</span><span class="w">     </span><span class="p" data-group-id="8359085298-5">[</span><span class="s">&quot;/view/siri_r10_dev/clearcase/otp/erts/lib/kernel/ebin&quot;</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8359085298-6">(</span><span class="mi">3</span><span class="p" data-group-id="8359085298-6">)</span><span class="w">            </span><span class="s">&quot;/view/siri_r10_dev/clearcase/otp/erts/lib/stdlib/ebin&quot;</span><span class="p" data-group-id="8359085298-5">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8359085298-7">(</span><span class="mi">4</span><span class="p" data-group-id="8359085298-7">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="8359085298-8">(</span><span class="mi">1</span><span class="p" data-group-id="8359085298-8">)</span><span class="w">     </span><span class="o">&lt;</span><span class="mf">0.1</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8359085298-9">(</span><span class="mi">5</span><span class="p" data-group-id="8359085298-9">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="8359085298-10">(</span><span class="mi">2</span><span class="p" data-group-id="8359085298-10">)</span><span class="w">     </span><span class="p" data-group-id="8359085298-11">{</span><span class="ss">state</span><span class="p">,</span><span class="p" data-group-id="8359085298-12">[</span><span class="p" data-group-id="8359085298-12">]</span><span class="p">,</span><span class="ss">none</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">6.7085890</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">undefined</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">7.9000327</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8359085298-13">(</span><span class="mi">6</span><span class="p" data-group-id="8359085298-13">)</span><span class="w">            </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">8.116480692</span><span class="o">&gt;</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.2</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">9.10708760</span><span class="o">&gt;</span><span class="p" data-group-id="8359085298-11">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8359085298-14">(</span><span class="mi">7</span><span class="p" data-group-id="8359085298-14">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="8359085298-15">(</span><span class="mi">3</span><span class="p" data-group-id="8359085298-15">)</span><span class="w">     </span><span class="ss">infinity</span></code></pre><p>When interpreting the data for a process, it is helpful to know that anonymous
│ │ │ +<code class="inline">(6)</code> in the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2963011376-1">(</span><span class="mi">1</span><span class="p" data-group-id="2963011376-1">)</span><span class="w">  </span><span class="mi">3</span><span class="ss">cac44</span><span class="w">   </span><span class="n">Return</span><span class="w"> </span><span class="ss">addr</span><span class="w"> </span><span class="mi">0</span><span class="nf">x13BF58</span><span class="w"> </span><span class="p" data-group-id="2963011376-2">(</span><span class="o">&lt;</span><span class="ss">terminate</span><span class="w"> </span><span class="ss">process</span><span class="w"> </span><span class="ss">normally</span><span class="o">&gt;</span><span class="p" data-group-id="2963011376-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2963011376-3">(</span><span class="mi">2</span><span class="p" data-group-id="2963011376-3">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="2963011376-4">(</span><span class="mi">0</span><span class="p" data-group-id="2963011376-4">)</span><span class="w">     </span><span class="p" data-group-id="2963011376-5">[</span><span class="s">&quot;/view/siri_r10_dev/clearcase/otp/erts/lib/kernel/ebin&quot;</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2963011376-6">(</span><span class="mi">3</span><span class="p" data-group-id="2963011376-6">)</span><span class="w">            </span><span class="s">&quot;/view/siri_r10_dev/clearcase/otp/erts/lib/stdlib/ebin&quot;</span><span class="p" data-group-id="2963011376-5">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2963011376-7">(</span><span class="mi">4</span><span class="p" data-group-id="2963011376-7">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="2963011376-8">(</span><span class="mi">1</span><span class="p" data-group-id="2963011376-8">)</span><span class="w">     </span><span class="o">&lt;</span><span class="mf">0.1</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2963011376-9">(</span><span class="mi">5</span><span class="p" data-group-id="2963011376-9">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="2963011376-10">(</span><span class="mi">2</span><span class="p" data-group-id="2963011376-10">)</span><span class="w">     </span><span class="p" data-group-id="2963011376-11">{</span><span class="ss">state</span><span class="p">,</span><span class="p" data-group-id="2963011376-12">[</span><span class="p" data-group-id="2963011376-12">]</span><span class="p">,</span><span class="ss">none</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">6.7085890</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">undefined</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">7.9000327</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2963011376-13">(</span><span class="mi">6</span><span class="p" data-group-id="2963011376-13">)</span><span class="w">            </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">8.116480692</span><span class="o">&gt;</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.2</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">9.10708760</span><span class="o">&gt;</span><span class="p" data-group-id="2963011376-11">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2963011376-14">(</span><span class="mi">7</span><span class="p" data-group-id="2963011376-14">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="2963011376-15">(</span><span class="mi">3</span><span class="p" data-group-id="2963011376-15">)</span><span class="w">     </span><span class="ss">infinity</span></code></pre><p>When interpreting the data for a process, it is helpful to know that anonymous
│ │ │  function objects (funs) are given the following:</p><ul><li>A name constructed from the name of the function in which they are created</li><li>A number (starting with 0) indicating the number of that fun within that
│ │ │  function</li></ul><h2 id="atoms" class="section-heading">
│ │ │    <a href="#atoms" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Atoms</span>
│ │ │  </h2>
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/driver.html
│ │ │ @@ -364,41 +364,41 @@
│ │ │  <p>Before a driver can be called from Erlang, it must be loaded and opened. Loading
│ │ │  is done using the <a href="../../../lib/kernel-10.2.7.1/doc/html/erl_ddll.html"><code class="inline">erl_ddll</code></a> module (the <a href="../../../lib/kernel-10.2.7.1/doc/html/erl_ddll.html"><code class="inline">erl_ddll</code></a> driver that loads dynamic
│ │ │  driver is actually a driver itself). If loading is successful, the port can be
│ │ │  opened with <a href="erlang.html#open_port/2"><code class="inline">open_port/2</code></a>. The port name must match the name of
│ │ │  the shared library and the name in the driver entry structure.</p><p>When the port has been opened, the driver can be called. In the <code class="inline">pg_sync</code>
│ │ │  example, we do not have any data from the port, only the return value from the
│ │ │  <a href="erlang.html#port_control/3"><code class="inline">port_control/3</code></a>.</p><p>The following code is the Erlang part of the synchronous postgres driver,
│ │ │ -<code class="inline">pg_sync.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0440470885-1">(</span><span class="ss">pg_sync</span><span class="p" data-group-id="0440470885-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">pg_sync.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2803867465-1">(</span><span class="ss">pg_sync</span><span class="p" data-group-id="2803867465-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0440470885-2">(</span><span class="n">DRV_CONNECT</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0440470885-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0440470885-3">(</span><span class="n">DRV_DISCONNECT</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0440470885-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0440470885-4">(</span><span class="n">DRV_SELECT</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="0440470885-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2803867465-2">(</span><span class="n">DRV_CONNECT</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2803867465-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2803867465-3">(</span><span class="n">DRV_DISCONNECT</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2803867465-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2803867465-4">(</span><span class="n">DRV_SELECT</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2803867465-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0440470885-5">(</span><span class="p" data-group-id="0440470885-6">[</span><span class="ss">connect</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">disconnect</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">select</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0440470885-6">]</span><span class="p" data-group-id="0440470885-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2803867465-5">(</span><span class="p" data-group-id="2803867465-6">[</span><span class="ss">connect</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">disconnect</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">select</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2803867465-6">]</span><span class="p" data-group-id="2803867465-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">connect</span><span class="p" data-group-id="0440470885-7">(</span><span class="n">ConnectStr</span><span class="p" data-group-id="0440470885-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="0440470885-8">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;pg_sync&quot;</span><span class="p" data-group-id="0440470885-8">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">connect</span><span class="p" data-group-id="2803867465-7">(</span><span class="n">ConnectStr</span><span class="p" data-group-id="2803867465-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="2803867465-8">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;pg_sync&quot;</span><span class="p" data-group-id="2803867465-8">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0440470885-9">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="0440470885-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="n">E</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="0440470885-10">(</span><span class="p" data-group-id="0440470885-11">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="p" data-group-id="0440470885-11">}</span><span class="p" data-group-id="0440470885-10">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2803867465-9">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="2803867465-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="n">E</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="2803867465-10">(</span><span class="p" data-group-id="2803867465-11">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="p" data-group-id="2803867465-11">}</span><span class="p" data-group-id="2803867465-10">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="0440470885-12">(</span><span class="p" data-group-id="0440470885-13">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p" data-group-id="0440470885-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0440470885-14">[</span><span class="p" data-group-id="0440470885-14">]</span><span class="p" data-group-id="0440470885-12">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="0440470885-15">(</span><span class="nf">port_control</span><span class="p" data-group-id="0440470885-16">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_CONNECT</span><span class="p">,</span><span class="w"> </span><span class="n">ConnectStr</span><span class="p" data-group-id="0440470885-16">)</span><span class="p" data-group-id="0440470885-15">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0440470885-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p" data-group-id="0440470885-17">}</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="2803867465-12">(</span><span class="p" data-group-id="2803867465-13">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p" data-group-id="2803867465-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2803867465-14">[</span><span class="p" data-group-id="2803867465-14">]</span><span class="p" data-group-id="2803867465-12">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="2803867465-15">(</span><span class="nf">port_control</span><span class="p" data-group-id="2803867465-16">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_CONNECT</span><span class="p">,</span><span class="w"> </span><span class="n">ConnectStr</span><span class="p" data-group-id="2803867465-16">)</span><span class="p" data-group-id="2803867465-15">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2803867465-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p" data-group-id="2803867465-17">}</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">Error</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Error</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">disconnect</span><span class="p" data-group-id="0440470885-18">(</span><span class="n">Port</span><span class="p" data-group-id="0440470885-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">R</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="0440470885-19">(</span><span class="nf">port_control</span><span class="p" data-group-id="0440470885-20">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_DISCONNECT</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p" data-group-id="0440470885-20">)</span><span class="p" data-group-id="0440470885-19">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">port_close</span><span class="p" data-group-id="0440470885-21">(</span><span class="n">Port</span><span class="p" data-group-id="0440470885-21">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">disconnect</span><span class="p" data-group-id="2803867465-18">(</span><span class="n">Port</span><span class="p" data-group-id="2803867465-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">R</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="2803867465-19">(</span><span class="nf">port_control</span><span class="p" data-group-id="2803867465-20">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_DISCONNECT</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p" data-group-id="2803867465-20">)</span><span class="p" data-group-id="2803867465-19">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">port_close</span><span class="p" data-group-id="2803867465-21">(</span><span class="n">Port</span><span class="p" data-group-id="2803867465-21">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">R</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">select</span><span class="p" data-group-id="0440470885-22">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Query</span><span class="p" data-group-id="0440470885-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">binary_to_term</span><span class="p" data-group-id="0440470885-23">(</span><span class="nf">port_control</span><span class="p" data-group-id="0440470885-24">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_SELECT</span><span class="p">,</span><span class="w"> </span><span class="n">Query</span><span class="p" data-group-id="0440470885-24">)</span><span class="p" data-group-id="0440470885-23">)</span><span class="p">.</span></code></pre><p>The API is simple:</p><ul><li><code class="inline">connect/1</code> loads the driver, opens it, and logs on to the database, returning
│ │ │ +</span><span class="nf">select</span><span class="p" data-group-id="2803867465-22">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Query</span><span class="p" data-group-id="2803867465-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">binary_to_term</span><span class="p" data-group-id="2803867465-23">(</span><span class="nf">port_control</span><span class="p" data-group-id="2803867465-24">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_SELECT</span><span class="p">,</span><span class="w"> </span><span class="n">Query</span><span class="p" data-group-id="2803867465-24">)</span><span class="p" data-group-id="2803867465-23">)</span><span class="p">.</span></code></pre><p>The API is simple:</p><ul><li><code class="inline">connect/1</code> loads the driver, opens it, and logs on to the database, returning
│ │ │  the Erlang port if successful.</li><li><code class="inline">select/2</code> sends a query to the driver and returns the result.</li><li><code class="inline">disconnect/1</code> closes the database connection and the driver. (However, it
│ │ │  does not unload it.)</li></ul><p>The connection string is to be a connection string for postgres.</p><p>The driver is loaded with <a href="../../../lib/kernel-10.2.7.1/doc/html/erl_ddll.html#load_driver/2"><code class="inline">erl_ddll:load_driver/2</code></a>. If this is successful, or if
│ │ │  it is already loaded, it is opened. This will call the <code class="inline">start</code> function in the
│ │ │  driver.</p><p>We use the <a href="erlang.html#port_control/3"><code class="inline">port_control/3</code></a> function for all calls into the
│ │ │  driver. The result from the driver is returned immediately and converted to
│ │ │  terms by calling <a href="erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a>. (We trust that the
│ │ │  terms returned from the driver are well-formed, otherwise the <a href="erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a>
│ │ │ @@ -536,51 +536,51 @@
│ │ │  successful, or error if it is not. If the connection is not yet established, we
│ │ │  simply return; <code class="inline">ready_io</code> is called again.</p><p>If we have a result from a connect, indicated by having data in the <code class="inline">x</code> buffer,
│ │ │  we no longer need to select on output (<a href="../../../erts-15.2.7/doc/html/driver_entry.html#ready_output" title=""><code class="inline">ready_output</code></a>), so we remove this by
│ │ │  calling <a href="../../../erts-15.2.7/doc/html/erl_driver.html#driver_select" title=""><code class="inline">driver_select</code></a>.</p><p>If we are not connecting, we wait for results from a <code class="inline">PQsendQuery</code>, so we get
│ │ │  the result and return it. The encoding is done with the same functions as in the
│ │ │  earlier example.</p><p>Error handling is to be added here, for example, checking that the socket is
│ │ │  still open, but this is only a simple example.</p><p>The Erlang part of the asynchronous driver consists of the sample file
│ │ │ -<code class="inline">pg_async.erl</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5524666530-1">(</span><span class="ss">pg_async</span><span class="p" data-group-id="5524666530-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">pg_async.erl</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6384179664-1">(</span><span class="ss">pg_async</span><span class="p" data-group-id="6384179664-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5524666530-2">(</span><span class="n">DRV_CONNECT</span><span class="p">,</span><span class="w"> </span><span class="sc">$C</span><span class="p" data-group-id="5524666530-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5524666530-3">(</span><span class="n">DRV_DISCONNECT</span><span class="p">,</span><span class="w"> </span><span class="sc">$D</span><span class="p" data-group-id="5524666530-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5524666530-4">(</span><span class="n">DRV_SELECT</span><span class="p">,</span><span class="w"> </span><span class="sc">$S</span><span class="p" data-group-id="5524666530-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6384179664-2">(</span><span class="n">DRV_CONNECT</span><span class="p">,</span><span class="w"> </span><span class="sc">$C</span><span class="p" data-group-id="6384179664-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6384179664-3">(</span><span class="n">DRV_DISCONNECT</span><span class="p">,</span><span class="w"> </span><span class="sc">$D</span><span class="p" data-group-id="6384179664-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6384179664-4">(</span><span class="n">DRV_SELECT</span><span class="p">,</span><span class="w"> </span><span class="sc">$S</span><span class="p" data-group-id="6384179664-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5524666530-5">(</span><span class="p" data-group-id="5524666530-6">[</span><span class="ss">connect</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">disconnect</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">select</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5524666530-6">]</span><span class="p" data-group-id="5524666530-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6384179664-5">(</span><span class="p" data-group-id="6384179664-6">[</span><span class="ss">connect</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">disconnect</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">select</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6384179664-6">]</span><span class="p" data-group-id="6384179664-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">connect</span><span class="p" data-group-id="5524666530-7">(</span><span class="n">ConnectStr</span><span class="p" data-group-id="5524666530-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="5524666530-8">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;pg_async&quot;</span><span class="p" data-group-id="5524666530-8">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">connect</span><span class="p" data-group-id="6384179664-7">(</span><span class="n">ConnectStr</span><span class="p" data-group-id="6384179664-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="6384179664-8">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;pg_async&quot;</span><span class="p" data-group-id="6384179664-8">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5524666530-9">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="5524666530-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="5524666530-10">(</span><span class="p" data-group-id="5524666530-11">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="5524666530-11">}</span><span class="p" data-group-id="5524666530-10">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="6384179664-9">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="6384179664-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="6384179664-10">(</span><span class="p" data-group-id="6384179664-11">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="6384179664-11">}</span><span class="p" data-group-id="6384179664-10">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="5524666530-12">(</span><span class="p" data-group-id="5524666530-13">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p" data-group-id="5524666530-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5524666530-14">[</span><span class="ss">binary</span><span class="p" data-group-id="5524666530-14">]</span><span class="p" data-group-id="5524666530-12">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">port_control</span><span class="p" data-group-id="5524666530-15">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_CONNECT</span><span class="p">,</span><span class="w"> </span><span class="n">ConnectStr</span><span class="p" data-group-id="5524666530-15">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">return_port_data</span><span class="p" data-group-id="5524666530-16">(</span><span class="n">Port</span><span class="p" data-group-id="5524666530-16">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="6384179664-12">(</span><span class="p" data-group-id="6384179664-13">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p" data-group-id="6384179664-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6384179664-14">[</span><span class="ss">binary</span><span class="p" data-group-id="6384179664-14">]</span><span class="p" data-group-id="6384179664-12">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">port_control</span><span class="p" data-group-id="6384179664-15">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_CONNECT</span><span class="p">,</span><span class="w"> </span><span class="n">ConnectStr</span><span class="p" data-group-id="6384179664-15">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">return_port_data</span><span class="p" data-group-id="6384179664-16">(</span><span class="n">Port</span><span class="p" data-group-id="6384179664-16">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="5524666530-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p" data-group-id="5524666530-17">}</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="6384179664-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p" data-group-id="6384179664-17">}</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">Error</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Error</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">disconnect</span><span class="p" data-group-id="5524666530-18">(</span><span class="n">Port</span><span class="p" data-group-id="5524666530-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">port_control</span><span class="p" data-group-id="5524666530-19">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_DISCONNECT</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p" data-group-id="5524666530-19">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">R</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">return_port_data</span><span class="p" data-group-id="5524666530-20">(</span><span class="n">Port</span><span class="p" data-group-id="5524666530-20">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">port_close</span><span class="p" data-group-id="5524666530-21">(</span><span class="n">Port</span><span class="p" data-group-id="5524666530-21">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">disconnect</span><span class="p" data-group-id="6384179664-18">(</span><span class="n">Port</span><span class="p" data-group-id="6384179664-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">port_control</span><span class="p" data-group-id="6384179664-19">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_DISCONNECT</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p" data-group-id="6384179664-19">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">R</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">return_port_data</span><span class="p" data-group-id="6384179664-20">(</span><span class="n">Port</span><span class="p" data-group-id="6384179664-20">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">port_close</span><span class="p" data-group-id="6384179664-21">(</span><span class="n">Port</span><span class="p" data-group-id="6384179664-21">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">R</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">select</span><span class="p" data-group-id="5524666530-22">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Query</span><span class="p" data-group-id="5524666530-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">port_control</span><span class="p" data-group-id="5524666530-23">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_SELECT</span><span class="p">,</span><span class="w"> </span><span class="n">Query</span><span class="p" data-group-id="5524666530-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">return_port_data</span><span class="p" data-group-id="5524666530-24">(</span><span class="n">Port</span><span class="p" data-group-id="5524666530-24">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">select</span><span class="p" data-group-id="6384179664-22">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Query</span><span class="p" data-group-id="6384179664-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">port_control</span><span class="p" data-group-id="6384179664-23">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">DRV_SELECT</span><span class="p">,</span><span class="w"> </span><span class="n">Query</span><span class="p" data-group-id="6384179664-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">return_port_data</span><span class="p" data-group-id="6384179664-24">(</span><span class="n">Port</span><span class="p" data-group-id="6384179664-24">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">return_port_data</span><span class="p" data-group-id="5524666530-25">(</span><span class="n">Port</span><span class="p" data-group-id="5524666530-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">return_port_data</span><span class="p" data-group-id="6384179664-25">(</span><span class="n">Port</span><span class="p" data-group-id="6384179664-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5524666530-26">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5524666530-27">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5524666530-27">}</span><span class="p" data-group-id="5524666530-26">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">binary_to_term</span><span class="p" data-group-id="5524666530-28">(</span><span class="n">Data</span><span class="p" data-group-id="5524666530-28">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="6384179664-26">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6384179664-27">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6384179664-27">}</span><span class="p" data-group-id="6384179664-26">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">binary_to_term</span><span class="p" data-group-id="6384179664-28">(</span><span class="n">Data</span><span class="p" data-group-id="6384179664-28">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The Erlang code is slightly different, as we do not return the result
│ │ │  synchronously from <a href="erlang.html#port_control/3"><code class="inline">port_control/3</code></a>, instead we get it from <a href="../../../erts-15.2.7/doc/html/erl_driver.html#driver_output" title=""><code class="inline">driver_output</code></a> as
│ │ │  data in the message queue. The function <code class="inline">return_port_data</code> above receives data
│ │ │  from the port. As the data is in binary format, we use
│ │ │  <a href="erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a> to convert it to an Erlang term. Notice
│ │ │  that the driver is opened in binary mode (<a href="erlang.html#open_port/2"><code class="inline">open_port/2</code></a> is
│ │ │  called with option <code class="inline">[binary]</code>). This means that data sent from the driver to the
│ │ │ @@ -677,59 +677,59 @@
│ │ │      *rp++ = ERL_DRV_LIST;
│ │ │      *rp++ = n+1;
│ │ │      driver_output_term(port, result, result_n);
│ │ │      delete[] result;
│ │ │      delete d;
│ │ │  }</code></pre><p>This driver is called like the others from Erlang. However, as we use
│ │ │  <a href="../../../erts-15.2.7/doc/html/erl_driver.html#driver_output_term" title=""><code class="inline">driver_output_term</code></a>, there is no need to call <a href="erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a>. The Erlang code
│ │ │ -is in the sample file <code class="inline">next_perm.erl</code>.</p><p>The input is changed into a list of integers and sent to the driver.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0405515683-1">(</span><span class="ss">next_perm</span><span class="p" data-group-id="0405515683-1">)</span><span class="p">.</span><span class="w">
│ │ │ +is in the sample file <code class="inline">next_perm.erl</code>.</p><p>The input is changed into a list of integers and sent to the driver.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6896875137-1">(</span><span class="ss">next_perm</span><span class="p" data-group-id="6896875137-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0405515683-2">(</span><span class="p" data-group-id="0405515683-3">[</span><span class="ss">next_perm</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">prev_perm</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">load</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">all_perm</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0405515683-3">]</span><span class="p" data-group-id="0405515683-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6896875137-2">(</span><span class="p" data-group-id="6896875137-3">[</span><span class="ss">next_perm</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">prev_perm</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">load</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">all_perm</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6896875137-3">]</span><span class="p" data-group-id="6896875137-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">load</span><span class="p" data-group-id="0405515683-4">(</span><span class="p" data-group-id="0405515683-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="0405515683-5">(</span><span class="ss">next_perm</span><span class="p" data-group-id="0405515683-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">load</span><span class="p" data-group-id="6896875137-4">(</span><span class="p" data-group-id="6896875137-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="6896875137-5">(</span><span class="ss">next_perm</span><span class="p" data-group-id="6896875137-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="0405515683-6">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;next_perm&quot;</span><span class="p" data-group-id="0405515683-6">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +            </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="6896875137-6">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;next_perm&quot;</span><span class="p" data-group-id="6896875137-6">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │                  </span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="0405515683-7">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="0405515683-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -                </span><span class="n">E</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="0405515683-8">(</span><span class="n">E</span><span class="p" data-group-id="0405515683-8">)</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="6896875137-7">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="6896875137-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ +                </span><span class="n">E</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="6896875137-8">(</span><span class="n">E</span><span class="p" data-group-id="6896875137-8">)</span><span class="w">
│ │ │              </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="0405515683-9">(</span><span class="p" data-group-id="0405515683-10">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;next_perm&quot;</span><span class="p" data-group-id="0405515683-10">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0405515683-11">[</span><span class="p" data-group-id="0405515683-11">]</span><span class="p" data-group-id="0405515683-9">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="0405515683-12">(</span><span class="ss">next_perm</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p" data-group-id="0405515683-12">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="6896875137-9">(</span><span class="p" data-group-id="6896875137-10">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;next_perm&quot;</span><span class="p" data-group-id="6896875137-10">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6896875137-11">[</span><span class="p" data-group-id="6896875137-11">]</span><span class="p" data-group-id="6896875137-9">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="6896875137-12">(</span><span class="ss">next_perm</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p" data-group-id="6896875137-12">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">ok</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">list_to_integer_binaries</span><span class="p" data-group-id="0405515683-13">(</span><span class="n">L</span><span class="p" data-group-id="0405515683-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0405515683-14">[</span><span class="p" data-group-id="0405515683-15">&lt;&lt;</span><span class="n">I</span><span class="p">:</span><span class="mi">32</span><span class="o">/</span><span class="ss">integer</span><span class="o">-</span><span class="ss">native</span><span class="p" data-group-id="0405515683-15">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0405515683-14">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">list_to_integer_binaries</span><span class="p" data-group-id="6896875137-13">(</span><span class="n">L</span><span class="p" data-group-id="6896875137-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6896875137-14">[</span><span class="p" data-group-id="6896875137-15">&lt;&lt;</span><span class="n">I</span><span class="p">:</span><span class="mi">32</span><span class="o">/</span><span class="ss">integer</span><span class="o">-</span><span class="ss">native</span><span class="p" data-group-id="6896875137-15">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6896875137-14">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">next_perm</span><span class="p" data-group-id="0405515683-16">(</span><span class="n">L</span><span class="p" data-group-id="0405515683-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">next_perm</span><span class="p" data-group-id="0405515683-17">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0405515683-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">next_perm</span><span class="p" data-group-id="6896875137-16">(</span><span class="n">L</span><span class="p" data-group-id="6896875137-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">next_perm</span><span class="p" data-group-id="6896875137-17">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6896875137-17">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">prev_perm</span><span class="p" data-group-id="0405515683-18">(</span><span class="n">L</span><span class="p" data-group-id="0405515683-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">next_perm</span><span class="p" data-group-id="0405515683-19">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0405515683-19">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">prev_perm</span><span class="p" data-group-id="6896875137-18">(</span><span class="n">L</span><span class="p" data-group-id="6896875137-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">next_perm</span><span class="p" data-group-id="6896875137-19">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6896875137-19">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">next_perm</span><span class="p" data-group-id="0405515683-20">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Nxt</span><span class="p" data-group-id="0405515683-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">load</span><span class="p" data-group-id="0405515683-21">(</span><span class="p" data-group-id="0405515683-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">B</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">list_to_integer_binaries</span><span class="p" data-group-id="0405515683-22">(</span><span class="n">L</span><span class="p" data-group-id="0405515683-22">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">port_control</span><span class="p" data-group-id="0405515683-23">(</span><span class="ss">next_perm</span><span class="p">,</span><span class="w"> </span><span class="n">Nxt</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="0405515683-23">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">next_perm</span><span class="p" data-group-id="6896875137-20">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Nxt</span><span class="p" data-group-id="6896875137-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">load</span><span class="p" data-group-id="6896875137-21">(</span><span class="p" data-group-id="6896875137-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">B</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">list_to_integer_binaries</span><span class="p" data-group-id="6896875137-22">(</span><span class="n">L</span><span class="p" data-group-id="6896875137-22">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">port_control</span><span class="p" data-group-id="6896875137-23">(</span><span class="ss">next_perm</span><span class="p">,</span><span class="w"> </span><span class="n">Nxt</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="6896875137-23">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="n">Result</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Result</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">all_perm</span><span class="p" data-group-id="0405515683-24">(</span><span class="n">L</span><span class="p" data-group-id="0405515683-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">New</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">prev_perm</span><span class="p" data-group-id="0405515683-25">(</span><span class="n">L</span><span class="p" data-group-id="0405515683-25">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">all_perm</span><span class="p" data-group-id="0405515683-26">(</span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0405515683-27">[</span><span class="n">New</span><span class="p" data-group-id="0405515683-27">]</span><span class="p" data-group-id="0405515683-26">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">all_perm</span><span class="p" data-group-id="6896875137-24">(</span><span class="n">L</span><span class="p" data-group-id="6896875137-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">New</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">prev_perm</span><span class="p" data-group-id="6896875137-25">(</span><span class="n">L</span><span class="p" data-group-id="6896875137-25">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">all_perm</span><span class="p" data-group-id="6896875137-26">(</span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6896875137-27">[</span><span class="n">New</span><span class="p" data-group-id="6896875137-27">]</span><span class="p" data-group-id="6896875137-26">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">all_perm</span><span class="p" data-group-id="0405515683-28">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0405515683-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">all_perm</span><span class="p" data-group-id="6896875137-28">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6896875137-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">all_perm</span><span class="p" data-group-id="0405515683-29">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Orig</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0405515683-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">New</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">prev_perm</span><span class="p" data-group-id="0405515683-30">(</span><span class="n">L</span><span class="p" data-group-id="0405515683-30">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">all_perm</span><span class="p" data-group-id="0405515683-31">(</span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">Orig</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0405515683-32">[</span><span class="n">New</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0405515683-32">]</span><span class="p" data-group-id="0405515683-31">)</span><span class="p">.</span></code></pre>
│ │ │ +</span><span class="nf">all_perm</span><span class="p" data-group-id="6896875137-29">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Orig</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6896875137-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">New</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">prev_perm</span><span class="p" data-group-id="6896875137-30">(</span><span class="n">L</span><span class="p" data-group-id="6896875137-30">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">all_perm</span><span class="p" data-group-id="6896875137-31">(</span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">Orig</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6896875137-32">[</span><span class="n">New</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6896875137-32">]</span><span class="p" data-group-id="6896875137-31">)</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="tty.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_cmd.html
│ │ │ @@ -149,26 +149,26 @@
│ │ │  runtime system, more specifically to the <code class="inline">init</code> system process, see <a href="init.html"><code class="inline">init</code></a>.</p><p>The <code class="inline">init</code> process itself interprets some of these flags, the <em>init flags</em>. It
│ │ │  also stores any remaining flags, the <em>user flags</em>. The latter can be retrieved
│ │ │  by calling <a href="init.html#get_argument/1"><code class="inline">init:get_argument/1</code></a>.</p><p>A small number of &quot;-&quot; flags exist, which now actually are emulator flags, see
│ │ │  the description below.</p></li><li><p>Plain arguments are not interpreted in any way. They are also stored by the
│ │ │  <code class="inline">init</code> process and can be retrieved by calling <a href="init.html#get_plain_arguments/0"><code class="inline">init:get_plain_arguments/0</code></a>.
│ │ │  Plain arguments can occur before the first flag, or after a <code class="inline">--</code> flag. Also,
│ │ │  the <code class="inline">-extra</code> flag causes everything that follows to become plain arguments.</p></li></ul><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl +W w -sname arnie +R 9 -s my_init -extra +bertie</span><span class="gp unselectable">
│ │ │ -(arnie@host)1&gt; </span><span class="nc">init</span><span class="p">:</span><span class="nf">get_argument</span><span class="p" data-group-id="6571632020-1">(</span><span class="ss">sname</span><span class="p" data-group-id="6571632020-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6571632020-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="6571632020-3">[</span><span class="p" data-group-id="6571632020-4">[</span><span class="s">&quot;arnie&quot;</span><span class="p" data-group-id="6571632020-4">]</span><span class="p" data-group-id="6571632020-3">]</span><span class="p" data-group-id="6571632020-2">}</span><span class="gp unselectable">
│ │ │ -(arnie@host)2&gt; </span><span class="nc">init</span><span class="p">:</span><span class="nf">get_plain_arguments</span><span class="p" data-group-id="6571632020-5">(</span><span class="p" data-group-id="6571632020-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6571632020-6">[</span><span class="s">&quot;+bertie&quot;</span><span class="p" data-group-id="6571632020-6">]</span></code></pre><p>Here <code class="inline">+W w</code> and <code class="inline">+R 9</code> are emulator flags. <code class="inline">-s my_init</code> is an init flag,
│ │ │ +(arnie@host)1&gt; </span><span class="nc">init</span><span class="p">:</span><span class="nf">get_argument</span><span class="p" data-group-id="2078254726-1">(</span><span class="ss">sname</span><span class="p" data-group-id="2078254726-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2078254726-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="2078254726-3">[</span><span class="p" data-group-id="2078254726-4">[</span><span class="s">&quot;arnie&quot;</span><span class="p" data-group-id="2078254726-4">]</span><span class="p" data-group-id="2078254726-3">]</span><span class="p" data-group-id="2078254726-2">}</span><span class="gp unselectable">
│ │ │ +(arnie@host)2&gt; </span><span class="nc">init</span><span class="p">:</span><span class="nf">get_plain_arguments</span><span class="p" data-group-id="2078254726-5">(</span><span class="p" data-group-id="2078254726-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2078254726-6">[</span><span class="s">&quot;+bertie&quot;</span><span class="p" data-group-id="2078254726-6">]</span></code></pre><p>Here <code class="inline">+W w</code> and <code class="inline">+R 9</code> are emulator flags. <code class="inline">-s my_init</code> is an init flag,
│ │ │  interpreted by <code class="inline">init</code>. <code class="inline">-sname arnie</code> is a user flag, stored by <code class="inline">init</code>. It is
│ │ │  read by Kernel and causes the Erlang runtime system to become distributed.
│ │ │  Finally, everything after <code class="inline">-extra</code> (that is, <code class="inline">+bertie</code>) is considered as plain
│ │ │  arguments.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -myflag 1</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nc">init</span><span class="p">:</span><span class="nf">get_argument</span><span class="p" data-group-id="0729654231-1">(</span><span class="ss">myflag</span><span class="p" data-group-id="0729654231-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0729654231-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="0729654231-3">[</span><span class="p" data-group-id="0729654231-4">[</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="0729654231-4">]</span><span class="p" data-group-id="0729654231-3">]</span><span class="p" data-group-id="0729654231-2">}</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nc">init</span><span class="p">:</span><span class="nf">get_plain_arguments</span><span class="p" data-group-id="0729654231-5">(</span><span class="p" data-group-id="0729654231-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0729654231-6">[</span><span class="p" data-group-id="0729654231-6">]</span></code></pre><p>Here the user flag <code class="inline">-myflag 1</code> is passed to and stored by the <code class="inline">init</code> process. It
│ │ │ +1&gt; </span><span class="nc">init</span><span class="p">:</span><span class="nf">get_argument</span><span class="p" data-group-id="2702487099-1">(</span><span class="ss">myflag</span><span class="p" data-group-id="2702487099-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2702487099-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="2702487099-3">[</span><span class="p" data-group-id="2702487099-4">[</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="2702487099-4">]</span><span class="p" data-group-id="2702487099-3">]</span><span class="p" data-group-id="2702487099-2">}</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nc">init</span><span class="p">:</span><span class="nf">get_plain_arguments</span><span class="p" data-group-id="2702487099-5">(</span><span class="p" data-group-id="2702487099-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2702487099-6">[</span><span class="p" data-group-id="2702487099-6">]</span></code></pre><p>Here the user flag <code class="inline">-myflag 1</code> is passed to and stored by the <code class="inline">init</code> process. It
│ │ │  is a user-defined flag, presumably used by some user-defined application.</p><h2 id="flags" class="section-heading">
│ │ │    <a href="#flags" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Flags</span>
│ │ │  </h2>
│ │ │  <p>In the following list, init flags are marked &quot;(init flag)&quot;. Unless otherwise
│ │ │ @@ -700,15 +700,15 @@
│ │ │  processes) into a smaller set of schedulers when schedulers frequently run
│ │ │  out of work. When disabled, the frequency with which schedulers run out of
│ │ │  work is not taken into account by the load balancing logic.</p><p><code class="inline">+scl false</code> is similar to <a href="#%2Bsub"><code class="inline">+sub true</code></a>, but <code class="inline">+sub true</code>
│ │ │  also balances scheduler utilization between schedulers.</p></li><li><p><strong><code class="inline" id="+sct">+sct CpuTopology</code></strong> - Sets a user-defined CPU topology.
│ │ │  The user-defined CPU topology overrides
│ │ │  any automatically detected CPU topology. The CPU topology is used when
│ │ │  <a href="#%2Bsbt">binding schedulers to logical processors</a>. This option must be before
│ │ │ -<a href="#%2Bsbt"><code class="inline">+sbt</code></a> on the command-line.</p><pre><code class="makeup erlang" translate="no"><span class="o">&lt;</span><span class="n">Id</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="3891135085-1">(</span><span class="p" data-group-id="3891135085-1">)</span><span class="p">;</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="o">&lt;</span><span class="n">Id</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mi">65535</span><span class="w">
│ │ │ +<a href="#%2Bsbt"><code class="inline">+sbt</code></a> on the command-line.</p><pre><code class="makeup erlang" translate="no"><span class="o">&lt;</span><span class="n">Id</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="3483404998-1">(</span><span class="p" data-group-id="3483404998-1">)</span><span class="p">;</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="o">&lt;</span><span class="n">Id</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mi">65535</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="n">IdRange</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">&lt;</span><span class="n">Id</span><span class="o">&gt;</span><span class="o">-</span><span class="o">&lt;</span><span class="n">Id</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="n">IdOrIdRange</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">&lt;</span><span class="n">Id</span><span class="o">&gt;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="o">&lt;</span><span class="n">IdRange</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="n">IdList</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">&lt;</span><span class="n">IdOrIdRange</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="n">IdOrIdRange</span><span class="o">&gt;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="o">&lt;</span><span class="n">IdOrIdRange</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="n">LogicalIds</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L</span><span class="o">&lt;</span><span class="n">IdList</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="n">ThreadIds</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="o">&lt;</span><span class="n">IdList</span><span class="o">&gt;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">t</span><span class="o">&lt;</span><span class="n">IdList</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="n">CoreIds</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">C</span><span class="o">&lt;</span><span class="n">IdList</span><span class="o">&gt;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">c</span><span class="o">&lt;</span><span class="n">IdList</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="n">ProcessorIds</span><span class="o">&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">&lt;</span><span class="n">IdList</span><span class="o">&gt;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">p</span><span class="o">&lt;</span><span class="n">IdList</span><span class="o">&gt;</span><span class="w">
│ │ │ @@ -733,30 +733,30 @@
│ │ │  node.</li><li><code class="inline">&lt;LogicalIds&gt;&lt;ThreadIds&gt;&lt;CoreIds&gt;&lt;NodeIds&gt;&lt;ProcessorIds&gt;</code>, that is, thread
│ │ │  is part of a core that is part of a NUMA node, which is part of a
│ │ │  processor.</li></ul><p>A CPU topology can consist of both processor external, and processor
│ │ │  internal NUMA nodes as long as each logical processor belongs to only one
│ │ │  NUMA node. If <code class="inline">&lt;ProcessorIds&gt;</code> is omitted, its default position is before
│ │ │  <code class="inline">&lt;NodeIds&gt;</code>. That is, the default is processor external NUMA nodes.</p><p>If a list of identifiers is used in an <code class="inline">&lt;IdDefs&gt;</code>:</p><ul><li><code class="inline">&lt;LogicalIds&gt;</code> must be a list of identifiers.</li><li>At least one other identifier type besides <code class="inline">&lt;LogicalIds&gt;</code> must also have a
│ │ │  list of identifiers.</li><li>All lists of identifiers must produce the same number of identifiers.</li></ul><p>A simple example. A single quad core processor can be described as follows:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl +sct L0-3c0-3</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="7793232018-1">(</span><span class="ss">cpu_topology</span><span class="p" data-group-id="7793232018-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7793232018-2">[</span><span class="p" data-group-id="7793232018-3">{</span><span class="ss">processor</span><span class="p">,</span><span class="p" data-group-id="7793232018-4">[</span><span class="p" data-group-id="7793232018-5">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="7793232018-6">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="7793232018-6">}</span><span class="p" data-group-id="7793232018-5">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="7793232018-7">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="7793232018-8">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7793232018-8">}</span><span class="p" data-group-id="7793232018-7">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="7793232018-9">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="7793232018-10">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7793232018-10">}</span><span class="p" data-group-id="7793232018-9">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="7793232018-11">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="7793232018-12">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7793232018-12">}</span><span class="p" data-group-id="7793232018-11">}</span><span class="p" data-group-id="7793232018-4">]</span><span class="p" data-group-id="7793232018-3">}</span><span class="p" data-group-id="7793232018-2">]</span></code></pre><p>A more complicated example with two quad core processors, each processor in
│ │ │ +1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="6103418186-1">(</span><span class="ss">cpu_topology</span><span class="p" data-group-id="6103418186-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6103418186-2">[</span><span class="p" data-group-id="6103418186-3">{</span><span class="ss">processor</span><span class="p">,</span><span class="p" data-group-id="6103418186-4">[</span><span class="p" data-group-id="6103418186-5">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="6103418186-6">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="6103418186-6">}</span><span class="p" data-group-id="6103418186-5">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="6103418186-7">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="6103418186-8">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6103418186-8">}</span><span class="p" data-group-id="6103418186-7">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="6103418186-9">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="6103418186-10">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6103418186-10">}</span><span class="p" data-group-id="6103418186-9">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="6103418186-11">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="6103418186-12">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6103418186-12">}</span><span class="p" data-group-id="6103418186-11">}</span><span class="p" data-group-id="6103418186-4">]</span><span class="p" data-group-id="6103418186-3">}</span><span class="p" data-group-id="6103418186-2">]</span></code></pre><p>A more complicated example with two quad core processors, each processor in
│ │ │  its own NUMA node. The ordering of logical processors is a bit weird. This
│ │ │  to give a better example of identifier lists:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl +sct L0-1,3-2c0-3p0N0:L7,4,6-5c0-3p1N1</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="5968121849-1">(</span><span class="ss">cpu_topology</span><span class="p" data-group-id="5968121849-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5968121849-2">[</span><span class="p" data-group-id="5968121849-3">{</span><span class="nb">node</span><span class="p">,</span><span class="p" data-group-id="5968121849-4">[</span><span class="p" data-group-id="5968121849-5">{</span><span class="ss">processor</span><span class="p">,</span><span class="p" data-group-id="5968121849-6">[</span><span class="p" data-group-id="5968121849-7">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="5968121849-8">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="5968121849-8">}</span><span class="p" data-group-id="5968121849-7">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="5968121849-9">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="5968121849-10">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5968121849-10">}</span><span class="p" data-group-id="5968121849-9">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="5968121849-11">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="5968121849-12">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5968121849-12">}</span><span class="p" data-group-id="5968121849-11">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="5968121849-13">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="5968121849-14">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5968121849-14">}</span><span class="p" data-group-id="5968121849-13">}</span><span class="p" data-group-id="5968121849-6">]</span><span class="p" data-group-id="5968121849-5">}</span><span class="p" data-group-id="5968121849-4">]</span><span class="p" data-group-id="5968121849-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5968121849-15">{</span><span class="nb">node</span><span class="p">,</span><span class="p" data-group-id="5968121849-16">[</span><span class="p" data-group-id="5968121849-17">{</span><span class="ss">processor</span><span class="p">,</span><span class="p" data-group-id="5968121849-18">[</span><span class="p" data-group-id="5968121849-19">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="5968121849-20">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="5968121849-20">}</span><span class="p" data-group-id="5968121849-19">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="5968121849-21">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="5968121849-22">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5968121849-22">}</span><span class="p" data-group-id="5968121849-21">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="5968121849-23">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="5968121849-24">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5968121849-24">}</span><span class="p" data-group-id="5968121849-23">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="5968121849-25">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="5968121849-26">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5968121849-26">}</span><span class="p" data-group-id="5968121849-25">}</span><span class="p" data-group-id="5968121849-18">]</span><span class="p" data-group-id="5968121849-17">}</span><span class="p" data-group-id="5968121849-16">]</span><span class="p" data-group-id="5968121849-15">}</span><span class="p" data-group-id="5968121849-2">]</span></code></pre><p>As long as real identifiers are correct, it is OK to pass a CPU topology
│ │ │ +1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="3704800404-1">(</span><span class="ss">cpu_topology</span><span class="p" data-group-id="3704800404-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3704800404-2">[</span><span class="p" data-group-id="3704800404-3">{</span><span class="nb">node</span><span class="p">,</span><span class="p" data-group-id="3704800404-4">[</span><span class="p" data-group-id="3704800404-5">{</span><span class="ss">processor</span><span class="p">,</span><span class="p" data-group-id="3704800404-6">[</span><span class="p" data-group-id="3704800404-7">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="3704800404-8">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="3704800404-8">}</span><span class="p" data-group-id="3704800404-7">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="3704800404-9">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="3704800404-10">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3704800404-10">}</span><span class="p" data-group-id="3704800404-9">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="3704800404-11">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="3704800404-12">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3704800404-12">}</span><span class="p" data-group-id="3704800404-11">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="3704800404-13">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="3704800404-14">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3704800404-14">}</span><span class="p" data-group-id="3704800404-13">}</span><span class="p" data-group-id="3704800404-6">]</span><span class="p" data-group-id="3704800404-5">}</span><span class="p" data-group-id="3704800404-4">]</span><span class="p" data-group-id="3704800404-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3704800404-15">{</span><span class="nb">node</span><span class="p">,</span><span class="p" data-group-id="3704800404-16">[</span><span class="p" data-group-id="3704800404-17">{</span><span class="ss">processor</span><span class="p">,</span><span class="p" data-group-id="3704800404-18">[</span><span class="p" data-group-id="3704800404-19">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="3704800404-20">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3704800404-20">}</span><span class="p" data-group-id="3704800404-19">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="3704800404-21">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="3704800404-22">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3704800404-22">}</span><span class="p" data-group-id="3704800404-21">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="3704800404-23">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="3704800404-24">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="3704800404-24">}</span><span class="p" data-group-id="3704800404-23">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="3704800404-25">{</span><span class="ss">core</span><span class="p">,</span><span class="p" data-group-id="3704800404-26">{</span><span class="ss">logical</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3704800404-26">}</span><span class="p" data-group-id="3704800404-25">}</span><span class="p" data-group-id="3704800404-18">]</span><span class="p" data-group-id="3704800404-17">}</span><span class="p" data-group-id="3704800404-16">]</span><span class="p" data-group-id="3704800404-15">}</span><span class="p" data-group-id="3704800404-2">]</span></code></pre><p>As long as real identifiers are correct, it is OK to pass a CPU topology
│ │ │  that is not a correct description of the CPU topology. When used with care
│ │ │  this can be very useful. This to trick the emulator to bind its schedulers
│ │ │  as you want. For example, if you want to run multiple Erlang runtime systems
│ │ │  on the same machine, you want to reduce the number of schedulers used and
│ │ │  manipulate the CPU topology so that they bind to different logical CPUs. An
│ │ │  example, with two Erlang runtime systems on a quad core machine:</p><pre><code class="text">% erl +sct L0-3c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname one
│ │ │  % erl +sct L3-0c0-3 +sbt db +S3:2 -detached -noinput -noshell -sname two</code></pre><p>In this example, each runtime system have two schedulers each online, and
│ │ │ @@ -923,18 +923,18 @@
│ │ │  </h2>
│ │ │  <p>The standard Erlang/OTP system can be reconfigured to change the default
│ │ │  behavior on startup.</p><ul><li><p><strong>The <code class="inline">.erlang</code> startup file</strong> - When Erlang/OTP is started, the system
│ │ │  searches for a file named <code class="inline">.erlang</code> in the
│ │ │  <a href="init.html#home">user's home directory</a> and then
│ │ │  <a href="../../../lib/stdlib-6.2.2.1/doc/html/filename.html#user_config"><code class="inline">filename:basedir(user_config, &quot;erlang&quot;)</code></a>.</p><p>If an <code class="inline">.erlang</code> file is found, it is assumed to contain valid Erlang
│ │ │  expressions. These expressions are evaluated as if they were input to the
│ │ │ -shell.</p><p>A typical <code class="inline">.erlang</code> file contains a set of search paths, for example:</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2610717355-1">(</span><span class="s">&quot;executing user profile in $HOME/.erlang\n&quot;</span><span class="p">,</span><span class="p" data-group-id="2610717355-2">[</span><span class="p" data-group-id="2610717355-2">]</span><span class="p" data-group-id="2610717355-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nc">code</span><span class="p">:</span><span class="nf">add_path</span><span class="p" data-group-id="2610717355-3">(</span><span class="s">&quot;/home/calvin/test/ebin&quot;</span><span class="p" data-group-id="2610717355-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nc">code</span><span class="p">:</span><span class="nf">add_path</span><span class="p" data-group-id="2610717355-4">(</span><span class="s">&quot;/home/hobbes/bigappl-1.2/ebin&quot;</span><span class="p" data-group-id="2610717355-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2610717355-5">(</span><span class="s">&quot;.erlang rc finished\n&quot;</span><span class="p">,</span><span class="p" data-group-id="2610717355-6">[</span><span class="p" data-group-id="2610717355-6">]</span><span class="p" data-group-id="2610717355-5">)</span><span class="p">.</span></code></pre></li><li><p><strong>user_default</strong> and <strong>shell_default</strong> - Functions in the shell that are not
│ │ │ +shell.</p><p>A typical <code class="inline">.erlang</code> file contains a set of search paths, for example:</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5494232321-1">(</span><span class="s">&quot;executing user profile in $HOME/.erlang\n&quot;</span><span class="p">,</span><span class="p" data-group-id="5494232321-2">[</span><span class="p" data-group-id="5494232321-2">]</span><span class="p" data-group-id="5494232321-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nc">code</span><span class="p">:</span><span class="nf">add_path</span><span class="p" data-group-id="5494232321-3">(</span><span class="s">&quot;/home/calvin/test/ebin&quot;</span><span class="p" data-group-id="5494232321-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nc">code</span><span class="p">:</span><span class="nf">add_path</span><span class="p" data-group-id="5494232321-4">(</span><span class="s">&quot;/home/hobbes/bigappl-1.2/ebin&quot;</span><span class="p" data-group-id="5494232321-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5494232321-5">(</span><span class="s">&quot;.erlang rc finished\n&quot;</span><span class="p">,</span><span class="p" data-group-id="5494232321-6">[</span><span class="p" data-group-id="5494232321-6">]</span><span class="p" data-group-id="5494232321-5">)</span><span class="p">.</span></code></pre></li><li><p><strong>user_default</strong> and <strong>shell_default</strong> - Functions in the shell that are not
│ │ │  prefixed by a module name are assumed to be functional objects (funs),
│ │ │  built-in functions (BIFs), or belong to the module <code class="inline">user_default</code> or
│ │ │  <code class="inline">shell_default</code>.</p><p>To include private shell commands, define them in a module <code class="inline">user_default</code> and
│ │ │  add the following argument as the first line in the <code class="inline">.erlang</code> file:</p><pre><code class="text">code:load_abs(&quot;..../user_default&quot;).</code></pre></li><li><p><strong>erl</strong> - If the contents of <code class="inline">.erlang</code> are changed and a private version of
│ │ │  <code class="inline">user_default</code> is defined, the Erlang/OTP environment can be customized. More
│ │ │  powerful changes can be made by supplying command-line arguments in the
│ │ │  startup script <code class="inline">erl</code>. For more information, see <a href="init.html"><code class="inline">init</code></a>.</p></li></ul><h2 id="see-also" class="section-heading">
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_dist_protocol.html
│ │ │ @@ -252,32 +252,32 @@
│ │ │  ---
│ │ │  sequenceDiagram
│ │ │      participant client as Client (or Node)
│ │ │      participant EPMD
│ │ │      
│ │ │      client -&gt;&gt; EPMD: NAMES_REQ
│ │ │      EPMD --&gt;&gt; client: NAMES_RESP</code></pre><table><thead><tr><th style="text-align: left;">1</th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">110</code></td></tr></tbody></table><p><em>Table: NAMES_REQ (110)</em></p><p>The response for a <code class="inline">NAMES_REQ</code> is as follows:</p><table><thead><tr><th style="text-align: left;">4</th><th style="text-align: left;"></th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">EPMDPortNo</code></td><td style="text-align: left;"><code class="inline">NodeInfo*</code></td></tr></tbody></table><p><em>Table: NAMES_RESP</em></p><p><code class="inline">NodeInfo</code> is a string written for each active node. When all <code class="inline">NodeInfo</code> has
│ │ │ -been written the connection is closed by the EPMD.</p><p><code class="inline">NodeInfo</code> is, as expressed in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5774863408-1">(</span><span class="s">&quot;name ~ts at port </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5774863408-2">[</span><span class="n">NodeName</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p" data-group-id="5774863408-2">]</span><span class="p" data-group-id="5774863408-1">)</span><span class="p">.</span></code></pre><h3 id="dump-all-data-from-epmd" class="section-heading">
│ │ │ +been written the connection is closed by the EPMD.</p><p><code class="inline">NodeInfo</code> is, as expressed in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5870792586-1">(</span><span class="s">&quot;name ~ts at port </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5870792586-2">[</span><span class="n">NodeName</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p" data-group-id="5870792586-2">]</span><span class="p" data-group-id="5870792586-1">)</span><span class="p">.</span></code></pre><h3 id="dump-all-data-from-epmd" class="section-heading">
│ │ │    <a href="#dump-all-data-from-epmd" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Dump All Data from EPMD</span>
│ │ │  </h3>
│ │ │  <p>This request is not really used, it is to be regarded as a debug feature.</p><pre><code class="mermaid">---
│ │ │  title: Dump All Data from EPMD
│ │ │  ---
│ │ │  sequenceDiagram
│ │ │      participant client as Client (or Node)
│ │ │      participant EPMD
│ │ │      
│ │ │      client -&gt;&gt; EPMD: DUMP_REQ
│ │ │      EPMD --&gt;&gt; client: DUMP_RESP</code></pre><table><thead><tr><th style="text-align: left;">1</th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">100</code></td></tr></tbody></table><p><em>Table: DUMP_REQ</em></p><p>The response for a <code class="inline">DUMP_REQ</code> is as follows:</p><table><thead><tr><th style="text-align: left;">4</th><th style="text-align: left;"></th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">EPMDPortNo</code></td><td style="text-align: left;"><code class="inline">NodeInfo*</code></td></tr></tbody></table><p><em>Table: DUMP_RESP</em></p><p><code class="inline">NodeInfo</code> is a string written for each node kept in the EPMD. When all
│ │ │ -<code class="inline">NodeInfo</code> has been written the connection is closed by the EPMD.</p><p><code class="inline">NodeInfo</code> is, as expressed in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0526090250-1">(</span><span class="s">&quot;active name     ~ts at port </span><span class="si">~p</span><span class="s">, fd = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="0526090250-2">[</span><span class="n">NodeName</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="0526090250-2">]</span><span class="p" data-group-id="0526090250-1">)</span><span class="p">.</span></code></pre><p>or</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3551526848-1">(</span><span class="s">&quot;old/unused name ~ts at port </span><span class="si">~p</span><span class="s">, fd = </span><span class="si">~p</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="3551526848-2">[</span><span class="n">NodeName</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="3551526848-2">]</span><span class="p" data-group-id="3551526848-1">)</span><span class="p">.</span></code></pre><h3 id="kill-epmd" class="section-heading">
│ │ │ +<code class="inline">NodeInfo</code> has been written the connection is closed by the EPMD.</p><p><code class="inline">NodeInfo</code> is, as expressed in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3916977044-1">(</span><span class="s">&quot;active name     ~ts at port </span><span class="si">~p</span><span class="s">, fd = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="3916977044-2">[</span><span class="n">NodeName</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="3916977044-2">]</span><span class="p" data-group-id="3916977044-1">)</span><span class="p">.</span></code></pre><p>or</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2836898321-1">(</span><span class="s">&quot;old/unused name ~ts at port </span><span class="si">~p</span><span class="s">, fd = </span><span class="si">~p</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="2836898321-2">[</span><span class="n">NodeName</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2836898321-2">]</span><span class="p" data-group-id="2836898321-1">)</span><span class="p">.</span></code></pre><h3 id="kill-epmd" class="section-heading">
│ │ │    <a href="#kill-epmd" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Kill EPMD</span>
│ │ │  </h3>
│ │ │  <p>This request kills the running EPMD. It is almost never used.</p><pre><code class="mermaid">---
│ │ │  title: Kill EPMD
│ │ │ @@ -407,54 +407,54 @@
│ │ │  received from <code class="inline">A</code> is correct and generates a digest from the challenge
│ │ │  received from <code class="inline">A</code>. The digest is then sent to <code class="inline">A</code>. The message is as follows:</p><table><thead><tr><th style="text-align: left;">1</th><th style="text-align: left;">16</th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">'a'</code></td><td style="text-align: left;"><code class="inline">Digest</code></td></tr></tbody></table><p><em>Table: The challenge_ack message</em></p><p><code class="inline">Digest</code> is the digest calculated by <code class="inline">B</code> for <code class="inline">A</code>'s challenge.</p></li><li><p><strong>7) check</strong> - <code class="inline">A</code> checks the digest from <code class="inline">B</code> and the connection is up.</p></li></ul><h3 id="semigraphic-view" class="section-heading">
│ │ │    <a href="#semigraphic-view" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Semigraphic View</span>
│ │ │  </h3>
│ │ │ -<pre><code class="makeup erlang" translate="no"><span class="n">A</span><span class="w"> </span><span class="p" data-group-id="6641783056-1">(</span><span class="ss">initiator</span><span class="p" data-group-id="6641783056-1">)</span><span class="w">                                      </span><span class="n">B</span><span class="w"> </span><span class="p" data-group-id="6641783056-2">(</span><span class="ss">acceptor</span><span class="p" data-group-id="6641783056-2">)</span><span class="w">
│ │ │ +<pre><code class="makeup erlang" translate="no"><span class="n">A</span><span class="w"> </span><span class="p" data-group-id="4526609730-1">(</span><span class="ss">initiator</span><span class="p" data-group-id="4526609730-1">)</span><span class="w">                                      </span><span class="n">B</span><span class="w"> </span><span class="p" data-group-id="4526609730-2">(</span><span class="ss">acceptor</span><span class="p" data-group-id="4526609730-2">)</span><span class="w">
│ │ │  
│ │ │  </span><span class="n">TCP</span><span class="w"> </span><span class="ss">connect</span><span class="w"> </span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">&gt;</span><span class="w">
│ │ │                                                     </span><span class="n">TCP</span><span class="w"> </span><span class="ss">accept</span><span class="w">
│ │ │  
│ │ │  </span><span class="ss">send_name</span><span class="w"> </span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">&gt;</span><span class="w">
│ │ │                                                     </span><span class="ss">recv_name</span><span class="w">
│ │ │  
│ │ │    </span><span class="o">&lt;-</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">-</span><span class="w"> </span><span class="ss">send_status</span><span class="w">
│ │ │  </span><span class="nf">recv_status</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6641783056-3">(</span><span class="k">if</span><span class="w"> </span><span class="ss">status</span><span class="w"> </span><span class="ss">was</span><span class="w"> </span><span class="ss">&#39;alive&#39;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4526609730-3">(</span><span class="k">if</span><span class="w"> </span><span class="ss">status</span><span class="w"> </span><span class="ss">was</span><span class="w"> </span><span class="ss">&#39;alive&#39;</span><span class="w">
│ │ │   </span><span class="ss">send_status</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                                                   </span><span class="ss">recv_status</span><span class="p" data-group-id="6641783056-3">)</span><span class="w">
│ │ │ +                                                   </span><span class="ss">recv_status</span><span class="p" data-group-id="4526609730-3">)</span><span class="w">
│ │ │  
│ │ │ -                          </span><span class="p" data-group-id="6641783056-4">(</span><span class="n">ChB</span><span class="p" data-group-id="6641783056-4">)</span><span class="w">                      </span><span class="n">ChB</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">gen_challenge</span><span class="p" data-group-id="6641783056-5">(</span><span class="p" data-group-id="6641783056-5">)</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="4526609730-4">(</span><span class="n">ChB</span><span class="p" data-group-id="4526609730-4">)</span><span class="w">                      </span><span class="n">ChB</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">gen_challenge</span><span class="p" data-group-id="4526609730-5">(</span><span class="p" data-group-id="4526609730-5">)</span><span class="w">
│ │ │    </span><span class="o">&lt;-</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">-</span><span class="w"> </span><span class="ss">send_challenge</span><span class="w">
│ │ │  </span><span class="nf">recv_challenge</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="6641783056-6">(</span><span class="k">if</span><span class="w"> </span><span class="ss">old</span><span class="w"> </span><span class="ss">send_name</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4526609730-6">(</span><span class="k">if</span><span class="w"> </span><span class="ss">old</span><span class="w"> </span><span class="ss">send_name</span><span class="w">
│ │ │   </span><span class="ss">send_complement</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                                                   </span><span class="ss">recv_complement</span><span class="p" data-group-id="6641783056-6">)</span><span class="w">
│ │ │ +                                                   </span><span class="ss">recv_complement</span><span class="p" data-group-id="4526609730-6">)</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">ChA</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">gen_challenge</span><span class="p" data-group-id="6641783056-7">(</span><span class="p" data-group-id="6641783056-7">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">OCA</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">out_cookie</span><span class="p" data-group-id="6641783056-8">(</span><span class="n">B</span><span class="p" data-group-id="6641783056-8">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">DiA</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">gen_digest</span><span class="p" data-group-id="6641783056-9">(</span><span class="n">ChB</span><span class="p">,</span><span class="w"> </span><span class="n">OCA</span><span class="p" data-group-id="6641783056-9">)</span><span class="w">
│ │ │ -                          </span><span class="p" data-group-id="6641783056-10">(</span><span class="n">ChA</span><span class="p">,</span><span class="w"> </span><span class="n">DiA</span><span class="p" data-group-id="6641783056-10">)</span><span class="w">
│ │ │ +</span><span class="n">ChA</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">gen_challenge</span><span class="p" data-group-id="4526609730-7">(</span><span class="p" data-group-id="4526609730-7">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">OCA</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">out_cookie</span><span class="p" data-group-id="4526609730-8">(</span><span class="n">B</span><span class="p" data-group-id="4526609730-8">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">DiA</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">gen_digest</span><span class="p" data-group-id="4526609730-9">(</span><span class="n">ChB</span><span class="p">,</span><span class="w"> </span><span class="n">OCA</span><span class="p" data-group-id="4526609730-9">)</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="4526609730-10">(</span><span class="n">ChA</span><span class="p">,</span><span class="w"> </span><span class="n">DiA</span><span class="p" data-group-id="4526609730-10">)</span><span class="w">
│ │ │  </span><span class="ss">send_challenge_reply</span><span class="w"> </span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="p">-&gt;</span><span class="w">
│ │ │                                                     </span><span class="ss">recv_challenge_reply</span><span class="w">
│ │ │ -                                                   </span><span class="n">ICB</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">in_cookie</span><span class="p" data-group-id="6641783056-11">(</span><span class="n">A</span><span class="p" data-group-id="6641783056-11">)</span><span class="p">,</span><span class="w">
│ │ │ +                                                   </span><span class="n">ICB</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">in_cookie</span><span class="p" data-group-id="4526609730-11">(</span><span class="n">A</span><span class="p" data-group-id="4526609730-11">)</span><span class="p">,</span><span class="w">
│ │ │                                                     </span><span class="nc">check</span><span class="p">:</span><span class="w">
│ │ │ -                                                   </span><span class="n">DiA</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nf">gen_digest</span><span class="w"> </span><span class="p" data-group-id="6641783056-12">(</span><span class="n">ChB</span><span class="p">,</span><span class="w"> </span><span class="n">ICB</span><span class="p" data-group-id="6641783056-12">)</span><span class="o">?</span><span class="w">
│ │ │ +                                                   </span><span class="n">DiA</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nf">gen_digest</span><span class="w"> </span><span class="p" data-group-id="4526609730-12">(</span><span class="n">ChB</span><span class="p">,</span><span class="w"> </span><span class="n">ICB</span><span class="p" data-group-id="4526609730-12">)</span><span class="o">?</span><span class="w">
│ │ │  </span><span class="w">                                                   </span><span class="p">-</span><span class="w"> </span><span class="na">if</span><span class="w"> </span><span class="n">OK</span><span class="p">:</span><span class="w">
│ │ │ -                                                    </span><span class="n">OCB</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">out_cookie</span><span class="p" data-group-id="6641783056-13">(</span><span class="n">A</span><span class="p" data-group-id="6641783056-13">)</span><span class="p">,</span><span class="w">
│ │ │ -                                                    </span><span class="n">DiB</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">gen_digest</span><span class="w"> </span><span class="p" data-group-id="6641783056-14">(</span><span class="n">ChA</span><span class="p">,</span><span class="w"> </span><span class="n">OCB</span><span class="p" data-group-id="6641783056-14">)</span><span class="w">
│ │ │ -                          </span><span class="p" data-group-id="6641783056-15">(</span><span class="n">DiB</span><span class="p" data-group-id="6641783056-15">)</span><span class="w">
│ │ │ +                                                    </span><span class="n">OCB</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">out_cookie</span><span class="p" data-group-id="4526609730-13">(</span><span class="n">A</span><span class="p" data-group-id="4526609730-13">)</span><span class="p">,</span><span class="w">
│ │ │ +                                                    </span><span class="n">DiB</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">gen_digest</span><span class="w"> </span><span class="p" data-group-id="4526609730-14">(</span><span class="n">ChA</span><span class="p">,</span><span class="w"> </span><span class="n">OCB</span><span class="p" data-group-id="4526609730-14">)</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="4526609730-15">(</span><span class="n">DiB</span><span class="p" data-group-id="4526609730-15">)</span><span class="w">
│ │ │    </span><span class="o">&lt;-</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="w"> </span><span class="ss">send_challenge_ack</span><span class="w">
│ │ │  </span><span class="ss">recv_challenge_ack</span><span class="w">                                  </span><span class="n">DONE</span><span class="w">
│ │ │ -</span><span class="n">ICA</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">in_cookie</span><span class="p" data-group-id="6641783056-16">(</span><span class="n">B</span><span class="p" data-group-id="6641783056-16">)</span><span class="p">,</span><span class="w">                                </span><span class="o">-</span><span class="w"> </span><span class="nc">else</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="n">ICA</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">in_cookie</span><span class="p" data-group-id="4526609730-16">(</span><span class="n">B</span><span class="p" data-group-id="4526609730-16">)</span><span class="p">,</span><span class="w">                                </span><span class="o">-</span><span class="w"> </span><span class="nc">else</span><span class="p">:</span><span class="w">
│ │ │  </span><span class="nc">check</span><span class="p">:</span><span class="w">                                              </span><span class="n">CLOSE</span><span class="w">
│ │ │ -</span><span class="n">DiB</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nf">gen_digest</span><span class="p" data-group-id="6641783056-17">(</span><span class="n">ChA</span><span class="p">,</span><span class="w"> </span><span class="n">ICA</span><span class="p" data-group-id="6641783056-17">)</span><span class="o">?</span><span class="w">
│ │ │ +</span><span class="n">DiB</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nf">gen_digest</span><span class="p" data-group-id="4526609730-17">(</span><span class="n">ChA</span><span class="p">,</span><span class="w"> </span><span class="n">ICA</span><span class="p" data-group-id="4526609730-17">)</span><span class="o">?</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="w"> </span><span class="na">if</span><span class="w"> </span><span class="n">OK</span><span class="p">:</span><span class="w">
│ │ │   </span><span class="n">DONE</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="w"> </span><span class="na">else</span><span class="p">:</span><span class="w">
│ │ │   </span><span class="n">CLOSE</span></code></pre><p><a href="" id="dflags"></a></p><h3 id="distribution-flags" class="section-heading">
│ │ │    <a href="#distribution-flags" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_ext_dist.html
│ │ │ @@ -436,15 +436,15 @@
│ │ │    </a>
│ │ │    <span class="text">SMALL_BIG_EXT</span>
│ │ │  </h2>
│ │ │  <table><thead><tr><th style="text-align: left;">1</th><th style="text-align: left;">1</th><th style="text-align: left;">1</th><th style="text-align: left;">n</th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">110</code></td><td style="text-align: left;"><code class="inline">n</code></td><td style="text-align: left;"><code class="inline">Sign</code></td><td style="text-align: left;"><code class="inline">d(0)</code> ... <code class="inline">d(n-1)</code></td></tr></tbody></table><p>Bignums are stored in unary form with a <code class="inline">Sign</code> byte, that is, 0 if the bignum is
│ │ │  positive and 1 if it is negative. The digits are stored with the least
│ │ │  significant byte stored first. To calculate the integer, the following formula
│ │ │  can be used:</p><pre><code class="makeup erlang" translate="no"><span class="n">B</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">256</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9499391716-1">(</span><span class="ss">d0</span><span class="o">*</span><span class="n">B</span><span class="err">^</span><span class="mi">0</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">d1</span><span class="o">*</span><span class="n">B</span><span class="err">^</span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">d2</span><span class="o">*</span><span class="n">B</span><span class="err">^</span><span class="mi">2</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="nf">d</span><span class="p" data-group-id="9499391716-2">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="9499391716-2">)</span><span class="o">*</span><span class="n">B</span><span class="err">^</span><span class="p" data-group-id="9499391716-3">(</span><span class="ss">n</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="9499391716-3">)</span><span class="p" data-group-id="9499391716-1">)</span></code></pre><h2 id="large_big_ext" class="section-heading">
│ │ │ +</span><span class="p" data-group-id="2322811221-1">(</span><span class="ss">d0</span><span class="o">*</span><span class="n">B</span><span class="err">^</span><span class="mi">0</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">d1</span><span class="o">*</span><span class="n">B</span><span class="err">^</span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">d2</span><span class="o">*</span><span class="n">B</span><span class="err">^</span><span class="mi">2</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="nf">d</span><span class="p" data-group-id="2322811221-2">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="2322811221-2">)</span><span class="o">*</span><span class="n">B</span><span class="err">^</span><span class="p" data-group-id="2322811221-3">(</span><span class="ss">n</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="2322811221-3">)</span><span class="p" data-group-id="2322811221-1">)</span></code></pre><h2 id="large_big_ext" class="section-heading">
│ │ │    <a href="#large_big_ext" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">LARGE_BIG_EXT</span>
│ │ │  </h2>
│ │ │  <table><thead><tr><th style="text-align: left;">1</th><th style="text-align: left;">4</th><th style="text-align: left;">1</th><th style="text-align: left;">n</th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">111</code></td><td style="text-align: left;"><code class="inline">n</code></td><td style="text-align: left;"><code class="inline">Sign</code></td><td style="text-align: left;"><code class="inline">d(0)</code> ... <code class="inline">d(n-1)</code></td></tr></tbody></table><p>Same as <a href="erl_ext_dist.html#small_big_ext"><code class="inline">SMALL_BIG_EXT</code></a> except that the length
│ │ │  field is an unsigned 4 byte integer.</p><h2 id="reference_ext-deprecated" class="section-heading">
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_nif.html
│ │ │ @@ -161,27 +161,27 @@
│ │ │  }
│ │ │  
│ │ │  static ErlNifFunc nif_funcs[] =
│ │ │  {
│ │ │      {&quot;hello&quot;, 0, hello}
│ │ │  };
│ │ │  
│ │ │ -ERL_NIF_INIT(niftest,nif_funcs,NULL,NULL,NULL,NULL)</code></pre><p>The Erlang module can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0367640429-1">(</span><span class="ss">niftest</span><span class="p" data-group-id="0367640429-1">)</span><span class="p">.</span><span class="w">
│ │ │ +ERL_NIF_INIT(niftest,nif_funcs,NULL,NULL,NULL,NULL)</code></pre><p>The Erlang module can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5851863814-1">(</span><span class="ss">niftest</span><span class="p" data-group-id="5851863814-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0367640429-2">(</span><span class="p" data-group-id="0367640429-3">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">hello</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0367640429-3">]</span><span class="p" data-group-id="0367640429-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5851863814-2">(</span><span class="p" data-group-id="5851863814-3">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">hello</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5851863814-3">]</span><span class="p" data-group-id="5851863814-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">nifs</span><span class="p" data-group-id="0367640429-4">(</span><span class="p" data-group-id="0367640429-5">[</span><span class="ss">hello</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0367640429-5">]</span><span class="p" data-group-id="0367640429-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">nifs</span><span class="p" data-group-id="5851863814-4">(</span><span class="p" data-group-id="5851863814-5">[</span><span class="ss">hello</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5851863814-5">]</span><span class="p" data-group-id="5851863814-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="0367640429-6">(</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0367640429-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="5851863814-6">(</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5851863814-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="0367640429-7">(</span><span class="p" data-group-id="0367640429-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -      </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="0367640429-8">(</span><span class="s">&quot;./niftest&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0367640429-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="5851863814-7">(</span><span class="p" data-group-id="5851863814-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +      </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="5851863814-8">(</span><span class="s">&quot;./niftest&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5851863814-8">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">hello</span><span class="p" data-group-id="0367640429-9">(</span><span class="p" data-group-id="0367640429-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -      </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="0367640429-10">(</span><span class="s">&quot;NIF library not loaded&quot;</span><span class="p" data-group-id="0367640429-10">)</span><span class="p">.</span></code></pre><p>Compile and test can look as follows (on Linux):</p><pre><code class="text">$&gt; gcc -fPIC -shared -o niftest.so niftest.c -I $ERL_ROOT/usr/include/
│ │ │ +</span><span class="nf">hello</span><span class="p" data-group-id="5851863814-9">(</span><span class="p" data-group-id="5851863814-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +      </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="5851863814-10">(</span><span class="s">&quot;NIF library not loaded&quot;</span><span class="p" data-group-id="5851863814-10">)</span><span class="p">.</span></code></pre><p>Compile and test can look as follows (on Linux):</p><pre><code class="text">$&gt; gcc -fPIC -shared -o niftest.so niftest.c -I $ERL_ROOT/usr/include/
│ │ │  $&gt; erl
│ │ │  
│ │ │  1&gt; c(niftest).
│ │ │  {ok,niftest}
│ │ │  2&gt; niftest:hello().
│ │ │  &quot;Hello world!&quot;</code></pre><p>In the example above the <a href="../../../doc/system/code_loading.html#on_load"><em><code class="inline">on_load</code></em></a>
│ │ │  directive is used get function <code class="inline">init</code> called automatically when the module is
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_prim_loader.html
│ │ │ @@ -398,15 +398,15 @@
│ │ │                          when Filename :: <a href="erlang.html#t:string/0">string</a>(), FileInfo :: <a href="../../../lib/kernel-10.2.7.1/doc/html/file.html#t:file_info/0">file:file_info</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Retrieves information about a file.</p><p>Returns <code class="inline">{ok, FileInfo}</code> if successful, otherwise <code class="inline">error</code>. <code class="inline">FileInfo</code> is a
│ │ │  record <a href="../../../lib/kernel-10.2.7.1/doc/html/file.html#t:file_info/0"><code class="inline">file_info</code></a>, defined in the Kernel include file
│ │ │   <code class="inline">file.hrl</code>. Include the following directive in the module from which the
│ │ │ -function is called:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="0131270640-1">(</span><span class="s">&quot;kernel/include/file.hrl&quot;</span><span class="p" data-group-id="0131270640-1">)</span><span class="p">.</span></code></pre><p>For more information about the record see <a href="../../../lib/kernel-10.2.7.1/doc/html/file.html#read_file_info/2"><code class="inline">file:read_file_info/2</code></a>.</p><p><code class="inline">Filename</code> can also be a file in an archive, for example,
│ │ │ +function is called:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="9008933426-1">(</span><span class="s">&quot;kernel/include/file.hrl&quot;</span><span class="p" data-group-id="9008933426-1">)</span><span class="p">.</span></code></pre><p>For more information about the record see <a href="../../../lib/kernel-10.2.7.1/doc/html/file.html#read_file_info/2"><code class="inline">file:read_file_info/2</code></a>.</p><p><code class="inline">Filename</code> can also be a file in an archive, for example,
│ │ │  <code class="inline">$OTPROOT/lib/mnesia-4.4.7.ez/mnesia-4.4.7/ebin/mnesia</code>. For information
│ │ │  about archive files, see <a href="../../../lib/kernel-10.2.7.1/doc/html/code.html"><code class="inline">code</code></a>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="read_link_info/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erl_tracer.html
│ │ │ @@ -145,44 +145,44 @@
│ │ │    <span class="text">Erl Tracer Module Example</span>
│ │ │  </h2>
│ │ │  <p>In this example, a tracer module with a NIF back end sends a message for each
│ │ │  <code class="inline">send</code> trace tag containing only the sender and receiver. Using this tracer
│ │ │  module, a much more lightweight message tracer is used, which only records who
│ │ │  sent messages to who.</p><p>The following is an example session using it on Linux:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$ </span><span class="ss">gcc</span><span class="w"> </span><span class="o">-</span><span class="n">I</span><span class="w"> </span><span class="ss">erts</span><span class="o">-</span><span class="mf">8.0</span><span class="o">/</span><span class="ss">include</span><span class="o">/</span><span class="w"> </span><span class="o">-</span><span class="ss">fPIC</span><span class="w"> </span><span class="o">-</span><span class="ss">shared</span><span class="w"> </span><span class="o">-</span><span class="ss">o</span><span class="w"> </span><span class="ss">erl_msg_tracer</span><span class="p">.</span><span class="ss">so</span><span class="w"> </span><span class="ss">erl_msg_tracer</span><span class="p">.</span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="sc">$ </span><span class="ss">erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">19</span><span class="w"> </span><span class="p" data-group-id="2346784505-1">[</span><span class="n">DEVELOPMENT</span><span class="p" data-group-id="2346784505-1">]</span><span class="w"> </span><span class="p" data-group-id="2346784505-2">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">8.0</span><span class="p" data-group-id="2346784505-2">]</span><span class="w"> </span><span class="p" data-group-id="2346784505-3">[</span><span class="ss">source</span><span class="o">-</span><span class="ss">ed2b56b</span><span class="p" data-group-id="2346784505-3">]</span><span class="w"> </span><span class="p" data-group-id="2346784505-4">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="2346784505-4">]</span><span class="w"> </span><span class="p" data-group-id="2346784505-5">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="2346784505-5">]</span><span class="w"> </span><span class="p" data-group-id="2346784505-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="2346784505-6">]</span><span class="w"> </span><span class="p" data-group-id="2346784505-7">[</span><span class="ss">hipe</span><span class="p" data-group-id="2346784505-7">]</span><span class="w"> </span><span class="p" data-group-id="2346784505-8">[</span><span class="ss">kernel</span><span class="o">-</span><span class="nc">poll</span><span class="p">:</span><span class="ss">false</span><span class="p" data-group-id="2346784505-8">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">19</span><span class="w"> </span><span class="p" data-group-id="0740665522-1">[</span><span class="n">DEVELOPMENT</span><span class="p" data-group-id="0740665522-1">]</span><span class="w"> </span><span class="p" data-group-id="0740665522-2">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">8.0</span><span class="p" data-group-id="0740665522-2">]</span><span class="w"> </span><span class="p" data-group-id="0740665522-3">[</span><span class="ss">source</span><span class="o">-</span><span class="ss">ed2b56b</span><span class="p" data-group-id="0740665522-3">]</span><span class="w"> </span><span class="p" data-group-id="0740665522-4">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0740665522-4">]</span><span class="w"> </span><span class="p" data-group-id="0740665522-5">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0740665522-5">]</span><span class="w"> </span><span class="p" data-group-id="0740665522-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="0740665522-6">]</span><span class="w"> </span><span class="p" data-group-id="0740665522-7">[</span><span class="ss">hipe</span><span class="p" data-group-id="0740665522-7">]</span><span class="w"> </span><span class="p" data-group-id="0740665522-8">[</span><span class="ss">kernel</span><span class="o">-</span><span class="nc">poll</span><span class="p">:</span><span class="ss">false</span><span class="p" data-group-id="0740665522-8">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V8</span><span class="p">.</span><span class="mi">0</span><span class="w">  </span><span class="p" data-group-id="2346784505-9">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="2346784505-9">)</span><span class="gp unselectable">
│ │ │ -1&gt; </span><span class="nf">c</span><span class="p" data-group-id="2346784505-10">(</span><span class="ss">erl_msg_tracer</span><span class="p" data-group-id="2346784505-10">)</span><span class="p">,</span><span class="w"> </span><span class="nc">erl_msg_tracer</span><span class="p">:</span><span class="nf">load</span><span class="p" data-group-id="2346784505-11">(</span><span class="p" data-group-id="2346784505-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V8</span><span class="p">.</span><span class="mi">0</span><span class="w">  </span><span class="p" data-group-id="0740665522-9">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="0740665522-9">)</span><span class="gp unselectable">
│ │ │ +1&gt; </span><span class="nf">c</span><span class="p" data-group-id="0740665522-10">(</span><span class="ss">erl_msg_tracer</span><span class="p" data-group-id="0740665522-10">)</span><span class="p">,</span><span class="w"> </span><span class="nc">erl_msg_tracer</span><span class="p">:</span><span class="nf">load</span><span class="p" data-group-id="0740665522-11">(</span><span class="p" data-group-id="0740665522-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="n">Tracer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2346784505-12">(</span><span class="k">fun</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="2346784505-13">(</span><span class="p" data-group-id="2346784505-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2346784505-14">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="2346784505-15">[</span><span class="n">M</span><span class="p" data-group-id="2346784505-15">]</span><span class="p" data-group-id="2346784505-14">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="2346784505-16">(</span><span class="p" data-group-id="2346784505-16">)</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="2346784505-12">)</span><span class="p">.</span><span class="w">
│ │ │ +2&gt; </span><span class="n">Tracer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0740665522-12">(</span><span class="k">fun</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="0740665522-13">(</span><span class="p" data-group-id="0740665522-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0740665522-14">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="0740665522-15">[</span><span class="n">M</span><span class="p" data-group-id="0740665522-15">]</span><span class="p" data-group-id="0740665522-14">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="0740665522-16">(</span><span class="p" data-group-id="0740665522-16">)</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="0740665522-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.37</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="gp unselectable">
│ │ │ -3&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="2346784505-17">(</span><span class="ss">new</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2346784505-18">[</span><span class="nb">send</span><span class="p">,</span><span class="p" data-group-id="2346784505-19">{</span><span class="ss">tracer</span><span class="p">,</span><span class="w"> </span><span class="ss">erl_msg_tracer</span><span class="p">,</span><span class="w"> </span><span class="n">Tracer</span><span class="p" data-group-id="2346784505-19">}</span><span class="p" data-group-id="2346784505-18">]</span><span class="p" data-group-id="2346784505-17">)</span><span class="p">.</span><span class="w">
│ │ │ +3&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="0740665522-17">(</span><span class="ss">new</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0740665522-18">[</span><span class="nb">send</span><span class="p">,</span><span class="p" data-group-id="0740665522-19">{</span><span class="ss">tracer</span><span class="p">,</span><span class="w"> </span><span class="ss">erl_msg_tracer</span><span class="p">,</span><span class="w"> </span><span class="n">Tracer</span><span class="p" data-group-id="0740665522-19">}</span><span class="p" data-group-id="0740665522-18">]</span><span class="p" data-group-id="0740665522-17">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">0</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2346784505-20">{</span><span class="nb">trace</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.39</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.27</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2346784505-20">}</span><span class="gp unselectable">
│ │ │ -4&gt; </span><span class="p" data-group-id="2346784505-21">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="2346784505-21">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="2346784505-22">(</span><span class="s">&quot;/tmp/tmp.data&quot;</span><span class="p">,</span><span class="p" data-group-id="2346784505-23">[</span><span class="ss">write</span><span class="p" data-group-id="2346784505-23">]</span><span class="p" data-group-id="2346784505-22">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2346784505-24">{</span><span class="nb">trace</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.486</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.40</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2346784505-24">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2346784505-25">{</span><span class="nb">trace</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.40</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.21</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2346784505-25">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2346784505-26">{</span><span class="nb">trace</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.487</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2346784505-26">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2346784505-27">{</span><span class="nb">trace</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.488</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2346784505-27">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2346784505-28">{</span><span class="nb">trace</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.489</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2346784505-28">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2346784505-29">{</span><span class="nb">trace</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.490</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2346784505-29">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2346784505-30">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.40</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2346784505-30">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2346784505-31">{</span><span class="nb">trace</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.41</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.27</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2346784505-31">}</span><span class="w">
│ │ │ -</span><span class="mi">5</span><span class="o">&gt;</span></code></pre><p><code class="inline">erl_msg_tracer.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9624004635-1">(</span><span class="ss">erl_msg_tracer</span><span class="p" data-group-id="9624004635-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0740665522-20">{</span><span class="nb">trace</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.39</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.27</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0740665522-20">}</span><span class="gp unselectable">
│ │ │ +4&gt; </span><span class="p" data-group-id="0740665522-21">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="0740665522-21">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="0740665522-22">(</span><span class="s">&quot;/tmp/tmp.data&quot;</span><span class="p">,</span><span class="p" data-group-id="0740665522-23">[</span><span class="ss">write</span><span class="p" data-group-id="0740665522-23">]</span><span class="p" data-group-id="0740665522-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0740665522-24">{</span><span class="nb">trace</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.486</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.40</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0740665522-24">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0740665522-25">{</span><span class="nb">trace</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.40</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.21</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0740665522-25">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0740665522-26">{</span><span class="nb">trace</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.487</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0740665522-26">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0740665522-27">{</span><span class="nb">trace</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.488</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0740665522-27">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0740665522-28">{</span><span class="nb">trace</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.489</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0740665522-28">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0740665522-29">{</span><span class="nb">trace</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.490</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0740665522-29">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0740665522-30">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.40</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0740665522-30">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0740665522-31">{</span><span class="nb">trace</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.41</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.27</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0740665522-31">}</span><span class="w">
│ │ │ +</span><span class="mi">5</span><span class="o">&gt;</span></code></pre><p><code class="inline">erl_msg_tracer.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6317424895-1">(</span><span class="ss">erl_msg_tracer</span><span class="p" data-group-id="6317424895-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9624004635-2">(</span><span class="p" data-group-id="9624004635-3">[</span><span class="ss">enabled</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="nb">trace</span><span class="p">/</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="ss">load</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9624004635-3">]</span><span class="p" data-group-id="9624004635-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6317424895-2">(</span><span class="p" data-group-id="6317424895-3">[</span><span class="ss">enabled</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="nb">trace</span><span class="p">/</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="ss">load</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6317424895-3">]</span><span class="p" data-group-id="6317424895-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">load</span><span class="p" data-group-id="9624004635-4">(</span><span class="p" data-group-id="9624004635-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="9624004635-5">(</span><span class="s">&quot;erl_msg_tracer&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9624004635-6">[</span><span class="p" data-group-id="9624004635-6">]</span><span class="p" data-group-id="9624004635-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">load</span><span class="p" data-group-id="6317424895-4">(</span><span class="p" data-group-id="6317424895-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="6317424895-5">(</span><span class="s">&quot;erl_msg_tracer&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6317424895-6">[</span><span class="p" data-group-id="6317424895-6">]</span><span class="p" data-group-id="6317424895-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">enabled</span><span class="p" data-group-id="9624004635-7">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9624004635-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">enabled</span><span class="p" data-group-id="6317424895-7">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6317424895-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">error</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">trace</span><span class="p" data-group-id="9624004635-8">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9624004635-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">trace</span><span class="p" data-group-id="6317424895-8">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6317424895-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">error</span><span class="p">.</span></code></pre><p><code class="inline">erl_msg_tracer.c</code>:</p><pre><code class="c">#include &lt;erl_nif.h&gt;
│ │ │  
│ │ │  /* NIF interface declarations */
│ │ │  static int load(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info);
│ │ │  static int upgrade(ErlNifEnv* env, void** priv_data, void** old_priv_data, ERL_NIF_TERM load_info);
│ │ │  static void unload(ErlNifEnv* env, void* priv_data);
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7/doc/html/erlang.html
│ │ │ @@ -6846,16 +6846,16 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> adler32(OldAdler, Data) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when OldAdler :: <a href="#t:non_neg_integer/0">non_neg_integer</a>(), Data :: <a href="#t:iodata/0">iodata</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Continues computing the adler32 checksum by combining the previous checksum,
│ │ │ -<code class="inline">OldAdler</code>, with the checksum of <code class="inline">Data</code>.</p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="5467533332-1">(</span><span class="n">Data1</span><span class="p" data-group-id="5467533332-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="5467533332-2">(</span><span class="n">X</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="5467533332-2">)</span><span class="p">.</span></code></pre><p>assigns the same value to <code class="inline">Y</code> as this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="4999986763-1">(</span><span class="p" data-group-id="4999986763-2">[</span><span class="n">Data1</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="4999986763-2">]</span><span class="p" data-group-id="4999986763-1">)</span><span class="p">.</span></code></pre>
│ │ │ +<code class="inline">OldAdler</code>, with the checksum of <code class="inline">Data</code>.</p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="4571961321-1">(</span><span class="n">Data1</span><span class="p" data-group-id="4571961321-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="4571961321-2">(</span><span class="n">X</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="4571961321-2">)</span><span class="p">.</span></code></pre><p>assigns the same value to <code class="inline">Y</code> as this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="6193920924-1">(</span><span class="p" data-group-id="6193920924-2">[</span><span class="n">Data1</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="6193920924-2">]</span><span class="p" data-group-id="6193920924-1">)</span><span class="p">.</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="adler32_combine/3">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#adler32_combine/3" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -6878,18 +6878,18 @@
│ │ │                               FirstAdler :: <a href="#t:non_neg_integer/0">non_neg_integer</a>(),
│ │ │                               SecondAdler :: <a href="#t:non_neg_integer/0">non_neg_integer</a>(),
│ │ │                               SecondSize :: <a href="#t:non_neg_integer/0">non_neg_integer</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Combines two previously computed adler32 checksums.</p><p>This computation requires the size of the data object for the second checksum
│ │ │ -to be known.</p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="1813428050-1">(</span><span class="n">Data1</span><span class="p" data-group-id="1813428050-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="1813428050-2">(</span><span class="n">Y</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="1813428050-2">)</span><span class="p">.</span></code></pre><p>assigns the same value to <code class="inline">Z</code> as this:</p><pre><code class="makeup erlang" translate="no"><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="8046672480-1">(</span><span class="n">Data1</span><span class="p" data-group-id="8046672480-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="8046672480-2">(</span><span class="n">Data2</span><span class="p" data-group-id="8046672480-2">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32_combine</span><span class="p" data-group-id="8046672480-3">(</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="nf">iolist_size</span><span class="p" data-group-id="8046672480-4">(</span><span class="n">Data2</span><span class="p" data-group-id="8046672480-4">)</span><span class="p" data-group-id="8046672480-3">)</span><span class="p">.</span></code></pre>
│ │ │ +to be known.</p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="8827437652-1">(</span><span class="n">Data1</span><span class="p" data-group-id="8827437652-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="8827437652-2">(</span><span class="n">Y</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="8827437652-2">)</span><span class="p">.</span></code></pre><p>assigns the same value to <code class="inline">Z</code> as this:</p><pre><code class="makeup erlang" translate="no"><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="5400329129-1">(</span><span class="n">Data1</span><span class="p" data-group-id="5400329129-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32</span><span class="p" data-group-id="5400329129-2">(</span><span class="n">Data2</span><span class="p" data-group-id="5400329129-2">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">adler32_combine</span><span class="p" data-group-id="5400329129-3">(</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="nf">iolist_size</span><span class="p" data-group-id="5400329129-4">(</span><span class="n">Data2</span><span class="p" data-group-id="5400329129-4">)</span><span class="p" data-group-id="5400329129-3">)</span><span class="p">.</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="crc32/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#crc32/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -6934,16 +6934,16 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> crc32(OldCrc, Data) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when OldCrc :: <a href="#t:non_neg_integer/0">non_neg_integer</a>(), Data :: <a href="#t:iodata/0">iodata</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Continues computing the crc32 checksum by combining the previous checksum,
│ │ │ -<code class="inline">OldCrc</code>, with the checksum of <code class="inline">Data</code>.</p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="2126532344-1">(</span><span class="n">Data1</span><span class="p" data-group-id="2126532344-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="2126532344-2">(</span><span class="n">X</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="2126532344-2">)</span><span class="p">.</span></code></pre><p>assigns the same value to <code class="inline">Y</code> as this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="5163951727-1">(</span><span class="p" data-group-id="5163951727-2">[</span><span class="n">Data1</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="5163951727-2">]</span><span class="p" data-group-id="5163951727-1">)</span><span class="p">.</span></code></pre>
│ │ │ +<code class="inline">OldCrc</code>, with the checksum of <code class="inline">Data</code>.</p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="4521897083-1">(</span><span class="n">Data1</span><span class="p" data-group-id="4521897083-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="4521897083-2">(</span><span class="n">X</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="4521897083-2">)</span><span class="p">.</span></code></pre><p>assigns the same value to <code class="inline">Y</code> as this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="8230179475-1">(</span><span class="p" data-group-id="8230179475-2">[</span><span class="n">Data1</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="8230179475-2">]</span><span class="p" data-group-id="8230179475-1">)</span><span class="p">.</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="crc32_combine/3">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#crc32_combine/3" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -6966,18 +6966,18 @@
│ │ │                             FirstCrc :: <a href="#t:non_neg_integer/0">non_neg_integer</a>(),
│ │ │                             SecondCrc :: <a href="#t:non_neg_integer/0">non_neg_integer</a>(),
│ │ │                             SecondSize :: <a href="#t:non_neg_integer/0">non_neg_integer</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Combines two previously computed crc32 checksums.</p><p>This computation requires the size of the data object for the second checksum
│ │ │ -to be known.</p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="0033262232-1">(</span><span class="n">Data1</span><span class="p" data-group-id="0033262232-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="0033262232-2">(</span><span class="n">Y</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="0033262232-2">)</span><span class="p">.</span></code></pre><p>assigns the same value to <code class="inline">Z</code> as this:</p><pre><code class="makeup erlang" translate="no"><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="8467269187-1">(</span><span class="n">Data1</span><span class="p" data-group-id="8467269187-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="8467269187-2">(</span><span class="n">Data2</span><span class="p" data-group-id="8467269187-2">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32_combine</span><span class="p" data-group-id="8467269187-3">(</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="nf">iolist_size</span><span class="p" data-group-id="8467269187-4">(</span><span class="n">Data2</span><span class="p" data-group-id="8467269187-4">)</span><span class="p" data-group-id="8467269187-3">)</span><span class="p">.</span></code></pre>
│ │ │ +to be known.</p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="9856377491-1">(</span><span class="n">Data1</span><span class="p" data-group-id="9856377491-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="9856377491-2">(</span><span class="n">Y</span><span class="p">,</span><span class="n">Data2</span><span class="p" data-group-id="9856377491-2">)</span><span class="p">.</span></code></pre><p>assigns the same value to <code class="inline">Z</code> as this:</p><pre><code class="makeup erlang" translate="no"><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="0596242095-1">(</span><span class="n">Data1</span><span class="p" data-group-id="0596242095-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32</span><span class="p" data-group-id="0596242095-2">(</span><span class="n">Data2</span><span class="p" data-group-id="0596242095-2">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">crc32_combine</span><span class="p" data-group-id="0596242095-3">(</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="nf">iolist_size</span><span class="p" data-group-id="0596242095-4">(</span><span class="n">Data2</span><span class="p" data-group-id="0596242095-4">)</span><span class="p" data-group-id="0596242095-3">)</span><span class="p">.</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="md5/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#md5/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -8129,19 +8129,19 @@
│ │ │  the <code class="inline">Info</code> map in the returned result will contain the key <code class="inline">node_type</code>
│ │ │  associated with the value <code class="inline">NodeTypeInfo</code>. Currently the following node types
│ │ │  exist:</p><ul><li><p><strong><code class="inline">visible</code></strong> - The node is connected to the node of the calling process
│ │ │  through an ordinary visible connection. That is, the node name would appear
│ │ │  in the result returned by <a href="#nodes/0"><code class="inline">nodes/0</code></a>.</p></li><li><p><strong><code class="inline">hidden</code></strong> - The node is connected to the node of the calling process
│ │ │  through a hidden connection. That is, the node name would <em>not</em> appear in
│ │ │  the result returned by <a href="#nodes/0"><code class="inline">nodes/0</code></a>.</p></li><li><p><strong><code class="inline">this</code></strong> - This is the node of the calling process.</p></li><li><p><strong><code class="inline">known</code></strong> - The node is not connected but known to the node of the calling
│ │ │ -process.</p></li></ul></li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(a@localhost)1&gt; </span><span class="nf">nodes</span><span class="p" data-group-id="1505138298-1">(</span><span class="p" data-group-id="1505138298-2">[</span><span class="ss">this</span><span class="p">,</span><span class="w"> </span><span class="ss">connected</span><span class="p" data-group-id="1505138298-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1505138298-3">#{</span><span class="ss">connection_id</span><span class="p">=&gt;</span><span class="ss">true</span><span class="p">,</span><span class="w"> </span><span class="ss">node_type</span><span class="p">=&gt;</span><span class="ss">true</span><span class="p" data-group-id="1505138298-3">}</span><span class="p" data-group-id="1505138298-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1505138298-4">[</span><span class="p" data-group-id="1505138298-5">{</span><span class="ss">c@localhost</span><span class="p">,</span><span class="p" data-group-id="1505138298-6">#{</span><span class="ss">connection_id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">13892108</span><span class="p">,</span><span class="ss">node_type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">hidden</span><span class="p" data-group-id="1505138298-6">}</span><span class="p" data-group-id="1505138298-5">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1505138298-7">{</span><span class="ss">b@localhost</span><span class="p">,</span><span class="p" data-group-id="1505138298-8">#{</span><span class="ss">connection_id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3067553</span><span class="p">,</span><span class="ss">node_type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">visible</span><span class="p" data-group-id="1505138298-8">}</span><span class="p" data-group-id="1505138298-7">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1505138298-9">{</span><span class="ss">a@localhost</span><span class="p">,</span><span class="p" data-group-id="1505138298-10">#{</span><span class="ss">connection_id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">undefined</span><span class="p">,</span><span class="ss">node_type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">this</span><span class="p" data-group-id="1505138298-10">}</span><span class="p" data-group-id="1505138298-9">}</span><span class="p" data-group-id="1505138298-4">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1505138298-11">(</span><span class="ss">a@localhost</span><span class="p" data-group-id="1505138298-11">)</span><span class="mi">2</span><span class="o">&gt;</span></code></pre>
│ │ │ +process.</p></li></ul></li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(a@localhost)1&gt; </span><span class="nf">nodes</span><span class="p" data-group-id="3599596042-1">(</span><span class="p" data-group-id="3599596042-2">[</span><span class="ss">this</span><span class="p">,</span><span class="w"> </span><span class="ss">connected</span><span class="p" data-group-id="3599596042-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3599596042-3">#{</span><span class="ss">connection_id</span><span class="p">=&gt;</span><span class="ss">true</span><span class="p">,</span><span class="w"> </span><span class="ss">node_type</span><span class="p">=&gt;</span><span class="ss">true</span><span class="p" data-group-id="3599596042-3">}</span><span class="p" data-group-id="3599596042-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3599596042-4">[</span><span class="p" data-group-id="3599596042-5">{</span><span class="ss">c@localhost</span><span class="p">,</span><span class="p" data-group-id="3599596042-6">#{</span><span class="ss">connection_id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">13892108</span><span class="p">,</span><span class="ss">node_type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">hidden</span><span class="p" data-group-id="3599596042-6">}</span><span class="p" data-group-id="3599596042-5">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3599596042-7">{</span><span class="ss">b@localhost</span><span class="p">,</span><span class="p" data-group-id="3599596042-8">#{</span><span class="ss">connection_id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3067553</span><span class="p">,</span><span class="ss">node_type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">visible</span><span class="p" data-group-id="3599596042-8">}</span><span class="p" data-group-id="3599596042-7">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3599596042-9">{</span><span class="ss">a@localhost</span><span class="p">,</span><span class="p" data-group-id="3599596042-10">#{</span><span class="ss">connection_id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">undefined</span><span class="p">,</span><span class="ss">node_type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">this</span><span class="p" data-group-id="3599596042-10">}</span><span class="p" data-group-id="3599596042-9">}</span><span class="p" data-group-id="3599596042-4">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3599596042-11">(</span><span class="ss">a@localhost</span><span class="p" data-group-id="3599596042-11">)</span><span class="mi">2</span><span class="o">&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="set_cookie/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#set_cookie/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -8237,17 +8237,17 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> abs(Float) -> <a href="#t:float/0">float</a>() when Float :: <a href="#t:float/0">float</a>();
│ │ │           (Int) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when Int :: <a href="#t:integer/0">integer</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns an integer or float that is the arithmetical absolute value of <code class="inline">Float</code>
│ │ │ -or <code class="inline">Int</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">abs</span><span class="p" data-group-id="8589323139-1">(</span><span class="o">-</span><span class="mf">3.33</span><span class="p" data-group-id="8589323139-1">)</span><span class="p">.</span><span class="w">
│ │ │ +or <code class="inline">Int</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">abs</span><span class="p" data-group-id="1751001871-1">(</span><span class="o">-</span><span class="mf">3.33</span><span class="p" data-group-id="1751001871-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">3.33</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">abs</span><span class="p" data-group-id="8589323139-2">(</span><span class="o">-</span><span class="mi">3</span><span class="p" data-group-id="8589323139-2">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">abs</span><span class="p" data-group-id="1751001871-2">(</span><span class="o">-</span><span class="mi">3</span><span class="p" data-group-id="1751001871-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="append_element/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#append_element/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -8269,16 +8269,16 @@
│ │ │            <pre translate="no"><span class="attribute">-spec</span> append_element(Tuple1, Term) -> Tuple2 when Tuple1 :: <a href="#t:tuple/0">tuple</a>(), Tuple2 :: <a href="#t:tuple/0">tuple</a>(), Term :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a new tuple that has one element more than <code class="inline">Tuple1</code>, and contains the
│ │ │  elements in <code class="inline">Tuple1</code> followed by <code class="inline">Term</code> as the last element.</p><p>Semantically equivalent to
│ │ │  <a href="#list_to_tuple/1"><code class="inline">list_to_tuple(tuple_to_list(Tuple1) ++ [Term])</code></a>, but much
│ │ │ -faster.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">append_element</span><span class="p" data-group-id="5012342734-1">(</span><span class="p" data-group-id="5012342734-2">{</span><span class="ss">one</span><span class="p">,</span><span class="w"> </span><span class="ss">two</span><span class="p" data-group-id="5012342734-2">}</span><span class="p">,</span><span class="w"> </span><span class="ss">three</span><span class="p" data-group-id="5012342734-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5012342734-3">{</span><span class="ss">one</span><span class="p">,</span><span class="ss">two</span><span class="p">,</span><span class="ss">three</span><span class="p" data-group-id="5012342734-3">}</span></code></pre>
│ │ │ +faster.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">append_element</span><span class="p" data-group-id="1174868420-1">(</span><span class="p" data-group-id="1174868420-2">{</span><span class="ss">one</span><span class="p">,</span><span class="w"> </span><span class="ss">two</span><span class="p" data-group-id="1174868420-2">}</span><span class="p">,</span><span class="w"> </span><span class="ss">three</span><span class="p" data-group-id="1174868420-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1174868420-3">{</span><span class="ss">one</span><span class="p">,</span><span class="ss">two</span><span class="p">,</span><span class="ss">three</span><span class="p" data-group-id="1174868420-3">}</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="atom_to_binary/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#atom_to_binary/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -8333,16 +8333,16 @@
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a binary corresponding to the text representation of <code class="inline">Atom</code>.</p><p>If <code class="inline">Encoding</code> is <code class="inline">latin1</code>, one byte exists for each character in the text
│ │ │  representation. If <code class="inline">Encoding</code> is <code class="inline">utf8</code> or <code class="inline">unicode</code>, the characters are encoded
│ │ │  using UTF-8 where characters may require multiple bytes.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>As from Erlang/OTP 20, atoms can contain any Unicode character and
│ │ │  <a href="#atom_to_binary/2"><code class="inline">atom_to_binary(Atom, latin1)</code></a> may fail if the text
│ │ │ -representation for <code class="inline">Atom</code> contains a Unicode character &gt; 255.</p></section><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">atom_to_binary</span><span class="p" data-group-id="6738317922-1">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p">,</span><span class="w"> </span><span class="ss">latin1</span><span class="p" data-group-id="6738317922-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6738317922-2">&lt;&lt;</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="6738317922-2">&gt;&gt;</span></code></pre>
│ │ │ +representation for <code class="inline">Atom</code> contains a Unicode character &gt; 255.</p></section><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">atom_to_binary</span><span class="p" data-group-id="6838938352-1">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p">,</span><span class="w"> </span><span class="ss">latin1</span><span class="p" data-group-id="6838938352-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6838938352-2">&lt;&lt;</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="6838938352-2">&gt;&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="atom_to_list/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#atom_to_list/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -8363,17 +8363,17 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> atom_to_list(Atom) -> <a href="#t:string/0">string</a>() when Atom :: <a href="#t:atom/0">atom</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a list of unicode code points corresponding to the text representation
│ │ │ -of <code class="inline">Atom</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="9321393769-1">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="9321393769-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="s">&quot;Erlang&quot;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="0883166211-1">(</span><span class="ss">&#39;你好&#39;</span><span class="p" data-group-id="0883166211-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0883166211-2">[</span><span class="mi">20320</span><span class="p">,</span><span class="mi">22909</span><span class="p" data-group-id="0883166211-2">]</span></code></pre><p>See <a href="../../../lib/stdlib-6.2.2.1/doc/html/unicode.html"><code class="inline">unicode</code></a> for how to convert the resulting list to different formats.</p>
│ │ │ +of <code class="inline">Atom</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="8520792765-1">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="8520792765-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="s">&quot;Erlang&quot;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="8395919565-1">(</span><span class="ss">&#39;你好&#39;</span><span class="p" data-group-id="8395919565-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8395919565-2">[</span><span class="mi">20320</span><span class="p">,</span><span class="mi">22909</span><span class="p" data-group-id="8395919565-2">]</span></code></pre><p>See <a href="../../../lib/stdlib-6.2.2.1/doc/html/unicode.html"><code class="inline">unicode</code></a> for how to convert the resulting list to different formats.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="binary_part/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#binary_part/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -8400,19 +8400,19 @@
│ │ │            <pre translate="no"><span class="attribute">-spec</span> binary_part(Subject, PosLen) -> <a href="#t:binary/0">binary</a>()
│ │ │                       when
│ │ │                           Subject :: <a href="#t:binary/0">binary</a>(),
│ │ │                           PosLen :: {Start :: <a href="#t:non_neg_integer/0">non_neg_integer</a>(), Length :: <a href="#t:integer/0">integer</a>()}.</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Extracts the part of the binary described by <code class="inline">PosLen</code>.</p><p>Negative length can be used to extract bytes at the end of a binary. </p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1901349932-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="1901349932-1">&gt;&gt;</span><span class="p">.</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nf">binary_part</span><span class="p" data-group-id="1901349932-2">(</span><span class="n">Bin</span><span class="p">,</span><span class="p" data-group-id="1901349932-3">{</span><span class="nf">byte_size</span><span class="p" data-group-id="1901349932-4">(</span><span class="n">Bin</span><span class="p" data-group-id="1901349932-4">)</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">5</span><span class="p" data-group-id="1901349932-3">}</span><span class="p" data-group-id="1901349932-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1901349932-5">&lt;&lt;</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="1901349932-5">&gt;&gt;</span></code></pre><p>Failure: <code class="inline">badarg</code> if <code class="inline">PosLen</code> in any way references outside the binary.</p><p><code class="inline">Start</code> is zero-based, that is:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8452137503-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8452137503-1">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -2&gt; </span><span class="nf">binary_part</span><span class="p" data-group-id="8452137503-2">(</span><span class="n">Bin</span><span class="p">,</span><span class="p" data-group-id="8452137503-3">{</span><span class="mi">0</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8452137503-3">}</span><span class="p" data-group-id="8452137503-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8452137503-4">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8452137503-4">&gt;&gt;</span></code></pre><p>For details about the <code class="inline">PosLen</code> semantics, see <a href="../../../lib/stdlib-6.2.2.1/doc/html/binary.html"><code class="inline">binary</code></a>.</p>
│ │ │ +<p>Extracts the part of the binary described by <code class="inline">PosLen</code>.</p><p>Negative length can be used to extract bytes at the end of a binary. </p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6907271687-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="6907271687-1">&gt;&gt;</span><span class="p">.</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nf">binary_part</span><span class="p" data-group-id="6907271687-2">(</span><span class="n">Bin</span><span class="p">,</span><span class="p" data-group-id="6907271687-3">{</span><span class="nf">byte_size</span><span class="p" data-group-id="6907271687-4">(</span><span class="n">Bin</span><span class="p" data-group-id="6907271687-4">)</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">5</span><span class="p" data-group-id="6907271687-3">}</span><span class="p" data-group-id="6907271687-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6907271687-5">&lt;&lt;</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="6907271687-5">&gt;&gt;</span></code></pre><p>Failure: <code class="inline">badarg</code> if <code class="inline">PosLen</code> in any way references outside the binary.</p><p><code class="inline">Start</code> is zero-based, that is:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6700024929-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6700024929-1">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +2&gt; </span><span class="nf">binary_part</span><span class="p" data-group-id="6700024929-2">(</span><span class="n">Bin</span><span class="p">,</span><span class="p" data-group-id="6700024929-3">{</span><span class="mi">0</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6700024929-3">}</span><span class="p" data-group-id="6700024929-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6700024929-4">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6700024929-4">&gt;&gt;</span></code></pre><p>For details about the <code class="inline">PosLen</code> semantics, see <a href="../../../lib/stdlib-6.2.2.1/doc/html/binary.html"><code class="inline">binary</code></a>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="binary_part/3">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#binary_part/3" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -8505,16 +8505,16 @@
│ │ │  capable of decoding any Unicode character. Earlier versions would fail if the
│ │ │  binary contained Unicode characters &gt; 255.</p></section><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The number of characters that are permitted in an atom name is limited. The
│ │ │  default limits can be found in the
│ │ │  <a href="../../../doc/system/system_limits.html">Efficiency Guide (section System Limits)</a>.</p></section><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>There is configurable limit on how many atoms that can exist and atoms are not
│ │ │  garbage collected. Therefore, it is recommended to consider whether
│ │ │  <a href="#binary_to_existing_atom/2"><code class="inline">binary_to_existing_atom/2</code></a> is a better option
│ │ │  than <a href="#binary_to_atom/2"><code class="inline">binary_to_atom/2</code></a>. The default limits can be found
│ │ │ -in <a href="../../../doc/system/system_limits.html#atoms">Efficiency Guide (section System Limits)</a>.</p></section><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_atom</span><span class="p" data-group-id="0796190953-1">(</span><span class="p" data-group-id="0796190953-2">&lt;&lt;</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="0796190953-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="ss">latin1</span><span class="p" data-group-id="0796190953-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">&#39;Erlang&#39;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_atom</span><span class="p" data-group-id="1579058980-1">(</span><span class="p" data-group-id="1579058980-2">&lt;&lt;</span><span class="mi">1024</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="1579058980-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="ss">utf8</span><span class="p" data-group-id="1579058980-1">)</span><span class="p">.</span><span class="w">
│ │ │ +in <a href="../../../doc/system/system_limits.html#atoms">Efficiency Guide (section System Limits)</a>.</p></section><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_atom</span><span class="p" data-group-id="7453707194-1">(</span><span class="p" data-group-id="7453707194-2">&lt;&lt;</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="7453707194-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="ss">latin1</span><span class="p" data-group-id="7453707194-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">&#39;Erlang&#39;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_atom</span><span class="p" data-group-id="4985222728-1">(</span><span class="p" data-group-id="4985222728-2">&lt;&lt;</span><span class="mi">1024</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="4985222728-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="ss">utf8</span><span class="p" data-group-id="4985222728-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">&#39;Ѐ&#39;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="binary_to_existing_atom/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#binary_to_existing_atom/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -8613,15 +8613,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> binary_to_float(Binary) -> <a href="#t:float/0">float</a>() when Binary :: <a href="#t:binary/0">binary</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns the float whose text representation is <code class="inline">Binary</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_float</span><span class="p" data-group-id="3356825141-1">(</span><span class="p" data-group-id="3356825141-2">&lt;&lt;</span><span class="s">&quot;2.2017764e+0&quot;</span><span class="p" data-group-id="3356825141-2">&gt;&gt;</span><span class="p" data-group-id="3356825141-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns the float whose text representation is <code class="inline">Binary</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_float</span><span class="p" data-group-id="0815647931-1">(</span><span class="p" data-group-id="0815647931-2">&lt;&lt;</span><span class="s">&quot;2.2017764e+0&quot;</span><span class="p" data-group-id="0815647931-2">&gt;&gt;</span><span class="p" data-group-id="0815647931-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">2.2017764</span></code></pre><p>The float string format is the same as the format for
│ │ │  <a href="../../../doc/system/data_types.html">Erlang float literals</a> except for that underscores
│ │ │  are not permitted.</p><p>Failure: <code class="inline">badarg</code> if <code class="inline">Binary</code> contains a bad representation of a float.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="binary_to_integer/1">
│ │ │  
│ │ │ @@ -8646,15 +8646,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> binary_to_integer(Binary) -> <a href="#t:integer/0">integer</a>() when Binary :: <a href="#t:binary/0">binary</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns an integer whose text representation is <code class="inline">Binary</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="3904963914-1">(</span><span class="p" data-group-id="3904963914-2">&lt;&lt;</span><span class="s">&quot;123&quot;</span><span class="p" data-group-id="3904963914-2">&gt;&gt;</span><span class="p" data-group-id="3904963914-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns an integer whose text representation is <code class="inline">Binary</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="1812042591-1">(</span><span class="p" data-group-id="1812042591-2">&lt;&lt;</span><span class="s">&quot;123&quot;</span><span class="p" data-group-id="1812042591-2">&gt;&gt;</span><span class="p" data-group-id="1812042591-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">123</span></code></pre><p><a href="#binary_to_integer/1"><code class="inline">binary_to_integer/1</code></a> accepts the same string formats
│ │ │  as <a href="#list_to_integer/1"><code class="inline">list_to_integer/1</code></a>.</p><p>Failure: <code class="inline">badarg</code> if <code class="inline">Binary</code> contains a bad representation of an integer.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="binary_to_integer/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │ @@ -8678,15 +8678,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> binary_to_integer(Binary, Base) -> <a href="#t:integer/0">integer</a>() when Binary :: <a href="#t:binary/0">binary</a>(), Base :: 2..36.</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns an integer whose text representation in base <code class="inline">Base</code> is <code class="inline">Binary</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="2934423096-1">(</span><span class="p" data-group-id="2934423096-2">&lt;&lt;</span><span class="s">&quot;3FF&quot;</span><span class="p" data-group-id="2934423096-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="2934423096-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns an integer whose text representation in base <code class="inline">Base</code> is <code class="inline">Binary</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="8175077628-1">(</span><span class="p" data-group-id="8175077628-2">&lt;&lt;</span><span class="s">&quot;3FF&quot;</span><span class="p" data-group-id="8175077628-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="8175077628-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1023</span></code></pre><p><a href="#binary_to_integer/2"><code class="inline">binary_to_integer/2</code></a> accepts the same string formats
│ │ │  as <a href="#list_to_integer/2"><code class="inline">list_to_integer/2</code></a>.</p><p>Failure: <code class="inline">badarg</code> if <code class="inline">Binary</code> contains a bad representation of an integer.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="binary_to_list/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │ @@ -8771,17 +8771,17 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> binary_to_term(Binary) -> <a href="#t:term/0">term</a>() when Binary :: <a href="#t:ext_binary/0">ext_binary</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns an Erlang term that is the result of decoding binary object <code class="inline">Binary</code>,
│ │ │  which must be encoded according to the
│ │ │ -<a href="erl_ext_dist.html">Erlang external term format</a>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="6234850212-1">(</span><span class="ss">hello</span><span class="p" data-group-id="6234850212-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6234850212-2">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="6234850212-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="ss">hello</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="6234850212-3">(</span><span class="n">Bin</span><span class="p" data-group-id="6234850212-3">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="erl_ext_dist.html">Erlang external term format</a>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="2864842509-1">(</span><span class="ss">hello</span><span class="p" data-group-id="2864842509-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2864842509-2">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="2864842509-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="ss">hello</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="2864842509-3">(</span><span class="n">Bin</span><span class="p" data-group-id="2864842509-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span></code></pre><section role="note" class="admonition warning"><h4 class="admonition-title warning">Warning</h4><p>When decoding binaries from untrusted sources, the untrusted source may submit
│ │ │  data in a way to create resources, such as atoms and remote references, that
│ │ │  cannot be garbage collected and lead to Denial of Service attack. In such
│ │ │  cases, consider using <a href="#binary_to_term/2"><code class="inline">binary_to_term/2</code></a> with the <code class="inline">safe</code>
│ │ │  option.</p></section><p>See also <a href="#term_to_binary/1"><code class="inline">term_to_binary/1</code></a> and <a href="#binary_to_term/2"><code class="inline">binary_to_term/2</code></a>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │ @@ -8820,30 +8820,30 @@
│ │ │  <p>Equivalent to <a href="#binary_to_term/1"><code class="inline">binary_to_term(Binary)</code></a>, but can be configured to
│ │ │  fit special purposes.</p><p>The allowed options are:</p><ul><li><p><strong><code class="inline">safe</code></strong> - Use this option when receiving binaries from an untrusted source.</p><p>When enabled, it prevents decoding data that can be used to attack the Erlang
│ │ │  runtime. In the event of receiving unsafe data, decoding fails with a <code class="inline">badarg</code>
│ │ │  error.</p><p>This prevents creation of new atoms directly, creation of new atoms indirectly
│ │ │  (as they are embedded in certain structures, such as process identifiers,
│ │ │  refs, and funs), and creation of new external function references. None of
│ │ │  those resources are garbage collected, so unchecked creation of them can
│ │ │ -exhaust available memory.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="6273726866-1">(</span><span class="p" data-group-id="6273726866-2">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6273726866-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6273726866-3">[</span><span class="ss">safe</span><span class="p" data-group-id="6273726866-3">]</span><span class="p" data-group-id="6273726866-1">)</span><span class="p">.</span><span class="w">
│ │ │ +exhaust available memory.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="0077572497-1">(</span><span class="p" data-group-id="0077572497-2">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0077572497-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0077572497-3">[</span><span class="ss">safe</span><span class="p" data-group-id="0077572497-3">]</span><span class="p" data-group-id="0077572497-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: bad argument</span><span class="gp unselectable">
│ │ │  &gt; </span><span class="ss">hello</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="6273726866-4">(</span><span class="p" data-group-id="6273726866-5">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6273726866-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6273726866-6">[</span><span class="ss">safe</span><span class="p" data-group-id="6273726866-6">]</span><span class="p" data-group-id="6273726866-4">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="0077572497-4">(</span><span class="p" data-group-id="0077572497-5">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0077572497-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0077572497-6">[</span><span class="ss">safe</span><span class="p" data-group-id="0077572497-6">]</span><span class="p" data-group-id="0077572497-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span></code></pre><section role="note" class="admonition warning"><h4 class="admonition-title warning">Warning</h4><p>The <code class="inline">safe</code> option ensures the data is safely processed by the Erlang runtime
│ │ │  but it does not guarantee the data is safe to your application. You must
│ │ │  always validate data from untrusted sources. If the binary is stored or
│ │ │  transits through untrusted sources, you should also consider
│ │ │  cryptographically signing it.</p></section></li><li><p><strong><code class="inline">used</code></strong> - Changes the return value to <code class="inline">{Term, Used}</code> where <code class="inline">Used</code> is the
│ │ │ -number of bytes actually read from <code class="inline">Binary</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Input</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1243516176-1">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="s">&quot;world&quot;</span><span class="p" data-group-id="1243516176-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1243516176-2">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p">,</span><span class="mi">119</span><span class="p">,</span><span class="mi">111</span><span class="p">,</span><span class="mi">114</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">100</span><span class="p" data-group-id="1243516176-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="p" data-group-id="1243516176-3">{</span><span class="n">Term</span><span class="p">,</span><span class="w"> </span><span class="n">Used</span><span class="p" data-group-id="1243516176-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="1243516176-4">(</span><span class="n">Input</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1243516176-5">[</span><span class="ss">used</span><span class="p" data-group-id="1243516176-5">]</span><span class="p" data-group-id="1243516176-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1243516176-6">{</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1243516176-6">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">split_binary</span><span class="p" data-group-id="1243516176-7">(</span><span class="n">Input</span><span class="p">,</span><span class="w"> </span><span class="n">Used</span><span class="p" data-group-id="1243516176-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1243516176-8">{</span><span class="p" data-group-id="1243516176-9">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="1243516176-9">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1243516176-10">&lt;&lt;</span><span class="s">&quot;world&quot;</span><span class="p" data-group-id="1243516176-10">&gt;&gt;</span><span class="p" data-group-id="1243516176-8">}</span></code></pre></li></ul><p>Failure: <code class="inline">badarg</code> if <code class="inline">safe</code> is specified and unsafe data is decoded.</p><p>See also <a href="#term_to_binary/1"><code class="inline">term_to_binary/1</code></a>, <a href="#binary_to_term/1"><code class="inline">binary_to_term/1</code></a>, and <a href="#list_to_existing_atom/1"><code class="inline">list_to_existing_atom/1</code></a>.</p>
│ │ │ +number of bytes actually read from <code class="inline">Binary</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Input</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6030122191-1">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="s">&quot;world&quot;</span><span class="p" data-group-id="6030122191-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6030122191-2">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p">,</span><span class="mi">119</span><span class="p">,</span><span class="mi">111</span><span class="p">,</span><span class="mi">114</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">100</span><span class="p" data-group-id="6030122191-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="p" data-group-id="6030122191-3">{</span><span class="n">Term</span><span class="p">,</span><span class="w"> </span><span class="n">Used</span><span class="p" data-group-id="6030122191-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="6030122191-4">(</span><span class="n">Input</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6030122191-5">[</span><span class="ss">used</span><span class="p" data-group-id="6030122191-5">]</span><span class="p" data-group-id="6030122191-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6030122191-6">{</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="6030122191-6">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">split_binary</span><span class="p" data-group-id="6030122191-7">(</span><span class="n">Input</span><span class="p">,</span><span class="w"> </span><span class="n">Used</span><span class="p" data-group-id="6030122191-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6030122191-8">{</span><span class="p" data-group-id="6030122191-9">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="6030122191-9">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6030122191-10">&lt;&lt;</span><span class="s">&quot;world&quot;</span><span class="p" data-group-id="6030122191-10">&gt;&gt;</span><span class="p" data-group-id="6030122191-8">}</span></code></pre></li></ul><p>Failure: <code class="inline">badarg</code> if <code class="inline">safe</code> is specified and unsafe data is decoded.</p><p>See also <a href="#term_to_binary/1"><code class="inline">term_to_binary/1</code></a>, <a href="#binary_to_term/1"><code class="inline">binary_to_term/1</code></a>, and <a href="#list_to_existing_atom/1"><code class="inline">list_to_existing_atom/1</code></a>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="bit_size/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#bit_size/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -8865,17 +8865,17 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> bit_size(Bitstring) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when Bitstring :: <a href="#t:bitstring/0">bitstring</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns an integer that is the size in bits of <code class="inline">Bitstring</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">bit_size</span><span class="p" data-group-id="1858727706-1">(</span><span class="p" data-group-id="1858727706-2">&lt;&lt;</span><span class="mi">433</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="mi">3</span><span class="p">:</span><span class="mi">3</span><span class="p" data-group-id="1858727706-2">&gt;&gt;</span><span class="p" data-group-id="1858727706-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns an integer that is the size in bits of <code class="inline">Bitstring</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">bit_size</span><span class="p" data-group-id="6197560175-1">(</span><span class="p" data-group-id="6197560175-2">&lt;&lt;</span><span class="mi">433</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="mi">3</span><span class="p">:</span><span class="mi">3</span><span class="p" data-group-id="6197560175-2">&gt;&gt;</span><span class="p" data-group-id="6197560175-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">19</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">bit_size</span><span class="p" data-group-id="1858727706-3">(</span><span class="p" data-group-id="1858727706-4">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1858727706-4">&gt;&gt;</span><span class="p" data-group-id="1858727706-3">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">bit_size</span><span class="p" data-group-id="6197560175-3">(</span><span class="p" data-group-id="6197560175-4">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6197560175-4">&gt;&gt;</span><span class="p" data-group-id="6197560175-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">24</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="bitstring_to_list/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#bitstring_to_list/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -8897,17 +8897,17 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> bitstring_to_list(Bitstring) -> [<a href="#t:byte/0">byte</a>() | <a href="#t:bitstring/0">bitstring</a>()] when Bitstring :: <a href="#t:bitstring/0">bitstring</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a list of integers corresponding to the bytes of <code class="inline">Bitstring</code>.</p><p>If the number of bits in the binary is not divisible by 8, the last element of
│ │ │ -the list is a bitstring containing the remaining 1-7 bits.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">bitstring_to_list</span><span class="p" data-group-id="8904556193-1">(</span><span class="p" data-group-id="8904556193-2">&lt;&lt;</span><span class="mi">433</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="8904556193-2">&gt;&gt;</span><span class="p" data-group-id="8904556193-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8904556193-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">177</span><span class="p" data-group-id="8904556193-3">]</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">bitstring_to_list</span><span class="p" data-group-id="8212810159-1">(</span><span class="p" data-group-id="8212810159-2">&lt;&lt;</span><span class="mi">433</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="mi">3</span><span class="p">:</span><span class="mi">3</span><span class="p" data-group-id="8212810159-2">&gt;&gt;</span><span class="p" data-group-id="8212810159-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8212810159-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">177</span><span class="p">,</span><span class="p" data-group-id="8212810159-4">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">3</span><span class="p" data-group-id="8212810159-4">&gt;&gt;</span><span class="p" data-group-id="8212810159-3">]</span></code></pre>
│ │ │ +the list is a bitstring containing the remaining 1-7 bits.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">bitstring_to_list</span><span class="p" data-group-id="0514545488-1">(</span><span class="p" data-group-id="0514545488-2">&lt;&lt;</span><span class="mi">433</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0514545488-2">&gt;&gt;</span><span class="p" data-group-id="0514545488-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0514545488-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">177</span><span class="p" data-group-id="0514545488-3">]</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">bitstring_to_list</span><span class="p" data-group-id="0240288173-1">(</span><span class="p" data-group-id="0240288173-2">&lt;&lt;</span><span class="mi">433</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="mi">3</span><span class="p">:</span><span class="mi">3</span><span class="p" data-group-id="0240288173-2">&gt;&gt;</span><span class="p" data-group-id="0240288173-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0240288173-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">177</span><span class="p">,</span><span class="p" data-group-id="0240288173-4">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">3</span><span class="p" data-group-id="0240288173-4">&gt;&gt;</span><span class="p" data-group-id="0240288173-3">]</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="byte_size/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#byte_size/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -8931,17 +8931,17 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> byte_size(Bitstring) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when Bitstring :: <a href="#t:bitstring/0">bitstring</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns an integer that is the number of bytes needed to contain <code class="inline">Bitstring</code>.
│ │ │  That is, if the number of bits in <code class="inline">Bitstring</code> is not divisible by 8, the
│ │ │ -resulting number of bytes is rounded <em>up</em>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">byte_size</span><span class="p" data-group-id="4010850875-1">(</span><span class="p" data-group-id="4010850875-2">&lt;&lt;</span><span class="mi">433</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="mi">3</span><span class="p">:</span><span class="mi">3</span><span class="p" data-group-id="4010850875-2">&gt;&gt;</span><span class="p" data-group-id="4010850875-1">)</span><span class="p">.</span><span class="w">
│ │ │ +resulting number of bytes is rounded <em>up</em>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">byte_size</span><span class="p" data-group-id="4290348875-1">(</span><span class="p" data-group-id="4290348875-2">&lt;&lt;</span><span class="mi">433</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="mi">3</span><span class="p">:</span><span class="mi">3</span><span class="p" data-group-id="4290348875-2">&gt;&gt;</span><span class="p" data-group-id="4290348875-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">byte_size</span><span class="p" data-group-id="4010850875-3">(</span><span class="p" data-group-id="4010850875-4">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4010850875-4">&gt;&gt;</span><span class="p" data-group-id="4010850875-3">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">byte_size</span><span class="p" data-group-id="4290348875-3">(</span><span class="p" data-group-id="4290348875-4">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4290348875-4">&gt;&gt;</span><span class="p" data-group-id="4290348875-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="ceil/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#ceil/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -8966,15 +8966,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> ceil(Number) -> <a href="#t:integer/0">integer</a>() when Number :: <a href="#t:number/0">number</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns the smallest integer not less than <code class="inline">Number</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">ceil</span><span class="p" data-group-id="9254862390-1">(</span><span class="mf">5.5</span><span class="p" data-group-id="9254862390-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns the smallest integer not less than <code class="inline">Number</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">ceil</span><span class="p" data-group-id="3024881776-1">(</span><span class="mf">5.5</span><span class="p" data-group-id="3024881776-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">6</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="decode_packet/3">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#decode_packet/3" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -9074,18 +9074,18 @@
│ │ │  <a href="https://www.ietf.org/rfc/rfc2732.txt">RFC2732 </a>.</p></li></ul><p>Options:</p><ul><li><p><strong><code class="inline">{packet_size, integer() &gt;= 0}</code></strong> - Sets the maximum allowed size of the
│ │ │  packet body. If the packet header indicates that the length of the packet is
│ │ │  longer than the maximum allowed length, the packet is considered invalid.
│ │ │  Defaults to 0, which means no size limit.</p></li><li><p><strong><code class="inline">{line_length, integer() &gt;= 0}</code></strong> - For packet type <code class="inline">line</code>, lines longer
│ │ │  than the indicated length are truncated.</p><p>Option <code class="inline">line_length</code> also applies to <code class="inline">http*</code> packet types as an alias for
│ │ │  option <code class="inline">packet_size</code> if <code class="inline">packet_size</code> itself is not set. This use is only
│ │ │  intended for backward compatibility.</p></li><li><p><strong><code class="inline">{line_delimiter, 0 =&lt; byte() =&lt; 255}</code></strong> - For packet type <code class="inline">line</code>, sets the
│ │ │ -delimiting byte. Default is the latin-1 character <code class="inline">$\n</code>.</p></li></ul><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">decode_packet</span><span class="p" data-group-id="2316149095-1">(</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="2316149095-2">&lt;&lt;</span><span class="mi">3</span><span class="p">,</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="2316149095-2">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="2316149095-3">[</span><span class="p" data-group-id="2316149095-3">]</span><span class="p" data-group-id="2316149095-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2316149095-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="2316149095-5">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2316149095-5">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="2316149095-6">&lt;&lt;</span><span class="s">&quot;d&quot;</span><span class="p" data-group-id="2316149095-6">&gt;&gt;</span><span class="p" data-group-id="2316149095-4">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">decode_packet</span><span class="p" data-group-id="2316149095-7">(</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="2316149095-8">&lt;&lt;</span><span class="mi">5</span><span class="p">,</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="2316149095-8">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="2316149095-9">[</span><span class="p" data-group-id="2316149095-9">]</span><span class="p" data-group-id="2316149095-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2316149095-10">{</span><span class="ss">more</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2316149095-10">}</span></code></pre>
│ │ │ +delimiting byte. Default is the latin-1 character <code class="inline">$\n</code>.</p></li></ul><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">decode_packet</span><span class="p" data-group-id="6446050974-1">(</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="6446050974-2">&lt;&lt;</span><span class="mi">3</span><span class="p">,</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="6446050974-2">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="6446050974-3">[</span><span class="p" data-group-id="6446050974-3">]</span><span class="p" data-group-id="6446050974-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6446050974-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="6446050974-5">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6446050974-5">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="6446050974-6">&lt;&lt;</span><span class="s">&quot;d&quot;</span><span class="p" data-group-id="6446050974-6">&gt;&gt;</span><span class="p" data-group-id="6446050974-4">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">decode_packet</span><span class="p" data-group-id="6446050974-7">(</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="6446050974-8">&lt;&lt;</span><span class="mi">5</span><span class="p">,</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="6446050974-8">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="6446050974-9">[</span><span class="p" data-group-id="6446050974-9">]</span><span class="p" data-group-id="6446050974-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6446050974-10">{</span><span class="ss">more</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6446050974-10">}</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="delete_element/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#delete_element/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -9106,16 +9106,16 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> delete_element(Index, Tuple1) -> Tuple2
│ │ │                          when Index :: <a href="#t:pos_integer/0">pos_integer</a>(), Tuple1 :: <a href="#t:tuple/0">tuple</a>(), Tuple2 :: <a href="#t:tuple/0">tuple</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a new tuple with element at <code class="inline">Index</code> removed from tuple <code class="inline">Tuple1</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">delete_element</span><span class="p" data-group-id="6010461602-1">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6010461602-2">{</span><span class="ss">one</span><span class="p">,</span><span class="w"> </span><span class="ss">two</span><span class="p">,</span><span class="w"> </span><span class="ss">three</span><span class="p" data-group-id="6010461602-2">}</span><span class="p" data-group-id="6010461602-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6010461602-3">{</span><span class="ss">one</span><span class="p">,</span><span class="ss">three</span><span class="p" data-group-id="6010461602-3">}</span></code></pre>
│ │ │ +<p>Returns a new tuple with element at <code class="inline">Index</code> removed from tuple <code class="inline">Tuple1</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">delete_element</span><span class="p" data-group-id="4970152323-1">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4970152323-2">{</span><span class="ss">one</span><span class="p">,</span><span class="w"> </span><span class="ss">two</span><span class="p">,</span><span class="w"> </span><span class="ss">three</span><span class="p" data-group-id="4970152323-2">}</span><span class="p" data-group-id="4970152323-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4970152323-3">{</span><span class="ss">one</span><span class="p">,</span><span class="ss">three</span><span class="p" data-group-id="4970152323-3">}</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="display/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#display/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -9165,15 +9165,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> element(N, Tuple) -> <a href="#t:term/0">term</a>() when N :: <a href="#t:pos_integer/0">pos_integer</a>(), Tuple :: <a href="#t:tuple/0">tuple</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns the <code class="inline">N</code>th element (numbering from 1) of <code class="inline">Tuple</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">element</span><span class="p" data-group-id="3761815491-1">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3761815491-2">{</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="3761815491-2">}</span><span class="p" data-group-id="3761815491-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns the <code class="inline">N</code>th element (numbering from 1) of <code class="inline">Tuple</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">element</span><span class="p" data-group-id="3630378640-1">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3630378640-2">{</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="3630378640-2">}</span><span class="p" data-group-id="3630378640-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">b</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="external_size/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#external_size/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -9195,18 +9195,18 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> external_size(Term) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when Term :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Calculates, without doing the encoding, the maximum byte size for a term encoded
│ │ │ -in the Erlang external term format.</p><p>The following condition applies always:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Size1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="1960694309-1">(</span><span class="nf">term_to_binary</span><span class="p" data-group-id="1960694309-2">(</span><span class="n">Term</span><span class="p" data-group-id="1960694309-2">)</span><span class="p" data-group-id="1960694309-1">)</span><span class="p">,</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Size2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">external_size</span><span class="p" data-group-id="1960694309-3">(</span><span class="n">Term</span><span class="p" data-group-id="1960694309-3">)</span><span class="p">,</span><span class="gp unselectable">
│ │ │ +in the Erlang external term format.</p><p>The following condition applies always:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Size1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="4103506742-1">(</span><span class="nf">term_to_binary</span><span class="p" data-group-id="4103506742-2">(</span><span class="n">Term</span><span class="p" data-group-id="4103506742-2">)</span><span class="p" data-group-id="4103506742-1">)</span><span class="p">,</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">Size2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">external_size</span><span class="p" data-group-id="4103506742-3">(</span><span class="n">Term</span><span class="p" data-group-id="4103506742-3">)</span><span class="p">,</span><span class="gp unselectable">
│ │ │  &gt; </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Size1</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">Size2</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">true</span></code></pre><p>This is equivalent to a call to:</p><pre><code class="makeup erlang" translate="no"><span class="nc">erlang</span><span class="p">:</span><span class="nf">external_size</span><span class="p" data-group-id="9112093487-1">(</span><span class="n">Term</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9112093487-2">[</span><span class="p" data-group-id="9112093487-2">]</span><span class="p" data-group-id="9112093487-1">)</span></code></pre>
│ │ │ +</span><span class="ss">true</span></code></pre><p>This is equivalent to a call to:</p><pre><code class="makeup erlang" translate="no"><span class="nc">erlang</span><span class="p">:</span><span class="nf">external_size</span><span class="p" data-group-id="0624259639-1">(</span><span class="n">Term</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0624259639-2">[</span><span class="p" data-group-id="0624259639-2">]</span><span class="p" data-group-id="0624259639-1">)</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="external_size/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#external_size/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -9235,16 +9235,16 @@
│ │ │                                  deterministic |
│ │ │                                  {minor_version, Version :: 0..2} |
│ │ │                                  local].</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Calculates, without doing the encoding, the maximum byte size for a term encoded
│ │ │ -in the Erlang external term format.</p><p>The following condition applies always:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Size1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="0093034782-1">(</span><span class="nf">term_to_binary</span><span class="p" data-group-id="0093034782-2">(</span><span class="n">Term</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="0093034782-2">)</span><span class="p" data-group-id="0093034782-1">)</span><span class="p">,</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Size2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">external_size</span><span class="p" data-group-id="0093034782-3">(</span><span class="n">Term</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="0093034782-3">)</span><span class="p">,</span><span class="gp unselectable">
│ │ │ +in the Erlang external term format.</p><p>The following condition applies always:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Size1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="1619197342-1">(</span><span class="nf">term_to_binary</span><span class="p" data-group-id="1619197342-2">(</span><span class="n">Term</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="1619197342-2">)</span><span class="p" data-group-id="1619197342-1">)</span><span class="p">,</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">Size2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">external_size</span><span class="p" data-group-id="1619197342-3">(</span><span class="n">Term</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="1619197342-3">)</span><span class="p">,</span><span class="gp unselectable">
│ │ │  &gt; </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Size1</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">Size2</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><p>Option <code class="inline">{minor_version, Version}</code> specifies how floats are encoded. For a
│ │ │  detailed description, see <a href="#term_to_binary/2"><code class="inline">term_to_binary/2</code></a>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="float/1">
│ │ │  
│ │ │ @@ -9269,15 +9269,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> float(Number) -> <a href="#t:float/0">float</a>() when Number :: <a href="#t:number/0">number</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a float by converting <code class="inline">Number</code> to a float.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">float</span><span class="p" data-group-id="2144130734-1">(</span><span class="mi">55</span><span class="p" data-group-id="2144130734-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns a float by converting <code class="inline">Number</code> to a float.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">float</span><span class="p" data-group-id="9748209880-1">(</span><span class="mi">55</span><span class="p" data-group-id="9748209880-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">55.0</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>If used on the top level in a guard, it tests whether the argument is a
│ │ │  floating point number; for clarity, use <a href="#is_float/1"><code class="inline">is_float/1</code></a> instead.</p><p>When <a href="#float/1"><code class="inline">float/1</code></a> is used in an expression in a guard, such as
│ │ │  '<code class="inline">float(A) == 4.0</code>', it converts a number as described earlier.</p></section>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="float_to_binary/1">
│ │ │  
│ │ │ @@ -9340,26 +9340,26 @@
│ │ │                                   {decimals, Decimals :: 0..253} |
│ │ │                                   {scientific, Decimals :: 0..249} |
│ │ │                                   compact | short.</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a binary corresponding to the text representation of <code class="inline">Float</code> using fixed
│ │ │ -decimal point formatting.</p><p><code class="inline">Options</code> behaves in the same way as <a href="#float_to_list/2"><code class="inline">float_to_list/2</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="9010008590-1">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9010008590-2">[</span><span class="p" data-group-id="9010008590-3">{</span><span class="ss">decimals</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="9010008590-3">}</span><span class="p" data-group-id="9010008590-2">]</span><span class="p" data-group-id="9010008590-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9010008590-4">&lt;&lt;</span><span class="s">&quot;7.1200&quot;</span><span class="p" data-group-id="9010008590-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="9010008590-5">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9010008590-6">[</span><span class="p" data-group-id="9010008590-7">{</span><span class="ss">decimals</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="9010008590-7">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compact</span><span class="p" data-group-id="9010008590-6">]</span><span class="p" data-group-id="9010008590-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9010008590-8">&lt;&lt;</span><span class="s">&quot;7.12&quot;</span><span class="p" data-group-id="9010008590-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="9010008590-9">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9010008590-10">[</span><span class="p" data-group-id="9010008590-11">{</span><span class="ss">scientific</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="9010008590-11">}</span><span class="p" data-group-id="9010008590-10">]</span><span class="p" data-group-id="9010008590-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9010008590-12">&lt;&lt;</span><span class="s">&quot;7.120e+00&quot;</span><span class="p" data-group-id="9010008590-12">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="9010008590-13">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9010008590-14">[</span><span class="ss">short</span><span class="p" data-group-id="9010008590-14">]</span><span class="p" data-group-id="9010008590-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9010008590-15">&lt;&lt;</span><span class="s">&quot;7.12&quot;</span><span class="p" data-group-id="9010008590-15">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="9010008590-16">(</span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9010008590-17">[</span><span class="ss">short</span><span class="p" data-group-id="9010008590-17">]</span><span class="p" data-group-id="9010008590-16">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9010008590-18">&lt;&lt;</span><span class="s">&quot;0.30000000000000004&quot;</span><span class="p" data-group-id="9010008590-18">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="9010008590-19">(</span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p" data-group-id="9010008590-19">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9010008590-20">&lt;&lt;</span><span class="s">&quot;3.00000000000000044409e-01&quot;</span><span class="p" data-group-id="9010008590-20">&gt;&gt;</span></code></pre>
│ │ │ +decimal point formatting.</p><p><code class="inline">Options</code> behaves in the same way as <a href="#float_to_list/2"><code class="inline">float_to_list/2</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="6317786855-1">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6317786855-2">[</span><span class="p" data-group-id="6317786855-3">{</span><span class="ss">decimals</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="6317786855-3">}</span><span class="p" data-group-id="6317786855-2">]</span><span class="p" data-group-id="6317786855-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6317786855-4">&lt;&lt;</span><span class="s">&quot;7.1200&quot;</span><span class="p" data-group-id="6317786855-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="6317786855-5">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6317786855-6">[</span><span class="p" data-group-id="6317786855-7">{</span><span class="ss">decimals</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="6317786855-7">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compact</span><span class="p" data-group-id="6317786855-6">]</span><span class="p" data-group-id="6317786855-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6317786855-8">&lt;&lt;</span><span class="s">&quot;7.12&quot;</span><span class="p" data-group-id="6317786855-8">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="6317786855-9">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6317786855-10">[</span><span class="p" data-group-id="6317786855-11">{</span><span class="ss">scientific</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6317786855-11">}</span><span class="p" data-group-id="6317786855-10">]</span><span class="p" data-group-id="6317786855-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6317786855-12">&lt;&lt;</span><span class="s">&quot;7.120e+00&quot;</span><span class="p" data-group-id="6317786855-12">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="6317786855-13">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6317786855-14">[</span><span class="ss">short</span><span class="p" data-group-id="6317786855-14">]</span><span class="p" data-group-id="6317786855-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6317786855-15">&lt;&lt;</span><span class="s">&quot;7.12&quot;</span><span class="p" data-group-id="6317786855-15">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="6317786855-16">(</span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6317786855-17">[</span><span class="ss">short</span><span class="p" data-group-id="6317786855-17">]</span><span class="p" data-group-id="6317786855-16">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6317786855-18">&lt;&lt;</span><span class="s">&quot;0.30000000000000004&quot;</span><span class="p" data-group-id="6317786855-18">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="6317786855-19">(</span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p" data-group-id="6317786855-19">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6317786855-20">&lt;&lt;</span><span class="s">&quot;3.00000000000000044409e-01&quot;</span><span class="p" data-group-id="6317786855-20">&gt;&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="float_to_list/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#float_to_list/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -9427,25 +9427,25 @@
│ │ │  are truncated. This option is only meaningful together with option <code class="inline">decimals</code>.</li><li>If option <code class="inline">scientific</code> is specified, the float is formatted using scientific
│ │ │  notation with <code class="inline">Decimals</code> digits of precision.</li><li>If option <code class="inline">short</code> is specified, the float is formatted with the smallest
│ │ │  number of digits that still guarantees that
│ │ │  <code class="inline">F =:= list_to_float(float_to_list(F, [short]))</code>. When the float is inside the
│ │ │  range (-2⁵³, 2⁵³), the notation that yields the smallest number of characters
│ │ │  is used (scientific notation or normal decimal notation). Floats outside the
│ │ │  range (-2⁵³, 2⁵³) are always formatted using scientific notation to avoid
│ │ │ -confusing results when doing arithmetic operations.</li><li>If <code class="inline">Options</code> is <code class="inline">[]</code>, the function behaves as <a href="#float_to_list/1"><code class="inline">float_to_list/1</code></a>.</li></ul><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4027244561-1">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4027244561-2">[</span><span class="p" data-group-id="4027244561-3">{</span><span class="ss">decimals</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="4027244561-3">}</span><span class="p" data-group-id="4027244561-2">]</span><span class="p" data-group-id="4027244561-1">)</span><span class="p">.</span><span class="w">
│ │ │ +confusing results when doing arithmetic operations.</li><li>If <code class="inline">Options</code> is <code class="inline">[]</code>, the function behaves as <a href="#float_to_list/1"><code class="inline">float_to_list/1</code></a>.</li></ul><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4743533139-1">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4743533139-2">[</span><span class="p" data-group-id="4743533139-3">{</span><span class="ss">decimals</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="4743533139-3">}</span><span class="p" data-group-id="4743533139-2">]</span><span class="p" data-group-id="4743533139-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;7.1200&quot;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4027244561-4">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4027244561-5">[</span><span class="p" data-group-id="4027244561-6">{</span><span class="ss">decimals</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="4027244561-6">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compact</span><span class="p" data-group-id="4027244561-5">]</span><span class="p" data-group-id="4027244561-4">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4743533139-4">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4743533139-5">[</span><span class="p" data-group-id="4743533139-6">{</span><span class="ss">decimals</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="4743533139-6">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compact</span><span class="p" data-group-id="4743533139-5">]</span><span class="p" data-group-id="4743533139-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;7.12&quot;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4027244561-7">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4027244561-8">[</span><span class="p" data-group-id="4027244561-9">{</span><span class="ss">scientific</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4027244561-9">}</span><span class="p" data-group-id="4027244561-8">]</span><span class="p" data-group-id="4027244561-7">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4743533139-7">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4743533139-8">[</span><span class="p" data-group-id="4743533139-9">{</span><span class="ss">scientific</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4743533139-9">}</span><span class="p" data-group-id="4743533139-8">]</span><span class="p" data-group-id="4743533139-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;7.120e+00&quot;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4027244561-10">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4027244561-11">[</span><span class="ss">short</span><span class="p" data-group-id="4027244561-11">]</span><span class="p" data-group-id="4027244561-10">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4743533139-10">(</span><span class="mf">7.12</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4743533139-11">[</span><span class="ss">short</span><span class="p" data-group-id="4743533139-11">]</span><span class="p" data-group-id="4743533139-10">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;7.12&quot;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4027244561-12">(</span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4027244561-13">[</span><span class="ss">short</span><span class="p" data-group-id="4027244561-13">]</span><span class="p" data-group-id="4027244561-12">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4743533139-12">(</span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4743533139-13">[</span><span class="ss">short</span><span class="p" data-group-id="4743533139-13">]</span><span class="p" data-group-id="4743533139-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;0.30000000000000004&quot;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4027244561-14">(</span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p" data-group-id="4027244561-14">)</span><span class="w">
│ │ │ +&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="4743533139-14">(</span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p" data-group-id="4743533139-14">)</span><span class="w">
│ │ │  </span><span class="s">&quot;3.00000000000000044409e-01&quot;</span></code></pre><p>In the last example, <a href="#float_to_list/1"><code class="inline">float_to_list(0.1+0.2)</code></a> evaluates to
│ │ │  <code class="inline">&quot;3.00000000000000044409e-01&quot;</code>. The reason for this is explained in
│ │ │  <a href="../../../doc/system/data_types.html#float_representation_problem">Representation of Floating Point Numbers</a>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="floor/1">
│ │ │  
│ │ │ @@ -9472,15 +9472,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> floor(Number) -> <a href="#t:integer/0">integer</a>() when Number :: <a href="#t:number/0">number</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns the largest integer not greater than <code class="inline">Number</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">floor</span><span class="p" data-group-id="9551408295-1">(</span><span class="o">-</span><span class="mf">10.5</span><span class="p" data-group-id="9551408295-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns the largest integer not greater than <code class="inline">Number</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">floor</span><span class="p" data-group-id="8938848927-1">(</span><span class="o">-</span><span class="mf">10.5</span><span class="p" data-group-id="8938848927-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">-</span><span class="mi">11</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="fun_info/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#fun_info/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -9600,25 +9600,25 @@
│ │ │  named <code class="inline">module</code>, <code class="inline">index</code> and <code class="inline">uniq</code> in the result of
│ │ │  <a href="#fun_info/1"><code class="inline">erlang:fun_info(Fun)</code></a>.</p></li><li><p><strong>uncompiled code</strong> - All funs created from fun expressions in uncompiled code
│ │ │  with the same arity are mapped to the same list by
│ │ │  <a href="#fun_to_list/1"><code class="inline">fun_to_list/1</code></a>.</p></li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Generally, one can not use <a href="#fun_to_list/1"><code class="inline">fun_to_list/1</code></a> to check if two
│ │ │  funs are equal as <a href="#fun_to_list/1"><code class="inline">fun_to_list/1</code></a> does not take the fun's
│ │ │  environment into account. See <a href="#fun_info/1"><code class="inline">erlang:fun_info/1</code></a> for how to
│ │ │  get the environment of a fun.</p></section><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>The output of <a href="#fun_to_list/1"><code class="inline">fun_to_list/1</code></a> can differ between Erlang
│ │ │ -implementations and may change in future versions.</p></section><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5979913297-1">(</span><span class="ss">test</span><span class="p" data-group-id="5979913297-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5979913297-2">(</span><span class="p" data-group-id="5979913297-3">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">add2</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">fun_tuple</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5979913297-3">]</span><span class="p" data-group-id="5979913297-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="5979913297-4">(</span><span class="n">A</span><span class="p" data-group-id="5979913297-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5979913297-5">(</span><span class="n">B</span><span class="p" data-group-id="5979913297-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add2</span><span class="p" data-group-id="5979913297-6">(</span><span class="p" data-group-id="5979913297-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="ss">add</span><span class="p">/</span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">fun_tuple</span><span class="p" data-group-id="5979913297-7">(</span><span class="p" data-group-id="5979913297-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5979913297-8">{</span><span class="nf">fun</span><span class="p" data-group-id="5979913297-9">(</span><span class="p" data-group-id="5979913297-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5979913297-10">(</span><span class="p" data-group-id="5979913297-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="5979913297-8">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="3446317198-1">{</span><span class="k">fun</span><span class="w"> </span><span class="nc">test</span><span class="p">:</span><span class="ss">add</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="nc">test</span><span class="p">:</span><span class="nf">add2</span><span class="p" data-group-id="3446317198-2">(</span><span class="p" data-group-id="3446317198-2">)</span><span class="p" data-group-id="3446317198-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3446317198-3">{</span><span class="k">fun</span><span class="w"> </span><span class="nc">test</span><span class="p">:</span><span class="ss">add</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">test</span><span class="p">.</span><span class="mf">1.107738983</span><span class="o">&gt;</span><span class="p" data-group-id="3446317198-3">}</span></code></pre><p>Explanation: <code class="inline">fun test:add/1</code> is upgradable but <code class="inline">test:add2()</code> is not upgradable.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="2773897521-1">{</span><span class="nc">test</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2773897521-2">(</span><span class="mi">1</span><span class="p" data-group-id="2773897521-2">)</span><span class="p">,</span><span class="w"> </span><span class="nc">test</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2773897521-3">(</span><span class="mi">42</span><span class="p" data-group-id="2773897521-3">)</span><span class="p" data-group-id="2773897521-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2773897521-4">{</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">test</span><span class="p">.</span><span class="mf">0.107738983</span><span class="o">&gt;</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">test</span><span class="p">.</span><span class="mf">0.107738983</span><span class="o">&gt;</span><span class="p" data-group-id="2773897521-4">}</span></code></pre><p>Explanation: <code class="inline">test:add(1)</code> and <code class="inline">test:add(42)</code> has the same string representation
│ │ │ -as the environment is not taken into account.</p><pre><code class="makeup erlang" translate="no"><span class="o">&gt;</span><span class="nc">test</span><span class="p">:</span><span class="nf">fun_tuple</span><span class="p" data-group-id="5117118489-1">(</span><span class="p" data-group-id="5117118489-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5117118489-2">{</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">test</span><span class="p">.</span><span class="mf">2.107738983</span><span class="o">&gt;</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">test</span><span class="p">.</span><span class="mf">3.107738983</span><span class="o">&gt;</span><span class="p" data-group-id="5117118489-2">}</span></code></pre><p>Explanation: The string representations differ because the funs come from
│ │ │ -different fun expressions.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="5810723495-1">{</span><span class="nf">fun</span><span class="p" data-group-id="5810723495-2">(</span><span class="p" data-group-id="5810723495-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5810723495-3">(</span><span class="p" data-group-id="5810723495-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="5810723495-1">}</span><span class="p">.</span><span class="w"> </span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5810723495-4">{</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">45.97283095</span><span class="o">&gt;</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">45.97283095</span><span class="o">&gt;</span><span class="p" data-group-id="5810723495-4">}</span></code></pre><p>Explanation: All funs created from fun expressions of this form in uncompiled
│ │ │ +implementations and may change in future versions.</p></section><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3884558714-1">(</span><span class="ss">test</span><span class="p" data-group-id="3884558714-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3884558714-2">(</span><span class="p" data-group-id="3884558714-3">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">add2</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">fun_tuple</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3884558714-3">]</span><span class="p" data-group-id="3884558714-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="3884558714-4">(</span><span class="n">A</span><span class="p" data-group-id="3884558714-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3884558714-5">(</span><span class="n">B</span><span class="p" data-group-id="3884558714-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add2</span><span class="p" data-group-id="3884558714-6">(</span><span class="p" data-group-id="3884558714-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="ss">add</span><span class="p">/</span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">fun_tuple</span><span class="p" data-group-id="3884558714-7">(</span><span class="p" data-group-id="3884558714-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3884558714-8">{</span><span class="nf">fun</span><span class="p" data-group-id="3884558714-9">(</span><span class="p" data-group-id="3884558714-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3884558714-10">(</span><span class="p" data-group-id="3884558714-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="3884558714-8">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="7904849241-1">{</span><span class="k">fun</span><span class="w"> </span><span class="nc">test</span><span class="p">:</span><span class="ss">add</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="nc">test</span><span class="p">:</span><span class="nf">add2</span><span class="p" data-group-id="7904849241-2">(</span><span class="p" data-group-id="7904849241-2">)</span><span class="p" data-group-id="7904849241-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7904849241-3">{</span><span class="k">fun</span><span class="w"> </span><span class="nc">test</span><span class="p">:</span><span class="ss">add</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">test</span><span class="p">.</span><span class="mf">1.107738983</span><span class="o">&gt;</span><span class="p" data-group-id="7904849241-3">}</span></code></pre><p>Explanation: <code class="inline">fun test:add/1</code> is upgradable but <code class="inline">test:add2()</code> is not upgradable.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="4293352805-1">{</span><span class="nc">test</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="4293352805-2">(</span><span class="mi">1</span><span class="p" data-group-id="4293352805-2">)</span><span class="p">,</span><span class="w"> </span><span class="nc">test</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="4293352805-3">(</span><span class="mi">42</span><span class="p" data-group-id="4293352805-3">)</span><span class="p" data-group-id="4293352805-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4293352805-4">{</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">test</span><span class="p">.</span><span class="mf">0.107738983</span><span class="o">&gt;</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">test</span><span class="p">.</span><span class="mf">0.107738983</span><span class="o">&gt;</span><span class="p" data-group-id="4293352805-4">}</span></code></pre><p>Explanation: <code class="inline">test:add(1)</code> and <code class="inline">test:add(42)</code> has the same string representation
│ │ │ +as the environment is not taken into account.</p><pre><code class="makeup erlang" translate="no"><span class="o">&gt;</span><span class="nc">test</span><span class="p">:</span><span class="nf">fun_tuple</span><span class="p" data-group-id="8122506629-1">(</span><span class="p" data-group-id="8122506629-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8122506629-2">{</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">test</span><span class="p">.</span><span class="mf">2.107738983</span><span class="o">&gt;</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">test</span><span class="p">.</span><span class="mf">3.107738983</span><span class="o">&gt;</span><span class="p" data-group-id="8122506629-2">}</span></code></pre><p>Explanation: The string representations differ because the funs come from
│ │ │ +different fun expressions.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="1018616002-1">{</span><span class="nf">fun</span><span class="p" data-group-id="1018616002-2">(</span><span class="p" data-group-id="1018616002-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1018616002-3">(</span><span class="p" data-group-id="1018616002-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="1018616002-1">}</span><span class="p">.</span><span class="w"> </span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1018616002-4">{</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">45.97283095</span><span class="o">&gt;</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">45.97283095</span><span class="o">&gt;</span><span class="p" data-group-id="1018616002-4">}</span></code></pre><p>Explanation: All funs created from fun expressions of this form in uncompiled
│ │ │  code with the same arity are mapped to the same list by
│ │ │  <a href="#fun_to_list/1"><code class="inline">fun_to_list/1</code></a>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="hd/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │ @@ -9642,16 +9642,16 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> hd(List) -> Head when List :: <a href="#t:nonempty_maybe_improper_list/0">nonempty_maybe_improper_list</a>(), Head :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns the head of <code class="inline">List</code>, that is, the first element.</p><p>It works with improper lists.</p><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="5108575737-1">(</span><span class="p" data-group-id="5108575737-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5108575737-2">]</span><span class="p" data-group-id="5108575737-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">1</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="5054549822-1">(</span><span class="p" data-group-id="5054549822-2">[</span><span class="ss">first</span><span class="p">,</span><span class="w"> </span><span class="ss">second</span><span class="p">,</span><span class="w"> </span><span class="ss">third</span><span class="p">,</span><span class="w"> </span><span class="ss">so_on</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">improper_end</span><span class="p" data-group-id="5054549822-2">]</span><span class="p" data-group-id="5054549822-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns the head of <code class="inline">List</code>, that is, the first element.</p><p>It works with improper lists.</p><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="1442672148-1">(</span><span class="p" data-group-id="1442672148-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1442672148-2">]</span><span class="p" data-group-id="1442672148-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">1</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="2939976382-1">(</span><span class="p" data-group-id="2939976382-2">[</span><span class="ss">first</span><span class="p">,</span><span class="w"> </span><span class="ss">second</span><span class="p">,</span><span class="w"> </span><span class="ss">third</span><span class="p">,</span><span class="w"> </span><span class="ss">so_on</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">improper_end</span><span class="p" data-group-id="2939976382-2">]</span><span class="p" data-group-id="2939976382-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">first</span></code></pre><p>Failure: <code class="inline">badarg</code> if <code class="inline">List</code> is an empty list <code class="inline">[]</code>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="insert_element/3">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#insert_element/3" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -9676,16 +9676,16 @@
│ │ │                          when
│ │ │                              Index :: <a href="#t:pos_integer/0">pos_integer</a>(), Tuple1 :: <a href="#t:tuple/0">tuple</a>(), Tuple2 :: <a href="#t:tuple/0">tuple</a>(), Term :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a new tuple with element <code class="inline">Term</code> inserted at position <code class="inline">Index</code> in tuple
│ │ │  <code class="inline">Tuple1</code>. All elements from position <code class="inline">Index</code> and upwards are pushed one step
│ │ │ -higher in the new tuple <code class="inline">Tuple2</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">insert_element</span><span class="p" data-group-id="1923998063-1">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1923998063-2">{</span><span class="ss">one</span><span class="p">,</span><span class="w"> </span><span class="ss">two</span><span class="p">,</span><span class="w"> </span><span class="ss">three</span><span class="p" data-group-id="1923998063-2">}</span><span class="p">,</span><span class="w"> </span><span class="ss">new</span><span class="p" data-group-id="1923998063-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1923998063-3">{</span><span class="ss">one</span><span class="p">,</span><span class="ss">new</span><span class="p">,</span><span class="ss">two</span><span class="p">,</span><span class="ss">three</span><span class="p" data-group-id="1923998063-3">}</span></code></pre>
│ │ │ +higher in the new tuple <code class="inline">Tuple2</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">insert_element</span><span class="p" data-group-id="4740886081-1">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4740886081-2">{</span><span class="ss">one</span><span class="p">,</span><span class="w"> </span><span class="ss">two</span><span class="p">,</span><span class="w"> </span><span class="ss">three</span><span class="p" data-group-id="4740886081-2">}</span><span class="p">,</span><span class="w"> </span><span class="ss">new</span><span class="p" data-group-id="4740886081-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4740886081-3">{</span><span class="ss">one</span><span class="p">,</span><span class="ss">new</span><span class="p">,</span><span class="ss">two</span><span class="p">,</span><span class="ss">three</span><span class="p" data-group-id="4740886081-3">}</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="integer_to_binary/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#integer_to_binary/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -9707,16 +9707,16 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> integer_to_binary(Integer) -> <a href="#t:binary/0">binary</a>() when Integer :: <a href="#t:integer/0">integer</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a binary corresponding to the text representation of <code class="inline">Integer</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="3509439777-1">(</span><span class="mi">77</span><span class="p" data-group-id="3509439777-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3509439777-2">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="3509439777-2">&gt;&gt;</span></code></pre>
│ │ │ +<p>Returns a binary corresponding to the text representation of <code class="inline">Integer</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="8573299103-1">(</span><span class="mi">77</span><span class="p" data-group-id="8573299103-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8573299103-2">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="8573299103-2">&gt;&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="integer_to_binary/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#integer_to_binary/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -9739,16 +9739,16 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> integer_to_binary(Integer, Base) -> <a href="#t:binary/0">binary</a>() when Integer :: <a href="#t:integer/0">integer</a>(), Base :: 2..36.</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a binary corresponding to the text representation of <code class="inline">Integer</code> in base
│ │ │ -<code class="inline">Base</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="5072474329-1">(</span><span class="mi">1023</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="5072474329-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5072474329-2">&lt;&lt;</span><span class="s">&quot;3FF&quot;</span><span class="p" data-group-id="5072474329-2">&gt;&gt;</span></code></pre>
│ │ │ +<code class="inline">Base</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="9368163932-1">(</span><span class="mi">1023</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="9368163932-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9368163932-2">&lt;&lt;</span><span class="s">&quot;3FF&quot;</span><span class="p" data-group-id="9368163932-2">&gt;&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="integer_to_list/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#integer_to_list/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -9768,15 +9768,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> integer_to_list(Integer) -> <a href="#t:string/0">string</a>() when Integer :: <a href="#t:integer/0">integer</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a string corresponding to the text representation of <code class="inline">Integer</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="7838854234-1">(</span><span class="mi">77</span><span class="p" data-group-id="7838854234-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns a string corresponding to the text representation of <code class="inline">Integer</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="2158766773-1">(</span><span class="mi">77</span><span class="p" data-group-id="2158766773-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;77&quot;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="integer_to_list/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#integer_to_list/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -9798,15 +9798,15 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> integer_to_list(Integer, Base) -> <a href="#t:string/0">string</a>() when Integer :: <a href="#t:integer/0">integer</a>(), Base :: 2..36.</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a string corresponding to the text representation of <code class="inline">Integer</code> in base
│ │ │ -<code class="inline">Base</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="9205611394-1">(</span><span class="mi">1023</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="9205611394-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">Base</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="2399566548-1">(</span><span class="mi">1023</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="2399566548-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;3FF&quot;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="iolist_size/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#iolist_size/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -9828,15 +9828,15 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> iolist_size(Item) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when Item :: <a href="#t:iolist/0">iolist</a>() | <a href="#t:binary/0">binary</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns an integer, that is the size in bytes, of the binary that would be the
│ │ │ -result of <a href="#iolist_to_binary/1"><code class="inline">iolist_to_binary(Item)</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">iolist_size</span><span class="p" data-group-id="0487736130-1">(</span><span class="p" data-group-id="0487736130-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">|</span><span class="p" data-group-id="0487736130-3">&lt;&lt;</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0487736130-3">&gt;&gt;</span><span class="p" data-group-id="0487736130-2">]</span><span class="p" data-group-id="0487736130-1">)</span><span class="p">.</span><span class="w">
│ │ │ +result of <a href="#iolist_to_binary/1"><code class="inline">iolist_to_binary(Item)</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">iolist_size</span><span class="p" data-group-id="5556516563-1">(</span><span class="p" data-group-id="5556516563-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">|</span><span class="p" data-group-id="5556516563-3">&lt;&lt;</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5556516563-3">&gt;&gt;</span><span class="p" data-group-id="5556516563-2">]</span><span class="p" data-group-id="5556516563-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="iolist_to_binary/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#iolist_to_binary/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -9858,22 +9858,22 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> iolist_to_binary(IoListOrBinary) -> <a href="#t:binary/0">binary</a>() when IoListOrBinary :: <a href="#t:iolist/0">iolist</a>() | <a href="#t:binary/0">binary</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a binary that is made from the integers and binaries in
│ │ │ -<code class="inline">IoListOrBinary</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1752297544-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1752297544-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1752297544-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1752297544-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1752297544-3">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1752297544-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1752297544-4">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1752297544-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1752297544-5">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="1752297544-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1752297544-6">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="1752297544-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">iolist_to_binary</span><span class="p" data-group-id="1752297544-7">(</span><span class="p" data-group-id="1752297544-8">[</span><span class="n">Bin1</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="1752297544-9">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="n">Bin2</span><span class="p" data-group-id="1752297544-9">]</span><span class="p">,</span><span class="mi">4</span><span class="p">|</span><span class="n">Bin3</span><span class="p" data-group-id="1752297544-8">]</span><span class="p" data-group-id="1752297544-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1752297544-10">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1752297544-10">&gt;&gt;</span></code></pre>
│ │ │ +<code class="inline">IoListOrBinary</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3441867539-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3441867539-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3441867539-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3441867539-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3441867539-3">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3441867539-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3441867539-4">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3441867539-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3441867539-5">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="3441867539-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3441867539-6">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="3441867539-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">iolist_to_binary</span><span class="p" data-group-id="3441867539-7">(</span><span class="p" data-group-id="3441867539-8">[</span><span class="n">Bin1</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="3441867539-9">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="n">Bin2</span><span class="p" data-group-id="3441867539-9">]</span><span class="p">,</span><span class="mi">4</span><span class="p">|</span><span class="n">Bin3</span><span class="p" data-group-id="3441867539-8">]</span><span class="p" data-group-id="3441867539-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3441867539-10">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="3441867539-10">&gt;&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="iolist_to_iovec/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#iolist_to_iovec/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -9899,31 +9899,31 @@
│ │ │  
│ │ │  <p>Returns an <a href="#t:iovec/0">iovec</a> that is made from the integers and binaries in
│ │ │  <code class="inline">IoListOrBinary</code>. This function is useful when you want to flatten an iolist but
│ │ │  you do not need a single binary. This can be useful for passing the data to nif
│ │ │  functions such as <a href="erl_nif.html#enif_inspect_iovec"><code class="inline">enif_inspect_iovec</code></a> or do
│ │ │  more efficient message passing. The advantage of using this function over
│ │ │  <a href="#iolist_to_binary/1"><code class="inline">iolist_to_binary/1</code></a> is that it does not have to copy
│ │ │ -<a href="../../../doc/system/binaryhandling.html#refc_binary">off-heap binaries</a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0060879991-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0060879991-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0060879991-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0060879991-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0060879991-3">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0060879991-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0060879991-4">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0060879991-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0060879991-5">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="0060879991-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0060879991-6">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="0060879991-6">&gt;&gt;</span><span class="w">
│ │ │ +<a href="../../../doc/system/binaryhandling.html#refc_binary">off-heap binaries</a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6236186459-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6236186459-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6236186459-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6236186459-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6236186459-3">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="6236186459-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6236186459-4">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="6236186459-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6236186459-5">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="6236186459-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6236186459-6">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="6236186459-6">&gt;&gt;</span><span class="w">
│ │ │  </span><span class="c1">%% If you pass small binaries and integers it works as iolist_to_binary</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">iolist_to_iovec</span><span class="p" data-group-id="0060879991-7">(</span><span class="p" data-group-id="0060879991-8">[</span><span class="n">Bin1</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="0060879991-9">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="n">Bin2</span><span class="p" data-group-id="0060879991-9">]</span><span class="p">,</span><span class="mi">4</span><span class="p">|</span><span class="n">Bin3</span><span class="p" data-group-id="0060879991-8">]</span><span class="p" data-group-id="0060879991-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0060879991-10">[</span><span class="p" data-group-id="0060879991-11">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="0060879991-11">&gt;&gt;</span><span class="p" data-group-id="0060879991-10">]</span><span class="w">
│ │ │ +&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">iolist_to_iovec</span><span class="p" data-group-id="6236186459-7">(</span><span class="p" data-group-id="6236186459-8">[</span><span class="n">Bin1</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="6236186459-9">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="n">Bin2</span><span class="p" data-group-id="6236186459-9">]</span><span class="p">,</span><span class="mi">4</span><span class="p">|</span><span class="n">Bin3</span><span class="p" data-group-id="6236186459-8">]</span><span class="p" data-group-id="6236186459-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6236186459-10">[</span><span class="p" data-group-id="6236186459-11">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6236186459-11">&gt;&gt;</span><span class="p" data-group-id="6236186459-10">]</span><span class="w">
│ │ │  </span><span class="c1">%% If you pass larger binaries, they are split and returned in a form</span><span class="w">
│ │ │  </span><span class="c1">%% optimized for calling the C function writev.</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">iolist_to_iovec</span><span class="p" data-group-id="0060879991-12">(</span><span class="p" data-group-id="0060879991-13">[</span><span class="p" data-group-id="0060879991-14">&lt;&lt;</span><span class="mi">1</span><span class="p" data-group-id="0060879991-14">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="0060879991-15">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">8096</span><span class="p" data-group-id="0060879991-15">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="0060879991-16">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">8096</span><span class="p" data-group-id="0060879991-16">&gt;&gt;</span><span class="p" data-group-id="0060879991-13">]</span><span class="p" data-group-id="0060879991-12">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0060879991-17">[</span><span class="p" data-group-id="0060879991-18">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="mi">0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0060879991-18">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0060879991-19">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0060879991-19">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0060879991-20">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0060879991-20">&gt;&gt;</span><span class="p" data-group-id="0060879991-17">]</span></code></pre>
│ │ │ +&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">iolist_to_iovec</span><span class="p" data-group-id="6236186459-12">(</span><span class="p" data-group-id="6236186459-13">[</span><span class="p" data-group-id="6236186459-14">&lt;&lt;</span><span class="mi">1</span><span class="p" data-group-id="6236186459-14">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="6236186459-15">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">8096</span><span class="p" data-group-id="6236186459-15">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="6236186459-16">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">8096</span><span class="p" data-group-id="6236186459-16">&gt;&gt;</span><span class="p" data-group-id="6236186459-13">]</span><span class="p" data-group-id="6236186459-12">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6236186459-17">[</span><span class="p" data-group-id="6236186459-18">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="mi">0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6236186459-18">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6236186459-19">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6236186459-19">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6236186459-20">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6236186459-20">&gt;&gt;</span><span class="p" data-group-id="6236186459-17">]</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="is_atom/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#is_atom/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -10253,19 +10253,19 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> is_map_key(Key, Map) -> <a href="#t:boolean/0">boolean</a>() when Key :: <a href="#t:term/0">term</a>(), Map :: <a href="#t:map/0">map</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns <code class="inline">true</code> if map <code class="inline">Map</code> contains <code class="inline">Key</code> and returns <code class="inline">false</code> if it does not
│ │ │ -contain the <code class="inline">Key</code>.</p><p>The call fails with a <code class="inline">{badmap,Map}</code> exception if <code class="inline">Map</code> is not a map.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3918656004-1">#{</span><span class="s">&quot;42&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="3918656004-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3918656004-2">#{</span><span class="s">&quot;42&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="3918656004-2">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">is_map_key</span><span class="p" data-group-id="3918656004-3">(</span><span class="s">&quot;42&quot;</span><span class="p">,</span><span class="n">Map</span><span class="p" data-group-id="3918656004-3">)</span><span class="p">.</span><span class="w">
│ │ │ +contain the <code class="inline">Key</code>.</p><p>The call fails with a <code class="inline">{badmap,Map}</code> exception if <code class="inline">Map</code> is not a map.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0919538393-1">#{</span><span class="s">&quot;42&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="0919538393-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0919538393-2">#{</span><span class="s">&quot;42&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="0919538393-2">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">is_map_key</span><span class="p" data-group-id="0919538393-3">(</span><span class="s">&quot;42&quot;</span><span class="p">,</span><span class="n">Map</span><span class="p" data-group-id="0919538393-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">is_map_key</span><span class="p" data-group-id="3918656004-4">(</span><span class="ss">value</span><span class="p">,</span><span class="n">Map</span><span class="p" data-group-id="3918656004-4">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">is_map_key</span><span class="p" data-group-id="0919538393-4">(</span><span class="ss">value</span><span class="p">,</span><span class="n">Map</span><span class="p" data-group-id="0919538393-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="is_number/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#is_number/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -10508,15 +10508,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> length(List) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when List :: [<a href="#t:term/0">term</a>()].</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns the length of <code class="inline">List</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">length</span><span class="p" data-group-id="4830846833-1">(</span><span class="p" data-group-id="4830846833-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p" data-group-id="4830846833-2">]</span><span class="p" data-group-id="4830846833-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns the length of <code class="inline">List</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">length</span><span class="p" data-group-id="3233101725-1">(</span><span class="p" data-group-id="3233101725-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p" data-group-id="3233101725-2">]</span><span class="p" data-group-id="3233101725-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">9</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="list_to_atom/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#list_to_atom/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -10546,15 +10546,15 @@
│ │ │  Unicode characters above 255.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The number of characters that are permitted in an atom name is limited. The
│ │ │  default limits can be found in the
│ │ │  <a href="../../../doc/system/system_limits.html">efficiency guide (section System Limits)</a>.</p></section><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>There is a <a href="../../../doc/system/system_limits.html#atoms">configurable limit</a>
│ │ │  on how many atoms that can exist and atoms are not
│ │ │  garbage collected. Therefore, it is recommended to consider if
│ │ │  <a href="#list_to_existing_atom/1"><code class="inline">list_to_existing_atom/1</code></a> is a better option than
│ │ │  <a href="#list_to_atom/1"><code class="inline">list_to_atom/1</code></a>. The default limits can be found in the
│ │ │ -<a href="../../../doc/system/system_limits.html">Efficiency Guide (section System Limits)</a>.</p></section><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="6557788440-1">(</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="6557788440-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="../../../doc/system/system_limits.html">Efficiency Guide (section System Limits)</a>.</p></section><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="5368419168-1">(</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="5368419168-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">&#39;Erlang&#39;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="list_to_binary/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#list_to_binary/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -10575,22 +10575,22 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> list_to_binary(IoList) -> <a href="#t:binary/0">binary</a>() when IoList :: <a href="#t:iolist/0">iolist</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a binary that is made from the integers and binaries in <code class="inline">IoList</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8568911434-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8568911434-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8568911434-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8568911434-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8568911434-3">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8568911434-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8568911434-4">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8568911434-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8568911434-5">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="8568911434-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8568911434-6">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="8568911434-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">list_to_binary</span><span class="p" data-group-id="8568911434-7">(</span><span class="p" data-group-id="8568911434-8">[</span><span class="n">Bin1</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="8568911434-9">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="n">Bin2</span><span class="p" data-group-id="8568911434-9">]</span><span class="p">,</span><span class="mi">4</span><span class="p">|</span><span class="n">Bin3</span><span class="p" data-group-id="8568911434-8">]</span><span class="p" data-group-id="8568911434-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8568911434-10">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8568911434-10">&gt;&gt;</span></code></pre>
│ │ │ +<p>Returns a binary that is made from the integers and binaries in <code class="inline">IoList</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9947865739-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9947865739-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9947865739-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9947865739-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9947865739-3">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9947865739-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9947865739-4">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9947865739-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9947865739-5">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="9947865739-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9947865739-6">&lt;&lt;</span><span class="mi">6</span><span class="p" data-group-id="9947865739-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">list_to_binary</span><span class="p" data-group-id="9947865739-7">(</span><span class="p" data-group-id="9947865739-8">[</span><span class="n">Bin1</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="9947865739-9">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="n">Bin2</span><span class="p" data-group-id="9947865739-9">]</span><span class="p">,</span><span class="mi">4</span><span class="p">|</span><span class="n">Bin3</span><span class="p" data-group-id="9947865739-8">]</span><span class="p" data-group-id="9947865739-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9947865739-10">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9947865739-10">&gt;&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="list_to_bitstring/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#list_to_bitstring/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -10612,22 +10612,22 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> list_to_bitstring(BitstringList) -> <a href="#t:bitstring/0">bitstring</a>() when BitstringList :: <a href="#t:bitstring_list/0">bitstring_list</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a bitstring that is made from the integers and bitstrings in
│ │ │  <code class="inline">BitstringList</code>. (The last tail in <code class="inline">BitstringList</code> is allowed to be a
│ │ │ -bitstring.)</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7931635890-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7931635890-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7931635890-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7931635890-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7931635890-3">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7931635890-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7931635890-4">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7931635890-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7931635890-5">&lt;&lt;</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="7931635890-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7931635890-6">&lt;&lt;</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="7931635890-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">list_to_bitstring</span><span class="p" data-group-id="7931635890-7">(</span><span class="p" data-group-id="7931635890-8">[</span><span class="n">Bin1</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="7931635890-9">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="n">Bin2</span><span class="p" data-group-id="7931635890-9">]</span><span class="p">,</span><span class="mi">4</span><span class="p">|</span><span class="n">Bin3</span><span class="p" data-group-id="7931635890-8">]</span><span class="p" data-group-id="7931635890-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7931635890-10">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="7931635890-10">&gt;&gt;</span></code></pre>
│ │ │ +bitstring.)</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9452714078-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9452714078-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9452714078-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9452714078-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9452714078-3">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9452714078-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9452714078-4">&lt;&lt;</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9452714078-4">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9452714078-5">&lt;&lt;</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="9452714078-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9452714078-6">&lt;&lt;</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="9452714078-6">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">list_to_bitstring</span><span class="p" data-group-id="9452714078-7">(</span><span class="p" data-group-id="9452714078-8">[</span><span class="n">Bin1</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="9452714078-9">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="n">Bin2</span><span class="p" data-group-id="9452714078-9">]</span><span class="p">,</span><span class="mi">4</span><span class="p">|</span><span class="n">Bin3</span><span class="p" data-group-id="9452714078-8">]</span><span class="p" data-group-id="9452714078-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9452714078-10">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="9452714078-10">&gt;&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="list_to_existing_atom/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#list_to_existing_atom/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -10683,15 +10683,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> list_to_float(String) -> <a href="#t:float/0">float</a>() when String :: <a href="#t:string/0">string</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns the float whose text representation is <code class="inline">String</code>. </p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_float</span><span class="p" data-group-id="8669604402-1">(</span><span class="s">&quot;2.2017764e+0&quot;</span><span class="p" data-group-id="8669604402-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns the float whose text representation is <code class="inline">String</code>. </p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_float</span><span class="p" data-group-id="3066351916-1">(</span><span class="s">&quot;2.2017764e+0&quot;</span><span class="p" data-group-id="3066351916-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">2.2017764</span></code></pre><p>The float string format is the same as the format for
│ │ │  <a href="../../../doc/system/data_types.html">Erlang float literals</a> except for that underscores
│ │ │  are not permitted.</p><p>Failure: <code class="inline">badarg</code> if <code class="inline">String</code> contains a bad representation of a float.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="list_to_integer/1">
│ │ │  
│ │ │ @@ -10714,17 +10714,17 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> list_to_integer(String) -> <a href="#t:integer/0">integer</a>() when String :: <a href="#t:string/0">string</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns an integer whose text representation is <code class="inline">String</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="9967311952-1">(</span><span class="s">&quot;123&quot;</span><span class="p" data-group-id="9967311952-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">123</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="3416542367-1">(</span><span class="s">&quot;-123&quot;</span><span class="p" data-group-id="3416542367-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">-</span><span class="mi">123</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="7253101038-1">(</span><span class="s">&quot;+123234982304982309482093833234234&quot;</span><span class="p" data-group-id="7253101038-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns an integer whose text representation is <code class="inline">String</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="8416194914-1">(</span><span class="s">&quot;123&quot;</span><span class="p" data-group-id="8416194914-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">123</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="5077060786-1">(</span><span class="s">&quot;-123&quot;</span><span class="p" data-group-id="5077060786-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">-</span><span class="mi">123</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="8562068650-1">(</span><span class="s">&quot;+123234982304982309482093833234234&quot;</span><span class="p" data-group-id="8562068650-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">123234982304982309482093833234234</span></code></pre><p><code class="inline">String</code> must contain at least one digit character and can have an optional
│ │ │  prefix consisting of a single &quot;<code class="inline">+</code>&quot; or &quot;<code class="inline">-</code>&quot; character (that is, <code class="inline">String</code> must
│ │ │  match the regular expression <code class="inline">&quot;^[+-]?[0-9]+$&quot;</code>).</p><p>Failure: <code class="inline">badarg</code> if <code class="inline">String</code> contains a bad representation of an integer.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="list_to_integer/2">
│ │ │  
│ │ │ @@ -10747,19 +10747,19 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> list_to_integer(String, Base) -> <a href="#t:integer/0">integer</a>() when String :: <a href="#t:string/0">string</a>(), Base :: 2..36.</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns an integer whose text representation in base <code class="inline">Base</code> is <code class="inline">String</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="2357256417-1">(</span><span class="s">&quot;3FF&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="2357256417-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">1023</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="2123253184-1">(</span><span class="s">&quot;+3FF&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="2123253184-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">1023</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="9594250215-1">(</span><span class="s">&quot;3ff&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="9594250215-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">1023</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="8934966184-1">(</span><span class="s">&quot;3fF&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="8934966184-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">1023</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="5716996647-1">(</span><span class="s">&quot;-3FF&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="5716996647-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns an integer whose text representation in base <code class="inline">Base</code> is <code class="inline">String</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="9062894276-1">(</span><span class="s">&quot;3FF&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="9062894276-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">1023</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="5379626568-1">(</span><span class="s">&quot;+3FF&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="5379626568-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">1023</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="3074763741-1">(</span><span class="s">&quot;3ff&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="3074763741-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">1023</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="4675291590-1">(</span><span class="s">&quot;3fF&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="4675291590-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">1023</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="7507592837-1">(</span><span class="s">&quot;-3FF&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">16</span><span class="p" data-group-id="7507592837-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">-</span><span class="mi">1023</span></code></pre><p>For example, when <code class="inline">Base</code> is 16, <code class="inline">String</code> must match the regular expression
│ │ │  <code class="inline">&quot;^[+-]?([0-9]|[A-F]|[a-f])+$&quot;</code>.</p><p>Failure: <code class="inline">badarg</code> if <code class="inline">String</code> contains a bad representation of an integer.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="list_to_pid/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │ @@ -10781,15 +10781,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> list_to_pid(String) -> <a href="#t:pid/0">pid</a>() when String :: <a href="#t:string/0">string</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a process identifier whose text representation is a <code class="inline">String</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_pid</span><span class="p" data-group-id="9316257310-1">(</span><span class="s">&quot;&lt;0.4.1&gt;&quot;</span><span class="p" data-group-id="9316257310-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns a process identifier whose text representation is a <code class="inline">String</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_pid</span><span class="p" data-group-id="1415449578-1">(</span><span class="s">&quot;&lt;0.4.1&gt;&quot;</span><span class="p" data-group-id="1415449578-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">1</span><span class="o">&gt;</span></code></pre><p>Failure: <code class="inline">badarg</code> if <code class="inline">String</code> contains a bad representation of a process
│ │ │  identifier.</p><section role="note" class="admonition warning"><h4 class="admonition-title warning">Warning</h4><p>This BIF is intended for debugging and is not to be used in application
│ │ │  programs.</p></section>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="list_to_port/1">
│ │ │  
│ │ │ @@ -10814,15 +10814,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> list_to_port(String) -> <a href="#t:port/0">port</a>() when String :: <a href="#t:string/0">string</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a port identifier whose text representation is a <code class="inline">String</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_port</span><span class="p" data-group-id="9298428782-1">(</span><span class="s">&quot;#Port&lt;0.4&gt;&quot;</span><span class="p" data-group-id="9298428782-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns a port identifier whose text representation is a <code class="inline">String</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_port</span><span class="p" data-group-id="3011691963-1">(</span><span class="s">&quot;#Port&lt;0.4&gt;&quot;</span><span class="p" data-group-id="3011691963-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="o">&gt;</span></code></pre><p>Failure: <code class="inline">badarg</code> if <code class="inline">String</code> contains a bad representation of a port
│ │ │  identifier.</p><section role="note" class="admonition warning"><h4 class="admonition-title warning">Warning</h4><p>This BIF is intended for debugging and is not to be used in application
│ │ │  programs.</p></section>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="list_to_ref/1">
│ │ │  
│ │ │ @@ -10847,15 +10847,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> list_to_ref(String) -> <a href="#t:reference/0">reference</a>() when String :: <a href="#t:string/0">string</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a reference whose text representation is a <code class="inline">String</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_ref</span><span class="p" data-group-id="2026677880-1">(</span><span class="s">&quot;#Ref&lt;0.4192537678.4073193475.71181&gt;&quot;</span><span class="p" data-group-id="2026677880-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns a reference whose text representation is a <code class="inline">String</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_ref</span><span class="p" data-group-id="5345378747-1">(</span><span class="s">&quot;#Ref&lt;0.4192537678.4073193475.71181&gt;&quot;</span><span class="p" data-group-id="5345378747-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Ref</span><span class="o">&lt;</span><span class="mf">0.4192537678</span><span class="p">.</span><span class="mf">4073193475.71181</span><span class="o">&gt;</span></code></pre><p>Failure: <code class="inline">badarg</code> if <code class="inline">String</code> contains a bad representation of a reference.</p><section role="note" class="admonition warning"><h4 class="admonition-title warning">Warning</h4><p>This BIF is intended for debugging and is not to be used in application
│ │ │  programs.</p></section>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="list_to_tuple/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │ @@ -10877,16 +10877,16 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> list_to_tuple(List) -> <a href="#t:tuple/0">tuple</a>() when List :: [<a href="#t:term/0">term</a>()].</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a tuple corresponding to <code class="inline">List</code>, for example</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_tuple</span><span class="p" data-group-id="7347178891-1">(</span><span class="p" data-group-id="7347178891-2">[</span><span class="ss">share</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7347178891-3">[</span><span class="ss">&#39;Ericsson_B&#39;</span><span class="p">,</span><span class="w"> </span><span class="mi">163</span><span class="p" data-group-id="7347178891-3">]</span><span class="p" data-group-id="7347178891-2">]</span><span class="p" data-group-id="7347178891-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7347178891-4">{</span><span class="ss">share</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7347178891-5">[</span><span class="ss">&#39;Ericsson_B&#39;</span><span class="p">,</span><span class="w"> </span><span class="mi">163</span><span class="p" data-group-id="7347178891-5">]</span><span class="p" data-group-id="7347178891-4">}</span></code></pre><p><code class="inline">List</code> can contain any Erlang terms.</p>
│ │ │ +<p>Returns a tuple corresponding to <code class="inline">List</code>, for example</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">list_to_tuple</span><span class="p" data-group-id="3641231909-1">(</span><span class="p" data-group-id="3641231909-2">[</span><span class="ss">share</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3641231909-3">[</span><span class="ss">&#39;Ericsson_B&#39;</span><span class="p">,</span><span class="w"> </span><span class="mi">163</span><span class="p" data-group-id="3641231909-3">]</span><span class="p" data-group-id="3641231909-2">]</span><span class="p" data-group-id="3641231909-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3641231909-4">{</span><span class="ss">share</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3641231909-5">[</span><span class="ss">&#39;Ericsson_B&#39;</span><span class="p">,</span><span class="w"> </span><span class="mi">163</span><span class="p" data-group-id="3641231909-5">]</span><span class="p" data-group-id="3641231909-4">}</span></code></pre><p><code class="inline">List</code> can contain any Erlang terms.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="make_ref/0">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#make_ref/0" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -10936,16 +10936,16 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> make_tuple(Arity, InitialValue) -> <a href="#t:tuple/0">tuple</a>() when Arity :: <a href="#t:arity/0">arity</a>(), InitialValue :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Creates a new tuple of the specified <code class="inline">Arity</code>, where all elements are
│ │ │ -<code class="inline">InitialValue</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">make_tuple</span><span class="p" data-group-id="6254162859-1">(</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6254162859-2">[</span><span class="p" data-group-id="6254162859-2">]</span><span class="p" data-group-id="6254162859-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6254162859-3">{</span><span class="p" data-group-id="6254162859-4">[</span><span class="p" data-group-id="6254162859-4">]</span><span class="p">,</span><span class="p" data-group-id="6254162859-5">[</span><span class="p" data-group-id="6254162859-5">]</span><span class="p">,</span><span class="p" data-group-id="6254162859-6">[</span><span class="p" data-group-id="6254162859-6">]</span><span class="p">,</span><span class="p" data-group-id="6254162859-7">[</span><span class="p" data-group-id="6254162859-7">]</span><span class="p" data-group-id="6254162859-3">}</span></code></pre>
│ │ │ +<code class="inline">InitialValue</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">make_tuple</span><span class="p" data-group-id="7746797554-1">(</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7746797554-2">[</span><span class="p" data-group-id="7746797554-2">]</span><span class="p" data-group-id="7746797554-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7746797554-3">{</span><span class="p" data-group-id="7746797554-4">[</span><span class="p" data-group-id="7746797554-4">]</span><span class="p">,</span><span class="p" data-group-id="7746797554-5">[</span><span class="p" data-group-id="7746797554-5">]</span><span class="p">,</span><span class="p" data-group-id="7746797554-6">[</span><span class="p" data-group-id="7746797554-6">]</span><span class="p">,</span><span class="p" data-group-id="7746797554-7">[</span><span class="p" data-group-id="7746797554-7">]</span><span class="p" data-group-id="7746797554-3">}</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="make_tuple/3">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#make_tuple/3" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -10971,16 +10971,16 @@
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Creates a tuple of size <code class="inline">Arity</code>, where each element has value <code class="inline">DefaultValue</code>,
│ │ │  and then fills in values from <code class="inline">InitList</code>.</p><p>Each list element in <code class="inline">InitList</code> must be a two-tuple, where the first element is
│ │ │  a position in the newly created tuple and the second element is any term. If a
│ │ │  position occurs more than once in the list, the term corresponding to the last
│ │ │ -occurrence is used.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">make_tuple</span><span class="p" data-group-id="1567921679-1">(</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1567921679-2">[</span><span class="p" data-group-id="1567921679-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1567921679-3">[</span><span class="p" data-group-id="1567921679-4">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">ignored</span><span class="p" data-group-id="1567921679-4">}</span><span class="p">,</span><span class="p" data-group-id="1567921679-5">{</span><span class="mi">5</span><span class="p">,</span><span class="ss">zz</span><span class="p" data-group-id="1567921679-5">}</span><span class="p">,</span><span class="p" data-group-id="1567921679-6">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">aa</span><span class="p" data-group-id="1567921679-6">}</span><span class="p" data-group-id="1567921679-3">]</span><span class="p" data-group-id="1567921679-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1567921679-7">{</span><span class="p" data-group-id="1567921679-8">[</span><span class="p" data-group-id="1567921679-8">]</span><span class="p">,</span><span class="ss">aa</span><span class="p">,</span><span class="p" data-group-id="1567921679-9">[</span><span class="p" data-group-id="1567921679-9">]</span><span class="p">,</span><span class="p" data-group-id="1567921679-10">[</span><span class="p" data-group-id="1567921679-10">]</span><span class="p">,</span><span class="ss">zz</span><span class="p" data-group-id="1567921679-7">}</span></code></pre>
│ │ │ +occurrence is used.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">make_tuple</span><span class="p" data-group-id="1422312232-1">(</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1422312232-2">[</span><span class="p" data-group-id="1422312232-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1422312232-3">[</span><span class="p" data-group-id="1422312232-4">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">ignored</span><span class="p" data-group-id="1422312232-4">}</span><span class="p">,</span><span class="p" data-group-id="1422312232-5">{</span><span class="mi">5</span><span class="p">,</span><span class="ss">zz</span><span class="p" data-group-id="1422312232-5">}</span><span class="p">,</span><span class="p" data-group-id="1422312232-6">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">aa</span><span class="p" data-group-id="1422312232-6">}</span><span class="p" data-group-id="1422312232-3">]</span><span class="p" data-group-id="1422312232-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1422312232-7">{</span><span class="p" data-group-id="1422312232-8">[</span><span class="p" data-group-id="1422312232-8">]</span><span class="p">,</span><span class="ss">aa</span><span class="p">,</span><span class="p" data-group-id="1422312232-9">[</span><span class="p" data-group-id="1422312232-9">]</span><span class="p">,</span><span class="p" data-group-id="1422312232-10">[</span><span class="p" data-group-id="1422312232-10">]</span><span class="p">,</span><span class="ss">zz</span><span class="p" data-group-id="1422312232-7">}</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="map_get/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#map_get/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -11006,16 +11006,16 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> map_get(Key, Map) -> Value when Map :: <a href="#t:map/0">map</a>(), Key :: <a href="#t:any/0">any</a>(), Value :: <a href="#t:any/0">any</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns value <code class="inline">Value</code> associated with <code class="inline">Key</code> if <code class="inline">Map</code> contains <code class="inline">Key</code>.</p><p>The call fails with a <code class="inline">{badmap,Map}</code> exception if <code class="inline">Map</code> is not a map, or with a
│ │ │  <code class="inline">{badkey,Key}</code> exception if no value is associated with <code class="inline">Key</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Key</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1337</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8127559144-1">#{</span><span class="mi">42</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value_two</span><span class="p">,</span><span class="mi">1337</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;value one&quot;</span><span class="p">,</span><span class="s">&quot;a&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8127559144-1">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="nf">map_get</span><span class="p" data-group-id="8127559144-2">(</span><span class="n">Key</span><span class="p">,</span><span class="n">Map</span><span class="p" data-group-id="8127559144-2">)</span><span class="p">.</span><span class="w">
│ │ │ +  </span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2879004245-1">#{</span><span class="mi">42</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value_two</span><span class="p">,</span><span class="mi">1337</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;value one&quot;</span><span class="p">,</span><span class="s">&quot;a&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2879004245-1">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="nf">map_get</span><span class="p" data-group-id="2879004245-2">(</span><span class="n">Key</span><span class="p">,</span><span class="n">Map</span><span class="p" data-group-id="2879004245-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;value one&quot;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="map_size/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#map_size/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -11040,15 +11040,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> map_size(Map) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when Map :: <a href="#t:map/0">map</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns an integer, which is the number of key-value pairs in <code class="inline">Map</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="5328654823-1">(</span><span class="p" data-group-id="5328654823-2">#{</span><span class="ss">a</span><span class="p">=&gt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">=&gt;</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p">=&gt;</span><span class="mi">3</span><span class="p" data-group-id="5328654823-2">}</span><span class="p" data-group-id="5328654823-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns an integer, which is the number of key-value pairs in <code class="inline">Map</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="8837753412-1">(</span><span class="p" data-group-id="8837753412-2">#{</span><span class="ss">a</span><span class="p">=&gt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">=&gt;</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p">=&gt;</span><span class="mi">3</span><span class="p" data-group-id="8837753412-2">}</span><span class="p" data-group-id="8837753412-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="match_spec_test/3">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#match_spec_test/3" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -11119,18 +11119,18 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> max(Term1, Term2) -> Maximum when Term1 :: <a href="#t:term/0">term</a>(), Term2 :: <a href="#t:term/0">term</a>(), Maximum :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns the largest of <code class="inline">Term1</code> and <code class="inline">Term2</code>. If the terms compare equal with the
│ │ │  <code class="inline">==</code> operator, <code class="inline">Term1</code> is returned.</p><p>The <a href="../../../doc/system/expressions.html#term-comparisons">Expressions section</a> contains
│ │ │ -descriptions of the <code class="inline">==</code> operator and how terms are ordered.</p><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">max</span><span class="p" data-group-id="3029259844-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3029259844-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">2</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">max</span><span class="p" data-group-id="0949746087-1">(</span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0949746087-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mf">1.0</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">max</span><span class="p" data-group-id="0447297276-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="0447297276-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">1</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">max</span><span class="p" data-group-id="6455352778-1">(</span><span class="s">&quot;abc&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;b&quot;</span><span class="p" data-group-id="6455352778-1">)</span><span class="p">.</span><span class="w">
│ │ │ +descriptions of the <code class="inline">==</code> operator and how terms are ordered.</p><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">max</span><span class="p" data-group-id="7667590932-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7667590932-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">2</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">max</span><span class="p" data-group-id="5717380809-1">(</span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5717380809-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mf">1.0</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">max</span><span class="p" data-group-id="9342874816-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="9342874816-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">1</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">max</span><span class="p" data-group-id="1645406903-1">(</span><span class="s">&quot;abc&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;b&quot;</span><span class="p" data-group-id="1645406903-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;b&quot;</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Allowed in guards tests from Erlang/OTP 26.</p></section>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="min/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#min/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -11155,18 +11155,18 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> min(Term1, Term2) -> Minimum when Term1 :: <a href="#t:term/0">term</a>(), Term2 :: <a href="#t:term/0">term</a>(), Minimum :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns the smallest of <code class="inline">Term1</code> and <code class="inline">Term2</code>. If the terms compare equal with the
│ │ │  <code class="inline">==</code> operator, <code class="inline">Term1</code> is returned.</p><p>The <a href="../../../doc/system/expressions.html#term-comparisons">Expressions section</a> contains
│ │ │ -descriptions of the <code class="inline">==</code> operator and how terms are ordered.</p><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">min</span><span class="p" data-group-id="2131252792-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2131252792-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">1</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">min</span><span class="p" data-group-id="5551232138-1">(</span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5551232138-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mf">1.0</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">min</span><span class="p" data-group-id="2482760894-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="2482760894-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">1</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">min</span><span class="p" data-group-id="1832309557-1">(</span><span class="s">&quot;abc&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;b&quot;</span><span class="p" data-group-id="1832309557-1">)</span><span class="p">.</span><span class="w">
│ │ │ +descriptions of the <code class="inline">==</code> operator and how terms are ordered.</p><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">min</span><span class="p" data-group-id="8975591697-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8975591697-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">1</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">min</span><span class="p" data-group-id="8290275920-1">(</span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8290275920-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mf">1.0</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">min</span><span class="p" data-group-id="7175618405-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="7175618405-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">1</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">min</span><span class="p" data-group-id="2104022589-1">(</span><span class="s">&quot;abc&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;b&quot;</span><span class="p" data-group-id="2104022589-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;abc&quot;</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Allowed in guards tests from Erlang/OTP 26.</p></section>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="node/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#node/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -11276,15 +11276,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> pid_to_list(Pid) -> <a href="#t:string/0">string</a>() when Pid :: <a href="#t:pid/0">pid</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a string corresponding to the text representation of <code class="inline">Pid</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">pid_to_list</span><span class="p" data-group-id="0426079693-1">(</span><span class="nf">self</span><span class="p" data-group-id="0426079693-2">(</span><span class="p" data-group-id="0426079693-2">)</span><span class="p" data-group-id="0426079693-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns a string corresponding to the text representation of <code class="inline">Pid</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">pid_to_list</span><span class="p" data-group-id="0272490918-1">(</span><span class="nf">self</span><span class="p" data-group-id="0272490918-2">(</span><span class="p" data-group-id="0272490918-2">)</span><span class="p" data-group-id="0272490918-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;&lt;0.85.0&gt;&quot;</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The <a href="erl_dist_protocol.html">creation</a> for the node is not included in the list
│ │ │  representation of <code class="inline">Pid</code>. This means that processes in different incarnations
│ │ │  of a node with a specific name can get the same list representation.</p></section>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="port_to_list/1">
│ │ │  
│ │ │ @@ -11367,18 +11367,18 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> round(Number) -> <a href="#t:integer/0">integer</a>() when Number :: <a href="#t:number/0">number</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns an integer by rounding <code class="inline">Number</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">round</span><span class="p" data-group-id="1227982835-1">(</span><span class="mf">42.1</span><span class="p" data-group-id="1227982835-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">42</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">round</span><span class="p" data-group-id="2320903829-1">(</span><span class="mf">5.5</span><span class="p" data-group-id="2320903829-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">6</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">round</span><span class="p" data-group-id="8617562460-1">(</span><span class="o">-</span><span class="mf">5.5</span><span class="p" data-group-id="8617562460-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">-</span><span class="mi">6</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">round</span><span class="p" data-group-id="8718357978-1">(</span><span class="mf">36028797018963969.0</span><span class="p" data-group-id="8718357978-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns an integer by rounding <code class="inline">Number</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">round</span><span class="p" data-group-id="6425502291-1">(</span><span class="mf">42.1</span><span class="p" data-group-id="6425502291-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">42</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">round</span><span class="p" data-group-id="3994753085-1">(</span><span class="mf">5.5</span><span class="p" data-group-id="3994753085-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">6</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">round</span><span class="p" data-group-id="3972328569-1">(</span><span class="o">-</span><span class="mf">5.5</span><span class="p" data-group-id="3972328569-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">-</span><span class="mi">6</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">round</span><span class="p" data-group-id="6339278392-1">(</span><span class="mf">36028797018963969.0</span><span class="p" data-group-id="6339278392-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">36028797018963968</span></code></pre><p>In the last example, <a href="#round/1"><code class="inline">round(36028797018963969.0)</code></a> evaluates to
│ │ │  <code class="inline">36028797018963968</code>. The reason for this is that the number
│ │ │  <code class="inline">36028797018963969.0</code> cannot be represented exactly as a float value. Instead,
│ │ │  the float literal is represented as <code class="inline">36028797018963968.0</code>, which is the closest
│ │ │  number that can be represented exactly as a float value. See
│ │ │  <a href="../../../doc/system/data_types.html#float_representation_problem">Representation of Floating Point Numbers</a>
│ │ │  for additional information.</p>
│ │ │ @@ -11408,16 +11408,16 @@
│ │ │            <pre translate="no"><span class="attribute">-spec</span> setelement(Index, Tuple1, Value) -> Tuple2
│ │ │                      when Index :: <a href="#t:pos_integer/0">pos_integer</a>(), Tuple1 :: <a href="#t:tuple/0">tuple</a>(), Tuple2 :: <a href="#t:tuple/0">tuple</a>(), Value :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a tuple that is a copy of argument <code class="inline">Tuple1</code> with the element specified
│ │ │  by integer argument <code class="inline">Index</code> (the first element is the element with index 1)
│ │ │ -replaced by argument <code class="inline">Value</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">setelement</span><span class="p" data-group-id="9756479840-1">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9756479840-2">{</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="p">,</span><span class="w"> </span><span class="ss">bottles</span><span class="p" data-group-id="9756479840-2">}</span><span class="p">,</span><span class="w"> </span><span class="ss">red</span><span class="p" data-group-id="9756479840-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9756479840-3">{</span><span class="mi">10</span><span class="p">,</span><span class="ss">red</span><span class="p">,</span><span class="ss">bottles</span><span class="p" data-group-id="9756479840-3">}</span></code></pre>
│ │ │ +replaced by argument <code class="inline">Value</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">setelement</span><span class="p" data-group-id="1427967982-1">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1427967982-2">{</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="p">,</span><span class="w"> </span><span class="ss">bottles</span><span class="p" data-group-id="1427967982-2">}</span><span class="p">,</span><span class="w"> </span><span class="ss">red</span><span class="p" data-group-id="1427967982-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1427967982-3">{</span><span class="mi">10</span><span class="p">,</span><span class="ss">red</span><span class="p">,</span><span class="ss">bottles</span><span class="p" data-group-id="1427967982-3">}</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="size/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#size/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -11440,17 +11440,17 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> size(Item) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when Item :: <a href="#t:tuple/0">tuple</a>() | <a href="#t:binary/0">binary</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns the number of elements in a tuple or the number of bytes in a binary or
│ │ │ -bitstring.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">size</span><span class="p" data-group-id="9910417017-1">(</span><span class="p" data-group-id="9910417017-2">{</span><span class="ss">morni</span><span class="p">,</span><span class="w"> </span><span class="ss">mulle</span><span class="p">,</span><span class="w"> </span><span class="ss">bwange</span><span class="p" data-group-id="9910417017-2">}</span><span class="p" data-group-id="9910417017-1">)</span><span class="p">.</span><span class="w">
│ │ │ +bitstring.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">size</span><span class="p" data-group-id="8943880717-1">(</span><span class="p" data-group-id="8943880717-2">{</span><span class="ss">morni</span><span class="p">,</span><span class="w"> </span><span class="ss">mulle</span><span class="p">,</span><span class="w"> </span><span class="ss">bwange</span><span class="p" data-group-id="8943880717-2">}</span><span class="p" data-group-id="8943880717-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">size</span><span class="p" data-group-id="9910417017-3">(</span><span class="p" data-group-id="9910417017-4">&lt;&lt;</span><span class="mi">11</span><span class="p">,</span><span class="w"> </span><span class="mi">22</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="9910417017-4">&gt;&gt;</span><span class="p" data-group-id="9910417017-3">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">size</span><span class="p" data-group-id="8943880717-3">(</span><span class="p" data-group-id="8943880717-4">&lt;&lt;</span><span class="mi">11</span><span class="p">,</span><span class="w"> </span><span class="mi">22</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="8943880717-4">&gt;&gt;</span><span class="p" data-group-id="8943880717-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span></code></pre><p>For bitstrings, the number of whole bytes is returned. That is, if the number of
│ │ │  bits in the bitstring is not divisible by 8, the resulting number of bytes is
│ │ │  rounded <em>down</em>.</p><p>See also <a href="#tuple_size/1"><code class="inline">tuple_size/1</code></a>, <a href="#byte_size/1"><code class="inline">byte_size/1</code></a>, and <a href="#bit_size/1"><code class="inline">bit_size/1</code></a>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="split_binary/2">
│ │ │  
│ │ │ @@ -11474,23 +11474,23 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> split_binary(Bin, Pos) -> {<a href="#t:binary/0">binary</a>(), <a href="#t:binary/0">binary</a>()} when Bin :: <a href="#t:binary/0">binary</a>(), Pos :: <a href="#t:non_neg_integer/0">non_neg_integer</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a tuple containing the binaries that are the result of splitting <code class="inline">Bin</code>
│ │ │ -into two parts at position <code class="inline">Pos</code>.</p><p>This is not a destructive operation. After the operation, there are three binaries altogether.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">B</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">list_to_binary</span><span class="p" data-group-id="6171406143-1">(</span><span class="s">&quot;0123456789&quot;</span><span class="p" data-group-id="6171406143-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6171406143-2">&lt;&lt;</span><span class="s">&quot;0123456789&quot;</span><span class="p" data-group-id="6171406143-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">byte_size</span><span class="p" data-group-id="6171406143-3">(</span><span class="n">B</span><span class="p" data-group-id="6171406143-3">)</span><span class="p">.</span><span class="w">
│ │ │ +into two parts at position <code class="inline">Pos</code>.</p><p>This is not a destructive operation. After the operation, there are three binaries altogether.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">B</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">list_to_binary</span><span class="p" data-group-id="0293902854-1">(</span><span class="s">&quot;0123456789&quot;</span><span class="p" data-group-id="0293902854-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0293902854-2">&lt;&lt;</span><span class="s">&quot;0123456789&quot;</span><span class="p" data-group-id="0293902854-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">byte_size</span><span class="p" data-group-id="0293902854-3">(</span><span class="n">B</span><span class="p" data-group-id="0293902854-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="p" data-group-id="6171406143-4">{</span><span class="n">B1</span><span class="p">,</span><span class="w"> </span><span class="n">B2</span><span class="p" data-group-id="6171406143-4">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">split_binary</span><span class="p" data-group-id="6171406143-5">(</span><span class="n">B</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6171406143-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6171406143-6">{</span><span class="p" data-group-id="6171406143-7">&lt;&lt;</span><span class="s">&quot;012&quot;</span><span class="p" data-group-id="6171406143-7">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="6171406143-8">&lt;&lt;</span><span class="s">&quot;3456789&quot;</span><span class="p" data-group-id="6171406143-8">&gt;&gt;</span><span class="p" data-group-id="6171406143-6">}</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">byte_size</span><span class="p" data-group-id="6171406143-9">(</span><span class="n">B1</span><span class="p" data-group-id="6171406143-9">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="p" data-group-id="0293902854-4">{</span><span class="n">B1</span><span class="p">,</span><span class="w"> </span><span class="n">B2</span><span class="p" data-group-id="0293902854-4">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">split_binary</span><span class="p" data-group-id="0293902854-5">(</span><span class="n">B</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0293902854-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0293902854-6">{</span><span class="p" data-group-id="0293902854-7">&lt;&lt;</span><span class="s">&quot;012&quot;</span><span class="p" data-group-id="0293902854-7">&gt;&gt;</span><span class="p">,</span><span class="p" data-group-id="0293902854-8">&lt;&lt;</span><span class="s">&quot;3456789&quot;</span><span class="p" data-group-id="0293902854-8">&gt;&gt;</span><span class="p" data-group-id="0293902854-6">}</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">byte_size</span><span class="p" data-group-id="0293902854-9">(</span><span class="n">B1</span><span class="p" data-group-id="0293902854-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">byte_size</span><span class="p" data-group-id="6171406143-10">(</span><span class="n">B2</span><span class="p" data-group-id="6171406143-10">)</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="nf">byte_size</span><span class="p" data-group-id="0293902854-10">(</span><span class="n">B2</span><span class="p" data-group-id="0293902854-10">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">7</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="term_to_binary/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#term_to_binary/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -11514,17 +11514,17 @@
│ │ │            <pre translate="no"><span class="attribute">-spec</span> term_to_binary(Term) -> <a href="#t:ext_binary/0">ext_binary</a>() when Term :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a binary data object that is the result of encoding <code class="inline">Term</code> according to
│ │ │  the <a href="erl_ext_dist.html">Erlang external term format.</a></p><p>This can be used for various purposes, for example, writing a term to a file in
│ │ │  an efficient way, or sending an Erlang term to some type of communications
│ │ │ -channel not supported by distributed Erlang.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="0262891738-1">(</span><span class="ss">hello</span><span class="p" data-group-id="0262891738-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0262891738-2">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="0262891738-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="ss">hello</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="0262891738-3">(</span><span class="n">Bin</span><span class="p" data-group-id="0262891738-3">)</span><span class="p">.</span><span class="w">
│ │ │ +channel not supported by distributed Erlang.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="3951707783-1">(</span><span class="ss">hello</span><span class="p" data-group-id="3951707783-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3951707783-2">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="3951707783-2">&gt;&gt;</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="ss">hello</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="3951707783-3">(</span><span class="n">Bin</span><span class="p" data-group-id="3951707783-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span></code></pre><p>See also <a href="#binary_to_term/1"><code class="inline">binary_to_term/1</code></a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>There is no guarantee that this function will return the same encoded
│ │ │  representation for the same term.</p></section>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="term_to_binary/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │ @@ -11741,18 +11741,18 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> tl(List) -> Tail when List :: <a href="#t:nonempty_maybe_improper_list/0">nonempty_maybe_improper_list</a>(), Tail :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns the tail of <code class="inline">List</code>, that is, the list minus the first element</p><p>It works with improper lists.</p><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tl</span><span class="p" data-group-id="1947457331-1">(</span><span class="p" data-group-id="1947457331-2">[</span><span class="ss">geesties</span><span class="p">,</span><span class="w"> </span><span class="ss">guilies</span><span class="p">,</span><span class="w"> </span><span class="ss">beasties</span><span class="p" data-group-id="1947457331-2">]</span><span class="p" data-group-id="1947457331-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1947457331-3">[</span><span class="ss">guilies</span><span class="p">,</span><span class="w"> </span><span class="ss">beasties</span><span class="p" data-group-id="1947457331-3">]</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tl</span><span class="p" data-group-id="1755519661-1">(</span><span class="p" data-group-id="1755519661-2">[</span><span class="ss">geesties</span><span class="p" data-group-id="1755519661-2">]</span><span class="p" data-group-id="1755519661-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1755519661-3">[</span><span class="p" data-group-id="1755519661-3">]</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tl</span><span class="p" data-group-id="0512506340-1">(</span><span class="p" data-group-id="0512506340-2">[</span><span class="ss">geesties</span><span class="p">,</span><span class="w"> </span><span class="ss">guilies</span><span class="p">,</span><span class="w"> </span><span class="ss">beasties</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">improper_end</span><span class="p" data-group-id="0512506340-2">]</span><span class="p" data-group-id="0512506340-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0512506340-3">[</span><span class="ss">guilies</span><span class="p">,</span><span class="w"> </span><span class="ss">beasties</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">improper_end</span><span class="p" data-group-id="0512506340-3">]</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tl</span><span class="p" data-group-id="8053914953-1">(</span><span class="p" data-group-id="8053914953-2">[</span><span class="ss">geesties</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">improper_end</span><span class="p" data-group-id="8053914953-2">]</span><span class="p" data-group-id="8053914953-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns the tail of <code class="inline">List</code>, that is, the list minus the first element</p><p>It works with improper lists.</p><p>Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tl</span><span class="p" data-group-id="8330342119-1">(</span><span class="p" data-group-id="8330342119-2">[</span><span class="ss">geesties</span><span class="p">,</span><span class="w"> </span><span class="ss">guilies</span><span class="p">,</span><span class="w"> </span><span class="ss">beasties</span><span class="p" data-group-id="8330342119-2">]</span><span class="p" data-group-id="8330342119-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8330342119-3">[</span><span class="ss">guilies</span><span class="p">,</span><span class="w"> </span><span class="ss">beasties</span><span class="p" data-group-id="8330342119-3">]</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tl</span><span class="p" data-group-id="1769994939-1">(</span><span class="p" data-group-id="1769994939-2">[</span><span class="ss">geesties</span><span class="p" data-group-id="1769994939-2">]</span><span class="p" data-group-id="1769994939-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1769994939-3">[</span><span class="p" data-group-id="1769994939-3">]</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tl</span><span class="p" data-group-id="5461672171-1">(</span><span class="p" data-group-id="5461672171-2">[</span><span class="ss">geesties</span><span class="p">,</span><span class="w"> </span><span class="ss">guilies</span><span class="p">,</span><span class="w"> </span><span class="ss">beasties</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">improper_end</span><span class="p" data-group-id="5461672171-2">]</span><span class="p" data-group-id="5461672171-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5461672171-3">[</span><span class="ss">guilies</span><span class="p">,</span><span class="w"> </span><span class="ss">beasties</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">improper_end</span><span class="p" data-group-id="5461672171-3">]</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tl</span><span class="p" data-group-id="9606464964-1">(</span><span class="p" data-group-id="9606464964-2">[</span><span class="ss">geesties</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">improper_end</span><span class="p" data-group-id="9606464964-2">]</span><span class="p" data-group-id="9606464964-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">improper_end</span></code></pre><p>Failure: <code class="inline">badarg</code> if <code class="inline">List</code> is an empty list <code class="inline">[]</code>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="trunc/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#trunc/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -11775,18 +11775,18 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> trunc(Number) -> <a href="#t:integer/0">integer</a>() when Number :: <a href="#t:number/0">number</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Truncates the decimals of <code class="inline">Number</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="9505437434-1">(</span><span class="mf">5.7</span><span class="p" data-group-id="9505437434-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">5</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="4240607784-1">(</span><span class="o">-</span><span class="mf">5.7</span><span class="p" data-group-id="4240607784-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">-</span><span class="mi">5</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="3200903439-1">(</span><span class="mi">5</span><span class="p" data-group-id="3200903439-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">5</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="6119155466-1">(</span><span class="mf">36028797018963969.0</span><span class="p" data-group-id="6119155466-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Truncates the decimals of <code class="inline">Number</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="6415896357-1">(</span><span class="mf">5.7</span><span class="p" data-group-id="6415896357-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">5</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="6817093276-1">(</span><span class="o">-</span><span class="mf">5.7</span><span class="p" data-group-id="6817093276-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">-</span><span class="mi">5</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="1534266978-1">(</span><span class="mi">5</span><span class="p" data-group-id="1534266978-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">5</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="1465093982-1">(</span><span class="mf">36028797018963969.0</span><span class="p" data-group-id="1465093982-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">36028797018963968</span></code></pre><p>In the last example, <a href="#trunc/1"><code class="inline">trunc(36028797018963969.0)</code></a> evaluates to
│ │ │  <code class="inline">36028797018963968</code>. The reason for this is that the number
│ │ │  <code class="inline">36028797018963969.0</code> cannot be represented exactly as a float value. Instead,
│ │ │  the float literal is represented as <code class="inline">36028797018963968.0</code>, which is the closest
│ │ │  number that can be represented exactly as a float value. See
│ │ │  <a href="../../../doc/system/data_types.html#float_representation_problem">Representation of Floating Point Numbers</a>
│ │ │  for additional information.</p>
│ │ │ @@ -11815,15 +11815,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> tuple_size(Tuple) -> <a href="#t:non_neg_integer/0">non_neg_integer</a>() when Tuple :: <a href="#t:tuple/0">tuple</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns an integer that is the number of elements in <code class="inline">Tuple</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="8018012222-1">(</span><span class="p" data-group-id="8018012222-2">{</span><span class="ss">morni</span><span class="p">,</span><span class="w"> </span><span class="ss">mulle</span><span class="p">,</span><span class="w"> </span><span class="ss">bwange</span><span class="p" data-group-id="8018012222-2">}</span><span class="p" data-group-id="8018012222-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns an integer that is the number of elements in <code class="inline">Tuple</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="7602920589-1">(</span><span class="p" data-group-id="7602920589-2">{</span><span class="ss">morni</span><span class="p">,</span><span class="w"> </span><span class="ss">mulle</span><span class="p">,</span><span class="w"> </span><span class="ss">bwange</span><span class="p" data-group-id="7602920589-2">}</span><span class="p" data-group-id="7602920589-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="tuple_to_list/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#tuple_to_list/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -11845,16 +11845,16 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> tuple_to_list(Tuple) -> [<a href="#t:term/0">term</a>()] when Tuple :: <a href="#t:tuple/0">tuple</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a list corresponding to <code class="inline">Tuple</code>. <code class="inline">Tuple</code> can contain any Erlang terms.
│ │ │ -Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tuple_to_list</span><span class="p" data-group-id="3901618030-1">(</span><span class="p" data-group-id="3901618030-2">{</span><span class="ss">share</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3901618030-3">{</span><span class="ss">&#39;Ericsson_B&#39;</span><span class="p">,</span><span class="w"> </span><span class="mi">163</span><span class="p" data-group-id="3901618030-3">}</span><span class="p" data-group-id="3901618030-2">}</span><span class="p" data-group-id="3901618030-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3901618030-4">[</span><span class="ss">share</span><span class="p">,</span><span class="p" data-group-id="3901618030-5">{</span><span class="ss">&#39;Ericsson_B&#39;</span><span class="p">,</span><span class="mi">163</span><span class="p" data-group-id="3901618030-5">}</span><span class="p" data-group-id="3901618030-4">]</span></code></pre>
│ │ │ +Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">tuple_to_list</span><span class="p" data-group-id="1690125944-1">(</span><span class="p" data-group-id="1690125944-2">{</span><span class="ss">share</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1690125944-3">{</span><span class="ss">&#39;Ericsson_B&#39;</span><span class="p">,</span><span class="w"> </span><span class="mi">163</span><span class="p" data-group-id="1690125944-3">}</span><span class="p" data-group-id="1690125944-2">}</span><span class="p" data-group-id="1690125944-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1690125944-4">[</span><span class="ss">share</span><span class="p">,</span><span class="p" data-group-id="1690125944-5">{</span><span class="ss">&#39;Ericsson_B&#39;</span><span class="p">,</span><span class="mi">163</span><span class="p" data-group-id="1690125944-5">}</span><span class="p" data-group-id="1690125944-4">]</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="unique_integer/0">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#unique_integer/0" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -12009,35 +12009,35 @@
│ │ │  
│ │ │  <p>Create an alias which can be used when sending messages to the process that
│ │ │  created the alias. When the alias has been deactivated, messages sent using the
│ │ │  alias will be dropped. An alias can be deactivated using <a href="#unalias/1"><code class="inline">unalias/1</code></a>.</p><p>Currently available options for <a href="#alias/1"><code class="inline">alias/1</code></a>:</p><ul><li><p><strong><code class="inline">explicit_unalias</code></strong> - The alias can only be deactivated via a call to
│ │ │  <a href="#unalias/1"><code class="inline">unalias/1</code></a>. This is also the default behaviour if no options
│ │ │  are passed or if <a href="#alias/0"><code class="inline">alias/0</code></a> is called.</p></li><li><p><strong><code class="inline">reply</code></strong> - The alias will be automatically deactivated when a reply message
│ │ │  sent via the alias is received. The alias can also still be deactivated via a
│ │ │ -call to <a href="#unalias/1"><code class="inline">unalias/1</code></a>.</p></li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server</span><span class="p" data-group-id="9079149626-1">(</span><span class="p" data-group-id="9079149626-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +call to <a href="#unalias/1"><code class="inline">unalias/1</code></a>.</p></li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server</span><span class="p" data-group-id="3845024305-1">(</span><span class="p" data-group-id="3845024305-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9079149626-2">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="9079149626-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">perform_request</span><span class="p" data-group-id="9079149626-3">(</span><span class="n">Request</span><span class="p" data-group-id="9079149626-3">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">AliasReqId</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9079149626-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9079149626-4">}</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3845024305-2">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="3845024305-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">perform_request</span><span class="p" data-group-id="3845024305-3">(</span><span class="n">Request</span><span class="p" data-group-id="3845024305-3">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">AliasReqId</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3845024305-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="3845024305-4">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="9079149626-5">(</span><span class="p" data-group-id="9079149626-5">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="3845024305-5">(</span><span class="p" data-group-id="3845024305-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="9079149626-6">(</span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="9079149626-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">AliasReqId</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alias</span><span class="p" data-group-id="9079149626-7">(</span><span class="p" data-group-id="9079149626-8">[</span><span class="ss">reply</span><span class="p" data-group-id="9079149626-8">]</span><span class="p" data-group-id="9079149626-7">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ServerPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9079149626-9">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="9079149626-9">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="3845024305-6">(</span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="3845024305-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">AliasReqId</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alias</span><span class="p" data-group-id="3845024305-7">(</span><span class="p" data-group-id="3845024305-8">[</span><span class="ss">reply</span><span class="p" data-group-id="3845024305-8">]</span><span class="p" data-group-id="3845024305-7">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ServerPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3845024305-9">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="3845024305-9">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%% Alias will be automatically deactivated if we receive a reply</span><span class="w">
│ │ │      </span><span class="c1">%% since we used the &#39;reply&#39; option...</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9079149626-10">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9079149626-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3845024305-10">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="3845024305-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">unalias</span><span class="p" data-group-id="9079149626-11">(</span><span class="n">AliasReqId</span><span class="p" data-group-id="9079149626-11">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">unalias</span><span class="p" data-group-id="3845024305-11">(</span><span class="n">AliasReqId</span><span class="p" data-group-id="3845024305-11">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="c1">%% Flush message queue in case the reply arrived</span><span class="w">
│ │ │              </span><span class="c1">%% just before the alias was deactivated...</span><span class="w">
│ │ │ -            </span><span class="k">receive</span><span class="w"> </span><span class="p" data-group-id="9079149626-12">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9079149626-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="w">
│ │ │ -            </span><span class="k">after</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="9079149626-13">(</span><span class="ss">timeout</span><span class="p" data-group-id="9079149626-13">)</span><span class="w">
│ │ │ +            </span><span class="k">receive</span><span class="w"> </span><span class="p" data-group-id="3845024305-12">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="3845024305-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="w">
│ │ │ +            </span><span class="k">after</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="3845024305-13">(</span><span class="ss">timeout</span><span class="p" data-group-id="3845024305-13">)</span><span class="w">
│ │ │              </span><span class="k">end</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Note that both the server and the client in this example must be executing on at
│ │ │  least OTP 24 systems in order for this to work.</p><p>For more information on process aliases see the
│ │ │  <a href="../../../doc/system/ref_man_processes.html#process-aliases"><em>Process Aliases</em></a> section of
│ │ │  the <em>Erlang Reference Manual</em>.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │ @@ -12096,17 +12096,17 @@
│ │ │            <pre translate="no"><span class="attribute">-spec</span> apply(Module, Function, Args) -> <a href="#t:term/0">term</a>()
│ │ │                 when Module :: <a href="#t:module/0">module</a>(), Function :: <a href="#t:atom/0">atom</a>(), Args :: [<a href="#t:term/0">term</a>()].</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns the result of applying <code class="inline">Function</code> in <code class="inline">Module</code> to <code class="inline">Args</code>. The applied
│ │ │  function must be exported from <code class="inline">Module</code>. The arity of the function is the length
│ │ │ -of <code class="inline">Args</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">apply</span><span class="p" data-group-id="7633348382-1">(</span><span class="ss">lists</span><span class="p">,</span><span class="w"> </span><span class="ss">reverse</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7633348382-2">[</span><span class="p" data-group-id="7633348382-3">[</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="7633348382-3">]</span><span class="p" data-group-id="7633348382-2">]</span><span class="p" data-group-id="7633348382-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7633348382-4">[</span><span class="ss">c</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7633348382-4">]</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nf">apply</span><span class="p" data-group-id="7633348382-5">(</span><span class="ss">erlang</span><span class="p">,</span><span class="w"> </span><span class="nb">atom_to_list</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7633348382-6">[</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="7633348382-6">]</span><span class="p" data-group-id="7633348382-5">)</span><span class="p">.</span><span class="w">
│ │ │ +of <code class="inline">Args</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">apply</span><span class="p" data-group-id="7051550536-1">(</span><span class="ss">lists</span><span class="p">,</span><span class="w"> </span><span class="ss">reverse</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7051550536-2">[</span><span class="p" data-group-id="7051550536-3">[</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="7051550536-3">]</span><span class="p" data-group-id="7051550536-2">]</span><span class="p" data-group-id="7051550536-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7051550536-4">[</span><span class="ss">c</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7051550536-4">]</span><span class="gp unselectable">
│ │ │ +&gt; </span><span class="nf">apply</span><span class="p" data-group-id="7051550536-5">(</span><span class="ss">erlang</span><span class="p">,</span><span class="w"> </span><span class="nb">atom_to_list</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7051550536-6">[</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="7051550536-6">]</span><span class="p" data-group-id="7051550536-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;Erlang&quot;</span></code></pre><p>If the number of arguments are known at compile time, the call is better written
│ │ │  as <code class="inline">Module:Function(Arg1, Arg2, ..., ArgN)</code>.</p><p>Failure: <a href="../../../lib/kernel-10.2.7.1/doc/html/error_handler.html#undefined_function/3"><code class="inline">error_handler:undefined_function/3</code></a> is called if the applied function
│ │ │  is not exported. The error handler can be redefined (see <a href="#process_flag/2"><code class="inline">process_flag/2</code></a>). If
│ │ │  <code class="inline">error_handler</code> is undefined, or if the user has redefined the default
│ │ │  <code class="inline">error_handler</code> so the replacement module is undefined, an error with reason
│ │ │  <code class="inline">undef</code> is generated.</p>
│ │ │    </section>
│ │ │ @@ -12213,17 +12213,17 @@
│ │ │                     when MonitorRef :: <a href="#t:reference/0">reference</a>(), OptionList :: [Option], Option :: flush | info.</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>The returned value is <code class="inline">true</code> unless <code class="inline">info</code> is part of <code class="inline">OptionList</code>.</p><p><a href="#demonitor/2"><code class="inline">demonitor(MonitorRef, [])</code></a> is equivalent to
│ │ │  <a href="#demonitor/1"><code class="inline">demonitor(MonitorRef)</code></a>.</p><p><code class="inline">Option</code>s:</p><ul><li><p><strong><code class="inline">flush</code></strong> - Removes (one) <code class="inline">{_, MonitorRef, _, _, _}</code> message, if there is
│ │ │  one, from the caller message queue after monitoring has been stopped.</p><p>Calling <a href="#demonitor/2"><code class="inline">demonitor(MonitorRef, [flush])</code></a> is equivalent to the
│ │ │ -following, but more efficient:</p><pre><code class="makeup erlang" translate="no"><span class="nf">demonitor</span><span class="p" data-group-id="1324928920-1">(</span><span class="n">MonitorRef</span><span class="p" data-group-id="1324928920-1">)</span><span class="p">,</span><span class="w">
│ │ │ +following, but more efficient:</p><pre><code class="makeup erlang" translate="no"><span class="nf">demonitor</span><span class="p" data-group-id="4075788974-1">(</span><span class="n">MonitorRef</span><span class="p" data-group-id="4075788974-1">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1324928920-2">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">MonitorRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1324928920-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4075788974-2">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">MonitorRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="4075788974-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w">
│ │ │  </span><span class="k">after</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre></li><li><p><strong><code class="inline">info</code></strong> - The returned value is one of the following:</p><ul><li><p><strong><code class="inline">true</code></strong> - The monitor was found and removed. In this case, no <code class="inline">'DOWN'</code>
│ │ │  message corresponding to this monitor has been delivered and will not be
│ │ │  delivered.</p></li><li><p><strong><code class="inline">false</code></strong> - The monitor was not found and could not be removed. This
│ │ │  probably because someone already has placed a <code class="inline">'DOWN'</code> message corresponding
│ │ │ @@ -12252,18 +12252,18 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> erase() -> [{Key, Val}] when Key :: <a href="#t:term/0">term</a>(), Val :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns the process dictionary and deletes it.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="5770772895-1">(</span><span class="ss">key1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5770772895-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5770772895-2">}</span><span class="p" data-group-id="5770772895-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="5770772895-3">(</span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5770772895-4">[</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="5770772895-4">]</span><span class="p" data-group-id="5770772895-3">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">erase</span><span class="p" data-group-id="5770772895-5">(</span><span class="p" data-group-id="5770772895-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5770772895-6">[</span><span class="p" data-group-id="5770772895-7">{</span><span class="ss">key1</span><span class="p">,</span><span class="p" data-group-id="5770772895-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5770772895-8">}</span><span class="p" data-group-id="5770772895-7">}</span><span class="p">,</span><span class="p" data-group-id="5770772895-9">{</span><span class="ss">key2</span><span class="p">,</span><span class="p" data-group-id="5770772895-10">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5770772895-10">]</span><span class="p" data-group-id="5770772895-9">}</span><span class="p" data-group-id="5770772895-6">]</span></code></pre>
│ │ │ +<p>Returns the process dictionary and deletes it.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="9958909798-1">(</span><span class="ss">key1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9958909798-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="9958909798-2">}</span><span class="p" data-group-id="9958909798-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="9958909798-3">(</span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9958909798-4">[</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="9958909798-4">]</span><span class="p" data-group-id="9958909798-3">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">erase</span><span class="p" data-group-id="9958909798-5">(</span><span class="p" data-group-id="9958909798-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9958909798-6">[</span><span class="p" data-group-id="9958909798-7">{</span><span class="ss">key1</span><span class="p">,</span><span class="p" data-group-id="9958909798-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9958909798-8">}</span><span class="p" data-group-id="9958909798-7">}</span><span class="p">,</span><span class="p" data-group-id="9958909798-9">{</span><span class="ss">key2</span><span class="p">,</span><span class="p" data-group-id="9958909798-10">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9958909798-10">]</span><span class="p" data-group-id="9958909798-9">}</span><span class="p" data-group-id="9958909798-6">]</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="erase/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#erase/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -12286,18 +12286,18 @@
│ │ │            <pre translate="no"><span class="attribute">-spec</span> erase(Key) -> Val | undefined when Key :: <a href="#t:term/0">term</a>(), Val :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns the value <code class="inline">Val</code> associated with <code class="inline">Key</code> and deletes it from the process
│ │ │  dictionary. Returns <code class="inline">undefined</code> if no value is associated with <code class="inline">Key</code>.</p><p>The average time complexity for the current implementation of this function is
│ │ │  O(<code class="inline">1</code>) and the worst case time complexity is O(<code class="inline">N</code>), where <code class="inline">N</code> is the number of
│ │ │ -items in the process dictionary.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="8956992398-1">(</span><span class="ss">key1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8956992398-2">{</span><span class="ss">merry</span><span class="p">,</span><span class="w"> </span><span class="ss">lambs</span><span class="p">,</span><span class="w"> </span><span class="ss">are</span><span class="p">,</span><span class="w"> </span><span class="ss">playing</span><span class="p" data-group-id="8956992398-2">}</span><span class="p" data-group-id="8956992398-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erase</span><span class="p" data-group-id="8956992398-3">(</span><span class="ss">key1</span><span class="p" data-group-id="8956992398-3">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8956992398-4">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="nf">erase</span><span class="p" data-group-id="8956992398-5">(</span><span class="ss">key1</span><span class="p" data-group-id="8956992398-5">)</span><span class="p" data-group-id="8956992398-4">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8956992398-6">{</span><span class="p" data-group-id="8956992398-7">{</span><span class="ss">merry</span><span class="p">,</span><span class="ss">lambs</span><span class="p">,</span><span class="ss">are</span><span class="p">,</span><span class="ss">playing</span><span class="p" data-group-id="8956992398-7">}</span><span class="p">,</span><span class="ss">undefined</span><span class="p" data-group-id="8956992398-6">}</span></code></pre>
│ │ │ +items in the process dictionary.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="5603485195-1">(</span><span class="ss">key1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5603485195-2">{</span><span class="ss">merry</span><span class="p">,</span><span class="w"> </span><span class="ss">lambs</span><span class="p">,</span><span class="w"> </span><span class="ss">are</span><span class="p">,</span><span class="w"> </span><span class="ss">playing</span><span class="p" data-group-id="5603485195-2">}</span><span class="p" data-group-id="5603485195-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erase</span><span class="p" data-group-id="5603485195-3">(</span><span class="ss">key1</span><span class="p" data-group-id="5603485195-3">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5603485195-4">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="nf">erase</span><span class="p" data-group-id="5603485195-5">(</span><span class="ss">key1</span><span class="p" data-group-id="5603485195-5">)</span><span class="p" data-group-id="5603485195-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5603485195-6">{</span><span class="p" data-group-id="5603485195-7">{</span><span class="ss">merry</span><span class="p">,</span><span class="ss">lambs</span><span class="p">,</span><span class="ss">are</span><span class="p">,</span><span class="ss">playing</span><span class="p" data-group-id="5603485195-7">}</span><span class="p">,</span><span class="ss">undefined</span><span class="p" data-group-id="5603485195-6">}</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="error/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#error/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -12321,22 +12321,22 @@
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Raises an exception of class <code class="inline">error</code> with the reason <code class="inline">Reason</code>.</p><p>As evaluating this function causes an exception to be thrown, it has no return value.</p><p>The intent of the exception class <code class="inline">error</code> is to signal that an unexpected error
│ │ │  has happened (for example, a function is called with a parameter that has an
│ │ │  incorrect type). See the guide about
│ │ │  <a href="../../../doc/system/errors.html">errors and error handling</a> for additional information.
│ │ │ -Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">error</span><span class="p" data-group-id="9639118514-1">(</span><span class="ss">foobar</span><span class="p" data-group-id="9639118514-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9639118514-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="9639118514-3">{</span><span class="ss">foobar</span><span class="p">,</span><span class="p" data-group-id="9639118514-4">[</span><span class="p" data-group-id="9639118514-5">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                        </span><span class="p" data-group-id="9639118514-6">[</span><span class="p" data-group-id="9639118514-7">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="9639118514-7">}</span><span class="p">,</span><span class="p" data-group-id="9639118514-8">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">906</span><span class="p" data-group-id="9639118514-8">}</span><span class="p" data-group-id="9639118514-6">]</span><span class="p" data-group-id="9639118514-5">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="9639118514-9">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="9639118514-10">[</span><span class="p" data-group-id="9639118514-11">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="9639118514-11">}</span><span class="p">,</span><span class="p" data-group-id="9639118514-12">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">677</span><span class="p" data-group-id="9639118514-12">}</span><span class="p" data-group-id="9639118514-10">]</span><span class="p" data-group-id="9639118514-9">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="9639118514-13">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">expr</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="p" data-group-id="9639118514-14">[</span><span class="p" data-group-id="9639118514-15">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="9639118514-15">}</span><span class="p">,</span><span class="p" data-group-id="9639118514-16">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">430</span><span class="p" data-group-id="9639118514-16">}</span><span class="p" data-group-id="9639118514-14">]</span><span class="p" data-group-id="9639118514-13">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="9639118514-17">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="9639118514-18">[</span><span class="p" data-group-id="9639118514-19">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="9639118514-19">}</span><span class="p">,</span><span class="p" data-group-id="9639118514-20">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">687</span><span class="p" data-group-id="9639118514-20">}</span><span class="p" data-group-id="9639118514-18">]</span><span class="p" data-group-id="9639118514-17">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="9639118514-21">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="9639118514-22">[</span><span class="p" data-group-id="9639118514-23">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="9639118514-23">}</span><span class="p">,</span><span class="p" data-group-id="9639118514-24">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">642</span><span class="p" data-group-id="9639118514-24">}</span><span class="p" data-group-id="9639118514-22">]</span><span class="p" data-group-id="9639118514-21">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="9639118514-25">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_loop</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="9639118514-26">[</span><span class="p" data-group-id="9639118514-27">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="9639118514-27">}</span><span class="p">,</span><span class="p" data-group-id="9639118514-28">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">627</span><span class="p" data-group-id="9639118514-28">}</span><span class="p" data-group-id="9639118514-26">]</span><span class="p" data-group-id="9639118514-25">}</span><span class="p" data-group-id="9639118514-4">]</span><span class="p" data-group-id="9639118514-3">}</span><span class="p" data-group-id="9639118514-2">}</span></code></pre>
│ │ │ +Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">error</span><span class="p" data-group-id="7487866918-1">(</span><span class="ss">foobar</span><span class="p" data-group-id="7487866918-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7487866918-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="7487866918-3">{</span><span class="ss">foobar</span><span class="p">,</span><span class="p" data-group-id="7487866918-4">[</span><span class="p" data-group-id="7487866918-5">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                        </span><span class="p" data-group-id="7487866918-6">[</span><span class="p" data-group-id="7487866918-7">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="7487866918-7">}</span><span class="p">,</span><span class="p" data-group-id="7487866918-8">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">906</span><span class="p" data-group-id="7487866918-8">}</span><span class="p" data-group-id="7487866918-6">]</span><span class="p" data-group-id="7487866918-5">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="7487866918-9">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="7487866918-10">[</span><span class="p" data-group-id="7487866918-11">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="7487866918-11">}</span><span class="p">,</span><span class="p" data-group-id="7487866918-12">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">677</span><span class="p" data-group-id="7487866918-12">}</span><span class="p" data-group-id="7487866918-10">]</span><span class="p" data-group-id="7487866918-9">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="7487866918-13">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">expr</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="p" data-group-id="7487866918-14">[</span><span class="p" data-group-id="7487866918-15">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="7487866918-15">}</span><span class="p">,</span><span class="p" data-group-id="7487866918-16">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">430</span><span class="p" data-group-id="7487866918-16">}</span><span class="p" data-group-id="7487866918-14">]</span><span class="p" data-group-id="7487866918-13">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="7487866918-17">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="7487866918-18">[</span><span class="p" data-group-id="7487866918-19">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="7487866918-19">}</span><span class="p">,</span><span class="p" data-group-id="7487866918-20">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">687</span><span class="p" data-group-id="7487866918-20">}</span><span class="p" data-group-id="7487866918-18">]</span><span class="p" data-group-id="7487866918-17">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="7487866918-21">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="7487866918-22">[</span><span class="p" data-group-id="7487866918-23">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="7487866918-23">}</span><span class="p">,</span><span class="p" data-group-id="7487866918-24">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">642</span><span class="p" data-group-id="7487866918-24">}</span><span class="p" data-group-id="7487866918-22">]</span><span class="p" data-group-id="7487866918-21">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="7487866918-25">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_loop</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="7487866918-26">[</span><span class="p" data-group-id="7487866918-27">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="7487866918-27">}</span><span class="p">,</span><span class="p" data-group-id="7487866918-28">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">627</span><span class="p" data-group-id="7487866918-28">}</span><span class="p" data-group-id="7487866918-26">]</span><span class="p" data-group-id="7487866918-25">}</span><span class="p" data-group-id="7487866918-4">]</span><span class="p" data-group-id="7487866918-3">}</span><span class="p" data-group-id="7487866918-2">}</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="error/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#error/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -12365,21 +12365,21 @@
│ │ │  <code class="inline">none</code>.</p><p>If <code class="inline">Args</code> is a list, it is used to provide the arguments for the current
│ │ │  function in the stack back-trace. If it is <code class="inline">none</code>, the arity of the calling
│ │ │  function is used in the stacktrace. As evaluating this function causes an
│ │ │  exception to be raised, it has no return value.</p><p>The intent of the exception class <code class="inline">error</code> is to signal that an unexpected error
│ │ │  has happened (for example, a function is called with a parameter that has an
│ │ │  incorrect type). See the guide about
│ │ │  <a href="../../../doc/system/errors.html">errors and error handling</a> for additional information.
│ │ │ -Example:</p><p><code class="inline">test.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4803352821-1">(</span><span class="ss">test</span><span class="p" data-group-id="4803352821-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4803352821-2">(</span><span class="p" data-group-id="4803352821-3">[</span><span class="ss">example_fun</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4803352821-3">]</span><span class="p" data-group-id="4803352821-2">)</span><span class="p">.</span><span class="w">
│ │ │ +Example:</p><p><code class="inline">test.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0627927150-1">(</span><span class="ss">test</span><span class="p" data-group-id="0627927150-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0627927150-2">(</span><span class="p" data-group-id="0627927150-3">[</span><span class="ss">example_fun</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0627927150-3">]</span><span class="p" data-group-id="0627927150-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">example_fun</span><span class="p" data-group-id="4803352821-4">(</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="n">A2</span><span class="p" data-group-id="4803352821-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">error</span><span class="p" data-group-id="4803352821-5">(</span><span class="ss">my_error</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4803352821-6">[</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="n">A2</span><span class="p" data-group-id="4803352821-6">]</span><span class="p" data-group-id="4803352821-5">)</span><span class="p">.</span></code></pre><p>Erlang shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">6&gt; </span><span class="nf">c</span><span class="p" data-group-id="2081343063-1">(</span><span class="ss">test</span><span class="p" data-group-id="2081343063-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2081343063-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">test</span><span class="p" data-group-id="2081343063-2">}</span><span class="gp unselectable">
│ │ │ -7&gt; </span><span class="nc">test</span><span class="p">:</span><span class="nf">example_fun</span><span class="p" data-group-id="2081343063-3">(</span><span class="ss">arg1</span><span class="p">,</span><span class="s">&quot;this is the second argument&quot;</span><span class="p" data-group-id="2081343063-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">example_fun</span><span class="p" data-group-id="0627927150-4">(</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="n">A2</span><span class="p" data-group-id="0627927150-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">error</span><span class="p" data-group-id="0627927150-5">(</span><span class="ss">my_error</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0627927150-6">[</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="n">A2</span><span class="p" data-group-id="0627927150-6">]</span><span class="p" data-group-id="0627927150-5">)</span><span class="p">.</span></code></pre><p>Erlang shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">6&gt; </span><span class="nf">c</span><span class="p" data-group-id="7416782329-1">(</span><span class="ss">test</span><span class="p" data-group-id="7416782329-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7416782329-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">test</span><span class="p" data-group-id="7416782329-2">}</span><span class="gp unselectable">
│ │ │ +7&gt; </span><span class="nc">test</span><span class="p">:</span><span class="nf">example_fun</span><span class="p" data-group-id="7416782329-3">(</span><span class="ss">arg1</span><span class="p">,</span><span class="s">&quot;this is the second argument&quot;</span><span class="p" data-group-id="7416782329-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: my_error
│ │ │       in function  test:example_fun/2
│ │ │           called as test:example_fun(arg1,&quot;this is the second argument&quot;)</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="error/3">
│ │ │  
│ │ │ @@ -12456,18 +12456,18 @@
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Raises an exception of class <code class="inline">exit</code> with exit reason <code class="inline">Reason</code>.</p><p>As evaluating this function causes an exception to be raised, it has no return value.</p><p>The intent of the exception class <code class="inline">exit</code> is that the current process should be
│ │ │  stopped (for example when a message telling a process to stop is received).</p><p>This function differ from <a href="#error/1"><code class="inline">error/1,2,3</code></a> by causing an exception of
│ │ │  a different class and by having a reason that does not include the list of
│ │ │  functions from the call stack.</p><p>See the guide about <a href="../../../doc/system/errors.html">errors and error handling</a> for
│ │ │ -additional information.</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">exit</span><span class="p" data-group-id="6328401750-1">(</span><span class="ss">foobar</span><span class="p" data-group-id="6328401750-1">)</span><span class="p">.</span><span class="w">
│ │ │ +additional information.</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">exit</span><span class="p" data-group-id="4631494660-1">(</span><span class="ss">foobar</span><span class="p" data-group-id="4631494660-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception exit: foobar</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="6328401750-2">(</span><span class="ss">foobar</span><span class="p" data-group-id="6328401750-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6328401750-3">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="ss">foobar</span><span class="p" data-group-id="6328401750-3">}</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>If a process calls <a href="#exit/1"><code class="inline">exit(kill)</code></a> and does not catch the exception,
│ │ │ +&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="4631494660-2">(</span><span class="ss">foobar</span><span class="p" data-group-id="4631494660-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4631494660-3">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="ss">foobar</span><span class="p" data-group-id="4631494660-3">}</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>If a process calls <a href="#exit/1"><code class="inline">exit(kill)</code></a> and does not catch the exception,
│ │ │  it will terminate with exit reason <code class="inline">kill</code> and also emit exit signals with exit
│ │ │  reason <code class="inline">kill</code> (not <code class="inline">killed</code>) to all linked processes. Such exit signals with
│ │ │  exit reason <code class="inline">kill</code> can be trapped by the linked processes. Note that this
│ │ │  means that signals with exit reason <code class="inline">kill</code> behave differently depending on how
│ │ │  they are sent because the signal will be untrappable if a process sends such a
│ │ │  signal to another process with <a href="#exit/2"><code class="inline">erlang:exit/2</code></a>.</p></section>
│ │ │    </section>
│ │ │ @@ -12660,19 +12660,19 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> get() -> [{Key, Val}] when Key :: <a href="#t:term/0">term</a>(), Val :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns the process dictionary as a list of <code class="inline">{Key, Val}</code> tuples. The items in
│ │ │ -the returned list can be in any order.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="4780991522-1">(</span><span class="ss">key1</span><span class="p">,</span><span class="w"> </span><span class="ss">merry</span><span class="p" data-group-id="4780991522-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="4780991522-2">(</span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">lambs</span><span class="p" data-group-id="4780991522-2">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="4780991522-3">(</span><span class="ss">key3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4780991522-4">{</span><span class="ss">are</span><span class="p">,</span><span class="w"> </span><span class="ss">playing</span><span class="p" data-group-id="4780991522-4">}</span><span class="p" data-group-id="4780991522-3">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">get</span><span class="p" data-group-id="4780991522-5">(</span><span class="p" data-group-id="4780991522-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4780991522-6">[</span><span class="p" data-group-id="4780991522-7">{</span><span class="ss">key1</span><span class="p">,</span><span class="ss">merry</span><span class="p" data-group-id="4780991522-7">}</span><span class="p">,</span><span class="p" data-group-id="4780991522-8">{</span><span class="ss">key2</span><span class="p">,</span><span class="ss">lambs</span><span class="p" data-group-id="4780991522-8">}</span><span class="p">,</span><span class="p" data-group-id="4780991522-9">{</span><span class="ss">key3</span><span class="p">,</span><span class="p" data-group-id="4780991522-10">{</span><span class="ss">are</span><span class="p">,</span><span class="ss">playing</span><span class="p" data-group-id="4780991522-10">}</span><span class="p" data-group-id="4780991522-9">}</span><span class="p" data-group-id="4780991522-6">]</span></code></pre>
│ │ │ +the returned list can be in any order.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="5860713296-1">(</span><span class="ss">key1</span><span class="p">,</span><span class="w"> </span><span class="ss">merry</span><span class="p" data-group-id="5860713296-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="5860713296-2">(</span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">lambs</span><span class="p" data-group-id="5860713296-2">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="5860713296-3">(</span><span class="ss">key3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5860713296-4">{</span><span class="ss">are</span><span class="p">,</span><span class="w"> </span><span class="ss">playing</span><span class="p" data-group-id="5860713296-4">}</span><span class="p" data-group-id="5860713296-3">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">get</span><span class="p" data-group-id="5860713296-5">(</span><span class="p" data-group-id="5860713296-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5860713296-6">[</span><span class="p" data-group-id="5860713296-7">{</span><span class="ss">key1</span><span class="p">,</span><span class="ss">merry</span><span class="p" data-group-id="5860713296-7">}</span><span class="p">,</span><span class="p" data-group-id="5860713296-8">{</span><span class="ss">key2</span><span class="p">,</span><span class="ss">lambs</span><span class="p" data-group-id="5860713296-8">}</span><span class="p">,</span><span class="p" data-group-id="5860713296-9">{</span><span class="ss">key3</span><span class="p">,</span><span class="p" data-group-id="5860713296-10">{</span><span class="ss">are</span><span class="p">,</span><span class="ss">playing</span><span class="p" data-group-id="5860713296-10">}</span><span class="p" data-group-id="5860713296-9">}</span><span class="p" data-group-id="5860713296-6">]</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="get/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#get/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -12695,19 +12695,19 @@
│ │ │            <pre translate="no"><span class="attribute">-spec</span> get(Key) -> Val | undefined when Key :: <a href="#t:term/0">term</a>(), Val :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns the value <code class="inline">Val</code> associated with <code class="inline">Key</code> in the process dictionary, or
│ │ │  <code class="inline">undefined</code> if <code class="inline">Key</code> does not exist.</p><p>The expected time complexity for the current implementation of this function is
│ │ │  O(<code class="inline">1</code>) and the worst case time complexity is O(<code class="inline">N</code>), where <code class="inline">N</code> is the number of
│ │ │ -items in the process dictionary.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="4337208020-1">(</span><span class="ss">key1</span><span class="p">,</span><span class="w"> </span><span class="ss">merry</span><span class="p" data-group-id="4337208020-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="4337208020-2">(</span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">lambs</span><span class="p" data-group-id="4337208020-2">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="4337208020-3">(</span><span class="p" data-group-id="4337208020-4">{</span><span class="ss">any</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4337208020-5">[</span><span class="ss">valid</span><span class="p">,</span><span class="w"> </span><span class="ss">term</span><span class="p" data-group-id="4337208020-5">]</span><span class="p" data-group-id="4337208020-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4337208020-6">{</span><span class="ss">are</span><span class="p">,</span><span class="w"> </span><span class="ss">playing</span><span class="p" data-group-id="4337208020-6">}</span><span class="p" data-group-id="4337208020-3">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">get</span><span class="p" data-group-id="4337208020-7">(</span><span class="p" data-group-id="4337208020-8">{</span><span class="ss">any</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4337208020-9">[</span><span class="ss">valid</span><span class="p">,</span><span class="w"> </span><span class="ss">term</span><span class="p" data-group-id="4337208020-9">]</span><span class="p" data-group-id="4337208020-8">}</span><span class="p" data-group-id="4337208020-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4337208020-10">{</span><span class="ss">are</span><span class="p">,</span><span class="ss">playing</span><span class="p" data-group-id="4337208020-10">}</span></code></pre>
│ │ │ +items in the process dictionary.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="9400285695-1">(</span><span class="ss">key1</span><span class="p">,</span><span class="w"> </span><span class="ss">merry</span><span class="p" data-group-id="9400285695-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="9400285695-2">(</span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">lambs</span><span class="p" data-group-id="9400285695-2">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="9400285695-3">(</span><span class="p" data-group-id="9400285695-4">{</span><span class="ss">any</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9400285695-5">[</span><span class="ss">valid</span><span class="p">,</span><span class="w"> </span><span class="ss">term</span><span class="p" data-group-id="9400285695-5">]</span><span class="p" data-group-id="9400285695-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9400285695-6">{</span><span class="ss">are</span><span class="p">,</span><span class="w"> </span><span class="ss">playing</span><span class="p" data-group-id="9400285695-6">}</span><span class="p" data-group-id="9400285695-3">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">get</span><span class="p" data-group-id="9400285695-7">(</span><span class="p" data-group-id="9400285695-8">{</span><span class="ss">any</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9400285695-9">[</span><span class="ss">valid</span><span class="p">,</span><span class="w"> </span><span class="ss">term</span><span class="p" data-group-id="9400285695-9">]</span><span class="p" data-group-id="9400285695-8">}</span><span class="p" data-group-id="9400285695-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9400285695-10">{</span><span class="ss">are</span><span class="p">,</span><span class="ss">playing</span><span class="p" data-group-id="9400285695-10">}</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="get_keys/0">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#get_keys/0" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -12730,19 +12730,19 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> get_keys() -> [Key] when Key :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a list of all keys present in the process dictionary. The items in the
│ │ │ -returned list can be in any order.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="0796497588-1">(</span><span class="ss">dog</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0796497588-2">{</span><span class="ss">animal</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0796497588-2">}</span><span class="p" data-group-id="0796497588-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="0796497588-3">(</span><span class="ss">cow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0796497588-4">{</span><span class="ss">animal</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0796497588-4">}</span><span class="p" data-group-id="0796497588-3">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="0796497588-5">(</span><span class="ss">lamb</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0796497588-6">{</span><span class="ss">animal</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0796497588-6">}</span><span class="p" data-group-id="0796497588-5">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">get_keys</span><span class="p" data-group-id="0796497588-7">(</span><span class="p" data-group-id="0796497588-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0796497588-8">[</span><span class="ss">dog</span><span class="p">,</span><span class="ss">cow</span><span class="p">,</span><span class="ss">lamb</span><span class="p" data-group-id="0796497588-8">]</span></code></pre>
│ │ │ +returned list can be in any order.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="8688233366-1">(</span><span class="ss">dog</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8688233366-2">{</span><span class="ss">animal</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8688233366-2">}</span><span class="p" data-group-id="8688233366-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="8688233366-3">(</span><span class="ss">cow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8688233366-4">{</span><span class="ss">animal</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8688233366-4">}</span><span class="p" data-group-id="8688233366-3">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="8688233366-5">(</span><span class="ss">lamb</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8688233366-6">{</span><span class="ss">animal</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8688233366-6">}</span><span class="p" data-group-id="8688233366-5">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">get_keys</span><span class="p" data-group-id="8688233366-7">(</span><span class="p" data-group-id="8688233366-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8688233366-8">[</span><span class="ss">dog</span><span class="p">,</span><span class="ss">cow</span><span class="p">,</span><span class="ss">lamb</span><span class="p" data-group-id="8688233366-8">]</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="get_keys/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#get_keys/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -12763,22 +12763,22 @@
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> get_keys(Val) -> [Key] when Val :: <a href="#t:term/0">term</a>(), Key :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a list of keys that are associated with the value <code class="inline">Val</code> in the process
│ │ │ -dictionary. The items in the returned list can be in any order.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="9291492673-1">(</span><span class="ss">mary</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9291492673-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9291492673-2">}</span><span class="p" data-group-id="9291492673-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="9291492673-3">(</span><span class="ss">had</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9291492673-4">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9291492673-4">}</span><span class="p" data-group-id="9291492673-3">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="9291492673-5">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9291492673-6">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9291492673-6">}</span><span class="p" data-group-id="9291492673-5">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="9291492673-7">(</span><span class="ss">little</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9291492673-8">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9291492673-8">}</span><span class="p" data-group-id="9291492673-7">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="9291492673-9">(</span><span class="ss">dog</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9291492673-10">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="9291492673-10">}</span><span class="p" data-group-id="9291492673-9">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">put</span><span class="p" data-group-id="9291492673-11">(</span><span class="ss">lamb</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9291492673-12">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9291492673-12">}</span><span class="p" data-group-id="9291492673-11">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">get_keys</span><span class="p" data-group-id="9291492673-13">(</span><span class="p" data-group-id="9291492673-14">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9291492673-14">}</span><span class="p" data-group-id="9291492673-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9291492673-15">[</span><span class="ss">mary</span><span class="p">,</span><span class="ss">had</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">little</span><span class="p">,</span><span class="ss">lamb</span><span class="p" data-group-id="9291492673-15">]</span></code></pre>
│ │ │ +dictionary. The items in the returned list can be in any order.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">put</span><span class="p" data-group-id="4864262226-1">(</span><span class="ss">mary</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4864262226-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4864262226-2">}</span><span class="p" data-group-id="4864262226-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="4864262226-3">(</span><span class="ss">had</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4864262226-4">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4864262226-4">}</span><span class="p" data-group-id="4864262226-3">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="4864262226-5">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4864262226-6">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4864262226-6">}</span><span class="p" data-group-id="4864262226-5">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="4864262226-7">(</span><span class="ss">little</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4864262226-8">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4864262226-8">}</span><span class="p" data-group-id="4864262226-7">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="4864262226-9">(</span><span class="ss">dog</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4864262226-10">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4864262226-10">}</span><span class="p" data-group-id="4864262226-9">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">put</span><span class="p" data-group-id="4864262226-11">(</span><span class="ss">lamb</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4864262226-12">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4864262226-12">}</span><span class="p" data-group-id="4864262226-11">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">get_keys</span><span class="p" data-group-id="4864262226-13">(</span><span class="p" data-group-id="4864262226-14">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4864262226-14">}</span><span class="p" data-group-id="4864262226-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4864262226-15">[</span><span class="ss">mary</span><span class="p">,</span><span class="ss">had</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">little</span><span class="p">,</span><span class="ss">lamb</span><span class="p" data-group-id="4864262226-15">]</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="group_leader/0">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#group_leader/0" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -12925,17 +12925,17 @@
│ │ │  <p><code class="inline">Pid</code> must refer to a process at the local node.</p><p>Returns <code class="inline">true</code> if the process exists and is alive, that is, is not exiting and
│ │ │  has not exited. Otherwise returns <code class="inline">false</code>.</p><p>If process <code class="inline">P1</code> calls <a href="#is_process_alive/1"><code class="inline">is_process_alive(P2Pid)</code></a> it is
│ │ │  guaranteed that all signals, sent from <code class="inline">P1</code> to <code class="inline">P2</code> (<code class="inline">P2</code> is the process with
│ │ │  identifier <code class="inline">P2Pid</code>) before the call, will be delivered to <code class="inline">P2</code> before the
│ │ │  aliveness of <code class="inline">P2</code> is checked. This guarantee means that one can use
│ │ │  <a href="#is_process_alive/1"><code class="inline">is_process_alive/1</code></a> to let a process <code class="inline">P1</code> wait until a
│ │ │  process <code class="inline">P2</code>, which has got an exit signal with reason <code class="inline">kill</code> from P1, is
│ │ │ -killed.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">exit</span><span class="p" data-group-id="9263790509-1">(</span><span class="n">P2Pid</span><span class="p">,</span><span class="w"> </span><span class="ss">kill</span><span class="p" data-group-id="9263790509-1">)</span><span class="p">,</span><span class="w">
│ │ │ +killed.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">exit</span><span class="p" data-group-id="0788869028-1">(</span><span class="n">P2Pid</span><span class="p">,</span><span class="w"> </span><span class="ss">kill</span><span class="p" data-group-id="0788869028-1">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="c1">% P2 might not be killed</span><span class="w">
│ │ │ -</span><span class="nf">is_process_alive</span><span class="p" data-group-id="9263790509-2">(</span><span class="n">P2Pid</span><span class="p" data-group-id="9263790509-2">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">is_process_alive</span><span class="p" data-group-id="0788869028-2">(</span><span class="n">P2Pid</span><span class="p" data-group-id="0788869028-2">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="c1">% P2 is not alive (the call above always return false)</span></code></pre><p>See the documentation about <a href="../../../doc/system/ref_man_processes.html#signals">signals</a>
│ │ │  and <a href="#exit/2">erlang:exit/2</a> for more information about signals and exit
│ │ │  signals.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="link/1">
│ │ │  
│ │ │ @@ -13016,24 +13016,24 @@
│ │ │            <pre translate="no"><span class="attribute">-spec</span> monitor(process, <a href="#t:monitor_process_identifier/0">monitor_process_identifier</a>()) -> MonitorRef when MonitorRef :: <a href="#t:reference/0">reference</a>();
│ │ │               (port, <a href="#t:monitor_port_identifier/0">monitor_port_identifier</a>()) -> MonitorRef when MonitorRef :: <a href="#t:reference/0">reference</a>();
│ │ │               (time_offset, clock_service) -> MonitorRef when MonitorRef :: <a href="#t:reference/0">reference</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Sends a monitor request of type <code class="inline">Type</code> to the entity identified by <code class="inline">Item</code>.</p><p id="monitor_message">If the monitored entity does not exist or it changes monitored state, the caller
│ │ │ -of <a href="#monitor/2"><code class="inline">monitor/2</code></a> is notified by a message on the following format:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6089528285-1">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">MonitorRef</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Object</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="6089528285-1">}</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The monitor request is an asynchronous signal. That is, it takes time before
│ │ │ +of <a href="#monitor/2"><code class="inline">monitor/2</code></a> is notified by a message on the following format:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7799887367-1">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">MonitorRef</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Object</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="7799887367-1">}</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The monitor request is an asynchronous signal. That is, it takes time before
│ │ │  the signal reaches its destination.</p></section><p><code class="inline">Type</code> can be one of the following atoms: <code class="inline">process</code>, <code class="inline">port</code> or <code class="inline">time_offset</code>.</p><p>A <code class="inline">process</code> or <code class="inline">port</code> monitor is triggered only once, after that it is removed
│ │ │  from both monitoring process and the monitored entity. Monitors are fired when
│ │ │  the monitored process or port terminates, does not exist at the moment of
│ │ │  creation, or if the connection to it is lost. If the connection to it is lost,
│ │ │  we do not know if it still exists. The monitoring is also turned off when
│ │ │  <a href="#demonitor/1"><code class="inline">demonitor/1</code></a> is called.</p><p>A <code class="inline">process</code> or <code class="inline">port</code> monitor by name resolves the <code class="inline">RegisteredName</code> to <a href="#t:pid/0"><code class="inline">pid/0</code></a>
│ │ │  or <a href="#t:port/0"><code class="inline">port/0</code></a> only once at the moment of monitor instantiation, later changes to
│ │ │  the name registration will not affect the existing monitor.</p><p>When a <code class="inline">process</code> or <code class="inline">port</code> monitor is triggered, a <code class="inline">'DOWN'</code> message is sent that
│ │ │ -has the following pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1288458395-1">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MonitorRef</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Object</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="1288458395-1">}</span></code></pre><p>In the monitor message <code class="inline">MonitorRef</code> and <code class="inline">Type</code> are the same as described
│ │ │ +has the following pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6651019425-1">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MonitorRef</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Object</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="6651019425-1">}</span></code></pre><p>In the monitor message <code class="inline">MonitorRef</code> and <code class="inline">Type</code> are the same as described
│ │ │  earlier, and:</p><ul><li><p><strong><code class="inline">Object</code></strong> - The monitored entity, which triggered the event. When
│ │ │  monitoring a process or a local port, <code class="inline">Object</code> will be equal to the <a href="#t:pid/0"><code class="inline">pid/0</code></a>
│ │ │  or <a href="#t:port/0"><code class="inline">port/0</code></a> that was being monitored. When monitoring process or port by
│ │ │  name, <code class="inline">Object</code> will have format <code class="inline">{RegisteredName, Node}</code> where
│ │ │  <code class="inline">RegisteredName</code> is the name which has been used with
│ │ │  <a href="#monitor/2"><code class="inline">monitor/2</code></a> call and <code class="inline">Node</code> is local or remote node name (for
│ │ │  ports monitored by name, <code class="inline">Node</code> is always local node name).</p></li><li><p><strong><code class="inline">Info</code></strong> - Either the exit reason of the process, <code class="inline">noproc</code> (process or port
│ │ │ @@ -13069,15 +13069,15 @@
│ │ │  offset is changed when the runtime system detects that the
│ │ │  <a href="time_correction.html#os-system-time">OS system time</a> has changed. The runtime
│ │ │  system does, however, not detect this immediately when it occurs. A task
│ │ │  checking the time offset is scheduled to execute at least once a minute, so
│ │ │  under normal operation this is to be detected within a minute, but during
│ │ │  heavy load it can take longer time.</p><p>The monitor is <em>not</em> automatically removed after it has been triggered. That
│ │ │  is, repeated changes of the time offset trigger the monitor repeatedly.</p><p>When the monitor is triggered a <code class="inline">'CHANGE'</code> message is sent to the monitoring
│ │ │ -process. A <code class="inline">'CHANGE'</code> message has the following pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5830466664-1">{</span><span class="ss">&#39;CHANGE&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MonitorRef</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Item</span><span class="p">,</span><span class="w"> </span><span class="n">NewTimeOffset</span><span class="p" data-group-id="5830466664-1">}</span></code></pre><p>where <code class="inline">MonitorRef</code>, <code class="inline">Type</code>, and <code class="inline">Item</code> are the same as described above, and
│ │ │ +process. A <code class="inline">'CHANGE'</code> message has the following pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5035902467-1">{</span><span class="ss">&#39;CHANGE&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MonitorRef</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Item</span><span class="p">,</span><span class="w"> </span><span class="n">NewTimeOffset</span><span class="p" data-group-id="5035902467-1">}</span></code></pre><p>where <code class="inline">MonitorRef</code>, <code class="inline">Type</code>, and <code class="inline">Item</code> are the same as described above, and
│ │ │  <code class="inline">NewTimeOffset</code> is the new time offset.</p><p>When the <code class="inline">'CHANGE'</code> message has been received you are guaranteed not to
│ │ │  retrieve the old time offset when calling
│ │ │  <a href="#time_offset/0"><code class="inline">erlang:time_offset/0</code></a>. Notice that you can observe the
│ │ │  change of the time offset when calling <a href="#time_offset/0"><code class="inline">erlang:time_offset/0</code></a> before you get
│ │ │  the <code class="inline">'CHANGE'</code> message.</p><p>Available since OTP 18.0.</p></li></ul><p>Making several calls to <a href="#monitor/2"><code class="inline">monitor/2</code></a> for the same <code class="inline">Item</code> and/or
│ │ │  <code class="inline">Type</code> is not an error; it results in as many independent monitoring instances.</p><p>The monitor functionality is expected to be extended. That is, other <code class="inline">Type</code>s and
│ │ │  <code class="inline">Item</code>s are expected to be supported in a future release.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>If or when <a href="#monitor/2"><code class="inline">monitor/2</code></a> is extended, other possible values for
│ │ │ @@ -13133,78 +13133,78 @@
│ │ │  via the alias is received. When a reply message is received via the alias
│ │ │  the monitor will also be automatically removed. This is useful in
│ │ │  client/server scenarios when a client monitors the server and will get the
│ │ │  reply via the alias. Once the response is received both the alias and the
│ │ │  monitor will be automatically removed regardless of whether the response is
│ │ │  a reply or a <code class="inline">'DOWN'</code> message. The alias can also still be deactivated via a
│ │ │  call to <a href="#unalias/1"><code class="inline">unalias/1</code></a>. Note that if the alias is removed using
│ │ │ -the <a href="#unalias/1"><code class="inline">unalias/1</code></a> BIF, the monitor will still be left active.</p></li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server</span><span class="p" data-group-id="8843965465-1">(</span><span class="p" data-group-id="8843965465-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +the <a href="#unalias/1"><code class="inline">unalias/1</code></a> BIF, the monitor will still be left active.</p></li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server</span><span class="p" data-group-id="7196309993-1">(</span><span class="p" data-group-id="7196309993-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8843965465-2">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="8843965465-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">perform_request</span><span class="p" data-group-id="8843965465-3">(</span><span class="n">Request</span><span class="p" data-group-id="8843965465-3">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">AliasReqId</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8843965465-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8843965465-4">}</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7196309993-2">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="7196309993-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">perform_request</span><span class="p" data-group-id="7196309993-3">(</span><span class="n">Request</span><span class="p" data-group-id="7196309993-3">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">AliasReqId</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7196309993-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">AliasReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7196309993-4">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="8843965465-5">(</span><span class="p" data-group-id="8843965465-5">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="7196309993-5">(</span><span class="p" data-group-id="7196309993-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="8843965465-6">(</span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="8843965465-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">AliasMonReqId</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="8843965465-7">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8843965465-8">[</span><span class="p" data-group-id="8843965465-9">{</span><span class="ss">alias</span><span class="p">,</span><span class="w"> </span><span class="ss">reply_demonitor</span><span class="p" data-group-id="8843965465-9">}</span><span class="p" data-group-id="8843965465-8">]</span><span class="p" data-group-id="8843965465-7">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ServerPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8843965465-10">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="n">AliasMonReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="8843965465-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="7196309993-6">(</span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="7196309993-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">AliasMonReqId</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="7196309993-7">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7196309993-8">[</span><span class="p" data-group-id="7196309993-9">{</span><span class="ss">alias</span><span class="p">,</span><span class="w"> </span><span class="ss">reply_demonitor</span><span class="p" data-group-id="7196309993-9">}</span><span class="p" data-group-id="7196309993-8">]</span><span class="p" data-group-id="7196309993-7">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ServerPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7196309993-10">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="n">AliasMonReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="7196309993-10">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%% Alias as well as monitor will be automatically deactivated if we</span><span class="w">
│ │ │      </span><span class="c1">%% receive a reply or a &#39;DOWN&#39; message since we used &#39;reply_demonitor&#39;</span><span class="w">
│ │ │      </span><span class="c1">%% as unalias option...</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8843965465-11">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">AliasMonReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8843965465-11">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7196309993-11">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">AliasMonReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7196309993-11">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Result</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8843965465-12">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">AliasMonReqId</span><span class="p">,</span><span class="w"> </span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">ExitReason</span><span class="p" data-group-id="8843965465-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">error</span><span class="p" data-group-id="8843965465-13">(</span><span class="n">ExitReason</span><span class="p" data-group-id="8843965465-13">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7196309993-12">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">AliasMonReqId</span><span class="p">,</span><span class="w"> </span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">ExitReason</span><span class="p" data-group-id="7196309993-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">error</span><span class="p" data-group-id="7196309993-13">(</span><span class="n">ExitReason</span><span class="p" data-group-id="7196309993-13">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Note that both the server and the client in this example must be executing on
│ │ │  at least OTP 24 systems in order for this to work.</p><p>For more information on process aliases see the
│ │ │  <a href="../../../doc/system/ref_man_processes.html#process-aliases"><em>Process Aliases</em></a> section
│ │ │  of the <em>Erlang Reference Manual</em>.</p></li><li><p><strong><code class="inline">{tag, UserDefinedTag}</code></strong> - Replace the default <code class="inline">Tag</code> with <code class="inline">UserDefinedTag</code>
│ │ │  in the <a href="#monitor_message">monitor message</a> delivered when the
│ │ │  monitor is triggered. For example, when monitoring a process, the <code class="inline">'DOWN'</code> tag
│ │ │  in the down message will be replaced by <code class="inline">UserDefinedTag</code>.</p><p>An example of how the <code class="inline">{tag, UserDefinedTag}</code> option can be used in order to
│ │ │  enable the new
│ │ │  <a href="../../../doc/system/eff_guide_processes.html#receiving-messages">selective receive optimization</a>,
│ │ │ -introduced in OTP 24, when making multiple requests to different servers:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server</span><span class="p" data-group-id="9071275296-1">(</span><span class="p" data-group-id="9071275296-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +introduced in OTP 24, when making multiple requests to different servers:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server</span><span class="p" data-group-id="0468706056-1">(</span><span class="p" data-group-id="0468706056-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9071275296-2">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="9071275296-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">perform_request</span><span class="p" data-group-id="9071275296-3">(</span><span class="n">Request</span><span class="p" data-group-id="9071275296-3">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9071275296-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9071275296-5">(</span><span class="p" data-group-id="9071275296-5">)</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9071275296-4">}</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0468706056-2">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0468706056-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">perform_request</span><span class="p" data-group-id="0468706056-3">(</span><span class="n">Request</span><span class="p" data-group-id="0468706056-3">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0468706056-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0468706056-5">(</span><span class="p" data-group-id="0468706056-5">)</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0468706056-4">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="9071275296-6">(</span><span class="p" data-group-id="9071275296-6">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="0468706056-6">(</span><span class="p" data-group-id="0468706056-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="9071275296-7">(</span><span class="n">ServerPids</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="9071275296-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_list</span><span class="p" data-group-id="9071275296-8">(</span><span class="n">ServerPids</span><span class="p" data-group-id="9071275296-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">ReqId</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="9071275296-9">(</span><span class="p" data-group-id="9071275296-9">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="9071275296-10">(</span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="9071275296-11">(</span><span class="n">ServerPid</span><span class="p" data-group-id="9071275296-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                          </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="9071275296-12">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w">
│ │ │ -                                      </span><span class="p" data-group-id="9071275296-13">[</span><span class="p" data-group-id="9071275296-14">{</span><span class="ss">tag</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9071275296-15">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p" data-group-id="9071275296-15">}</span><span class="p" data-group-id="9071275296-14">}</span><span class="p" data-group-id="9071275296-13">]</span><span class="p" data-group-id="9071275296-12">)</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="n">ServerPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9071275296-16">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9071275296-17">(</span><span class="p" data-group-id="9071275296-17">)</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="9071275296-16">}</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="0468706056-7">(</span><span class="n">ServerPids</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0468706056-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_list</span><span class="p" data-group-id="0468706056-8">(</span><span class="n">ServerPids</span><span class="p" data-group-id="0468706056-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ReqId</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="0468706056-9">(</span><span class="p" data-group-id="0468706056-9">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="0468706056-10">(</span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0468706056-11">(</span><span class="n">ServerPid</span><span class="p" data-group-id="0468706056-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                          </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="0468706056-12">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w">
│ │ │ +                                      </span><span class="p" data-group-id="0468706056-13">[</span><span class="p" data-group-id="0468706056-14">{</span><span class="ss">tag</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0468706056-15">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p" data-group-id="0468706056-15">}</span><span class="p" data-group-id="0468706056-14">}</span><span class="p" data-group-id="0468706056-13">]</span><span class="p" data-group-id="0468706056-12">)</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="n">ServerPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0468706056-16">{</span><span class="ss">request</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0468706056-17">(</span><span class="p" data-group-id="0468706056-17">)</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0468706056-16">}</span><span class="w">
│ │ │                    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -                  </span><span class="n">ServerPids</span><span class="p" data-group-id="9071275296-10">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">receive_replies</span><span class="p" data-group-id="9071275296-18">(</span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9071275296-19">(</span><span class="n">ServerPids</span><span class="p" data-group-id="9071275296-19">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9071275296-20">[</span><span class="p" data-group-id="9071275296-20">]</span><span class="p" data-group-id="9071275296-18">)</span><span class="p">.</span><span class="w">
│ │ │ +                  </span><span class="n">ServerPids</span><span class="p" data-group-id="0468706056-10">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">receive_replies</span><span class="p" data-group-id="0468706056-18">(</span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0468706056-19">(</span><span class="n">ServerPids</span><span class="p" data-group-id="0468706056-19">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0468706056-20">[</span><span class="p" data-group-id="0468706056-20">]</span><span class="p" data-group-id="0468706056-18">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">receive_replies</span><span class="p" data-group-id="9071275296-21">(</span><span class="p">_</span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9071275296-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">receive_replies</span><span class="p" data-group-id="0468706056-21">(</span><span class="p">_</span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0468706056-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">receive_replies</span><span class="p" data-group-id="9071275296-22">(</span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9071275296-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">receive_replies</span><span class="p" data-group-id="0468706056-22">(</span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0468706056-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% The compiler will detect that we match on the &#39;ReqId&#39;</span><span class="w">
│ │ │      </span><span class="c1">%% reference in all clauses, and will enable the selective</span><span class="w">
│ │ │      </span><span class="c1">%% receive optimization which makes the receive able to</span><span class="w">
│ │ │      </span><span class="c1">%% skip past all messages present in the message queue at</span><span class="w">
│ │ │      </span><span class="c1">%% the time when the &#39;ReqId&#39; reference was created...</span><span class="w">
│ │ │      </span><span class="n">Res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">receive</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="9071275296-23">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9071275296-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="0468706056-23">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0468706056-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                    </span><span class="c1">%% Here we typically would have deactivated the</span><span class="w">
│ │ │                    </span><span class="c1">%% monitor by a call to demonitor(Mon, [flush]) but</span><span class="w">
│ │ │                    </span><span class="c1">%% we ignore this in this example for simplicity...</span><span class="w">
│ │ │ -                  </span><span class="p" data-group-id="9071275296-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9071275296-24">}</span><span class="p">;</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="9071275296-25">{</span><span class="p" data-group-id="9071275296-26">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p" data-group-id="9071275296-26">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Mon</span><span class="p">,</span><span class="w"> </span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">ExitReason</span><span class="p" data-group-id="9071275296-25">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                  </span><span class="p" data-group-id="9071275296-27">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">ExitReason</span><span class="p" data-group-id="9071275296-27">}</span><span class="w">
│ │ │ +                  </span><span class="p" data-group-id="0468706056-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0468706056-24">}</span><span class="p">;</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="0468706056-25">{</span><span class="p" data-group-id="0468706056-26">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">ReqId</span><span class="p" data-group-id="0468706056-26">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Mon</span><span class="p">,</span><span class="w"> </span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">ExitReason</span><span class="p" data-group-id="0468706056-25">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                  </span><span class="p" data-group-id="0468706056-27">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">ServerPid</span><span class="p">,</span><span class="w"> </span><span class="n">ExitReason</span><span class="p" data-group-id="0468706056-27">}</span><span class="w">
│ │ │            </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">receive_replies</span><span class="p" data-group-id="9071275296-28">(</span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9071275296-29">[</span><span class="n">Res</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9071275296-29">]</span><span class="p" data-group-id="9071275296-28">)</span><span class="p">.</span></code></pre><p>In order for this example to work as intended, the client must be executing on
│ │ │ +    </span><span class="nf">receive_replies</span><span class="p" data-group-id="0468706056-28">(</span><span class="n">ReqId</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0468706056-29">[</span><span class="n">Res</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0468706056-29">]</span><span class="p" data-group-id="0468706056-28">)</span><span class="p">.</span></code></pre><p>In order for this example to work as intended, the client must be executing on
│ │ │  at least an OTP 24 system, but the servers may execute on older systems.</p></li></ul>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="nif_error/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#nif_error/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -13910,15 +13910,15 @@
│ │ │                    (sensitive, Boolean) -> OldBoolean when Boolean :: <a href="#t:boolean/0">boolean</a>(), OldBoolean :: <a href="#t:boolean/0">boolean</a>();
│ │ │                    ({monitor_nodes, <a href="#t:term/0">term</a>()}, <a href="#t:term/0">term</a>()) -> <a href="#t:term/0">term</a>();
│ │ │                    (monitor_nodes, <a href="#t:term/0">term</a>()) -> <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Sets the process flag indicated to the specified value. Returns the previous value
│ │ │ -of the flag.</p><p><code class="inline">Flag</code> is one of the following:</p><ul><li><pre id="process_flag_async_dist"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="6073829077-1">(</span><span class="ss">async_dist</span><span class="p">,</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="6073829077-2">(</span><span class="p" data-group-id="6073829077-2">)</span><span class="p" data-group-id="6073829077-1">)</span></code></pre><p>Enable or disable <em>fully asynchronous distributed signaling</em> for the calling
│ │ │ +of the flag.</p><p><code class="inline">Flag</code> is one of the following:</p><ul><li><pre id="process_flag_async_dist"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="3110064724-1">(</span><span class="ss">async_dist</span><span class="p">,</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="3110064724-2">(</span><span class="p" data-group-id="3110064724-2">)</span><span class="p" data-group-id="3110064724-1">)</span></code></pre><p>Enable or disable <em>fully asynchronous distributed signaling</em> for the calling
│ │ │  process. When disabled, which is the default, the process sending a distributed
│ │ │  signal will block in the send operation if the buffer for the distribution
│ │ │  channel reach the <a href="erl_cmd.html#%2Bzdbbl">distribution buffer busy limit</a>. The
│ │ │  process will remain blocked until the buffer shrinks enough. This might in some
│ │ │  cases take a substantial amount of time. When <code class="inline">async_dist</code> is enabled, send
│ │ │  operations of distributed signals will always buffer the signal on the outgoing
│ │ │  distribution channel and then immediately return. That is, these send operations
│ │ │ @@ -13935,22 +13935,22 @@
│ │ │  caller.</p><p>The <code class="inline">async_dist</code> flag can also be set on a new process when spawning it using
│ │ │  the <a href="#spawn_opt/4"><code class="inline">spawn_opt()</code></a> BIF with the option
│ │ │  <a href="#spawn_opt_async_dist"><code class="inline">{async_dist, Enable}</code></a>. The default
│ │ │  <code class="inline">async_dist</code> flag to use on newly spawned processes can be set by passing the
│ │ │  command line argument <a href="erl_cmd.html#%2Bpad"><code class="inline">+pad &lt;boolean&gt;</code></a> when starting the
│ │ │  runtime system. If the <code class="inline">+pad &lt;boolean&gt;</code> command line argument is not passed, the
│ │ │  default value of the <code class="inline">async_dist</code> flag will be <code class="inline">false</code>.</p><p>You can inspect the state of the <code class="inline">async_dist</code> process flag of a process by
│ │ │ -calling <a href="#process_info_async_dist"><code class="inline">process_info(Pid, async_dist)</code></a>.</p></li><li><pre id="process_flag_trap_exit"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="4078937571-1">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="4078937571-2">(</span><span class="p" data-group-id="4078937571-2">)</span><span class="p" data-group-id="4078937571-1">)</span></code></pre><p>When <code class="inline">trap_exit</code> is set to <code class="inline">true</code>, exit signals arriving to a process are
│ │ │ +calling <a href="#process_info_async_dist"><code class="inline">process_info(Pid, async_dist)</code></a>.</p></li><li><pre id="process_flag_trap_exit"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="9955033097-1">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="9955033097-2">(</span><span class="p" data-group-id="9955033097-2">)</span><span class="p" data-group-id="9955033097-1">)</span></code></pre><p>When <code class="inline">trap_exit</code> is set to <code class="inline">true</code>, exit signals arriving to a process are
│ │ │  converted to <code class="inline">{'EXIT', From, Reason}</code> messages, which can be received as
│ │ │  ordinary messages. If <code class="inline">trap_exit</code> is set to <code class="inline">false</code>, the process exits if it
│ │ │  receives an exit signal other than <code class="inline">normal</code> and the exit signal is propagated to
│ │ │ -its linked processes. Application processes are normally not to trap exits.</p><p>See also <a href="#exit/2"><code class="inline">exit/2</code></a>.</p></li><li><pre id="process_flag_error_handler"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="8190844019-1">(</span><span class="ss">error_handler</span><span class="p">,</span><span class="w"> </span><span class="nf">module</span><span class="p" data-group-id="8190844019-2">(</span><span class="p" data-group-id="8190844019-2">)</span><span class="p" data-group-id="8190844019-1">)</span></code></pre><p>Used by a process to redefine the <a href="../../../lib/kernel-10.2.7.1/doc/html/error_handler.html"><code class="inline">error_handler</code></a> for undefined function calls and
│ │ │ +its linked processes. Application processes are normally not to trap exits.</p><p>See also <a href="#exit/2"><code class="inline">exit/2</code></a>.</p></li><li><pre id="process_flag_error_handler"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="2766703711-1">(</span><span class="ss">error_handler</span><span class="p">,</span><span class="w"> </span><span class="nf">module</span><span class="p" data-group-id="2766703711-2">(</span><span class="p" data-group-id="2766703711-2">)</span><span class="p" data-group-id="2766703711-1">)</span></code></pre><p>Used by a process to redefine the <a href="../../../lib/kernel-10.2.7.1/doc/html/error_handler.html"><code class="inline">error_handler</code></a> for undefined function calls and
│ │ │  undefined registered processes. Use this flag with substantial caution, as code
│ │ │ -auto-loading depends on the correct operation of the error handling module.</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="5660159848-1">(</span><span class="ss">fullsweep_after</span><span class="p">,</span><span class="w">  </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5660159848-2">(</span><span class="p" data-group-id="5660159848-2">)</span><span class="p" data-group-id="5660159848-1">)</span></code></pre><p>Changes the maximum number of generational collections before forcing a
│ │ │ -fullsweep for the calling process.</p></li><li><pre id="process_flag_min_heap_size"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="5934359357-1">(</span><span class="ss">min_heap_size</span><span class="p">,</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5934359357-2">(</span><span class="p" data-group-id="5934359357-2">)</span><span class="p" data-group-id="5934359357-1">)</span></code></pre><p>Changes the minimum heap size for the calling process.</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="5879716081-1">(</span><span class="ss">min_bin_vheap_size</span><span class="p">,</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5879716081-2">(</span><span class="p" data-group-id="5879716081-2">)</span><span class="p" data-group-id="5879716081-1">)</span></code></pre><p>Changes the minimum binary virtual heap size for the calling process.</p></li><li><pre id="process_flag_max_heap_size"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="2932036121-1">(</span><span class="ss">max_heap_size</span><span class="p">,</span><span class="w"> </span><span class="nf">max_heap_size</span><span class="p" data-group-id="2932036121-2">(</span><span class="p" data-group-id="2932036121-2">)</span><span class="p" data-group-id="2932036121-1">)</span></code></pre><p>This flag sets the maximum heap size for the calling process. If <code class="inline">MaxHeapSize</code>
│ │ │ +auto-loading depends on the correct operation of the error handling module.</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="3716677274-1">(</span><span class="ss">fullsweep_after</span><span class="p">,</span><span class="w">  </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="3716677274-2">(</span><span class="p" data-group-id="3716677274-2">)</span><span class="p" data-group-id="3716677274-1">)</span></code></pre><p>Changes the maximum number of generational collections before forcing a
│ │ │ +fullsweep for the calling process.</p></li><li><pre id="process_flag_min_heap_size"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="5162342010-1">(</span><span class="ss">min_heap_size</span><span class="p">,</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5162342010-2">(</span><span class="p" data-group-id="5162342010-2">)</span><span class="p" data-group-id="5162342010-1">)</span></code></pre><p>Changes the minimum heap size for the calling process.</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="2679706678-1">(</span><span class="ss">min_bin_vheap_size</span><span class="p">,</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2679706678-2">(</span><span class="p" data-group-id="2679706678-2">)</span><span class="p" data-group-id="2679706678-1">)</span></code></pre><p>Changes the minimum binary virtual heap size for the calling process.</p></li><li><pre id="process_flag_max_heap_size"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="8235763011-1">(</span><span class="ss">max_heap_size</span><span class="p">,</span><span class="w"> </span><span class="nf">max_heap_size</span><span class="p" data-group-id="8235763011-2">(</span><span class="p" data-group-id="8235763011-2">)</span><span class="p" data-group-id="8235763011-1">)</span></code></pre><p>This flag sets the maximum heap size for the calling process. If <code class="inline">MaxHeapSize</code>
│ │ │  is an integer, the system default values for <code class="inline">kill</code> and <code class="inline">error_logger</code> are used.</p><p>For details on how the heap grows, see
│ │ │  <a href="garbagecollection.html#sizing-the-heap">Sizing the heap</a> in the ERTS internal
│ │ │  documentation.</p><ul><li><p><strong><code class="inline">size</code></strong> - The maximum size in words of the process. If set to zero, the
│ │ │  heap size limit is disabled. <code class="inline">badarg</code> is be thrown if the value is smaller
│ │ │  than <a href="#process_flag_min_heap_size"><code class="inline">min_heap_size</code></a>. The size check
│ │ │  is only done when a garbage collection is triggered.</p><p><code class="inline">size</code> is the entire heap of the process when garbage collection is triggered.
│ │ │  This includes all generational heaps, the process stack, any
│ │ │ @@ -13978,27 +13978,27 @@
│ │ │  of it is referred by the process.</p><p>If <code class="inline">include_shared_binaries</code> is not defined in the map, the system default is
│ │ │  used. The default system default is <code class="inline">false</code>. It can be changed by either the
│ │ │  option <a href="erl_cmd.html#%2Bhmaxib">+hmaxib</a> in <a href="erl_cmd.html">erl</a>, or
│ │ │  <a href="#system_flag_max_heap_size"><code class="inline">erlang:system_flag(max_heap_size, MaxHeapSize)</code></a>.</p></li></ul><p>The heap size of a process is quite hard to predict, especially the amount of
│ │ │  memory that is used during the garbage collection. When contemplating using this
│ │ │  option, it is recommended to first run it in production with <code class="inline">kill</code> set to
│ │ │  <code class="inline">false</code> and inspect the log events to see what the normal peak sizes of the
│ │ │ -processes in the system is and then tune the value accordingly.</p></li><li><pre id="process_flag_message_queue_data"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="1585006120-1">(</span><span class="ss">message_queue_data</span><span class="p">,</span><span class="w"> </span><span class="nf">message_queue_data</span><span class="p" data-group-id="1585006120-2">(</span><span class="p" data-group-id="1585006120-2">)</span><span class="p" data-group-id="1585006120-1">)</span></code></pre><p>Determines how messages in the message queue are stored, as follows:</p><ul><li><p><strong><code class="inline">off_heap</code></strong> - <em>All</em> messages in the message queue will be stored outside
│ │ │ +processes in the system is and then tune the value accordingly.</p></li><li><pre id="process_flag_message_queue_data"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="7874783481-1">(</span><span class="ss">message_queue_data</span><span class="p">,</span><span class="w"> </span><span class="nf">message_queue_data</span><span class="p" data-group-id="7874783481-2">(</span><span class="p" data-group-id="7874783481-2">)</span><span class="p" data-group-id="7874783481-1">)</span></code></pre><p>Determines how messages in the message queue are stored, as follows:</p><ul><li><p><strong><code class="inline">off_heap</code></strong> - <em>All</em> messages in the message queue will be stored outside
│ │ │  the process heap. This implies that <em>no</em> messages in the message queue will be
│ │ │  part of a garbage collection of the process.</p></li><li><p><strong><code class="inline">on_heap</code></strong> - All messages in the message queue will eventually be placed on
│ │ │  the process heap. They can, however, be temporarily stored off the heap. This
│ │ │  is how messages have always been stored up until ERTS 8.0.</p></li></ul><p>The default value of the <code class="inline">message_queue_data</code> process flag is determined by the
│ │ │  command-line argument <a href="erl_cmd.html#%2Bhmqd"><code class="inline">+hmqd</code></a> in <a href="erl_cmd.html">erl</a>.</p><p>If the process may potentially accumulate a large number of messages in its
│ │ │  queue it is recommended to set the flag value to <code class="inline">off_heap</code>. This is due to the
│ │ │  fact that the garbage collection of a process that has a large number of
│ │ │  messages stored on the heap can become extremely expensive and the process can
│ │ │  consume large amounts of memory. The performance of the actual message passing
│ │ │  is, however, generally better when the flag value is <code class="inline">on_heap</code>.</p><p>Changing the flag value causes any existing messages to be moved. The move
│ │ │  operation is initiated, but not necessarily completed, by the time the function
│ │ │ -returns.</p></li><li><pre id="process_flag_priority"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="1971084874-1">(</span><span class="ss">priority</span><span class="p">,</span><span class="w"> </span><span class="nf">priority_level</span><span class="p" data-group-id="1971084874-2">(</span><span class="p" data-group-id="1971084874-2">)</span><span class="p" data-group-id="1971084874-1">)</span></code></pre><p>Sets the process priority. <code class="inline">Level</code> is an atom. Four priority levels exist:
│ │ │ +returns.</p></li><li><pre id="process_flag_priority"><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="9063953304-1">(</span><span class="ss">priority</span><span class="p">,</span><span class="w"> </span><span class="nf">priority_level</span><span class="p" data-group-id="9063953304-2">(</span><span class="p" data-group-id="9063953304-2">)</span><span class="p" data-group-id="9063953304-1">)</span></code></pre><p>Sets the process priority. <code class="inline">Level</code> is an atom. Four priority levels exist:
│ │ │  <code class="inline">low</code>, <code class="inline">normal</code>, <code class="inline">high</code>, and <code class="inline">max</code>. Default is <code class="inline">normal</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Priority level <code class="inline">max</code> is reserved for internal use in the Erlang runtime
│ │ │  system, and is <em>not</em> to be used by others.</p></section><p>Internally in each priority level, processes are scheduled in a round robin
│ │ │  fashion.</p><p>Execution of processes on priority <code class="inline">normal</code> and <code class="inline">low</code> are interleaved. Processes
│ │ │  on priority <code class="inline">low</code> are selected for execution less frequently than processes on
│ │ │  priority <code class="inline">normal</code>.</p><p>When runnable processes on priority <code class="inline">high</code> exist, no processes on priority <code class="inline">low</code>
│ │ │  or <code class="inline">normal</code> are selected for execution. Notice however that this does <em>not</em> mean
│ │ │  that no processes on priority <code class="inline">low</code> or <code class="inline">normal</code> can run when processes are
│ │ │ @@ -14019,24 +14019,24 @@
│ │ │  process during the call. Even if this is not the case with one version of the
│ │ │  code that you have no control over, it can be the case in a future version of
│ │ │  it. This can, for example, occur if a <code class="inline">high</code> priority process triggers code
│ │ │  loading, as the code server runs on priority <code class="inline">normal</code>.</p><p>Other priorities than <code class="inline">normal</code> are normally not needed. When other priorities
│ │ │  are used, use them with care, <em>especially</em> priority <code class="inline">high</code>. A process on
│ │ │  priority <code class="inline">high</code> is only to perform work for short periods. Busy looping for long
│ │ │  periods in a <code class="inline">high</code> priority process causes most likely problems, as important
│ │ │ -OTP servers run on priority <code class="inline">normal</code>.</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="2594970119-1">(</span><span class="ss">save_calls</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span><span class="p">.</span><span class="mi">10000</span><span class="p" data-group-id="2594970119-1">)</span></code></pre><p><code class="inline">N</code> must be an integer in the interval 0..10000. If <code class="inline">N</code> &gt; 0, call saving is made
│ │ │ +OTP servers run on priority <code class="inline">normal</code>.</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="2828821026-1">(</span><span class="ss">save_calls</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span><span class="p">.</span><span class="mi">10000</span><span class="p" data-group-id="2828821026-1">)</span></code></pre><p><code class="inline">N</code> must be an integer in the interval 0..10000. If <code class="inline">N</code> &gt; 0, call saving is made
│ │ │  active for the process. This means that information about the <code class="inline">N</code> most recent
│ │ │  global function calls, BIF calls, sends, and receives made by the process are
│ │ │  saved in a list, which can be retrieved with
│ │ │  <a href="#process_info/2"><code class="inline">process_info(Pid, last_calls)</code></a>. A global function call is
│ │ │  one in which the module of the function is explicitly mentioned. Only a fixed
│ │ │  amount of information is saved, as follows:</p><ul><li>A tuple <code class="inline">{Module, Function, Arity}</code> for function calls</li><li>The atoms <code class="inline">send</code>, <code class="inline">'receive'</code>, and <code class="inline">timeout</code> for sends and receives
│ │ │  (<code class="inline">'receive'</code> when a message is received and <code class="inline">timeout</code> when a receive times
│ │ │  out)</li></ul><p>If <code class="inline">N</code> = 0, call saving is disabled for the process, which is the default.
│ │ │ -Whenever the size of the call saving list is set, its contents are reset.</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="4003311340-1">(</span><span class="ss">sensitive</span><span class="p">,</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="4003311340-2">(</span><span class="p" data-group-id="4003311340-2">)</span><span class="p" data-group-id="4003311340-1">)</span></code></pre><p>Sets or clears flag <code class="inline">sensitive</code> for the current process. When a process has been
│ │ │ +Whenever the size of the call saving list is set, its contents are reset.</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="4747047083-1">(</span><span class="ss">sensitive</span><span class="p">,</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="4747047083-2">(</span><span class="p" data-group-id="4747047083-2">)</span><span class="p" data-group-id="4747047083-1">)</span></code></pre><p>Sets or clears flag <code class="inline">sensitive</code> for the current process. When a process has been
│ │ │  marked as sensitive by calling
│ │ │  <a href="#process_flag/2"><code class="inline">process_flag(sensitive, true)</code></a>, features in the runtime
│ │ │  system that can be used for examining the data or inner working of the process
│ │ │  are silently disabled.</p><p>Features that are disabled include (but are not limited to) the following:</p><ul><li>Tracing. Trace flags can still be set for the process, but no trace messages
│ │ │  of any kind are generated. (If flag <code class="inline">sensitive</code> is turned off, trace messages
│ │ │  are again generated if any trace flags are set.)</li><li>Sequential tracing. The sequential trace token is propagated as usual, but no
│ │ │  sequential trace messages are generated.</li></ul><p><code class="inline">process_info/1,2</code> cannot be used to read out the message queue or the process
│ │ │ @@ -14280,16 +14280,16 @@
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns a list of process identifiers corresponding to all the processes
│ │ │  currently existing on the local node.</p><p>Notice that an exiting process exists, but is not alive. That is,
│ │ │  <a href="#is_process_alive/1"><code class="inline">is_process_alive/1</code></a> returns <code class="inline">false</code> for an exiting
│ │ │  process, but its process identifier is part of the result returned from
│ │ │ -<a href="#processes/0"><code class="inline">processes/0</code></a>.</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">processes</span><span class="p" data-group-id="7581606575-1">(</span><span class="p" data-group-id="7581606575-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7581606575-2">[</span><span class="o">&lt;</span><span class="mf">0.0</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.2</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.5</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.7</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.8</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7581606575-2">]</span></code></pre>
│ │ │ +<a href="#processes/0"><code class="inline">processes/0</code></a>.</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">processes</span><span class="p" data-group-id="9250422396-1">(</span><span class="p" data-group-id="9250422396-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9250422396-2">[</span><span class="o">&lt;</span><span class="mf">0.0</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.2</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.4</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.5</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.7</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.8</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="9250422396-2">]</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="put/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#put/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -14313,18 +14313,18 @@
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Adds a new <code class="inline">Key</code> to the process dictionary, associated with the value <code class="inline">Val</code>, and
│ │ │  returns <code class="inline">undefined</code>. If <code class="inline">Key</code> exists, the old value is deleted and replaced by
│ │ │  <code class="inline">Val</code>, and the function returns the old value.</p><p>The average time complexity for the current implementation of this function is
│ │ │  O(<code class="inline">1</code>) and the worst case time complexity is O(<code class="inline">N</code>), where <code class="inline">N</code> is the number of
│ │ │ -items in the process dictionary.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">put</span><span class="p" data-group-id="6644216488-1">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">walrus</span><span class="p" data-group-id="6644216488-1">)</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">put</span><span class="p" data-group-id="6644216488-2">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">carpenter</span><span class="p" data-group-id="6644216488-2">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">get</span><span class="p" data-group-id="6644216488-3">(</span><span class="ss">name</span><span class="p" data-group-id="6644216488-3">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6644216488-4">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="6644216488-4">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6644216488-5">{</span><span class="ss">undefined</span><span class="p">,</span><span class="ss">walrus</span><span class="p">,</span><span class="ss">carpenter</span><span class="p" data-group-id="6644216488-5">}</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The values stored when <code class="inline">put</code> is evaluated within the scope of a <code class="inline">catch</code> are
│ │ │ +items in the process dictionary.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">put</span><span class="p" data-group-id="9274991654-1">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">walrus</span><span class="p" data-group-id="9274991654-1">)</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">put</span><span class="p" data-group-id="9274991654-2">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">carpenter</span><span class="p" data-group-id="9274991654-2">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">get</span><span class="p" data-group-id="9274991654-3">(</span><span class="ss">name</span><span class="p" data-group-id="9274991654-3">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9274991654-4">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="9274991654-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9274991654-5">{</span><span class="ss">undefined</span><span class="p">,</span><span class="ss">walrus</span><span class="p">,</span><span class="ss">carpenter</span><span class="p" data-group-id="9274991654-5">}</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The values stored when <code class="inline">put</code> is evaluated within the scope of a <code class="inline">catch</code> are
│ │ │  not retracted if a <code class="inline">throw</code> is evaluated, or if an error occurs.</p></section>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="raise/3">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#raise/3" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -14395,15 +14395,15 @@
│ │ │        </div>
│ │ │  
│ │ │  <p>Registers the name <code class="inline">RegName</code> with a process identifier (pid) or a port
│ │ │  identifier in the
│ │ │  <a href="../../../doc/system/ref_man_processes.html#runtime-service"><code class="inline">name registry</code></a>.
│ │ │  <code class="inline">RegName</code>, which must be an atom, can be used instead of the pid or port
│ │ │  identifier in send operator (<code class="inline">RegName ! Message</code>) and most other BIFs that take
│ │ │ -a pid or port identifies as an argument.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">register</span><span class="p" data-group-id="8615268210-1">(</span><span class="ss">db</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="8615268210-1">)</span><span class="p">.</span><span class="w">
│ │ │ +a pid or port identifies as an argument.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">register</span><span class="p" data-group-id="4830212761-1">(</span><span class="ss">db</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="4830212761-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><p>The registered name is considered a
│ │ │  <a href="../../../doc/system/ref_man_processes.html#visible-resources">Directly Visible Erlang Resource</a>
│ │ │  and is automatically unregistered when the process terminates.</p><p>Failures:</p><ul><li><p><strong><code class="inline">badarg</code></strong> - If <code class="inline">PidOrPort</code> is not an existing local process or port.</p></li><li><p><strong><code class="inline">badarg</code></strong> - If <code class="inline">RegName</code> is already in use.</p></li><li><p><strong><code class="inline">badarg</code></strong> - If the process or port is already registered (already has a
│ │ │  name).</p></li><li><p><strong><code class="inline">badarg</code></strong> - If <code class="inline">RegName</code> is the atom <code class="inline">undefined</code>.</p></li></ul>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="registered/0">
│ │ │ @@ -14427,16 +14427,16 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> registered() -> [RegName] when RegName :: <a href="#t:atom/0">atom</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns a list of names that have been registered using <a href="#register/2"><code class="inline">register/2</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">registered</span><span class="p" data-group-id="9116964130-1">(</span><span class="p" data-group-id="9116964130-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9116964130-2">[</span><span class="ss">code_server</span><span class="p">,</span><span class="w"> </span><span class="ss">file_server</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="ss">user</span><span class="p">,</span><span class="w"> </span><span class="ss">my_db</span><span class="p" data-group-id="9116964130-2">]</span></code></pre>
│ │ │ +<p>Returns a list of names that have been registered using <a href="#register/2"><code class="inline">register/2</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">registered</span><span class="p" data-group-id="4358150043-1">(</span><span class="p" data-group-id="4358150043-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4358150043-2">[</span><span class="ss">code_server</span><span class="p">,</span><span class="w"> </span><span class="ss">file_server</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="ss">user</span><span class="p">,</span><span class="w"> </span><span class="ss">my_db</span><span class="p" data-group-id="4358150043-2">]</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="resume_process/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#resume_process/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │        <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -14491,15 +14491,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> self() -> <a href="#t:pid/0">pid</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns the process identifier of the calling process.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">self</span><span class="p" data-group-id="6701449012-1">(</span><span class="p" data-group-id="6701449012-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Returns the process identifier of the calling process.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">self</span><span class="p" data-group-id="0684142762-1">(</span><span class="p" data-group-id="0684142762-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.26</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="send/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#send/2" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -14741,15 +14741,15 @@
│ │ │  <p>Returns the process identifier of a new process started by the application of
│ │ │  <code class="inline">Module:Function</code> to <code class="inline">Args</code>.</p><p><a href="../../../lib/kernel-10.2.7.1/doc/html/error_handler.html"><code class="inline">error_handler:undefined_function(Module, Function, Args)</code></a> is
│ │ │   evaluated by the new process if <code class="inline">Module:Function/Arity</code> does not exist
│ │ │  (where <code class="inline">Arity</code> is the length of <code class="inline">Args</code>). The error handler can be redefined
│ │ │  (see <a href="#process_flag/2"><code class="inline">process_flag/2</code></a>). If
│ │ │  <code class="inline">error_handler</code> is undefined, or the user has redefined the default
│ │ │  <code class="inline">error_handler</code> and its replacement is undefined, a failure with reason <code class="inline">undef</code>
│ │ │ -occurs.</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">spawn</span><span class="p" data-group-id="7501650847-1">(</span><span class="ss">speed</span><span class="p">,</span><span class="w"> </span><span class="ss">regulator</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7501650847-2">[</span><span class="ss">high_speed</span><span class="p">,</span><span class="w"> </span><span class="ss">thin_cut</span><span class="p" data-group-id="7501650847-2">]</span><span class="p" data-group-id="7501650847-1">)</span><span class="p">.</span><span class="w">
│ │ │ +occurs.</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">spawn</span><span class="p" data-group-id="4758082159-1">(</span><span class="ss">speed</span><span class="p">,</span><span class="w"> </span><span class="ss">regulator</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4758082159-2">[</span><span class="ss">high_speed</span><span class="p">,</span><span class="w"> </span><span class="ss">thin_cut</span><span class="p" data-group-id="4758082159-2">]</span><span class="p" data-group-id="4758082159-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.13</span><span class="p">.</span><span class="mi">1</span><span class="o">&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="spawn/4">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#spawn/4" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -15689,22 +15689,22 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> throw(Any) -> <a href="#t:no_return/0">no_return</a>() when Any :: <a href="#t:term/0">term</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Raises an exception of class <code class="inline">throw</code>. Intended to be used to do non-local
│ │ │  returns from functions.</p><p>If evaluated within a <a href="../../../doc/system/expressions.html#catch-and-throw">catch expression</a>, the
│ │ │ -catch expression returns value <code class="inline">Any</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="1736041841-1">(</span><span class="p" data-group-id="1736041841-2">{</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">there</span><span class="p" data-group-id="1736041841-2">}</span><span class="p" data-group-id="1736041841-1">)</span><span class="p">.</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="1736041841-3">{</span><span class="ss">hello</span><span class="p">,</span><span class="ss">there</span><span class="p" data-group-id="1736041841-3">}</span></code></pre><p>If evaluated within a <code class="inline">try</code>-block of a
│ │ │ +catch expression returns value <code class="inline">Any</code>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="4793527922-1">(</span><span class="p" data-group-id="4793527922-2">{</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">there</span><span class="p" data-group-id="4793527922-2">}</span><span class="p" data-group-id="4793527922-1">)</span><span class="p">.</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="4793527922-3">{</span><span class="ss">hello</span><span class="p">,</span><span class="ss">there</span><span class="p" data-group-id="4793527922-3">}</span></code></pre><p>If evaluated within a <code class="inline">try</code>-block of a
│ │ │  <a href="../../../doc/system/expressions.html#try">try expression</a>, the value <code class="inline">Any</code> can be caught
│ │ │  within the catch block.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w">
│ │ │ -    </span><span class="nf">throw</span><span class="p" data-group-id="3409396774-1">(</span><span class="p" data-group-id="3409396774-2">{</span><span class="ss">my_exception</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Something happened&quot;</span><span class="p" data-group-id="3409396774-2">}</span><span class="p" data-group-id="3409396774-1">)</span><span class="w">
│ │ │ +    </span><span class="nf">throw</span><span class="p" data-group-id="7801528629-1">(</span><span class="p" data-group-id="7801528629-2">{</span><span class="ss">my_exception</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Something happened&quot;</span><span class="p" data-group-id="7801528629-2">}</span><span class="p" data-group-id="7801528629-1">)</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ -    </span><span class="nc">throw</span><span class="p">:</span><span class="p" data-group-id="3409396774-3">{</span><span class="ss">my_exception</span><span class="p">,</span><span class="w"> </span><span class="n">Desc</span><span class="p" data-group-id="3409396774-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3409396774-4">(</span><span class="ss">standard_error</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Error: </span><span class="si">~s</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3409396774-5">[</span><span class="n">Desc</span><span class="p" data-group-id="3409396774-5">]</span><span class="p" data-group-id="3409396774-4">)</span><span class="w">
│ │ │ +    </span><span class="nc">throw</span><span class="p">:</span><span class="p" data-group-id="7801528629-3">{</span><span class="ss">my_exception</span><span class="p">,</span><span class="w"> </span><span class="n">Desc</span><span class="p" data-group-id="7801528629-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7801528629-4">(</span><span class="ss">standard_error</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Error: </span><span class="si">~s</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7801528629-5">[</span><span class="n">Desc</span><span class="p" data-group-id="7801528629-5">]</span><span class="p" data-group-id="7801528629-4">)</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>Failure: <code class="inline">nocatch</code> if not caught by an exception handler.</p><p>See the guide about <a href="../../../doc/system/errors.html">errors and error handling</a> for
│ │ │  additional information.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="unalias/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │ @@ -15774,17 +15774,17 @@
│ │ │  <a href="#process_flag_trap_exit">trapping exits</a>, an
│ │ │  <code class="inline">{'EXIT', Id, ExitReason}</code> message due to the link may have been placed in the
│ │ │  message queue of the caller before the <a href="#unlink/1"><code class="inline">unlink(Id)</code></a> call
│ │ │  completed. Also note that the <code class="inline">{'EXIT', Id, ExitReason}</code> message may be the
│ │ │  result of the link, but may also be the result of the unlikee sending the caller
│ │ │  an exit signal by calling the <a href="#exit/2"><code class="inline">exit/2</code></a> BIF. Therefore, it may or may not be
│ │ │  appropriate to clean up the message queue after a call to
│ │ │ -<a href="#unlink/1"><code class="inline">unlink(Id)</code></a> as follows, when trapping exits:</p><pre><code class="makeup erlang" translate="no"><span class="nf">unlink</span><span class="p" data-group-id="4043610338-1">(</span><span class="n">Id</span><span class="p" data-group-id="4043610338-1">)</span><span class="p">,</span><span class="w">
│ │ │ +<a href="#unlink/1"><code class="inline">unlink(Id)</code></a> as follows, when trapping exits:</p><pre><code class="makeup erlang" translate="no"><span class="nf">unlink</span><span class="p" data-group-id="3812441717-1">(</span><span class="n">Id</span><span class="p" data-group-id="3812441717-1">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4043610338-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Id</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="4043610338-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3812441717-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Id</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3812441717-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w">
│ │ │  </span><span class="k">after</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The link removal is performed asynchronously. If such a link does not exist,
│ │ │  nothing is done. A detailed description of the
│ │ │  <a href="erl_dist_protocol.html#link_protocol">link protocol</a> can be found in the
│ │ │  <em>Distribution Protocol</em> chapter of the <em>ERTS User's Guide</em>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>For some important information about distributed signals, see the
│ │ │ @@ -15815,15 +15815,15 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> unregister(RegName) -> true when RegName :: <a href="#t:atom/0">atom</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Removes the <a href="#register/2"><code class="inline">registered name</code></a> <code class="inline">RegName</code> associated with a
│ │ │  process identifier or a port identifier from the
│ │ │ -<a href="../../../doc/system/ref_man_processes.html#runtime-service"><code class="inline">name registry</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">unregister</span><span class="p" data-group-id="8229146018-1">(</span><span class="ss">db</span><span class="p" data-group-id="8229146018-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="../../../doc/system/ref_man_processes.html#runtime-service"><code class="inline">name registry</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">unregister</span><span class="p" data-group-id="7772201814-1">(</span><span class="ss">db</span><span class="p" data-group-id="7772201814-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><p>Keep in mind that you can still receive signals associated with the registered
│ │ │  name after it has been unregistered as the sender may have looked up the name
│ │ │  before sending to it.</p><p>Users are advised not to unregister system processes.</p><p>Failure: <code class="inline">badarg</code> if <code class="inline">RegName</code> is not a registered name.</p>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="whereis/1">
│ │ │  
│ │ │ @@ -15849,15 +15849,15 @@
│ │ │            <pre translate="no"><span class="attribute">-spec</span> whereis(RegName) -> <a href="#t:pid/0">pid</a>() | <a href="#t:port/0">port</a>() | undefined when RegName :: <a href="#t:atom/0">atom</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │  <p>Returns the process identifier or port identifier with the
│ │ │  <a href="#register/2"><code class="inline">registered name</code></a> <code class="inline">RegName</code> from the
│ │ │  <a href="../../../doc/system/ref_man_processes.html#runtime-service"><code class="inline">name registry</code></a>. Returns
│ │ │ -<code class="inline">undefined</code> if the name is not registered.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">whereis</span><span class="p" data-group-id="6391706900-1">(</span><span class="ss">db</span><span class="p" data-group-id="6391706900-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">undefined</code> if the name is not registered.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">whereis</span><span class="p" data-group-id="0877523275-1">(</span><span class="ss">db</span><span class="p" data-group-id="0877523275-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.43</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="yield/0">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#yield/0" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -15924,15 +15924,15 @@
│ │ │  
│ │ │        <div class="specs">
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> halt() -> <a href="#t:no_return/0">no_return</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Equivalent to calling <a href="#halt/2"><code class="inline">halt(0, [])</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">halt</span><span class="p" data-group-id="6763390439-1">(</span><span class="p" data-group-id="6763390439-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Equivalent to calling <a href="#halt/2"><code class="inline">halt(0, [])</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">halt</span><span class="p" data-group-id="5463479767-1">(</span><span class="p" data-group-id="5463479767-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">os_prompt</span><span class="c1">%</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="halt/1">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │      <a href="#halt/1" class="detail-link" data-no-tooltip aria-label="Link to this function">
│ │ │ @@ -15955,15 +15955,15 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> halt(Status :: <a href="#t:non_neg_integer/0">non_neg_integer</a>()) -> <a href="#t:no_return/0">no_return</a>();
│ │ │            (Abort :: abort) -> <a href="#t:no_return/0">no_return</a>();
│ │ │            (CrashDumpSlogan :: <a href="#t:string/0">string</a>()) -> <a href="#t:no_return/0">no_return</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Equivalent to calling <a href="#halt/2"><code class="inline">halt(HaltType, [])</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">halt</span><span class="p" data-group-id="5446588379-1">(</span><span class="mi">17</span><span class="p" data-group-id="5446588379-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Equivalent to calling <a href="#halt/2"><code class="inline">halt(HaltType, [])</code></a>.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">halt</span><span class="p" data-group-id="2892450346-1">(</span><span class="mi">17</span><span class="p" data-group-id="2892450346-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">os_prompt</span><span class="c1">% echo $?</span><span class="w">
│ │ │  </span><span class="mi">17</span><span class="w">
│ │ │  </span><span class="ss">os_prompt</span><span class="c1">%</span></code></pre>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="halt/2">
│ │ │  
│ │ │ @@ -15990,15 +15990,15 @@
│ │ │  
│ │ │            <pre translate="no"><span class="attribute">-spec</span> halt(Status :: <a href="#t:non_neg_integer/0">non_neg_integer</a>(), Options :: <a href="#t:halt_options/0">halt_options</a>()) -> <a href="#t:no_return/0">no_return</a>();
│ │ │            (Abort :: abort, Options :: <a href="#t:halt_options/0">halt_options</a>()) -> <a href="#t:no_return/0">no_return</a>();
│ │ │            (CrashDumpSlogan :: <a href="#t:string/0">string</a>(), Options :: <a href="#t:halt_options/0">halt_options</a>()) -> <a href="#t:no_return/0">no_return</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Halt the runtime system.</p><ul><li><pre id="halt_status_2"><code class="makeup erlang" translate="no"><span class="nf">halt</span><span class="p" data-group-id="2416527000-1">(</span><span class="n">Status</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2416527000-2">(</span><span class="p" data-group-id="2416527000-2">)</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">halt_options</span><span class="p" data-group-id="2416527000-3">(</span><span class="p" data-group-id="2416527000-3">)</span><span class="p" data-group-id="2416527000-1">)</span></code></pre><p>Halt the runtime system with status code <code class="inline">Status</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>On many platforms, the OS supports only status codes 0-255. A too large
│ │ │ +<p>Halt the runtime system.</p><ul><li><pre id="halt_status_2"><code class="makeup erlang" translate="no"><span class="nf">halt</span><span class="p" data-group-id="2825721442-1">(</span><span class="n">Status</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2825721442-2">(</span><span class="p" data-group-id="2825721442-2">)</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">halt_options</span><span class="p" data-group-id="2825721442-3">(</span><span class="p" data-group-id="2825721442-3">)</span><span class="p" data-group-id="2825721442-1">)</span></code></pre><p>Halt the runtime system with status code <code class="inline">Status</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>On many platforms, the OS supports only status codes 0-255. A too large
│ │ │  status code is truncated by clearing the high bits.</p></section><p>Currently the following options are valid:</p><ul><li><p><strong><code class="inline" id="halt_flush">{flush, EnableFlushing}</code></strong> - If <code class="inline">EnableFlushing</code> equals
│ │ │  <code class="inline">true</code>, which also is the default behavior, the runtime system will perform
│ │ │  the following operations before terminating:</p><ul><li>Flush all outstanding output.</li><li>Send all Erlang ports exit signals and wait for them to exit.</li><li>Wait for all async threads to complete all outstanding async jobs.</li><li>Call all installed <a href="erl_nif.html#on_halt">NIF <em>on halt</em> callbacks</a>.</li><li>Wait for all ongoing
│ │ │  <a href="erl_nif.html#delay_halt">NIF calls with the <em>delay halt</em> setting</a> enabled
│ │ │  to return.</li><li>Call all installed <code class="inline">atexit</code>/<code class="inline">on_exit</code> callbacks.</li></ul><p>If <code class="inline">EnableFlushing</code> equals <code class="inline">false</code>, the runtime system will terminate
│ │ │  immediately without performing any of the above listed operations.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Runtime systems prior to OTP 26.0 called all installed <code class="inline">atexit</code>/<code class="inline">on_exit</code>
│ │ │  callbacks also when <code class="inline">flush</code> was disabled, but as of OTP 26.0 this is no
│ │ │ @@ -16007,18 +16007,18 @@
│ │ │  termination of the runtime system. <code class="inline">Timeout</code> is in milliseconds. The default
│ │ │  value is determined by the the <code class="inline">erl</code> <a href="erl_cmd.html#+zhft"><code class="inline">+zhft &lt;Timeout&gt;</code></a>
│ │ │  command line flag.</p><p>If flushing has been ongoing for <code class="inline">Timeout</code> milliseconds, flushing operations
│ │ │  will be interrupted and the runtime system will immediately be terminated
│ │ │  with the exit code <code class="inline">255</code>. If flushing is not enabled, the timeout will have
│ │ │  no effect on the system.</p><p>See also the <code class="inline">erl</code> <a href="erl_cmd.html#+zhft"><code class="inline">+zhft &lt;Timeout&gt;</code></a> command line flag.
│ │ │  Note that the shortest timeout set by the command line flag and the
│ │ │ -<code class="inline">flush_timeout</code> option will be the actual timeout value in effect.</p><p>Since: OTP 27.0</p></li></ul></li><li><pre id="halt_abort_2"><code class="makeup erlang" translate="no"><span class="nf">halt</span><span class="p" data-group-id="7121800983-1">(</span><span class="n">Abort</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">halt_options</span><span class="p" data-group-id="7121800983-2">(</span><span class="p" data-group-id="7121800983-2">)</span><span class="p" data-group-id="7121800983-1">)</span></code></pre><p>Halt the Erlang runtime system by aborting and produce a core dump if core
│ │ │ +<code class="inline">flush_timeout</code> option will be the actual timeout value in effect.</p><p>Since: OTP 27.0</p></li></ul></li><li><pre id="halt_abort_2"><code class="makeup erlang" translate="no"><span class="nf">halt</span><span class="p" data-group-id="4507180314-1">(</span><span class="n">Abort</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">halt_options</span><span class="p" data-group-id="4507180314-2">(</span><span class="p" data-group-id="4507180314-2">)</span><span class="p" data-group-id="4507180314-1">)</span></code></pre><p>Halt the Erlang runtime system by aborting and produce a core dump if core
│ │ │  dumping has been enabled in the environment that the runtime system is
│ │ │  executing in.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The <a href="#halt_flush"><code class="inline">{flush, boolean()}</code></a> option will be ignored, and
│ │ │ -flushing will be disabled.</p></section></li><li><pre id="halt_crash_dump_2"><code class="makeup erlang" translate="no"><span class="nf">halt</span><span class="p" data-group-id="2725241639-1">(</span><span class="n">CrashDumpSlogan</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="2725241639-2">(</span><span class="p" data-group-id="2725241639-2">)</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">halt_options</span><span class="p" data-group-id="2725241639-3">(</span><span class="p" data-group-id="2725241639-3">)</span><span class="p" data-group-id="2725241639-1">)</span></code></pre><p>Halt the Erlang runtime system and generate an
│ │ │ +flushing will be disabled.</p></section></li><li><pre id="halt_crash_dump_2"><code class="makeup erlang" translate="no"><span class="nf">halt</span><span class="p" data-group-id="8815657856-1">(</span><span class="n">CrashDumpSlogan</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="8815657856-2">(</span><span class="p" data-group-id="8815657856-2">)</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">halt_options</span><span class="p" data-group-id="8815657856-3">(</span><span class="p" data-group-id="8815657856-3">)</span><span class="p" data-group-id="8815657856-1">)</span></code></pre><p>Halt the Erlang runtime system and generate an
│ │ │  <a href="crash_dump.html">Erlang crash dump</a>. The string <code class="inline">CrashDumpSlogan</code> will be used
│ │ │  as slogan in the Erlang crash dump created. The slogan will be trunkated if
│ │ │  <code class="inline">CrashDumpSlogan</code> is longer than 1023 characters.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The <a href="#halt_flush"><code class="inline">{flush, boolean()}</code></a> option will be ignored, and
│ │ │  flushing will be disabled.</p></section><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Behavior changes compared to earlier versions:</p><ul><li>Before OTP 24.2, the slogan was truncated if <code class="inline">CrashDumpSlogan</code> was longer
│ │ │  than 200 characters. Now it will be truncated if longer than 1023
│ │ │  characters.</li><li>Before OTP 20.1, only code points in the range 0-255 were accepted in the
│ │ │  slogan. Now any Unicode string is valid.</li></ul></section></li></ul>
│ │ │ @@ -16195,19 +16195,19 @@
│ │ │                  (wall_clock) -> {Total_Wallclock_Time, Wallclock_Time_Since_Last_Call}
│ │ │                      when
│ │ │                          Total_Wallclock_Time :: <a href="#t:non_neg_integer/0">non_neg_integer</a>(),
│ │ │                          Wallclock_Time_Since_Last_Call :: <a href="#t:non_neg_integer/0">non_neg_integer</a>().</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Returns statistics about the current system.</p><p>The possible flags are:</p><ul><li><pre id="statistics_active_tasks"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="6941988884-1">(</span><span class="ss">active_tasks</span><span class="p" data-group-id="6941988884-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6941988884-2">[</span><span class="nf">non_neg_integer</span><span class="p" data-group-id="6941988884-3">(</span><span class="p" data-group-id="6941988884-3">)</span><span class="p" data-group-id="6941988884-2">]</span></code></pre><p>Returns the same as
│ │ │ +<p>Returns statistics about the current system.</p><p>The possible flags are:</p><ul><li><pre id="statistics_active_tasks"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="2367040433-1">(</span><span class="ss">active_tasks</span><span class="p" data-group-id="2367040433-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2367040433-2">[</span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2367040433-3">(</span><span class="p" data-group-id="2367040433-3">)</span><span class="p" data-group-id="2367040433-2">]</span></code></pre><p>Returns the same as
│ │ │  <a href="#statistics_active_tasks_all"><code class="inline">statistics(active_tasks_all)</code></a> with
│ │ │  the exception that no information about the dirty IO run queue and its
│ │ │  associated schedulers is part of the result. That is, only tasks that are
│ │ │ -expected to be CPU bound are part of the result.</p><p>Available since OTP 18.3</p></li><li><pre id="statistics_active_tasks_all"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="5718671758-1">(</span><span class="ss">active_tasks_all</span><span class="p" data-group-id="5718671758-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5718671758-2">[</span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5718671758-3">(</span><span class="p" data-group-id="5718671758-3">)</span><span class="p" data-group-id="5718671758-2">]</span></code></pre><p>Returns a list where each element represents the amount of active processes and
│ │ │ +expected to be CPU bound are part of the result.</p><p>Available since OTP 18.3</p></li><li><pre id="statistics_active_tasks_all"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="7854515149-1">(</span><span class="ss">active_tasks_all</span><span class="p" data-group-id="7854515149-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7854515149-2">[</span><span class="nf">non_neg_integer</span><span class="p" data-group-id="7854515149-3">(</span><span class="p" data-group-id="7854515149-3">)</span><span class="p" data-group-id="7854515149-2">]</span></code></pre><p>Returns a list where each element represents the amount of active processes and
│ │ │  ports on each run queue and its associated schedulers. That is, the number of
│ │ │  processes and ports that are ready to run, or are currently running. Values for
│ │ │  normal run queues and their associated schedulers are located first in the
│ │ │  resulting list. The first element corresponds to scheduler number 1 and so on.
│ │ │  If support for dirty schedulers exist, an element with the value for the dirty
│ │ │  CPU run queue and its associated dirty CPU schedulers follow and then as last
│ │ │  element the value for the dirty IO run queue and its associated dirty IO
│ │ │ @@ -16221,44 +16221,44 @@
│ │ │  migrate to other normal run queues. This has to be taken into account when
│ │ │  evaluating the result.</p></section><p>See also
│ │ │  <a href="#statistics_total_active_tasks"><code class="inline">statistics(total_active_tasks)</code></a>,
│ │ │  <a href="#statistics_run_queue_lengths"><code class="inline">statistics(run_queue_lengths)</code></a>,
│ │ │  <a href="#statistics_run_queue_lengths_all"><code class="inline">statistics(run_queue_lengths_all)</code></a>,
│ │ │  <a href="#statistics_total_run_queue_lengths"><code class="inline">statistics(total_run_queue_lengths)</code></a>,
│ │ │  and
│ │ │ -<a href="#statistics_total_run_queue_lengths_all"><code class="inline">statistics(total_run_queue_lengths_all)</code></a>.</p><p>Available since OTP 20.0</p></li><li><pre id="statistics_context_switches"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="6601638440-1">(</span><span class="ss">context_switches</span><span class="p" data-group-id="6601638440-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6601638440-2">{</span><span class="nf">non_neg_integer</span><span class="p" data-group-id="6601638440-3">(</span><span class="p" data-group-id="6601638440-3">)</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6601638440-2">}</span></code></pre><p>Returns the total number of context switches since the system started.</p></li><li><pre id="statistics_exact_reductions"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="5646502650-1">(</span><span class="ss">exact_reductions</span><span class="p" data-group-id="5646502650-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5646502650-2">{</span><span class="n">Total</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5646502650-3">(</span><span class="p" data-group-id="5646502650-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">SinceLastCall</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5646502650-4">(</span><span class="p" data-group-id="5646502650-4">)</span><span class="p" data-group-id="5646502650-2">}</span></code></pre><p>Returns the number of exact reductions.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p><a href="#statistics/1"><code class="inline">statistics(exact_reductions)</code></a> is a more expensive operation
│ │ │ -than <a href="#statistics_reductions">statistics(reductions)</a>.</p></section></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="9157629248-1">(</span><span class="ss">garbage_collection</span><span class="p" data-group-id="9157629248-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9157629248-2">{</span><span class="w"> </span><span class="n">NumerOfGCs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="9157629248-3">(</span><span class="p" data-group-id="9157629248-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">WordsReclaimed</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="9157629248-4">(</span><span class="p" data-group-id="9157629248-4">)</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="9157629248-2">}</span></code></pre><p>Returns information about garbage collection, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">statistics</span><span class="p" data-group-id="4236409677-1">(</span><span class="ss">garbage_collection</span><span class="p" data-group-id="4236409677-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4236409677-2">{</span><span class="mi">85</span><span class="p">,</span><span class="mi">23961</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4236409677-2">}</span></code></pre><p>This information can be invalid for some implementations.</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="6308626366-1">(</span><span class="ss">io</span><span class="p" data-group-id="6308626366-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6308626366-2">{</span><span class="p" data-group-id="6308626366-3">{</span><span class="ss">input</span><span class="p">,</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="6308626366-4">(</span><span class="p" data-group-id="6308626366-4">)</span><span class="p" data-group-id="6308626366-3">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6308626366-5">{</span><span class="ss">output</span><span class="p">,</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="6308626366-6">(</span><span class="p" data-group-id="6308626366-6">)</span><span class="p" data-group-id="6308626366-5">}</span><span class="p" data-group-id="6308626366-2">}</span></code></pre><p>Returns <code class="inline">Input</code>, which is the total number of bytes received through ports, and
│ │ │ -<code class="inline">Output</code>, which is the total number of bytes output to ports.</p></li><li><pre id="statistics_microstate_accounting"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="6728400581-1">(</span><span class="ss">microstate_accounting</span><span class="p" data-group-id="6728400581-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6728400581-2">[</span><span class="n">MSAcc_Thread</span><span class="p" data-group-id="6728400581-2">]</span></code></pre><p>Microstate accounting can be used to measure how much time the Erlang runtime
│ │ │ +<a href="#statistics_total_run_queue_lengths_all"><code class="inline">statistics(total_run_queue_lengths_all)</code></a>.</p><p>Available since OTP 20.0</p></li><li><pre id="statistics_context_switches"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="5533526887-1">(</span><span class="ss">context_switches</span><span class="p" data-group-id="5533526887-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5533526887-2">{</span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5533526887-3">(</span><span class="p" data-group-id="5533526887-3">)</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5533526887-2">}</span></code></pre><p>Returns the total number of context switches since the system started.</p></li><li><pre id="statistics_exact_reductions"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="2874020605-1">(</span><span class="ss">exact_reductions</span><span class="p" data-group-id="2874020605-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2874020605-2">{</span><span class="n">Total</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2874020605-3">(</span><span class="p" data-group-id="2874020605-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">SinceLastCall</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2874020605-4">(</span><span class="p" data-group-id="2874020605-4">)</span><span class="p" data-group-id="2874020605-2">}</span></code></pre><p>Returns the number of exact reductions.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p><a href="#statistics/1"><code class="inline">statistics(exact_reductions)</code></a> is a more expensive operation
│ │ │ +than <a href="#statistics_reductions">statistics(reductions)</a>.</p></section></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="9238335545-1">(</span><span class="ss">garbage_collection</span><span class="p" data-group-id="9238335545-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9238335545-2">{</span><span class="w"> </span><span class="n">NumerOfGCs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="9238335545-3">(</span><span class="p" data-group-id="9238335545-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">WordsReclaimed</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="9238335545-4">(</span><span class="p" data-group-id="9238335545-4">)</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="9238335545-2">}</span></code></pre><p>Returns information about garbage collection, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">statistics</span><span class="p" data-group-id="0727646908-1">(</span><span class="ss">garbage_collection</span><span class="p" data-group-id="0727646908-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0727646908-2">{</span><span class="mi">85</span><span class="p">,</span><span class="mi">23961</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="0727646908-2">}</span></code></pre><p>This information can be invalid for some implementations.</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="4023597344-1">(</span><span class="ss">io</span><span class="p" data-group-id="4023597344-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4023597344-2">{</span><span class="p" data-group-id="4023597344-3">{</span><span class="ss">input</span><span class="p">,</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="4023597344-4">(</span><span class="p" data-group-id="4023597344-4">)</span><span class="p" data-group-id="4023597344-3">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4023597344-5">{</span><span class="ss">output</span><span class="p">,</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="4023597344-6">(</span><span class="p" data-group-id="4023597344-6">)</span><span class="p" data-group-id="4023597344-5">}</span><span class="p" data-group-id="4023597344-2">}</span></code></pre><p>Returns <code class="inline">Input</code>, which is the total number of bytes received through ports, and
│ │ │ +<code class="inline">Output</code>, which is the total number of bytes output to ports.</p></li><li><pre id="statistics_microstate_accounting"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="5866140877-1">(</span><span class="ss">microstate_accounting</span><span class="p" data-group-id="5866140877-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5866140877-2">[</span><span class="n">MSAcc_Thread</span><span class="p" data-group-id="5866140877-2">]</span></code></pre><p>Microstate accounting can be used to measure how much time the Erlang runtime
│ │ │  system spends doing various tasks. It is designed to be as lightweight as
│ │ │  possible, but some overhead exists when this is enabled. Microstate accounting
│ │ │  is meant to be a profiling tool to help finding performance bottlenecks. To
│ │ │  <code class="inline">start</code>/<code class="inline">stop</code>/<code class="inline">reset</code> microstate accounting, use system flag
│ │ │  <a href="#system_flag_microstate_accounting"><code class="inline">microstate_accounting</code></a>.</p><p><a href="#statistics/1"><code class="inline">statistics(microstate_accounting)</code></a> returns a list of maps
│ │ │  representing some of the OS threads within ERTS. Each map contains <code class="inline">type</code> and
│ │ │  <code class="inline">id</code> fields that can be used to identify what thread it is, and also a counters
│ │ │  field that contains data about how much time has been spent in the various
│ │ │ -states.</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5983050722-1">(</span><span class="ss">microstate_accounting</span><span class="p" data-group-id="5983050722-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5983050722-2">[</span><span class="p" data-group-id="5983050722-3">#{</span><span class="ss">counters</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5983050722-4">#{</span><span class="ss">aux</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1899182914</span><span class="p">,</span><span class="w">
│ │ │ +states.</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="3512398689-1">(</span><span class="ss">microstate_accounting</span><span class="p" data-group-id="3512398689-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3512398689-2">[</span><span class="p" data-group-id="3512398689-3">#{</span><span class="ss">counters</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3512398689-4">#{</span><span class="ss">aux</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1899182914</span><span class="p">,</span><span class="w">
│ │ │                   </span><span class="ss">check_io</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2605863602</span><span class="p">,</span><span class="w">
│ │ │                   </span><span class="ss">emulator</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">45731880463</span><span class="p">,</span><span class="w">
│ │ │                   </span><span class="ss">gc</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1512206910</span><span class="p">,</span><span class="w">
│ │ │                   </span><span class="ss">other</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5421338456</span><span class="p">,</span><span class="w">
│ │ │                   </span><span class="ss">port</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">221631</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="ss">sleep</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5150294100</span><span class="p" data-group-id="5983050722-4">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="ss">sleep</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5150294100</span><span class="p" data-group-id="3512398689-4">}</span><span class="p">,</span><span class="w">
│ │ │     </span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">scheduler</span><span class="p" data-group-id="5983050722-3">}</span><span class="p">|</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5983050722-2">]</span></code></pre><p>The time unit is the same as returned by <a href="../../../lib/kernel-10.2.7.1/doc/html/os.html#perf_counter/0"><code class="inline">os:perf_counter/0</code></a>. So, to convert it
│ │ │ -to milliseconds, you can do something like this:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="2645812010-1">(</span><span class="w">
│ │ │ -  </span><span class="nf">fun</span><span class="p" data-group-id="2645812010-2">(</span><span class="p" data-group-id="2645812010-3">#{</span><span class="w"> </span><span class="ss">counters</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Cnt</span><span class="w"> </span><span class="p" data-group-id="2645812010-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p" data-group-id="2645812010-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -         </span><span class="n">MsCnt</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="2645812010-4">(</span><span class="nf">fun</span><span class="p" data-group-id="2645812010-5">(</span><span class="p">_</span><span class="n">K</span><span class="p">,</span><span class="w"> </span><span class="n">PerfCount</span><span class="p" data-group-id="2645812010-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                                    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">convert_time_unit</span><span class="p" data-group-id="2645812010-6">(</span><span class="n">PerfCount</span><span class="p">,</span><span class="w"> </span><span class="ss">perf_counter</span><span class="p">,</span><span class="w"> </span><span class="mi">1000</span><span class="p" data-group-id="2645812010-6">)</span><span class="w">
│ │ │ -                           </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Cnt</span><span class="p" data-group-id="2645812010-4">)</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="n">M</span><span class="p" data-group-id="2645812010-7">#{</span><span class="w"> </span><span class="ss">counters</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">MsCnt</span><span class="w"> </span><span class="p" data-group-id="2645812010-7">}</span><span class="w">
│ │ │ -  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="2645812010-8">(</span><span class="ss">microstate_accounting</span><span class="p" data-group-id="2645812010-8">)</span><span class="p" data-group-id="2645812010-1">)</span><span class="p">.</span></code></pre><p>Notice that these values are not guaranteed to be the exact time spent in each
│ │ │ +   </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">scheduler</span><span class="p" data-group-id="3512398689-3">}</span><span class="p">|</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3512398689-2">]</span></code></pre><p>The time unit is the same as returned by <a href="../../../lib/kernel-10.2.7.1/doc/html/os.html#perf_counter/0"><code class="inline">os:perf_counter/0</code></a>. So, to convert it
│ │ │ +to milliseconds, you can do something like this:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7470406269-1">(</span><span class="w">
│ │ │ +  </span><span class="nf">fun</span><span class="p" data-group-id="7470406269-2">(</span><span class="p" data-group-id="7470406269-3">#{</span><span class="w"> </span><span class="ss">counters</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Cnt</span><span class="w"> </span><span class="p" data-group-id="7470406269-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p" data-group-id="7470406269-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +         </span><span class="n">MsCnt</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7470406269-4">(</span><span class="nf">fun</span><span class="p" data-group-id="7470406269-5">(</span><span class="p">_</span><span class="n">K</span><span class="p">,</span><span class="w"> </span><span class="n">PerfCount</span><span class="p" data-group-id="7470406269-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                                    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">convert_time_unit</span><span class="p" data-group-id="7470406269-6">(</span><span class="n">PerfCount</span><span class="p">,</span><span class="w"> </span><span class="ss">perf_counter</span><span class="p">,</span><span class="w"> </span><span class="mi">1000</span><span class="p" data-group-id="7470406269-6">)</span><span class="w">
│ │ │ +                           </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Cnt</span><span class="p" data-group-id="7470406269-4">)</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="n">M</span><span class="p" data-group-id="7470406269-7">#{</span><span class="w"> </span><span class="ss">counters</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">MsCnt</span><span class="w"> </span><span class="p" data-group-id="7470406269-7">}</span><span class="w">
│ │ │ +  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="7470406269-8">(</span><span class="ss">microstate_accounting</span><span class="p" data-group-id="7470406269-8">)</span><span class="p" data-group-id="7470406269-1">)</span><span class="p">.</span></code></pre><p>Notice that these values are not guaranteed to be the exact time spent in each
│ │ │  state. This is because of various optimisation done to keep the overhead as
│ │ │  small as possible.</p><p><code class="inline">MSAcc_Thread_Type</code>s:</p><ul><li><p><strong><code class="inline">scheduler</code></strong> - The main execution threads that do most of the work. See
│ │ │  <a href="erl_cmd.html#%2BS">erl +S</a> for more details.</p></li><li><p><strong><code class="inline">dirty_cpu_scheduler</code></strong> - The threads for long running cpu intensive work.
│ │ │  See <a href="erl_cmd.html#%2BSDcpu">erl +SDcpu</a> for more details.</p></li><li><p><strong><code class="inline">dirty_io_scheduler</code></strong> - The threads for long running I/O work. See
│ │ │  <a href="erl_cmd.html#%2BSDio">erl +SDio</a> for more details.</p></li><li><p><strong><code class="inline">async</code></strong> - Async threads are used by various linked-in drivers (mainly the
│ │ │  file drivers) do offload non-CPU intensive work. See
│ │ │  <a href="erl_cmd.html#async_thread_pool_size">erl +A</a> for more details.</p></li><li><p><strong><code class="inline">aux</code></strong> - Takes care of any work that is not specifically assigned to a
│ │ │ @@ -16282,28 +16282,28 @@
│ │ │  states this time is part of the <code class="inline">gc</code> state.</p></li><li><p><strong><code class="inline">nif</code></strong> - Time spent in NIFs. Without extra states this time is part of the
│ │ │  <code class="inline">emulator</code> state.</p></li><li><p><strong><code class="inline">send</code></strong> - Time spent sending messages (processes only). Without extra
│ │ │  states this time is part of the <code class="inline">emulator</code> state.</p></li><li><p><strong><code class="inline">timers</code></strong> - Time spent managing timers. Without extra states this time is
│ │ │  part of the <code class="inline">other</code> state.</p></li></ul><p>The utility module <a href="../../../lib/runtime_tools-2.1.1/doc/html/msacc.html"><code class="inline">msacc</code></a> can be used to more easily analyse these
│ │ │  statistics.</p><p>Returns <code class="inline">undefined</code> if system flag
│ │ │  <a href="#system_flag_microstate_accounting"><code class="inline">microstate_accounting</code></a> is
│ │ │  turned off.</p><p>The list of thread information is unsorted and can appear in different order
│ │ │ -between calls.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The threads and states are subject to change without any prior notice.</p></section><p>Available since OTP 19.0</p></li><li><pre id="statistics_reductions"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="6508472165-1">(</span><span class="ss">reductions</span><span class="p" data-group-id="6508472165-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6508472165-2">{</span><span class="n">Reductions</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="6508472165-3">(</span><span class="p" data-group-id="6508472165-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">SinceLastCall</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="6508472165-4">(</span><span class="p" data-group-id="6508472165-4">)</span><span class="p" data-group-id="6508472165-2">}</span></code></pre><p>Returns information about reductions, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">statistics</span><span class="p" data-group-id="8115742144-1">(</span><span class="ss">reductions</span><span class="p" data-group-id="8115742144-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8115742144-2">{</span><span class="mi">2046</span><span class="p">,</span><span class="mi">11</span><span class="p" data-group-id="8115742144-2">}</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>As from ERTS 5.5 (Erlang/OTP R11B), this value does not include reductions
│ │ │ +between calls.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The threads and states are subject to change without any prior notice.</p></section><p>Available since OTP 19.0</p></li><li><pre id="statistics_reductions"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="0926214714-1">(</span><span class="ss">reductions</span><span class="p" data-group-id="0926214714-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0926214714-2">{</span><span class="n">Reductions</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="0926214714-3">(</span><span class="p" data-group-id="0926214714-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">SinceLastCall</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="0926214714-4">(</span><span class="p" data-group-id="0926214714-4">)</span><span class="p" data-group-id="0926214714-2">}</span></code></pre><p>Returns information about reductions, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">statistics</span><span class="p" data-group-id="1039108157-1">(</span><span class="ss">reductions</span><span class="p" data-group-id="1039108157-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1039108157-2">{</span><span class="mi">2046</span><span class="p">,</span><span class="mi">11</span><span class="p" data-group-id="1039108157-2">}</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>As from ERTS 5.5 (Erlang/OTP R11B), this value does not include reductions
│ │ │  performed in current time slices of currently scheduled processes. If an exact
│ │ │  value is wanted, use
│ │ │ -<a href="#statistics_exact_reductions"><code class="inline">statistics(exact_reductions)</code></a>.</p></section></li><li><pre id="statistics_run_queue"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="8933853615-1">(</span><span class="ss">run_queue</span><span class="p" data-group-id="8933853615-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="8933853615-2">(</span><span class="p" data-group-id="8933853615-2">)</span></code></pre><p>Returns the total length of all normal and dirty CPU run queues. That is, queued
│ │ │ +<a href="#statistics_exact_reductions"><code class="inline">statistics(exact_reductions)</code></a>.</p></section></li><li><pre id="statistics_run_queue"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="2422813401-1">(</span><span class="ss">run_queue</span><span class="p" data-group-id="2422813401-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2422813401-2">(</span><span class="p" data-group-id="2422813401-2">)</span></code></pre><p>Returns the total length of all normal and dirty CPU run queues. That is, queued
│ │ │  work that is expected to be CPU bound. The information is gathered atomically.
│ │ │  That is, the result is a consistent snapshot of the state, but this operation is
│ │ │  much more expensive compared to
│ │ │  <a href="#statistics_total_run_queue_lengths"><code class="inline">statistics(total_run_queue_lengths)</code></a>,
│ │ │ -especially when a large amount of schedulers is used.</p></li><li><pre id="statistics_run_queue_lengths"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="3000127057-1">(</span><span class="ss">run_queue_lengths</span><span class="p" data-group-id="3000127057-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3000127057-2">[</span><span class="nf">non_neg_integer</span><span class="p" data-group-id="3000127057-3">(</span><span class="p" data-group-id="3000127057-3">)</span><span class="p" data-group-id="3000127057-2">]</span></code></pre><p>Returns the same as
│ │ │ +especially when a large amount of schedulers is used.</p></li><li><pre id="statistics_run_queue_lengths"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="4953144601-1">(</span><span class="ss">run_queue_lengths</span><span class="p" data-group-id="4953144601-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4953144601-2">[</span><span class="nf">non_neg_integer</span><span class="p" data-group-id="4953144601-3">(</span><span class="p" data-group-id="4953144601-3">)</span><span class="p" data-group-id="4953144601-2">]</span></code></pre><p>Returns the same as
│ │ │  <a href="#statistics_run_queue_lengths_all"><code class="inline">statistics(run_queue_lengths_all)</code></a>
│ │ │  with the exception that no information about the dirty IO run queue is part of
│ │ │  the result. That is, only run queues with work that is expected to be CPU bound
│ │ │ -is part of the result.</p><p>Available since OTP 18.3</p></li><li><pre id="statistics_run_queue_lengths_all"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="2023734054-1">(</span><span class="ss">run_queue_lengths_all</span><span class="p" data-group-id="2023734054-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2023734054-2">[</span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2023734054-3">(</span><span class="p" data-group-id="2023734054-3">)</span><span class="p" data-group-id="2023734054-2">]</span></code></pre><p>Returns a list where each element represents the amount of processes and ports
│ │ │ +is part of the result.</p><p>Available since OTP 18.3</p></li><li><pre id="statistics_run_queue_lengths_all"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="8434396450-1">(</span><span class="ss">run_queue_lengths_all</span><span class="p" data-group-id="8434396450-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8434396450-2">[</span><span class="nf">non_neg_integer</span><span class="p" data-group-id="8434396450-3">(</span><span class="p" data-group-id="8434396450-3">)</span><span class="p" data-group-id="8434396450-2">]</span></code></pre><p>Returns a list where each element represents the amount of processes and ports
│ │ │  ready to run for each run queue. Values for normal run queues are located first
│ │ │  in the resulting list. The first element corresponds to the normal run queue of
│ │ │  scheduler number 1 and so on. If support for dirty schedulers exist, values for
│ │ │  the dirty CPU run queue and the dirty IO run queue follow (in that order) at the
│ │ │  end. The information is <em>not</em> gathered atomically. That is, the result is not
│ │ │  necessarily a consistent snapshot of the state, but instead quite efficiently
│ │ │  gathered.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Each normal scheduler has one run queue that it manages. If dirty schedulers
│ │ │ @@ -16315,21 +16315,21 @@
│ │ │  evaluating the result.</p></section><p>See also
│ │ │  <a href="#statistics_run_queue_lengths"><code class="inline">statistics(run_queue_lengths)</code></a>,
│ │ │  <a href="#statistics_total_run_queue_lengths_all"><code class="inline">statistics(total_run_queue_lengths_all)</code></a>,
│ │ │  <a href="#statistics_total_run_queue_lengths"><code class="inline">statistics(total_run_queue_lengths)</code></a>,
│ │ │  <a href="#statistics_active_tasks"><code class="inline">statistics(active_tasks)</code></a>,
│ │ │  <a href="#statistics_active_tasks_all"><code class="inline">statistics(active_tasks_all)</code></a>, and
│ │ │  <a href="#statistics_total_active_tasks"><code class="inline">statistics(total_active_tasks)</code></a>,
│ │ │ -<a href="#statistics_total_active_tasks_all"><code class="inline">statistics(total_active_tasks_all)</code></a>.</p><p>Available since OTP 20.0</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="5598914289-1">(</span><span class="ss">runtime</span><span class="p" data-group-id="5598914289-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5598914289-2">{</span><span class="n">Total</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5598914289-3">(</span><span class="p" data-group-id="5598914289-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">SinceLastCall</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5598914289-4">(</span><span class="p" data-group-id="5598914289-4">)</span><span class="p" data-group-id="5598914289-2">}</span></code></pre><p>Returns information about runtime, in milliseconds.</p><p>This is the sum of the runtime for all threads in the Erlang runtime system and
│ │ │ +<a href="#statistics_total_active_tasks_all"><code class="inline">statistics(total_active_tasks_all)</code></a>.</p><p>Available since OTP 20.0</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="8984735790-1">(</span><span class="ss">runtime</span><span class="p" data-group-id="8984735790-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8984735790-2">{</span><span class="n">Total</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="8984735790-3">(</span><span class="p" data-group-id="8984735790-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">SinceLastCall</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="8984735790-4">(</span><span class="p" data-group-id="8984735790-4">)</span><span class="p" data-group-id="8984735790-2">}</span></code></pre><p>Returns information about runtime, in milliseconds.</p><p>This is the sum of the runtime for all threads in the Erlang runtime system and
│ │ │  can therefore be greater than the wall clock time.</p><section role="note" class="admonition warning"><h4 class="admonition-title warning">Warning</h4><p>This value might wrap due to limitations in the underlying functionality
│ │ │ -provided by the operating system that is used.</p></section><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">statistics</span><span class="p" data-group-id="7442210883-1">(</span><span class="ss">runtime</span><span class="p" data-group-id="7442210883-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7442210883-2">{</span><span class="mi">1690</span><span class="p">,</span><span class="mi">1620</span><span class="p" data-group-id="7442210883-2">}</span></code></pre></li><li><pre id="statistics_scheduler_wall_time"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="5356162917-1">(</span><span class="ss">scheduler_wall_time</span><span class="p" data-group-id="5356162917-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5356162917-2">[</span><span class="p" data-group-id="5356162917-3">{</span><span class="n">Id</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">pos_integer</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ActiveTime</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5356162917-4">(</span><span class="p" data-group-id="5356162917-4">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">TotalTime</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5356162917-5">(</span><span class="p" data-group-id="5356162917-5">)</span><span class="p" data-group-id="5356162917-3">}</span><span class="p" data-group-id="5356162917-2">]</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │ +provided by the operating system that is used.</p></section><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">statistics</span><span class="p" data-group-id="6851301857-1">(</span><span class="ss">runtime</span><span class="p" data-group-id="6851301857-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6851301857-2">{</span><span class="mi">1690</span><span class="p">,</span><span class="mi">1620</span><span class="p" data-group-id="6851301857-2">}</span></code></pre></li><li><pre id="statistics_scheduler_wall_time"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="2306659711-1">(</span><span class="ss">scheduler_wall_time</span><span class="p" data-group-id="2306659711-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2306659711-2">[</span><span class="p" data-group-id="2306659711-3">{</span><span class="n">Id</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">pos_integer</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ActiveTime</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2306659711-4">(</span><span class="p" data-group-id="2306659711-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">TotalTime</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2306659711-5">(</span><span class="p" data-group-id="2306659711-5">)</span><span class="p" data-group-id="2306659711-3">}</span><span class="p" data-group-id="2306659711-2">]</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │    </span><span class="ss">undefined</span></code></pre><p>Returns information describing how much time
│ │ │  <a href="#system_info_schedulers">normal</a> and
│ │ │  <a href="#system_info_dirty_cpu_schedulers">dirty CPU</a> schedulers in the
│ │ │  system have been busy. This value is normally a better indicator of how much
│ │ │  load an Erlang node is under instead of looking at the CPU utilization provided
│ │ │  by tools such as <code class="inline">top</code> or <code class="inline">sysstat</code>. This is because <code class="inline">scheduler_wall_time</code> also
│ │ │  includes time where the scheduler is waiting for some other reasource (such as
│ │ │ @@ -16361,60 +16361,60 @@
│ │ │  Dirty CPU schedulers will have scheduler identifiers in the range
│ │ │  <code class="inline">erlang:system_info(schedulers) &lt; SchedulerId =&lt; erlang:system_info(schedulers) +</code><a href="#system_info_dirty_cpu_schedulers"><code class="inline">erlang:system_info(dirty_cpu_schedulers)</code></a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The different types of schedulers handle specific types of jobs. Every job is
│ │ │  assigned to a specific scheduler type. Jobs can migrate between different
│ │ │  schedulers of the same type, but never between schedulers of different types.
│ │ │  This fact has to be taken under consideration when evaluating the result
│ │ │  returned.</p></section><p>You can use <code class="inline">scheduler_wall_time</code> to calculate scheduler utilization. First you
│ │ │  take a sample of the values returned by
│ │ │ -<code class="inline">erlang:statistics(scheduler_wall_time)</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_flag</span><span class="p" data-group-id="8651309982-1">(</span><span class="ss">scheduler_wall_time</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8651309982-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">erlang:statistics(scheduler_wall_time)</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_flag</span><span class="p" data-group-id="9527399377-1">(</span><span class="ss">scheduler_wall_time</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9527399377-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="n">Ts0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="8651309982-2">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="8651309982-3">(</span><span class="ss">scheduler_wall_time</span><span class="p" data-group-id="8651309982-3">)</span><span class="p" data-group-id="8651309982-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ +&gt; </span><span class="n">Ts0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="9527399377-2">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="9527399377-3">(</span><span class="ss">scheduler_wall_time</span><span class="p" data-group-id="9527399377-3">)</span><span class="p" data-group-id="9527399377-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>Some time later the user takes another snapshot and calculates scheduler
│ │ │ -utilization per scheduler, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Ts1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="5076239233-1">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5076239233-2">(</span><span class="ss">scheduler_wall_time</span><span class="p" data-group-id="5076239233-2">)</span><span class="p" data-group-id="5076239233-1">)</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ +utilization per scheduler, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Ts1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="3819876895-1">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="3819876895-2">(</span><span class="ss">scheduler_wall_time</span><span class="p" data-group-id="3819876895-2">)</span><span class="p" data-group-id="3819876895-1">)</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="gp unselectable">
│ │ │ -&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="5076239233-3">(</span><span class="nf">fun</span><span class="p" data-group-id="5076239233-4">(</span><span class="p" data-group-id="5076239233-5">{</span><span class="p" data-group-id="5076239233-6">{</span><span class="n">I</span><span class="p">,</span><span class="w"> </span><span class="n">A0</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p" data-group-id="5076239233-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5076239233-7">{</span><span class="n">I</span><span class="p">,</span><span class="w"> </span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="5076239233-7">}</span><span class="p" data-group-id="5076239233-5">}</span><span class="p" data-group-id="5076239233-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5076239233-8">{</span><span class="n">I</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5076239233-9">(</span><span class="n">A1</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">A0</span><span class="p" data-group-id="5076239233-9">)</span><span class="o">/</span><span class="p" data-group-id="5076239233-10">(</span><span class="n">T1</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">T0</span><span class="p" data-group-id="5076239233-10">)</span><span class="p" data-group-id="5076239233-8">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">zip</span><span class="p" data-group-id="5076239233-11">(</span><span class="n">Ts0</span><span class="p">,</span><span class="n">Ts1</span><span class="p" data-group-id="5076239233-11">)</span><span class="p" data-group-id="5076239233-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5076239233-12">[</span><span class="p" data-group-id="5076239233-13">{</span><span class="mi">1</span><span class="p">,</span><span class="mf">0.9743474730177548</span><span class="p" data-group-id="5076239233-13">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5076239233-14">{</span><span class="mi">2</span><span class="p">,</span><span class="mf">0.9744843782751444</span><span class="p" data-group-id="5076239233-14">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5076239233-15">{</span><span class="mi">3</span><span class="p">,</span><span class="mf">0.9995902361669045</span><span class="p" data-group-id="5076239233-15">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5076239233-16">{</span><span class="mi">4</span><span class="p">,</span><span class="mf">0.9738012596572161</span><span class="p" data-group-id="5076239233-16">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5076239233-17">{</span><span class="mi">5</span><span class="p">,</span><span class="mf">0.9717956667018103</span><span class="p" data-group-id="5076239233-17">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5076239233-18">{</span><span class="mi">6</span><span class="p">,</span><span class="mf">0.9739235846420741</span><span class="p" data-group-id="5076239233-18">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5076239233-19">{</span><span class="mi">7</span><span class="p">,</span><span class="mf">0.973237033077876</span><span class="p" data-group-id="5076239233-19">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5076239233-20">{</span><span class="mi">8</span><span class="p">,</span><span class="mf">0.9741297293248656</span><span class="p" data-group-id="5076239233-20">}</span><span class="p" data-group-id="5076239233-12">]</span></code></pre><p>Using the same snapshots to calculate a total scheduler utilization:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="2525877589-1">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2525877589-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="2525877589-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2525877589-3">(</span><span class="p" data-group-id="2525877589-4">{</span><span class="p" data-group-id="2525877589-5">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A0</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p" data-group-id="2525877589-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2525877589-6">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="2525877589-6">}</span><span class="p" data-group-id="2525877589-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2525877589-7">{</span><span class="n">Ai</span><span class="p">,</span><span class="n">Ti</span><span class="p" data-group-id="2525877589-7">}</span><span class="p" data-group-id="2525877589-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2525877589-8">{</span><span class="n">Ai</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="2525877589-9">(</span><span class="n">A1</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">A0</span><span class="p" data-group-id="2525877589-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Ti</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="2525877589-10">(</span><span class="n">T1</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">T0</span><span class="p" data-group-id="2525877589-10">)</span><span class="p" data-group-id="2525877589-8">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2525877589-11">{</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2525877589-11">}</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">zip</span><span class="p" data-group-id="2525877589-12">(</span><span class="n">Ts0</span><span class="p">,</span><span class="n">Ts1</span><span class="p" data-group-id="2525877589-12">)</span><span class="p" data-group-id="2525877589-2">)</span><span class="p">,</span><span class="w">
│ │ │ +&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="3819876895-3">(</span><span class="nf">fun</span><span class="p" data-group-id="3819876895-4">(</span><span class="p" data-group-id="3819876895-5">{</span><span class="p" data-group-id="3819876895-6">{</span><span class="n">I</span><span class="p">,</span><span class="w"> </span><span class="n">A0</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p" data-group-id="3819876895-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3819876895-7">{</span><span class="n">I</span><span class="p">,</span><span class="w"> </span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="3819876895-7">}</span><span class="p" data-group-id="3819876895-5">}</span><span class="p" data-group-id="3819876895-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3819876895-8">{</span><span class="n">I</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3819876895-9">(</span><span class="n">A1</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">A0</span><span class="p" data-group-id="3819876895-9">)</span><span class="o">/</span><span class="p" data-group-id="3819876895-10">(</span><span class="n">T1</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">T0</span><span class="p" data-group-id="3819876895-10">)</span><span class="p" data-group-id="3819876895-8">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">zip</span><span class="p" data-group-id="3819876895-11">(</span><span class="n">Ts0</span><span class="p">,</span><span class="n">Ts1</span><span class="p" data-group-id="3819876895-11">)</span><span class="p" data-group-id="3819876895-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3819876895-12">[</span><span class="p" data-group-id="3819876895-13">{</span><span class="mi">1</span><span class="p">,</span><span class="mf">0.9743474730177548</span><span class="p" data-group-id="3819876895-13">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3819876895-14">{</span><span class="mi">2</span><span class="p">,</span><span class="mf">0.9744843782751444</span><span class="p" data-group-id="3819876895-14">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3819876895-15">{</span><span class="mi">3</span><span class="p">,</span><span class="mf">0.9995902361669045</span><span class="p" data-group-id="3819876895-15">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3819876895-16">{</span><span class="mi">4</span><span class="p">,</span><span class="mf">0.9738012596572161</span><span class="p" data-group-id="3819876895-16">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3819876895-17">{</span><span class="mi">5</span><span class="p">,</span><span class="mf">0.9717956667018103</span><span class="p" data-group-id="3819876895-17">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3819876895-18">{</span><span class="mi">6</span><span class="p">,</span><span class="mf">0.9739235846420741</span><span class="p" data-group-id="3819876895-18">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3819876895-19">{</span><span class="mi">7</span><span class="p">,</span><span class="mf">0.973237033077876</span><span class="p" data-group-id="3819876895-19">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3819876895-20">{</span><span class="mi">8</span><span class="p">,</span><span class="mf">0.9741297293248656</span><span class="p" data-group-id="3819876895-20">}</span><span class="p" data-group-id="3819876895-12">]</span></code></pre><p>Using the same snapshots to calculate a total scheduler utilization:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="5270257442-1">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5270257442-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="5270257442-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5270257442-3">(</span><span class="p" data-group-id="5270257442-4">{</span><span class="p" data-group-id="5270257442-5">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A0</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p" data-group-id="5270257442-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5270257442-6">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="5270257442-6">}</span><span class="p" data-group-id="5270257442-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5270257442-7">{</span><span class="n">Ai</span><span class="p">,</span><span class="n">Ti</span><span class="p" data-group-id="5270257442-7">}</span><span class="p" data-group-id="5270257442-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5270257442-8">{</span><span class="n">Ai</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="5270257442-9">(</span><span class="n">A1</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">A0</span><span class="p" data-group-id="5270257442-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Ti</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="5270257442-10">(</span><span class="n">T1</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">T0</span><span class="p" data-group-id="5270257442-10">)</span><span class="p" data-group-id="5270257442-8">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5270257442-11">{</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5270257442-11">}</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">zip</span><span class="p" data-group-id="5270257442-12">(</span><span class="n">Ts0</span><span class="p">,</span><span class="n">Ts1</span><span class="p" data-group-id="5270257442-12">)</span><span class="p" data-group-id="5270257442-2">)</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="n">TotalSchedulerUtilization</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="o">/</span><span class="n">T</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">0.9769136803764825</span></code></pre><p>Total scheduler utilization will equal <code class="inline">1.0</code> when all schedulers have been
│ │ │  active all the time between the two measurements.</p><p>Another (probably more) useful value is to calculate total scheduler utilization
│ │ │ -weighted against maximum amount of available CPU time:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">WeightedSchedulerUtilization</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2769688028-1">(</span><span class="n">TotalSchedulerUtilization</span><span class="w">
│ │ │ -                                  </span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="2769688028-2">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="2769688028-3">(</span><span class="ss">schedulers</span><span class="p" data-group-id="2769688028-3">)</span><span class="w">
│ │ │ -                                     </span><span class="o">+</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="2769688028-4">(</span><span class="ss">dirty_cpu_schedulers</span><span class="p" data-group-id="2769688028-4">)</span><span class="p" data-group-id="2769688028-2">)</span><span class="p" data-group-id="2769688028-1">)</span><span class="w">
│ │ │ -                                 </span><span class="o">/</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="2769688028-5">(</span><span class="ss">logical_processors_available</span><span class="p" data-group-id="2769688028-5">)</span><span class="p">.</span><span class="w">
│ │ │ +weighted against maximum amount of available CPU time:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">WeightedSchedulerUtilization</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0133266986-1">(</span><span class="n">TotalSchedulerUtilization</span><span class="w">
│ │ │ +                                  </span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="0133266986-2">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="0133266986-3">(</span><span class="ss">schedulers</span><span class="p" data-group-id="0133266986-3">)</span><span class="w">
│ │ │ +                                     </span><span class="o">+</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="0133266986-4">(</span><span class="ss">dirty_cpu_schedulers</span><span class="p" data-group-id="0133266986-4">)</span><span class="p" data-group-id="0133266986-2">)</span><span class="p" data-group-id="0133266986-1">)</span><span class="w">
│ │ │ +                                 </span><span class="o">/</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="0133266986-5">(</span><span class="ss">logical_processors_available</span><span class="p" data-group-id="0133266986-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">0.9769136803764825</span></code></pre><p>This weighted scheduler utilization will reach <code class="inline">1.0</code> when schedulers are active
│ │ │  the same amount of time as maximum available CPU time. If more schedulers exist
│ │ │  than available logical processors, this value may be greater than <code class="inline">1.0</code>.</p><p>As of ERTS version 9.0, the Erlang runtime system will as default have more
│ │ │  schedulers than logical processors. This due to the dirty schedulers.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p><code class="inline">scheduler_wall_time</code> is by default disabled. To enable it, use
│ │ │ -<a href="#system_flag_scheduler_wall_time"><code class="inline">erlang:system_flag(scheduler_wall_time, true)</code></a>.</p></section><p>Available since OTP R15B01</p></li><li><pre id="statistics_scheduler_wall_time_all"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="3793105920-1">(</span><span class="ss">scheduler_wall_time_all</span><span class="p" data-group-id="3793105920-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="3793105920-2">[</span><span class="p" data-group-id="3793105920-3">{</span><span class="n">Id</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">pos_integer</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ActiveTime</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="3793105920-4">(</span><span class="p" data-group-id="3793105920-4">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">TotalTime</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="3793105920-5">(</span><span class="p" data-group-id="3793105920-5">)</span><span class="p" data-group-id="3793105920-3">}</span><span class="p" data-group-id="3793105920-2">]</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │ +<a href="#system_flag_scheduler_wall_time"><code class="inline">erlang:system_flag(scheduler_wall_time, true)</code></a>.</p></section><p>Available since OTP R15B01</p></li><li><pre id="statistics_scheduler_wall_time_all"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="6788251965-1">(</span><span class="ss">scheduler_wall_time_all</span><span class="p" data-group-id="6788251965-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6788251965-2">[</span><span class="p" data-group-id="6788251965-3">{</span><span class="n">Id</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">pos_integer</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ActiveTime</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="6788251965-4">(</span><span class="p" data-group-id="6788251965-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">TotalTime</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="6788251965-5">(</span><span class="p" data-group-id="6788251965-5">)</span><span class="p" data-group-id="6788251965-3">}</span><span class="p" data-group-id="6788251965-2">]</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │    </span><span class="ss">undefined</span></code></pre><p>Equivalent to
│ │ │  <a href="#statistics_scheduler_wall_time"><code class="inline">statistics(scheduler_wall_time)</code></a>,
│ │ │  except that it also include information about all dirty I/O schedulers.</p><p>Dirty IO schedulers will have scheduler identifiers in the range
│ │ │  <a href="#system_info_schedulers"><code class="inline">erlang:system_info(schedulers)</code></a><code class="inline">+</code><a href="#system_info_dirty_cpu_schedulers"><code class="inline">erlang:system_info(dirty_cpu_schedulers)</code></a><code class="inline">&lt; SchedulerId =&lt; erlang:system_info(schedulers) + erlang:system_info(dirty_cpu_schedulers) +</code><a href="#system_info_dirty_io_schedulers"><code class="inline">erlang:system_info(dirty_io_schedulers)</code></a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Note that work executing on dirty I/O schedulers are expected to mainly wait
│ │ │  for I/O. That is, when you get high scheduler utilization on dirty I/O
│ │ │ -schedulers, CPU utilization is <em>not</em> expected to be high due to this work.</p></section><p>Available since OTP 20.0</p></li><li><pre id="statistics_total_active_tasks"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="7661392996-1">(</span><span class="ss">total_active_tasks</span><span class="p" data-group-id="7661392996-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="7661392996-2">(</span><span class="p" data-group-id="7661392996-2">)</span></code></pre><p>Equivalent to calling
│ │ │ +schedulers, CPU utilization is <em>not</em> expected to be high due to this work.</p></section><p>Available since OTP 20.0</p></li><li><pre id="statistics_total_active_tasks"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="0862100722-1">(</span><span class="ss">total_active_tasks</span><span class="p" data-group-id="0862100722-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="0862100722-2">(</span><span class="p" data-group-id="0862100722-2">)</span></code></pre><p>Equivalent to calling
│ │ │  <code class="inline">lists:sum(</code><a href="#statistics_active_tasks"><code class="inline">statistics(active_tasks)</code></a><code class="inline">)</code>,
│ │ │ -but more efficient.</p><p>Available since OTP 18.3</p></li><li><pre id="statistics_total_active_tasks_all"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="4605180018-1">(</span><span class="ss">total_active_tasks_all</span><span class="p" data-group-id="4605180018-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="4605180018-2">(</span><span class="p" data-group-id="4605180018-2">)</span></code></pre><p>Equivalent to calling
│ │ │ +but more efficient.</p><p>Available since OTP 18.3</p></li><li><pre id="statistics_total_active_tasks_all"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="2977052357-1">(</span><span class="ss">total_active_tasks_all</span><span class="p" data-group-id="2977052357-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2977052357-2">(</span><span class="p" data-group-id="2977052357-2">)</span></code></pre><p>Equivalent to calling
│ │ │  <code class="inline">lists:sum(</code><a href="#statistics_active_tasks_all"><code class="inline">statistics(active_tasks_all)</code></a><code class="inline">)</code>,
│ │ │ -but more efficient.</p><p>Available since OTP 20.0</p></li><li><pre id="statistics_total_run_queue_lengths"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="8711895258-1">(</span><span class="ss">total_run_queue_lengths</span><span class="p" data-group-id="8711895258-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="8711895258-2">(</span><span class="p" data-group-id="8711895258-2">)</span></code></pre><p>Equivalent to calling
│ │ │ +but more efficient.</p><p>Available since OTP 20.0</p></li><li><pre id="statistics_total_run_queue_lengths"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="7473195516-1">(</span><span class="ss">total_run_queue_lengths</span><span class="p" data-group-id="7473195516-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="7473195516-2">(</span><span class="p" data-group-id="7473195516-2">)</span></code></pre><p>Equivalent to calling
│ │ │  <code class="inline">lists:sum(</code><a href="#statistics_run_queue_lengths"><code class="inline">statistics(run_queue_lengths)</code></a><code class="inline">)</code>,
│ │ │ -but more efficient.</p><p>Available since OTP 18.3</p></li><li><pre id="statistics_total_run_queue_lengths_all"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="0539185721-1">(</span><span class="ss">total_run_queue_lengths_all</span><span class="p" data-group-id="0539185721-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="0539185721-2">(</span><span class="p" data-group-id="0539185721-2">)</span></code></pre><p>Equivalent to calling
│ │ │ +but more efficient.</p><p>Available since OTP 18.3</p></li><li><pre id="statistics_total_run_queue_lengths_all"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="9950508830-1">(</span><span class="ss">total_run_queue_lengths_all</span><span class="p" data-group-id="9950508830-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="9950508830-2">(</span><span class="p" data-group-id="9950508830-2">)</span></code></pre><p>Equivalent to calling
│ │ │  <code class="inline">lists:sum(</code><a href="#statistics_run_queue_lengths_all"><code class="inline">statistics(run_queue_lengths_all)</code></a><code class="inline">)</code>,
│ │ │ -but more efficient.</p><p>Available since OTP 20.0</p></li><li><pre id="statistics_wall_clock"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="4062136403-1">(</span><span class="ss">wall_clock</span><span class="p" data-group-id="4062136403-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4062136403-2">{</span><span class="n">Total</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="4062136403-3">(</span><span class="p" data-group-id="4062136403-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">SinceLastCall</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="4062136403-4">(</span><span class="p" data-group-id="4062136403-4">)</span><span class="p" data-group-id="4062136403-2">}</span></code></pre><p>Returns information about wall clock. <code class="inline">wall_clock</code> can be used in the same
│ │ │ +but more efficient.</p><p>Available since OTP 20.0</p></li><li><pre id="statistics_wall_clock"><code class="makeup erlang" translate="no"><span class="nf">statistics</span><span class="p" data-group-id="1797139212-1">(</span><span class="ss">wall_clock</span><span class="p" data-group-id="1797139212-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1797139212-2">{</span><span class="n">Total</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="1797139212-3">(</span><span class="p" data-group-id="1797139212-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">SinceLastCall</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="1797139212-4">(</span><span class="p" data-group-id="1797139212-4">)</span><span class="p" data-group-id="1797139212-2">}</span></code></pre><p>Returns information about wall clock. <code class="inline">wall_clock</code> can be used in the same
│ │ │  manner as <code class="inline">runtime</code>, except that real time is measured as opposed to runtime or
│ │ │  CPU time.</p></li></ul>
│ │ │    </section>
│ │ │  </section>
│ │ │  <section class="detail" id="system_flag/2">
│ │ │  
│ │ │    <div class="detail-header">
│ │ │ @@ -16478,65 +16478,65 @@
│ │ │                       when
│ │ │                           Tracer :: <a href="#t:pid/0">pid</a>() | <a href="#t:port/0">port</a>() | {<a href="#t:module/0">module</a>(), <a href="#t:term/0">term</a>()} | false,
│ │ │                           PrevTracer :: <a href="#t:pid/0">pid</a>() | <a href="#t:port/0">port</a>() | {<a href="#t:module/0">module</a>(), <a href="#t:term/0">term</a>()} | false;
│ │ │                   (reset_seq_trace, true) -> true.</pre>
│ │ │  
│ │ │        </div>
│ │ │  
│ │ │ -<p>Sets a system flag to the given value.</p><p>The possible flags to set are:</p><ul><li><pre><code class="makeup erlang" translate="no"><span class="nf">system_flag</span><span class="p" data-group-id="5459531900-1">(</span><span class="ss">backtrace_depths</span><span class="p">,</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5459531900-2">(</span><span class="p" data-group-id="5459531900-2">)</span><span class="p" data-group-id="5459531900-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5459531900-3">(</span><span class="p" data-group-id="5459531900-3">)</span></code></pre><p> Sets the maximum depth of call stack back-traces in the exit reason element of
│ │ │ +<p>Sets a system flag to the given value.</p><p>The possible flags to set are:</p><ul><li><pre><code class="makeup erlang" translate="no"><span class="nf">system_flag</span><span class="p" data-group-id="7108048643-1">(</span><span class="ss">backtrace_depths</span><span class="p">,</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="7108048643-2">(</span><span class="p" data-group-id="7108048643-2">)</span><span class="p" data-group-id="7108048643-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="7108048643-3">(</span><span class="p" data-group-id="7108048643-3">)</span></code></pre><p> Sets the maximum depth of call stack back-traces in the exit reason element of
│ │ │  <code class="inline">'EXIT'</code> tuples. The flag also limits the stacktrace depth returned by
│ │ │ -<a href="#process_info/2"><code class="inline">process_info/2</code></a> item <a href="#process_info_current_stacktrace"><code class="inline">current_stacktrace</code></a>.</p><p>Returns the old value of the flag.</p></li><li><pre id="system_flag_cpu_topology"><code class="makeup erlang" translate="no"><span class="nf">system_flag</span><span class="p" data-group-id="0621804995-1">(</span><span class="ss">cpu_topology</span><span class="p">,</span><span class="w"> </span><span class="nf">cpu_topology</span><span class="p" data-group-id="0621804995-2">(</span><span class="p" data-group-id="0621804995-2">)</span><span class="p" data-group-id="0621804995-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">cpu_topology</span><span class="p" data-group-id="0621804995-3">(</span><span class="p" data-group-id="0621804995-3">)</span></code></pre><section role="note" class="admonition warning"><h4 class="admonition-title warning">Warning</h4><p><em>This argument is deprecated.</em> Instead of using this argument, use
│ │ │ +<a href="#process_info/2"><code class="inline">process_info/2</code></a> item <a href="#process_info_current_stacktrace"><code class="inline">current_stacktrace</code></a>.</p><p>Returns the old value of the flag.</p></li><li><pre id="system_flag_cpu_topology"><code class="makeup erlang" translate="no"><span class="nf">system_flag</span><span class="p" data-group-id="1653943850-1">(</span><span class="ss">cpu_topology</span><span class="p">,</span><span class="w"> </span><span class="nf">cpu_topology</span><span class="p" data-group-id="1653943850-2">(</span><span class="p" data-group-id="1653943850-2">)</span><span class="p" data-group-id="1653943850-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">cpu_topology</span><span class="p" data-group-id="1653943850-3">(</span><span class="p" data-group-id="1653943850-3">)</span></code></pre><section role="note" class="admonition warning"><h4 class="admonition-title warning">Warning</h4><p><em>This argument is deprecated.</em> Instead of using this argument, use
│ │ │  command-line argument <a href="erl_cmd.html#%2Bsct"><code class="inline">+sct</code></a> in <a href="erl_cmd.html">erl</a>.</p><p>When this argument is removed, a final CPU topology to use is determined at
│ │ │  emulator boot time.</p></section><p>Sets the user-defined <code class="inline">CpuTopology</code>. The user-defined CPU topology overrides any
│ │ │  automatically detected CPU topology. By passing <code class="inline">undefined</code> as <code class="inline">CpuTopology</code>,
│ │ │  the system reverts to the CPU topology automatically detected. The returned
│ │ │  value equals the value returned from <code class="inline">erlang:system_info(cpu_topology)</code> before
│ │ │  the change was made.</p><p>Returns the old value of the flag.</p><p>The CPU topology is used when binding schedulers to logical processors. If
│ │ │  schedulers are already bound when the CPU topology is changed, the schedulers
│ │ │  are sent a request to rebind according to the new CPU topology.</p><p>The user-defined CPU topology can also be set by passing command-line argument
│ │ │  <a href="erl_cmd.html#%2Bsct"><code class="inline">+sct</code></a> to <a href="erl_cmd.html">erl</a>.</p><p>For information on type <code class="inline">CpuTopology</code> and more, see
│ │ │  <a href="#system_info_cpu_topology"><code class="inline">erlang:system_info(cpu_topology)</code></a> as
│ │ │  well as command-line flags <a href="erl_cmd.html#%2Bsct"><code class="inline">+sct</code></a> and
│ │ │ -<a href="erl_cmd.html#%2Bsbt"><code class="inline">+sbt</code></a> in <a href="erl_cmd.html">erl</a>.</p></li><li><pre id="system_flag_dirty_cpu_schedulers_online"><code class="makeup erlang" translate="no"><span class="nf">system_flag</span><span class="p" data-group-id="2383754370-1">(</span><span class="ss">dirty_cpu_schedulers_online</span><span class="p">,</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="2383754370-2">(</span><span class="p" data-group-id="2383754370-2">)</span><span class="p" data-group-id="2383754370-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="2383754370-3">(</span><span class="p" data-group-id="2383754370-3">)</span></code></pre><p>Sets the number of dirty CPU schedulers online. Range is
│ │ │ +<a href="erl_cmd.html#%2Bsbt"><code class="inline">+sbt</code></a> in <a href="erl_cmd.html">erl</a>.</p></li><li><pre id="system_flag_dirty_cpu_schedulers_online"><code class="makeup erlang" translate="no"><span class="nf">system_flag</span><span class="p" data-group-id="5785173729-1">(</span><span class="ss">dirty_cpu_schedulers_online</span><span class="p">,</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="5785173729-2">(</span><span class="p" data-group-id="5785173729-2">)</span><span class="p" data-group-id="5785173729-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="5785173729-3">(</span><span class="p" data-group-id="5785173729-3">)</span></code></pre><p>Sets the number of dirty CPU schedulers online. Range is
│ │ │  <code class="inline">1 &lt;= DirtyCPUSchedulersOnline &lt;= N</code>, where <code class="inline">N</code> is the smallest of the return
│ │ │  values of <code class="inline">erlang:system_info(dirty_cpu_schedulers)</code> and
│ │ │  <code class="inline">erlang:system_info(schedulers_online)</code>.</p><p>Returns the old value of the flag.</p><p>The number of dirty CPU schedulers online can change if the number of schedulers
│ │ │  online changes. For example, if 12 schedulers and 6 dirty CPU schedulers are
│ │ │  online, and <a href="#system_flag/2"><code class="inline">system_flag/2</code></a> is used to set the number of
│ │ │  schedulers online to 6, then the number of dirty CPU schedulers online is
│ │ │  automatically decreased by half as well, down to 3. Similarly, the number of
│ │ │  dirty CPU schedulers online increases proportionally to increases in the number
│ │ │  of schedulers online.</p><p>For more information, see
│ │ │  <a href="#system_info_dirty_cpu_schedulers"><code class="inline">erlang:system_info(dirty_cpu_schedulers)</code></a>
│ │ │  and
│ │ │ -<a href="#system_info_dirty_cpu_schedulers_online"><code class="inline">erlang:system_info(dirty_cpu_schedulers_online)</code></a>.</p><p>Available since OTP 17.0</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">system_flag</span><span class="p" data-group-id="0907068717-1">(</span><span class="ss">erts_alloc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0907068717-2">{</span><span class="n">Alloc</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="0907068717-3">(</span><span class="p" data-group-id="0907068717-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="0907068717-4">(</span><span class="p" data-group-id="0907068717-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0907068717-5">(</span><span class="p" data-group-id="0907068717-5">)</span><span class="p" data-group-id="0907068717-2">}</span><span class="p" data-group-id="0907068717-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<a href="#system_info_dirty_cpu_schedulers_online"><code class="inline">erlang:system_info(dirty_cpu_schedulers_online)</code></a>.</p><p>Available since OTP 17.0</p></li><li><pre><code class="makeup erlang" translate="no"><span class="nf">system_flag</span><span class="p" data-group-id="0904811826-1">(</span><span class="ss">erts_alloc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0904811826-2">{</span><span class="n">Alloc</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="0904811826-3">(</span><span class="p" data-group-id="0904811826-3">)</span><span class="p">,</span><span class="

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